WO2022118056A1

WO2022118056A1 - Floating installation having a reduced excursion around a desired position

Info

Publication number: WO2022118056A1
Application number: PCT/IB2020/001073
Authority: WO
Inventors: Michel GLOAGUEN; Begnat HEGUIAPHAL
Original assignee: Totalenergies Onetech
Priority date: 2020-12-01
Filing date: 2020-12-01
Publication date: 2022-06-09

Abstract

A floating installation (10) comprising: • - a floating support (16), floating on a body of water (12): • - mooring lines (20), connecting the floating support to a bottom of the body of water; • - at least a dampening structure (22), the dampening structure being moveable and/or extendible with respect to the floating support. Each mooring line is a tensioned or rigid line having a lower end connected to the bottom of the body of water (12). Each mooring line is also connected to the dampening structure, the dampening structure providing a partial mechanical decoupling between the floating support and the mooring line.

Description

Floating installation having a reduced excursion around a desired position

The present invention concerns a floating installation comprising:

- a floating support, floating on a body of water:

- mooring lines, connecting the floating support to a bottom of the body of water.

The installation according to the invention applies to any floating body that has to keep a position as close as possible from a central desired position.

For example, the installation is used to collect fluid recovered from the bottom of a body of water, or and/to produce energy or/and to accommodate people. More generally, the installation is suitable to all types of operations at sea where a limited excursion of the floating body is required to ease the design of equipment connecting the floating body to the sea bottom.

It applies as well to operations at sea where a limited excursion of the floating body is required to ease all surface movements or interactions of other fixed or floating bodies in the vicinity of the floating body.

Such installations generally comprise a floating support anchored in a body of water at a specific location.

Generally, the anchoring of the floating support is done with catenary flexible mooring lines. Each mooring line is connected at its upper end to the floating support and at its lower end to the bottom of the body of water.

The catenary mooring lines are for example connected to the corners of the floating support at the front and at the rear of the floating support.

The catenary mooring lines are generally able to limit the horizontal excursion of the floating support in reference to a central balanced position at a maximum excursion, which can reach 15% of the water depth, even more in some situations.

Such standards of horizontal excursion are generally acceptable at shallow or intermediate depths. However, in deep offshore, depths can range up to 3,000 m and sometimes even 4,000 m, even 5,000 m. At such depths, the floating support is prone to undergo by nature large horizontal excursions, which can be in the order of several hundred meters (typically between 300 m and 600 m).

Consequently, a specific design must be applied on the liaisons (for example all types of risers) between the floating body and the sea bottom or on the liaisons (for example all types of flexible connections) between the floating body and fixed or floating surrounding installations.

Specific procedures have to be applied to organize all surface movements around the surrounding floating objects, vessels or fixed objects to avoid all types of detrimental interactions. Moreover, the catenary mooring lines made of chain, steel or synthetic cable require using expensive winches for their set-up and sometimes, to adjust the tensions during the exploitation of the floating support.

Additionally, in the case of a floating installation collecting fluid, the floating support is at certain times substantially loaded or on the contrary almost unloaded, during the exploitation phase. The corresponding draught variations impact the geometry of the mooring system and consequently its mechanical behavior and its response to the external forces induced by wind, swell and currents.

One aim of the invention is to provide a floating installation in which the horizontal excursion after anchoring is greatly reduced, even in deep offshore locations.

To this aim, the subject matter of the invention is a floating installation of the above type, characterized by:

- at least a dampening structure, the dampening structure being moveable and/or extendible with respect to the floating support; at least one mooring line being a tensioned or rigid line having a lower end connected to the bottom of the body of water, the at least one mooring line being connected to the dampening structure, the dampening structure providing a partial mechanical decoupling between the floating support and the mooring line.

Thanks to the claimed invention, the mooring system functioning based on catenary dampening is partially or preferably totally replaced with a stiffer system comprising at least one tensioned mooring line. Mooring lines remain stiff at all times, and the catenary effect is limited or avoided, which substantially reduces the above-mentioned excursions.

The dampening structure, connected to the mooring lines and partially decoupling the mooring lines from the floating support, absorbs force peaks applying on the mooring system. The dampening structure is adapted to the weather and/or offshore conditions, while limiting excursions of the floating support to a minimum.

The decoupling is sufficient to allow the mooring lines to adopt a constant geometry, length or/and angle under various draughts of the floating support (depending for example on the variation of the volume of fluid held in the floating support).

These effects are enhanced in particular when the mooring lines have a low elasticity (for example in the order of magnitude of steel elasticity), and/or the lines have a substantially neutral buoyancy when immersed in the body of water.

The claimed installation is particularly adapted to deep ocean floors, e.g. greater than 2000 m, for floating supports which must keep a permanent position at the surface of the body of water. Thus, excursions can be reduced to about 1 % to 2 % of the water depth. This minimizes motions of the floating support and thus fatigue of the lines (which can be flexible, partly rigid, or fully rigid) connecting the floating support to the floor at the bottom of the body of water.

In addition, the mooring system is as much as possible independent of the draught variations of the floating support, in particular in case fluid is loaded in the floating support and/or unloaded from the floating support.

The floating installation according to the invention may comprise one or more of the following feature(s), taken solely, or according to any technical feasible combination:

- the dampening structure is mounted in the floating support or on the floating support, an upper end of the mooring line being connected to the dampening structure or mechanically interacting with the dampening structure;

- the floating support has an outer surface, the dampening structure being mounted on the outer surface;

- the floating support comprises an inner compartment at least partially filled with a liquid, the dampening structure being at least partially received in the inner compartment:

- the inner compartment is at least partially filled with water from the body of water, the floating structure comprising at least a valve fluidly connecting the inner compartment to the body of water;

.- the dampening structure comprises at least a buoyant column, the buoyant column, preferably comprising a caisson filled with gas or/and ballast;

- the dampening structure comprises at least a spring, in particular a compression spring, the spring being able to generate a restoring force biasing the floating support towards a center position;

- the dampening structure is translatable along a vertical axis with respect to the floating support;

- the dampening structure comprises a mechanical or hydraulic dampener having a base attached to the floating structure and a dampening member movable with regards to the base, the dampening member being mechanically biased by the mooring line.;

- the dampening structure comprises at least a dampener mounted in line on the mooring line;

.- the floating structure has a variable draught, the mooring line having at least one upper linear section having a top, the upper linear section making an inclination angle with a vertical axis passing by the top of the upper linear section, the floating installation comprising a height variation compensation system able to maintain constant the height of the top of the upper section or/and the inclination angle of the upper section when the draught of the floating structure varies;

- the mooring line material has at least one upper rigid section having a stiffness greater than 1 .5 x 10⁹ N/m;

- the mooring line has an apparent linear weight in the body of water smaller than 10kg/m; the mooring line has a linear inclined tensioned top section connected to the dampening structure;

- the floating support is a barge, a FPSO, a FLNG, a FSU, an offshore power production support advantageously bearing at least a wind turbine or at least a solar panel, or/and an offshore housing or facility support;

- the floating installation comprises at least two dampening structures, mounted on or in the floating support on opposite sides of the floating support, and for each respective dampening structure, at least one mooring line having a lower end connected to the bottom of the body of water and an upper end connected to the respective dampening structure to move jointly with the respective dampening structure;

- the floating installation comprises a guide fixedly mounted on the floating support, the dampening structure being movably mounted on the guide;

- the or each mooring line is formed of one single rigid section or comprises a plurality of rigid sections connected end to end to one another;

- horizontal and/or vertical excursions of the floating support are less than 3,5 %, preferably less than 2,5 %, more preferably less than 1 ,5% of the water depth below the floating support ;

- the tension on the top section of the at least one mooring line are greater than 10 000 N, in particular greater than 1 000 kN and in particular between 5 000 kN and 20 000 kN ;

- the pretension in the top section of the at least one mooring line is smaller than 40% of the minimum breaking load (MBL) of the top section, in particular smaller than 10% to 15% of the minimum breaking load (MBL) of the top section, when installing the mooring lines.

The invention will be better understood, upon reading the following description, given solely as an example, and made in reference to the appended drawings, describing preferred embodiments of the invention, in which:

- [Fig 1] figure 1 is an elevation view of a first floating installation in its central balanced position;

- [Fig 2] figure 2 is a view similar to figure 1 , in a position shifted in a first direction from the central position; - [Fig 3] figure 3 is a view similar to figure 2, shifted in an opposite second direction;

- [Fig 4] figure 4 is a view similar to figure 1 , where the buoyancy of the floating support is greater, its draught being increased;

- [Fig 5] figure 5 is a view of a variant of the installation of figure 1 ;

- [Fig 6] figure 6 is a view of another variant of the installation of figure 1 ;

-[Fig 7] is a view partially in section of another installation according to the invention;

-[Fig 8] is a view similar to figure 7 of another installation according to the invention;

-[Fig 9] is a view similar to figure 7 of another installation according to the invention, with a deep draught and;

-[Fig 10] is a view of the installation of figure 9, when the draught is smaller.

A first floating installation 10 according to the invention is shown in figure 1. The installation 10 is intended for carrying out operations at the surface of a body of water 12 on a stable floating support 16.

The operations include for example fluid exploitation, in particular collection and storage of fluid produced from the bottom 14 of the body of water 12, and/or fluid treatment, for example purification, separation or/and liquefaction.

In a variant, the operations include energy production, for example from at least a wind turbine or/and at least a solar panel mounted on the floating support 16.

In another variant, the installation 10 comprises facilities, in particular accommodations or plants mounted on the floating support 16.

The body of water 12 is a lake, a river, a sea, and/or an ocean. The depth of the body of water 12, at the floating installation 10 is for example greater than 1500 m and is notably comprised between 1500 m and 5000 m.

As shown in figure 1 , the floating installation 10 comprises the floating support 16, here floating at the surface 18 of the body of water 12.

The floating installation 10 further comprises a mooring system comprising mooring lines 20 to anchor the floating support 16 at the bottom 14 of the body of water 12, and at least one dampening structure 22, preferably several dampening structures 22.

As will be described below, the mooring system configuration (mooring lines 20 angles in reference to a vertical plane and mooring lines 20 pre-tensions) is independent from the floating support 16 draught.

Whatever the draught variation of the floating support 16, for example due to loading/unloading of fluid, the geometry of the mooring system remains unchanged.

In the particular example of figure 1 , the dampening structures 22 are moveably mounted on the floating support 16 to connect the mooring lines 20 to the floating support 16. Moreover, the floating installation 10 further comprises, for each dampening structure 22, a guide 24 fixed on the floating support 16 to guide the vertical movement of the dampening structure 22.

In the case of a fluid exploitation, the floating support 16 is for example a barge, a FPSO, a FLNG, or a FSU. The floating installation 10 advantageously comprises at least a fluid transport line 26 extending between the bottom 14 of the body of water 12 and the floating support 16.

More generally, the floating support 16 comprises at least a hull 30 floating in the body of water 12, preferentially at the surface of the body of water 12.

The hull 30 defines an outer peripheral surface 32 which advantageously has a side shell plating generally vertical or inclined of a small angle with regard to a vertical axis, for example of an angle smaller than 45°.

In the example of figure 1 , the outer peripheral surface 32 preferably defines at least two sides 34A, 34B which are opposite in reference to a central vertical plane P of the floating support 16.

The floating support 16 is subject to various forces resulting from the movements of the body of water 12 and/or from weather conditions. These forces are for example generated by currents in the body of water 12, winds, and swell.

The forces are able to move the floating support 16 between a central balanced position shown in figure 1 , and maximal excursion positions, whose examples are shown respectively in figure 2 and figure 3.

In each maximal excursion position, the axial vertical plane P is shifted from a reference plane R it occupies in the central balanced position by a horizontal excursion E.

The mooring lines 20 connected to the dampening structures 22 limit the excursion E. The mooring lines 20 are located for example at the corners of the floating support 16. They connect the bottom 14 of the body of water 12 to the floating support 16 through the dampening structures 22.

Each mooring line 20 extends away from the floating support 16 to a connection point 40 at the bottom 14 of the body of water 12 materialized for example by a pile. Any type of anchor can be placed at the connection point 40 depending on the horizontal and vertical components loads.

In this example, each mooring line 20 extends linearly from its lower end 42 at the connection point 40 to its upper end 44 connected to a dampening structure 22.

The mooring line 20 comprises at least a tensioned section 46 and a bottom connection 48. In the example of figure 1 , the mooring line 20 comprises a single tensioned section 46 extending from the lower end 42 to the upper end 44.

The tensioned section 46 is made of a cable, in particular a polymer cable. In a potential embodiment, the cable is a braided cable, comprising braided spiral strand wires. The strand wires are advantageously made of polymer, in particular of polyolefin such as high modulus polyethylene (HMPE) also named ultra-high-molecular-weight polyethylene (UHMWPE). In a variant, the cable is made of metal or polyester strands. The cable is then fitted with buoyant material, such as foam, to provide a neutral or nearly neutral buoyancy of the mooring line 20.

In a variant, the mooring line 20 comprises a single rigid section 46 or several highly rigid sections 46 connected end to end, as shown in figure 5.

Each rigid section 46 could be for example made of a rigid tube of welded pipe.

The pipe may be fitted with a buoyant material, such as foam, to provide a neutral or nearly neutral buoyancy of the mooring line 20.

Generally, the mooring line 20 has a high stiffness. The mooring line 20 stiffness is, for non-braided material, defined by the product of the Young’s Modulus of the material of the mooring line by the transverse surface of the mooring line 20 divided by the length of the mooring line 20. For braided materials, the stiffness is a function of the braid type, the number of strands composing the braided cable divided by the strand diameter. The stiffness of a braided cable is generally about 4 times less than the stiffness of nonbraided cable.

Based on the stiffness of each individual mooring line 20 attached to each dampening structure 22, on the orientation of the mooring line 20 in projection in a horizontal plane, on the vertical angle of the mooring line 20 and on the pretension of each mooring line 20, a global mooring stiffness is obtained. The global mooring stiffness has to be high enough to meet the maximum excursion of the floating support 16.

The mooring lines 20 (number, orientation, pretension) are arranged to obtain an optimized tension to cost ratio.

The stiffness of the mooring line 20 depends on the stiffness of the material forming the mooring line 20. The mooring line 20 material stiffness is, for non-braided material, defined by the product of the Young’s Modulus of the material of the mooring line by the transverse surface of the mooring line 20.

The mooring line 20 material stiffness is defined during the design phase. The mooring line 20 material stiffness is for example greater than 1 .5 x 10⁹ N/m.

Preferably, the linear apparent weight of the mooring line 20 immersed in the body of water 12 is low. Its linear apparent mass is for example smaller than 10 kg/m. Advantageously, the maximum tension in the mooring line 20 is greater than 10 000 N, in particular greater than 1 000 kN and notably between 5 000 kN and 20 000 kN, for example 12 000 kN to 15 000 kN.

This value depends on the minimum breaking load (MBL), which is linked to the type of material used, the geometry and other physical parameters such as temperature or anchoring mechanism.

The pre-tension in the top section mooring line 20, applied in the mooring line 20 when installing the mooring line 20, is, as an illustration, smaller than 10% to 15% of the minimum breaking load (MBL) of the top section of the mooring line 20.

Theoretically, pre-tensions have no lower limits if the mooring line 20 has a neutral linear apparent mass in the body of water 12.

The bottom connection 48 allows at least one degree of freedom in rotation between the mooring line 20 and the connection point 40. The bottom connection 48 is for example a hinge, a chain, a cable or a ball joint.

Preferentially, at least one mooring line 20, in particular several mooring lines 20 are connected to each dampening structure 22. The number of mooring lines 20 connected at each dampening structure 22 is defined at the design phase. It is generally comprised between 2 and 7. The upper limit in the number of mooring lines is generally linked to the economics.

In the example of figure 1 , the floating installation 10 comprises at least two opposite dampening structures 22, preferentially four dampening structures 22 located at corners of the floating support 16.

In the example of figure 3, each dampening structure 22 is moveable along a vertical translation axis, which runs along a side 34A, 34B of the outer peripheral surface 32.

Each dampening structure 22 comprises at least one buoyant column 60 here having a caisson 62 filled with gas or/and liquid.

A liquid ballasting system is installed to allow for pre-tensioning purposes, or adjustments during the system life.

The dimensions of the column 60 (waterplane, height) are determined from engineering calculations. The column 60 is for example of cylindrical shape or of polygonal shape. The column 60 cross section may vary from top to bottom.

The buoyancy of the caisson 62 is defined when the installation 10 is designed.

The caisson 62 generally has a volume smaller than the volume of the floating support 16. The guide comprises at least one vertical rail 70 fixedly mounted on the floating support 16 outer peripheral surface 32. The dampening structure 22 defines a slide receiving the rail 70 or has wheels guided by the rail 70.

The set-up of the floating installation 10 in the body of water 12 will now be described.

Initially, the mooring lines 20 are laid in the body of water 12 at an exploitation site. The mooring lines 20 are fixed at their lower ends 42 through bottom connections 48 installed on the connection point 40.

Then, the floating support 16 is carried on the surface 18 of the body of water 12 to the exploitation site. The dampening structures 22 are ballasted so that the columns 60 are maintained in their lower position or in a position close to their lower position.

The upper end 44 of each line 20 is then lifted towards a dampening structure 22 to be connected to the dampening structure 22 through a small length of chain or cable.

Once all the mooring lines 20 have been fixed to dampening structures 22, the dampening structures 22 are de-ballasted by pumping out water and filling the caissons 62 with a gas, in particular with air. Tension applies on the mooring lines 20.

While the floating structure 16 moves from the center balanced position to the maximal excursion position, the mooring lines 20 remain substantially linear.

Each dampening structure 22 located in the direction in which the floating support 16 moves (illustrated by an arrow in figures 2 and 3) therefore translates upwardly along the guide 24 towards its upper end position.

On the contrary, each dampening structure 22 located in the direction opposed to the direction in which the floating support 16 moves, translates downwardly along the guide 24 and settles in the body of water 12.

Due to the buoyancy of the buoyant column 60, the settling of the dampening structure 22 in the body of water 12 creates a resisting upwards force, which limits the extent of the horizontal excursion of the floating support 16, and dampens the movement of the floating support 16.

Therefore, contrary to a fully rigid attachment of the floating support 16, the partial mechanical decoupling of the mooring lines 20 connected to the dampening structures 22 allow a degree of flexibility of movement of the floating support 16.

Nevertheless, the dampening structure 22 limits the extent of horizontal excursion of the floating support 16 under the effect of the buoyancy of the dampening structure 22 when it translates downwardly in the body of water 12.

Hence, the maximal horizontal excursions of the floating support 16 are greatly reduced, as compared to the excursions with catenary mooring systems. The dampening structure 22 is a passive system which auto adjusts and does not require an external artificial energy source to operate.

Limited excursions of the floating support 16 greatly simplify the design of any line, connections, liaisons connected to the floating support 16.

In addition, the set-up of the installation 10 according to the invention is very simple, since the mooring lines 20 can be easily laid with S-Lay or J-Lay techniques. The tensioning of the mooring lines 20 may not require massive tensioning winches, since it can be carried out by de-ballasting the dampening structures 22.

The installation 10 also easily adapts to variations of draught of the floating support 16 along time. These variations occur for example when the floating support 16 receives a large amount of cargo (fluid or any kind of heavy loads) or on the contrary, when cargo is discharged from the floating support 16. In these situations, the floating support 16 is able to vertically translate relatively to the dampening structure 22, without affecting the anchoring geometry, as shown in figure 4.

In a variant, shown in figure 6, the anchor lines 20 are hybrid lines. They comprise at least one upper rigid section 46 as defined above, and at least a lower flexible section 80 extending in a catenary shape from the lower end 42 of the anchor line 20 to the rigid section 46.

Preferably, the length LF of the flexible section 80 is smaller than the cumulative length LR of the or each rigid section 46.

The hybrid anchor line 20 is adapted in case the stiffness of the dampening structure 22 is too high, resulting in strain peaks which are too large or generating dynamic adverse effects.

The dampening resulting from the catenary effect of the flexible sections 80 supplements the dampening resulting from the immersion of the columns 60 of the dampening structures 22.

In a variation, the dampening structures 22 comprise elements with a positive buoyancy without caissons 62, such as solid foam buoys.

Another floating installation 10 according to the invention is shown in figure 7.

In the floating installation of figure 7, the hull 30 defines at least one inner compartment 100 receiving the dampening structure 22. The inner compartment 100 receives liquid 102, preferentially water from the body of water 12.

The inner compartment 100 is connected to the body of water 12 through a communicating valve 104. The communicating valve 104 is set up to substantially equalize the surface levels of liquid 102 in the inner compartment 100 and in the body of water 12, while dampening the waves, currents and swell effects. The dampening structure 22 comprises a floating column having a lower buoyant caisson 62, at least partially immersed in the liquid 102 of the inner compartment 100, an upper support 106 holding the upper ends 44 of the mooring lines 20 and a rigid connection 108 between the lower caisson 62 and the upper support 106.

The lower caisson 62 floats in the liquid 102 received in the inner compartment 100. It is able to vertically move in the inner compartment 102, relatively to the hull 30.

Thus, the lower caisson 62 remains substantially at the same height, even if the hull 30 moves vertically in the body of water, for example due to draught variations. This is illustrated in figure 7 with the dotted lines showing the position of the hull 30 with a deep draught (for example when fluid has been loaded in the hull 30) and with the solid lines showing the position of the hull 30 with a smaller draught (for example when fluid has been unloaded in the hull 30).

The horizontal projection of the lower caisson 62 is substantially complementary to the horizontal projection of the inner compartment 100 to minimize the free surface between the lower caisson 102 and the boundaries of the inner compartment 100. Thus, free surface effects are minimized when the lower caisson 62 vertically moves in the inner compartment 100. The dampening effect provided by the lower caisson 62 is therefore maximized.

Just as the caissons 62 described before for the floating installation 10 of figure 1 , the caisson 62 shown in figure 7 is able to be selectively filled in with air and/or ballasting liquid whose volume can be adjusted depending on the conditions.

The upper support 106 holds an end plate 110 to which at least one upper end 44 of a mooring line 20, preferably two opposed upper ends 44 of two opposed mooring lines 20 are connected. The end plate 110 jointly moves horizontally with the hull 30 of the floating support 16.

The dampening structure 22 also comprises, for each mooring line 20, a pulley 114, redirecting the end section of the mooring line 20 on the upper support 106. In this example, the end section of the mooring line 20 is redirected horizontally on the upper support 106 to connect to the end plate 110.

The dampening structure 22 further comprises, for each mooring line 20, a compression spring 112 having one end fixed on the upper support 106, and one free end. Each compression spring 20 is able to be compressed by the end plate 110 when the end plate 110 moves horizontally jointly with the hull 30 in the direction towards the free end of the compression spring 112.

Thus, when the hull 30 moves horizontally in one direction from its center position (respectively to the left or to the right in figure 7), the end plate 110 compresses the compression spring 112 in this direction. The deformed compression spring 112, thus generates a restoring force in the opposed direction, biasing the end plate 110 and thus the hull 30 towards the center position.

In this example, the upper support 106 protrudes out of the hull 30, above an upper surface 118 of the hull 30.

The connection 108 comprises at least one pillar 116, preferentially several pillars 116 connecting the caisson 62 to the upper support 106 through an upper surface 118 of the hull 30. The pillars 116 are vertically translatable through the upper surface 118, preferentially via a bearing 120, in particular a static bearing or/and an elastomeric bearing.

Thanks to the floating installation 10 of figure 7, the upper ends 44 of the mooring lines 20 remain at the same height and position, whatever the draught of the hull 30.

Indeed, if the draught of the hull 30 increases, for example due to loading of fluid in the hull 30, water enters the inner compartment 100 through the valve 104, maintaining the floating caisson 62 at the same height.

The dampening structure 22 therefore automatically and passively adapts to the draught of the hull 30, and maintains the geometry of the mooring lines 20, in particular their heights, their inclination and / or their length substantially constant.

The dampening structure 22 also automatically dampens horizontal and vertical movements of the hull 30, and provides a partial mechanical decoupling between the floating support 16 and the tensioned mooring lines 20, simultaneously limiting force peaks and decreasing excursions.

In the variant of figure 8, the upper support 106 further comprises a height variation compensation system 130 able to absorb height variations of the lower caisson 62, for example when substantial vertical forces components of the mooring lines 62 apply on the inner caisson 62 via the upper support 106 and the connection 108.

The height variation compensation system 130 comprises, for each mooring line 20, a rack and pinion mechanism 132 whose pinion is connected in rotation to the pulley 114 and whose rack is vertical.

The pulley 114 is therefore able to translate vertically via the rack and pinion mechanism 132 when variations of height of the caisson 62 occur in the inner compartment 100.

This vertical translation of the pulley 114 maintains the height at which the pulley 114 is located, and hence the height of the upper end 44 of the mooring line 20 and its geometry. In order to accommodate the vertical excursion of the pulley 114, the compression springs 112 are inclined with regard to the horizontal axis, such that the projection of each spring 112 on a vertical axis covers the vertical excursion of the pulley 114.

The dampening structure 22 does not comprise and end plate 110. The upper end 44 of each mooring line 20 is connected to the free end of a respective compression spring 112. In figure 8, the free end of the compression spring 112 is the lower end of compression spring 112, whereas the upper end of the spring 112 is fixed on the upper support 106.

Thus, when the hull 30 horizontally moves in one direction from the center position, at least one of the spring 102 compresses between the fixed end of the spring 102 and the free end of the spring 102, generating a restoring force biasing the hull 30 towards the center position.

In the floating installation of figures 9 and 10, the dampening structure 22 does not comprise a floating caisson 62.

In this example, the dampening structure 22 comprises a connector 150 for connecting the end of at least one mooring line 20, preferentially the ends of several mooring lines 20, a connection chain 52, a redirecting pulley 154, mounted on a dampener 155 and a height variation compensation system 130 comprising a fairlead 156.

The connector 150 here comprises an end plate, to which the upper end 44 of each mooring line 20 is attached and to which the lower end of the chain 152 is also attached.

The chain 152 is mounted on the pulley 154 and on the fairlead 156. It acts on the dampener 155 via the pulley 154.

The dampener 155 comprises a base 156 fixed on the hull 30, and a dampening member 158 movable with regard to the base 156. In the example of figures 9 and 10, the dampening member 158 is vertically movable with regard to the base 156.

The dampener 155 is for example a mechanical dampener or a hydraulic dampener which provides elastic dampening.

If vertical forces and displacements resulting from variations of tension in the mooring lines 20 are transmitted from the mooring lines 20 to the chain 152, and from the chain 152 to the pulley 154, these variations are dampened by the dampener 155.

Thus, the dampening of the dampener 155 provides a partial mechanical decoupling between the floating support 16 and the tensioned mooring lines 20, simultaneously limiting force peaks and decreasing excursions.

The fairlead 156 advantageously comprises a marked wheel and a motor able to rotate the marked wheel. The marked wheel is able to block and retain the chain 152 in position. The motor is able to rotate the marked wheel to release or pull an end section of the chain 152.

When the draught of the hull 30 significantly varies, for example when fluid is loaded in the hull 30 (see figure 9), or when fluid is unloaded from the full 30 (see figure 10), the compensation system 132 comprising the fairlead 156 is activated to compensate the height variation by releasing or pulling an end section of the chain 152.

The activation of the compensation system 132 can be continuous or can be incremental, for example each time a predetermined height has been modified.

Thanks to this dampening structure 22, the connector 150 and hence the ends 44 of the mooring lines 20 are substantially at the same position, with substantially the same angle, even if the draught of the hull 30 changes.

In a variant, shown in dotted lines in Figure 10, the dampening structure 22 comprises at least one inline mechanical or hydraulic dampener 180 mounted in the chain 152. The inline dampener 180 complements or substitutes the dampener 155. The inline dampener 180 is extendible with regards to the floating support 16, to allow a partial mechanical decoupling between the mooring line 20 and the floating support 16.

Claims

1.- Floating installation (10), comprising:

- a floating support (16), floating on a body of water (12):

- mooring lines (20), connecting the floating support (16) to a bottom (14) of the body of water (12); characterized by:

- at least a dampening structure (22), the dampening structure (22) being moveable and/or extendible with respect to the floating support (16); at least one mooring line (20) being a tensioned or rigid line having a lower end (42) connected to the bottom (14) of the body of water (12), the at least one mooring line (20) being connected to the dampening structure (22), the dampening structure (22) providing a partial mechanical decoupling between the floating support (16) and the mooring line (20).

2.- Floating installation (10) according to claim 1 , wherein the dampening structure (22) is mounted in the floating support (16) or on the floating support (16), an upper end of the mooring line (20) being connected to the dampening structure (22) or mechanically interacting with the dampening structure (22).

3.- Floating installation (10) according to claim 2, wherein the floating support (16) has an outer surface (32), the dampening structure (22) being mounted on the outer surface (32).

4.- Floating installation (10) according to claim 2, wherein the floating support (16) comprises an inner compartment (100) at least partially filled with a liquid (102), the dampening structure (22) being at least partially received in the inner compartment (100).

5.- Floating installation (10) according to claim 4, wherein the inner compartment (100) is at least partially filled with water from the body of water (12), the floating structure (16) comprising at least a valve (104) fluidly connecting the inner compartment (100) to the body of water (12).

6.- Floating installation (10) according to any one of claims 2 to 5, wherein the dampening structure (22) comprises at least a buoyant column (60), the buoyant column (60), preferably comprising a caisson (62) filled with gas or/and ballast.

7.- Floating installation (10) according to any one of claims 2 to 6, wherein the dampening structure (22) comprises at least a spring (112), in particular a compression spring (112), the spring (112) being able to generate a restoring force biasing the floating support (16) towards a center position.

8.- Floating installation (10) according to any one of claims 2 to 7, wherein the dampening structure (22) is translatable along a vertical axis with respect to the floating support (16).

9.- Floating installation (10) according to claim 2, wherein the dampening structure (22) comprises a mechanical or hydraulic dampener (155) having a base (156) attached to the floating structure (16) and a dampening member (158) movable with regards to the base (156), the dampening member (158) being mechanically biased by the mooring line (20).

10. Floating installation (10) according to any one of the preceding claims, wherein the dampening structure (22) comprises at least a dampener (180) mounted in line on the mooring line (20).

11.- Floating installation (10) according to any one of the preceding claims, wherein the floating structure (16) has a variable draught, the mooring line (20) having at least one upper linear section having a top, the upper linear section making an inclination angle with a vertical axis passing by the top of the upper linear section, the floating installation (10) comprising a height variation compensation system (130) able to maintain constant the height of the top of the upper section or/and the inclination angle of the upper section when the draught of the floating structure (16) varies.

12.- Floating installation (10) according to any one the preceding claims, wherein the mooring line (20) material has at least one upper rigid section (46) having a stiffness greater than 1 .5 x 10⁹ N/m.

13. Floating installation (10) according to any one the preceding claims, wherein the mooring line (20) has an apparent linear weight in the body of water (12) smaller than 10kg/m. 17

14.- Floating installation (10) according to any one the preceding claims, wherein the mooring line (20) has a linear inclined tensioned top section connected to the dampening structure (22).

15.- Floating installation (10), wherein the floating support (16) is a barge, a FPSO, a

FLNG, a FSU, an offshore power production support advantageously bearing at least a wind turbine or at least a solar panel, or/and an offshore housing or facility support.