Abstract:
Acoustic resonators are formed by injection molding or other process that allows the shape, size, orientation, and arrangement of each resonator to be customized. Customizing the features of the resonators allows their resonance frequency to be adjusted based on their intended deployment. A non-periodic or non-uniform arrangement of the resonators can increase the level of noise reduction compared to a periodic or uniform arrangement of the resonators. A chain guard includes a recess to receive a chain that supports a plurality of resonator rows or frames. In the stowed configuration, the chain guard pivots towards the row/frame to more compactly stow a panel of resonators.

Description:
TECHNICAL FIELD 
       [0001]    The present disclosure relates to noise abatement devices for reduction of underwater sound emissions, such as noise from seafaring vessels, oil and mineral drilling operations, and marine construction and demolition. 
       RELATED APPLICATIONS 
       [0002]    This application claims priority to U.S. Provisional Application No. 62/181,374, filed on Jun. 18, 2015, entitled “Injection Molded Noise Abatement Assembly and Deployment System,” which is hereby incorporated by reference. 
       BACKGROUND 
       [0003]    Various underwater noise abatement apparatuses have been proposed. Some are embodied in a form factor that encloses or is deployed at or near a source of underwater noise. U.S. Patent Application Publication Number 2011/0031062, entitled “Device for Damping and Scattering Hydrosound in a Liquid,” describes a plurality of buoyant gas enclosures (balloons containing air) tethered to a rigid underwater frame that absorb underwater sound in a frequency range determined by the size of the gas enclosures. Patent application U.S. Patent Application Publication Number 2015/0170631, entitled “Underwater Noise Reduction System Using Open-Ended Resonator Assembly and Deployment Apparatus,” discloses systems of submersible open-ended gas resonators that can be deployed in an underwater noise environment to attenuate noise therefrom. These and their related applications and documentation are incorporated herein by reference. 
         [0004]    Underwater noise reduction systems are intended to mitigate man-made noise so as to reduce its environmental impact. Pile driving for offshore construction, oil and gas drilling platforms, and seafaring vessels are examples of noise that can be undesirable and that should be mitigated. However, the installation, deployment and packaging of underwater noise abatement systems can be challenging, as these apparatuses are typically bulky and cumbersome to store and deploy. 
         [0005]    In addition, current noise reduction systems rely on a combination of materials, such as rubber, plastic, and/or metal. Systems constructed from non-homogenous systems can be costlier to manufacture than homogenous systems manufactured from a single material. 
         [0006]    The present application relates to underwater noise reduction devices and systems and methods of storing and deploying such devices. 
       SUMMARY 
       [0007]    Example embodiments described herein have innovative features, no single one of which is indispensable or solely responsible for their desirable attributes. The following description and drawings set forth certain illustrative implementations of the disclosure in detail, which are indicative of several exemplary ways in which the various principles of the disclosure may be carried out. The illustrative examples, however, are not exhaustive of the many possible embodiments of the disclosure. Without limiting the scope of the claims, some of the advantageous features will now be summarized. Other objects, advantages and novel features of the disclosure will be set forth in the following detailed description of the disclosure when considered in conjunction with the drawings, which are intended to illustrate, not limit, the invention. 
         [0008]    In an aspect, the invention is directed to a resonator for damping acoustic energy from a source in a liquid. The resonator includes a base having a first planar surface and a second planar surface, said first and second planar surfaces parallel with one another. The resonator also includes a hollow body having, in a cross section orthogonal to said second planar surface of said base, a first end, a second end, and a sidewall therebetween, said second end integrally connected to said second surface of said base, said body having an aperture defined in said first end, said aperture extending from said first end to said second end, said aperture defining a volume in said hollow body, said hollow body configured to retain a gas in said volume when said resonator is disposed in said liquid while said aperture is aligned with a direction of gravitational pull. 
         [0009]    In another aspect, the invention is directed to an apparatus for damping acoustic energy from a source in a liquid. The apparatus includes a base having a first planar surface and a second planar surface, said first and second planar surfaces parallel with one another. The apparatus also includes a plurality of hollow bodies, each hollow body having, in a cross section orthogonal to said second planar surface, a first end, a second end, and a sidewall therebetween, said second end integrally connected to said second surface of said base, said body having an aperture defined in said first end, said aperture extending from said first end to said second end, said aperture defining a volume in said hollow body, said hollow body configured to retain a gas in said volume when said resonator is disposed in said liquid while said aperture is aligned with a direction of gravitational pull. The apparatus also includes a plurality of holes defined in said base, said holes disposed between at least some of said hollow bodies. 
         [0010]    In another aspect, the invention is directed to a noise abatement system. The system includes a plurality of collapsible frames. The system also includes a chain passing through an aperture defined in each collapsible frame, said chain mechanically connecting and supporting said collapsible frames. The system also includes a plurality of elongated chain guards, each chain guard pivotally connected to said frame proximal to said aperture, said chain guard having a body that defines a recess along a length of said chain guard to at least partially receive the chain, said chain guard configured to pivot (a) from an open position wherein said length of said chain guard is orthogonal to said respective frame (b) to a closed position wherein said length of said chain guard is parallel to said respective frame. The system also includes a plurality of resonators disposed on each said frame, each resonator including a hollow body having an open end, a closed end, and a sidewall therebetween, said closed end integrally connected to a first surface of a base disposed on said respective frame. 
     
    
     
       IN THE DRAWINGS 
         [0011]    For a fuller understanding of the nature and advantages of the present invention, reference is made to the following detailed description of preferred embodiments and in connection with the accompanying drawings, in which: 
           [0012]      FIG. 1  illustrates an underwater noise reduction apparatus according to an embodiment; 
           [0013]      FIG. 2  illustrates an an example of a panel on resonators in a collapsed or stowed configuration according to an embodiment; 
           [0014]      FIG. 3  illustrates an example of an acoustic resonator that can be disposed on the apparatus of  FIG. 1 ; 
           [0015]      FIG. 4  illustrates a perspective view of a plurality of rows of resonators in a panel according to an embodiment; 
           [0016]      FIG. 5  illustrates a magnified view of the chains and elongated support illustrated in  FIG. 4 ; 
           [0017]      FIG. 6  illustrates a magnified view of chains and chain guides in a partially-collapsed or partially-stowed state; 
           [0018]      FIG. 7  is a perspective view of chains and chain guides; 
           [0019]      FIG. 8  is a top view of the chain guide illustrated in  FIG. 7  disposed in a representative row of resonators; 
           [0020]      FIG. 9  is a perspective view of a plurality of panels in a deployed configuration; 
           [0021]      FIG. 10  is a perspective view of a panel in a stowed configuration; 
           [0022]      FIG. 11  is a perspective view of an array of resonators in a periodic array; 
           [0023]      FIG. 12  is a perspective view of an array of resonators in a random or non-periodic array; 
           [0024]      FIG. 13  is a top view of an array of resonators according to an embodiment; 
           [0025]      FIG. 14  is a view of the array illustrated in  FIG. 13  from an opposing side of the base; 
           [0026]      FIG. 15  illustrates a resonator that has a generally balloon-shape in cross section; 
           [0027]      FIG. 16  illustrates a resonator having a generally mushroom-shaped cross section; 
           [0028]      FIG. 17  illustrates a resonator having a wider cross section at its first end than the resonators illustrated in  FIGS. 15 and 16 ; 
           [0029]      FIG. 18  illustrates a resonator where the cross-sectional width at the first end is greater than the cross-sectional width at the second end; 
           [0030]      FIG. 19  illustrates a simplified representation of a resonator; 
           [0031]      FIG. 20  is a graph illustrating a comparison of the mathematic model versus experimental data of resonance frequency versus depth of deployment of a resonator; 
           [0032]      FIG. 21  illustrates a prototype of a randomized resonator assembly and a periodic resonator assembly; and 
           [0033]      FIG. 22  is a graph illustrating a comparison of the random versus. periodic resonator assembly sound reduction measured in a test. 
       
    
    
     DETAILED DESCRIPTION 
       [0034]      FIG. 1  illustrates an underwater noise reduction apparatus  100  according to an embodiment. The noise reduction apparatus  100  can be lowered into a body of water around or proximal to a noise-generating event or thing such as a drilling platform, ship, or other machine. A plurality of resonators  125  disposed on a vertically-deployed panel of the noise reduction apparatus  100  resonate so as to absorb sound energy and therefore reduce the radiated sound energy emanating from the location of the noise-generating event or thing. The resonators  125  include a cavity to retain a gas, such as air, nitrogen, argon, or combination thereof in some embodiments. For example, the resonators  125  can be the type of resonators disclosed in U.S. Ser. No. 14/494,700, filed on Sep. 24, 2014, entitled “Underwater Noise Abatement Panel and Resonator Structure,” which is hereby incorporated herein by reference. In some embodiments, the resonators  125  are arranged in a two- or three-dimensional array. The resonators  125  can be arranged in rows  110 , and each row can be connected to the adjacent row(s) by a plurality of lines  120 . 
         [0035]    The apparatus  100  can be towed behind a noisy sea faring vessel. Several such apparatuses can be assembled into a system for reducing underwater noise emissions from the vessel. Also, a system like this can be assembled around one or more facets of a mining or drilling rig. 
         [0036]    The noise reducing apparatus  100  can be expandable and deployable, for example as described in U.S. Ser. No. 14/590,177, filed on Jan. 6, 2015, entitled “Underwater Noise Abatement Apparatus and Deployment System,” which is hereby incorporated herein by reference. One or more lines connecting each row of the resonator panel can be raised or lowered, which can cause the panel to collapse vertically, similar to a venetian blind. An example of a panel  200  in a collapsed or stowed configuration is illustrated in  FIG. 2 . 
         [0037]      FIG. 3  illustrates an example of an acoustic resonator  325  that can be disposed on apparatus  100 . The resonator  325  is applied to a two-fluid environment where a first fluid is represented in the drawing by “A” and the second fluid is represented by “B.” For the purpose of illustration only, the two-fluid environment can be a liquid-gas environment. In a more particular illustrative example, the liquid  330  may be water and the gas may be air. In a yet more particular example, the liquid may be sea water (or other natural body of water) and the gas may be atmospheric air. For example, the first fluid “A” can be sea water and the second fluid “B” can be air. 
         [0038]    An embodiment of resonator  325  has an outer body or shell  310  with a main volume  315  of fluid B contained therein. The body  310  may be substantially spherical, cylindrical, or bulbous. A tapered section  312  near one end brings down the walls of the body  310  to a narrowed neck section  314 . The neck section  314  has a mouth  316  providing an opening that puts the fluids A and B in fluid communication with one another in or near the neck section  314  at a two-fluid interface  320 . In operation, pressure oscillations (acoustic noise) present outside the resonator  325  in fluid A will be felt in or near the neck section  314  of the resonator. Expansion, contraction, pressure variations and other hydrodynamic variables can cause the fluid interface to move about within the area of the neck  314  as illustrated by dashed line  322 . 
         [0039]    The resonator of  FIG. 3  is therefore configured to allow reduction of sound energy in the vicinity of the resonator  325  through Helmholtz resonator oscillations, which depend on a number of factors such as the composition of fluids A and B and the volume of the second fluid B with respect to the volume of the fluids B and/or A in the neck section  314 , the cross-sectional area of opening  216 , and other factors. 
         [0040]      FIG. 4  illustrates a perspective view of a plurality of rows  410  of resonators  425  in a panel  400  according to an embodiment. Each row  410  is connected to the adjacent row(s) by a first chain  430  and a second chain  440 . The chains  430 ,  440  are each mechanically connected to a chain guide  450  that can collapse and/or pivot from a vertical or orthogonal position with respect to the plane of row  410  to a horizontal or parallel position with respect to the row. The chain guide  450  connected to row  410 ′ is in a partially deployed (or collapsed) configuration The chain guide  450  can be an elongated support that can be made out of a rigid plastic or a metal (e.g., a corrosion-resistant metal). 
         [0041]      FIG. 5  illustrates a magnified view  500  of the chains and elongated support described above. As illustrated, the chains  530 ,  540  are mechanically connected to a respective guide  550 . Each guide  550  has a planar surface  560  with two sidewalls  562 ,  564  that extend from the planar surface  560  towards the respective chain  530 ,  540 . The sidewalls  562 ,  564  also extend towards a proximal edge  515  of the row  510  when the elongated support  350  is in a vertical orientation with respect to the row  510 . The sidewalls define a recess  570  to receive the chain  330 ,  340 . The recess  570  can have a depth that is greater than or equal to the width of the chain, such that the width of the chain is fully disposed in the recess  570 . 
         [0042]    A row recess or opening  575  is defined in the row  510  to receive the guide  550  when the guide  550  is in the horizontal/stowed position (i.e., when the length of the guide  550  is parallel to the plane defined by the row  510 ). The row recess/opening  575  can extend partially or all the way through (e.g., a hole) the depth of the row  510 . In some embodiments, the recess/opening  575  extends across the width of the row. In some embodiments, the recess/opening  575  substantially conforms to the shape of the guide  550 . The recess/opening  575  can have a depth sufficient to fully receive the guide  550  in the horizontal or stowed position. 
         [0043]      FIG. 6  illustrates a magnified view  600  of the chains  630  and chain guides  650  in a partially-collapsed or partially-stowed state. The chain guides  650  are disposed on a chain guide apparatus  660 . The apparatus  660  includes a structure onto which the guides  650  are attached, for example at pivot point  670  that pivotally connects the apparatus  660  to an end of the guide  650 . The apparatus  660  can have a height  665  that is greater than or equal to a depth  655  of the guide  650  such that a recess  680  in the apparatus  660  can fully receive the guide  650  in its horizontal or stowed position. The apparatus  660  can be disposed on a row of a resonator panel, as discussed above, for example in an aperture or hole defined in the row to receive the apparatus  660 . 
         [0044]      FIG. 7  is a perspective view  700  of the chains  630  and guide  650  described above. As illustrated, the guides  650  have pivoted down to the horizontal or stowed position. In the horizontal position, the guides  650  are disposed in the recess  680  of the apparatus  660 . If the apparatus  660  is fully disposed in a recess in a row of a resonator panel, as discussed above, the guides  650  lie in the plane defined by the row. The recess  680  that receives the guide  650  allows for a more compact configuration in a collapsed/stowed state, for example when the guides  350  are deployed in a panel having a plurality of rows. 
         [0045]    In some embodiments, the chains  7630  are disposed on the inside or unexposed surfaces of the guides  650  (i.e., on the surface of guide  650  that faces the recess  680  when guide  650  is in the horizontal position). In some embodiments, one chain is disposed on the exposed surface of the guide  650  while the other chain is disposed on the inside/unexposed surface of the guide  650 . 
         [0046]      FIG. 8  is a top view  800  of the chain guide  650  disposed in a representative row  810  of resonators  820 . The chains  630  are disposed on the exposed surface of the guides  650  in the illustrated collapsed or stowed configuration. 
         [0047]      FIG. 9  is a perspective view of a plurality of panels  900  in a deployed configuration. Each panel  900  includes rows having chains and guides as described above. 
         [0048]      FIG. 10  is a perspective view of a panel  1000  in a stowed configuration. As illustrated, the panel  1000  can be stowed very compactly due to the pivotable/rotatable guide described above. 
         [0049]      FIG. 11  is a perspective view of an array  1100  of resonators  1110 . The resonators  1110  are disposed on a planar base  1120 . The resonators  1110  are generally cylindrical in shape and extend from the base  1120 . An aperture  1130  is defined at a distal end of the resonator  1110  from the base  1120 . The array  1100  includes a plurality of rows  1115  and columns  1125  or resonators  1110 . However, the resonators  1110  can be disposed in other configurations, such as in irregularly spaced and/or irregularly aligned rows  1115  and columns  1125  as described above. 
         [0050]    In operation, the resonator array  1100  is deployed in an ocean (or other body of water) with the apertures  1130  of the resonators  1110  facing towards the direction of gravitational pull (i.e., towards the ocean bottom). Such deployment causes air to be trapped between the aperture  1130  and the base  1120  to form a resonating body. 
         [0051]    The resonators  1110  can be manufactured by injection molding, for example, using a thermoplastic material. Similar manufacturing processes (e.g., liquid injection molding, reaction injection molding, etc.) are considered and included in this disclosure. In an injection molding process, the resonators  1110  can be integrally connected to the base  1120 . The resonators  1110  and base  1120  can be formed of the same material, such as a thermoplastic material as discussed above. By manufacturing the resonators  1110  using injection molding (or similar/equivalent processes), the shape, alignment, orientation, spacing, size, etc. of the resonators  1110  can be varied as desired. 
         [0052]    For example, the array  1100  can include resonators  1110  having different sizes and/or shapes to enhance the acoustic dampening of the array of resonators. For example, some resonators can have a generally circular cross section while others can have a generally rectangular cross section. In addition or in the alternative, some resonators can have a first aperture size (e.g., a narrow aperture) while other resonators can have a second aperture size (e.g., a wide aperture). In addition, or in the alternative, some resonators can have a first body having a first height and/or a first wall thickness while other resonators can have a second body having a second height and/or a second wall thickness. Such sizes and/or shapes can be regularly or irregularly distributed throughout the array. In addition or in the alternative, the spacing between adjacent resonators can be regular or irregular. In addition or in the alternative, the alignment of resonators in a given row  1115  and/or column  1125  can be regular or irregular, such array  1200  illustrated in  FIG. 12 . 
         [0053]      FIG. 13  is a top view of an array  1300  of resonators  1310  according to an embodiment. As illustrated, the resonators  1310  are irregularly spaced or offset and thus not every resonator  1310  is fully aligned in a row  1315  or column  1325 . Instead, the spacing of at least some of the resonators  1310  is offset positively or negatively so that some resonators  1310  are spaced closer together to each other while other resonators  1310  are spaced further apart from each other. A plurality of holes  1340  is defined in base  1320  of array  1300 . The holes  1340  are disposed between adjacent resonators  1310  and are arranged in columns and rows parallel to columns  1325  and rows  1315  (without the negative/positive offset discussed above). The holes  1340  can facilitate the submersion of the array  1300  into a liquid such as a water body (e.g., a lake or the ocean) by allowing air bubbles to pass through the holes  1625 . As the liquid displaces the air bubbles, the array  1300  becomes less buoyant and submerges more readily into the ocean. 
         [0054]    In some embodiments, the holes  1340  are only disposed between some adjacent resonators  1310 . The holes  1340  can be offset between adjacent resonators  1310  where a hole  1340  is closer to a first resonator  1310  than a second resonator  1310 . In addition, or in the alternative, the holes  1340  can be arranged in a regular or irregular pattern. In addition, or in the alternative, the holes  1340  can have different sizes and/or shapes. As discussed above, the array  1300  is deployed in a liquid (e.g., an ocean or other body of water) with the apertures  1330  facing toward the direction of gravitational pull (e.g., toward the bottom of the ocean). 
         [0055]      FIG. 14  is a view of the array  1300  from an opposing side of the base  1320 . Since the resonators  1310  are on the opposing side of the base  1320 , only the holes  1340  are viewable from in this figure. In operation, the exposed surface shown in  FIG. 14  would face towards the ocean surface while the opposing side (with the resonators  1310  extending therefrom) would face towards the ocean floor. A second set of holes  1350  is defined in the base  1320  to receive respective lines that are disposed between each array to form a panel of resonators, as described above. The lines can be tethered to a boat or a structure to raise or lower the panel. 
         [0056]      FIGS. 15-18  illustrate cross sections of alternative shapes of a resonator according to exemplary embodiments. For example,  FIG. 15  illustrates resonator  1500  that has a generally balloon-shape in cross section, with a narrow cross-sectional width at a first end  1510  and a large-cross sectional width at a second end  1520 . The first end  1510  includes an aperture  1530  that faces the ocean floor in the deployed orientation. As such, water can enter the aperture and fill a portion of the resonator  1500  up to a water line  1540  which can be a function of the cross-sectional width of the aperture  1530 , the cross-sectional width of the the first end  1510 , the cross-sectional of the second end  1520 , and the depth of deployment of the resonator  1500 . As the resonator  1500  is deployed deeper into the ocean, the water pressure on the external surface of the resonator  1500  can increase. The increased water pressure can cause more water to enter the resonator  1500  and thus cause the water line  1540  to be disposed higher in the resonator  1500  (i.e., towards the second end  1520  of the resonator  1500 ). 
         [0057]    As the resonator  1500  fills with water, the effective mass of the resonator  1500  increases. Thus, the effective mass of the resonator  1500  can be customized by varying one or more of the aperture  1530  size, the dimensions (e.g., cross-sectional width) of the resonator  1500  (e.g., the ratio of cross sections at the first and second ends  1510 ,  1520 ), and the depth of deployment of the resonator  1500  in the ocean. By adjusting the effective mass, the resonance frequency of the resonator  1500  can be “tuned” to abate a given undersea noise more effectively. In addition, a higher effective mass of the resonator  1500  can have enhanced acoustical dampening properties due to the corresponding higher inertia of the resonator  1500 . 
         [0058]      FIG. 16  illustrates a resonator  1600  having a generally mushroom-shaped cross section with a representative water line  1640 .  FIG. 17  illustrates a resonator  1700  having a wider cross section at first end  1710  than in  FIG. 16 or 17 . In addition, the cross-sectional width of the first end  1710  is greater than the cross-sectional width of the second end  1720 , and the cross-sectional width of a middle portion  1730  is greater than the cross-sectional width of the first and second ends  1710 ,  1720 . A representative water line  1740  is also illustrated in  FIG. 17 .  FIG. 18  illustrates a resonator  1800  where the cross-sectional width at the first end  1810  is greater than the cross-sectional width at the second end  1820 . In general, resonator  1800  has a shape similar to a cone. The wider cross-sectional width at the first end  1810  (and corresponding wider aperture  1830 ) can cause the water line  1840  to be lower (i.e., closer to the first end/aperture) compared to resonators  1500 ,  1600 , or  1700 . It is noted that the cross-sectional shapes illustrated in  FIGS. 15-18  are provided as examples and the disclosure contemplates any and all cross-sectional arrangements and shapes of resonators. In addition, the resonators illustrated in  FIGS. 15-18  can be generally circular or oval, rectangular, symmetrical, or asymmetrical in a second cross section orthogonal to the cross-sectional plane illustrated in  FIGS. 15-18 . 
         [0059]    The resonators  1500 ,  1600 ,  1700 , and/or  1800  can be integrated into an array, for example as illustrated in  FIGS. 11-14 . Such an array can be homogenous (e.g., the array includes the resonators having the same or similar shape) or inhomogeneous (e.g., the array includes various shapes, such as both the resonators  1600  and  1900 ). The spacing between adjacent resonators, alignment or offsetting of resonators in rows/columns, and/or size of the resonators can be adjusted or varied as described above, for example to reduce or increase the acoustical resonance of the array. In addition, or in the alternative, a panel of arrays can include a first panel having a first array with a first shape of resonators and a second array with a second shape of resonators. In addition, or in the alternative, the panel can include at least one inhomogeneous array and/or at least one homogenous array. Multiple panels can be deployed with the same or different resonator configuration, which can increase the spectrum of resonance frequencies to provide for enhanced noise abatement and/or enhanced acoustical performance (e.g., due to decreased resonance/echoing between panels). 
         [0060]      FIG. 19  illustrates a simplified representation of a resonator  1900 . The resonator  1900  includes a hollow cavity  1925  and a neck portion  1950  having an aperture  1975 . The hollow cavity  1925  is configured to retain a volume of air, Vair, while the resonator  1900  is deployed in a liquid (e.g., water) and the neck portion  1950  is oriented towards a direction of gravitational pull (e.g., towards the bottom of the ocean). When the resonator  1900  is in the deployed state, the neck portion  1950  fills at least partially with the liquid. Thus, the resonator  1900  can function as a two-fluid Helmholtz resonator. 
         [0061]    The acoustic behavior of the resonator is governed by the gas volume (Vair), the length of the neck portion  1950  filled with the liquid (Lneck), and the surface area (SA_aper) of the aperture  1975 . The gas volume (Vair) and the length of the neck portion  1950  filled with the liquid (Lneck) are dependent on the pressure exerted on the resonator  1900  by the liquid (e.g., water pressure), which is a function of the depth of deployment of the resonator  1900 . The depth dependence of these parameters can cause the resonance frequency and acoustic dampening of the resonator  1900  to also be depth-dependent. The relationship between resonance frequency, deployment depth, Vair, Lneck, and SA_aper may be mathematically modeled as would be appreciated by those skilled in the art. 
         [0062]    A comparison of the mathematic model versus experimental data of resonance frequency versus depth of deployment is illustrated in  FIG. 20 . The comparison is repeated for a first resonator size  2025  and a second resonator size  2050  as illustrated on the right-hand side of the figure. The experimental data was taken in a tank (data points with “x&#39;s”) and in a fresh water lake (data points with circles) using resonators made of different materials (steel, aluminum, and PVC). 
         [0063]      FIG. 21  illustrates a prototype of randomized resonator assembly  2100 A and a periodic resonator assembly  2100 B that incorporate the resonators described herein. The assemblies were fabricated on an automated router using 2 inch by 16 inch by 16 inch blocks of ultrahigh molecular weight polyethylene (UHMW PE). The internal dimensions of each individual resonator were 0.875 inch diameter and 1.75 inch height, which corresponds to a resonance frequency near 100 Hz when deployed within the first few meters of a liquid. The resonators&#39; positions in the random array  2100 A were generated by perturbing the periodic array positions with a pseudorandom number generator as described below. 
         [0064]    For ease of manufacturing and assembly, an array of individual resonator cavities was designed into a single unit part. The part can be described as a flat plate with a discrete number of hollow, cylindrical protrusions that are open to the atmosphere on the end opposite of the plate. Each protrusion forms a single resonator. The placement of the resonators on the face of the plate can be determined by pseudo-random perturbations to a square grid. A unit length in the square grid can be set to be twice that of the inner diameter of the resonators. A pseudo-random number generator can be used to determine a 2-dimensional (i.e., in an x-y plane perpendicular to the protrusions) perturbation of each node in the grid. The magnitude of the perturbation can be limited such that the outer diameters of adjacent resonators do not come into contact. With these factors, the center axis of each resonator can be defined as a specific perturbed node. 
         [0065]    As described above, the spatial structure of the resonator array can have an effect on the sound transmitted through or radiated by the array. The sound transmission or radiation can either by enhanced or inhibited by the array depending on the structure. Randomizing the locations of the resonators in the array can help to ensure that the phases of the scattered and re-radiated sound waves passing through the array are incoherent so that the net transmission of sound is minimized. In an experiment, the randomized resonator assembly  2100 A achieved about 6 dB more sound reduction than the periodic resonator assembly  2100 B near the individual resonator resonance frequency, which was about 85 Hz at the test water depth. A comparison of the random vs. periodic resonator assembly sound reduction measured in the test is illustrated in  FIG. 22 . 
         [0066]    Those skilled in the art will appreciate upon review of the present disclosure that the ideas presented herein can be generalized, or particularized to a given application at hand. As such, this disclosure is not intended to be limited to the exemplary embodiments described, which are given for the purpose of illustration. Many other similar and equivalent embodiments and extensions of these ideas are also comprehended hereby.