Field of invention

The invention relates to unmanned underwater vehicles, and more specifically to subsea autonomous shuttle systems.

Background

Research Disclosure 662093 (published 20 May 2019) describes a subsea shuttle system, using autonomous subsea shuttles for transportation and storage purposes. Research Disclosure 677082 (published 21 August 2020) provides further detail regarding possible shuttle structure and support, applications, e.g., on/offloading of a payload, and the propulsion system of the subsea shuttle.

Statement of invention

According to a first aspect of the invention, there is provided an unmanned underwater vehicle, comprising: an outer hull defining an internal volume; a pressure communication channel between the internal volume and the exterior of the outer hull, arranged to control the pressure in the internal volume based on the exterior pressure; an inflatable cushion provided outside the hull and at the bottom side of the underwater vehicle, wherein the inflatable cushion is arranged between the hull and the seabed when the vehicle is landed on the seabed; a first fluid pump and fluid conduit between the first fluid pump and the inflatable cushion, for inflating or deflating the inflatable volume.

Optionally, the inflatable cushion is at least partially shaped as one of: a torus; a bladder; a sheet sealingly attached against the hull.

When the inflatable cushion is at least partially shaped as a torus, the vehicle may further comprise a second pump and a fluid conduit between the second pump and a central cavity defined by the torus, for pumping seawater out of the central cavity or into the central cavity. The vehicle may further comprise a barrier protruding from the hull and suitable for extending into the seabed when the vehicle is landed and defining an enclosed volume, and wherein the enclosed volume is inside said central cavity, or encompasses said central cavity. The barrier may be retractable into the hull, or, alternatively, be arranged underneath the inflatable cushion.

When the inflatable cushion is a sheet, the vehicle may further comprise a rim for sealingly receiving the sheet.

The underwater vehicle may further comprise one or more detectors for detecting the distance between the vehicle and the seabed, and/or a pressure sensor arranged to measure the pressure within the inflatable cushion. A controller may be provided, arranged to control the first fluid pump. The controller may further be arranged to receive a signal from the one or more detectors and/or the pressure sensor.

According to a second aspect of the invention, there is provided a method of landing an unmanned underwater vehicle, wherein the vehicle comprises an outer hull defining an internal volume and a pressure communication channel between the internal volume and the exterior of the outer hull; the method comprising: inflating an inflatable cushion provided outside the hull and at the bottom side of the underwater vehicle before landing by pumping fluid into the inflatable cushion with a first fluid pump and through a fluid conduit between the first fluid pump and the inflatable cushion.

The inflatable cushion may have a toroidal shape and the vehicle may further comprise a second pump, the method may further comprise pumping seawater out of, or into, a central cavity defined by the toroidal shape.

The method may further comprise lowering a barrier into the seabed.

The method may further comprise detecting the distance between the vehicle and the seabed. The method may further comprise detecting the pressure within the inflatable cushion. The method may further comprise: in response to said detecting, adjusting one or more of: the inflating, the buoyancy, the landing or take-off process, a loading or un-loading process.

Drawings

Some embodiments of the invention will now be described by way of example only and with reference to the accompanying drawings, in which:

Figure 1 is a vertical cross section through a schematic drawing of a subsea shuttle;

Figure 2 is a vertical cross section through a schematic drawing of a landing and support arrangement;

Figure 3 is a vertical cross section through a schematic drawing of a cushion;

Figure 4 provides different schematic views of a cushion;

Figure 5 is a vertical cross section through a schematic drawing of a suction skirt; and Figure 6 is a method diagram.

Specific description

Figure 1 illustrates a schematic underwater vehicle. The underwater vehicle (or ‘shuttle’) may be an autonomous underwater vehicle (AUV), or a remotely operated underwater vehicle (ROV). The vehicle comprises an outer hull 10, having a hydrodynamic shape to reduce drag. An elliptical outer hull 10 is shown in Figure 1, but other hydrodynamic shapes known in the art are suitable. Within the outer hull 10, a cargo container or payload 12 is arranged. The payload may be a fluid tank, or could be instrumentation for surveying the subsea environment, or any other desirable payload. The cargo 12 may be fixed within the outer hull 10 using a frame or other rigid supports (not shown). In this way, a space between the outer hull 10 and cargo 12 is formed. The outer hull 10 has a channel 14, which is in fluid communication, or pressure communication, with the surrounding seawater when the vehicle is submerged. When the vehicle is submerged, the space between the outer hull 10 and cargo 12 at least partially filled with seawater, depending on the net buoyancy requirements. In some embodiments, a part of the outer hull 10 volume is occupied by one or more compartments for containing gas (e.g. ballast tanks). In some embodiments, the channel 14 is selectively closed (e.g. via operation of a valve) to allow or block fluid communication through the channel.

Although the word ‘sea’ and ‘seawater’ are used throughout, these may equally be understood as ‘lake’ and ‘freshwater’, respectively, and the invention is envisaged to be used in any large body of water. Similarly, when the words ‘seabed’ or ‘sea surface’ are used, this is not intended to be limited to a sea in a strict sense but should also be understood to cover ‘ocean bed’ or ‘ocean surface’, or similar terms for any large body of water.

At the stern (back end) of the vehicle, a propeller 16 is provided. The propeller is coupled to a power source and control unit (not shown) to enable autonomous and/or remote operation of the vehicle. An electric power source is preferably used. In some embodiments, the vehicle includes a buoyancy controller 18. The movement in the horizontal direction is generally controlled by the propeller, while the depth position is generally controlled by the buoyancy controller 18. Additional propellers or other drivers, such as water or gas jets, may be provided for further control of the movement and position of the shuttle.

The vehicle structure shown in Figure 1 is different from that of conventional submarines because instead of having a pressure hull maintained at or near to atmospheric pressure to accommodate personnel, the inner structure is maintained at a pressure similar to the external hydrostatic pressure. An advantage of the pressure communication is that a relatively light-weight hull structure can be used. By “similar” to the external hydrostatic pressure, it is meant that the internal pressure is kept suitably close to the external pressure so that the pressure differential dP (i.e. overpressure or under-pressure) is not too large. A slight overpressure may be maintained to ensure that the hull keeps its desired shape and is not deformed by currents or other external pressures. The shuttle may land on the seabed by creating negative buoyancy. A dedicated landing area may be provided which has been prepared in advance, for example by removing obstacles or levelling the seabed. Alternatively, the shuttle may land in an area which has not been prepared for landing in advance. A landing arrangement 20 is provided at the bottom of the shuttle to enable the shuttle to land in different conditions.

The landing arrangement is illustrated schematically in Fig. 2. The arrangement includes one or more inflatable landing cushions 21, a controller unit 22, one or more sensors 23, and inflation pumps 24. Each of these elements will be described in more detail below. Some of the elements may be omitted, and the landing system may still work without the sensors 23, for example.

The inflatable landing cushions 21 comprise an inflatable bladder. Alternatively, a cushion comprises a flexible sheet sealingly attached to the hull, thereby defining an inflatable volume between the flexible sheet and the hull. The inflatable landing cushions are deflated during transport of the shuttle and can be inflated by pumping seawater or another fluid into the cushions when approaching the seabed. Seawater is a preferred inflation fluid as it is readily available. The seawater can be pumped into the cushions by pumps 24, either taking the seawater from the internal cavity of the shuttle which, as mentioned above, is at least partially filled with seawater and in pressure or fluid communication with the surrounding seawater, or by taking seawater from the seawater surrounding the shuttle. In yet another embodiment, a dedicated fluid is taken from a storage tank provided within the hull (not illustrated).

The inflated cushions will be at an overpressure due to the cushions comprising a flexible sheet material. The flexibility of the material will cause a back pressure as it is biased towards a deflated arrangement. The cushions will further be at an overpressure due to the negative buoyancy of the shuttle when landed, because the cushions will be compressed to some extent between the seabed and the shuttle in order to carry out its function of enabling stable landing. The pumps 24 therefore include valves to regulate the inflow and outflow of fluid into the cushions. The valves can also be arranged independently of the pumps.

One or more sensors 23 are provided to monitor one or more of: the distance between the seabed and the shuttle, the orientation of the shuttle; and the profile of the seabed. Examples of sensors are: acoustic, optical, electromagnetic, or a combination thereof. For measuring the distance to the seabed, or the profile of the seabed, an acoustic or electromagnetic signal is emitted and the reflected signal is received and analysed. An optical detector (which may be considered a specific example of an electromagnetic system) may use an illumination source and a camera in the corresponding wavelength range to view the seabed.

The controller unit 22 receives the output of sensors 23 and further sends control signals to pumps 24 and the corresponding valves. The controller may operate in collaboration with the shuttle’s general control system to enable the shuttle to land autonomously, or, alternatively, the controller unit operates in communication with a remote personal or machine operator.

A pressure sensor 25 is further provided within the inflatable cushion, or indirectly connected to the interior of the inflatable cushion by way of a pressure communication channel. The pressure within the hull and outside the shuttle is already monitored by the existing systems of the shuttle, as mentioned previously. By measuring the pressure differential between the inside and outside, the downwards force, or negative buoyancy, can be determined by the controller unit. During loading or off-loading of cargo, or during take-off and landing, this pressure differential is a parameter to monitor, as the sensors 23 may only detect small variations in distance to the seabed while the pressure increase could be large. In response to detected changes in pressure, an action could be taken, such as adjusting the buoyancy or adjusting the loading procedure if there is un-even or excessive pressure in the cushions. The pressure within multiple cushions can be monitored and compared to determine the balance of the shuttle.

As stated above, the inflatable cushion may be an inflatable bladder arranged against the outside of the hull, or it may be a flexible sheet sealingly attached to the hull. The second option is illustrated schematically in Fig. 3 in a vertical cross section. Fig. 3A shows the cushion in deflated state, while Fig. 3B shows the cushion inflated. The outer hull 31 of the shuttle provides one side of the inflatable volume and flexible sheet 32 provides the other side, together forming the cushion. The flexible sheet may include some rubber and other materials, somewhat like an inner tyre, to provide the desired properties of flexibility and strength. Additional protective layers, for example Kevlar layers, may be integrated in the material or provided on the outside to reduce the risk of punctures. A rim or profile 33 receives the sheet 32 in a sealing manner. The shape of the profile seen from the front, i.e. looking at the hull from the outside of the hull, may be oval, circular, rectangular or any appropriate shape and will follow the curvature of the hull. The inlet with valve 34 is illustrated as being arranged to be in fluid communication with the hull, but alternatively the fluid communication may be with the seawater outside the hull as mentioned above.

In yet another example, the cushion may comprise a re-enforced surface where the cushion will make contact with the seabed when landed on the seabed. This may be an area of the sheet made of the same material as the rest of the sheet, but simply thicker. Alternatively, or in addition, the re-enforced surface includes a different material, like an outer tyre of a bike or car, or even one or more steel outer panels. The re-enforces surface will be less flexible than the rest of the sheet, or even not flexible or expandable at all, but the skilled person will be able to optimise the trade-off between overall flexibility or inflatability and strength in the area of contact.

The landing of the shuttle and subsequent resting position on the seabed is primarily controlled by adjusting the negative buoyancy of the shuttle. The inventors have realised that, when in the resting position, the position and orientation of the shuttle can further be secured by the use of a suction skirt. Although the shuttle will be protected from wave motion and weather conditions, there may still be some currents or, in shallow waters, indirect forces from wave motion. Also, during loading or unloading of a cargo, the buoyancy will fluctuate and may inadvertently become positive, in which case an additional means for securing the shuttle to the seabed is desirable. The suction skirt will help secure the shuttle to the seabed. Figure 4 illustrates an example of a suction skirt. The skirt includes an inflatable structure like the landing cushions, but the inflatable structure has a doughnut shape defining a central opening and it is surrounded by a barrier, or has a barrier beneath, which extends into the seabed when the shuttle is landed. A doughnut shape is an everyday term for a torus, but is used herein as an equivalent term. The inflatable structure primarily provides a function similar to that of the cushions of supporting the shuttle hull and controlling the distance between the shuttle and the seabed. The barrier provides a seal around the inflatable structure and defines an enclosed space between the seabed and the shuttle. The pressure within the enclosed space is lowered with a pump, thus creating suction. Figure 5 is a schematic vertical cross section through the suction skirt. The barrier 51 provides a sealing connection between the hull 52 and the seabed 53. The barrier extends into the seabed, in practice to a depth of 50cm to 1m, in order to prevent leak paths and provide a good seal. The barrier 51 may be retractable to prevent disrupting the hydrodynamic shape of the hull during transport. The inflatable structure 54 supports the shuttle. The compression of the inflatable structure will depend on the shape of the seabed, as illustrated in the figure by the left side being more compressed than the right side. A pump 55 is provided for pumping water out of the internal volume defined by the barrier and into the surrounding seawater. Alternatively, the removed seawater can be pumped into the internal volume of the hull 52. An under-pressure will thus be created within the internal volume which helps to secure the shuttle to the seabed. When the shuttle needs to leave, the pump can be run in reverse to create an overpressure to help extract the barrier from the seabed. A pump 56 for inflating the inflatable structure is also provided, and includes valves, like for the landing cushions.

Figure 5 illustrates barrier 51 being arranged around inflatable structure 54, but the arrangement may also be the other way around, whereby the inflatable structure 54 is arranged around barrier 51.

The barrier 51 is illustrated in combination with toroidal inflatable structure 54, but the barrier could also be combined with the other examples of an inflatable cushion, such as the sheet or the bladder.

Any number and combination of suction skirts and inflatable cushions can be used and distributed along the underside of the shuttle, depending on the overall dimensions of the shuttle.

The inflatable cushions may have a shape of a doughnut similar to the shape of the inflatable structure 54, and indeed the suction skirt can be considered as a specific example of a landing cushion with additional elements of the barrier 51 and pump 55 added for additional functionality. The barrier 51 improves the seal between the hull and the seabed, but without the barrier the inflated doughnut shaped cushion will still provide a seal although to a lesser extent. With a barrier 51, pump 55 can establish a reduced pressure within the sealed cavity and subsequently switch off until the pressure difference has dropped to a level requiring a renewed pumping action. Without a barrier 51, the pump 55 can run continuously to maintain a pressure difference between the cavity and the surrounding sea water. The seabed is likely to have an irregular structure, providing many leak paths. The structure and material of the seabed will also determine a particular choice of equipment: if the seabed comprises primarily uncompressed sand then the barrier 51 can relatively easily be inserted into the seabed; if, however, the seabed comprises primarily solid rock, then the barrier 51 cannot be used and instead only a doughnut cushion is employed. At the same time, a flat rock surface would enable a relatively good seal between the seabed and the cushion.

Figure 4 illustrates an alternative arrangement of the suction skirt, whereby the barrier 51 is arranged underneath the inflatable cushion instead of being directly attached to the hull. Figure 4a is a schematic cross section of the shuttle with suction skirt and inflatable cushions, figure 4B is a perspective view of a toroidal cushion used for the suction skirt, and figure 4C is a vertical cross section through a schematic cushion like 4B with a barrier underneath.

By way of example, a method of operating the landing arrangement 20 is now described. The shuttle approaches a desired landing site, for example a site for off loading C02. The central control system and engine control the approach to the landing location. When the shuttle is near the landing site, the buoyancy is adjusted such that the shuttle has a net negative buoyancy. The sensors 23 will start scanning the seabed to determine whether there are any large obstacles preventing a successful landing, in which case a new landing site will be determined. Assuming there are no large obstacles or large slope of the seabed, the shuttle will continue its approach to the seabed. The inflatable landing cushions 21 will be inflated and the suction skirts will be extended and inflated as well. As the shuttle touches down on the seabed, the degree of inflation will be adjusted to balance the shuttle, and a small slope can be compensated by inflating some of the cushions more than others such that the orientation of the shuttle is horizontal, or more horizontal than without compensation. The inflatable structures 54 of the one or more suction skirts are also inflated and the pumps are activated to pull the shuttle towards the seabed. The pressure within the cushion may be monitored to determine the downward forces and orientation of the shuttle, and optionally be followed up by an action such as adjusting one or more of: the inflating, the buoyancy, the landing or take-off process, a loading or un-loading process

Although the invention has been described in terms of preferred embodiments as set forth above, it should be understood that these embodiments are illustrative only and that the claims are not limited to those embodiments. Those skilled in the art will be able to make modifications and alternatives in view of the disclosure which are contemplated as falling within the scope of the appended claims. Each feature disclosed or illustrated in the present specification may be incorporated in the invention, whether alone or in any appropriate combination with any other feature disclosed or illustrated herein.