A wave-activated buoyancy regulator

Abstract

A wave-activated buoyancy regulator for structures positioned in a body of water, wherein a wave-activated pump is used to provide neutral, negative and positive buoyancy in response to prevailing ambient wave conditions, through the variation of the ratio of a first fluid to a second fluid within a ballast tank.

Description

[0001] Title

[0002] A wave-activated buoyancy regulator

[0003] Field

[0004] The present application relates to marine structures, more particularly aquaculture structures, and in particular to methods and systems for adjusting their buoyancy.

[0005] Background

[0006] Aquaculture, includes for example but is not limited to, the farming of fish, shellfish and seaweeds.

[0007] In aquaculture, a structure is provided to support or hold the fish, shellfish or seaweeds.

[0008] For many reasons, it is desirable that aquaculture is performed offshore, including availability of space and environmental reasons.

[0009] However, as support structures are moved away from sheltered waters to offshore conditions, they are exposed to greater stresses arising from wave action. One solution is to partially submerge or submerge the aquaculture structures so as to reduce the stresses caused by wave action. This can be achieved by adjusting the buoyancy of the aquaculture structure.

[0010] In general, the buoyancy of any aquaculture structure can be altered by varying the ballast of the structure, e.g. by using a ballast tank containing a mix of air and water, such that the buoyancy of the structure can be altered and controlled by varying the ratio of the air to water contained in the ballast tank.

[0011] International publication WO 2011 / 067124 A2 describes a wave powered buoyancy control system, for controlling the submersion of a floating section of a wave power plant, where a wave-powered pump is used to pump the compressible fluid from a ballast chamber to a high pressure accumulator, in order to let ambient seawater flood the permeable ballast chamber through an opening. However, WO 2011 / 067124 A2 does not teach how such a system may apply to aquaculture structures.

[0012] KR20000007853A describes the control of fish holding cultivation platform using a similar approach, with a wave pump coupled to a to a buoyancy adjustment device. The buoyancy adjustment device constitutes a singular ballast tank with a piston head and a bellows-type bladder to form an air chamber. The singular ballast tank is located centrally in the fish holding cultivation platform. High pressure seawater from the wave pump serves to displace compressed air from the ballast chamber to affect the buoyancy changes. However, KR20000007853A does not teach about how such ballast tanks could be integrated with the elongated and slender structures, typically associated with aquaculture, while maintaining good stability in operation.

[0013] European Patent EP4138548 “A variable buoyancy structure for aquaculture”, describes a variable buoyancy structure for aquaculture comprising an inflatable tube which acts a ballast tank and can provide neutral, negative and positive buoyancy through the combination of a negatively buoyant constituent and the controlled variation of the ratio of air to water within the tube. A number of fish pen designs are now submersible or semi-submersible. These include the “Atlantis Subsea Farming” fish pen proposed by AKVA Group, the OCEANIS fish pens sold by Badinotti and the Sea Station pens developed by Innovasea. These pens are designed to be selectively submersed, including in storm conditions when wave action may threaten the structure or its contained biomass. In all cases these pens rely on the ballast changes of one or more of the voids within the pen structure in order to vary the buoyancy and or to affect submersion.

[0014] As aquaculture structures are generally unmanned, there is a need for an effective method of automatically adjusting the buoyancy of aquaculture structures to reduce wave induced stresses.

[0015] The present application provides a solution.

[0016] Summary The present application provides a wave-activated buoyancy regulator. This has a number of advantages: a) Wave-powered pumping: It uses wave-power to pump ballast fluid, because there is a perfect correlation between the availability of wave power and the need to move ballast to create a buoyancy condition that can avoid the negative effects of waves; b) Autonomous control: A passive control response, whereby desirable buoyancy changes are autonomously affected, correlated to the level of ambient wave energy present in the body of water where the structure is positioned; c) Load reductions: A wave-pump integrated at one or more mooring attachment points that will dissipate excess energy and reduce the peak loads at such critical attachment points; d) Leak tolerance: As the availability of the energy is ubiquitous at the time it is needed most, where there might be small leaks in the system, the available pumping pressure will overcome these and safely affect the required buoyancy change when it is needed most. e) Stability: A series of bladders arranged along a longitudinal axis of a ballast tank, secured to an internal structure of the ballast tank, so as to secure them in the position and such that the combined centre of gravity of the ballast tank, including the first fluid and the second fluid, remains in a generally constant location and does not compromise the overall stability of the variable buoyancy structure. f) Pressurise Inflatable Structures: Where the structure is an “inflatable beam” or “pressure supported structure” such as that described in Claim 5 of EP4138548, the structure relies on the internal pressure being elevated over ambient pressure in order to maintain its structural properties. A wave-activated buoyancy regulator will ensure that the pressure will be regularly “topped up” in the presence of ambient wave energy. This puts less dependence on regular inspections to ensure that such inflatable structures are at their target operating pressure in advance of storms and the like.

[0017] Accordingly, the present application provides a wave-activated buoyancy regulator (110) suitable for use in a variable buoyancy structure (100) positioned in a body of water (1110), the wave-activated buoyancy regulator (110) comprising: A ballast tank (2), wherein the ballast tank (2) is configured to retain a first fluid (8a) of a first density and a second fluid (8b) of a second density, wherein the buoyancy of the structure (100) is controlled by variation of a ratio of the first fluid (8a) to the second fluid (8b) within the ballast tank (2), and wherein at least one internal bladder (10) formed by a flexible impermeable membrane is provided within the ballast tank (2) for separating the first fluid (8a) from the second fluid (8b); at least one wave-activated pump (40), mechanically coupled to the ballast tank (2) of the variable buoyancy structure (100), and wherein the wave-activated pump (40) is configured to cause at least one of the first fluid (8a) or the second fluid (8b) to flow through at least one inlet (51) or outlet (52) of the ballast tank (2); characterised in that the ballast tank (2) is an elongated ballast tube (2) and the at least one bladder comprises a plurality of internal bladders (10) distributed at locations within the elongated ballast tube (2), wherein the plurality of internal bladders (10) is secured longitudinally in order to maintain their general position within the ballast tank (2) for overall ballast stability.

[0018] The at least one wave-activated pump (40)is configured such that when there are ambient waves present, the wave-activated pump (40) can convert the resulting forces and motions into pressure and flow of at least one of the first fluid (8a) or the second fluid (8b) at an inlet (51) to the ballast tank (2), optionally being an outlet (52). a flow controller (50) comprising a system of conduits (41), valves (42,43,45) and flow regulators (44) that determines the ratio of the first fluid (8a) to the second fluid (8b) within the ballast tank (2), using the pressure and flow of at least one of the first fluid (8a) or the second fluid (8b), as made available by the wave-activated pump (40).

[0019] The first fluid (8a) is suitably a gas and the second fluid (8b) is suitably a liquid. In one embodiment, the first fluid (8a) may be a lower density compressible gas such as ambient air and the second fluid (8b) may be a higher density incompressible fluid such as ambient sea water.

[0020] The variable buoyancy beam (100) previously outlined in prior art EP4138548 is particularly well suited to being integrated with a wave-activated buoyancy regulator, wherein the ballast tank (2) is formed by the variable buoyancy beam (100) itself, which comprises a hollow elongated tube that is configured to hold at least one of a first fluid (8a) and a second fluid (8b). The hollow-elongated tube can form a ballast tube (2), comprising an impermeable wall (16), optionally formed by a flexible material that can form a beam when supported by the internal pressure of the ballast tube (2), as described in Claim 5 of EP4138548. EP4138548 also describes at least one flexible bladder (10) provided internal to the ballast tank (2) to separate the first and second fluids, while still permitting the pressure of the fluids to be communicated to one another within the ballast tank (2). The bladder (10) may be a sealed tube made of flexible impermeable material. In an alternative arrangement, the bladder comprises a flexible membrane dividing the ballast tank (2) along its longitudinal axis to create a first longitudinal compartment for the first fluid (8a) and a second longitudinal compartment for the second fluid (8b). The at least one flexible bladder (10) may comprise a series of bladders (10) arranged along any longitudinal axis of the ballast tank (2). Advantageously, these may be secured to an internal structure of the ballast tank (2), so as to secure them in the position and such that the combined centre of gravity of the ballast tank (2) including the first fluid (8a) and the second fluid (8b) remains in a generally constant location and does not compromise the overall stability of the variable buoyancy structure (100).

[0021] The ballast tank (2) suitably has at least one inlet (51) and at least one outlet (52) to allow for the introduction / release of at least one of the fluids. In certain arrangements, there is at least a first inlet and a first outlet for the first fluid and at least a second inlet and a second outlet for the second fluid. In the case of the inlet, this allows the connection to the source of at least one fluid (8a, 8b), optionally being a connection (41) to the outlet of the wave-activated pump (40). Each inlet may be an outlet. In the case of the outlet, this allows the release of a fluid from the ballast tank (2), optionally to the ambient environment or to some containment reservoir of the fluid, optionally being a return of ambient sea water and / or ambient air to the ambient environment. Each outlet may be an inlet. A suitable valve arrangement allows for the opening or closure of the inlets / outlets as required to affect the desired ratio of the first fluid (8a) to the second fluid (8b) within the ballast tank (2). The one or more wave-activated pumps may comprise a hose-pump, similar to that described in Swedish patent SE-B-409 493, developed further in the worldwide patent publication WO / 1997 / 041350. Alternatively, the one or more wave-activated pumps may comprise a cylindrical bellowed elastomeric member which acts under axial compression and tension to generate pressure and flow of a fluid through the cylindrical bellowed elastomeric member. Alternatively, the one or more wave- activated pumps may comprise a deformable chamber of any other polymer material, the chamber being capable of pressurising the fluid contained within it, when acted upon by loads caused by ambient waves. Preferably the elastic properties of the polymer material forming the chamber will form a centralising spring so that the wave-activated pump chamber volumetrically oscillates, generally about a central equilibrium volume.

[0022] Alternatively, the wave activated pump (40) may comprise a linear piston pump, comprising a piston rod and a cylinder with a linear bearing between the two, a chamber being formed between the piston and the cylinder such that forces acting on the piston and cylinder generate a variable pressure in the fluid contained in the chamber. Preferably, the wave activated pump (40) comprising a linear piston will include a centralising mechanical spring so that the wave-activated pump chamber volumetrically oscillates about a central equilibrium volume.

[0023] The wave-activated pump (40) suitably has at least one inlet and at least one outlet to allow for the suction / pumping of at least one of the first fluid (8a) or the second fluid (8b). In certain arrangements, there is at least a first inlet and a first outlet for the first fluid (8a) and at least a second inlet and a second outlet for the second fluid (8b). In the case of the inlet, this allows the connection to the source of fluid, optionally being a connection to the ambient sea water for the second fluid (8b) or ambient air for the first fluid (8a). In the case of the outlet, this allows a connection (41) to the ballast tank (2) to which at least one of the first fluid (8a) or second fluid (8b) can be pumped, when the pump (40) is activated by the presence of waves (1110). An umbilical (41 ), pipe, or other fluid-carrying conduit may be provided to give fluid connectivity between the outlet of the wave-activated pump (40) and the inlet of the ballast tank (2). A suitable valve arrangement allows for the opening or closure of the inlets / outlets as required to affect the pumping operation. For example, check valves (42) at the inlet and outlet of the wave-activated pump (40) may be configured to regulate wave-induced oscillating pressures in a piston to induce the flow of at least one of the fluids from its source to the ballast tank (2).

[0024] The present application has a number of adoptions of a wave-activated buoyancy regulator (110) which may be employed to advantage either alone or in any combination with the other adoptions, a variable buoyancy structure (100).

[0025] In a first adoption, the outlet of the ballast tank (2) may be fitted with a pressure relief valve (43) designed to open to release at least one of the first fluid (8a) or a second incompressible fluid (8b), once the pressure in the ballast tank (2) exceeds a threshold. Optionally, the threshold could be set to be the normal operating pressure of the ballast tank (2) in calm sea conditions. Optionally, wherein the ballast tank (2) is formed by the tube of an inflatable, pressure-supported beam such as that described in Claim 5 of EP4138548, this pressure would be set to ensure the beam has the desired structural characteristics.

[0026] In a second adoption, the outlet of the ballast tank (2) may be fitted with a flow regulator (44) at an outlet, designed to regulate the rate of release of a second incompressible, high density fluid (8b) from the ballast tank, when the pressure inside the ballast tank (2) is above the pressure external to the ballast tank (2), the rate of release of the second incompressible fluid (8b) through the regulator depending on the pressure gradient. At a large pressure gradient there is a correspondingly larger rate of release of the second incompressible fluid (8b) from the ballast tank (2). The flow regulator (44) is preferably configured such that the difference in pressure required for the rate of release of the second high density incompressible fluid (8b) to be equal to the rate of its replenishment at the inlet (42) of the ballast tank (2), caused by the wave-activated pump (40), is sufficient to cause the first low density compressible fluid (8a) within the ballast tank to compress in volume. This will cause a change in the ratio of the volume of first low density compressible fluid (8a) to the volume of second high density incompressible fluid (8b) contained within the ballast tank (2), thus varying the buoyancy of the structure (100). As the pressure difference is being caused by the wave-activated pump (40) introducing the second incompressible fluid (8b) into the ballast tank (2) at an elevated pressure and flow, the buoyancy of the structure (100) will autonomously vary according to the amount of wave energy acting on the wave-activated pump (40) to deliver the flow and pressure of the second fluid (8b) to the ballast tank (2). Where a variable flow regulator (44) is employed, it will be possible to adjust the regulator to either:

[0027] A) release more of the second fluid (8b), thereby increasing the amount of ambient wave energy that would be required to cause a pressure increase inside the ballast tank, a compression of the first compressible fluid (8a) and a corresponding reduction in the buoyancy of the variable buoyancy structure (100), or;

[0028] B) release less of the second fluid 8(b), thereby decreasing the amount of ambient wave energy that would be required to affect a pressure increase inside the ballast tank, a compression of the first compressible fluid (8a) and a corresponding reduction in the buoyancy of the variable buoyancy structure (100), thereby creating an adjustable but autonomous response to regulate the buoyancy of the structure (100) in the presence of waves. In the absence of ambient waves (1110), the pressure in the ballast tank (2) will over time equalise with the external pressure and the compressible fluid (8a) will expand to expel the second fluid (8b), such that the pressure in the buoyancy tank (2) approaches equilibrium with the external pressure, and the buoyancy of the structure (100) is maximised. Where a flow regulator (44) is optionally introduced in series with the pressure relief valve (43) described in the first adoption, a minimum threshold pressure can be established, corresponding to the desired minimum operating pressure of the ballast tank (2) and correspondingly the maximum desired buoyancy condition of the structure (100) when the ambient wave energy present is too low to affect an increase in the pressure of the ballast tank (2).

[0029] In a third adoption, at least one safety relief valve (45) is provided in the ballast tank (2), such that if the pressure and flow of at least one of the first fluid (8a) or a second incompressible fluid (8b) introduced by the wave-activated pump (40) at an inlet of the ballast tank (2) causes the pressure within the ballast tank to exceed a desirable or safe pressure threshold, that the safety valve would open and release at least one of the first fluid (8a) or the second fluid (8b) at rate of flow that would rapidly reduce the pressure to safe levels before the safety relief valve would close again (45). Where such a safety relief valve is optionally provided in parallel to a pressure relief valve as described in the first adoption or in parallel to the flow regulator described in the second adoption, the safety relief valve will be set to open at a high threshold pressure and would not affect the operation of the wave-activated buoyancy regulator (110) within its intended range of operating pressure.

[0030] In a fourth adoption, the more than one bladders (10) can be formed by a flexible closed-cell foam (26), the closed-cells of the foam forming the more than one bladders (10) configured to contain a first compressible fluid (8a). This closed-cell foam (26) may be used in place of or in addition to the flexible bladder (10) of the fourth adoption.

[0031] In a fifth adoption, a valve arrangement is provided to adjust the ratio of the first fluid to the second fluid in the ballast tank (2), in response to changes in the weight of material, e.g. aquaculture, attached to the variable buoyancy structure (100) comprising a wave-activated buoyancy regulator. More particularly, the weight of an aquaculture, e.g. seaweed or shellfish, may increase as it grows, causing a supporting structure (100) to slowly sink under the increasing weight. The valve arrangement is configured to release the denser fluid (8b) from the ballast tank (2) as this happens to restore the buoyancy of the structure (100) and suspended aquaculture to a desired level. In other cases, where the weight of an aquaculture decreases as it grows through positive buoyancy, the valve arrangement is configured to release the lower density fluid (8a) from the structure (100) to restore the buoyancy of the structure to a desired level. The valve arrangement may comprise a pressure-actuated valve or a float-actuated valve configured to open once the structure’s submergence exceeds a desirable envelope, such that one of the first fluid (8a) or second fluid (8b) is expelled from the buoyancy tank (2) and so that the buoyancy of the structure changes advantageously. For example, where the energy of a compressed first fluid (8a) may be used to expel a second incompressible fluid (8b) of higher specific gravity through such a pressure actuated or float-actuated valve, a buoyancy increase is affected to passively compensate for changes in external loading on the structure (100), for example due to the weight of shellfish biomass growing on attached ropes. Advantageously, such a passive solution does not necessarily rely on external power sources or active logical control. Suitably the pressure-actuated valve or float-actuated valve is configured to have a damped or delayed response to short term pressure fluctuations, such that the valve will not open in response to passing waves, instead responding only to longer term changes in mean submergence. The pressure in the ballast tank (2) may then be advantageously replenished by the wave-activated pump (40) using the at least one of a first fluid (8a) or a second fluid (8b).

[0032] These five adoptions of a wave-activated buoyancy regulator (110) may be employed in isolation or combined together to advantage in any combination a variable buoyancy structure (100) and may be deployed in a variety of different aquaculture or marine structures (200,300,400,500), as will become apparent from the description which follows.

[0033] Preferably, the wall (16) of the ballast tank (2) is configured such that it can withstand pressures in excess of external ambient pressures such that the first fluid (8a) and the second fluid (8b) can be retained at elevated pressures, preferably at pressure within the range of 0.5 bar to 20 bar in excess of external ambient pressure.

[0034] Where the first fluid (8a) and second fluid (8b) are separated from each other through at least one internal bladder (10) inside the tube, the bladder may be formed by a suitably flexible impermeable membrane that may either fully enclose a volume of the first fluid (8a) or fully enclose a volume of the second fluid (8b) or alternatively may be attached to the wall of the tube in such a way as to separate volumes of the two fluids enclosed by the tube wall and the membrane. The bladder (10) is configured such that the ratio of the volume of the first fluid (8a) to the second fluid (8b) within the ballast tank (2) may be varied, while the fluid volumes are kept separate to facilitate separate valve connections and the like. The membrane material of the bladder is preferably flexible, such that the stresses induced in the bladder wall are small over the required range of volume changes and such that the difference in pressures on either side of the bladder wall at a given location over the required range of volumetric variation do not exceed 1 bar, preferably not exceeding 0.1 bar. As such, the membrane material of the bladder is preferably of a flexural rigidity not exceeding 1 Nm, where the flexural rigidity is affected by the membrane thickness and materials properties, notably the Young’s modulus and Poisson’s ratio. The bladder membrane will have sufficient surface area to take up the required volume change or optionally be of a suitably low in-plane stiffness to stretch to the required volumes, while inducing only a limited pressure differential between the first fluid and the second fluid. Suitable bladder membrane materials include but are not limited to natural or synthetic rubber sheeting such as butyl, latex or silicone rubber, PVC, polyurethene or polyethelene sheet materials and rubber-coated fabric membranes using polyester, nylon or aramid fibres or other impermeable fabric materials such as those under the brand names of Dacron or Gore-Tex. Preferably the wall thickness of the bladder membrane will not exceed 2% of the ballast tank diameter (in a range of 1 mm for 50 mm diameter tanks up to 30 mm for 1 .5 m diameter tanks). The bladder may be provided as a single bladder or, for example, comprise a plurality of internal bladders distributed at a variety of locations within the tube. Where there is a plurality of bladders, the bladders may be discretely formed or they may be co-formed together. In one arrangement, the plurality of internal bladders are at least partially provided by the cells of a flexible closed cell foam structure, for example foams formed by expansion of gas bubbles through materials like polyurethane, polyethylene or ethylene-vinyl acetate (EVA) polymers, or similar. Other suitable materials for a flexible closed-cell foam are ethylene propylene diene monomer (EPDM) rubbers or other natural or synthetic rubbers from which a closed- cellular foam can be expanded by bubbles of gas to form a plurality of microbladders (10).

[0035] Suitably the internal bladders or closed-cell foam substrates can be secured within a positional envelope using internal attachments, for example rope, so that their general position within the ballast tank is maintained in order to provide general ballast stability under dynamic loading of the variable buoyancy structure.

[0036] Suitably, as described in Claim 5 of EP4138548, the wall of the ballast tank may be formed using an impermeable tensile membrane that is foldable when it is not pretensioned by internal pressure of the ballast tank. Such a ballast tank can be in the form of a tube, configured using an anisotropic membrane material with a low flexural rigidity but with a high planar stiffness, such that it is possible to inflate the tube to a rigid form at pressures significantly in excess of the external ambient pressure. The bending and compression strength of the tube may then be operatively varied by introduction of at least one of the first fluid or the second fluid in order to provide pre-stress in the tube’s membrane wall so that the tube resists bending or buckling due to external loads applied to the tube. In this way, the ballast tank may form the dual function of a structural member as part of the variable buoyancy structure (100) itself. Suitably, the flexural rigidity of a 1 m diameter tube wall may be less than 10 Nm while the planar tensile stiffness will exceed 1000 MN / m. Suitable materials for such a flexible tube wall include rubber-coated fabric materials of polyester, nylon, aramid or polyethylene fabrics or other impermeable fabric materials based on high-tenacity fibres. The thickness of a flexible tube wall may be limited to give a low flexural rigidity, preferably not exceeding 5% of the sectional diameter.

[0037] Suitably, the plurality of internal bladders are in fluid communication with at least one connection point external to the tube. This fluid communication may be provided using pipes or hoses. Optionally, a common manifold may be provided connecting a plurality of bladders to the at least one external connection point. Control valves may be provided for flow control between the manifold and individual internal bladders. The control valves may be check valves, solenoid control valves or other actuated valves that affect active logical control of fluid flows.

[0038] Suitably, the plurality of internal bladders can be inflated from a single common inflation manifold with check valves at the inlet to each bladder. The check valves passively prevent the movement of fluid between individual bladders connected to the single common inflation manifold, while allowing all bladders to be inflated from a common external inlet to a common inflation pressure.

[0039] Suitably, the plurality of internal bladders can be deflated from a single common deflation manifold with check valves at the outlet from each bladder. The check valves will prevent the movement of fluid between individual bladders connected to the single common deflation manifold, while allowing all bladders to be deflated to a common external outlet to a common deflation pressure, including to affect the full volumetric collapse of the plurality of internal bladders.

[0040] The variable buoyancy structure (100) may be used to suspend a containment net for fin-fish aquaculture or a support medium, such as for example ropes, for the culture of shellfish or seaweed.

[0041] Where negatively buoyancy forces are required to be applied to the attached aquaculture structure, the variable buoyancy structure may also comprise a negatively buoyant constituent extending about or within the structure, the buoyancy of the structure being a combination of a buoyancy of the ballast tank with the negatively buoyant constituent.

[0042] Suitably, the first fluid has a density less dense than the density of the water in which the variable buoyancy structure (100) is to be positioned.

[0043] The ballast tank (2) may be provided in a collapsed state. In this collapsed state, the ballast tank (2) may be pressurised through the introduction of at least one of the first fluid or the second fluid in order to provide rigidity to the ballast tank (2) in an expanded state.

[0044] The variable buoyancy structure (100) comprising a wave-activated buoyancy regulator (110) is configured to adopt a floating state of variable emergence or a fully-submerged state of variable buoyancy through selective variation of the ratio of the first fluid to the second fluid within the ballast tank (2).

[0045] Suitably, the first fluid is compressible so that the selective variation of the ratio of the first fluid to the second fluid within the ballast tank (2) can be achieved through variation of a second fluid only, while simultaneously varying the pre-tension in the wall of the ballast tank (2) and any encapsulating net structure.

[0046] Suitably, the first fluid stores energy when it is compressed and has a low specific gravity and the second fluid is generally incompressible with a higher specific gravity, so that the stored energy of the compressed first fluid can be used to expel the second incompressible fluid from the ballast tank without the need for another source of energy. In the case where the first fluid is air and the second fluid is water, it will be appreciated that the air may be compressed air.

[0047] The wave-activated buoyancy regulator (110) may comprise a control valve, wherein the valve is configured to control the access and egress of at least one of the first fluid or the second fluid between the interior of the ballast tank and the exterior of the ballast tank. The access and egress may be via the common inflating manifold or the common deflating manifold.

[0048] The wave-activated buoyancy regulator (110) comprising at least one wave-activated pump (40) may also contain at least one other pump, wherein the pumps are configured to move at least one of the first fluid or the second fluid between the interior of the tube and the exterior of the tube via the valve. This movement may be via the common inflating manifold or the common deflating manifold.

[0049] The wave-activated buoyancy regulator (110) may comprise at least one umbilical which is configured to connect the valve to a source of the first fluid or the second fluid.

[0050] In certain arrangements, as will be detailed below, it is necessary to ballast the wave activated structure (100) comprising a wave-activated buoyancy regulator (110) with a negatively buoyant constituent. The negatively buoyant constituent may be positioned to be in intimate contact with the wave activated structure (100). Suitably, the negatively buoyant constituent comprises a high-density ballasting material, for example a metal. Suitably, when the high density ballasting material is metal, it is provided in the form of wire or chain.

[0051] Suitably, one or more ballast tanks (2), in the form of tubes of the type described in EP4138548, are configured to form a generally toroidal variable buoyancy structure (100), such as a curved ring or polygonal toroid. Optionally, the one or more ballast tanks forming a curved ring or polygonal toroid are connected to a hub structure with spoked beams, struts or cables, optionally being stabilising elastic tendons in order to form a centrally-supported polygonal toroid structure (400). Optionally, one or more wave-activated pumps (40) may be integrated with the one or more spokes of the centrally-supported polygonal toroid (400), which in combination with the ballast tanks (2) forming a polygonal toroid can form a variable buoyancy structure (100,400) comprising a wave-activated buoyancy regulator.

[0052] The diameter of the curved ring or toroid may suitably be at least 50 times the diameter or equivalent cross-sectional dimension of the one or more ballast tank comprising a tube (2).

[0053] Suitably, the ballast tanks, in the form of tubes, may be connected at their ends to form a truss structure (404).

[0054] Suitably, the one or more wave-activated pumps (40) of the wave-activated buoyancy regulator (110) may be connected between the variable buoyancy structure (100) and an anchor (1105), as part of a mooring (1110), such that the wave-activated pump (40) can exploit the relative motion of the variable-buoyancy structure (100) and the seabed. The mooring cable can comprise the wave-activated pump (40) as well as weights, floats, and cables, the cables being formed from one or more ropes, chain, rods, tendons. In the presence of ambient wave energy, the mooring cable will have oscillatory tensions that act on the wave-activated pump (40) in order to generate pressure and flow of at least one of a first fluid (8a) or second fluid (8b).

[0055] Suitably, the one or more wave-activated pumps (40) of the wave-activated buoyancy regulator (110) may be connected between the variable buoyancy structure (100) and a second wave-activated float, such that the wave-activated pump (40) can exploit the relative motion of the wave-activated float and the variable-buoyancy structure (100) when ambient wave energy is present in the general area where the structure (100) is positioned.

[0056] Suitably, the one or more wave-activated pumps (40) of the wave-activated buoyancy regulator (110) may be connected to one or more wave-activated structures, entirely separate to the variable buoyancy structure, such that the wave- activated pump (40) can exploit the relative motion between one or more wave- activated structures, and another reference structure, optionally being the sea bed, when ambient wave energy is present in the general area where the structure (100) is positioned. In such cases the wave-activated pump (40) need only have a fluid connection to the ballast tank (2) of the variable buoyancy structure (100).

[0057] These and other features, advantages and details of the wave-activated buoyancy regulator and the adoptions will become apparent from the description which follows.

[0058] Brief Description Of The Drawings

[0059] The present application will now be described with reference to the accompanying drawings in which:

[0060] Figure 1 illustrates two identical semi-submersible column structures, wherein the buoyancy of the structure is regulated by a wave-activated buoyancy regulator, in a way that is similar to the combined prior art in WO 2011 / 067124 A2 and KR20000007853A;

[0061] Figure 2 illustrates an example of a prior art variably buoyancy beam structure as described in EP4138548, the variable buoyancy beam also being suitable for use as a ballast tank in a wave-activated buoyancy regulator;

[0062] Figure 3a illustrates a variably buoyancy beam wherein the buoyancy of the beam is regulated by a wave-activated buoyancy regulator, and wherein the ambient waves are small, such that the variably buoyancy beam has a positive buoyancy and is floating on the surface;

[0063] Figure 3b illustrates the same variably buoyancy beam as in Figure 3a, wherein the ambient waves are large, such that the variably buoyancy beam has a negative buoyancy and is submerged below the surface;

[0064] Figure 4 illustrates a similar variable buoyancy beam to that illustrated in Figure 3b, wherein the ambient waves are large, such that the variably buoyancy beam has a negative buoyancy and is submerged below the surface, and wherein the addition of a float-activated valve limits the depth of submergence of the variable-buoyancy beam;

[0065] Figure 5 illustrates an example of a prior art pen structure as described in EP4138548, wherein the pen structure comprises a float ring and a sinker ring, where either or both of the float ring and sinker ring may be formed by one or more variable buoyancy beams;

[0066] Figure 6a illustrates a submersible pen structure, similar to the pen structure illustrated in Figure 5, wherein the addition of a wave-activated buoyancy regulator is used to vary the buoyancy of either or both of the float ring and sinker ring, formed by one or more variable buoyancy beams, and wherein the ambient waves are smaller, such that the pen has a positive buoyancy and the float ring is floating on the surface;

[0067] Figure 6b illustrates the same submersible pen structure as illustrated in Figure 6a, wherein the ambient waves are larger, such that the pen has a negative buoyancy and the float ring is submerged below the surface;

[0068] Figure 7 illustrates a prior art submersible mussel culture system as described in EP4138548 with a head beam in a submerged position, formed by one or more variable buoyancy beams and in which the buoyancy of the submerged head beam is controlled by float-activated valves that open when its submergence exceeds a threshold value.

[0069] Figure 8a illustrates a submersible mussel culture system, similar to the mussel culture system illustrated in Figure 7, wherein according to the present teaching, the addition of a wave-activated buoyancy regulator is used to vary the buoyancy of the head beam, and wherein the ambient waves are smaller, such that the head beam has a positive buoyancy and the head beam is floating on the surface;

[0070] Figure 8b illustrates the same submersible mussel culture system as illustrated in Figure 8a, wherein the ambient waves are larger, such that the head beam has a negative buoyancy and the head beam is submerged below the surface;

[0071] Figure 9 illustrates a general layout of a prior art mussel and seaweed culture system as described in EP4138548, having a centrally-supported polygonal ring, the polygonal ring being formed by one or more variable buoyancy beams;

[0072] Figure 10a illustrates a submersible mussel and seaweed culture system, similar to the mussel and seaweed culture system illustrated in Figure 9, wherein according to the present teaching, the addition of a wave-activated buoyancy regulator is used to vary the buoyancy of the centrally-supported polygonal ring, and wherein the wave- activated pumps are integrated with the spokes of the centrally-supported polygonal ring, and where the ambient waves are smaller, such that the polygonal ring is suspended at a small depth of submergence; Figure 10b illustrates the same submersible mussel culture system as illustrated in Figure 10a, wherein the ambient waves are larger, such that the wave-activated buoyancy regulator has caused the polygonal ring to be at a larger depth of submergence;

[0073] Figure 11 illustrates a ballast tank suitable for use in a wave-activated buoyancy regulator, wherein the ballast tank is formed by a tube with an impermeable wall, configured to contain a first fluid of a first density and a second fluid of a second density as well as a negatively buoyant constituent and such that the ballast tank can also function as a variable buoyancy beam structure;

[0074] Figure 12 illustrates a ballast tank suitable for use in a wave-activated buoyancy regulator, wherein the ballast tank is formed by a tube with an impermeable wall, configured to contain a first fluid of a first density and a second fluid of a second density, wherein the first fluid is contained in 3 bladders to separate it from the second fluid and wherein the ballast tank is encapsulated in a net structure, such that the ballast tank is also suitable for use as a variable buoyancy beam structure; Figure 13 illustrates a ballast tank suitable for use in a wave-activated buoyancy regulator, wherein the ballast tank is formed by a tube with an impermeable wall, configured to contain a first fluid of a first density and a second fluid of a second density, wherein the first fluid is contained in a flexible closed-cell foam structure to separate it from the second fluid and wherein the ballast tank is encapsulated in a net structure, such that the ballast tank is also suitable for use as a variable buoyancy beam structure;

[0075] Figure 14 illustrates how a number (7 shown) of variable buoyancy beams of the type illustrated in Figure 2 may be connected by end connectors to form a variable buoyancy truss structure, which may be used in aquaculture or other marine applications, such that the variable buoyancy truss structure is also suitable for use as a ballast tank in a wave-activated buoyancy regulator;

[0076] Figures 15a and 15b both illustrate a perspective view of a ballast tank suitable for use in a wave-activated buoyancy regulator, being similar to that illustrated in Figure 11 with a negatively buoyant constituent, such that the ballast tank is also suitable for use as a variable-buoyancy ring structure for aquaculture;

[0077] Figure 15b illustrates a view of a sinker ring showing an alternative negatively buoyant constituent to that of Figure 15a in the form of intermittently spaced high- density ballasting materials in a rigid tube of variable buoyancy; Figure 16 illustrates a centrally-supported polygonal toroid formed from 6 ballast tanks of the type illustrated in Figure 12 or Figure 13, being suitable for use in a wave-activated buoyancy regulator;

[0078] Figure 17a illustrates a cross section of a ballast tank similar to that illustrated in Figure 12 in a partially collapsed (deflated) and buoyant configuration;

[0079] Figure 17b illustrates a cross section of the ballast tank similar to that illustrated in Figure 12 in an inflated and buoyant configuration;

[0080] Figure 18 illustrates a series of cross sections of a ballast tank suitable for use in a wave-activated buoyancy regulator, being suitable also for use as a variable buoyancy beam, in a deployment sequence where the tube is in various stages of collapse and buoyant configuration depending on the density of the fluids within the tube and the pressure maintained within the tube at each stage;

[0081] Detailed Description Of The Drawings

[0082] The present application will now be described in greater detail with reference to some examples of how a wave-activated buoyancy regulator (110) may be employed for floating structures (100, 500) including aquaculture structures (200, 300, 400).

[0083] With reference to the figures there is provided a wave-activated buoyancy regulator (110) that may be employed and adapted for a variety of different aquaculture and marine structures.

[0084] With reference to Figure 1 , a wave-activated buoyancy regulator (110) is employed for a semi-submersible column structure (500), floating in a body of water with a free surface (1110). Gravity waves propagate in the body of water disturbing the free surface (1110) from its equilibrium, disturbing also any structures within the body of water, including the semi-submersible column structure (500). Two identical semisubmersible column structures (500) are depicted in the body of water in Figure 1 , the first being exposed to small ambient gravity waves and the second being exposed to large ambient gravity waves. Each semi-submersible column structure (500) is connected to the seabed with a mooring and an anchor (1105). Each semisubmersible column structure (500) comprises a wave-activated buoyancy regulator (110), comprising a ballast tank (2) and a wave-activated pump (40). The ballast tank (2) is configured to hold a first compressible fluid (8a), optionally being ambient air and a second incompressible fluid (8b), optionally being the ambient water in which the semi-submersible structure (500) is floating. The wave-activated pump is connected between the mooring anchor (1105) and the semi-submersible structure (500), such that the pump (40) is activated by the wave-induced motions of the floating semi-submersible structure (500). A fluid carrying conduit (41) is connected between the ballast tank (2) and the wave-activated pump (40). In Figure 1 , the wave-activated pump (40) is configured to generate pressure and pump the second fluid (8b) to the ballast tank (2) through the conduit (41 ) when it is acted upon by the wave-activated motions of the semi-submersible structure (500). This elevates the pressure within the ballast tank (2), compresses the first fluid (8a) and decreases the ratio of a first fluid (8a) to a second fluid (8b) within the ballast tank, resulting in a reduction of the buoyancy of the semi-submersible structure (500).

[0085] The wave-activated buoyancy regulator (110) in Figure 1 further comprises a flow controller, the flow controller comprising a pressure relief valve (43) and an adjustable flow regulator (44) in series with one another. The pressure-relief valve (43) opens once the pressure in the ballast tank exceeds a threshold allowing the second fluid (2) to flow through the outlet of the ballast tank. The adjustable flow regulator (44), further limits the rate of flow of the second fluid (8b) in proportion to the difference between the internal pressure of the ballast tank (2) and the external pressure of the low pressure store of the second fluid (8b), being the ambient external water pressure in Figure 1 . When the outlet return flow of the second fluid through the regulator (44) is less than the in-flow of the second fluid at the inlet caused by the wave-activated pump (40), the buoyancy will continue to reduce until the pressure in the ballast tank (2) increases to a point that the outlet flow through the regulator (44) balances the flow at the inlet caused by the wave-activated pump, thereby achieving a new buoyancy equilibrium for the given ambient wave conditions.

[0086] The overall effect for the semi-submersible column structure (500) comprising a wave-activated buoyancy regulator is that the semi-submersible column structure (500) will tend to autonomously increase submergence in the presence of ambient waves and autonomously decrease submergence in the absence of wave energy, with intermediate levels of submergence occurring in proportion to the level of wave energy. Figure 1 depicts two buoyancy conditions, on the left corresponding to low ambient wave energy conditions and on the right, corresponding to high ambient wave energy conditions.

[0087] It will be appreciated that alternative configurations of the wave-activated buoyancy regulator (110) can be readily devised whereby the opposite happens, such that the semi-submersible column structure (500) will tend to autonomously decrease submergence in the presence of ambient waves and autonomously increase submergence in the absence of wave energy. For example, where the check valves are revered such that the wave-activated pump (40) removes the second fluid (8b), being ambient sea water, from the ballast tank (2), creating a reduced pressure and a partial vacuum in the ballast tank (2). In this arrangement, the pressure relief valve (43) can also be configured such that below a threshold vacuum pressure it will open and allow the in-flow of ambient water to replenish the ballast tank through the flow regulator (44) at a pre-determined rate. In other alternative arrangements to the arrangement illustrated in Figure 1 , the wave-activated pump (40) can instead be used to act on the first compressible fluid (8a) being ambient air, in order to provide further alternative wave-activated buoyancy regulation strategies.

[0088] A simple spring-stabilised piston pump (40) is depicted in Figure 1 , but it could be any of the pump types described in this application or some other prior-art wave- activated pump (40). Due to the presence of wave energy and wave-disturbances of the ambient water surface (1110), and its effect on the motion of the semisubmersible column structure (500), relative forces and motions are induced on the wave pump (40). The available wave-induced forces will correlate to conditions that could cause damage and for which a change in buoyancy of the semi-submersible structure (500) is desirable. Advantageously, the energy dissipated by the wave pump will alleviate such potentially damaging dynamic loading on the structure and particularly at mooring attachment interfaces.

[0089] With reference to Figure 2, a prior art variable buoyancy beam (100) is illustrated as described in EP4138548 “A variable buoyancy structure for aquaculture”. The beam (100) comprises a ballast tank formed by a sealed hollow tube (2) such that the bending and buckling resistance of the beam (100) may be provided by the ballast tube (2). The ballast tube (2) is configured to retain a first fluid (8a) of a first density and second fluid (8b) of a second density, wherein buoyancy of the beam (100) may be operatively varied by selective variation of a ratio of the first fluid (8a) to the second fluid (8b) within the ballast tube (2). Suitably, the tube wall (16) is formed by a rigid material like steel or concrete, or suitably the tube wall (16) may be formed by a semi-rigid polymer plastic such as high density polyethylene or fibre-reinforced plastics like glass-reinforced epoxy or carbon fibre reinforced plastics, the material choice being driven by the preferred bending and buckling properties desired for the beam (100). In a preferred arrangement the tube is formed by an impermeable tensile membrane such that the bending and buckling resistance of the beam (100) may be provided by the inflation pressure of the ballast tube (2), being operatively varied by introduction of at least one of the first fluid (8a) or the second fluid (8b) in order to provide pre-stress in the tube’s membrane wall so that the ballast tube (2) resists bending or buckling due to external loads applied to the beam (100). Suitably, the material employed for the tube wall is such to allow the tube to be folded or rolled when it is not pre-tensioned.

[0090] The tube wall (16) is suitably formed by an impermeable membrane. The impermeable membrane may be selected such that it only resists substantial loads that put the membrane in positive tensile stress along its plane. Examples of suitable membranes are sheets of polymer-based materials (for example rubber, PVC or polyurethane) that may also be used as a matrix material for reinforcing fibres such as nylon, polyester, aramid or steel fibres. Textiles like canvas, GORE-TEX™ could also be utilised to form a suitable membrane material. Fine-meshed fabric sheets can also be coated in rubber or have flexible polymers extruded along their length in order to produce strong, fabric-reinforced membranes that are impermeable to fluids. Although the tube may be formed from typical sheet membrane materials, the thickness of materials could be significant at the intended scale, but are unlikely to exceed 5% of the tube diameter in practical implementations (e.g. up to 25mm on a 500mm diameter ballast tube (2) ) and as such some moderate bending loads may still be required to assist collapsing of larger tubes. As shown in Figure 12, Figure 13 and Figure 17, the ballast tube (2) may be externally encapsulated in a re-enforcing net structure (20) that may also be pretensioned by the membrane wall tube as it expands, such that the encapsulating net structure (20) can resist additional bending or buckling due to external loads applied to the beam. The encapsulating net structure (20) may optionally be used to provide attachment points for suspended aquaculture structures (4, 306, 308, 312), moorings (1100) or any other ropes, cables or structures.

[0091] The mechanical properties of the beam (100) with respect to its bending stiffness and buckling capacity are determined by selection of materials and section areas of the membrane wall (16) and any encapsulating net (20) elements. The beam (100) can be configured to have a desirable bending stiffness about an axis transverse to the beam axis by considering: a) the aggregate sectional moment of area of all tensile materials in the wall (16) and in any encapsulating net (20) about that axis, b) the tensile modulus of those tensile materials and c) the alignment of tensile elements relative to the beam axis, especially with respect to the reinforcing fibres in the membrane wall (16) or cable elements in any encapsulating net (20). These features can be selected by design to deliver a desirable overall bending stiffness of the beam in consideration of the aquaculture applications for which examples are detailed below. For a head beam (302), such as that depicted in Figure 7, considering a 250 mm cross-sectional diameter, a desirable bending stiffness is likely to be of the order of 100 kNm2. For a large sinker ring (204), such as that depicted in Figure 5, considering a 60 m toroidal diameter and 1.0 m beam section diameter, a desirable bending stiffness is likely to be of the order of 100 MNm2. The bending stiffness of the tube can also be operatively varied to some degree during deployment using the inflation pressure, where cable elements in any encapsulating net (20) or the tube wall materials (16) exhibit a non-linear relationship between the applied load and material extension (i.e. a non-linear stiffness), which is the case for many materials. In this case the beam (100) may exhibit a higher bending stiffness when configured to operate at a higher inflation pressure of the tube (2) such that reinforcing elements of any encapsulating net (20) and tube wall (16) operate about a higher pre-tension and therefore exhibit a typically stiffer material characteristic. In one application, such a beam (100) can be advantageously configured to suspend a mussel culture longline (300) such that the buckling strength of the beam (100) can be used to eliminate the need for pre-tension in the external anchoring system of the longline (300), while the bending stiffness of the beam (100) can also be optimally configured to attenuate the response to high frequency or steep waves that may induce detrimental loads and accelerations in the mussel drop lines (308).

[0092] The mechanical properties of the beam (100) with respect to compressive buckling resistance strength relate also to the bending stiffness. However, the bending strength and buckling limit of this inflatable variable buoyancy beam (100), can also be operatively configured using the inflation pressure to occur when the longitudinal tensile stress at a point in the tube wall (16) due to the internal pressure is less than the longitudinal compressive stress at the same point in the tube as a result of external loads applied to the beam (100). At this point the tube wall is no longer in tension and will begin to collapse or “wrinkle” with the associated bending moment capacity referred to as the “wrinkle moment” in the art, where the “wrinkle moment” is proportional to the product of the internal pressure and the cube of the diameter of an inflatable circular tube (2) section. As such the inflation pressure of the tube (2) is operatively configured so that the tube may resist significant bending moments and compressive loads when deployed, or may be set to collapse safely at a desirable “overload” limit, while still being able to return to its form once the load is removed or it may be set so that the tube can be readily collapsed with minimal applied loads such that it can be folded for handling, transport and storage.

[0093] In its inflated and deployed form, the ballast tube (2) of the variable buoyancy beam (100) may be configured to be of any desirable cross-sectional shape in order to affect the moment of area preferentially to the application, for example a non- axisymmetric bending property. The tube (2) may also be axisymmetric and of circular cross-section.

[0094] The length of the beam (100) will depend on the desired application, being at least 5 times its cross-sectional diameter. In many applications, the length of the beam will be at least 10 times its cross-sectional diameter. For longline mussel aquaculture, typical head rope lengths can be 200 m or more in prior art and where a head beam (302) might be applied as depicted in Figure 7 the cross-sectional diameter will be in a range of 100 mm to 400 mm. If formed from a single head beam, the length of such a head beam (302) would be of the order of 1000 times its diameter, though practical solutions may be formed by connecting a number of head beam (302) elements to make up the required structure.

[0095] Figure 2 shows a beam (100) configured to be a generally straight beam (100) with sealed end fittings (24) that facilitate connections to moorings, aquaculture structures or other beam elements. End connections can be incorporated into the end fitting (24). The end connections may include a flanged joint to facilitate bolt fasteners or the inclusion of pad-eyes to receive conventional attachments such as shackles or other cable termination options. In one configuration, the end fitting will provide a grooved or barbed outer cylindrical surface of a diameter similar to the inner diameter of the wall (16) of the ballast tube (2), commonly referred to as a “hose tail”, in the art. With such an approach, the wall (16) of the ballast tube (2) fits tightly over the “hose tail” forming a sealed interface between the tube (2) and the end fitting (24). Flexible sealant materials such as silicone or bitumen can be added at the interface to improve the sealing performance. The end fitting can also comprise adjustable clamps in order to apply pressure to the outside of the wall (16) of the tube to increase the contact force at the sealed interface, commonly being threaded “hose clips” in the art or segmented clamps with threaded screw features to apply a distributed contact load at the interface.

[0096] The sealed end fittings (24) can also be configured to optionally provide termination points for an encapsulating net structure (20), such that the net structure is pretensioned to a desirable degree upon inflation of the tube (2). The end fittings (24) can also be configured to provide threaded cable tensioners to adjust the level of pre-tension in individual cable elements (22) of the encapsulating net structure (20), similar to a “turnbuckle” or “bottle screw”, which would be familiar to those skilled in the art.

[0097] Alternatively, Figure 12 and Figure 13 show beams (100) configured to be a generally straight beam (100) where the membrane wall (16) is extended to form a generally continuous hemispherical or torispherical shell to seal the ends of the ballast tube (2). In Figure 12 and Figure 17 an encapsulating net structure (20) is shown to extend around the ends of the tube such that it can be longitudinally pre- tensioned by the pressurised ballast tube (2) and can also be used to facilitate end- to-end connections of multiple beams using state of the art cable connectors. Cable elements (22) can be pre-tensioned by including features known in the art such as “turnbuckles” or webbing tensioners with ratchets and clamps which would be familiar to those skilled in the art.

[0098] A combination of end fittings (24) with a seat to receive a continuous extension of the membrane wall (16) can also be used to mechanically terminate and seal the end of the tube (2) to form connectable beams, tensioning features and the like.

[0099] Any such variable buoyancy beam (100) can be configured to connect to one another in order to create a variable buoyancy truss structure (404) as shown in Figure 14. Such a truss may have application for marine structures generally and is not necessarily restricted to aquatic structures.

[0100] Figure 11 and Figure 15a show a beam (100) that is generally curved. A variable buoyancy beam (100) may be curved by a non-axisymmetric tube properties such that as the tube is inflated to induce pre-stress in the membrane wall (16) and any encapsulating net (20) that the balance of pre-stress in these elements serve to form a curved beam shape. A curved beam (100) may also be formed by an axisymmetric beam (beam) that is straight in its inflated equilibrium condition but is bent to a curved form through the application of external bending moments by connected structures or by connection of each end (24) of the beam to the other in order so that the beam’s inflated equilibrium pre-stress is altered to form a toroidal beam. A curved beam that extends to the point that its ends meet each other can optionally be formed from a continuous sealed toroidal tube (2) ring without end fittings (24).

[0101] Alternatively, more than one separate straight beams (100) with sealed ends can equally be connected end-to-end to form a polygonal toroidal structure. Figure 16 shows a centrally supported toroidal beam structure (402), formed from 6 straight variable buoyancy beams (100) that are also supported by spoke elements (tendons, struts or beams) that connect the toroidal structure to a supporting hub structure. The use of multiple separate beams (100) may be advantageous should manufacturing constraints limit the length of the individual beams (100). Separate but connected beams (100) with independently controlled buoyancy may allow control of the buoyancy distribution and floating attitude of the overall structure. This may be advantageous for operational reasons. Separate beams (100) advantageously also provide additional redundancy functions as the failure of one beam element does not necessarily result in the failure of the entire structure (200, 202, 204, 206, 300, 302, 400, 402, 404).

[0102] Two or more beams, each floating with a waterplane-area may be braced side by side in order to provide hydrostatic roll stability and potentially to support an access deck walkway structure or any other structure that requires such stability, for example for a float ring (202). Otherwise, any floating or submerged beams may be braced side by side to provide desirable bending or buoyancy properties in aggregate.

[0103] If a mixture of two or more fluids (8a, 8b) is used to pressurise the ballast tube (2), in order to vary the combined density of the mix of pressuring fluids, the two or more fluids (8a, 8b) must be of different densities and the ratio of those fluids (8a, 8b) in the mixture must be controllable. At least one of those fluids (8a, 8b) must have a density equal to or lower than that of the ambient water in which the variable buoyancy beam (100) will be submerged. The fluids (8a, 8b) may be compressible or incompressible or a mixture of both. The fluids (8a, 8b) may be separated from each other using at least one internal bladder (10). In certain arrangements, e.g where the re-enforcing net is employed, the bladder (10) may be omitted and some of the advantage of using the re-enforcing net still be achieved where the fluids can be free to contact one another in the tube (2). However, the use of internal bladders (10) ensures that fluids can be controlled separately and remain un-mixed for ballast control. Preferably, the bladders are formed by a membrane of suitably low flexural rigidity and such that the pressure differential between the first fluid and the second fluid is small. Internal bladders (10) or other cell membranes may be advantageously used to control the movement of the varying density fluids (8a, 8b) within the tube (2) so that general internal ballast distribution is maintained. As such, the internal bladders (10) can be secured within a positional envelope within the tube (2) using ropes or other means to improve ballast stability under dynamic loading.

[0104] The bladder (10) is formed by a suitably flexible impermeable membrane that may either fully enclose a volume of the first fluid or fully enclose a volume of the second fluid or alternatively may be attached to the wall (16) of the tube (2) in such a way as to separate volumes of the two fluids (8a, 8b) enclosed by the tube wall (16) and the bladder (10) membrane. The bladder (10) is configured such that the ratio of the volume of the first fluid (8a) to the second fluid (8b) within the tube (2) may be varied. The membrane material of the bladder (10) is preferably flexible, such that the stresses induced in the bladder (10) wall are small over the required range of volume changes and such that the difference in pressures on either side of the bladder (10) wall at a given location over the required range of volumetric variation do not exceed 2 bar, preferably not exceeding 0.5 bar. As such, the membrane material of the bladder is preferably of a flexural rigidity not exceeding 1 Nm for tubes of 500 mm diameter or smaller, where the flexural rigidity is affected by the membrane thickness and materials properties, notably the Young’s modulus and Poisson’s ratio. The bladder (10) membrane will have sufficient surface area to take up the required volume change or optionally be of a suitably low in-plane stiffness to stretch to the required volumes, while inducing only a limited pressure differential between the first fluid (8a) and the second fluid (8b). Suitable bladder membrane materials include but are not limited to natural or synthetic rubber sheeting such as Butyl, latex or silicone rubber, PVC, Polyurethane or Polyethylene sheet materials and rubber-coated fabric membranes using polyester, nylon or aramid fibres or other impermeable fabric materials such as those under the brand names of Dacron or Gore-Tex. Preferably the wall thickness of the bladder membrane will not exceed 2% of the beam diameter (in a range of up to 1 mm for 50 mm diameter beams and up to 30 mm for 1 .5 m diameter beams, for example).

[0105] The at least one bladder (10) may comprise a plurality of internal bladders distributed at a variety of locations within the tube. Where there is a plurality of bladders, the bladders may be discretely formed, or they may be co-formed together. Optionally, such plurality of internal bladders being formed by a flexible closed cell foam structure. In one mode of operation, the pressurising fluid would be a mixture of air and water (suitably seawater). Air and water (suitably seawater) are advantageous as they are readily available in the ambient environment for most aquaculture structures. In the case where there are internal bladders, these may be used to store one or other of the air and water within of a variable buoyancy beam (100). The internal volume of the tube (2) can be operatively pressurised and depressurised through controlled movement of at least one of the first fluid (8a) or the second fluid (8b) between the exterior and the interior of the tube (2). In order to effectively control the buoyancy of the beam (100), the ratio of the first fluid (8a) to the second fluid (8b) is carefully controlled. The at least two fluids (8a, 8b) may be combined in a mixture comprising the at least two fluids. In use, the ballast tank (2), optionally being a ballast tube (2) may be filled completely with either the first fluid (8a) or the second fluid (8b) or a combination thereof. It will be appreciated that within the present context, a fluid may be a liquid or gas. Examples of suitable fluids are air and saltwater. It will be understood however that the other fluids can be used to affect a variation in the pressure of the ballast tube (2) and a change of buoyancy of the overall structure (500, 100) within the present context.

[0106] In order to use air as either the first fluid (8a) or second fluid (8b), a single pressurised manifold of air can be connected to a plurality of internal bladders (10) at locations around the ballast tank (2), optionally being a ballast tube (2) by pipes and controllable valves (30). Optionally, the control valves can be solenoid control valves or other actuated valves to effect active logical control of fluid flows. In such an arrangement the internal volume of the ballast tube (2) is segmented into discrete smaller volumes and the volume of air within the individual segments can be individually varied with a resultant change in buoyancy and buoyancy distribution within the beam (100). Segmented fluid volumes that restrict the movement of fluids within the ballast tube (2) are important where such movement of fluid ballast may result in loss of stability of the beam (100) and its connected structures (200,300,400,402,404).

[0107] In one arrangement, as shown in Figure 2, a variable buoyancy beam (100) is provided with a plurality of internal bladders (10). The individual internal bladders (10) are inflated from a single common inflation manifold (33) with check valves (42) at the inlet to each bladder (10).

[0108] The check valves (42) passively prevent the movement of fluid between individual bladders (10) connected to the single common inflation manifold (33).

[0109] At the same time, the check valve and common inflation manifold allow all bladders to be inflated from a common external inlet to a common inflation pressure. In this case, a second common manifold (34) connecting the plurality of internal bladders (10) can be configured to allow deflation with check valves (42) at the outlet from each bladder. The check valves (42) will again prevent the movement of fluid between individual bladders connected to the single common deflation manifold (34), while allowing all bladders to be deflated to a common external outlet to a common deflation pressure, including to affect the full volumetric collapse of the plurality of internal bladders (10). The two manifold system described here using check valves (42) allows inflation and deflation of a plurality of internal bladders (10) from two external connections. At the same time, the arrangement prevents fluid flow between the internal bladders (10) in response to attitude changes of the beam (100) under dynamic loading. Advantageously, this solution requires no active control of internal valves.

[0110] An alternative approach uses 2-way pressure relief valves, such that a threshold pressure differential must be reached before fluid will transfer between individual bladder (10) volumes, such threshold pressure set so that fluid transfer does not occur under installed operating conditions but can be operatively made to occur during inflation and deflation of the beam (100).

[0111] An alternative arrangement as shown in Figure 13 employs a closed-cell foam (26) to contain the first compressible fluid (8a) so that general movement of the fluids along the beam is then greatly reduced. A drawback of this approach is that It difficult to change the mass of compressible fluid (8a) contained in the closed cell foam and / or to affect the full collapse of the ballast tube (2) structure where the wall (16) is formed by a tensile membrane.

[0112] One arrangement provides a fixed mass of compressible gas (8a), pre-installed in one or more bladders (10) or in a flexible closed-cells foam (26), with no connections, i.e. the mass of air, the first fluid (8a), within the tube is fixed at deployment. In this case, a change in volume of gas (8a) will be operatively affected through its compressibility, under pressurisation by the second fluid (8b) acting on the bladder (10) or closed cell foam (26), which will determine the overall variation in buoyancy and any internal pressure exerted on the ballast tube wall (16), and its resultant effect on rigidity of the overall beam structure (100).

[0113] In order to use water, for example seawater, as either the first fluid (8a) or second fluid (8b), a pump, preferably being a wave-activated pump (40), may be provided in fluid communication with one or more points around the tube (2) to deliver water at elevated pressures and / or to extract water from the internal volume of the ballast tube to reduce the pressure in the ballast tube (2). A shut-off valve (30) and / or check valve (42) can be included for each connection.

[0114] It is noteworthy that air is a low-density compressible fluid, while water is a substantially incompressible fluid of a density equal or similar to the ambient fluid in which the beam (100) is immersed. Where air is the first fluid (8a) and seawater is the second fluid (8b) and the mass of air within the ballast tube (2) is fixed, the buoyancy of the beam (100) can be reduced by adding water to the interior of the ballast tube (2) in a manner such that the fixed mass of air (8a) is compressed to a reduced volume with a correspondingly reduced buoyancy. For a floating beam (100) formed by a ballast tube (2) with a tensile membrane wall (16), this can be used advantageously to simultaneously increase beam stiffness and to reduce the freeboard of the beam in order to attenuate wave-induced response of the structure, such as a mussel longline (300). Where the beam (100) also includes a negatively buoyant constituent (6), water can be added to reduce the volume of air to the point at which no longer provides sufficient buoyancy to keep the beam (100) afloat. By continuing to add water to a beam (100) with a negatively buoyant constituent (6) the volume of air can be reduced to the point at which it is strongly negatively buoyant. A negatively buoyant beam (100) can be deployed advantageously to aquaculture structures that may require a negatively buoyant pre-tensioning force, such as for a sinker ring (204) as depicted in Figure 5 and Figure 6. The fixed mass of air (8a) may be pressurised to approximately 10 bar thus resulting in a substantial reduction of volume of the fixed mass of air (8a). The increased pressure in the ballast tube (2) formed by a tensile membrane wall (16) also affects the desired stiffness and increases the buckling strength of the beam (100) in its reduced buoyancy, pressurised condition.

[0115] In order to provide additional buoyancy to the beam (100), valves (30,35,43,44,45) can be opened such that the energy stored in compressed air (8a) pressure pushes water (8b) out of the interior of the tube (2) and such that the buoyancy is increased in a controlled way as the air (8a) expands to displace the emitted water (8b). It will be appreciated that such an operation will also need to consider the effects of ambient pressure at the installed depth. Tube inflation pressures up to the order of 10 bar over the ambient are anticipated, which may be at depths in the range of 5m to 50m (0.5 to 5 bar ambient pressures). Importantly, the fluid density and pressure can be controlled by adding or removing water only, such that a fixed mass of compressible air in the ballast tube (2) would change volume correspondingly as water is introduced I removed from the internal volume, to affect a density change of the fluid mixture (8a and 8b). This means a good level of control can be achieved by exchanging only water with the internal ballast tube (2) volume. Advantageously, this requires only one control umbilical (41) and the stored energy in the compressed air can be used to de-ballast the beam (100) and thus any attached aquaculture structure (200) simply by allowing internal water to be released to the ambient environment at a controlled rate.

[0116] This arrangement also presents an opportunity to optionally include a pressure- actuated or a float-actuated valve (35). The valve (35) is fluidly connected to the water in the beam. This valve (35) is suitably configured to passively open when a submergence threshold for the beam is exceeded. As the valve is opened, water ballast (8b) is released to increase buoyancy. Once beam submergence is returned to threshold level, the valve passively closes.

[0117] The use of such a valve, advantageously, presents an opportunity to passively compensate for increases in biomass on attached structures (4,308,312) so that a desired beam submergence envelope is maintained as biomass accumulates on attached structures. Other advantages of using a compressible fluid for the internal fluid (8a, 8b) relates to managing the consequence of failures of the tube (2), wherein if a leak develops in the tube (2), the pressure will vary more slowly due to the accumulated energy of compressed air. Furthermore, any leak will result in an increase in the overall buoyancy of the beam (100) as compressed air expands to take up more volume, such that the structure will tend to rise to the surface where repairs can be affected, rather than sink to the seabed.

[0118] With reference to Figure 3a and Figure 3b, a wave-activated buoyancy regulator (110) is employed on a variable buoyancy beam structure (100) of a type similar to that described in Figure 2, floating in a body of water with a free surface (1110). Gravity waves propagate in the body of water disturbing the free surface (1110) from its equilibrium, disturbing also any structures within the body of water, including the variable buoyancy beam (100). The variable buoyancy beam (100) illustrated in Figure 3a is being exposed to small ambient gravity waves and the variable buoyancy beam (100) illustrated in Figure 3b is being exposed to large ambient gravity waves. Each variable buoyancy beam structure (100) is connected to the seabed with a mooring and an anchor (1105). Each structure (100) comprises a wave-activated buoyancy regulator (110), comprising a ballast tube (2) and a wave- activated pump (40). The ballast tube (2) is configured to hold a first compressible fluid (8a), optionally being ambient air and a second incompressible fluid (8b), optionally being the ambient water in which the variable buoyancy beam structure (100) is floating. The wave-activated pump (40) is connected between the mooring anchor (1105) and the variable buoyancy beam structure (100), such that the pump (40) is activated by the wave-induced motions of the variable buoyancy beam structure (100). A fluid carrying conduit (41 ) is connected between the ballast tube (2) and the wave-activated pump (40). The wave-activated pump (40) is configured to generate pressure and pump the second fluid (8b) to the ballast tube (2) through the conduit (41) when it is acted upon by the wave-activated motions of the variable buoyancy beam structure (100). This elevates the pressure within the ballast tube (2), compresses the first fluid (8a) and decreases the ratio of a first fluid (8a) to a second fluid (8b) within the ballast tube (2), resulting in a reduction of the buoyancy of variable buoyancy beam structure (100). The wave-activated buoyancy regulator (110) in Figure 3a and Figure 3b further comprises a flow controller, the flow controller comprising a pressure relief valve (43) and an adjustable flow regulator (44) in series with one another. The pressure-relief valve (43) opens once the pressure in the ballast tube exceeds a threshold allowing the second fluid (2) to flow through the outlet of the ballast tank. The adjustable flow regulator (44), further limits the rate of flow of the second fluid (8b) in proportion to the difference between the internal pressure of the ballast tube (2) and the external pressure of the low pressure store of the second fluid (8b), being the ambient external water pressure in Figure 3a and Figure 3b. When the outlet return flow of the second fluid through the regulator (44) is less than the in-flow of the second fluid at the inlet caused by the wave-activated pump (40), the buoyancy will continue to reduce until the pressure in the ballast tube (2) increases to a point that the outlet flow through the regulator (44) balances the flow at the inlet caused by the wave- activated pump, thereby achieving a new buoyancy equilibrium for the given ambient wave conditions.

[0119] The overall effect for the variable buoyancy beam structure (100) comprising a wave- activated buoyancy regulator^ 10) is that the variable buoyancy structure (100) will tend to autonomously increase submergence in the presence of large ambient waves, including to affect full submergence of the structure (see Figure 3b) and autonomously decrease submergence in the presence of smaller ambient wave energy, including to affect emergence of the structure (See Figure 3a), with intermediate levels of submergence and emergence occurring in proportion to the level of wave energy present.

[0120] Similar to the case of the semi-submersible column structure (500), it will be appreciated that alternative configurations of the wave-activated buoyancy regulator (110) can be readily devised for the variable buoyancy beam structure (100), whereby the opposite happens, such that the structure (100) will tend to autonomously decrease submergence in the presence of ambient waves and autonomously increase submergence in the absence of wave energy. For example, where the check valves are reversed such that the wave-activated pump (40) removes the second fluid (8b), being ambient sea water, from the ballast tank (2), creating a reduced pressure and a partial vacuum in the ballast tube (2). In this arrangement, the pressure relief valve (43) can also be configured such that below a threshold vacuum pressure it will open and allow the in-flow of ambient water to replenish the ballast tank through the flow regulator (44) at a pre-determined rate. In other alternative arrangements to the arrangement illustrated in Figure 3a and Figure 3b, the wave-activated pump (40) can instead be used to act on the first compressible fluid (8a) being ambient air, in order to provide further alternative wave-activated buoyancy regulation strategies.

[0121] A simple spring-stabilised piston pump (40) is depicted in Figure 3, but it could be any of the pump types described in this application or some other prior-art wave- activated pump (40). The available wave-induced forces will correlate to conditions that could cause damage and for which a change in buoyancy of the semisubmersible structure (500) is desirable. Advantageously, the energy dissipated by the wave pump will alleviate such potentially damaging dynamic loading on the structure and particularly at mooring attachment interfaces.

[0122] Figure 4 shows a variable buoyancy beam comprising a wave-activated buoyancy regulator, where there is added a float-activated valve. This valve (35) is suitably configured to passively open when a submergence threshold for the beam is exceeded. As the valve is opened, water ballast (8b) is released to increase buoyancy. Once beam submergence is returned to threshold level, the valve passively closes. The use of such a valve, advantageously, presents an opportunity to passively set a pre-determined maximum submergence depth so that a desired beam submergence envelope is maintained as biomass accumulates on attached structures.

[0123] It is therefore observed that the variable buoyancy beam (100) described in EP4138548 is particularly well suited to being employed with a wave-activated buoyancy regulator, because the tube of the variable buoyancy beam (100) forms a ballast tube (2) for the wave-activated buoyancy regulator as well as providing the desired structural properties of the beam. Similarly, the advantages of the wave- activated buoyancy regulator can extend to the variety of aquaculture structures (200,300,400) that can be configured based on the variable buoyancy beam (100), as outlined further below.

[0124] A) Finfish Aquaculture

[0125] The use of the beams (100) above will now be described with reference to an exemplary deployment, comprising a variable buoyancy beam (100) deployed in a floater ring (202), a sinker ring (204) for an aquaculture fish pen structure (200).

[0126] It will be appreciated that whilst the term ring has been employed, i.e. “Floater ring” or “sinker ring”, that it is not intended that they be limited in structure to a true ring type geometry and it will be appreciated that the structural form may adopt any number of shapes which fulfil the flotation or sinking function as exemplified in the following description.

[0127] As exemplified with initial reference to Figure 5, a floater ring (202) may be formed by a variable buoyancy beam (100), which comprises a hollow tube (2) configured to retain at least a first fluid (8a) and second fluid (8b). The beam (100) has a variable buoyancy and, by changing the buoyancy of the beam (100), it is possible to control the freeboard or residual buoyancy of the floater ring (202) as well as compensate for any changes in the gravity loads applied to the floater ring (202) by the attached net (4), sinker ring (204) or anchor (1105) connections. To entrap the fluids, the beam (100) may be selected to be impermeable. For ease of storage, transport and deployment, the hollow tube (2), is preferably sufficiently flexible to allow it to be collapsed and folded.

[0128] A sinker ring (204) is formed by one or more variable buoyancy beams (100), which comprise a hollow tube (2) formed with a membrane wall (16), configured to retain at least a first fluid (8a) and second fluid (8b), and a negatively buoyant constituent (6). The beam or beams (100) employed for the sinker ring have a variable buoyancy and, by changing the buoyancy of the beam (100), it is possible to facilitate installation and a periodic raising / lowering of the sinker ring (204) to facilitate various activities such as crowding of fish for treatments or harvesting, net (4) installation and removal, the submergence of nets (4) to protect against wave loading or parasite I algae infestations or the raising of nets (4) for cleaning and inspection near the surface.

[0129] In addition, and per conventional and known usage of fixed buoyancy sinker rings, the variable buoyancy sinker ring (204) in its fully submerged, minimum buoyancy state, also maintains negative buoyancy forces within the overall aquaculture pen structure (200) and maintains pre-tension in the net (4) by applying a counter-posing gravity force to the positively buoyant floater ring (202). The bend resistance and the buoyancy of the variable buoyancy beam (100) used in the floater ring (202) and in the sinker ring (204) are configured to advantageously maintain maximum containment volume of the attached tensile net (4) under loading from currents, independently of the need to apply pre-tension from external anchor loads, whilst also attenuating the response to wave loading or dynamic operating loads that may result in detrimental loads and accelerations being imparted to the net (4). In effect, the normal usage of a sinker ring to maintain downward pressure on the netting of the aquaculture pen structure is provided by the one or more variable buoyancy beams (100) while the normal usage of a floater ring to maintain positive buoyancy and overall heave stability of the aquaculture pen structure is also provided by the one or more variable buoyancy beams (100) in accordance with the present teaching.

[0130] Suitably, the floater ring (202) and the sinker ring (204) comprising the one or more variable buoyancy beams (100) can preferably be collapsed and folded when the first fluid (8a) and second fluid (8b) are removed from the hollow tube (2) such that there is insufficient internal pressure to maintain pre-tension in the membrane wall (16).

[0131] Furthermore, the floater ring (202) and the sinker ring (204) comprising the one or more variable buoyancy beams (100) can be optimally configured by selection of the tensile properties of the membrane wall (16) and encapsulating net (20), as well as operatively controlled by variation of the internal pressure of the tube (2) when any of the first fluid (8a) and second fluid (8b) are added or removed from the hollow tube (2). Suitably, the aquaculture fish pen (200) comprising one or more variable buoyancy beams (100) can be configured to adopt a floating state of variable emergence or a fully-submerged state of variable buoyancy through selective variation of the ratio of the first fluid (8a) to the second fluid (8b) within the ballast tube (2) of one or more variable buoyancy beams (100), thereby enabling the dynamic response of the fish pen to waves to be optimised, while also allowing the buoyancy to be adjusted to compensate for biomass growth in attached structures, for example. Importantly, the first fluid (8a) and the second fluid (8b) may be separated by means of an internal bladder (10) or a plurality of internal bladders (10) such that their volume may be independently controlled and segmented to maintain general ballast stability.

[0132] The sinker ring (204) may comprise a variable buoyancy beam (100) that includes also a negatively buoyant constituent (6) is configured to adopt either a positive buoyancy mode (to float to the surface to aid operations) or a negative buoyancy mode (to act as a net tensioning feature). It is possible to switch between positive buoyancy or negative buoyancy once or multiple times with relative ease as required.

[0133] In respect of the application to a sinker ring (204), in addition to the pressurised fluids (8a, 8b) inside the tube (2) of the one or more variable buoyancy beams (100), a constituent is required in order to assist in making the sinker ring (204) negatively buoyant. The negative buoyancy constituent (6) may be provided in the form of a high-density ballast material (14) which in turn may be distributed along and around the tube (2) so as to maintain the stability of the tube in a substantially horizontal plane. In this context, a high-density ballast material (14) is a material with a density which is greater than the density of seawater. The high-density ballast material (14) would thus be negatively buoyant in seawater if it were placed in seawater in isolation. As the high-density ballast material (14) is not placed in the water in isolation, but is part of the one or more variable buoyancy beams (100) forming the sinker ring (204) - the negative buoyancy of the high-density ballast material (14) works against the positive buoyancy of at least one of the fluids (8a, 8b) in the tube (2). Thus, the gradual reduction of buoyancy of the mixture of fluids (8a, 8b) will result in the effect of the high-density ballast material (14) becoming increasingly dominant until a threshold is reached wherein the sinker ring (204) is neutrally buoyant. Further reduction of buoyancy of the mixture of fluids (8a, 8b) beyond this point will cause the sinker ring (100) to become increasingly negatively buoyant.

[0134] The density of the high-density ballast material (14) should be significantly more than that of the ambient water, preferable in excess of 3000 kg / m3and ideally in the density ranges of ferrous metals (7000 - 8000 kg / m3). The high-density ballast material (14) will be of fixed mass, using either a number of discrete weights or a continuous, dense but pliable structure along the length of the tube (2) such as a chain, steel rope, or wire such as shown in Figure 15a and 15b or unconsolidated sediment aggregates, so that the tube (2) retains its characteristic feature of being collapsible, foldable and / or easily transported.

[0135] The high-density ballast material (14) can be installed inside the enclosed volume of the tube (2) or integrated with the collapsible membrane wall (16) of the tube (2), potentially as a reinforcing structural material, or it can be suspended outside but integral to the tube (2), potentially forming a part of the encapsulating net structure (20)

[0136] In the arrangement of a variable buoyancy beam (100) applied to a sinker ring (204), the high-density ballast material (14) will be formed by a steel wire rope installed along the length, and extending circumferentially about, the tube (2), potentially forming part of an encapsulating net structure (20). This advantageously provides a redundant structural element, if the tube (2) structure fails.

[0137] There are known examples of fish pens in prior art that do not use beams oriented in the horizontal plane to suspend containment nets. As exemplified with reference to the company “Innovasea” and their “SeaStation” which is a fish pen that uses a central spar in a generally vertical orientation in conjunction with a sinker ring (204) structure, may be used in order to suspend a pre-tensioned net (4). The central spar may be formed by a semi-submersible column structure (500).

[0138] With reference to Figure 6a and Figure 6b, a wave-activated buoyancy regulator (110) is employed on a fish pen structure (200) of a type similar to the prior art described in Figure 5 and comprising one or more variable buoyancy tubes (100), floating in a body of water with a free surface (1110). Gravity waves propagate in the body of water disturbing the free surface (1110) from its equilibrium, disturbing also any structures within the body of water, including the fish pen structure (200) and the wave activated floats in its mooring lines (1100). The fish pen structure (200) illustrated in Figure 6a is positioned in calm water, while the fish pen (200) illustrated in Figure 3b is being exposed to large ambient waves. A wave-activated pump (40) is positioned within the mooring lines (1100) and connected to one or more ballast tubes (2) within the one or more variable buoyancy beams (100) with an umbilical (41).

[0139] The wave-activated buoyancy regulator (110) in Figure 6a and Figure 6b further comprises a flow controller, similar to that described for the variable buoyancy beam(100) in Figure 3a, the flow controller comprising at least one of a pressure relief valve or an adjustable flow regulator. The overall effect for the fish pen structure (200) comprising a wave-activated buoyancy regulator (110) is that the fish pen structure (100) will tend to autonomously increase submergence in the presence of large ambient waves, including to affect full submergence of the structure (see Figure 6b) and autonomously decrease submergence in the presence of smaller ambient wave energy, including to affect emergence of the structure (See Figure 6a), with intermediate levels of submergence and emergence occurring in proportion to the level of wave energy present.

[0140] B) Shellfish & Seaweed Culture

[0141] A prior art head beam (302) for a mussel culture system (300) employing a variable buoyancy beam (100) adapted for the culture of seaweed, shellfish or other aquaculture biomass may be provided as shown in Figure 7, based upon EP4138548. A prior-art centrally-supported polygonal ring (402) adapted for the culture of seaweed, shellfish or other aquaculture biomass may be provided as shown in Figure 9, also based on EP4138548.

[0142] Figure 7 illustrates a general layout of a prior art mussel culture system (300). The mussel culture system (300) comprises a head beam (302) formed by one or more variable buoyancy beams (100), which comprise a ballast tube (2) formed with a wall (16), configured to retain at least a first fluid (8a) and second fluid (8b). Suitably, the wall (16) is impermeable. Preferably, the material of the wall (16) is suitably selected so that when fluid is removed from the beam (100), the beam (100) may collapse upon itself. For ease of storage and deployment / retrieval, the beam is preferably foldable when collapsed. The beam (100) has a variable buoyancy and, by changing the buoyancy of the beam (100), it is possible to control the freeboard or residual buoyancy of the head beam (302) as well as compensate for any changes in the gravity loads applied to the head beam (302) by the attached mussel culture drop ropes (308). In one arrangement, the variable buoyancy beam (100) of the head beam (302) is encapsulated in a rope net (20), such that the net provides attachment points for the drop ropes (308).

[0143] The bending stiffness and strength of the head beam (302) are configured to optimally attenuate the dynamic response of the head beam (302) to high frequency or steep waves by selection of suitable materials and section areas of the ballast tube wall (16) and any encapsulating net (20) elements. The bending stiffness and buckling strength of the head beam (302) are operatively varied using the inflation pressure, where cable elements in any encapsulating net (20) or the tube wall materials (16) exhibit a non-linear relationship between the applied load and material extension (i.e. a non-linear stiffness), which is the case for many materials. In this case the beam (100) will exhibit a higher bending stiffness when configured to operate at a higher inflation pressure of the tube (2) such that reinforcing elements of any encapsulating net (20) and tube wall (16) operate about a higher pre-tension and therefore exhibit a typically stiffer material characteristic. The head beam (302) may be advantageously configured to suspend a mussel culture longline (300) such that the buckling strength of the beam (100) can be used to eliminate the need for pretension in the external anchoring system of the longline (300), while the bending stiffness of the beam (100) can also be optimally configured to attenuate the response to high frequency or steep waves that may induce detrimental loads and accelerations in the mussel drop lines (32).

[0144] Figure 9 illustrates a general layout of an exemplary prior art mussel and seaweed culture system (400) in a normal operating position. The mussel and seaweed culture system (400) comprises a centrally-supported polygonal ring (402) attached to a floating hub structure. The centrally-supported polygonal ring is formed by one or more variable buoyancy beams (100), which comprise a hollow ballast tube (2) formed with a wall (16), configured to retain at least a first fluid (8a) and a second fluid (8b). As with the other beams described herein, the wall is suitably impermeable, preferably with the beam being collapsible when the fluid(s) are substantially removed and foldable, once collapsed. In one arrangement the one or more variable buoyancy beams (100) of the centrally-supported polygonal ring (402) are encapsulated in a rope net (20) and optionally includes a negatively buoyant constituent (6). The one or more beams (100) have a variable buoyancy and, by changing the buoyancy of the one or more beams (100), it is possible to control the freeboard or residual buoyancy of the centrally-supported polygonal ring (402) as well as compensate for any changes in the gravity loads applied to the ring (402) by any attached mussel culture drop ropes (308) or attached seaweed biomass (312). It is further possible to fully submerge the centrally-supported polygonal ring (402), which can be stabilised about a hub structure by the elastic properties of the centrally supported polygonal toroid (402) such that its level of submergence can be configured or varied depending on the buoyancy of the of the one or more variable buoyancy beams (100), including through the application of a pressure-activated or float-activated valve (35) as described above to release water when submergence exceeds a threshold in response to biomass weight increases.

[0145] Figure 8a shows the layout of a mussel culture system (300) based on the present teaching, being similar to the mussel culture system described in Figure 7, except where a wave-activated buoyancy regulator is employed to regulate the buoyancy of the structure (300). A wave-activated pump is integrated in the mooring (1100) at either end of the prior-art head beam (302), comprises a ballast tank (2) as described above.

[0146] With reference to Figure 8b, gravity waves propagate in the body of water disturbing the free surface (1110) from its equilibrium, disturbing also any structures within the body of water, including the mussel culture system (300). The mussel culture system (300) illustrated in Figure 8a is positioned in calm water, while the mussel culture system (300) illustrated in Figure 8b is being exposed to large ambient waves. The wave-activated pumps (40) are positioned within the mooring lines (1100) and connected to one or more ballast tubes (2) within the head beam (302) with an umbilical (41).

[0147] The wave-activated buoyancy regulator (110) in Figure 8a and Figure 8b further comprises a flow controller, similar to that described for the variable buoyancy beam (100) in Figure 3a, the flow controller comprising at least one of a pressure relief valve or an adjustable flow regulator. The overall effect for the mussel culture system (300) comprising a wave-activated buoyancy regulator (110) is that the structure (300) will tend to autonomously increase submergence in the presence of large ambient waves, including to affect full submergence of the head beam (302) (see Figure 8b) and autonomously decrease submergence in the presence of smaller ambient wave energy, including to affect emergence of the head beam (See Figure 8a), with intermediate levels of submergence and emergence occurring in proportion to the level of wave energy present.

[0148] Figure 8b further illustrates the application of a float-activated valve (35) as described above to release water when submergence exceeds a threshold in response to biomass weight increases. This can set a pre-determined limit on the level of submergence to be delivered in the presence of large ambient wave energy as indicated in Figure 8b.

[0149] It is noteworthy that air is a low-density compressible fluid, while sea water is a substantially incompressible fluid of a density equal to the ambient fluid in which the variable buoyancy exemplar structures (100,200,300,400,500) are immersed. Where air is the first fluid (8a) and seawater is the second fluid (8b) and the mass of air within the ballast tank(2) is fixed, the buoyancy of the sinker ring (204) can be made negative by adding seawater to the interior of the ballast tank (2) in a manner such that the fixed mass of air (8a) is compressed to a volume with a corresponding density which results in a significant reduction of buoyancy of the structures (100,200,300,400,500), including to affect submergence, where there is a negatively buoyant constituent (6). In such an approach, the fixed mass of air (8a) may be pressurised up to the order of 10 bar above ambient pressure by adding seawater, thus resulting in a substantial reduction of volume of the fixed mass of air (8a) and a submergence of the structure. Where the structure includes a ballast tube (2,100) that is collapsible, the increased pressure in the ballast tube (2) affects the desired rigidity of the ballast tube (2,100) in its submerged, pressurised condition. To raise the ballast tube (2, 100), valves can be opened such that the air (8a) pressure pushes seawater (8b) out of the interior of the ballast tube (2) and such that the buoyancy is increased in a controlled way as the air (8a) expands to displace the emitted seawater (8b). It will be appreciated that such an operation may also need to consider the effects of ambient pressure at the installed depth. Tube inflation pressures of the order of 10 bar over the ambient are anticipated, which may be at depths in the range of 10m to 50m (1 to 5 bar ambient pressures). Importantly, the fluid density and pressure can be controlled by adding or removing water only, such that a fixed mass of compressible air in the tube (2) would change volume correspondingly as water is introduced I removed from the internal volume, to affect a density change of the fluid mixture. This means a good level of control can be achieved by exchanging only water with the internal tube (2) volume.

[0150] Advantageously, this requires only one control umbilical (41) and the stored energy in the compressed air can be used to de-ballast the tube (2), and thus any structures into which it is integrated (100,200,300,400,500), simply by allowing internal water to be released to the ambient environment at a controlled rate. In addition to the pressurised fluids (8a, 8b) inside the tube (2), a constituent may be required to assist in making the sinker ring (204) negatively buoyant. This negative buoyancy constituent (6) may be provided in the form of a high-density ballast material (14) which is distributed along and around the tube (2) to maintain the stability of the tube in a substantially horizontal plane. In this context, a high-density ballast material (14) is a material with a density which is greater than the density of seawater. The high-density ballast material (14) would thus be negatively buoyant in seawater if it were placed in seawater in isolation. As the high-density ballast material (14) is not placed in the water in isolation, but is part of the structure

[0151] (100.200.300.400), the negative buoyancy of the high-density ballast material (14) works against the positive buoyancy of at least one of the fluids (8a, 8b) in the ballast tube (2). Thus, the gradual removal of at the fluids (8a, 8b) which provides positive buoyancy will result in the effect of the high-density ballast material (14) becoming increasingly dominant until a threshold is reach wherein the structure

[0152] (100.200.300.400) is neutrally buoyant. Further removal of the fluid (8a, 8b) which is provides positive buoyancy beyond this point will cause the structure

[0153] (100,200,300,400) to become increasingly negatively buoyant.

[0154] The density of the high-density ballast material (14) should be significantly more than that of the ambient water, preferably in excess of 3000 kg / m3and ideally in the density ranges of ferrous metals (7000 - 8000 kg / m3). The high-density ballast material (14) will be of fixed mass, using either a number of discrete weights or a continuous, dense, but pliable structure along the length of the tube (2) such as a chain, steel rope, or wire such as shown in Figure 15a and 15b or unconsolidated sediment aggregates, so that the ballast tube (2) retains its characteristic feature of being collapsed, folded and / or easily transported.

[0155] Figure 1 illustrates 2 identical semi-submersible column structures (500), wherein the buoyancy of the structure is regulated by a wave-activated buoyancy regulator (110). The ballast tank in the column structure is impermeable and contains a first fluid low- density compressible fluid (8a) and a second higher density incompressible fluid (8b), such that gravity keeps the fluids separated within the column. A flow regulator (50) is configured to cause the structure to increase submergence in the presence of larger ambient waves. Figure 2 illustrates an example of a prior art variably buoyancy beam structure (100) as described in EP4138548, the variable buoyancy beam (100) also being suitable for use as a tubular ballast tank (2) in a wave-activated buoyancy regulator (110). The ballast tube (2) is configured to contain a first fluid (8a) contained in for bladders (10) connected by a common inflation manifold with an inlet valve (30,51) and a common deflation manifold with an outlet valve (30, 52). The ballast tube is configured to contain a second fluid (8b), with a single inlet (30,51) which also acts as an outlet (52) for the second fluid connected to an umbilical (41 ) suitable for onward connection to a flow controller (50) or a wave activated pump (40).

[0156] Figure 3a illustrates a variably buoyancy beam (100) of a type similar to that shown in Figure 2, wherein the buoyancy of the beam (100) is regulated by a wave- activated buoyancy regulator (110) as per the present teaching, and wherein the ambient waves are small, such that the variably buoyancy beam has a positive buoyancy and is floating on the surface. As per the present teaching the wave- activated buoyancy regular comprises a wave-activated pump (40) and a flow controller (50).

[0157] Figure 3b illustrates the same variably buoyancy beam (100) as in Figure 3a, wherein the ambient waves are large, such that the wave-activated buoyancy regulator (110) has caused the pressure in the ballast tube (2) to be increased by the addition of a second fluid (8b) resulting in the compression of the first fluid (8a) in the bladders, such that the variably buoyancy beam (100) has a negative buoyancy and is submerged below the surface;

[0158] Figure 4 illustrates a similar variable buoyancy beam (100) to that illustrated in Figure 3b, wherein the ambient waves are large, such that the wave-activated buoyancy regulator (110) has caused the variably buoyancy beam (100) to submerge below the surface, and wherein the addition of a float-activated valve limits the depth of submergence of the variable-buoyancy beam.

[0159] Figure 5 illustrates an example of a prior art pen structure (200) as described in EP4138548, wherein the pen structure (200) comprises a float ring (202) and a sinker ring (204), where either or both of the float ring (202) and sinker ring (204) may be formed by one or more variable buoyancy beams (100) of a type similar to that shown in Figure 15;

[0160] Figure 6a illustrates a submersible pen structure (200), similar to the pen structure (200) illustrated in Figure 5, wherein accordance with the present teaching, the addition of a wave-activated buoyancy regulator (110) causes the buoyancy of either or both of the float ring (202) and sinker ring (204), formed by one or more variable buoyancy beams (100) to change in accordance with the ambient wave conditions and wherein the ambient waves are smaller, such that the pen has a positive buoyancy and the float ring (202) is floating on the surface. In Figure 6a, the wave- activated pump is integrated in a mooring (1100) between a wave activated structure (60) and an anchor (1105).

[0161] Figure 6b illustrates the same submersible pen structure (200) as illustrated in Figure 6a, wherein the ambient waves are larger, such that the pen (200) has a negative buoyancy and the float ring (202) is submerged below the surface;

[0162] Figure 7 illustrates a prior art submersible mussel culture system (300) as described in EP4138548 with a head beam (302) in a submerged position, formed by one or more variable buoyancy beams (100) and in which the buoyancy of the submerged head beam (302) is controlled by float-activated valves (35) that open when its submergence exceeds a threshold value.

[0163] Figure 8a illustrates a submersible mussel culture system (300), similar to the mussel culture system (300) illustrated in Figure 7, wherein according to the present teaching, the addition of a wave-activated buoyancy regulator (110) is used to vary the buoyancy of the head beam (302) according to the ambient wave conditions, and wherein the ambient waves are smaller, such that the head beam (302) has a positive buoyancy and the head beam (302) is floating on the surface. The wave- activated pump (40) is integrated in the mooring (1100) to exploit the relative motion of the head beam (302) relative to the anchor (1105) when ambient waves are present. Figure 8b illustrates the same submersible mussel culture system (300) as illustrated in Figure 8a, wherein the ambient waves are larger, such that the head beam (302) has a negative buoyancy and the head beam is submerged below the surface.

[0164] Figure 9 illustrates a general layout of a prior art mussel and seaweed culture system (400) as described in EP4138548, having a centrally-supported polygonal ring (402) similar to the type illustrated in Figure 16, the polygonal ring (402) being formed by one or more variable buoyancy beams (100).

[0165] Figure 10a illustrates a submersible mussel and seaweed culture system (400), similar to the mussel and seaweed culture system (400) illustrated in Figure 9, wherein according to the present teaching, the addition of a wave-activated buoyancy regulator (110) is used to vary the buoyancy of the centrally-supported polygonal ring (402), and wherein the wave-activated pumps (40) are integrated with the spokes of the centrally-supported polygonal ring (402), and where the hub is a wave-activated structure (60). In Figure 10a the ambient waves are smaller, such that the polygonal ring is suspended at a small depth of submergence;

[0166] Figure 10b illustrates the same submersible mussel culture system (400) as illustrated in Figure 10a, wherein the ambient waves are larger, such that the wave- activated buoyancy regulator (110) has caused the polygonal ring to be at a larger depth of submergence;

[0167] Figure 11 illustrates a ballast tube (2) suitable for use as a ballast tank (2) in a wave- activated buoyancy regulator (110), wherein the ballast tube (2) is formed by a tube with an impermeable wall (16), configured to contain a first fluid (8a) of a first density and a second fluid (8b) of a second density as well as a negatively buoyant constituent (6) and such that the ballast tank can also function as a variable buoyancy beam structure (100);

[0168] Figure 12 illustrates a ballast tube (2) suitable for use as a ballast tank (2) in a wave- activated buoyancy regulator (110), wherein the ballast tube (2) is formed by a tube with an impermeable wall (16), configured to contain a first fluid (8a) of a first density and a second fluid (8b) of a second density, wherein the first fluid (8a) is contained in 3 bladders (10) to separate it from the second fluid (8b) and wherein the ballast tube (2) is encapsulated in a net structure (20), such that the ballast tube (2) is also suitable for use as a variable buoyancy beam structure (100);

[0169] Figure 13 illustrates a ballast tube (2) suitable for use as a ballast tank (2) in a wave- activated buoyancy regulator (110), wherein the ballast tube (2) is formed by a tube with an impermeable wall (16), configured to contain a first fluid (8a) of a first density and a second fluid (8b) of a second density, wherein the first fluid (8a) is contained in a flexible closed-cell foam structure (26) to separate it from the second fluid (8b) and wherein the ballast tube (2) is encapsulated in a net structure (20), such that the ballast tube (2) is also suitable for use as a variable buoyancy beam structure (100);

[0170] Figure 14 illustrates how a number (7 shown) of variable buoyancy beams (100) of the type illustrated in Figure 2 may be connected by end connectors (24) to form a variable buoyancy truss structure (404), which may be used in aquaculture or other marine applications, such that the variable buoyancy truss structure (404) is also suitable for use as a ballast tank (2) in a wave-activated buoyancy regulator (110); Figures 15a and 15b both illustrate a perspective view of a ballast tank (2) suitable for use in a wave-activated buoyancy regulator (110), being similar to that illustrated in Figure 11 with a negatively buoyant constituent, such that the ballast tank (2) is also suitable for use as a variable-buoyancy ring structure for aquaculture (202, 204). Figure 15b illustrates a view of a sinker ring showing an alternative negatively buoyant constituent to that of Figure 15a in the form of intermittently spaced high- density ballasting materials in a rigid tube of variable buoyancy.

[0171] Figure 16 illustrates a centrally-supported polygonal toroid (402) formed from 6 variable buoyancy beams (100) of the type illustrated in Figure 12 or Figure 13, being suitable for use as a ballast tube (2) in a wave-activated buoyancy regulator (110).

[0172] Figure 17a illustrates a cross section of a variable buoyancy beam (100) similar to that illustrated in Figure 12, suitable for use as a ballast tube (2) in a wave-activated buoyancy regulator (110), in a partially collapsed (deflated) and buoyant configuration; Figure 17b illustrates a cross section of a variable buoyancy beam (100) similar to that illustrated in Figure 12, suitable for use as a ballast tube (2) in a wave-activated buoyancy regulator (110) in an inflated and buoyant configuration;

[0173] Figure 18 illustrates a series of cross sections of a variable buoyancy beam (100) similar to that illustrated in Figure 12, suitable for use as a ballast tube (2) in a wave- activated buoyancy regulator (110), in a deployment sequence where the tube is in various stages of collapse and buoyant configuration depending on the density of the fluids (8a, 8b) within the tube (2) and the pressure maintained within the tube at each stage;

[0174] The above exemplary arrangements of a wave-activated buoyancy regulator (110) are provided to assist the person of skill in an understanding of the present teaching, and should not be construed as limiting the scope of the invention to that which has been explicitly described. Whilst the present application has been explained with reference to supporting aquaculture structures, it will be appreciated that the arrangements may be employed to support other marine structures.

Claims

Claims1 A wave-activated buoyancy regulator (110) suitable for use in a variable buoyancy structure (100) positioned in a body of water (1110), the wave-activated buoyancy regulator (110) comprising:A ballast tank (2), wherein the ballast tank (2) is configured to retain a first fluid (8a) of a first density and a second fluid (8b) of a second density, wherein the buoyancy of the structure (100) is controlled by variation of a ratio of the first fluid (8a) to the second fluid (8b) within the ballast tank (2), and wherein at least one internal bladder (10) formed by a flexible impermeable membrane is provided within the ballast tank (2) for separating the first fluid (8a) from the second fluid (8b); at least one wave-activated pump (40), mechanically coupled to the ballast tank (2) of the variable buoyancy structure (100), and wherein the wave-activated pump (40) is configured to cause at least one of the first fluid (8a) or the second fluid (8b) to flow through at least one inlet (51) or outlet (52) of the ballast tank (2); characterised in that the ballast tank (2) is an elongated ballast tube (2) and the at least one bladder comprises a plurality of internal bladders (10) distributed at locations within the elongated ballast tube (2), wherein the plurality of internal bladders (10) is secured longitudinally in order to maintain their general position within the ballast tank (2) for overall ballast stability.

2. A wave-activated buoyancy regulator (110) according to claim 1 , wherein the wall (16) of the ballast tank (2) is impermeable and configured with a strength such that the first fluid (8a) and the second fluid (8b) can be stored at pressures suitably above or suitably below the ambient pressure external to the ballast tank (2).

3. A wave-activated buoyancy regulator (110) according to claim 2, wherein the ballast tank (2) is configured with a strength to form a variable buoyancy beam structure (100).4 A wave-activated buoyancy regulator (110) according to claim 3 wherein one or more variable buoyancy beams (100) are configured to form one of a truss structure (404) or a toroidal structure, such as a curved ring (202, 204) or polygonal toroid (402).

5. A wave-activated buoyancy regulator (110) according to any previous claim, wherein a flow controller (50) regulates the flow of at least one of the first fluid (8a) or the second fluid (8b) at the inlet (51 ) or the outlet (52) of the ballast tank (2).

6. A wave-activated buoyancy regulator (110) according to claim 4, wherein the flow controller (50) comprises at least one passive flow-regulator, optionally being an orifice of fixed sectional area and preferably being an adjustable flow regulator (44), such that the rate of flow of at least one of the first fluid (8a) or the second fluid (8b) through the inlet (51 ) or outlet (52) of the ballast tank (2), is pre-determined depending on the containment pressure of at least one of the first fluid (8a) or the second fluid (8b) within the ballast tank (2);7. A wave-activated buoyancy regulator (110) according to claim 4 or 5, where the flow controller (50) comprises at least one passive valve, being a check valve (42), a pressure relief valve (43) or a safety relief valve (45), such that the valves will open or close under pre-determined conditions, relating to the pressure of at least one of the first fluid (8a) or the second fluid (8b) within the ballast tank (2);8. A wave-activated buoyancy regulator (110) according to claim 4, where the flow controller comprises at least one active control valve that will be actuated in response to electronic control signals from a programmable logic controller or from remote supervisory control signals.

9. The wave-activated buoyancy regulator (110) according to any of claims 6 to 8, wherein the flow controller (50) is configured such that the variable buoyancy structure (100,202,204,402,404) will autonomously adopt an advantageous floating state of variable emergence or a predetermined advantageous submerged state of variable weight, according to the variable ambient wave energy conditions present in the body of water (1110).

10. A wave-activated buoyancy regulator (110) according to any previous claim, wherein the internal bladder is defined by a membrane extending in a planeextending longitudinally along a tubular ballast tank (2), with the sides of the membrane defined by the start and end points of an arc of an internal wall of the ballast tube (2) such that the membrane is effectively dividing the ballast tube (2) into a first volume for the first fluid (8a) and a second volume for the second fluid (8b).11 . The wave-activated buoyancy regulator (110) according to any previous claim, where the plurality of internal bladders (10) comprises at least one closed-cell foam structure (26), the closed-cell foam structure being formed by a flexible impermeable foam containing a first compressible fluid (8a).

12. A wave-activated buoyancy regulator (110) according to any previous claim, wherein the first fluid (8a) is a compressible gas and the second fluid (8b) is an incompressible liquid and wherein the selective variation of the ratio of the first fluid (8a) to the second fluid (8b) within the elongated ballast tube (2) is achieved through variation of the mass of the second incompressible fluid (8b) within the ballast tank (2) only;13. A wave-activated buoyancy regulator (110) according to any previous claim, wherein the at least one ballast tank (2) is comprised by at least one variable buoyancy structure (100, 202, 204, 402, 404) with attachment points for suspending aquaculture structures (4, 306, 308, 312) in an aquatic environment.

14. A wave-activated buoyancy regulator (110) according to any previous claim, wherein the wall (16) of the ballast tank (2) is formed from a flexible membrane, the ballast tank (2) having a collapsed state and an expanded state.

15. A culture system (200,300,400) for fish, shellfish or seaweed comprising a wave-activated buoyancy regulator (110) as claimed in any preceding claim.

16. A marine or other floating structure comprising a wave-activated buoyancy regulator (110) as claimed in any preceding claim.

17. The wave-activated buoyancy regulator (110) according to any preceding claim, where the wave-activated pump (40) is coupled to the mooring (1100) of thevariable buoyancy structure (100,202,204,402,404,200,300,400), the mooring comprising an anchor (1105), such that the pump (40) is activated by the wave- induced motions of the variable buoyancy structure (100,202,204,402,404,200,300,400) relative to the anchor (1105).

18. The wave-activated buoyancy regulator (110) according to any of claims 1 to 16, where the at least one wave-activated pump is coupled between the variable buoyancy structure (100,202,204,402,404,200,300,400) and at least one wave- activated structure (60), such that the pump (40) is activated by the wave-induced motions of the at least one wave-activated structure (60) relative to the variable buoyancy structure (100,202,204,402,404,200,300,400).

19. The wave-activated buoyancy regulator (110) according to any of claims 1 to 16, where the at least one wave-activated pump (40) is coupled between at least one wave-activated structure (60) and an anchor (1105), such that the pump (40) is activated by the wave-induced motions of the at least one wave-activated structure (60) relative to an anchor (1105), the wave-activated structure (60) and the anchor (1105) being mechanically separate from the variable buoyancy structure (100,202,204,402,404,200,300,400) comprising the ballast tank (2) to which the wave-activated pump is fluidly connected by a flexible umbilical (41 ).

20. The wave-activated buoyancy regulator (110) according to claim 4, where the one or more beams (100) are configured to form a centrally-supported polygonal toroid (402), wherein the one or more beams (100) are connected to a hub structure by at least one wave-activated pump (40).21 . The wave-activated buoyancy regulator (110) according to any previous claim, with a negatively buoyant constituent (6) extending about or within the variable buoyancy structure (100,202,204,402,404,200,300,400), the buoyancy being a combination of the buoyancy of the structure and the negatively buoyant constituent (6).

22. The wave-activated buoyancy regulator (110) according to any of the previous claims, further comprising an auxiliary pump wherein the pump is configured to moveat least one of a first fluid (8a) or a second fluid (8b) between the interior of the ballast tube (2) and the exterior of the ballast tube (2) via at least one valve (30,35,42,43,44,45,35), optionally being a conduit (41).

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