The present invention relates to scour protector and to a method of arranging a scour protector on a seabed.

Scour is the removal by hydrodynamic forces of granular bed material in the vicinity of coastal structures, and is a specific form of the more general term "erosion". Scour occurs whenever the hydrodynamic bottom shear stresses exceed the sediment critical shear stress, and is therefore typically present in fast running waters with granular soil.

Scour imposes a significant problem for subsea structures, such as monopile bases, jackets and also pipelines that are arranged on the seabed, where the scour takes place on the downstream side.

For vertical piles, a scour hole with a depth to about twice the pile diameter may result. For pipelines lying on the seabed, the scour can lead to partial burial of these pipelines. The scour can lead to a partial burial of these pipelines, and the problems are caused when a differential scour takes place due to different soil types, possibly leaving a pipeline spanning a gap.

Scour is normally prevented by the arrangement of large numbers of heavy rocks, preferably of different size, near a subsea structure. These heavy rocks must be transported to the desired location at sea, which is a logistic challenge.

Whereas rocks may be arranged around a monopile foundation, this may be difficult for foundations of other types. For example, for a tripod or tri-pile foundation, it is difficult to arrange scour protection in the form of heavy rocks. After all, the tripod or tri-pile foundation encloses an area between the three piles where it is difficult to arrange heavy rocks.

WO 95/24531 Al is considered the closest prior art, and discloses a flexible and collapsible formwork, particularly for use when casting submarine areas as well areas above water level. The formwork bag is formed by a top cloth and bottom cloth. Intermediate the two cloths, a number of spacers are placed, so that the formwork forms a substantially flat formwork bag. The formwork bags provide a scour protector with a rectangular shape that is e.g. used as the bottom of ferry landings. If used for scour protection of e.g. a monopile base, the offered protection would be limited.

GB 2 418 948 A and GB 2 497 581 A are acknowledged as further prior art.

An object of the present invention is to provide scour protection, that is improved relative to the prior art and wherein at least one of the above stated problems is obviated.

Such objectives as indicated above, and/or other benefits or inventive effects, are attained according to the present disclosure by the assembly of features in the appended independent device claim and in the appended independent method claim. Said object is achieved with the scour protector according to the present invention, comprising one or more than one cover, wherein said scour protector comprises a passage having a shape and dimensioned to accommodate a monopile base and to surround the monopile base in a sunken state of said scour protector.

Due to the scour protector surrounding the monopile base, it provides an efficient and reliable scour protection. The passage having a shape and dimensioned to accommodate a monopile base and to surround the monopile base in a sunken state of said scour protector provides a scour protector that may have a flat design. A scour protector with a flat design is more reliable than e.g. stacked formwork bags, and less susceptible to being moved by currents.

The prior art, e.g. WO 95/24531 Al, proposes rectangular formwork bags. In order to enclose a tubular construction such as a monopile base, multiple rectangular formwork bags will have to be used. Moreover, in order to place such prior art bags close to a monopile base, they need to be arranged partly on top of each other, increasing the height and vulnerability of the scour protection. After all, an upper formwork bag is exposed to currents. Moreover, placing multiple formwork bags on the seabed is a laborious and complex task. Using the scour protector according to the present invention, a correct placement is simple and safe, and also guarantees optimal scour protection.

In a preferred embodiment, the passage is dimensioned to closely surround the monopile base in a sunken state of said scour protector. The amount of space or gaps between the scour protector and the monopile base is limited if the passage is dimensioned to closely surround the monopile base, resulting in improved scour protection.

Said object is furthermore achieved with the method of arranging a scour protector on a seabed according to the present invention, comprising the steps of providing a scour protector that comprises a passage having a shape and dimensioned to accommodate a monopile base, and sinking the scour protector, wherein the scour protector in a sunken state thereof surrounds a monopile base of said monopile.

In the following description preferred embodiments of the present invention are further elucidated with reference to the drawing, in which:

Figure 1 is a perspective view of a monopile base of a wind turbine, wherein a scour protector is arranged on the seabed;

Figure 2 is a side view of a monopile base of a wind turbine that experiences scour;

Figure 3 is a side view of a monopile base of a wind turbine that is provided with a scour protector according to the invention;

Figures 4 and 5 show cross-sectional side views of successive steps of providing and floating a cover of a scour protector on the sea surface next to a monopile base; Figure 6 shows a top view of a scour protector according to the present invention; Figures 7 and 8 show cross-sectional side views of successive steps of sinking (Figure 7) a scour protector, and arranging said scour protector on the seabed (Figure 8);

Figure 9 shows a cross-sectional side view of a scour protector after being arranged on the seabed;

Figure 10 shows three successive steps how the situation of Figure 9 is obtained after some time;

Figure 11 shows a cross-sectional side view of a cover of the scour protector according to the present invention;

Figure 12 shows a further preferred embodiment wherein the top surface of the cover of the scour protector is provided with a plurality of outlet openings;

Figures 13-15 show cross-sectional side views of successive steps of arranging a scour protector according to an alternative embodiment on a seabed;

Figure 16: shows a perspective view of a scour protector according to a further preferred embodiment, in a collapsed state thereof;

Figure 17: shows a perspective view of the scour protector of Figure 16, in an extended state thereof;

Figure 18: shows a perspective detailed view of a ratchet-type arrangement of the arms of the scour protector of Figures 16 and 17;

Figure 19: shows a perspective view conform Figure 17, wherein the cover is filled with a filling medium;

Figures 20-25: show successive steps of a first installation method of the scour protector of Figures 16-19; and

Figures 26 and 27: show successive steps of a second installation method of the scour protector of Figures 16-19.

The scour protector 1 of Figures 1-15 comprises one or more than one cover 2, wherein said cover 2 is capable of floating when filled with air. Thus, the cover 2 may have a state wherein said cover 2 is configured to float on water (Figure 5). In this floating state, the one or more than one cover 2 may be easily arranged at a desired position, and possibly connected to further covers 2. Although initial floating of the cover 2 is not essential to provide a subsea scour protection in a final stage, the skilled person will understand that this capability to float may provide easy and comfortable placement of the scour protector around e.g. a monopile base.

In Figure 1 , a scour protector 1 comprising four connected covers 2 is arranged on the seabed 66 and around a subsea structure 50. The subsea structure 50 is a monopile base 52 that supports a wind turbine 54. Said monopile base 52 has a cable guide 56 through which an electricity cable 58 is guided to the seabed 66. And electricity cable 58 is, similar to a pipeline, also vulnerable to scour, and may be protected by a further scour protector 1 ' . For the sake of simplicity, the further scour protector 1 ' shown in Figure 1 comprises a single cover 2, but the skilled person will understand that multiple covers 2 may be connected with each other and form a chain of covers 2 that may be arranged over an electricity cable 58 or a (not shown) pipeline.

When the scour protector 1 is arranged on the seabed 66 as shown in Figure 1 , it provides protection against scour, so that a scour hole 66 as shown in Figure 2 may be prevented. Over time, the scour protector 1 will experience a small-scale scour effect near its edges 8, and because the covers 2 are preferably substantially flexible, these edges 8 of the cover 2 will be buried to some extent, as shown in Figure 3. This process will be further elucidated using Figures 9 and 10. Once the situation shown in Figure 3 is obtained, the scour protector 1 offers optimum scour protection to the subsea structure 50.

Although the cover 2 may be floating if it is made of a mass density lower than the mass density of water, it may also float because air or another fluid is introduced into the cover 2. For the latter situation, said cover 2 comprises a compartment 10 with at least one inlet opening 12. In this embodiment, the cover 2 forms a mattress.

The covers 2, which are preferable made of textile, may be transported in a coiled state, i.e. in the form of a roll. When the cover 2 is filled with air, it automatically expands and will uncoil into an elongate rectangular shape. Once filled with air, the cover 2 is capable of floating on the sea surface 64 and may be arranged near a subsea structure 50, such as monopile base 52, that partly extends above the sea surface 64. The part of the subsea structure 50 that extends above the sea surface 64 is accommodated in an accommodation 28 of said cover 2. The accommodation 28 of the cover 2 is dimensioned to accommodate and surround at least a part of a subsea structure 50 in a sunken state of said cover 2. As shown in Figure 1, also the cable guide 56 is accommodated in accommodation 28.

The scour protector 1 comprises a passage having a shape and dimensioned to accommodate a monopile base to surround the monopile base in a sunken state of said scour protector 1. In Figure 1 , two accommodations 28 of connected covers 2 form the passage of the scour protector 1. The passage preferably closely surrounds the monopile base in the sunken state thereof.

Although not explicitly shown in the figures, the step of Figures 4 and 5 is preferably executed when the monopile base 52 is being installed and still only extends for a limited height above the sea surface 64. Thus, in Figures 4 and 5, the wind turbine 54 may not have been arranged yet.

According to an alternative (not shown) method, the scour protector 1 may be arranged on the seabed 66, said scour protector 1 having an accommodation dimensioned to accommodate a subsea structure 50. This subsea structure 50, for instance a monopile base 52 may be arranged through said accommodation after the scour protector has been arranged on the seabed 66. As this (not shown) method puts high demands on the exact positioning of the scour protector 1 and aligning the subsea structure 50 with the accommodation of said subsea structure 50, it is preferred to arrange the scour protector 1 around and/or against a subsea structure 50 that is already arranged on the sea bed 66.

It is furthermore noted that the accommodation 28 of the cover 2 of the scour protector 1 according to the invention, also allows this scour protector 1 to be arranged easily around piles of other types of foundations, such as a tripod or tri-pile foundation.

In order to obtain the scour protector 1 as shown in Figure 1 , couples of covers 2 are connected with at least one cover connector 26 when they are floating on the sea surface 64. Each cover 2 preferably comprises multiple cover connectors 26.

After the optional step of floating one or more than one cover 2 on the sea surface 64, and eventually connecting multiple covers 2 with cover connectors 26 in order to obtain an assembled scour protector 1 (Figure 6), the next step is sinking the at least one cover 2, i.e. the scour protector 1, into the sea (Figure 7).

The covers 2 comprise a compartment 10 with at least one inlet opening 12, wherein said compartment 10 is fillable with a filling medium 42 that has a mass density equal to or lower than the mass density of water. In Figure 7, the compartment 10 of the cover 2 is filled with water as filling medium 42. When water is introduced from vessel 46 via a filling conduit 48 and through the inlet opening 12 into compartment 10, the air 40 inside said compartment 10 is compressed and leaves compartment 10 through outlet opening 14. Outlet opening 14 may comprise a valve 16, that is preferably a pressure valve.

The filling medium 42 may also comprise water with suspended particles in order to increase the mass density of this suspension, and thereby accelerate the sinking process.

In an alternative embodiment, shown in Figure 12, multiple outlet openings 14 of said compartment 10 are arranged on a top surface 4 of said cover 2, said multiple outlet openings 14 comprising valves 16 configured for evenly releasing fluid 40, 42 out of the compartment 10 of said cover 2.

When water as filling medium 42 replaces the air as filling medium 40 inside compartment 10, the weight of the cover 2, and consequently the weight of the scour protector 1, increases, and the cover 2, and consequently the scour protector 1, will sink into the sea (Figure 7).

Once the scour protector 1 has reached the seabed 66, a preferred step of further increasing the weight of at least one cover 2 of said scour protector 1 may be executed. This step comprises at least partially replacing the filling medium 42 water in said compartment 10 with a further filling medium 44 that has a higher mass density than the filling medium 42 used for sinking said cover 2. Said further filling medium 44 preferably comprises sand. When sand as filling medium 44 replaces the water as filling medium 42 inside compartment 10, the weight of the cover 2, and consequently the weight of the scour protector 1, increases further, and the cover 2, and consequently the scour protector 1 , will be arranged even more secure on the seabed 66 (Figure 8).

Preferably, in Figure 8, compartment 10 is only partially filled with sand as the further filling medium 42, thereby maintaining flexibility of said cover 2. Flexibility of the cover 2 provides an increased scour protection, as will be explained using Figures 9 and 10.

In Figure 9, the edges 8 of the cover 2 of the scour protector 1 also experience a scour effect, as already shortly described above. This scour effect can be best seen in Figure 10, wherein a small scour hole 70 is formed adjacent the edge 8 of cover 2. When this scour hole 70 grows, the edge 8 of the cover 2 will fall into the scour hole 70. This falling into the scour hole 70 of the edge 8 of the cover 2 is possible due to the flexibility of the cover 2.

The edges 8 of cover 2 are preferably tapered, so that the scour protector 1 is more aerodynamic and less susceptible for fluid flow. Furthermore, tapered edges 8 increase the flexibility of said edges 8, contributing to the effect shown in Figure 10.

In the state shown in Figure 9, at least one of the inlet opening 12 and outlet opening 14 are left open, which also contributes to the flexibility of the scour protector 1.

In Figure 11 , cover 2 comprises a bottom 6 and a top surface 4 with a connector 18 arranged in between, said connector 18 having a predetermined length defining the thickness of the cover 2 when in use. When the compartment 10 of the cover 2 is filled with a filling medium 40, 42, 44, one or more than one connector 18 prevent bulging out of the scour protector 1.

Although the connectors 18 may theoretically be rigid bars, it is preferred that the connectors 18 are capable of being rolled up together with the cover 2. As flaps could interfere with certain types of filling medium, especially sand, it is preferred that the connectors are strings 20. The strings 20 may comprise one or more than one fiber 22, and preferably a plurality of fibers 22. If said fibers 22 comprise glass fibers, this adds to the weight of the scour protector 1.

The strings 20 of the connector 18 preferably comprise a bundle, and multiple connectors 18 are arranged in a pattern in the compartment 10 of the cover 2, wherein this pattern leaves channels 24 for said filling medium, which is especially advantageous for the further filling medium 44 that preferably comprises sand.

According to an alternative embodiment, shown in Figures 13-15, the cover 2 is again preferably made out of textile, wherein the top surface 4 comprises pores 5, and wherein the bottom surface 6 comprises pores 7. Due to the pores 5, 7, the top and bottom surfaces 4, 6 are permeable for water and air.

In the Figure 13, the covers 2 of the scour protector 1 are preferably continuously pressurized with air, that partly escapes from the compartments 10 of the covers 2 through the pores 5, 7, as can be seen in Figure 13. It is noted that substantially continuously pressurizing means that a substantially continuous overpressure is maintained, but the skilled person will understand that small interruptions in pressurizing will not negatively influence the floatability of the cover 2.

When the covers 2 are assembled to form a scour protector 1 , and said scour protector 1 has been positioned in the desired position, pressurizing of the compartment 10 with air is stopped. Although the filling conduit 48 that introduced the air as filling medium 40 into the compartment 10 may be disconnected, it may also remain connected (as shown in Figure 14) so that it can be used in a later step for filling the compartment 10 of the cover 2 with a further filling medium 44, e.g. sand.

In Figure 14, water enters the compartment 10 through the pores 7 in the bottom surface 6 of the cover 2. The pores 7 function as inlet openings 12, and the water as filling medium 42 replaces the air as previous filling medium 40. The air is released from the compartment 10 through the pores 5 in the top surface 4 of the cover 2. The pores 5 in the top surface 4 function as outlet openings 14, and further outlet openings 14 comprising pressure relief valves 16 may also be arranged in the top surface 4. Due to the water replacing the air in the compartment 10, the weight of the cover 2 increases and the cover 2 starts to sink into the sea.

Once the scour protector 1 has reached the seabed 66, a preferred step of further increasing the weight of at least one cover 2 of said scour protector 1 may be executed. This step comprises at least partially replacing the filling medium 42 water in said compartment 10 with a further filling medium 44 that has a higher mass density than the filling medium 42 used for sinking said cover 2, similar to Figure 8.

Preferably, said further filling medium 44 comprises sand with seeds of water plants. The water plants 72, such as sea weed, may grow through the pores 5 in the top surface 4 of the cover 2. In addition to providing underwater flora and contributing to underwater life, the plants 72 also influence the flow of water around the subsea structure 50. The water flow is reduced, and therefore contributes to the scour protection.

An alternative and further preferred embodiment of a scour protector according to the invention is shown in Figures 16-27.

The scour protector 101 comprises a ring 102 that is dimensioned to surround the monopile base 52 in a sunken state of said scour protector 101. The ring 102 has an

accommodation 103 that defines the passage having a shape and dimensioned to accommodate and surround the monopile base 52 in a sunken state of said scour protector 101.

The scour protector 101 further comprises a plurality of arms 104 that are configured to radially extend from said ring 102 in a sunken state of said scour protector 101, wherein one or more than one cover 105 is connected to one or more than one of said plurality of arms 104. When the arms 104 are extended, the cover 105 preferably spans between neighboring arms 104.

Figure 16 shows the scour protector 101 in a collapsed state, wherein it may be easily transported on board of a ship and arranged around a monopile base 52. Perspective views of an extended state of said scour protector 101, wherein the plurality of arms 103 radially extend from said ring 102 are shown in Figures 17 and 19.

In Figures 16 and 17, the cover 105 is made transparent in order to show the plurality of arms 104. The cover 105 may be a sheet, such as a fabric or cloth, or alternatively a mattress-type cover as described in relation to the embodiment of Figures 1-15. A cover 105 that is capable of floating when filled with air is preferred.

The arms 104 are arranged on the ring 102 with a ratchet-type arrangement 106 that is configured to allow a downward movement of the arms 104 relative to the ring 102 and to prevent an upward movement of the arms 104 relative to the ring 102. The advantages thereof will be explained here below with reference to Figures 24 and 25.

In Figure 19, the scour protector 101 is shown in its sunken and active state. The arms 104 extend radially from the ring 102 that defines the accommodation 103 for

accommodating the monopile base 52. The cover 105 is filled with a filling medium, preferably water and/or sand via inlet opening 106. Air or other medium that may have been in the cover prior to the filling medium is introduced, may leave the cover via outlet opening 107. The principle of filling the cover 105, as well as the construction of the cover with connectors 108 is identical to the embodiment shown in Figures 1-15.

Figures 20-27 show simplified representations of the scour protector shown in Figures 16-19, wherein only two oppositely arranged arms 104 are shown.

Although not explicitly shown in Figures 20 and 21, the step of placing the accommodation 103 of the scour protector 101, that defines the passage, around a subsea structure, i.e. the monopile base 52, is preferably executed when the monopile base 52 is installed and only extends for a limited height above the sea surface 64. Thus, in Figures 20 and 21, a wind turbine may not have been arranged yet.

In order to allow the accommodation 103 that is defined by the ring 102 to be arranged around a monopile base 52 in retrofit, said ring 102 preferably comprises at least two ring parts 102a, 102b. In a preferred embodiment, the ring parts 102a, 102b are pivotally connected.

Figures 20-25 show successive steps of a first installation method of the scour protector 101. As described above, the scour protector 101 is arranged around the monopile base 52, wherein the monopile base 52 is accommodated in the accommodation 103 defined by the ring 102. Afterwards, the arms 104 are radially extended by pivoting them relative to the ring 102

(Figure 22), while the cover 105 is filled with air. When the cover 105 is filled with air, the scour protector 101 will float (Figure 22), thereby providing the opportunity for personnel to safely walk on the scour protector 101 and execute any desired preparation before the scour protector 101 is sunk (Figure 23). Sinking the scour protector 101 may comprise the step of filling the cover 105 with water, while air is removed from the cover 105, e.g. via outlet opening 107.

Once the scour protector 101 is sunk and has reached the seabed 66, the water as filling medium may be replaced by a further filling medium, such as sand. The ratchet-type arrangement 106 shown in Figure 18 guarantees that the scour protector 101 is safely and reliably arranged on the seabed 66. When currents result in erosion below an arm 104, it may move downward - see left arm 104 in Figure 25. The ratchet- type arrangement 106 prevents an upward movement of said arm 104, and in this way the scour protector 101 will gradually dig itself into the seabed 66. If, on the other hand, sand is displaced by currents on top of the scour protector 101, this will also increase the stability of the scour protector 101 - see right arm 104 in Figure 25..

Figures 26 and 27 show successive steps of a second installation method of the scour protector 101. This second installation method differs from the first installation method described above, in that the scour protector 101 is first immersed below the sea level 64 in its collapsed state, and only during or after sinking the arms 104 are moved to their radially extending state.

Although they show preferred embodiments of the invention, the above described embodiments are intended only to illustrate the invention and not to limit in any way the scope of the invention. Although the second embodiment of Figure 16-27 show a scour protector 101 with a cover 105 of a mattress-type, the skilled person will understand that the cover 105 of this embodiment may also be a sheet, such as a fabric or cloth. However, a cover 105 that is capable of floating when filled with air is preferred.

It should be understood that where features mentioned in the appended claims are followed by reference signs, such signs are included solely for the purpose of enhancing the intelligibility of the claims and are in no way limiting on the scope of the claims. Furthermore, it is particularly noted that the skilled person can combine technical measures of the different embodiments. The scope of the invention is therefore defined solely by the following claims.