GB2602284A

GB2602284A - An offshore floating support

Info

Publication number: GB2602284A
Application number: GB2020353.5A
Authority: GB
Inventors: Paul O'flynn Donal; Smith David
Original assignee: Individual
Current assignee: Individual
Priority date: 2020-12-22
Filing date: 2020-12-22
Publication date: 2022-06-29
Also published as: GB202020353D0; WO2022136524A1

Abstract

An offshore floating support, comprising a submersible base extending from which is an elongate tower riser 14 for supporting a wind turbine, the base including two or more independent enclosures 16 adapted to provide buoyancy to the support when the base is submerged; and two or more external platforms 18 each located between an adjacent pair of the independent enclosures and adapted to receive and retain ballast thereon. Preferably the enclosures and external platforms have a substantially wedge-shaped footprint increasing in width with increasing radial distance from the central axis, and are disposed in a circular array about the central axis. There may be a ballast distribution system, such as a pump, operable to manage ballast levels within the two or more enclosures. A wave deflection system may comprise one or more deflector plates extending from the tower riser, and a current deflection system may be defined by profiled edges on the base.

Description

An Offshore Floating Support

Field of the invention

The present invention relates to an offshore floating support, in particular a support comprising a submersible base extending from which is an elongate tower riser for supporting a wind turbine or the like, although many other alternative applications are envisaged.

Background of the invention

Offshore installations such as used in the oil and gas industry, in addition to offshore floating wind turbines, employ various platforms on which the installation is located, and generally take the form of a piled structure on which the hardware is supported, a floating platform which may be anchored or otherwise secured in place, or a caisson type system which may be adhered to the seabed by generating a vacuum within the caisson base of the platform or by the introduction of large quantifies of ballast. Other platform types include the semi-submersible platform and the spar platform. The semi-submersible structure is susceptible to high waves and storm conditions while the Spar system requires deep port infrastructure for the construction due to the large draft.

These platforms are generally large in scale and require significant infrastructure and logistics operations to support their construction and deployment. Once deployed the structures can be exposed to extreme weather conditions, in particular large waves and wind which are amplified during storms and other extreme weather events. As a result the platforms must be designed for these events which are relatively infrequent but result in increased manufacture and transportation costs.

It is therefore an object of the present invention to provide an offshore floating platform which 30 reduces the impact of the above mentioned disadvantages.

Summary of the invention

According to the present invention there is provided an offshore floating support comprising a submersible base defining two or more independent enclosures adapted to provide buoyancy to the support when the base is submerged; two or more external platforms each located between an adjacent pair of the independent enclosures and adapted to receive and retain ballast thereon; and a tower riser extending from the base.

Preferably, the enclosures and the external platforms are circumferentially disposed about a central axis.

Preferably, the enclosures and the external platforms are disposed in a circular array about the 5 central axis.

Preferably, the enclosures are equally distributed about the central axis.

Preferably, the enclosures have a substantially wedge shaped footprint increasing in width with 10 increasing radial distance from the central axis.

Preferably, the external platforms have a substantially wedge shaped footprint increasing in width with increasing radial distance from the central axis.

Preferably, the support comprises a ballast distribution system operable to manage ballast levels within the two or more enclosures.

Preferably, the ballast distribution system comprises a pump operable to displace ballast from one enclosure to another.

Preferably, the ballast distribution system comprises a control unit and one or more sensors operable to monitor the orientation and/or motion of the support and to actively manage the ballast levels within the two or more enclosures to stabilise support.

Preferably, the control unit comprises a receiver operable to receive externally transmitted local environmental data.

Preferably, the support comprises a wave deflection system.

Preferably, the wave deflection system comprises one or more deflector plates extending from the tower riser below an upper end thereof Preferably, the support comprises a current deflection system.

Preferably, the current deflection system is defined by one or more profiled edges on the base.

Preferably, the profiled edges are chamfered.

Preferably, the support comprises a mooring system to secure the support to the seabed.

Preferably, the base comprises a cast concrete structure.

Preferably, the tower riser comprises an elongate hollow cylinder.

Preferably, the tower riser comprises a cast concrete structure.

Preferably, the base and tower riser are a single cast concrete structure.

Preferably, the base has a substantially circular or multilateral footprint.

Preferably, the base has a triangular, rectangular or hexagonal footprint.

As used herein, the term "tower riser" is intended to described both the base or foundation for a larger tower structure such as a steel tower or the like which may be secured to the tower riser and on which a wind turbine or the like may be supported, in addition to meaning a fully formed tower 15 structure to which a wind turbine or the like may be directly mounted or otherwise secured.

Brief description of the drawings

The present invention will now be described with reference to the accompanying drawings, in which: Figure 1 illustrates a perspective view of an offshore floating support according to an embodiment of the present invention; Figure 2 illustrates a plan view of the support shown in Figure 1; Figure 3 illustrates a side view, in outline, of the support shown in Figures 1 and 2; Figure 4 illustrates a front elevation of the platform shown in Figures Ito 3, with an outer wall of an 30 enclosure is omitted to reveal the interior of the enclosure: Figure 5 illustrates a perspective view from beneath of the support shown in Figures 1 to 4; and Figure 6 illustrates various alternative configurations for the support of the invention.

Detailed description of the drawings

Referring now to Figures 1 to 5 of the accompanying drawings there is illustrated an offshore floating 40 support, generally indicated as 10, for use is securing or supporting various large scale marine applications such as wind turbines (not shown) or the like thereon.

The support 10 comprises a base 12 and an elongate tower riser 14 extending upwardly therefrom, and onto which a wind turbine (not shown) or other marine application may be either directly located, although the preferred construction technique involves the subsequent additional of a full height tower structure (not shown) such as a hollow steel or reinforced concrete mast or the like to the tower riser 14 and onto which tower structure (not shown) the wind turbine or other marine application is then mounted or otherwise secured as described further below. It will of course be understood that the base 12 may also be utilised to carry or otherwise support one or more elements of the marine application. The support 10 is designed, as described in detail hereinafter, to be deployed in a body of water, most likely an offshore marine deployment, with the base 12 submerged below the water surface but buoyant, such that the tower riser 14 projects out of the water to carry the wind turbine or other application. This design is inherently stable, having a relatively large mass in the form of the base 12 at the lower extremity, from which projects a central support in the form of the tower riser 14. However the support 10 is additionally operable to actively monitor and control stability such as to maintain a desired orientation regardless of the external environmental forces acting thereon. The support 10 may also be moored to the seabed for additional stability and to maintain a fixed position, as will be described hereinafter.

In the preferred embodiment illustrated the base 12 and the tower riser 14 are cast from concrete, preferably reinforced concrete, which provides a number of benefits over alternative materials and construction techniques as detailed below. The tower riser 14 is preferably hollow and tapers towards the upper end in order to reduce the overall weight of the tower riser 14. The base 12 comprises at least two, and in the embodiment illustrated, four discrete hollow enclosures or tanks 16 equally circumferentially distributed about a central vertical axis AA of the platform 10. In the preferred embodiment each enclosure 16 has a wedge shaped footprint, increasing in width with increasing radial distance from the central axis AA, although other configurations may be employed. Referring to Figure 4 an outer circumferential wall of the central enclosure 16 has been omitted for illustrative purposes in order to reveal the internal structure of the enclosure 16. In use the enclosures 16 may be partially filled with ballast, preferably a displaceable medium, and most preferably water from the surrounding body of water in which the support 10 is deployed. As described below, this ballast is preferably only added to the enclosures 16 once the support 10 has been transported to the intended deployment site, which may be a significant distance offshore, for example in the region of 150km. Thus by omitting the ballast during transport the weight and therefore energy required to transport the support 10 is significantly reduced. However there may of course exist circumstances in which it is preferably to include some level of ballast prior to reaching the deployment site, for example to provide stability or a desired draught during the transport phase.

Located between adjacent pairs of the enclosures 16 are openly accessible platforms 18 which preferably fully span the space between the adjacent enclosures 16, and as a result also have a substantially wedge shaped footprint in the preferred embodiment. The platforms 18 are preferably positioned at or adjacent a lower end of the base 12 such as to define an externally accessible compartment framed by the platform 18 and opposed sidewalls of the adjacent enclosures 16, into which compartment solid ballast may be located following deployment of the support 10, again as will be detailed hereinafter. An outer wall 20 extends between and connects the adjacent enclosures 16 in order to provide a barrier to retain ballast located into the compartment, but no upper wall or roof is present, thereby allowing access to the compartments from above, permitting ballast to be introduced as required, and preferably only once the support 10 has been located at the intended deployment site. The outer wall 20 is preferably cast as pad of the base 12 but could be formed from a separate component suitably secured in place. Such an arrangement could allow the wall 20 to be temporarily removed should it be necessary to remove ballast located in the compartment, for example were it necessary to decommission the support 10 or transport to an alternative deployment site. The foremost wall 20 in Figure 1 is illustrated as being transparent for illustrative purposes only.

The enclosures 16 and platforms 18 are preferably arranged in a circular array around the central axis AA, and are arranged to provide an equal weight distribution about the axis AA such that the support 10 will tend to adopt a substantially upright or vertical orientation in the absence of destabilising external forces. The support 10 utilises a combination of buoyancy, along with static and active ballast, in order to maintain stability in use and under harsh environmental conditions. As used herein the terms "upright" and "vertical" are intended to mean that the support is oriented with the central axis AA extending substantially vertically, with the tower riser 14 projecting upwardly from the base 12.

The support 10 is designed such that the plurality of enclosures 16 provide sufficient buoyancy to allow the base 12 to be submerged a relatively short distance below the surface of the body of water, but buoyant at the desired depth such as to effectively have a neutral buoyancy, with the tower riser 14 then projecting above the surface of the water. The tower riser 14 may be dimensioned to project the necessary height above the surface of the water for the particular application, for example to carry a wind turbine at a suitable height above the water to ensure proper operation and blade clearance above the water. In the preferred arrangement the tower riser 14 is provided as a foundation for a full height hollow steel tower structure, and is dimensioned accordingly. In an exemplary embodiment the support 10 is designed such that on deployment the base 12 is submerged to a level where an upper surface of the base 12 is located approximately 30m to 50m below the surface of the water, and in the case of an offshore installation at that depth below the mean sea level. It will be appreciated that this depth may be varied as required by the application. The enclosures 16 are also designed to retain a displaceable or active ballast therein, for example water or the like, whereby the amount of ballast within each of the enclosures 16 may be actively varied on site, and preferably automatically as described hereinafter.. This allows the distribution of ballast about the central axis AA of the support 10 to be varied in order to improve stability and/or correct the orientation of the support 10 in real time.

In order to facilitate the above active stabilisation the support 10 comprises a ballast distribution system 22 which is operable to add or remove ballast, preferably seawater, from one or more of the enclosures 16. The ballast distribution system 22 may include any suitable hardware to achieve the displacement of ballast, for example one or more pumps (not shown) associated with each enclosure 16 and which may be arranged to pump surrounding seawater into the enclosures 16 or out of the enclosures 16 into the surrounding water. Additionally or alternatively the ballast distribution system may be operable to displace ballast from one enclosure 16 directly into another enclosure 16, for example transferring ballast from one side of the base 12 to the other in order to counteract a vertical offset of the support 10 arising from external forces acting on the support 10. Referring to Figure 2, in the exemplary support 10 the ballast distribution system 22 comprises a conduit 24 extending from a manifold (not shown) located internally of the tower riser 14 and into a respective enclosure 16, via which water can be pumped into or out of the enclosure. The manifold facilitates selective fluid communication between the enclosures 16 allowing ballast water to be pumped between enclosures 16 as required in order to maintain the stability of the support 10. It will of course be understood that any other functional alternative to the conduits 24 and manifold may be employed. Any suitable power source may be employed for the ballast distribution system 22, for example solar power, a wind turbine if deployed on the support 10, or any other suitable alternative. The ballast distribution system may comprise one or more batteries (not shown) which may be charged from a wind turbine if present, or from onshore power connected to the support 10 through any suitable means. Power transmission cables may be extended between an onshore station and the support 10, particularly where the support 10 is carrying a wind turbine in order to allow the power to be transmitted ashore.

The ballast distribution system 22 thus additionally comprise a control unit (not shown) and one or more sensors (not shown) distributed about the support 10, in order to be capable of monitoring various parameters and enabling feedback control in managing the distribution of the ballast around the enclosures 16. The one or more sensors may include a tilt sensor, wind anemometer, wave height sensor, water/tidal current sensor, etc. The control unit may also comprise a receiver operable to receive externally transmitted data regarding local environmental conditions, which data may for example be obtained by satellite transmission or any other suitable means. The control unit can thus have access to real time environmental data, for example to provide advance warning of a storm surge or the like, and which may allow the support 10 to prepare for such conditions through ballast distribution. Data from one or more of the above sensors can therefore be used to provide feedback control to the ballast distribution system, allowing ballast to be distributed about the enclosures 16 to provide counterbalance and enhanced stability.

The base 12 and tower riser 14 are preferably cast in concrete as a single monolithic structure, although it is also envisaged that the base 12 and tower riser 14 could be fabricated as separate items and subsequently joined by any suitable means. However by fabricating the support 10 as a single cast concrete structure, many benefits can be achieved. Construction of the support can be undertaken closer to the intended deployment site, as fabrication of the support 10 does not require deep port infrastructure. In an exemplary embodiment the support 10 can be manufactured from readily available reinforced concrete and does not require a specialized or dedicated manufacturing site. The support 10 can be manufactured in local dry dock facilities, creating a sustainable structure that supports local employment and avoids excess marine transportation and construction activities. The use of concrete significantly reduces maintenance requirements as a result of the durability of the material, avoiding the requirement for periodic painting or the use of anti corrosion devices such as anode/cathode based systems.

By omitting ballast from within the enclosures 16 and on the platforms 18, in addition to the relative wide base 12, the support 10 has a significantly reduced draft when transporting from a dry dock or other manufacturing centre, and does not therefore require deep water ports, further increasing the number of sites suitable to support construction. In an exemplary embodiment a draft of approximately 5m to 10m is sufficient. The above benefits will therefore significantly reduce manufacturing and transportation costs.

The support 10 is preferably manufactured as close as practicable to the intended deployment site, and most preferably in a dry dock. Once manufacture is complete the dry dock is flooded and the support 10 will be buoyant and floated to a quayside or the like, where a full height tower structure (not shown) can be suitable secured to the tower rise 14, preferably utilising a plug and socket type connection in which a hollow cylindrical steel or concrete tower structure is lowered over the tower riser 14 and secured thereto. This construction technique avoids the requirement for any subsurface works to be carried out in securing the full height tower structure to the tower rise 14, significantly reducing the complexity of the operation. A wind turbine (not shown) or other hardware can be added as appropriate to the tower structure (not shown) once secured to the tower riser 14. While the tower riser 14 could be cast to define the full height tower structure this would add to the cost and complexity of the manufacturing and initial transport process The support 10 is then transported to the deployment site, preferably by floating the support 10 and using one or more transport vessels to tow the support 10 to the deployment site. Once at the deployment site ballast can be introduced to the base 12 in order to achieve the appropriate submersion of the base 12 for the application in question. The support 10 is also preferably moored to the seabed or other suitable anchor (not shown), for example via a number of chains 28 secured to the underside of the base 12. It will be appreciated that the chains 28 or other mooring hardware may be secured to any other suitable location about the support 10, and may be of any other suitable configuration.

The support 10 utilises three type of ballast, which can be classified as permanent ballast derived from the weight of the base 12 and tower riser 14, solid ballast B in the form of suitable material placed on the platforms 18, and active ballast derived from the water or other displaceable material selectively locatable within the enclosures 16 by the ballast distribution system. These ballasts, combined with the buoyancy established by the sealed enclosures 16, allow the support 10 to be positioned at the required submersion and attitude within the water at the deployment site, and to actively manage the stability and there improved performance of the support 10. The platforms 18 allow the relatively easy and accurate placement of ballast thereon in order to avoid damage to the support 10. This ballast B may be brought to the deployment site with the towing vessel, and lowered into position therefrom by any suitable means, for example one or more cranes. Once the solid ballast has been added to the requisite level the support 10 is fully deployed, and the active ballast distribution system can then be activated in order to maintain the orientation and stability of the support 10. The plurality of discrete and isolated enclosures 16 also provide redundancy to the support 10 in the event of damage to one of the enclosures 16. Thus the enclosures 16 effectively act as baffle walls to prevent loss of buoyancy should there be a leak in one of the enclosures 16.

In order to reduce the effects of water current on the stability of the support 10 a current deflection system is integrated into the support 10 in the form of chamfered or otherwise profiled edges 30 on the exterior circumferential edges of the base 12, in particular the upper and lower edges of each enclosure 16 and platform 18. The chamfered edges 30 improve streamlining of the base 12 in order to reduce drag and turbulence, which will also serve to reduce vibrations and reduce tension on the mooring chains 28. Reduced turbulence and vibration on the support 10 will also assist with the deterioration of the turbine blades, thus reducing operation and maintenance costs.

Referring in particular to Figure 3 the support 10 preferably additionally comprises a wave deflection system 32 comprising at least one deflection plate or vane 32 which is provided on the tower riser 14 and projecting radially outward therefrom. The deflection vane 32 preferably fully circumscribes the tower riser 14 in order to provide wave deflection from all directions. The defection system 32 is particularly beneficial when the tower riser 14 is carrying a wind turbine (not shown) or the like as it will act to deflect waves which might otherwise impact the blades of the turbine and negatively effect the performance thereof, in addition to reducing repairs and maintenance costs and time.

Referring to Figure 6 there are illustrated alternative configurations of support 10 in which the base 12 which although preferably cylindrical in shape, may be of any other suitable shape, and the 25 number, shape and configuration of the enclosures and platforms may be varied.

The support 10 of the present invention is therefore of relatively low complexity and cost to manufacture, yet provides an advanced means of actively monitoring and maintaining stability by actively managing the distribution of ballast.

Claims

Claims 1 An offshore floating support comprising a submersible base defining two or more independent enclosures adapted to provide buoyancy to the support when the base is submerged; two or more external platforms each located between an adjacent pair of the independent enclosures and adapted to receive and retain ballast thereon; and a tower riser extending from the base.
2. An offshore floating support according to claim 1 in which the enclosures and the external platforms are circumferentially disposed about a central axis.
3. An offshore floating support according to claim 2 in which the enclosures and the external platforms are disposed in a circular array about the central axis.
4. An offshore floating support according to claim 2 or 3 in which the enclosures are equally distributed about the central axis.
5. An offshore floating support according to any of claims 2 to 4 in which the enclosures have a substantially wedge shaped footprint increasing in width with increasing radial distance from the central axis.
6. An offshore floating support according to any of claims 2 to 5 in which the external platforms have a substantially wedge shaped footprint increasing in width with increasing radial distance from the central axis.
7. An offshore floating support according to any preceding claim comprising a ballast distribution system operable to manage ballast levels within the two or more enclosures.
8. An offshore floating support according to claim 7 in which the ballast distribution system comprises a pump operable to displace ballast from one enclosure to another.
9. An offshore floating support according to claim 7 or 8 in which the ballast distribution system comprises a control unit and one or more sensors operable to monitor the orientation and/or motion of the support and to actively manage the ballast levels within the two or more enclosures to stabilise the platform.
10. An offshore floating support according to claim 9 in which the control unit comprises a receiver operable to receive externally transmitted local environmental data.
11. An offshore floating support according to any preceding claim comprising a wave deflection system.
12. An offshore floating support according to claim 11 in which the wave deflection system comprises one or more deflector plates extending from the tower riser below an upper end thereof.
13. An offshore floating support according to any preceding claim comprising a current deflection system.
14. An offshore floating support according to claim 13 in which the current deflection system is defined by one or more profiled edges on the base.
15. An offshore floating support according to claim 14 in which the profiled edges are chamfered.
16. An offshore floating support according to any preceding claim comprising a mooring system to secure the support to the seabed.
17. An offshore floating support according to any preceding claim in which the base comprises a cast concrete structure.
18. An offshore floating platform according to any preceding claim in which the tower riser comprises a cast concrete structure.
19. An offshore floating support according to any preceding claim in which the base and tower riser are a single cast concrete structure.
20. An offshore floating support according to any preceding claim in which the base has a substantially circular footprint.