Patent Application
20230415855
The invention relates to floating offshore structures to support above sea facilities including, for instance, wind turbines and offshore hydrocarbon exploration & production.
The installation of offshore structures, particularly for tension leg platforms, are highly capital intensive structures and also involve high operational costs.
It is therefore beneficial to increase the efficacy of current design of supporting systems for said structures.
In a first aspect, the invention provides a mooring connection including: a linkage comprising a plurality of articulated parts, adjacent articulated parts of said linkage in pin joint engagement and arranged to pivot at the pin joint about a first axis; wherein at least one pin joint within the linkage arranged to pivot about a second axis, said second axis orthogonal to the first axis.
In a second aspect, the invention provides a gravity anchor for an offshore structure, said gravity anchor comprising; a base for contacting a seabed; interference members arranged to project from the base and arranged to embed into the seabed.
In a third aspect, the invention provides a sub-structure for an offshore structure, the sub-structure comprising: an inlet and an outlet, both positioned above water level; said inlet and outlet in fluid communication through an air flow path; said air flow path having at least a portion below the water level; wherein the air flow path is in heat transfer communication with the water, and arranged to transfer heat from said air flow to said water.
It will be appreciated that, whilst each of the aspect may be used together for use with a floating platform, equally, each aspect may be used individually. The designer of a floating platform may therefore improve the construction and/or operation of a floating platform by using any one, or a combination, of the various aforementioned aspects and achieve a superior result to that of platforms according to the prior art. Thus, the use of any of these aspects of the invention is not contingent on using any of the other aspects.
It will be convenient to further describe the present invention with respect to the accompanying drawings that illustrate possible arrangements of the invention. Other arrangements of the invention are possible and consequently, the particularity of the accompanying drawings is not to be understood as superseding the generality of the preceding description of the invention.
For a floating offshore structure, a typical mooring line fixed connection to the hull is via padeye or equivalent. For such connections, the padeye can represent a weak link where cracks may propagate. A padeye type connection may also be weaker in out of plane moments. Hence for long term high intensity load cycle applications with stochastic loading (hence cyclic loading also on its weaker axes), padeye type connections may not be suitable.
The adapter plates 20 may be short 105 or long 110 and can be fabricated to any prescribed length, as shown in
The TLP interface 25 engages with a twisted Y-link 30 according to the present invention. The Y-link comprises a bifurcated flange at a first end for receiving a single flange therebetween. At the opposed end, the Y-link has a single flange. Where the Y-link differs from the prior art is that each end pivots about orthogonal axes 50, 55, 60. The Y-link then connects 40 to the adaptor plate 20 to transfer tensile load from the interface 25 to the mooring line 15. Thus, regardless of the direction in which the structure moves, there is free rotation about the two principal axes 50, 55, 60 within the horizontal plane and so redistributing load away from a weaker axis and consequently providing articulation about each horizontal axis.
When considering conventional TLP construction, the use of steel tendons for mooring lines is uniformly adopted. Not only is the initial capital expense significant, corrosion problems and general maintenance represent substantial life cycle costs also.
To this end, in one embodiment, the TLP includes the application of composite and/or polymer type rope/line as tendons for the TLP. Composites fibres may be Kevlar, Aramid, Polyester, HDPE, PP, nylon, UHMWPE or carbon.
Apart from the superior corrosion performance, composite and polymer ropes, having a specific gravity close to 1, are also buoyant or only slightly negatively buoyant. With the self-weight of a steel tendon contributing to the over design and extensive installation regime of offshore structures, the buoyancy benefits of polymer rope represent a reduction in sizing of other components, leading to a holistic reduction on capital expenditure and offshore operations risks.
As shown in
Gravity based anchor design is unsuitable for a sea floor having soft clay and weak soils. The main issues faced is the settlement and sliding of the gravity anchor which will cause the floating structure to be non-functional, lose station-keeping or become unstable and is a risk to assets in its vicinity such as in Oil and Gas development areas where there are many pipelines and marine cables around its' vicinity. Major sliding of gravity anchor may cause catastrophic disasters leading to pipeline burst or cable breakage. On the other hand, if fully enclosed skirts are utilized to enhance lateral stability (and vertical capacity), there may be challenges related to proper soil consolidation, egress of expulsed soil from underneath the gravity based anchor due to immediate settlement, coupled-suction effects which may impede proper ‘sitting’ of the gravity anchor and pose major long-term behaviour uncertainties. This is especially true for thick layer of soft topsoil, having a high proportion of mud, clay and/or peat without site preparation for shallow foundations.
In overcoming the problems with lateral movements whilst engaged with soft soil on the seabed, the present invention includes several interference members arranged to increase the lateral resistance of the gravity anchor and so hinder sliding. The interference members are arranged to embed within the soft soil of the seabed and so create greater interference with the soil of the seabed through a greater bearing surface as compared to only the friction of the base of the gravity anchor.
In
In an alternate embodiment, the skirts may be a single member on each side of the gravity anchor, however, in this embodiment each skirt member includes a slit 150 separating the skirt members 145, 155 through which the soft soil of the seabed can flow. These slits 150 allow the egress or expulsion of soil particles following immediate settlement and consolidation in order for the gravity anchor 140 to find an equilibrium position relative to the seabed. This feature is especially crucial in the case of soft soil such as clay, mud and/or peat. Having the gravity anchor according to the present invention to achieve an equilibrium position permits better and more predictable embedment in soft soil which reduces the risk of excessive differential settlement and unpredictable long-term consolidation.
In a further embodiment, additional skirt members 185 may be mounted to the gravity anchor base 170 and not merely about the periphery, in order to provide greater resistance 180 against lateral sliding and on-bottom stability. It is the premise of this feature that the additional skirt members possess a depth that is less than or equal to the periphery skirts. The additional skirt members 185 may also be included for purposes of structural stiffening or strengthening of the gravity anchor base 170 in addition to providing greater resistance 180 against sliding and on-bottom stability. To this end, whilst additional skirts members may be positioned to prevent or limit lateral movement, reinforcing skirt members may be used on the underside of the core which are positioned to add reinforcement, and so may not be aligned to prevent or limit lateral movement, but instead to provide a structural function.
Further, the gravity anchor 140 may benefit from buoyancy bag assistance for load out and/or transportation of the gravity anchor to open water via wet tow in order to meet draft or Under Keel Clearance (UKC) requirements of yards/ports/quaysides/channels/shallow water regions.
It will be appreciated that the projections may be more easily embeddable into the seabed as compared to the skirt members. The number of projections used will therefore depend upon a balance between lateral resistance 200 and the ability to embed under the weight of the gravity anchor 140.
In a further embodiment, the projections 194 maybe in sliding engagement with the gravity anchor core 142, with the core 142 having apertures 192, which may include ducts, that allow sliding of the projections 192 relative to the core 142. Sliding may then be controlled by the use of a shear grips 195 mounted to each projection 194. It will be appreciated that the consistency of the seabed may vary about the gravity anchor 140 and therefore some projections may meet greater resistance to penetration than others. If the soil of the seabed in one area is considerably stiffer than elsewhere, the projection 194 may buckle and potentially damage the gravity anchor 140. Further, the gravity anchor may not sit flush on the seabed due to the lack of penetration of one or more projections that are not fully embedded. Thus, in this further embodiment the a shear grip 195 may berated to resist an applied axial force to each projection. For instance, each shear grip 195 may be rated for a release force equal to the gravity anchor weight divided by the number of projections. A safety factor may or may not apply. Such a safety factor may include preventing the shear grip from releasing on impact, and thus a creep factor may also be adopted to prevent release on impact of the gravity anchor contacting the sea floor.
If one projection 205A exceeds the rated force due to stiffer soil resisting penetration, the shear grip will release and push the unpenetrated length 205B of the projection upwards thus allowing the gravity anchor to settle flush on the seabed. It will be noted that even a partially penetrated projection 205A may still provide sliding resistance 210. In a still further embodiment of the interference member invention,
In the equatorial regions/tropical countries, the above water portions of offshore structures, including drilling platforms and wind turbine towers, may experience an unwanted heat build-up due to high ambient temperature, sun radiation, etc. Aside from being a heat related safety hazard, this is not favourable for temperature sensitive equipment such as converters/batteries, to name a few. To date the conventional solution involves energy intensive options such as air conditioning systems/HVAC.
Capturing the air may be through naturally or forcefully directing wind into the sub-structure. For instance, movable louvres arranged to rotate into the direction of the wind may be used and to direct the air flow downward into the sub-structure.
Alternatively, fans along the fluid path may draw an air flow into the sub-structure.
Further, the sub-structure may be adapted, or purposely built, to provide fins and other heat exchanging devices to optimise the heat dissipation from the heated air to the cooler sub-structure. This can be in the form of dual purpose structural members such as in the case of a floating structure, whereby the hull stiffeners are used in dual purpose as both structural reinforcements as well as cooling fins/protrusions.
| Number | Date | Country | Kind |
|---|---|---|---|
| PI2020005158 | Oct 2021 | MY | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/MY2021/050082 | 10/1/2021 | WO |
