A marine aquaculture system

Abstract

A buoyancy structure (10) comprising a buoyancy element (20) for use at an operation depth range, operation pressure range and an operation temperature range, the buoyancy element comprising an outer housing (21) with two spaces. A first fluid is provided in the first space (22) and in a second space (20), a second fluid with a quality between 1 and 0 is provided. When the volume of the first fluid is changed, the internal pressure may remain the same while the buoyancy of the structure changes.

Description

[0001] 24244EP00

[0002] 1

[0003] A MARINE AQUACULTURE SYSTEM

[0004] The present invention relates to a submersible system being a buoyancy structure comprising two spaces where a liquid with a particular boiling point is provided in one space and an incompressible fluid, with a variable volume, is provided in the other space. By varying the volume of the incompressible fluid, the buoyancy of the structure may be controlled.

[0005] Relevant technology may be seen in US4244323, US10945417, US2016 / 096597, WO2021 / 214087, KR2015 / 0120845, US10051844, US2021 / 074413, CN217446262, US9395461, CA2147011, EP1045634, EP3937624, US5655938, DE102018009014A1 and US8136470.

[0006] A first aspect of the invention relates to a buoyancy structure comprising a buoyancy element for use within a predetermined temperature range, within a predetermined pressure range and within a predetermined depth range, such as at a predetermined depth at a predetermined temperature , the buoyancy element comprising an outer housing comprising:

[0007] a fluid reservoir comprising a first, incompressible fluid,

[0008] a first space and a second space inside the outer housing,

[0009] a fluid conduit between the fluid reservoir and the first space, a flexible wall portion delimiting the first space from the second space, the second space being confined by the flexible wall inside the outer housing, a second fluid is provided in the second space,

[0010] a pump configured for driving first fluid between the fluid reservoir and the first space,

[0011] wherein the second fluid is in both a liquid and a gaseous phase and has a vapor pressure, and

[0012] wherein at an operation pressure corresponding to a pressure exerted on the outer housing by the surrounding water, preferably at a maximum operation depth and at a minimum operation temperature, the vapor pressure is within a predetermined level below the operation pressure, and

[0013] wherein the second fluid is in thermal equilibrium with the surrounding water, such as within the predetermined temperature range.24244EP00

[0014] 2

[0015] The buoyancy element is provided for use within a predetermined temperature range, within a predetermined pressure range and within a predetermined depth range. At a predefined operation condition of the structure, a depth and a temperature may be determined within the respective ranges.

[0016] The second fluid may have a vapor pressure, the vapor pressure being the pressure at which the second fluid is at equilibrium in both liquid and gas phases. The vapor pressure may be above the pressure required by the outer housing to withstand ambient buckling pressure at the deepest predetermined operation depth for the lowest temperature within the predetermined temperature range.

[0017] The second fluid is in both the liquid and gaseous phase and thus has a vapor pressure. Preferably, the second fluid is configured to, or selected as to, have a vapor pressure such that the outer housing withstands buckling at a maximum operation depth and at a minimum operation temperature. This further implies that the overall structure may be configured so that the outer housing tolerates a predetermined pressure difference between the inside and the outside e.g. between inner and outer sides of the outer housing as the outer housing may buckle inwards due to outer pressures during use.

[0018] At an operation pressure corresponding to a pressure exerted on the outer housing by the surrounding water at the predefined operation condition, the vapor pressure of the second fluid is within a predetermined amount / level below the operation pressure. The predefined condition may be at a maximum operation depth and at a minimum operation temperature. Pressure difference, that is ambient pressure minus inner pressure, may be a value above 0 bar but its negative value may need to be considered due to possible buckling of the outer housing, such as above -1 bar at the highest outer pressure corresponding to the maximum operation depth. The selection of the second fluid may ensure that the vapor pressure stays within a predetermined margin for the operation temperature and pressure ranges.

[0019] In some embodiments, at the maximum operation depth and at the minimum operation temperature, the second fluid in the second space has a pressure above the operation pressure.

[0020] Moreover, the second fluid is in thermal equilibrium with the surrounding water, such as within the predetermined temperature range.

[0021] When pumping the first fluid into the first space and compressing the second fluid, the speed of compression may be limited by the thermal conductivity of the second fluid to the24244EP00

[0022] 3

[0023] surrounding water. Speed of action may be limited to so as the second fluid temperature may stay within the predetermined temperature limits for a given setup.

[0024] In some embodiments, a difference between the temperatures of the second fluid and the surrounding water is less than 5 degrees Celsius, preferably less than 2 degrees Celsius, preferably less than 1 degrees Celsius. The difference between the temperatures of the second fluid and the surrounding water may be out of balance, but the temperature of the second fluid may be kept within the predetermined temperature limits. This may be done by specifying or requiring an upper bound on the flow speed of the second fluid. Other than that, the system may reach equilibrium with its surrounding automatically. For increased endurance of equipment, it may be preferable to keep temperature difference below 5 degrees Celsius, then preferably less than 2 degrees Celsius, or even below 1 degrees Celsius. In some embodiments the second fluid and the surrounding water are in thermal equilibrium, such as within the predetermined temperature range wherein both the second fluid and the surrounding water are at the same temperature or at temperatures within a defined tolerance or a range.

[0025] An advantage of keeping the second fluid temperature close to the surrounding water temperature may be that the internal pressure of the buoyancy element becomes inherently defined by the vapor pressure of the second (working) fluid at ambient temperature. This eliminates the need for active heating or cooling devices to regulate pressure or phase ratio. As a result, system complexity, energy consumption, and failure risk are reduced.

[0026] Furthermore, because the vapor pressure is governed by the thermodynamic properties of the selected working (second) fluid, the internal pressure remains predictable and stable across the intended operating temperature range. By appropriate fluid selection, the internal pressure may be maintained within a predefined structural limit, for example to prevent inward buckling or collapse of a buoyancy element while avoiding excessive structural loading.

[0027] The predeterminded depth range may be defined as a range between the followings Depthmin Minimum depth of buoyancy structure may be zero such as when the structure is at surface.

[0028] Depthmax Maximum expected operation depth of the buoyancy structure, e.g. 10m,

[0029] 20m, 30m. Depthmax may take into account the dynamic behaviour due to water / ocean currents and the setup of the mooring system.

[0030] The predetermined temperature range may be defined as a range between the followings24244EP00

[0031] 4

[0032] Tmin Minimum expected environment temperature (e.g. above freezing point at cold locations)

[0033] Tmax Maximum expected environment temperature (e.g. 20°C near Iceland or upto 50 °C on shore in tropical areas)

[0034] The predeterminded pressure range may be defined as a range between the followings Pmin Minimum pressure inside outer housing that prevents buckling of the outer housing at Depthmax.

[0035] Pmax Maximum pressure inside outer housing that it can withstand at Depthmin and Tmax. When for example a selected second fluid has vapor pressure above selected Pmax, a lower than Pmax pressure relief valve may be provided for the first fluid and / or Pmax pressure relief valve for the second fluid.

[0036] Thus, the second fluid may be selected such that, at an ambient water temperature between Tmin and Tmax the second fluid provides gas pressure or vapor pressure between Pmin and Pmax. The buoyancy adjustment is achieved by mechanical displacement of the flexible wall portion through operation of the pump.

[0037] Thus, the internal pressure of the second fluid in the second space may prevent structural collapse of the buoyancy element without requiring continuous addition or removal of second fluid and without relying on active heating or cooling. The present disclosure thus takes advantage of thermodynamic properties of the selected second fluid to achieve pressure stabilization and buoyancy control, in contrast to systems that depend on thermally induced phase transitions.

[0038] When the second fluid is in gas phase only such as air, CO2 e.t.c. for relevant temperatures and pressures, part or all of the second fluid may be removed in order to reach lowest buoyancy values because of unmanageable pressures if it is not removed. The second fluid may however simplify the equipment as it becomes liquid when its volume is restricted thereby allowing the structure to reach low buoyancy without removing second fluid.

[0039] The first space and the second space may be mechanically coupled, such as by means of the flexible wall. The transfer of the first fluid by the pump may modify a volume available to the second fluid.

[0040] The second fluid may be at a pressure corresponding to an operation pressure that is at least equal to the hydrostatic pressure exerted on the outer housing at the predetermined depth. The operation pressure may be defined corresponding to at least a pressure exerted on the24244EP00

[0041] 5

[0042] outer housing by the surrounding water at the predetermined depth. The pressure of the second fluid may exceed the ambient pressure, i.e. the operation pressure on the outer housing.

[0043] In some embodiments, the second fluid is provided in the second space at a pressure exceeding the operation pressure.

[0044] It may be desired that the outer compartment has a fixed volume, as this makes the controlling of the volume for the first fluid and the second fluid simple. Maintaining internal pressure significantly higher than outer operation pressure (i.e. ambient pressure within depth range) ensures a fixed volume of the outer compartment.

[0045] A pump configured to transferthe first fluid in and out of the buoyancy structure. The pump is configured for driving first fluid between the fluid reservoir and the first space. Accordingly, volume available to the second fluid may be modified.

[0046] In some embodiment, a ratio between the liquid and the gaseous phases is variable based on the driven first fluid between the fluid reservoir and the first space by the pump and wherein the operation pressure of the outer housing (i.e. ambient pressure within depth range) is maintained within a predefined range.

[0047] Accordingly, adjustment of buoyancy may be achieved by mechanical modification of the volume available to the second fluid and without active heating or cooling of the second fluid.

[0048] Thus, the buoyancy adjustment may be based on solely hydraulic displacement of the first incompressible fluid. In some embodiment, the control unit is configured to adjust buoyancy based on solely hydraulic displacement of the first incompressible fluid.

[0049] In some embodiments, the buoyancy element comprises a valve between the first space and surroundings of the outer housing.

[0050] A controller may be provided for controlling the flow of the first fluid through the fluid conduit and thus the buoyancy of the buoyancy structure.

[0051] In some embodiments, a buoyancy structure may comprise a control unit configured to activate the pump and to control a flow of the first fluid through the fluid conduit.24244EP00

[0052] 6

[0053] In some embodiments, the buoyancy structure comprises one or more of the following sensors: depth sensor, pressure sensor, temperature sensor, flow sensor.

[0054] Control unit may be configured to actuate / activate the pump in response to at least one sensor data. The sensor data may be selected from a depth sensor data, pressure sensor data, or buoyancy sensor data.

[0055] In some embodiments, the control unit is configured to adjust buoyancy based on hydraulic displacement of the first incompressible fluid.

[0056] In this context, a buoyancy structure is a structure which may be brought to a position within a body of water, i.e. a position between the surface and the bottom of the body of water. Often, this will entail selection or setting of a desired buoyancy of the buoyancy structure, and in many situations, as will be described below, this may also entail adapting or correcting the buoyancy of the buoyancy structure.

[0057] The first fluid is incompressible and could be water or any other liquid. The first fluid may be salt water, purified to take out particles and / or living organisms, and / or water added a biocide if desired.

[0058] The second fluid may be a so-called working fluid. The second fluid acts in the same manner which will be described in the following: When a buoyancy structure is submerged, its temperature will equalise with the surrounding medium. A working fluid can be in a liquid state, a two-phase state or gaseous state at temperature between Tmin and Tmax. When a working fluid is in the two-phase state, its vapor pressureis a function of temperature. This function is a property of the selected working fluid. If the surrounding temperature decreases, the working fluid condenses, and the pressure decreases until the fluid reaches the vapor pressure of the new temperature. If the surrounding temperature increases, the working fluid heats and boils to increase the gaseous state until the vapor pressure corresponding to the new temperature of the surroundings is reached. When the amount of second fluid is not changed and when the volume it occupies does not change, this does not result in a change in buoyancy, only in pressure change within the second fluid in the volume. During operation, the temperature of the surroundings determine the temperature of the second fluid. When not in the two-phase state i.e. when quality is 1, the pressure is a function of two variables, for example density and temperature. For the same temperature, the proportions of liquid and gaseous phases changes if the total volume of the second fluid is changed. Clearly, this will alter the overall density of the second fluid in this space and thus the buoyancy. Preferably this is obtained by deformation or reshaping the flexible wall portion caused by a variation of the volume of the first fluid by removing or injecting the first fluid.24244EP00

[0059] 7

[0060] Allowing the first fluid to flow out of the buoy preferably allows the volume of the second fluid to increase, leading to insignificant pressure drop within the second fluid while in two-phase state, (where the temperature does not change drastically), reducing its boiling point so the second fluid starts to boil until it has reached thermal equilibrium at the am bient temperature while filling the additional volume. How fast the second fluid reaches equilibrium depends on thermal contact between the second fluid and the ambient water.

[0061] Clearly, the second fluid could be selected to be in the two-phase state at the operation temperature and around the pressure of operation or perhaps above the pressure of operation, if the pressure inside the outer housing is desired higher than the pressure of operation. Then, one could select the second fluid as that which has the lowest pressure at the highest foreseen temperature while having a sufficiently high pressure at the lowest foreseen temperature. This could minimize strength requirements on the outer housing. Naturally, other considerations may come into play, like chemical suitability, toxicity or environmental friendliness.

[0062] Then, the expected use scenario may be assisting in selecting a suitable second fluid. One second fluid may be more suitable for use in warmer water and lower pressure than others which are more suitable for use in colder water or higher pressures. Typical use scenario could be temperatures ranging between -2 and 30 degrees Celsius and ambient pressure of 4 bars absolute [bara] corresponding to about 30m depth. For areas where the temperature can go below 0°C, it would be preferably to select a first fluid which does not freeze, so that sweet water may not be preferable (unless mixed with antifreeze substance) where salty water with a sufficiently high salt concentration could be. For a buoyancy structure to have the second fluid pressure alone push first fluid out of the structure at 30m depth, the pressure of the selected second fluid preferably should be above the 4 bara at the lowest operating temperature, such as -2 degrees Celsius. At 30 degrees Celsius, the given second fluid will be at a pressure calculated by its characteristic boiling point function. The outer housing then preferably is able to handle at least that pressure.

[0063] A common way to describe the ratio of liquid to gaseous phases is the quality of the fluid. The quality relates to the ratio of liquid to gaseous phases and ranges from 1, where all of the fluid is in the gaseous phase, and 0, where all of the fluid in in the liquid phase. At quality 1, the pressure follows the normal gas laws which in simplified form is P*V=n*R*T relating pressure P, volume V, quantity n and temperature T. Thus, the second fluid is in a state where some of it is in the liquid phase and the rest in the gaseous phase, when its quality is between 0 and 1.24244EP00

[0064] 8

[0065] Then, the parameters of the second fluid may be adapted to a use situation of the buoyancy structure, such as the temperature of the water in which the structure is intended positioned and the depth of operation. It may be desired that the internal pressure, created by the second fluid, in the outer housing is above that of the surrounding water, but where the overpressure is within a desired interval or below a maximum pressure difference vis-a-vis the surrounding operation pressure. In such a situation, the second fluid should be selected based not precisely on the depth of operation but at the pressure desired within the outer housing at operation - and at the temperature at that depth.

[0066] Even higher pressures may be desired for deep water operation, or where the internal pressure is used for maintaining a shape of the outer housing or the like. Other temperatures may be useful for use in particular waters or in other situations in liquids with extreme temperatures.

[0067] For a given buoyancy element having a maximum internal volume (VolMax), a minimum required mass of the second fluid may be determined such that, at Tmin and when occupying VolMax, the internal pressure reaches Pmin. At this condition the second fluid may be in a gaseous state. By providing an amount of second fluid exceeding this minimum mass, the fluid may enter a two-phase equilibrium state at operating conditions, thereby enabling volume variation primarily through phase ratio adjustment while maintaining pressure substantially governed by saturation pressure.

[0068] In some embodiments, a mass of the second fluid in the second space is constant.

[0069] The outer housing preferably is stiff or inflexible, especially if desired connected to a load bearing structure, or has a fixed or near invariable inner volume. In this manner, the volume change of the second fluid is determined and defined by the amount of the incompressible first fluid added to the first space. Typical housing materials may be metals, such as steel, polyethylene (PE), poly vinyl chloride (PVC), Hypalon, or 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 SeaStrut, Dacron or Gore-Tex. It may be desired to have the outer housing rather stiff, such as if made of metal with a thickness of l-30mm.

[0070] The outer housing may be configured to handle a desired increased internal pressure at an operation depth, but also the corresponding, even higher pressure, when at the surface, such as at deployment or retrieval where the surrounding temperature often will be higher.24244EP00

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[0072] The first and second spaces as well as the flexible wall portion may take up all space in the outer housing. Naturally, other elements may be provided in the outer housing, such as sensors, electronics, other components or even other spaces for different purposes.

[0073] The flexible wall portion is configured to allow the volume of the first and second spaces to vary. It may be preferred that when the first space decreases in volume by a particular amount, the second space increases in volume by the same amount due to the flexible wall reshaping accordingly. The flexible wall preferably is impenetrable to the first fluid and the second fluid, where the impenetrability is at least a penetrability of less than 1% during a period of operation of the buoyancy structure. The period of operation may be 1, 2, 3, 10 or 24 hours, 1,2, 5 or 10 weeks, 1, 2, 5 or 10 months or 1-5 years, depending on what the buoyancy structure is used for. Typical materials for the flexible wall may be polyethylene (PE), poly vinyl chloride (PVC), Hypalon or 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 SeaStrut, Dacron or Gore-Tex.

[0074] Naturally the volumes of the first and second spaces may be determined or selected for e.g. a maximum desired amount of first fluid in the first space and a lowest intended amount of second fluid in the second space, as this describes the buoyancy interval of the structure. This interval may be selected to match a purpose of the structure, such as based on a load intended supported by the structure.

[0075] The fluid reservoir is capable of holding an amount of the first fluid. In some situations, first fluid will be provided manually form a service boat or by other means in the first space even at launch, whereby a relatively low buoyancy is provided. This may be the situation when supporting a weight will increase over time. It may be preferred that the fluid reservoir is capable of holding a volume of first fluid being up to 95% of the combined volumes of the first and second spaces, but it may be allowed that this percentage is reduced to 1-75% of the combined volumes. In another situation, no or only a little first fluid is provided in the first space, e.g. at harvest of fully grown shellfish , such as to support a payload which is desired brought to the surface of a body of water and subsequent addition of juvenile shellfish to cultivation lines for launch of a new cultivation period into the water. Increasing, thereafter, the amount of first fluid in the first space will decrease the buoyancy and thus lower the payload into the water.

[0076] A conduit is a hollow element, often a tube or hose, configured to transport the first fluid therein and there through. The conduit preferably is impermeable to water and the first fluid in order for the first fluid transported to not be lost or polluted by e.g. outside water. The24244EP00

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[0078] conduit preferably is flexible in order to allow the buoyancy element and fluid reservoir to move in relation to each other. Preferably, the conduit is capable of handling first fluid of at least a pressure of 1 bara, such as at least 5 bara, such as at least 10 bara, such as at least 15 bara. Pressure below 1 bara (suction) may also be desired and should then be handled by the conduit. The conduit may be connected to a pump for driving first fluid between the first space and the fluid reservoir, as well as a flow meter forquantifying the amount of first fluid transported. The change in the amount of first fluid in the buoyancy element will determine a change in its buoyancy.

[0079] In one embodiment, the flexible wall portion comprises a flexible bag or container provided in the outer housing. Then, the first space may be inside the bag or outside of the bag. Naturally, this may be reversed. Alternatively, the flexible wall portion may be shaped as a membrane delimiting the first and second spaces with the aid of e.g. an inner surface of the outer housing.

[0080] A valve may be provided between the first space and the surroundings of the outer housing. If the pressure within the outer housing exceeds that of the surrounding water, opening this valve will allow first fluid to exit the first space, allowing the second space and thus the second fluid to expand, increasing the buoyancy of the buoyancy structure.

[0081] Any number of buoyancy elements may be used as well as any size of buoyancy elements may be selected. The number of buoyancy elements may exceed 10, such as exceeding 20, such as exceeding 50, such as exceeding 100. Buoyancy elements employing sensors may be provided with an outer housing with a volume of 50 I or less, such as 30 I or less or even 20 I or less, whereas buoyancy elements configured to support a load may be larger, so that the outer housing has an inner volume of 100 I or more, such as 250 I or more, such as 500 I or more, such as 1000 I or more.

[0082] The same fluid reservoir may be used for some of or all of the buoyancy elements.

[0083] The buoyancy structure may be used for positioning in a body of water forthe monitoring the body of water, so that the buoyancy elements may be supplied with sensors for determining parameters of the body of water or objects travelling thereon or therein. For this use, the buoyancy elements may be desired positioned at a selected height over the bottom of the body of water or at a selected depth therein, and this height / depth may be desired determined, set, maintained and / or altered depending on the situation. For example, it may be desired to be able to increase the depth of the structure if a vessel or ship is approaching or if a large wave height is foreseen, such as during a storm. Sonar sensors may be used for sensing approaching ships, wildlife and the like. On the other hand, it may be desired to24244EP00

[0084] 11

[0085] decrease the depth if a submarine or whales are approaching in order to avoid collisions or during harvest.

[0086] Wave height, direction and frequency may be better measured if the depth of the buoys is low, depending on the sensor type used. Wave parameters may be determined if all buoyancy elements are set to the same depth, for example. Water temperature may be determined at different depths when the depth of the buoys may be set or altered, and different buoyancy elements may be set at different depths if desired.

[0087] A single conduit may be used for conveying the first fluid to all first spaces. For each space, a valve may be provided for allowing and preventing fluid flow between the conduit and the pertaining first space. A conduit may extend from the first fluid reservoir or a pump connected thereto and to a first space.

[0088] The fluid reservoir may be any type of storage, such as be a storage capable of having a variable volume, such as a flexible bag or container, thus having the same pressure as the external environment.

[0089] In one embodiment, the structure further comprises a controller configured to determine a buoyancy of each buoyancy element. In this context, the buoyancy may relate to the mean density or overall density of the buoyancy element comprising the outer housing and the flexible wall as well as any other element. Part of the conduit(s) may also be considered to form part of the buoyancy element when determining the buoyancy thereof. Naturally, the buoyancy will depend on the amount of, and the density of, the first and second fluid in the outer housing.

[0090] Then, the amount of the first and / or second fluid in the buoy may be determined based on e.g. the amount of first fluid added to and / or removed from the buoyancy element. For this reason, a flow meter, optionally coupled with computer and accounting softwa re may be used for determining and keeping accounts of such variation in the amount of first fluid and the determination may be based on combined net output from such a flow meter.

[0091] In one embodiment, the controller is further configured to control a buoyancy of each buoyancy element. This controlling may be a controlling of the addition of first fluid to and / or removal thereof from the buoy, as the weight of the other components of the outer housing, such as the outer housing, the second fluid and the flexible wall is normally desired kept24244EP00

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[0093] constant. The first and second volumes, however, may be desired altered during the controlling of the buoyancy.

[0094] The buoyancy may be controlled by varying a ratio of the volumes or amounts of the first and second fluids in the buoyancy element.

[0095] Then, the controlling may be based on an operation of the pump(s) driving the first fluid.

[0096] The controlling may be aimed at controlling of the buoyancy toward a desired buoyancy or a controlling of a depth below the surface or a height above the bottom of the body of water. The controlling may not be a controlling to a particular or desired buoyancy but to a buoyancy resulting in the desired vertical position of the buoyancy element in the body of water.

[0097] In one embodiment, the one or more first fluid conduits comprise a single conduit fluidly connecting the one or more pumps and the first spaces, each buoyancy element further comprising a valve for closing the pertaining first space to the conduit. In this manner, a simpler solution is obtained where the single conduit extends from the pump(s) to each of the first spaces. By opening and closing the individual valves, the fluid driven by the pump(s) will enter / exit buoyancy element with open valves but not those with closed valves. Thus, the buoyancy of selected buoyancy element may be controlled without affecting the buoyancy of other buoyancy element.

[0098] In one embodiment, each buoyancy element comprises a sensor configured to output a signal representing a depth / height of the buoyancy element. Even though this may be obtained using dedicated depth sensors or e.g. a downwardly directed sonar, the depth of each buoyancy element is preferably determined by a pressure sensordetermining the pressure in the single conduit at a position of the buoyancy element. This gives relative depth measures which may be combined with an absolute measurement made at a buoyancy element or the fluid reservoir.

[0099] A suitable use of the buoyancy structure described above would be one where the structure further comprises a load bearing structure attached to each buoyancy element.

[0100] In some embodiments, a submersible structure comprises a plurality of buoyancy elements and the fluid conduit being provided between the fluid reservoir and the first space of each buoyancy element.24244EP00

[0101] 13

[0102] In some embodiment, the submersible structure further comprises a controller, such as a control unit, configured to determine a buoyancy of each buoyancy element.

[0103] In some embodiment, the submersible structure further comprises a load bearing structure attached to each buoyancy element.

[0104] A load bearing structure may be any type of structure, such as based on a net structure, woven structure, non-woven structure, wires, ropes or other elongate elements, baskets, shelves or the like. The load bearing structure preferably is capable of or provided for supporting one or more types of product, such as a cultivated organism, which may grow or proliferate under water, such as shellfish, bivalves, seaweed or other plants, or the like. The weight of the load bearing structure may then increase over time, as the product supported thereby grows or proliferates. The weight of the load bearing structure may also decrease over time, in case of fall-off from cultivation ropes, predation, and / or reduction in weight due to spawning or little access to nutrition.

[0105] The load bearing structure is attached to the buoyancy element and will normally be provided below the buoyancy element but can be provided above buoyancy element, such as in case of seaweed. The attachment may be permanent or releasable. The attachment may be via elements, such as a collar, twine, or the like, engaging the individual buoyancy element in a manner so that the load bearing structure remains engaged with the buoyancy element during operation.

[0106] In some embodiments, the pump may be configured to adjust buoyancy of each of the buoyancy elements in response to an increase or decrease in weight of the load -bearing structure.

[0107] It is noted that a rather different use would be a shelf or other structure capable of supporting a ROV (Remote Operable Vehicle), person, sensing platform or the like, where the buoyancy of the buoyancy element may be reduced to allow the structure to reach the bottom of the body of water to deliver the ROV or the like to the bottom of the body of water. The buoyancy elements may then revert to a more shallow position to either receive more elements for delivery to the bottom or the like. The buoyancy may then again be lowered to bring the structure to the bottom to receive the ROV or the like when it is to be retrieved again.

[0108] In one embodiment, the structure further comprises one or more elongate balancing lines each being attached, directly or indirectly, at a first end, to one of the plurality of buoyancy24244EP00

[0109] 14

[0110] element, a second end thereof resting on a bottom of the body of water in which the structure sits.

[0111] Balancing lines have the advantage that the suspended portion of the balancing lines, i.e. the portion between the first end and a portion of the balancing lines the farthest from the first portion which does not touch the bottom, will add to the weight supported by the buoyancy element. However, when the buoyancy element sinks to a larger depth, a smaller portion of the balancing line is suspended, so that the weight thereof is reduced, whereas if the buoyancy element rises to a lower depth, the suspended portion, and thus weight, of the balancing line will increase.

[0112] An advantage of the balancing lines, when used in connection with a load bearing structure, is that as the weight of the load bearing structure increases, dragging the buoyancy element downwardly, the weight of the suspended portion of the balancing lines will decrease. Thus, an equilibrium may be obtained even when the buoyancy of the buoyancy element is unaltered.

[0113] However, as the buoyancy of the buoyancy element will now also support the balancing lines, it is preferable that each buoyancy element is brought to the same average height below the surface of the sea (or above the seabed), so that the weight of the balancing line(s) supported by the buoyancy element is the same, whereby any change over time of the buoyancy element buoyancy is made only to take into account a change in weight of the load bearing structure carried by the buoy and thus an increase in weight of the products held thereby.

[0114] Clearly, it may be desirable to provide a conduit or manifold also for delivering second fluid to or removing second fluid from the second space(s) of the structure. Then, a structure similar to that of controlling the amount of the first fluid may be employed.

[0115] A second aspect of the invention relates to a method of operating buoyancy structure according to the first aspect, the structure comprising an outer compartment comprising:

[0116] a fluid reservoir comprising a first, incompressible fluid,

[0117] a first space and a second space inside the outer housing,

[0118] a fluid conduit between the fluid reservoir and the first space, a flexible wall portion delimiting the first space from the second space, the second space being confined by the flexible wall inside the outer housing, and a second fluid in the second space,24244EP00

[0119] 15

[0120] a pump configured for driving first fluid between the fluid reservoir and the first space,

[0121] the method comprising lowering the structure into a body of water of a first temperature within a predetermined temperature range and at a predetermined depth within a predetermined depth range,

[0122] wherein the second fluid provides a vapor pressure and in both the liquid and gaseous form when at the first temperature within the second space and wherein a pressure is exerted on the outer housing by the surrounding water at the predetermined depth, and

[0123] wherein the method further comprises

[0124] controlling a buoyancy of the buoyancy structure by transporting the first fluid, via the pump and the fluid conduit, between the fluid reservoir and the first space,

[0125] and wherein a temperature of the second fluid stays within the predefined temperature range.lt is noted that all embodiments, considerations, situations and the like mentioned in relation to the first aspect are equally relevant to the second aspect.

[0126] Thus, the second fluid may reach thermal equilibrium with the surrounding water.

[0127] The predetermined temperature range may be between Tmin and Tmax and the predetermined depth range may be between Depthmin and Depthmax. The second fluid may provide either gas pressure (i.e. is in gaseous phase only) or vapor pressure. The second fluid's pressure may be high enough to prevent buckling of the outer housing at any given depth between Depthmin and Depthmax, and low enough so that the outer housing retains structural integrity.

[0128] In some embodiments, the second fluid is provided in the second space at a pressure exceeding the minimum pressure required to prevent buckling of the outer housing at the predetermined depth.

[0129] In some embodiments, the second fluid is provided in the second space at a pressure exceeding the pressure exerted on the outer housing by the surrounding water at the predetermined depth.24244EP00

[0130] 16

[0131] In one embodiment, the method may further comprise opening a valve between the first space and surroundings of the outer housing. This may allow the second fluid to drive at least a portion of the first fluid out of the first space, increasing the buoyancy and thus allowing the structure to move upwards in the column of water.

[0132] In one embodiment, the method further comprises the step of determining a buoyancy of each buoyancy element. Different types of sensors may be used, as described above.

[0133] In that or other embodiments, the method further comprises the step of controlling a buoyancy of each buoyancy element. Naturally, the buoyancy of each buoyancy element may be controlled independently of that of the other buoyancy element, or groups of buoyancy element may be controlled in unison.

[0134] In one embodiment, the method further comprises the step of a sensor of each buoyancy element outputting a signal representing a depth / height of the buoy. As mentioned above, such sensors may be a mix of absolute depth / height sensors and relative depth / height sensors.

[0135] It may be desired that the structure further comprises a load bearing structure, where individual portions of the load bearing structure is attached to each buoyancy element, the method further comprising the step of determining a weight of the portion of the load bearing structure attached to at least one of the buoyancy elements. In this context, the load bearing structure may be a monolithic structure supported by a plurality of the buoyancy element, such as where each of the supporting buoyancy element are connected to the load bearing structure. In other situations, the load bearing structure may be formed by a number of individual portions each supported by a single buoyancy element. A buoyancy element may support multiple of such portions.

[0136] Then, it may be desired to know the weight of the structure supported by one or more of the supporting buoyancy elements. From the weight supported by all supporting buoyancy element, the total weight of the load bearing structure may be determined.

[0137] The total weight may be used for ascertaining that a payload, such as a ROV, is supported by or forms part of the load bearing structure. The total weight may also be an indication of a weight of a growing product (cultivated organism) forming part of the structure.

[0138] From the weight supported by one buoyancy element, the product weight supported by that buoyancy element may be determined.24244EP00

[0139] 17

[0140] In general and also in the above embodiment, the buoyancy structure may further comprise one or more elongate balancing lines attached, at a first end, to one of the buoyancy element, a second end thereof resting on a bottom of the body of water in which the structure sits, the method further comprising estimating a weight of the load bearing structure supported by one of the plurality of buoyancy element by controlling the buoyancy of the buoyancy element to bring the buoyancy element to a predetermined height above the bottom, and determining the weight based on the buoyancy of the buoyancy element. The advantage of such balancing lines is described above.

[0141] In some embodiments the method may comprise the step of selecting a second fluid suitable for providing a vapor pressure within the predetermined pressure range and the predetermined temperature range and / or determining a minimum amount of second fluid required, for example when a first fluid volume is zero, such that the second fluid provides vapor pressure, such as the second fluid is in both the liquid and the gaseous phase, within the predetermined pressure range and within the predetermined temperature range.

[0142] The second fluid may be selected such that it provides gas pressure or vapor pressure between Pmin and Pmax as defined above, for all temperatures between Tmin and Tmax (liquid only state is excluded as any pressure can be reached if pushed by a first fluid pump beyond the liquid only state).

[0143] The step of determining a minimum amount of second fluid may be provided such that the second fluid fulfills the Pmin requirement stated above at temperature Tmin for the given maximum volume it is supposed to fill.

[0144] The buoyancy structure may be designed to operate within specific depth-, temperature- and pressure -range as defined above. The method may comprise selecting a second fluid whose gas pressure or vapor pressure stay within those limits for the given ranges.

[0145] Tmin may represent a minimum operational ambient temperature at the location of use. For example, in sea that freezes at -2°C, at locations where sea is expected to freeze. Tmin may then be -2°C. Tmax may represent a maximum operational ambient temperature at the location of use.

[0146] Pmin may represent a minimum operational pressure of second fluid which is chosen so that the outer housing of buoyancy element will not buckle at Depthmax, i.e. maximum operational depth of buoyancy element, for any temperature between Tmin and Tmax.24244EP00

[0147] 18

[0148] Pmax may represent a maximum operational pressure of second fluid which is chosen so that the outer housing of buoyancy element will endure at Depthmin, i.e. minimum depth relative to surface of body of liquid, and Tmax.

[0149] In the case where structure is taken out of the environment for which Tmax is specified, pressure may become higher than Pmax (for example sun shining on buoyancy elements on a boat or ashore) a relieve valve may be provided to release the first fluid and / or the second fluid.

[0150] The method may additionally or alternatively comprise determining a minimum amount of second fluid. For the given buoyancy element, a maximum volume that the second fluid is desired to fill, VolMax, i.e. the maximum volume of the second space in a given buoyancy element, may be determined. VolMax may be equal to or close to, such as more than 95% of, the total inner volume of the respective buoyancy element. Notice that buoyance element may be broadly specified as for example first spaces could overlap e.g. one first space expands into volume that the next first space could occupy as well.

[0151] Subsequently, the amount of second fluid, SFmassMin, may be determined based on Pmin, Tmin and VolMax. The determined amount of second fluid may provide Pmin pressure at Tmin temperature when confined within VolMax. At this state, the second fluid may be in gas phase only. If more amount of second fluid is added above SFmassMin, pressure may increase until vapor pressure is reached which is defined by the properties of the second fluid.

[0152] Alternatively, the present disclosure may further relate to a method of operating the buoyancy structure comprising the buoyancy element according to any one of the previous embodiments. Such a method may further comprise selecting the second fluid and / or determining a minimum amount of second fluid as described above.

[0153] Clearly, all embodiments, situations and considerations made in relation to the previous aspects are equally relevant to this aspect of the invention in which a method for determining a second fluid and / or a method for determining minimum amount of second fluid is disclosed.

[0154] A third aspect of the invention relates to a buoyancy structure comprising a buoyancy element comprising an outer housing, the buoyancy structure comprising:

[0155] a first space containing a first fluid and a second space containing a second fluid inside the outer housing,24244EP00

[0156] 19

[0157] a flexible wall portion delimiting the first space from the second space, the second space being confined by the flexible wall inside the outer housing, and a valve between the first space and surroundings of the outer housing,

[0158] wherein the first fluid has a vapor pressure, so that the first fluid is in both the liquid and the gaseous phases, and the vapor pressure corresponds to or above a pressure exerted on the outer housing by the surrounding water at a predetermined depth and a temperature.

[0159] Clearly, all embodiments, situations and considerations made in relation to the first and second aspects are equally relevant to the third aspect of the invention.

[0160] This third aspect needs no fluid reservoir and fluid conduit as it is aimed at another purpose. Still, the second fluid is selected so that at the operation depth and temperature, the second fluid has a quality greater than 0 but below 1 and the vapor pressure is higher than the outer pressure at the maximum intended depth. The internal pressure in the outer housing preferably exceeds the water pressure at the operation depth so that when opening the valve, part or all of the first fluid will be forced out of the first housing, allowing the second fluid to expand, whereby the quality thereof will rise (more second fluid in the gaseous state), . This will overall increase the buoyancy of the structure which will then rise toward the surface.

[0161] Thus, this may be used for rising sunken elements or as an emergency rising component on subsea or submarine equipment.

[0162] An advantage of this structure is that the only energy required to initiate this process is that required for opening the valve .

[0163] Then, a small built-in battery pack or the like may be employed for this structure to be self-powered and thus be operable even if a submarine, ROV or other element has a power cut.

[0164] A fourth aspect of the invention relates to a buoyancy structure comprising a buoyancy element comprising an outer housing made of a flexible material and defining an inner space, the buoyancy structure comprising:

[0165] a first fluid in the inner space,

[0166] means for varying a shape of the outer housing to vary a volume of the inner space,24244EP00

[0167] 20

[0168] wherein the first fluid has a vapor pressure, so that the first fluid is in both the liquid and the gaseous phases, and the vapor pressure corresponds to or above a pressure exerted on the outer housing by the surrounding water at a predetermined depth and a temperature.

[0169] Clearly, all embodiments, situations and considerations made in relation to the first and second aspects are equally relevant to the third aspect of the invention.

[0170] This fourth aspect also needs no fluid reservoir or fluid conduit as it is aimed at another purpose, such as to an emergency surfacing. This embodiment needs only the one space and the first fluid, which will be as the above second fluid. The operation and the variation or control of the buoyancy is now obtained merely by varying the volume of the inner space. In this manner, the same buoyancy control is seen and when the fluid is in the two-phase state, the inner pressure thereof may not need to vary greatly during operation. As before vapor pressure is temperature dependent.

[0171] The variation of the volume is now obtained by deforming the outer housing which is now made of a flexible material such as any of the materials mentioned above useful as the flexible wall portion.

[0172] Still, the fluid is selected so that at the operation depth and temperature, the fluid has a quality between 0 and 1. When allowing the housing to expand, overall buoyancy of the structure will increase which will then rise toward the surface. In the following, preferred embodiments will be described with reference to the drawing, wherein:

[0173] Fig. 1 illustrates a cross section of a first embodiment of a structure according to the invention,

[0174] Fig. 2 illustrates a cross section of a second embodiment of a structure according to the invention

[0175] Fig. 3 illustrates vapor pressure for examples of different fluids at different temperatures,

[0176] Fig. 4 illustrates a first embodiment with multiple buoyancy elements,

[0177] Fig. 5 illustrates a second embodiment with multiple buoyancy elements,

[0178] Fig. 6 a control element for use in structure of the invention,

[0179] Fig. 7 illustrates an interfacing element or node (containing valves, pressure sensors, bus interface and possibly microcontroller etc.), useful in the structure of the invention,

[0180] Fig. 8 illustrates a structure of the invention used in culturing the respective organism, and

[0181] Fig. 9 illustrates a manner of reducing a housing volume.24244EP00

[0182] 21

[0183] Figs. lOa-lOc illustrate manners of calculating minimum amount of second fluid.

[0184] Figure 1 illustrates a buoyancy structure 10 comprising a buoyancy element 20, in the following denoted a buoy 20, The buoy 20 comprises an outer housing 21, which may or may not be rigid. A rigid outer housing 21 has the advantage that its internal volume is constant.

[0185] Within the outer housing 21, a flexible compartment 22 is provided. In figure 1, the flexible compartment 22 defines a first space and is filled with water 24 or another at least substantially incompressible liquid.

[0186] Inside the outer housing 21 but outside of the flexible compartment 22 a second fluid is present. This fluid could be a working fluid as described above. It is capable of existing in two phases, as liquid phase 28 and a gas phase 26, at the same time. The second fluid may be at boiling point over part of the temperature at which the buoy 20 is to be used i.e. has quality between 0 and 1. In the ocean, the ocean temperature may be between -2 and 30 degrees Celsius, so different second fluids may be selected for use in different oceans or in different places. If temperature goes below 0° care must be taken so that the first fluid does not freeze. Also, the second fluid has vapor pressure that is dependent on temperature. The vopour pressure is dependent on choice of second fluid , but may be desired selected close to the pressure exerted on the outer housing 21 when in operation. Often, the pressure will be in the interval of 1-40 bara, such as 2-20 bara, for example, and the operating temperature in the range -2-40 degrees Celsius, such as -2-20 degrees Celsius. Figure 3 indicates the vapor pressure function for a few examples of second fluids suitable for the temperature and pressure ranges described. Figure 3 indicates vapor pressure in absolute units, bara.

[0187] A second fluid could be selected as that which has the lowest vapor pressure at the high range of temperature while having high enough gas pressure at the lowest temperature. This would minimize strength requirements on containers. Other considerations may come into play, like chemical suitability, toxicity or environmental friendliness.

[0188] When the second fluid is compressed by decreasing the volume it occupies, the second fluid will tend to condensate and transfer to its liquid state 28 without increasing pressure significantly on the outer housing 21.. For the temperature range of -2 - 30 degrees Celsius, the second fluid density ratio between liquid and gaseous state can for example be n-Propane : 20 - 54, for R.124 : 49-149, for Propylene : 18-47.

[0189] Then, the increasing of the volume of the flexible compartment 22 will cause more of the second fluid to condensate without any large change to the internal pressure of the outer housing 21.24244EP00

[0190] 22

[0191] This has the advantage that the outer housing 21 is required to handle a lower differential pressure than if the second fluid was replaced by a gas which would not condensate at the temperatures and pressures in question. This also has the advantage that it is never required to remove second fluid from the structure so, in principle, the second fluid can be added only once and for all.

[0192] This also has the advantage that the buoyancy of the buoy 20 may be controlled simply by controlling the amount of water in the flexible compartment 22.

[0193] Water 24 may be added or removed in one of two ways. A fluid reservoir 30 is connected to the compartment 22 via a controlling element or node 31 and a conduit 25. A pump may be used for moving first fluid between the compartment 22 and the fluid reservoir 30. A flow meter (see below) may be used for quantifying the amount of first fluid added or removed, so that a buoyancy of the structure 10 or the buoy 20 may be determined. In this manner, a position of the buoy 20 in a water column may be determined, set and mainta ined or altered simply by the transport of the first fluid between the compartment 22 and the fluid reservoir.

[0194] Alternatively, a valve 27 is provided between the inner volume of the flexible compartment 22 and surroundings of the outer housing 21, either directly or through the reservoir 30. Opening this valve will allow the first fluid to flow to the surroundings of the outer housing 21. Then, if the amount of second fluid is sufficiently high, it will start boiling and thus gasify and thus push first fluid into the surroundings, increasing the buoyancy of the buoy 20 and optionally the structure 10, allowing for e.g. an emergency rising or surfacing if desired. The cooling of the second fluid during evaporation leads to heat flow into the system from the outside, effectively using thermal energy from the outside to keep up the pressure in the second fluid. The speed of evaporation will then be influenced by the thermal conductivity between compartment 22 and the ambient fluid. Thus, it may be desired to provide the outer housing with a high thermal conductivity for the buoyancy to more closely follow the volume variation of the first fluid. In one embodiment, the outer housing is made of a metal to increase the thermal conductivity. Also, the flexible wall may be desired with a high thermal conductivity especially in the situation seen in figure 2.

[0195] In fact, a separate technology, not forming part of the present invention, would be the buoy 20 without the fluid reservoir 30, the conduit and the node 31. The first and second fluids may be added and the outer housing 21 sealed (apart from the valve 27) to have a desired buoyancy. This assembly or buoy 20 may be fastenedtoa ROV, submarine or the like which will then operate as desired. If a problem is encountered which makes surfacing difficult or impossible, the valve 27 may be opened, allowing the second fluid to expel the first fluid to increase the buoyancy of the buoy 20 to assist the ROV / submarine to surface or rise in the24244EP00

[0196] 23

[0197] body of water in which it sits. The same buoy 20 may be used for lifting structures from the ocean floor by again providing them with the first and second fluids and attaching the buoy to the submerged structure and then opening the valve 27, increasing the buoyancy and, if the buoyancy is sufficient, lifting the structure from the bottom. It is noted that the only energy required for this operation is that required for opening the valve 27, and as opposed to a pressure gas flask, the relative pressure overthe outer housing may be rather modest at the depth of operation.

[0198] In figure 2, the water is outside of the flexible compartment 22 now housing the second fluid. In this embodiment, the water is added / removed, via a valve 27, to / from the space outside of the flexible compartment 22 and / or via the conduit 25 and node 31 to / from the fluid reservoir 30.

[0199] We note that in general the flexible compartment or wall portion may be left out. Viable embodiments exist where the second and first fluids exist in the same space. Removal of the first fluid may then take place at the bottom of the space, as the first fluid usually is of a higher density than the liquid phase of the second fluid and thus will sit at the bottom of the space.

[0200] We note that swift changes in pressure may affect the overall temperature of the second fluid and thus the pressure thereof, so that more slow changes in the volume of the flexible compartment 42 may be found more suitable. Alternatively, the heating or cooling brought about by the addition or removal of the first fluid may deliver or absorb heat from the surroundings so that the buoyancy structure and especially the second fluid will soon have the temperature of the surrounding water.

[0201] This type of buoy 20 may be used for a wide range of uses, such as submarine drones, ROVs, submarines, rescue equipment such as emergency up-drift equipment for divers.

[0202] As mentioned, the outer housing 21 is preferably sealed so that a pressure therein may differ from that of the surroundings. Often the internal pressure exceeds that of the surroundings. This is especially interesting when the vent 27 is provided.

[0203] In figure 4, an embodiment of the structure is illustrated comprising a plurality of buoys 20 and a single fluid reservoir and where individual conduits 25 are provided between the fluid reservoir 30 and the individual buoys 20.

[0204] In figure 5, another embodiment of the structure is illustrated in which the individual conduits 25 between the fluid reservoir 30 and the individual buoys 20 are replaced by a single24244EP00

[0205] 24

[0206] conduit (manifold) 25 extending from the fluid reservoir 30 and sequentially to all buoys 20. In order to allow individual control of each buoy 20, each buoy 20 has a node 31 being connected to the conduit 25 to be able to transport first fluid between the conduit 25 and the space 22 in the situation seen in figure 1.

[0207] This node 31 is further illustrated in figure 7, where it is seen that the node 31 has a valve 311 capable of controlling fluid flow between the conduit 25 and the space 22. In this manner, the fluid reservoir 30 may cause a flow of first fluid to or from a single buoy 20 by closing the valves 311 of the other buoys 20 and keeping the valve 311 of the desired buoy 20 open while creating the desired flow.

[0208] In addition to this individual controlling of the buoyancy of each buoy 20, the amount of first fluid transported through the conduit 25 or passing the valve 311 may be quantified by using a flow meter. The flow meter may be provided in the control element 30, or at the balance drive 35 or in the node 31, such as flow meter 312. Thus, the valve 311 may be controlled to be open whereafter a flow of the first fluid takes place while being quantified by the flow meter 312. In this manner, the amount of fluid in the space 22 may be constantly known and controlled.

[0209] Naturally, the node 31 may comprise a controller 313, which may control the operation of the valve 311 and receive, potentially analyse, and forward readings from the pressure sensor (not shown) or flow-meter 312. The pressure sensors may be placed within the manifold at the nodes 31, or provided one for each pipe as shown in figure 4 at the balance drive 35. The controllers 313 communicate via a cable 252 with a controller of the fluid reservoir 30 which is the balance drive 35. The cable 252 clearly may also provide electric power from a battery provided in the balance drive 35.

[0210] A balance drive 35 comprising the fluid reservoir 30 is illustrated in figure 6 and it comprises, in addition to the fluid reservoir 30, a controlling portion 33 comprising a controller 32 and usually also one or more pumps, a battery, a plurality of different valves, a flow meter, pressure sensors and the like.

[0211] The balance drive 35 acts to control a flow of the first fluid between the fluid reservoir 30 and the spaces 22 (or spaces 24 if the embodiment of figure 2 is employed).

[0212] It is preferred that the balance drive 35 has a pump, where the nodes 31 are provided so that a single pump may control flow in the conduit 25 and where the valves 311 are controlled to ensure that the flow provided is for the correct space 22.24244EP00

[0213] 25

[0214] It may also be desired to determine not only the buoyancy of a buoy 20 but also its depth or height over the bottom. This is especially relevant when the buoy 20 supports a weight, which may or may not be known.

[0215] A particularly interesting use of the structure is in structures forgrowing underwater produce, such as bivalves and seaweed. A structure of this type is illustrated in figure 8 where the buoys 20 support a load bearing structure, here embodied as a number of cultivating lines 26, is hanging from some of or all of the buoys 20. The cultivating lines 26 may be used for cultivating the pertinent organism.

[0216] In general, a load bearing structure may be a structure supported below the buoys 20 and often a structure which varies in weight, requiring a variation in the buoyancy of the buoys 20. An alternative to the vertical cultivating lines 26 could be an elongate cultivating line attached at different positions along its length to different buoys 20.

[0217] Cultivating pertinent organism involves providing seed organisms on the cultivating lines and keeping these in a body of water while the organisms grow to a desired size, whereafter they are harvested.

[0218] In order to keep the cultivating lines and the product sufficiently below the surface, to be out of reach of birds of prey, and away from the bottom, to be out of reach of e.g. crabs, starfish etc., the lines 26 are suspended below the buoys 20 which are maintained at a buoyancy keeping them submerged at a desired depth or height above the bottom 44 of the body of water.

[0219] To keep the structure 10 in place, stretching buoys 41 are provided at each end of the structure 10 and mooring anchors 40 are provided on the seabed 44 to keep the structure 10 in place both horizontally and at least partially vertically. Alternatively, the structure 10 may be anchored less strictly so as to e.g. be allowed to follow the direction of a current of the body of water in which it sits.

[0220] A communication buoy 42 is provided at the surface 43 of the body of water. The buoy 42 is capable of communicating with the balance drive 35 via a cable 421 and with a remote service central, such as via satellite communication or GSM, and provide status information, such as battery status, from the structure 10 and receive operation instructions such as for an emergency dive. The buoy 42 or the structure 10 may comprise additional sensors, such as for sensing approaching vessels, ships, submarines, for sensing whales or other wildlife, sensing water temperature, air temperature, wave height / frequency / direction or the like. Such sensor data may be output by the buoy 42. Besides the above, the buoy 42 can be24244EP00

[0221] 26

[0222] equipped with solar cells, solar marine light, radar reflector, cable connections, controller and other known devices in marine buoys.

[0223] Controlling of the buoyancy of the structure 10 is advantageous fora number of reasons one being to take into account the situation that the cultivating lines 26 increase in weight over time. Other reasons could be to allow the structure to make an emergency dive in case of a storm, high waves, passing ships, or the like.

[0224] The buoys 20 may receive information either via the buoy 42 or from sensors of the structure 10 that vessels or drifting ice are closing in, or that a storm is coming, so that the buoyancy of the buoys 20 may be reduced to have the structure do an emergency dive to not be impacted by high waves, an iceberg, a vessel or ship.

[0225] Below the buoys 20, and only optionally, are balancing lines 36 which extend to the bottom 44 and at the lower end, at least, of which are provided chains 361.

[0226] The balance lines 36 have the advantage that due to the chains 361, the weight of a balance line 36 decreases with the depth of the buoy 20, as with increasing depth, an increasing portion of the chain 361 will be supported by the bottom 44. This has the advantage that as the weight of the cultivating lines 26 increases, the buoy 20 (with no change in buoyancy) will be drawn toward the bottom 44. The balancing lines 36 will then decrease in suspended weight until an equilibrium is found. Then, the operation of the balancing lines 36 is to achieve an equilibrium when the weight of the cultivating lines 26 changes and before the buoyancy of the buoy 20 is altered.

[0227] Then, when installing the structure 10, each buoy 20 is provided with a small buoyancy allowing the balancing lines 36 to reach the bottom 44. The depth of the buoy 20 is normally selected so that the cultivating lines 26 do not reach the bottom 44 so that crabs and the like cannot get to the cultivated organism. On the other hand, the depth of the cultivation lines 26 should also be so that predatory birds cannot reach the bivalves from the surface 43 of the sea. Also, the use of the submerged buoys 41, being invisible from the surface of the sea 43, assists in not alerting the birds that cultivated organisms are cultivated here. The buoy 42 may be floating 10-200m from the buoys 20 in order not to indicate location of cultivated organisms to predatory birds.

[0228] The determined height of the buoy 20 is set, whereby the suspended weight of the balancing lines is set.24244EP00

[0229] 27

[0230] During growth of the cultivated organism, the weight of the cultivating lines 26 will increase, the buoys 20 will sink and be corrected by correcting the buoyancy of the buoy 20 until the same height over the bottom 44 is reached. The depth determined (distance to the surface) will vary due to waves, tides and the like but may be predicted and evened out.

[0231] When the buoy 20 is at the set depth, the increase in buoyancy since the launch is caused by the increase in weight of the cultivated organisms, as the suspended weight of the balancing lines 36 is the same.

[0232] Thus, from the increase in buoyancy of the buoy 20, the overall weight of the cultivated organism supported thereby may be determined. The increased buoyancy may be determined by measuring by flow meter volume of first fluid removed from the space 22, recording the volume of each ingress / egress in an accounting software in a controller thereby constantly monitoring the net combined volume of egress and ingress of liquid volume from space 22. The net combined egress and ingress of liquid fluid equals the change in submerged weight of the cultivated organism. In addition, as this is determined for each buoy 20, the cultivated organism weight supported by each individual buoy 20 may be determined.

[0233] Alternatively, the weight of cultivated organism could potentially also be measured by force sensors attached between the buoys 20 and the cultivation lines 26.

[0234] The depth of a buoy 20 may be determined in a number of manners, such as by sonar device or from a fluid pressure of the first fluid in the conduit 25 at the nodes 31. This pressure will be a relative depth measure which may be combined with an absolute depth measurement at a node or at the balance drive 35.

[0235] Figure 9 illustrates an interesting solution where the fluid, of the type of the above second fluid, is provided in a housing of a flexible material. The amount of the fluid is not altered in the housing, but the volume in which the fluid sits is varied. To the left, the housing material is wound on to a core element and more or less emptied from the fluid by rollers to reduce the inner volume of the housing.

[0236] Then, when the volume changes, so does the density and the buoyancy, whereby the variation of the housing volume will vary the buoyancy.

[0237] Then, this manner of varying the buoyancy may be used as an alternative to those described above.24244EP00

[0238] 28

[0239] Figures lOa-lOc illustrate relations between pressure, temperature and Vratio which is the ratio of second space to VolMax , e.g. the second fluid according to the present invention. For given amount of second fluid, density can be calculated as Vratio * VolMax I second fluid mass.

[0240] Taking n-Propane as an example, with Tmin=-2°C, Tmax=30°C, Pmin = 3 bar (absolute) and Pmax= 12 bar (absolute). In that case SFmassMin = 28.3kg. Figures 10a, 10b and 10c show how pressure (y-axis) is related to Vratio (x-axis), at different temperatures for amounts 28, 43 and 105 kg placed in VolMax=4,5 m3of n-Propane over the -2 to 30°C and 3 to 12 bar absolute. Vratio is defined as the volume of second space divided by VolMax that is the maximum volume of second space in a given buoyancy element.

[0241] Notice that as Vratio decreases, pressure stops increasing when the second fluid enters two phase state (assuming steady state or relatively slow changes). Using such second fluid effectively provides an upper value on pressure for decreasing Vratio. This upper value is temperature dependent as shown for different lines in Figures 10a, 10b, 10c. It is also dependent on fluid type, i.e. type of the second fluid. Hence a selection of fluid type is required for given operational temperature and strength of outer housing wall.

[0242] In Figure 10a, the minimum amount of second fluid SFmassMin is used (28,3 kg) according to selection criteria, i.e. whose vapor pressure is above Pmin at Tmin and whose pressure at Tmax is less that Pmax. In Figure 10a, 28.3kg of n-Propane is assumed and VolMax=4,5 m3.

[0243] In Figure 10b an additional 15kg is assumed, SFmassMin of 43kg of n-Propane is assumed and VolMax=4,5 m3. Figure 10c shows the graph for an amount of 104 kg n-Propane is assumed and VolMax=4,5 m3. These amounts are selected so as to keep the second fluid in two phase state over the entire specified pressure and temperature ranges that are assumed. The selected amount may also be determined such that the Pmin limit is respected even in case of some significant loss of second fluid.

[0244] Selecting a proper working fluid provides a temperature dependent upper bound on Pmax that is much lower than what is required if gas only solution is used without quantity control. This method of pressure control is critical in enabling to select economical material for its buoyancy systems which is sensitive to Pmin and Pmax.

Claims

24244EP0029CLAIMS1. A buoyancy structure comprising a buoyancy element for use within a predetermined temperature range and within a predetermined pressure range and within a predetermined depth range, such as at a predetermined depth at a predetermined temperature, the buoyancy element comprising an outer housing, the buoyancy structure comprising: a fluid reservoir comprising a first, incompressible fluid,a first space and a second space inside the outer housing,a fluid conduit between the fluid reservoir and the first space, a flexible wall portion delimiting the first space from the second space, the second space being confined by the flexible wall inside the outer housing, a second fluid is provided in the second space,a pump configured for driving first fluid between the fluid reservoir and the first space,wherein the second fluid is in both a liquid and a gaseous phase and has a vapor pressure, andwherein at an operation pressure corresponding to a pressure exerted on the outer housing by the surrounding water, preferably at a maximum operation depth and at a minimum operation temperature, the vapor pressure is within a predetermined level below the operation pressure, andwherein the second fluid is in thermal equilibrium with the surrounding water, such as within the predetermined temperature range.

2. A buoyancy structure according to claim 1, wherein at the maximum operation depth and at the minimum operation temperature, the second fluid in the second space has a pressure above the operation pressure.

3. A buoyancy structure according to any of the preceding claims, wherein in the thermal equilibrium, a difference between the temperatures of the second fluid and the surrounding water is less than 5 degrees Celsius, preferably less than 2 degrees Celsius, preferably less than 1 degrees Celsius.

4. A buoyancy structure according to any of the preceding claims, further comprising a valve between the first space and surroundings of the outer housing.24244EP00305. A buoyancy structure according to any of the preceding claims, wherein a ratio between the liquid and the gaseous phases is variable based on the driven first fluid between the fluid reservoir and the first space by the pump.

6. A buoyancy structure according to any of the preceding claims, wherein a mass of the second fluid in the second space is constant.

7. A buoyancy structure according to any of the preceding claims, comprising a control unit configured to activate the pump and to control a flow of the first fluid through the fluid conduit.

8. A buoyancy structure according to claim 7, wherein the control unit is configured to vary buoyancy based on, such as solely, hydraulic displacement of the first incompressible fluid.

9. A buoyancy structure according to any of the preceding claims, comprising one or more of the following sensors: depth sensor, pressure sensor, temperature sensor, flow sensor.

10. A submersible structure, the structure comprising a plurality of buoyancy elements according to any of the preceding claims, the fluid conduit being provided between the fluid reservoir and the first space of each buoyancy element.

11. A submersible structure according to claim 10 , further comprising a controller, such as a control unit, configured to determine a buoyancy of each buoyancy element.

12. A submersible structure according to any of the preceding claims 10-11, further comprising a load bearing structure attached to each buoyancy element.

13. A submersible structure according to any of the preceding claims 10-12, wherein the pump is configured to adjust buoyancy of each of the buoyancy elements in response to an increase or decrease in weight of the load-bearing structure.

14. A method of operating buoyancy structure comprising a buoyancy element comprising an outer housing, the buoyancy structure comprising:a fluid reservoir comprising a first, incompressible fluid,a first space and a second space inside the outer housing,a fluid conduit between the fluid reservoir and the first space,24244EP0031a flexible wall portion delimiting the first space from the second space, the second space being confined by the flexible wall inside the outer housing, and a second fluid in the second space,a pump configured for driving first fluid between the fluid reservoir and the first space,the method comprising lowering the structure into a body of water of a first temperature within a predetermined temperature range and at a predetermined depth within a predetermined depth range,wherein the second fluid provides a vapor pressure and is in both a liquid and a gaseous form when at the first temperature within the second space and wherein a pressure is exerted on the outer housing by the surrounding water at the predetermined depth, andwherein the method further comprises controlling a buoyancy of the buoyancy structure by transporting the first fluid, via the pump and the fluid conduit, between the fluid reservoir and the first space, andwherein a temperature of the second fluid stays within the predefined temperature range.

15. A method according to claim 14, wherein the second fluid is provided in the second space at a pressure exceeding the minimum pressure required to prevent buckling of the outer housing at the predetermined depth..

16. A method according to claim 14-15, further comprising opening a valve between the first space and surroundings of the outer housing.

17. A method according to any of claims 14-16, wherein the structure comprises a plurality of buoyancy elements, the controlling step comprising controlling the buoyancy of each individual buoyancy element by transporting the first fluid between the fluid reservoir and the first space of the pertaining buoyancy element.

18. A method according to any of claims 14-17, further comprising the step of determining a buoyancy of the buoyancy element and / or the step of controlling a buoyancy of the buoyancy element.

19. A method according to any of claims 14-18, wherein the structure further comprises a load bearing structure, where individual portions of the load bearing structure is attached to24244EP0032each buoyancy element, the method further comprising the step of determining a weight of the portion of the load bearing structure attached to at least one of the buoyancy elements.

20. A method according to any of claims 14-19, further comprising the step of selecting a second fluid suitable for providing a vapor pressure within a predetermined pressure range and the predetermined temperature range and / or determining a minimum amount of second fluid required, for example when a first fluid volume is zero, such that the second fluid provides vapor pressure, such as the second fluid is in both the liquid and the gaseous phase, within the predetermined pressure range and within the predetermined temperature range.

21. A buoyancy structure comprising a buoyancy element comprising an outer housing, the buoyancy structure comprising:a first space containing a first fluid and a second space containing a second fluid inside the outer housing,a flexible wall portion delimiting the first space from the second space, the second space being confined by the flexible wall inside the outer housing, and a valve between the first space and surroundings of the outer housing,wherein the first fluid has a vapor pressure, so that the first fluid is in both a liquid and a gaseous phases, and the vapor pressure corresponds to or above a pressure exerted on the outer housing by the surrounding water at a predetermined depth and a temperature.

22. A buoyancy structure comprising a buoyancy element comprising an outer housing made of a flexible material and defining an inner space, the buoyancy structure comprising:a first fluid in the inner space,means for varying a shape of the outer housing to vary a volume of the inner space,wherein the first fluid has a vapor pressure, so that the first fluid is in both a liquid and a gaseous phases, and the vapor pressure corresponds to or above a pressure exerted on the outer housing by the surrounding water at a predetermined depth and a temperature.

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