Apparatus and method for limiting sound transmission

Abstract

In summary, there is provided an apparatus (1) for restricting the transmission of sound from a sound-producing body (2), the apparatus comprising a container (4) arranged to at least partially surround the sound-producing body, the container holding a liquid, the liquid containing at least 2% dissolved oxygen, the apparatus further comprising an agitator (6) configured to agitate the liquid, thereby causing the formation of gas bubbles (8) in the liquid.

Description

[Technical Field]

[0001] The present invention relates to an apparatus and related method for limiting the transmission of sound in a liquid. [Background technology]

[0002] Noise pollution, especially caused by heavy machinery, can be a serious problem affecting wildlife and the ability of humans to enjoy their environment. Many governments impose limits on the amount of noise that can occur in certain areas (including aquatic environments), both in terms of the absolute peak intensity of the noise that can be generated and the noise that can occur within a particular period of time (e.g., a month or a year).

[0003] Nevertheless, in some cases, a need arises to operate machinery that produces such noise, and therefore a need arises to limit the transmission of such noise. Current equipment for limiting the transmission of noise is large, expensive, requires large amounts of energy to operate, and typically operates only over a relatively narrow frequency band.

[0004] It is within this context that the present disclosure has been conceived. Summary of the Invention

[0005] A first aspect of the present invention provides an apparatus configured to restrict the transmission of sound from a sound-producing body (e.g., through a liquid), the apparatus comprising a housing arranged to at least partially surround the sound-producing body (e.g., said housing), the housing holding a liquid, the liquid comprising at least 2% by volume (optionally at least 10% by volume) dissolved oxygen, the apparatus further comprising an agitator configured to agitate (e.g., at least a portion of) the liquid (within the housing), thereby causing the formation of gas (e.g., oxygen) bubbles in the liquid (within the housing).

[0006] The inventors have discovered that the formation of gas (e.g., oxygen) bubbles in a liquid limits the transmission of sound through the liquid over a wide frequency range (e.g., including, but not limited to, frequencies audible to humans, including ultrasonic frequencies). Agitation of a liquid containing at least 2% (e.g., at least 10%) oxygen has been found to be a particularly effective method of inducing bubble formation. This is because agitation releases a portion of the oxygen dissolved in the liquid from the liquid, thereby forming a large number of gas (oxygen) bubbles as the liquid is agitated. Therefore, because bubbles can be formed without forcing gas bubbles through the liquid using a compressor or similar device, the present apparatus is also more efficient than when a compressor is used for this purpose. Furthermore, a greater proportion (e.g., number) of bubbles are generated more rapidly than when a compressor or conventional bubble curtain generator is used to generate bubbles. At least some of the bubbles may be formed by nucleation. At least some of the bubbles may be formed by cavitation.

[0007] While not wishing to be bound by theory, the inventors believe that sound transmission is limited by the bubbles in the liquid because, when sound waves reach the bubbles, they repeatedly encounter liquid-gas and gas-liquid interfaces (e.g., as the sound waves enter and exit each bubble). Some scattering and absorption may occur at each such interface, resulting in the absorption of sound energy and attenuation of the sound. The reflection and absorption coefficients are believed to be a function of the acoustic impedance of the gas and liquid. Additionally, there may be some resonant absorption if the sound waves are at the appropriate frequency to cause resonance in some of the bubbles. Because a large number of bubbles are generated and these bubbles have a wide range of sizes, a correspondingly wide range of different sound wavelengths may be scattered and absorbed by the bubbles. In other words, sound attenuation at a particular frequency is believed to be a function of bubble size. Additionally, it is believed that the liquid contains a large proportion of gas in the form of bubbles, which reduces the speed of sound. Therefore, it is understood that the frequency spectrum of sound waves in which sound transmission is restricted (eg, the frequency spectrum of sound waves that are attenuated) is a broad frequency spectrum and depends on the bubble size and the distribution of bubble sizes.

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

[0009] The liquid may contain at least 2% by volume (e.g., at least 10% by volume) of dissolved oxygen. The liquid may contain at least 25% by volume, e.g., at least 50% by volume, e.g., at least 75% by volume, e.g., at least 80% by volume of dissolved oxygen. The liquid may contain less than 100% by volume, e.g., less than 99% by volume, e.g., less than 90% by volume of dissolved oxygen. 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 be supersaturated with oxygen, e.g., having an oxygen saturation of greater than 100%. The liquid may have an oxygen saturation of at least 120%. The liquid may have an oxygen saturation of less than 200%, e.g., less than 150%. When a higher dissolved oxygen percentage is present in the liquid, the saturated oxygen is more easily released from the liquid when the liquid is agitated, thereby forming gas (oxygen) bubbles.

[0010] In some examples, the liquid may contain at least 5 grams of dissolved oxygen per kilogram of liquid (i.e., the liquid having dissolved oxygen, optionally water), for example, at least 10 grams of dissolved oxygen per kilogram of liquid, for example, at least 20 grams of dissolved oxygen per kilogram of liquid, for example, at least 50 grams of dissolved oxygen per kilogram of liquid, for example, at least 100 grams of dissolved oxygen per kilogram of liquid. The liquid may contain less than 1,000 grams of dissolved oxygen per kilogram of liquid (i.e., the liquid having dissolved oxygen, optionally water), for example, less than 750 grams of dissolved oxygen per kilogram of liquid, for example, less than 500 grams of dissolved oxygen per kilogram of liquid.

[0011] The container may have at least one opening defined therein, allowing gas bubbles to exit the container through the opening. The container may have multiple openings defined therein. The at least one opening may be at an upper portion of the container, e.g., at or above the surface of the liquid. The container may have an open upper side, e.g., at or above the surface of the liquid. During use, gas (e.g., oxygen) bubbles are continuously generated, rise under buoyancy (in the case of very small bubbles, this may occur after coalescing with other bubbles, thereby forming larger bubbles), and may exit through the opening(s).

[0012] The opening must be at least 1 cm 2 , e.g., at least 5 cm 2 , e.g., at least 10 cm 2 The opening may define an area of ​​10 m 2 Less than, for example, 7m 2 Less than, for example, 5m 2 The opening may define an area of ​​less than 1 m. The opening may span the entire top surface of the enclosure. The opening may define an area of ​​at least 50%, such as at least 80%, of the entire top surface of the enclosure. If multiple openings are provided, the total combined area of ​​the openings may be at least 1 m. 2 , e.g., at least 2 m 2 , e.g., at least 5 m 2 If multiple openings are provided, the total area of ​​the openings may not exceed 50m 2 Less than, for example, 40m 2 Less than, for example, 30m 2 It may be less than.

[0013] Because gas (e.g., oxygen) bubbles tend to migrate upward due to buoyancy (possibly after coalescing with other bubbles), it is necessary to continue to generate additional gas (e.g., oxygen) bubbles by agitating the liquid so that there is a continuous flow of gas (e.g., oxygen) bubbles distributed throughout the container, e.g., across the container's height. Providing an opening allows the gas (e.g., oxygen) bubbles to exit the container without significantly increasing the pressure within the container. Thus, during use, gas (e.g., oxygen) bubbles are continuously generated and exit through the opening(s) to be replaced by new gas (e.g., oxygen) bubbles as the liquid continues to be agitated.

[0014] The agitator may include a stirrer (e.g., it may be a stirrer). The agitator may include a mixer (e.g., it may be a mixer). The agitator may include an agitation pump, optionally in fluid communication with the interior of the enclosure, e.g., via a conduit (e.g., it may be an agitation pump). The agitator may include a flexible sheet (e.g., it may be a flexible sheet) (e.g., it may be more flexible than the walls of the enclosure). The agitator may include a tarpaulin, e.g., a tarpaulin that is at least partially immersed in the liquid and moves under the action of waves in the liquid (e.g., it may be a tarpaulin). The agitator may include an actuator (e.g., it may be an actuator). The agitator may include a transducer (e.g., it may be a frequency generator) (optionally an additional sounding body, usually a sounding body other than the sounding body that emits the sound whose transmission is limited by the device). The agitator may include a bubble curtain generator (e.g., it may 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-producing body. 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, the cylinder being defined by the liquid (e.g., within the container) containing the gas bubbles (i.e., between the inner and outer radii and below the height), and for example, there may be at least two times (e.g., at least three times, e.g., at least five times, optionally less than 100,000 times) more gas bubbles present within the bubble curtain than there are outside the bubble curtain. The bubble curtain generator may include a compressor. Those skilled in the art will understand that the pressure and volumetric output of the compressor may be selected depending on the volume of the container.

[0015] Use of a bubble curtain generator to agitate a liquid (e.g., within a container) allows for the generation of more gas bubbles in the liquid (i.e., some resulting from the agitation releasing dissolved oxygen from the liquid, thereby forming gas bubbles, and some resulting from the bubble curtain generator itself.) More gas bubbles provide more effective sound attenuation and limit sound transmission more effectively.

[0016] The housing may hold the sounding body. The housing may enclose the sounding body. The housing may contain the sounding body. The sounding body may be immersed in a liquid (e.g., within the housing). Restriction of sound transmission is more effective when the sounding body is held within a housing and / or immersed in a liquid.

[0017] The housing may be a first housing having one or more first housing walls. The device may include a second housing having one or more second housing walls. The second housing may at least partially surround the sound-producing body. The first housing may at least partially surround the second housing and be spaced apart from the second housing. In other words, the first housing may hold the sound-producing body, or the sound-producing body may be held within the second housing, and the first housing may also be considered to hold the sound-producing body.

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

[0019] The or each first enclosure wall may be flexible (e.g., elastically deformable) and / or may include one or more flexible (e.g., elastically deformable) portions. The or each second enclosure wall may be flexible (e.g., elastically deformable) and / or may include one or more flexible (e.g., elastically deformable) portions. The or each first enclosure wall may include a tarpaulin. The or each second enclosure wall may include a tarpaulin. The or each first enclosure wall may be water-resistant, e.g., waterproof. The or each second enclosure wall may be water-resistant, e.g., waterproof.

[0020] The or each first housing wall and / or the or each second housing wall may include (e.g., be formed of) a water-resistant material. The or each first housing wall and / or the or each second housing wall may include (e.g., be formed of) a UV-resistant material. The or each first housing wall and / or the or each second housing wall may include (e.g., be formed of) a hydrogen peroxide-resistant material. The or each first housing wall and / or the or each second housing wall may include (e.g., be formed of) a coating. The coating may be a saltwater-resistant coating. The coating may be a UV-resistant coating. The coating may be a hydrogen peroxide-resistant coating. The coating may be an anti-fouling coating. The or each first enclosure wall and / or the or each second enclosure wall may include (e.g., be formed of) a material that is strong enough to withstand tidal forces. The or each first enclosure wall and / or the or each second enclosure wall may include a reinforcing structure.

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

[0022] The second housing may be within the first housing and spaced apart from the first housing. Thus, a space may be defined between the first housing and the second housing (e.g., between the first housing wall and the second housing wall). A liquid (optionally, a portion of the liquid) may be held in the space between the first housing and the second housing (e.g., between the first housing wall and the second housing wall) within the first housing. A liquid (optionally, a portion of the liquid) may be held between the first housing wall and the second housing wall. An agitator may be held in the space between the first housing and the second housing (e.g., between the first housing wall and the second housing wall). Advantageously, this provides the option of the second housing holding the sound-producing body but not necessarily holding the liquid. This is particularly useful in devices or machines that cannot operate when the sound-producing body is immersed in liquid. In this case, the agitator may be used to agitate the liquid in the space between the first and second containers (e.g., between the walls of the first and second containers), thereby creating bubbles that limit sound transmission as the sound moves from the sound-generating body to the space. The second container may hold liquid (e.g., a portion of the liquid).

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

[0024] The liquid may include (e.g., can be) water. The liquid may include (e.g., can be) an aqueous solution. Water is abundant and inexpensive. Water is also particularly useful when the sounding body is offshore piling equipment, since in such instances water already surrounds the sounding body in use. The liquid may include (e.g., can be) seawater, an aqueous solution optionally including seawater. The liquid may include (e.g., can be) freshwater, an aqueous solution optionally including freshwater. The liquid may include (e.g., can be) saline, an aqueous solution optionally including saline. The liquid may include (e.g., can be) pure water (e.g., water having a resistivity of about 10 MΩ·cm at 25°C), or an aqueous solution including pure water.

[0025] The liquid may include (e.g., contain) hydrogen peroxide (i.e., H2O2). The liquid may include (e.g., be) an aqueous solution containing hydrogen peroxide. Hydrogen peroxide readily decomposes to form water and oxygen according to the following equation: 2H2O2 → 2H2O + O2

[0026] Hydrogen peroxide is thermodynamically unstable and can spontaneously decompose to form oxygen and water. Thus, a liquid containing hydrogen peroxide (or an aqueous solution thereof) provides both a source of dissolved oxygen and, potentially, a source of gas (e.g., oxygen) bubbles.

[0027] The liquid may comprise an aqueous solution containing hydrogen peroxide at a concentration of 0.001 mg / L or more, or 0.01 mg / L or more, or 0.1 mg / L or more, or 1 mg / L or more, or 20 mg / L or more, or 50 mg / L or more, or 80 mg / L or more, or 200 mg / L or more, or 500 mg / L or more, or 800 mg / L or more, or 1,000 mg / L or more. The liquid may comprise an aqueous solution containing hydrogen peroxide at a concentration of 2,500 mg / L or less, or 2,200 mg / L or less, or 1,500 mg / L or less. The liquid may include an aqueous solution containing hydrogen peroxide at a concentration of 20 mg / L to 2,500 mg / L (inclusive), or 200 mg / L to 2,500 mg / L (inclusive), or 20 mg / L to 2,200 mg / L (inclusive), or 200 mg / L to 2,200 mg / L (inclusive). The liquid may include an aqueous solution containing hydrogen peroxide at a concentration of about 1,500 mg / L (e.g., a concentration of 1,300 mg / L to 1,700 mg / L (inclusive)). The aqueous solution may include hydrogen peroxide at a concentration of 500 mg / L to 1,500 mg / L (inclusive).

[0028] In one example, hydrogen peroxide at a concentration of 1,500 mg / L can decompose to produce 0.609 liters of oxygen per liter, which is more than is needed to form enough bubbles to limit sound transmission.

[0029] Furthermore, if at least 10% of the volume of the containment body is made up of gas (e.g., oxygen) bubbles (e.g., released from dissolved oxygen in the liquid as a result of agitation of the liquid), this will reduce the speed of sound in the liquid and bubbles to about 30 ms -1 It is possible that the

number

[0030] The absorption of sound (e.g., restriction of sound transmission) by liquids and bubbles is further believed to be related to the total distance (e.g., path length) traveled by sound waves through bubbles and the total distance (e.g., path length) traveled by sound waves through a liquid in terms of multiples of the wavelengths of the sound waves. Thus, reducing the size of the wavelength of a sound wave at a given frequency (e.g., by traveling the sound wave in a medium where the speed of sound is reduced compared to the speed of sound in air or water) results in enhanced absorption of sound at that frequency, thus improving the restriction of sound transmission from the sound source. As discussed above, the speed of sound in a liquid containing a high density of bubbles is believed to be lower than the speed of sound in air and lower than the speed of sound in a liquid. Thus, a liquid containing a high density of bubbles is more effective at restricting sound transmission than, for example, an air gap. Furthermore, bubbles caused by oxygen released from water containing a high percentage of dissolved oxygen are, at least initially, extremely small (e.g., microscopic, e.g., on the order of a few microns in diameter or less) and therefore are particularly effective at restricting the transmission of higher frequencies.

[0031] The liquid may include (e.g., contain) an enzyme for the decomposition of hydrogen peroxide. The enzyme may be peroxidase. The enzyme may be catalase, optionally a synthetic catalase (e.g., as opposed to naturally occurring catalase). The aqueous solution may include (e.g., contain) an enzyme for the decomposition of hydrogen peroxide. The liquid (optionally an aqueous solution) may include an enzyme for catalytic decomposition of hydrogen peroxide at a concentration of 0.0001% w / w of water to 5% w / w of water, or 0.001% w / w of water to 5% w / w of water, or 0.05% w / w of water to 5% w / w of water, or 0.1% w / w of water to 4% w / w of water, or 0.5% w / w of water to 3% w / w of water. The aqueous solution may contain an enzyme for catalytic decomposition of hydrogen peroxide at a concentration of at least 0.0001% w / w of water, or at least 0.001% w / w of water, or at least 0.01% w / w of water, or at least 0.03% w / w of water. The aqueous solution may contain 6% w / w or less of enzyme / water. The aqueous solution may contain 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), optionally up to 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 enzyme can 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 hydrogen peroxide to enzyme ratios described herein result in sufficient reaction of the hydrogen peroxide to form bubbles (e.g., greater than 95% of the hydrogen peroxide reacts). The aqueous solution can optionally contain at least 10 mg / L, 50 mg / L, 200 mg / L, 300 mg / L, 400 mg / L, or 500 mg / L of enzyme (e.g., catalase).

[0032] The liquid (optionally an aqueous solution) may contain 1 kU to 100 kU of enzyme (e.g., catalase) per liter of water. The liquid (optionally an aqueous solution) may contain at least 5 kU, or at least 10 kU, or at least 20 kU of enzyme (e.g., catalase) per liter of water. The liquid (optionally an aqueous solution) may contain no more than 150 kU, or no more than 170 kU, or no more than 200 kU, or no more than 500 kU of enzyme (e.g., catalase) per liter of water. It will be understood that 1 U (1 enzyme unit) of enzyme (e.g., catalase) is the amount that will decompose 1 μmol of hydrogen peroxide per minute at pH 7.0 and 25° C. (e.g., as the hydrogen peroxide concentration decreases from 10.3 mM to 9.2 mM), and that 1 kU is 1,000 times this amount. One skilled in the art may choose to use a larger amount of enzyme (e.g., catalase) so that the enzyme (e.g., catalase) may be present in excess.

[0033] Advantageously, the use of a liquid (or aqueous solution) containing hydrogen peroxide and an enzyme for catalytic decomposition of hydrogen peroxide means that more hydrogen peroxide is decomposed into oxygen and water (and / or this decomposition occurs at an accelerated rate) than if the liquid (or aqueous solution) contained hydrogen peroxide and no (or little) such enzyme. The total amount of oxygen produced depends on the concentration of hydrogen peroxide used (e.g., the amount of hydrogen peroxide). The use of an enzyme means that lower concentrations of hydrogen peroxide can be used.

[0034] The device can be configured (and / or can include a liquid, optionally an aqueous solution) so that the concentration of hydrogen peroxide (e.g., when provided with an initial concentration of 750 mg / L hydrogen peroxide) decreases by at least 5% in 1 hour, e.g., at least 10% in 1 hour, optionally at least 25% in 1 hour, typically by less than 80% in 1 hour, e.g., less than 70% in 1 hour, e.g., less than 60% in 1 hour. Advantageously, the decomposition of hydrogen peroxide at these rates results in a steady supply of bubbles without too few bubbles for too long a period of time, or too many bubbles that would then require resupplying hydrogen peroxide to generate more bubbles. The device can be configured to allow for resupply of hydrogen peroxide at predetermined intervals (e.g., every hour, or every two hours, or every three hours).

[0035] The liquid may include (e.g., contain) a surfactant. The liquid may include an aqueous solution containing a surfactant. Advantageously, when a surfactant is provided, gas bubbles are less likely to exit the container at the liquid surface, and therefore more gas may be retained (because the gas bubbles may be encouraged to flow back into the liquid, for example, as a result of the liquid flow caused by a pump). This means that gas (e.g., oxygen) and / or gas (e.g., oxygen) bubbles in the liquid do not need to be replaced as frequently, thus saving energy from having an agitator agitate the liquid. In some cases, this also means that fewer chemicals (such as hydrogen peroxide and enzymes for decomposing hydrogen peroxide) are required.

[0036] The surfactant can be a surfactant rated safe for use in marine environments. The surfactant can be a surfactant rated safe for use in freshwater environments. The surfactant can include soapberry. The surfactant can include yucca extract. The surfactant can include lecithin. The surfactant can include a monoglyceride. The surfactant can include a diglyceride. The surfactant can include a fatty acid. The surfactant can include a functionalized protein. The surfactant can include a natural surfactant (e.g., a natural surfactant). The surfactant can include a synthetic surfactant (e.g., a synthetic surfactant). The surfactant can include a tween surfactant. The surfactant can include sodium stearoyl lactylate. The surfactant can include calcium stearoyl lactylate. The surfactant can include a sucrose ester.

[0037] A stirring region may surround the stirrer. The stirrer may optionally be configured to form sufficient bubbles such that after 60 seconds, e.g., after 2 minutes, e.g., after 5 minutes (optionally, after less than 20 minutes, e.g., less than 18 minutes, e.g., less than 15 minutes) of activation of the stirrer, the total volume of the bubbles is at least 1% of the total volume of the stirring region (e.g., described above) surrounding the stirrer (e.g., the stirrer is located at the bottom of the stirring region). For example, sufficient bubbles may be formed such that the total volume of the bubbles is at least 2% (optionally 10%) of the total volume of the stirring region, e.g., at least 25% of the total volume of the stirring region. The stirrer may be configured to form sufficient bubbles such that the total volume of the bubbles is less than 99%, e.g., less than 90%, e.g., less than 75% of the total volume of the stirring region. The liquid and the bubbles may together form a foam, e.g., a fluid foam. A high proportion of bubbles in the liquid (e.g., a high number of bubbles relative to the total volume of the liquid and / or a large total volume of bubbles) may be more effective at limiting the transmission of sound from the sound-producing body through the liquid.

[0038] The device (e.g., an agitator, optionally in combination with a fluid) can be configured to activate the agitator for a (e.g., initial) activation period, thereby causing sufficient bubble generation such that the bubbles are then suspended in the fluid for a decay period longer than the (e.g., initial) activation period. For example, the device can be configured to activate the agitator 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), resulting in 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 understand that appropriate initial activation periods and subsequent decay periods depend on various factors, including the composition of the fluid, the temperature of the fluid, the size and configuration of the containment body, the peak acoustic pressure emitted by the sound-generating body, etc. By selecting an actuation period that results in sufficient bubble generation such that the decay period is longer than the actuation period (optionally taking into account the composition and / or temperature of the fluid, and / or the size and configuration of the containment body, and / or the peak acoustic pressure exerted by the sounding body, etc.), it is possible to provide a more efficient device since less energy is required to continuously operate the agitator.

[0039] The agitator may be configured to generate gas bubbles, the gas bubbles having an average (e.g., mean) diameter of at least 0.5 micrometers, e.g., at least 1 micrometer, e.g., at least 0.01 cm, e.g., at least 0.05 cm, e.g., at least 0.1 cm. The agitator may be configured to generate gas bubbles, the gas bubbles having an average (e.g., mean) diameter of less than 1 cm, e.g., less than 0.5 cm, e.g., less than 0.2 cm. At least 50% of the generated gas bubbles may have a diameter of between 1 micrometer and 0.1 cm, e.g., at least 75% of the generated gas bubbles may have a diameter of between 1 micrometer and 0.1 cm, e.g., at least 85% of the generated gas bubbles may have a diameter of between 1 micrometer and 0.1 cm. In one example, the agitator may be configured to generate gas bubbles, the gas bubbles having an average (e.g., mean) diameter of 5 mm. Those skilled in the art will understand that the above diameter may refer to the maximum diameter of the bubble within 3 seconds of initiation, optionally within 15 seconds of initiation, optionally within 1 minute of initiation (and that this may depend on the size of the container), and that the size of the bubble may change over time (e.g., due to changes in pressure as it rises through the liquid or due to coalescence with other bubbles).

[0040] The presence of hydrogen peroxide has been found to be particularly effective in causing the generation of smaller bubbles. When a liquid contains water, hydrogen peroxide, and an enzyme for decomposing hydrogen peroxide and the liquid is agitated, it is possible to form bubbles sufficient to limit the transmission of sound in less than 30 seconds. Thus, an apparatus (e.g., a mixer, e.g., containing a liquid) can be configured to form bubbles sufficient to limit the transmission of sound in less than 30 seconds, e.g., less than 20 seconds, e.g., less than 10 seconds, e.g., less than 5 seconds. An apparatus (e.g., a mixer, e.g., containing a liquid) can be configured to form bubbles sufficient to limit the transmission of sound (e.g., reduce the sound pressure by at least 20 decibels) within one second, e.g., three seconds. For example, an agitator can be configured to agitate a sufficient volume of liquid in a sufficiently short time to form bubbles sufficient to limit the transmission of sound (e.g., reduce the sound pressure by at least 20 decibels) within one second, e.g., three seconds. It has also been found that when a liquid contains hydrogen peroxide and an enzyme for the decomposition of hydrogen peroxide, agitation of the liquid increases the rate at which the hydrogen peroxide decomposes into water and oxygen. Furthermore, such liquids limit the transmission of sound more effectively than water containing air bubbles, which take longer to dissipate when agitation is stopped and reform more quickly when agitation is resumed.

[0041] The agitator may be configured to generate at least 1,000 bubbles in a 1 liter volume per minute that the agitator is operating, e.g., at least 10,000 bubbles in a 1 liter volume, e.g., at least 100,000 bubbles in a 1 liter volume. The agitator may be configured to generate less than 5,000,000 bubbles in a 1 liter volume per minute that the agitator is operating, e.g., less than 1,000,000 bubbles in a 1 liter volume, e.g., less than 500,000 bubbles in a 1 liter volume. Those skilled in the art will understand that the size and amount of bubbles generated will depend on several factors, including, but not limited to, the temperature of the liquid, the pH 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 rate of flow of the liquid caused by the agitator), the presence or absence of any substances in the liquid, the type and concentration of any substances in the liquid (e.g., hydrogen peroxide, enzymes, surfactants), etc.

[0042] The first container is at least 0.5 m 3 , e.g., 1m 3 , e.g., at least 5 m 3 , e.g., at least 10 m 3 , e.g., at least 15 m 3 The first containment body may define a volume of 5,000 m (optionally including the volume of the second containment body, if present). 3 Less than, for example, 2,500 m 3 Less than, for example, 1,000 m 3 The second containment may define a volume of at least 0.25 m (optionally including the volume of the second containment, if present). 3 , e.g., at least 0.5 m 3 , e.g., at least 4m 3 , e.g., at least 8m 3 , e.g., at least 10 m 3 The second containment body may define a volume of 2,000 m 3 Less than, for example, 1,000 m 3 Less than, for example, 500m 3The space between the first and second enclosures (e.g., between the first and second enclosure walls) may define a volume of at least 0.25 m 3 , e.g., at least 0.5 m 3 , e.g., at least 1 m 3 , e.g., at least 2 m 3 , e.g., at least 5 m 3 The space between the first enclosure and the second enclosure (e.g., between the first enclosure wall and the second enclosure wall) may define a volume of 3,000 m 3 Less than, for example, 1,500 m 3 Less than, for example, 500m 3 The device may define a volume of less than 1 / 4" (1 / 2 inch). Those skilled in the art will appreciate that the scale of the device, and therefore the scale of the enclosure(s), may be selected depending on the scale of the sound-producing body. Such a volume may be suitable for enclosing (e.g., at least partially) a large sound-producing body, such as, for example, heavy machinery such as drilling equipment, offshore piling equipment, etc.

[0043] The container may include one or more partitions, the or each partition extending at least partially across the interior of the container, thereby forming a plurality of sub-containers. Each of the plurality of sub-containers may have a respective agitator disposed therein. Each of the plurality of sub-containers may have a respective opening defined therein, each respective opening being positioned to allow air bubbles to exit the respective sub-container (and optionally the container). One or more partitions may extend horizontally. One or more partitions may extend vertically. One or more partitions may extend in a direction inclined relative to the horizontal. One or more partitions may be planar. One or more partitions may extend between one or more of the first container walls and one or more of the second container walls. Each sub-container may have a volume of at least 5%, e.g., at least 10%, e.g., at least 20% of the total volume of the (e.g., first) container. Each sub-container may have a volume that is less than 80%, e.g., less than 60%, e.g., less than 50% of the total volume of the (e.g., first) containment. Each sub-container may be the same size as each of the other sub-containers, but this is not required. In one example, one or more (optionally each) of the plurality of sub-containers may have a (vertical) height of at least 5 meters, e.g., at least 20 meters, e.g., at least 40 meters. One or more (optionally) of the plurality of sub-containers may each have a (vertical) height of less than 100 meters, e.g., less than 75 meters, e.g., less than 60 meters. The or each partition may include (e.g., be formed of) a relatively low acoustic impedance material. The or each partition may include (e.g., be formed of) a sound-absorbing material. The sub-containers may be stacked vertically (e.g., a first sub-container positioned above a second sub-container, etc.). The agitators may be stacked vertically.

[0044] When the sound-producing body is particularly large, it can be useful to provide a particularly large containment body to (e.g., at least partially) surround the sound-producing body. However, it takes some time for bubbles to move upward under buoyancy (especially for very small bubbles, this may occur only after they coalesce with other bubbles, thereby forming larger bubbles) or move in other directions as the fluid flows through the containment body. Therefore, if an agitator is provided in only one location within a large containment body, it may take a long time before there are enough bubbles throughout the liquid in the containment body to effectively limit sound transmission. By providing a partition within the containment body (effectively dividing the containment into multiple sub-containers) and providing an agitator within each sub-container, it is possible to reduce the time required to provide enough bubbles. It should also be noted that both bubble size and the speed of sound are pressure-dependent, and pressure increases as a function of depth. Providing sub-containers as described herein can help control this.

[0045] The device may include a pump configured to induce a flow of liquid at a liquid surface. The pump may include a pump inlet at an upper portion of the container (e.g., at or near the liquid surface). The pump may include a pump outlet at or near the bottom of the container. There may be a conduit extending between the pump inlet and the pump outlet. The pump may be configured to induce a flow of liquid in a downward direction. The device may include one or more pumps configured to induce a flow of liquid within the container. Each sub-container may optionally include a respective pump at an upper portion of the sub-container configured to induce a flow of liquid, for example, in a downward direction.

[0046] Providing a pump configured to induce a flow of liquid at the liquid surface provides the advantage of allowing air bubbles that rise to the surface due to buoyancy to be forced back down into the containment body (e.g., by forcing the fluid to flow in a downward direction). This means that fewer air bubbles need to be replaced, the agitator can be operated more discontinuously or at a lower speed, a lower percentage of dissolved oxygen is required, a lower concentration of hydrogen peroxide is required, or a smaller amount of enzyme for decomposing hydrogen peroxide is required. In short, the use of such a pump allows for a more efficient device.

[0047] The pump(s) may be configured, for example, to move at least 1 L per minute, for example, at least 500 L per minute, for example, at least 1000 L per minute (optionally in combination). The pump(s) may be configured to move up to 50,000 L per minute, for example, up to 25,000 L per minute, for example, up to 10,000 L per minute (optionally in combination). One skilled in the art will understand that the type and capacity of the pump may be selected depending on the size of the container. For example, the pump may be configured to move 100% of the container's volume at least once every 30 minutes, for example, at least once every 15 minutes, for example, at least once every 10 minutes. The pump may be configured to move 100% of the container's volume at least once every 3 minutes, for example, at least once every 5 minutes.

[0048] The agitator may be configured to cause sufficient bubbles to form in a stirring region surrounding the agitator (e.g., described above) such that the optical (e.g., light) intensity of (e.g., visible) light (e.g., within a wavelength range of 300 nm to 800 nm, e.g., 350 nm to 780 nm, e.g., 380 nm to 750 nm) that has traveled through 10 centimeters of the liquid (within the stirring region) is reduced by at least 10% (e.g., at least 50%, e.g., at least 80%, optionally up to 99%) compared to the intensity of that light before it traveled through the liquid. The agitator may be configured to cause sufficient bubbles to form in a stirring region surrounding the agitator such that the optical (e.g., light) intensity of (e.g., visible) light (e.g., within a wavelength range of 300 nm to 800 nm, e.g., 350 nm to 780 nm, e.g., 380 nm to 750 nm) traveling through 10 centimeters of liquid (within the stirring region) is reduced by at least 10% (e.g., at least 50%, e.g., at least 80%, optionally up to 99%) compared to the intensity of light traveling through 10 centimeters of liquid that does not contain bubbles.

[0049] Those skilled in the art will appreciate that the optical (eg, light) intensity of the light can be calculated according to the following formula:

number

[0050] where x is the distance through the liquid (including any air bubbles in the liquid), I(x) is the intensity of the light at distance x, I0 is the initial intensity of the light at distance x=0, and κ vis the opacity of the liquid, and ρ is the mass density of the liquid. Thus, in this context, optical (e.g., light) intensity should be understood as a function of the opacity of the medium through which the light travels. A liquid containing a relatively high density (e.g., relatively small) of gas bubbles will have a higher opacity than a liquid containing a relatively low density (e.g., relatively small) of gas bubbles. It should also be understood that a liquid containing a higher percentage of dissolved oxygen may have a different opacity to light compared to a liquid containing a lower percentage of dissolved oxygen. Furthermore, if saltwater (e.g., seawater) contains dissolved oxygen, it may also have a different opacity to light than freshwater containing dissolved oxygen.

[0051] If enough bubbles are generated such that the optical (e.g., light) intensity of (visible) light is reduced as described above, the inventors have found that the transmission of sound is also effectively restricted.

[0052] However, it will be appreciated that bubbles of a sufficiently small diameter may effectively attenuate sound waves without (e.g., significantly) changing the opacity of the liquid. Surprisingly, it has been found that bubbles less than 1 mm in diameter and in numbers that do not significantly change the opacity of 10 centimeters of water still provide a damping effect. An apparatus (e.g., an agitator) can be configured to cause the generation of bubbles less than 1 mm in diameter (typically greater than 1 μm). The apparatus (e.g., an agitator) can be configured to form sufficient bubbles in an agitation region surrounding the agitator (e.g., as described above) such that the optical (e.g., light) intensity of (e.g., visible) light (e.g., within a wavelength range of 300 nm to 800 nm, e.g., 350 nm to 780 nm, e.g., 380 nm to 750 nm) that has traveled through 10 centimeters of liquid (within the agitation region) is reduced by less than 10% (e.g., less than 5%, e.g., less than 2%) compared to the intensity of that light before traveling through the liquid.

[0053] The device may include a (e.g., visible) light detector configured to output an indication of the intensity of light transmitted through a distance of the liquid. The device may include a (e.g., visible) light emitter configured to emit light (e.g., that can be detected by the light detector). The distance may be at least 5 centimeters, e.g., at least 10 centimeters, e.g., at least 20 centimeters. The distance may be a distance within the stirring region. The device may include a sound detector configured to output an indication of the intensity of sound transmitted outside the (e.g., first) containment body. Providing such a light detector and / or sound detector(s) provides an indication of whether sufficient air bubbles have been generated to effectively limit the transmission of sound. Providing a sound detector provides an indication of the transmission of sound. Both detectors may be useful for monitoring the operation of the device, especially by a user who may be away from the device.

[0054] The apparatus may include a controller. The controller may be configured to receive (e.g., from a photodetector) an indication (e.g., above) of the intensity of (e.g., visible) light that has passed through (e.g., the above) distance of the liquid and, in response to the received indication, adjust the amount of agitation caused by the agitator, thereby maintaining a target light intensity. The target light intensity may be within a range of light intensity. The range of light intensity may be 90% to 10%, optionally 80% to 20%, e.g., 60% to 40%, of the intensity of (e.g., visible) light that has not passed through (e.g., the above) distance of the liquid. The target light intensity may be less than a threshold light intensity. The threshold light intensity may be 30% of the intensity of (e.g., visible) light that has not passed through (e.g., the above) distance of the liquid, or 20% of the intensity of (e.g., visible) light that has not passed through (e.g., the above) distance of the liquid, or 10% of the intensity of (e.g., visible) light that has not passed through (e.g., the above) distance of the liquid. The light detector may be configured to compare the intensity of light that has passed through a (e.g., the above) distance of the liquid with the intensity of light of a reference beam, the reference beam being a beam of light that has not passed through the liquid, and optionally the reference beam being a beam of light from the same light source as the light source of the light that has passed through the above-mentioned distance of the liquid.

[0055] If there are enough air bubbles present such that the light intensity is reduced as the light passes through the liquid, this also indicates that the transmission of sound through the liquid is limited. Agitation of the liquid by the agitator causes air bubbles to form, and when agitation stops, the air bubbles steadily exit the liquid (e.g., under buoyancy, for example, through an opening in the container). Thus, by providing a controller as described herein, it is possible to configure a feedback system in which the agitator activates when the light intensity increases above a threshold or outside a range (because this indicates the presence of fewer air bubbles and therefore the potential for more sound transmission), and the agitator does not activate when the light intensity is below a threshold or within a range (because this indicates the presence of more air bubbles and therefore the potential for less sound transmission). This makes the device more efficient, as it means that the agitator does not need to be continuously activated.

[0056] The gas (e.g., oxygen) bubbles may form a gas (e.g., oxygen) bubble curtain. The gas (e.g., oxygen) bubble curtain may include gas (e.g., oxygen) bubbles formed as a result of agitation of a fluid by an agitator. The gas (e.g., oxygen) bubbles may form a gas (e.g., oxygen) bubble curtain that at least partially surrounds the sound-producing body. The gas (e.g., oxygen) bubble curtain may be an annular gas (e.g., oxygen) bubble curtain, for example, a relatively higher density of gas (e.g., oxygen) bubbles may be found within the annular space (gas (e.g., oxygen) bubble curtain) within the containment body than outside the annular space. There may be at least two times (e.g., at least three times, e.g., at least five times, optionally less than 100,000 times) more gas bubbles within the gas (e.g., oxygen) bubble curtain than there are outside the gas (e.g., oxygen) bubble curtain. The annular space may have an inner perimeter, an outer perimeter, and a height, and the sound-producing body may be surrounded by the inner perimeter. The thickness of the annular space (e.g., between the inner and outer peripheries) can be at least 5 centimeters, e.g., at least 10 centimeters, e.g., at least 50 centimeters. The thickness of the annular space can be less than 10 meters, e.g., less than 5 meters, e.g., less than 1 meter. However, those skilled in the art will understand that the oxygen bubble curtain can be formed in virtually any shape (e.g., through the positioning of the agitator and / or the positioning and use of the pump) and can be configured to partially or completely surround the sound-producing body. For example, the oxygen bubble curtain can be generally rectangular shaped, having a length parallel to the bottom of the enclosure, a height parallel to the height dimension of the enclosure, and a width perpendicular to the height. The width of the oxygen bubble curtain (e.g., between the inner and outer peripheries) can be at least 5 centimeters, e.g., at least 10 centimeters, e.g., at least 50 centimeters. The width of the oxygen bubble curtain can be less than 10 meters, e.g., less than 5 meters, e.g., less than 1 meter. The inventors have surprisingly found that the air bubbles within the bubble curtain effectively limit the transmission of sound even when the bubble curtain has a relatively small thickness or width (e.g., less than 50 centimeters).

[0057] The device may be configured to generate sufficient bubbles to reduce sound transmission such that the sound pressure of the sound emitted by the sound-producing body after passing through the bubbles is at least 20 decibels lower than the sound pressure of the sound emitted by the sound-producing body before passing through the bubbles, e.g., at least 40 decibels, e.g., at least 60 decibels, e.g., at least 100 decibels lower. The device may be configured to generate sufficient bubbles to prevent at least 60% in amplitude, e.g., at least 80% in amplitude, e.g., at least 90% in amplitude, of the sound from the sound-producing body from being transmitted across the bubbles. The device may be configured to generate sufficient bubbles to reduce the peak frequency of sound waves from the sound-producing body from being transmitted across the bubbles by at least 60%, e.g., at least 80%, e.g., at least 90% in amplitude. The device may be configured to generate sufficient bubbles such that substantially no sound from the sound-producing body is transmitted across the bubbles.

[0058] The controller may be configured to receive an indication (e.g., as described above) of sound intensity outside the (e.g., first) enclosure and, in response to the received indication of sound intensity, adjust the amount of agitation caused by the agitator, thereby maintaining a target sound intensity. The target sound intensity may be within a range of sound intensity. The range of sound intensity may be 0 to 500 decibels, such as 1 to 300 decibels, such as 5 to 100 decibels. The target sound intensity may be less than a threshold sound intensity. The threshold sound intensity may be less than 150 decibels, such as less than 80 decibels, such as less than 50 decibels, such as less than 20 decibels.

[0059] The device may include a temperature sensor configured to output an indication of the temperature of the liquid. The device may include a heater configured to heat the liquid. The device may include a thermal regulator (e.g., including a heat exchanger) configured to regulate the temperature of the liquid. The thermal regulator (e.g., a heat exchanger) may transfer heat from within the enclosure to the liquid outside the enclosure, or vice versa. The device may include a cooler configured to cool the liquid. The controller may be configured to receive an indication of the temperature of the liquid (e.g., as described above) and adjust the amount of agitation caused by the agitator in response to the received indication of the temperature of the liquid. This is useful because the amount and size of bubbles generated by operation of the agitator may depend on the temperature. The controller may be configured to adjust the temperature of the liquid, for example, in response to the received indication of the temperature of the liquid, thereby optionally maintaining a target temperature. The target temperature may be within a range of temperatures. The temperature range may be between 5°C and 50°C, inclusive, for example, between 10°C and 30°C, inclusive, for example, between 18°C ​​and 22°C, inclusive.

[0060] The device may include a pH sensor configured to output an indication of the pH of the liquid. The pH sensor may be calibrated to the salinity of the liquid in the container. The controller may be configured to receive the indication of the pH of the liquid (e.g., as described above) and adjust the amount of agitation caused by the agitator in response to the received indication of the pH of the liquid. This is useful because the amount and size of bubbles generated by operation of the agitator may depend on the pH.

[0061] The apparatus may include, for example, a pressure sensor configured to output an indication of the pressure of the liquid in the agitation region. The controller may be configured to receive the indication (e.g., as described above) of the pressure of the liquid and adjust the amount of agitation caused by the agitator in response to the received indication of the pressure of the liquid. This is useful because the amount and size of bubbles generated by operation of the agitator may depend on the pressure.

[0062] The device may include an oxygen detector configured to output an indication of the percentage of oxygen saturation of the liquid. The controller may be configured to receive the indication of the percentage of oxygen saturation of the liquid (e.g., as described above) and to adjust the amount of agitation caused by the agitator in response to the received indication of the percentage of oxygen saturation of the liquid. This is useful because the amount and size of bubbles generated by operation of the agitator may depend on the amount of dissolved oxygen in the liquid.

[0063] The sound-generating body may include a mechanical device, such as a mechanical actuator. The sound-generating body may include a mechanical machine. The sound-generating body may include an offshore pile driving rig. Offshore pile driving rigs are particularly loud devices, making limiting sound transmission from offshore pile driving equipment particularly difficult. However, limiting sound transmission from such equipment represents a significant benefit to marine life. In particular, marine mammals and some cetaceans can hear sounds at frequencies much higher than those within the human audible frequency range, including some frequencies generated by offshore pile driving (frequencies above the human audible frequency range). As described herein, the sound-generating body may emit sound waves having a peak frequency in the range of 50 Hz to 200 kHz, inclusive, optionally 10 Hz to 300 kHz, inclusive, and optionally 5 Hz to 500 kHz, inclusive. The device may be configured to restrict the transmission of sound waves having peak frequencies in the range of 50 Hz to 200 kHz inclusive, optionally 10 Hz to 300 kHz inclusive, optionally 5 Hz to 500 kHz inclusive.

[0064] The sounding body may include a valve, such as a control valve. For example, the sounding body may include a valve (e.g., a control valve) in a gas distribution line. The gas distribution line may include a very large valve (e.g., a control valve) that, in this role, manages a high-energy flow and generates significant noise under normal steady-state operation.

[0065] The sound-producing body may emit (e.g., may be configured to emit) a sound in the human audible frequency range. The sound-producing body may emit (e.g., may be configured to emit) an ultrasonic wave. The sound-producing body may emit (e.g., may be configured to emit) a sound having a frequency below the human audible frequency range. For example, the sound-producing body may emit (e.g., may be configured to emit) a sound wave having a peak frequency of at least 1 Hz, e.g., at least 20 Hz, e.g., at least 50 Hz. The sound-producing body may emit (e.g., may be configured to emit) a sound wave having a peak frequency less than 500 kHz, e.g., less than 200 kHz, e.g., less than 100 kHz. The sound-producing body may emit (e.g., may be configured to emit) a sound wave having a peak frequency between 50 Hz and 100 kHz (inclusive), e.g., between 1 kHz and 50 kHz (inclusive), e.g., between 10 kHz and 50 kHz (inclusive). In one example, the sound-producing body may emit (e.g., may be configured to emit) a sound wave in a frequency range between 13 Hz and 3 kHz.

[0066] In some examples, bubbles at relatively deep depths may be relatively small (e.g., on average, e.g., mean) in diameter and therefore more effective at restricting the transmission of relatively high frequency sound, while bubbles at relatively shallow depths may be relatively large (e.g., on average, e.g., mean) in diameter and therefore more effective at restricting the transmission of relatively low frequency sound. The device may be configured to restrict the transmission of sound waves within a first frequency range at a first depth and to restrict 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 frequency range higher than the second frequency range.

[0067] In some exemplary embodiments, the container may include one or more partitions, thereby forming the multiple subcontainers described herein. The multiple subcontainers may include one or more deep subcontainers positioned at a relatively large depth and one or more shallow subcontainers positioned at a relatively small (e.g., shallow) depth. Advantageously, this allows for a balance of bubbles under higher pressure (e.g., in the deep subcontainer), thus allowing for smaller bubbles, thereby maintaining the absorption frequency range. Higher pressure at depth means smaller bubbles and therefore higher frequency absorption.

[0068] A liquid (e.g., water, e.g., an aqueous solution) containing at least 2% (e.g., at least 10% by volume) dissolved oxygen can be formed by combining water and hydrogen peroxide and allowing the hydrogen peroxide to decompose (e.g., naturally) into water and oxygen. A liquid (e.g., water, e.g., an aqueous solution) containing at least 2% (e.g., at least 10% by volume) dissolved oxygen can be formed by combining water, hydrogen peroxide, and an enzyme for decomposing hydrogen peroxide (e.g., catalase) and allowing the hydrogen peroxide to decompose into water and oxygen under the action of the enzyme. A liquid (e.g., water, e.g., an aqueous solution) containing at least 2% (e.g., at least 10% by volume) dissolved oxygen can be formed by forcing oxygen (optionally oxygen bubbles) into a liquid (e.g., water, e.g., an aqueous solution), optionally using a mechanical system. Water containing at least 2% (e.g., at least 10% by volume) dissolved oxygen can be formed by using an oxygenation system, for example, by injecting oxygen in a membrane diffusion (e.g., oxygenation) system. The device may include a membrane diffusion (e.g., oxygenation) system. If the device includes a membrane diffusion (e.g., oxygenation) system, the bubbles may include oxygen bubbles, and / or nitrogen bubbles, and / or air bubbles. Water containing at least 2% by volume (e.g., at least 10% by volume) dissolved oxygen may be formed by a micro-bubbling system. The device may include a micro-bubbling system. Water containing at least 2% by volume (e.g., at least 10% by volume) dissolved oxygen may be formed by using a Venturi system. The device may include a Venturi system.

[0069] The apparatus may include a gas (e.g., oxygen) tank. The apparatus may include one or more gas supply conduits extending between the gas (e.g., oxygen) tank and a membrane diffusion (e.g., oxygenation) system, each conduit including at least one valve configured to place the gas (e.g., oxygen) tank in fluid communication with the membrane diffusion (e.g., oxygenation) system or block fluid communication. The apparatus may include one or more gas supply conduits extending between the gas (e.g., oxygen) tank and a microbubbling system, each conduit including at least one valve configured to place the gas (e.g., oxygen) tank in fluid communication with the microbubbling system or block fluid communication. The apparatus may include one or more gas supply conduits extending between the gas (e.g., oxygen) tank and a venturi system, each conduit including at least one valve configured to place the gas (e.g., oxygen) tank in fluid communication with the venturi system or block fluid communication.

[0070] The housing may surround (e.g., completely) the sound-producing body in all directions, except for the opening. For example, the second housing wall may be configured to surround the sound-producing body in all directions except for the location where the first opening is provided, and the first housing wall may be configured to surround the second housing wall in all directions except for the location where the second opening is provided, and the first opening and the second opening may be offset from each other. The first housing wall may surround (e.g., completely) the sound-producing body in all directions, except for the location where the opening is provided. The second housing wall may surround (e.g., completely) the sound-producing body in all directions, except for the location where the opening is provided. The housing may have a closable opening. The housing may have a door configured to open and close the opening.

[0071] Nevertheless, it will be understood that a housing arranged to at least partially surround a sound-producing body need not restrict sound transmission in all directions. For example, the housing may be an open-topped cylinder, thereby restricting sound transmission from the sound-producing body in downward and lateral directions, but not (or less so) in an upward direction. Similarly, a housing arranged to at least partially surround a sound-producing body may restrict sound transmission in one direction or over a range of angles outward from the sound-producing body. It is useful to provide a housing in the form of a barrier, which restricts sound transmission from the sound-producing body to a specific space. The housing may be provided in the form of a barrier. The device (e.g., the housing) may be configured to restrict sound transmission from the sound-producing body to a specific space.

[0072] Thus, a further aspect of the present invention provides an apparatus for restricting the transmission of sound from a sound-producing body, the apparatus comprising a sound barrier comprising a container for holding a liquid, the liquid containing at least 2% by volume (e.g., at least 10% by volume) dissolved oxygen, and an agitator configured to agitate the liquid, thereby causing the formation of gas (e.g., oxygen) bubbles in the liquid. Advantageously, where there is a space near the sound-producing body and it is desired to restrict sound from entering the space, the sound barrier may be positioned between the sound-producing body and the space, and the liquid and gas bubbles then restrict the transmission of sound into the space.

[0073] A further aspect of the invention provides a method of limiting the transmission of sound (e.g., in a liquid) from a sound-producing body, the sound-producing body being at least partially surrounded by a container (optionally a first container), the container holding a liquid containing at least 2% by volume (e.g., at least 10% by volume) dissolved oxygen, the method comprising causing agitation (e.g., stirring) of (e.g., at least a portion of) the liquid within the container, thereby causing the formation of gas (e.g., oxygen) bubbles in the liquid. Forming gas (e.g., oxygen) bubbles may include releasing oxygen from the liquid, thereby forming the bubbles.

[0074] Agitation of a liquid containing at least 2% by volume (e.g., at least 10% by volume) dissolved oxygen has been found to be a particularly effective method of causing the formation of sufficient gas bubbles to limit the transmission of sound in (e.g., through) the liquid.

[0075] The method may optionally include receiving, from a light detector, an indication of the intensity of the (e.g., visible) light that has traveled a certain distance through the liquid. The method may include adjusting the amount of agitation induced in response to the received indication, thereby maintaining a target light intensity. The target light intensity may be within a range of light intensity. The range of light intensity may be 90% to 10%, optionally 95% to 5%, optionally 80% to 20%, e.g., 60% to 40%, of the intensity of the (e.g., visible) light that has not traveled said distance through the liquid. The target light intensity may be less than a threshold light intensity. The threshold light intensity may be 30% of the intensity of the (e.g., visible) light that has not traveled said distance through the liquid, or 20% of the intensity of the (e.g., visible) light that has not traveled said distance through the liquid, or 10% of the intensity of the (e.g., visible) light that has not traveled said distance through the liquid. The method may include comparing the intensity of the light that has passed through a (e.g., above) distance of the liquid with the intensity of light of a reference beam, the reference beam being a beam of light that has not passed through the liquid, and optionally the reference beam being a beam of light from the same light source as the light source of the light that has passed through the above distance of the liquid.

[0076] The method may include receiving an indication of sound intensity outside the enclosure (optionally outside the first enclosure) and adjusting the amount of induced agitation in response to the received indication of sound intensity, thereby maintaining a target sound intensity. The target sound intensity may be within a range of sound intensity. The range of sound intensity may be between 0 and 100 decibels, for example, between 1 and 80 decibels, for example, between 5 and 40 decibels. The target sound intensity may be less than a threshold sound intensity. The threshold sound intensity may be less than 100 decibels, for example, less than 50 decibels, for example, less than 20 decibels.

[0077] Those skilled in the art will understand that the size and amount of bubbles generated will depend on several factors, including, but not limited to, the temperature of the liquid, the pH 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 rate of flow of the liquid caused by the agitator), the presence or absence of any substances in the liquid, the type and concentration of any substances (e.g., hydrogen peroxide, enzymes, surfactants) in the liquid, etc.

[0078] Thus, the method may include receiving an indication of the temperature of the liquid. The method may include adjusting the temperature of the liquid (e.g., in response to the received indication of the temperature of the liquid) to thereby maintain a target temperature. The target temperature may be within a range of temperatures. The temperature range may be between 5°C and 50°C, inclusive, such as between 10°C and 30°C, inclusive, such as between 18°C ​​and 22°C, inclusive. The method may include adjusting an amount of agitation induced in response to the received indication of the temperature of the liquid.

[0079] The method may include receiving an indication of a pH of the liquid. The method may include adjusting an amount of agitation induced in response to the received indication of a pH of the liquid.

[0080] The method may include, for example, receiving an indication of a pressure of the liquid in the agitation region. The method may include adjusting an amount of agitation induced in response to the received indication of the pressure of the liquid.

[0081] The method may include receiving an indication of a volume of liquid in the container. The method may include causing additional liquid to be dispensed into the container. The method may include dispensing additional liquid into the container. The method may include causing excess liquid to leave the container. The method may include removing the excess liquid.

[0082] A further aspect of the invention provides a method of forming a liquid comprising water and at least 2% by volume (e.g., at least 10% by volume) dissolved oxygen, as described above, the method comprising causing mixing (e.g., mixing) water, hydrogen peroxide, and a catalyst for decomposition of hydrogen peroxide.

[0083] It is easier to form oxygen bubbles in water containing at least 2% (by volume) (e.g., at least 10% (by volume)) dissolved oxygen by agitating the water than to form oxygen bubbles in water containing a lower percentage of dissolved oxygen.

[0084] The liquid may contain at least 2% by volume (e.g., at least 10% by volume) dissolved oxygen. The liquid may contain at least 25% by volume, such as at least 50% by volume, for example, at least 75% by volume, for example, at least 80% by volume dissolved oxygen. The liquid may contain less than 100% dissolved oxygen, such as less than 99%, for example 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 be supersaturated with oxygen, for example, having an oxygen saturation of greater than 100%. The liquid may have an oxygen saturation of at least 120%. The liquid may have an oxygen saturation of less than 200%, for example, less than 150%. When a higher proportion of dissolved oxygen is present in the liquid (e.g., particularly when the liquid contains at least 10% dissolved oxygen by volume, although some effects are also observed when the liquid contains at least 2% dissolved oxygen by volume), oxygen is more readily released from the liquid when the liquid is agitated, thereby forming oxygen bubbles.

[0085] The controller may include one or more processors and a computer-readable memory (e.g., a non-transitory computer-readable storage medium) that stores instructions that, when executed by the one or more processors, cause the controller to perform actions that the controller is configured to perform.

[0086] The sounding body may be a sounding body in a body of water (e.g., an ocean, sea, lake, loch, reservoir, pond, etc.) having a water surface and a floor (e.g., ocean floor, seabed, lakebed, etc.). The device may be positioned in the body of water. The method may include installing the device in the body of water. The liquid surface within the enclosure may be higher than the water surface outside the enclosure (e.g., as a result of water pressure acting on the enclosure walls). Gas (e.g., oxygen) bubbles that form as a result of agitation of the liquid and then reach the liquid surface may cause some liquid to move out of the enclosure (e.g., by bubble eruptions). In some examples, the sounding body may emit sound of a sufficiently high acoustic pressure such that the sound waves cause collapse of (e.g., at least some of) the bubbles in the liquid. The method may include providing additional liquid and / or causing the formation of additional bubbles to replace the collapsed bubbles. The apparatus may comprise a liquid supply conduit configured to supply additional liquid to the container (e.g., to replace liquid leaving the container when air bubbles reach the liquid surface and / or liquid exiting the container due to a container leak). The apparatus may comprise a liquid supply pump configured to supply additional liquid to the container, for example, via the liquid supply conduit. The method may include causing the additional liquid to be supplied to the container, optionally via the liquid supply conduit. The method may include supplying the additional liquid to the container, optionally via the liquid supply conduit.

[0087] The device may include a liquid volume detector configured to output an indication of the volume of liquid in the container. The device may include an excess liquid outlet. The opening may include (e.g., be) an excess liquid outlet (e.g., as described above). The controller may be configured to receive the indication (e.g., as described above) of the volume of liquid in the container and, in response to the received indication of the volume of liquid in the container indicating that the volume has fallen below a low liquid threshold, cause additional liquid to be supplied to the container (e.g., via a liquid supply conduit, optionally by causing operation of a liquid supply pump). The low liquid threshold may be 95% of the container's capacity, optionally 90% of the container's capacity, or optionally 85% of the container's capacity. The controller may be configured to receive the indication (e.g., as described above) of the volume of liquid in the container and, in response to the received indication of the volume of liquid in the container indicating that the volume has exceeded a high liquid threshold, cause excess liquid to exit the container (e.g., via the excess liquid outlet). The high liquid threshold may be greater than 95% of the volume of the container, such as greater than 98% of the volume of the container, such as greater than 99% of the volume of the container.

[0088] The device may include one or more container supply conduits configured to (e.g., selectively) supply one or more substances (e.g., hydrogen peroxide, optionally enzymes, etc.) to the container. The controller may be configured to receive an indication (e.g., as described above) of the temperature of the liquid and accordingly adjust the supply of liquid to the container, optionally via the liquid supply conduits, optionally using a liquid supply pump). The controller may be configured to receive an indication (e.g., as described above) of the pH of the liquid and accordingly adjust the supply of substances (e.g., liquid, salt, hydrogen peroxide, buffer, acid, base, surfactant, enzyme, etc.) into the container (optionally via one or more supply conduits, e.g., liquid supply conduits, optionally using a liquid supply pump). The controller may be configured to receive an indication (e.g., as described above) of the percentage of oxygen saturation of the liquid and accordingly adjust the supply of liquid (e.g., liquid comprising hydrogen peroxide) to the container (optionally via the liquid supply conduits, optionally using a liquid supply pump). The controller may be configured to regulate the supply of hydrogen peroxide to the container, for example to replace decomposed hydrogen peroxide, optionally according to a predetermined decomposition rate, which may depend on several factors, including, but not limited to, the peak acoustic pressure of the sound emitted by the sound-generating body.

[0089] 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 (e.g., information) over the wired communication link. The method may include transmitting and / or receiving data (e.g., information) over the wired communication link. The device may be configured to transmit and / or receive data (e.g., information) over a wireless communication link. The method may include transmitting and / or receiving data (e.g., information) over a wireless communication link. The device may be configured to transmit and / or receive data (e.g., information) over Wi-Fi™. The method may include transmitting and / or receiving data (e.g., information) over Wi-Fi™. Wi-Fi™ is a family of wireless network protocols based on the IEEE 802.11 family of standards.

[0090] It will be understood that the liquid may be water, or water optionally containing one or more other substances (e.g., salts, hydrogen peroxide, enzymes, buffers, surfactants, etc.). It will be understood that the bubbles may be oxygen bubbles or air bubbles, and may include, for example, nitrogen. When referring to light, it will be understood to mean light in the visible spectrum. Furthermore, when referring to sound or noise, this includes, but is not limited to, sounds in the human audible range, and may extend to, for example, ultrasound. The sound-generating element may emit sound, including sound waves having peak frequencies in the ranges of 50 Hz to 200 kHz, inclusive, optionally 10 Hz to 300 kHz, inclusive, and optionally 5 Hz to 500 kHz, inclusive. The device may be configured to restrict the transmission of sound, including sound waves having peak frequencies in the ranges of 50 Hz to 200 kHz, inclusive, optionally 10 Hz to 300 kHz, inclusive, and optionally 5 Hz to 500 kHz, inclusive.

[0091] Offshore piling equipment can emit sound in the form of a "shock pulse" (a sound typically caused by an impact and including substantially all frequencies). Conventional bubble curtains generally produce only one size of bubble, making them less effective than the bubble curtain provided by the present disclosure. This is because the bubble curtain provided by the present disclosure includes bubbles having a wide range of sizes, thereby limiting (e.g., attenuating) the transmission of sound over a wide range of frequencies. The sudden increase in sound pressure level of the "shock pulse" from the offshore piling equipment can cause the bubbles to collapse. Therefore, some time may be required to induce the formation of additional gas bubbles in the liquid (e.g., as a result of agitation of the liquid by an agitator) so that the sound transmission of subsequent shock pulses can be limited (e.g., attenuated).

[0092] Thus, the device may include a shock pulse detector configured to output an indication of the detection of a shock pulse. The device may be configured to receive an indication of the occurrence of a shock pulse, e.g., from the offshore pile driving rig, e.g., when a pile driving strike is being performed. The controller may be configured to receive the (e.g., above) indication of the detection (optionally occurrence) of a shock pulse and to send a signal to the offshore pile driving rig (optionally its user) to pause for a waiting period before performing a (e.g., subsequent) pile driving strike. The waiting period may depend on one or more of the following: an indication (e.g., above) of the intensity of (e.g., visible) light passing a certain distance of the liquid being below a threshold; an indication (e.g., above) of the sound intensity outside the containment body being below a threshold; an indication (e.g., above) of the pressure of the liquid; an indication (e.g., above) of the temperature of the liquid; or an indication (e.g., above) of the pH of the liquid. The waiting period may be at least 5 seconds, e.g., at least 10 seconds, e.g., at least 30 seconds, e.g., at least 1 minute, and optionally less than 60 minutes, e.g., less than 30 minutes, e.g., less than 15 minutes.

[0093] The method may include receiving an indication of detection (optionally occurrence) of an impact pulse. The method may include causing the offshore pile driving rig (and optionally a user thereof) to transmit a signal to pause for a waiting period before performing (e.g., a subsequent) pile driving strike. The method may include transmitting a signal to the offshore pile driving rig (and optionally a user thereof) to pause for a waiting period before performing (e.g., a subsequent) pile driving strike.

[0094] The apparatus may be configured to (or the method may include) increase the proportion of dissolved oxygen by at least 2% by volume (e.g., at least 10%, such as at least 25%, for example, at least 50%, for example, at least 75%, for example, at least 80%) over the proportion of dissolved oxygen present in the water when the apparatus (or method) is not used.

[0095] In some applications, the enclosure may be omitted. This may lead to more rapid dissipation of dissolved oxygen and gas bubbles, which may be acceptable in some use cases. Such rapid dissipation may be addressed, for example, by supplying additional oxygen to the liquid or supplying (e.g., near the agitator) additional liquid containing at least 2% (optionally at least 10%) dissolved oxygen by volume. The apparatus may be configured to allow for the supply of additional oxygen to the liquid and / or the supply of additional liquid containing at least 2% (optionally at least 10%) dissolved oxygen by volume. For example, the apparatus may include a conduit configured to receive a fluid and supply the fluid toward the agitator. The method may include providing additional oxygen to the liquid and / or providing additional liquid containing at least 2% (optionally at least 10%) dissolved oxygen by volume. For example, the method may include supplying the fluid toward the agitator, optionally via a conduit.

[0096] This in itself is considered to be an inventive step. Accordingly, a further aspect of the present invention provides an apparatus configured to limit the transmission of sound from a sound-producing body (e.g., through a liquid), the apparatus including a liquid, the liquid including at least 2% by volume (optionally at least 10% by volume) dissolved oxygen, the apparatus further comprising an agitator disposed in the liquid, the agitator configured to agitate (e.g., at least a portion of) the liquid proximate the agitator, thereby causing the formation of gas (e.g., oxygen) bubbles in the liquid. Optional features of the other aspects described above may also be optional features of this further aspect.

[0097] A further aspect of the present invention provides a method of limiting the transmission of sound from a sound-producing body, the sound-producing body being at least partially surrounded by a liquid containing at least 2% by volume of dissolved oxygen, the method comprising causing agitation of the liquid, thereby causing the formation of gas bubbles in the liquid. Optional features of the other aspects described above may also be optional features of this further aspect.

[0098] It will be understood that the method steps described above with respect to any one particular method may be combined with any other method described herein in substantially any combination, except where essentially incompatible. It will be further understood that method steps may be performed in an order other than the order listed, and in some cases may be performed simultaneously, except where essentially impossible. Features of any one embodiment may be optional features of any other embodiment. [Brief explanation of the drawings]

[0099] Exemplary embodiments of the present invention will now be described with reference to the following drawings.

[0100] [Figure 1] 1 is a side cross-sectional view of a first exemplary embodiment of an apparatus according to the present invention; [Figure 2] FIG. 2 is a second cross-sectional side view of the first exemplary embodiment of the device according to the present invention. [Figure 3] 1 is a side cross-sectional view of a second exemplary embodiment of an apparatus according to the present invention. [Figure 4] FIG. 10 is a side cross-sectional view of a third exemplary embodiment of an apparatus according to the present invention. [Figure 5] 10 is a plan elevation view of a further exemplary embodiment of an apparatus according to the present invention; [Figure 6] 3 is a flowchart of method steps according to an exemplary embodiment of the present invention. [Figure 7] 1 is a schematic diagram of an apparatus according to an exemplary embodiment of the present invention; [Figure 8] A plot of the speed of sound through a fluid. DETAILED DESCRIPTION OF THE INVENTION

[0101] It will be understood by those skilled in the art that any dimensions and relative orientations, such as low and high, above and below, and directions such as vertical, horizontal, upper, lower, longitudinal, axial, radial, lateral, circumferential, etc., referred to herein relate to the technical field and the apparatus and methods described, are within expected structural tolerances and limits, and should be interpreted with this in mind.

[0102] FIG. 1 is a side view of a first exemplary embodiment of an apparatus 1 according to the present invention. Here, the sound-generating body 2 is an offshore pile and is part of a series of offshore piling rigs 10. A container 4 is arranged to surround the offshore pile 2 and is filled with a liquid, in this case seawater containing 50% dissolved oxygen by volume. The lower part of the container 4 is provided with an agitator in the form of a mixer 6 that, during use, agitates the fluid, thereby releasing oxygen from the water and forming gas bubbles 8. The upper part of the container 4 is provided with a pump 22 configured to cause liquid near the top of the container and near the liquid surface 18 to flow in a downward direction, as indicated by arrow 24. In FIG. 1, the mixer 6 has only been running for a few seconds, resulting in the generation of a relatively small number of gas bubbles.

[0103] The offshore pile 2 is partially submerged in the liquid within the containment body, in that approximately 85% of the offshore pile 2 is below the liquid surface 18. The containment body 4 is then partially surrounded by the sea, and therefore by seawater. The containment body 4 extends from above the seawater surface 20 to the seabed 26. The containment body 4 has a cylindrical outer wall 30 that is open at its bottom and its top. The cylindrical outer wall 30 is provided with a weight (not shown) that presses down on the wall, bringing it into sealed contact with the seabed 26. Thus, in this example, the seabed 26 can be considered to provide the bottom of the containment body 4. The open top provides an opening in the containment body 4 through which air bubbles 8 can exit the containment body as they, for example, rise through the liquid under buoyancy. The cylindrical outer wall 30 of the containment body 4 extends both above the liquid surface 18 and above the seawater surface 20. In this example, the liquid surface 18 is slightly above the seawater surface 20. This is because the density of the fluid is slightly lower than seawater, so hydrostatic pressure acts on the containment body 4 (which is slightly flexible), thereby compressing it slightly and causing a hydrostatic head within the containment body 4.

[0104] 2 is a second side view of the first exemplary embodiment of the apparatus 1. Here, the mixer 6 has been operating for a longer period of time (approximately 60 minutes), resulting in the formation of a larger number of gas bubbles 8. The gas bubbles 8 are continuously formed as a result of the mixer 6 agitating the fluid. The gas bubbles 8 tend to float upward through the fluid due to buoyancy. As the gas bubbles 8 approach the fluid surface 18, the flow caused by the pump 22 tends to move some of the gas bubbles 8 back downward through the fluid, rather than allowing all of the gas bubbles 8 to exit the fluid upon reaching the fluid surface 18. As a result, an annular bubble curtain 32 has been formed that partially surrounds the offshore pile (i.e., the portion of the pile below the liquid surface 18 is radially surrounded by the bubble curtain 32).

[0105] FIG. 3 is a side cross-sectional view of a second exemplary embodiment of an apparatus 101 according to the present invention. Similar to the embodiment of FIGS. 1 and 2, the apparatus 101 includes a containment body arranged to surround a sound-generating body (also in the form of an offshore piling rig 110), the containment body being filled with a liquid. In this example, the containment body is in the form of a flat disk with two horizontal partitions 114a, 114b, each having a central hole 116a, 116b. Each of the horizontal partitions 114a, 114b extends partway across the interior of the containment body from the inside of the cylindrical wall toward the center of the containment body, with the holes 116a, 116b surrounding the offshore piling and leaving a space between each partition 114a, 114b and the piling. It can thus be seen that the containment body is 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, during use, agitate the fluid within the respective sub-container 104a, 104b, 104c, thereby releasing oxygen from the water and forming bubbles 108.

[0106] The partition 114b forms the top of the bottom sub-container 104c, has a hole 116b surrounding the stake, and is positioned to provide space between the stake and the partition 114b so that air bubbles 108 reaching the top of the sub-container 104c can exit the sub-container 104c and move through the hole 116b to the middle sub-container 104b. Similarly, the partition 114a forms the top of the middle sub-container 104b, has a hole 116a surrounding the stake, and is positioned to provide space between the stake and the partition 114a so that air bubbles 108 reaching the top of the sub-container 104b can exit the sub-container 104b and enter the top sub-container 104a through the hole 116a. The top sub-container 104a is open at its top, allowing air bubbles 108 that reach the top of the top sub-container 104a to escape at the liquid surface 118. The top of each sub-container 104a, 104b, 104c is provided with a pump (not shown) configured to drive liquid downward near the top of each respective sub-container 104a, 104b, 104c and near the liquid surface 118. In Figure 3, each mixer 106a, 106b, 106c, 106d, 106e, 106f is only operating for a few seconds, so a relatively small number of air bubbles are generated by each mixer 106a, 106b, 106c, 106d, 106e, 106f. However, because each sub-container 104a, 104b, 104c is smaller than the container 4 of Figures 1 and 2 and each sub-container is provided with two mixers 106a, 106b, 106c, 106d, 106e, 106f, a significantly larger amount of air bubbles per liter of liquid can be generated in a relatively short period of time.

[0107] Similar to FIGS. 1 and 2, the offshore piles are partially submerged in the liquid within the containment body, in that approximately 85% of the offshore piles are below the liquid surface 18. The containment body is partially surrounded by the water, with subcontainers 104b and 104c being surrounded by the water, and subcontainer 104a being partially surrounded by the water and partially extending above the water surface 120. The containment body extends from above the water surface 120 to the seabed. The containment body has a weighted cylindrical outer wall but is open at its bottom and top. Thus, in this example, the seabed can be considered to provide the bottom of the lowest subcontainer 104c. The open top provides an opening for the top subcontainer 104a, through which air bubbles 8 can exit the containment body as they rise through the liquid, for example, under buoyancy. The cylindrical outer wall of the containment body extends both above the liquid surface 118 and above the water surface 120.

[0108] In use, the mixers 6, 106a, 106b, 106c, 106d, 106e, and 106f are switched on and begin agitating the fluid within the container 4 or subcontainer 104a, 104b, and 104c. As the fluid is agitated, oxygen dissolved in the fluid is released from the fluid, thereby forming gas bubbles 8, 108. The gas bubbles 8, 108 move upward within the fluid and within the container 4 or subcontainer 104a, 104b, and 104c toward the liquid surface 18 or the top of the subcontainer 104b and 104c. At the liquid surface 18 or the top of the subcontainer 104b and 104c, a flow induced by the pump 22 (not shown in FIG. 3 ) moves the liquid and some of the gas bubbles 8, 108 therein downward, as indicated by arrow 24 (not shown in FIG. 3 ). This causes the bubbles 8, 108 to circulate within the container 4 or sub-containers 104a, 104b, 104c, and a bubble curtain 32 surrounding the sound generating body 2 is formed (or can be formed within each sub-container).

[0109] Once the bubble curtain 32 is formed, the sound-generating body (here, the offshore pile) 2 can be activated. Sound travels outward from the sound-generating body 2, specifically from the point where the offshore pile 2 contacts the seabed 26. The sound waves travel through the liquid until they contact the bubble curtain 32. Upon reaching the bubble curtain 32, the sound waves repeatedly pass through multiple liquid-gas boundaries and are scattered. Each bubble 8, 108 that encounters the sound waves represents two such boundaries: a first boundary as the sound wave travels from the liquid to the gas in the bubble 8, 108, and a second boundary as the sound wave travels from the gas in the bubble 8, 108 back into the liquid surrounding the bubble 8, 108. While not wishing to be bound by theory, the inventors believe that the scattering and absorption of the sound waves at each such interface results in limited sound transmission, resulting in absorption of sound energy and attenuation of the sound after multiple interactions with the bubbles 8, 108 within the bubble curtain 32. As a result, very little sound can travel completely through the bubble curtain 32 and escape beyond the enclosure 4 (or sub-enclosures 104a, 104b, 104c) into the ocean.

[0110] Offshore piling can generate pressures of over 180 decibels 750 meters from the offshore piling, which is harmful to marine life. The bubbles 8, 108 generated by the operation of the devices 1, 101, 201 limit sound transmission such that the sound pressure on the other side of the bubbles 8, 108 from the sound source 2 is reduced by 40 decibels compared to the sound pressure on the same side of the bubbles 8, 108 as the sound source 2. Therefore, application of the devices 1, 101, 201 is beneficial to marine life and leads to a reduction in the environmental acoustic footprint.

[0111] Once the offshore piling operation is completed (or paused), the mixers 6, 106a, 106b, 106c, 106d, 106e, 106f and pump 22 are stopped. The air bubbles 8, 108 steadily exit the fluid and containment body 4 as they rise under buoyancy to the fluid surface 18, 118. If no further offshore piling is required, the apparatus 1, 101 can be removed and optionally moved to the next offshore piling 2.

[0112] Figure 4 is a cross-sectional side view of a third exemplary embodiment of an apparatus 201 according to the present invention. Similar to the embodiments of Figures 1, 2, and 3, the apparatus 201 includes a housing 204 arranged to surround a sound-producing body 202 (here, a generator), the housing 204 being filled with a liquid. In this example, the housing 204 is an annular outer housing 204 having an interior space 212 filled with air. The interior space 212 may be considered as a cylindrical inner housing 212 that holds the sound-producing body 202. The outer housing 204 is provided with an agitator in the form of a mixer 206 that, during use, agitates the fluid within the outer housing 204, thereby releasing oxygen from the water and forming gas bubbles 208.

[0113] The top of the outer container 204 includes a pump 222 configured to drive the liquid near the liquid surface 218 in a downward direction, as indicated by arrow 224. In Figure 4, the mixer 206 has only been running for a few seconds, resulting in the generation of a relatively small number of air bubbles.

[0114] In this exemplary embodiment, the sound source is within the inner containment 212, which is partially surrounded by the outer containment 204 and, in turn, by the liquid within the outer containment 204. The outer containment 204 has a cylindrical outer wall 230, a cylindrical inner wall 236, and a bottom 238, but is open at its top. The cylindrical inner wall 236 of the outer containment 204 forms the cylindrical wall of the inner containment 212. The inner containment 212 also has a bottom 240 and a top wall 242. The open top of the outer containment 204 provides an opening in the outer containment 204 through which air bubbles 208 can exit the outer containment 204 as they rise through the liquid, for example, under buoyancy. The cylindrical outer wall 230 of the outer containment 204 extends above the liquid surface 218.

[0115] Apparatus 201 also has a light detector 215 (here a photodetector) and a light source 217 (here in the form of an LED) positioned within outer housing 204. Light detector 215 is configured to detect light emitted by LED 217 and output an indication of the intensity of the detected light. The distance between light detector 215 and LED 217 is 20 centimeters. Apparatus 201 also has a controller (not shown) configured to receive an indication of the intensity of the detected light and to adjust the amount of agitation caused by mixer 206 in response to the received indication, thereby maintaining a target light intensity.

[0116] Bubbles 208 are continuously formed as a result of mixer 206 agitating the fluid. Bubbles 208 tend to float upward through the fluid due to buoyancy. As bubbles 208 approach the liquid surface 218, the flow caused by pump 222 tends to move some of the bubbles 208 back downward through the fluid, rather than allowing all of the bubbles 208 to exit the fluid upon reaching fluid surface 218. As a result, an annular bubble curtain (not shown in FIG. 4 ) forms in outer containment body 204, such that sound-producing body 202 is partially surrounded by the bubble curtain.

[0117] The sound waves travel from the sound generating body 202 through the air within the inner housing 212 until they reach the inner cylindrical wall 236. The sound waves travel through the inner cylindrical wall 236, enter the fluid within the outer housing 204, and continue to travel through this fluid until they reach the bubble curtain, where they are absorbed and scattered by the air bubbles 208, as described in connection with Figures 1, 2, and 3. The mixer 206 and pump 224 may operate continuously, or may operate only when the sound generating body 202 is emitting sound.

[0118] Light travels from the LED 217 through the liquid in the outer containment body 204 and is scattered by the air bubbles. Thus, when the mixer 206 is not operating (and thus relatively few air bubbles are present), less light scattering occurs and more light is detected by the photodetector 215. Thus, the photodetector 215 outputs an indication that a relatively high intensity of light is being detected. Conversely, when the mixer 206 is operating (and thus relatively more air bubbles are present), more light scattering occurs and therefore the photodetector 215 outputs an indication that a relatively low intensity of light is being detected.

[0119] If there are no bubbles to scatter light, there will also be no bubbles to scatter sound. Thus, when the controller receives an indication that the intensity of light received by the photodetector 215 is below a threshold, the controller increases the degree of agitation caused by the mixer 206 (e.g., by increasing the speed of the mixer 206). When the controller receives an indication that the intensity of light received by the photodetector 215 is above a threshold, the controller decreases or stops the degree of agitation caused by the mixer 206 (e.g., by decreasing the speed of the mixer 206). In this manner, the mixer 206 does not need to be operated continuously, allowing the device 201 to operate more efficiently. In one 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, at which point the mixer can be allowed to mix the fluid until the light intensity is again found to have decreased.

[0120] FIG. 5 is a plan elevation view of a further exemplary embodiment of an apparatus 301 according to the present invention. Similar to the embodiment of FIGS. 1-4, the apparatus 301 includes a housing 304 arranged to surround a sound-producing body 302, the housing 304 being filled with a liquid. In this example, the housing is an open-topped rectangular parallelepiped having four vertical side walls 330a, 330b, 330c, and 330d and a bottom (not shown). The housing 304 is provided with an agitator in the form of a mixer 306 that, during use, agitates the fluid within the housing 304, thereby releasing oxygen from the water and forming bubbles (not shown in FIG. 5). The top of the housing 304 is provided with a pump (not shown in FIG. 5) configured to cause the liquid near the liquid surface to flow in a downward direction.

[0121] In this example, sound generator 302 is a control valve 302 for a gas distribution pipe 311. The enclosure has an opening to allow for inlet and outlet pipes 311. The enclosure 304 is sealed at the opening around the pipes 311 so that liquid cannot pass through it to leave the enclosure.

[0122] Bubbles are continuously formed as a result of the mixer 306 agitating the fluid. Bubbles tend to float upward through the fluid due to buoyancy. As the bubbles approach the top of the container 306, the flow caused by the pump tends to move some of the bubbles back downward through the fluid rather than allowing all of the bubbles to reach the fluid surface and exit the fluid. As a result, a bubble curtain (not shown in FIG. 5 ) forms within the container 304, thereby partially surrounding the sound-producing body 302. Sound waves travel from the sound-producing body 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 case described in connection with FIGS. 1, 2, and 4. This is particularly useful for limiting the transmission of sound from the control valve 302 to the air that would otherwise surround the control valve. Without the device 301, the control valve 302 would be surrounded by air by default, which could cause Helmholtz resonance.

[0123] The average (mean) diameter of the bubbles 8, 108, 208 is 0.05 cm when considered in terms of the maximum size the bubbles have from the moment the bubbles 8, 108, 208 are generated up to 3 seconds after the bubbles are generated. After this, the bubbles 8, 108, 208 typically change size, particularly as they move upward through the liquid. The bubble curtain 32 contains at least 1,000 bubbles in each liter of volume in which the bubble curtain 32 resides. However, those skilled in the art will understand that a relatively large number of air bubbles 8, 108, 208 will typically be present near the mixer 6, 106a, 106b, 106c, 106d, 106e, 106f, 206, 306, and that over time the air bubbles 8, 108, 208 will disperse to some extent, resulting in fewer air bubbles 8, 108, 208 being present further away from the mixer 6, 106a, 106b, 106c, 106d, 106e, 106f, 206, 306.

[0124] The walls of the containers 4, 104, 204 are made of tarpaulin with a reinforced webbing layer. The walls of the container 304 are made of high-density polyethylene (HDPE). The or each mixer 6, 106a, 106b, 106c, 106d, 106e, 106f, 206, 306 is a paddle stirrer having two steel paddles rotatable about an axis at 100 rpm by an electric motor. The pump 22, 222 is a positive displacement pump configured to move 1000 L per minute (although those skilled in the art will understand that the choice of pump will depend on the size of the container). The dividers 114a, 114b (if present) are made of HDPE discs.

[0125] The liquid in the container 4, 104, 204, 304 is water containing 50% dissolved oxygen by volume. The water also contains 20 mg / L hydrogen peroxide and 5 kU catalase per liter of water. The catalase decomposes the hydrogen peroxide into water and oxygen. Some of the oxygen immediately forms additional bubbles, while some dissolves in the water and can form additional bubbles as the liquid is agitated by the mixers 6, 106a, 106b, 106c, 106d, 106e, 106f, 206, 306. The catalase increases the rate at which the hydrogen peroxide is decomposed. The mixers 6, 106a, 106b, 106c, 106d, 106e, 106f, 206, 306 prevent the catalase from settling to the bottom of the container, keeping the catalase in suspension. This improves the efficiency with which the catalase acts on the hydrogen peroxide.

[0126] Advantageously, the formation of oxygen bubbles 8, 108, 208 in the liquid limits the transmission of sound through the liquid. Agitation of a liquid containing at least 50% by volume of dissolved oxygen has been found to be a particularly effective way of causing the formation of bubbles 8, 108, 208. This is because as the liquid is agitated, some of the oxygen dissolved in the liquid is released from the liquid, thereby forming a large amount of oxygen bubbles 8, 108, 208. Thus, because the bubbles 8, 108, 208 can be formed without using a compressor or similar device to force gas bubbles through the liquid, the apparatus 1, 101, 201, 301 is also more efficient than if a compressor were used.

[0127] 6 is a flowchart of method steps according to an exemplary embodiment of the present invention, where the steps include providing a sound-producing body within a container (50) and causing agitation of a liquid within the container (52).

[0128] FIG. 7 is a schematic diagram of device 1 according to an exemplary embodiment of the present invention. Device 1 includes at least one mixer 6 and a controller 40. Controller 40 is configured to transmit a signal 42 to mixer 6. Controller 40 is also typically configured to transmit data elsewhere, e.g., to additional components of device 1 and / or to devices external to device 1 via a wireless data connection. Signal 42 includes a signal generated by controller 40 in response to data received by controller 40, e.g., from user input and / or photodetector 215. Controller 40 in this example is implemented by one or more processors 44 and 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. While controller 40 is shown as being part of device 1, it will be understood that one or more components of controller 40, or even controller 40 as a whole, may be provided separately from device 1. For example, controller 40 may be remote from device 1 and communicate signals with mixer 6 via wireless communication.

[0129] Figure 8 is a plot of the speed of sound through a fluid as a function of 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, but 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 sound of a given frequency having a correspondingly lower wavelength in a fluid containing a water and air mixture than in a fluid composed solely of water or a fluid composed solely of air. This, in turn, changes how sound can be attenuated by either individual bubbles or bubble curtains (e.g., bubble curtains generated by mixing a liquid containing a high percentage of dissolved oxygen, thereby forming bubbles, as described herein).

[0130] While the above examples show the agitators 6, 106, 206, 306 in the form of mixers, this is not required, and other means for agitating the liquid may alternatively be used. For example, in some embodiments, the agitator may be a bubble curtain generator in the form of a compressor connected to a perforated pipe, thereby forcing gas bubbles through the liquid. The compressor may be a single compressor or may be provided by a group of compressors (e.g., 7 bar) with a combined output of 10,000 L / min. The compressors may be positioned to generate a bubble curtain around the lower periphery of the enclosure. The use of a bubble curtain generator to agitate the liquid allows for more gas bubbles to be generated in the liquid (i.e., some resulting from the agitation releasing dissolved oxygen from the liquid, thereby forming gas bubbles, and some from the bubble curtain generator itself). More gas bubbles provide more effective sound attenuation and limit sound transmission.

[0131] Experimental Test Overview The inventors have conducted testing of an example of the device and method described herein, and the following summary of this testing provides a non-limiting example of how the device and method may be used.

[0132] 3m on the tarpaulin enclosure wall 3 A container was formed and filled with an aqueous solution, in this case seawater. 30 L of hydrogen peroxide was added to the container along with 100 ml of catalase (which accelerates the decomposition of hydrogen peroxide). The mixer (in this case an air mixer) was run for 2 minutes, generating numerous buoyant bubbles with an average (mean) diameter of approximately 5 mm. The resulting fluid was clear.

[0133] A sound source in the form of a frequency generator was activated to apply 10 ms sound pulses at a frequency of approximately 190 dB, starting at approximately 2 kHz and increasing in steps of approximately 500 Hz to approximately 13 kHz, with 100 ms between each pulse.

[0134] Using a hydrophone, sound was recorded through the aqueous solution at depths of 1 m and 2 m at distances of 0.5 m, 1 m, and 2 m from the sound source. After a 2-minute run time of the mixer, sound levels were not measurable with the hydrophone for a period exceeding 2 hours. However, it was found that the sound could be recognized by playback with amplification. This method allowed for the confirmation of increasing attenuation as a function of increasing distance (i.e., the distance traveled by the sound wave through the fluid).

[0135] It was also found that the concentration of hydrogen peroxide decreased by approximately 27% over a two-hour period. This testing also found that the attenuation effect was greatest at shallow depths, with deeper hydrophones detecting sound earlier than shallower hydrophones. It should be noted that the speed of sound is a function of pressure (and pressure is greater at greater depths), and bubble size is also a function of pressure (higher pressure results in smaller bubbles). Furthermore, it has been observed that, at least in some cases, the attenuation effect is observed at shallower depths before it is observed at greater depths (which also corresponds to the effect ceasing earlier at greater depths). Thus, those skilled in the art will understand that depth and buoyancy are only two of several parameters to consider when attempting to practice the present invention. It should also be understood that the rate of dissolved gas production is believed to depend on (e.g., at least) the hydrogen peroxide concentration, the amount of enzymes (e.g., catalase) present, and the presence (and amount) of biomass (e.g., fish).

[0136] It was noted that wave action on the tarpaulin provided gentle fluid movement which provided further mixing during the test and may have contributed to the relatively long period during which sound attenuation was effective.

[0137] Further tests with frequent mixing yielded similar attenuation, but initial results suggest that some mixing regimes may lead to less stable fluid conditions (e.g., greater variability in bubble counts). However, varying the concentrations of hydrogen peroxide and catalase (i.e., in addition to mixing) also appears to affect fluid stability in this sense.

[0138] The attenuation effect appears to be most pronounced for small gas bubbles, rather than large ones. The attenuation achieved was found to be greater than previous noise abatement strategies (e.g., simple bubble curtains). Surprisingly, it was found that excessive mixing can reduce the effectiveness of sound attenuation in some circumstances. The optimal mixing rate to promote hydrogen peroxide decomposition (and thus gas bubbles and dissolved oxygen) without reducing effectiveness depends on the conditions within the liquid.

[0139] Throughout the description and claims of this specification, the terms "comprise" and "include" and variations thereof mean "including but not limited to," and they do not contemplate or exclude other components, elements, or steps. Throughout the description and claims of this specification, the singular encompasses the plural unless the context requires otherwise. In particular, where the indefinite article is used, the specification should be understood as contemplating the plural as well as the singular, unless the context requires otherwise.

[0140] It is understood that any feature, element, characteristic, or group described in connection with a particular aspect, embodiment, or example of the invention is applicable to any other aspect, embodiment, or example described herein, except where inconsistent. All features disclosed in this specification (including the accompanying claims, abstract, and drawings) and / or all steps of any method or process so disclosed may be combined in any combination, except combinations in which at least some of such features and / or steps are mutually exclusive. The invention is not limited to the details of any foregoing embodiment. The invention extends to any novel one or any novel combination of features disclosed in this specification (including the accompanying claims, abstract, and drawings), or any novel one or any novel combination of steps of any method or process so disclosed.

[0141] In summary, there is provided an apparatus (1) for restricting the transmission of sound from a sound-producing body (2), the apparatus comprising a container (4) arranged to at least partially surround the sound-producing body, the container holding a liquid, the liquid containing at least 2% dissolved oxygen, the apparatus further comprising an agitator (6) configured to agitate the liquid, thereby causing the formation of gas bubbles (8) in the liquid.

Claims

1. 1. A device for limiting the transmission of sound from a sound-generating body, the device comprising: a container disposed to at least partially surround the sound-generating body, the container holding a liquid; the liquid contains at least 2% by volume of dissolved oxygen; The apparatus further comprises an agitator configured to agitate the liquid, thereby causing the formation of gas bubbles in the liquid.

2. 10. The device of claim 1, wherein the container has at least one opening defined therein to allow the air bubble to exit the container through the opening.

3. 3. The apparatus of claim 1 or 2, wherein the agitator optionally includes a bubble curtain generator arranged to generate a bubble curtain that at least partially surrounds the sound-producing body.

4. 10. A device according to any one of the preceding claims, wherein the housing holds the sounding body, the sounding body being immersed in the liquid.

5. the enclosure is a first enclosure having one or more first enclosure walls; the device comprises a second housing having one or more second housing walls, the second housing at least partially surrounding the sound-producing body; 10. Apparatus according to any one of the preceding claims, wherein the first housing at least partially surrounds and is spaced apart from the second housing.

6. The device of claim 5 , wherein the liquid is held between the first and second housing walls.

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

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

9. 9. The device of claim 8, wherein the liquid comprises an enzyme for the decomposition of hydrogen peroxide.

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

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

12. 10. The apparatus of claim 9, wherein an agitation zone surrounds the agitator, the agitator being configured to form sufficient bubbles such that the total volume of the bubbles is at least 1% of the total volume of the agitation zone.

13. The first container is at least 0.5 m ３ 10. An apparatus according to any one of the preceding claims, defining a volume of

14. 10. Apparatus according to any one of the preceding claims, wherein the container comprises one or more partitions, the or each partition extending across the interior of the container thereby forming a plurality of sub-containers, optionally each of the plurality of sub-containers having a respective agitator provided therein.

15. 10. Apparatus according to any one of the preceding claims, comprising a pump configured to induce a flow of liquid at the liquid surface, optionally in a downward direction.

16. 10. Apparatus according to any one of the preceding claims, wherein an agitation region surrounds the agitator, the agitator being configured to cause sufficient gas bubbles to form in the agitation region such that the optical intensity of light having travelled through 10 centimetres of the liquid is reduced by at least 10% compared to the intensity of the light before travelling through the liquid.

17. 10. Apparatus according to any one of the preceding claims, comprising a light detector arranged to output an indication of the intensity of light that has passed a distance of the liquid.

18. receiving the indication of the intensity of the light that has passed through the distance of the liquid; 20. The apparatus of claim 17, comprising a controller configured to adjust an amount of agitation caused by the agitator in response to the received indication, thereby maintaining a target light intensity.

19. 10. Apparatus according to any one of the preceding claims, wherein the sound-generating body comprises an offshore pile driving rig.

20. 1. A device for limiting the transmission of sound from a sound-producing body, comprising: a sound barrier comprising a container for holding a liquid, the liquid comprising at least 2% by volume of dissolved oxygen; an agitator configured to agitate the liquid, thereby causing the formation of gas bubbles in the liquid.

21. 10. Apparatus according to any one of the preceding claims, wherein the apparatus is configured to operate the agitator for an activation period, thereby causing the generation of sufficient gas bubbles such that the gas bubbles are then suspended in the fluid for a decay period that is longer than the activation period.

22. 1. A method of limiting the transmission of sound from a sound-producing body, the method comprising: at least partially surrounding the sound-producing body with a containment body, the containment body holding a liquid having at least 2% dissolved oxygen by volume; The method comprises: causing agitation of the liquid in the container, thereby causing formation of gas bubbles in the liquid.

23. 23. The method of claim 22, wherein forming gas bubbles comprises releasing oxygen from the liquid, thereby forming gas bubbles.

24. The method comprises: receiving an indication of the intensity of light that has passed through a distance of the liquid; and adjusting the amount of agitation induced in response to the received indication, thereby maintaining a target light intensity.

25. 23. A method of forming a liquid comprising water and at least 2% by volume of dissolved oxygen according to claim 1, 20 or 22, comprising: A method comprising causing a mixture of water, hydrogen peroxide, and a catalyst for decomposition of hydrogen peroxide.

26. 1. An apparatus configured to limit the transmission of sound from a sound-generating body, the apparatus comprising a liquid, the liquid comprising at least 2% dissolved oxygen by volume, the apparatus further comprising an agitator disposed in the liquid, the agitator configured to agitate the liquid proximate the agitator, thereby causing the formation of gas bubbles in the liquid.

27. 1. A method of limiting the transmission of sound from a sound-producing body, wherein the sound-producing body is at least partially surrounded by a liquid containing at least 2% by volume of dissolved oxygen, the method comprising causing agitation of the liquid, thereby causing the formation of gas bubbles in the liquid.

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