Single pile for wind turbine

Abstract

The present invention relates to a single pile for a wind turbine, the single pile when positioned having an upper end and a lower end and comprising a tubular lower portion extending upwardly from the lower end, and wherein there is an injection nozzle inside the tubular lower portion. The single pile is provided with one or more openings at a higher elevation. The injection nozzle is positioned at a distance from the lower end and is directed to inject a flow of water toward the lower end in at least tangential and axial directions.

Description

Technical Field

[0001] A monopile for a wind turbine, the monopile having an upper end and a lower end when positioned, and comprising a tubular lower portion extending upwardly from the lower end and provided with an injection nozzle, and wherein the monopile is provided with one or more openings at a higher elevation. Background Art

[0002] EP3464734B1 describes a monopile for wind turbines in which there is a ring of movable tips at the lower end of the tubular monopile. By means of the movement of these tips, the soil is scraped away. Water can also be injected at the tips in order to generate a water flow on the inside and outside of the wall of the monopile. These two measures make it possible to install the monopile without or with less use of a vibrating hammer.

[0003] WO2020 / 207903 describes a monopile for a wind turbine having a lower end consisting of an annular element with outlets for water jets directed upwards and downwards. The annular element is further provided with a vibrating member.

[0004] WO2019 / 206690 describes a monopile provided with a nozzle directed at an angle between 90 and 180 degrees to the insertion direction of the monopile. The disclosure states that by angling the nozzle upwards, the movement of soil within the monopile is enhanced. This results in a reduction in inward bearing failure below the lower end (referred to as the pile tip). The pile tip has an inwardly tapered design to direct soil to the lower open end of the monopile. There is a pumping member to pump out the resulting suspension within the monopile to reduce the vertical downward stress that would otherwise increase the installation resistance. The pumping system can also extract air from the lower region of the monopile. Since the lower region of the monopile can be closed from the upper region, a suction effect can be produced to reduce the pressure of the suspension within the monopile.

[0005] WO2021 / 228510 is another example of a monopile provided with a nozzle at its lower end, and wherein a pumping system is used to control the suspension pressure at the lower end of the monopile.

[0006] Vibratory hammers are known for driving foundation piles (such as monopiles) into underwater riverbeds, as described in WO03 / 100178. In this method, a tubular foundation pile of a monopile is penetrated through the seabed using a vibratory arrangement clamped to the upper end of the foundation pile. The vibratory arrangement may weigh 40 to 50 tons and may be one such as described in US5653556. The disadvantage of vibratory hammers is that they produce too much noise for marine life and that metal foundation piles may be damaged by the strain of the vibratory hammer.

[0007] The problem with monopiles in current technology is their complexity. For example, as described in EP3464734B1 and WO2020 / 207903, the presence of a vibrating member at the lower end of the monopile leads to a complex design. The monopiles of WO2019 / 206690 and WO2021 / 228510 are complex due to the pumping member. The object of the present invention is to provide a simpler design and method for installing a monopile on the seabed. Summary of the invention

[0008] This is achieved by the following monopile for a wind turbine. A monopile for a wind turbine having an upper end and a lower end and comprising a tubular lower portion extending upwardly from the lower end when positioned, and wherein inside the tubular lower portion there is an injection nozzle, wherein the monopile is provided with one or more openings at a higher elevation, and wherein the injection nozzle is positioned at a distance from the lower end and is directed to inject a water flow towards the lower end in at least tangential and axial directions.

[0009] The applicant has found that when water is injected from a distance from the lower end and towards the lower end, as claimed, an eddy current is generated, which enhances the insertion of the monopile into the soil of the seabed. By injecting water from a distance from the lower end, it has been found that most or even all of the water is retained in the monopile, while enhancing the penetration of the monopile into the soil. It is disadvantageous for a large amount of water to escape from the lower end to the surrounding soil, especially in sandier types of soil, because this water can have a negative impact on the structure of the soil around the monopile. By keeping the water as injected in the monopile, this escape is avoided. The applicant has found that no pumping means are required to achieve the desired penetration into the soil. Instead, the excess water and soil are discharged via an opening present at a higher elevation. In this way, the pressure of the suspension in the monopile will be similar to the soil pressure at the lower end. This avoids that water can flow to the soil or water can flow from the soil to the interior of the monopile. Having a lower suspension pressure as in the prior art method has the following disadvantages: too much soil enters the monopile and thus has a negative impact on the soil support of the monopile. Therefore, the present invention also relates to a monopile in which there is no pumping system for extracting fluid from the monopile. Thus, a monopile of simpler design is achieved. The simple design allows the nozzle to remain in the installed monopile, thus avoiding a complex detachable structure as described in WO2020 / 207903.

[0010] The invention also relates to a method for installing a monopile for a wind turbine according to the invention in soil covered by a body of water, by positioning the lower end on the soil surface and by spraying water from an injection nozzle towards the lower end in a direction having at least a tangential and an axial direction, thereby causing the sprayed water to penetrate the soil at the lower end to cause a soil suspension of water and soil particles, which soil suspension swirls upwards within the monopile towards one or more openings, through which the soil suspension is discharged to the body of water.

[0011] In this application, reference will be made to terms such as upper, lower, above, below, horizontal and vertical. These terms are used to more clearly describe the monopile in its installation orientation in, for example, the seabed. These terms should not be used to limit the claims to the monopile only in this orientation. In particular, the stored and / or transported monopile (which will be described by the claims as the installed monopile) should be understood as part of the present invention.

[0012] To achieve optimal penetration into the soil, it has been found that the majority of the water (preferably more than 80 vol%, more preferably more than 90 vol% and most preferably all of the water) is injected toward the lower end in a direction having at least tangential and axial directions. It has been found that there is no additional benefit to directing the injection nozzle horizontally upwards as in prior art designs.

[0013] Additionally, the monopile preferably has no nozzles directing water radially away from the monopile and / or has no nozzles directing water upwardly along the outer wall surface of the lower tubular end. As explained above, supplying a certain amount of water to the soil around the tubular lower portion may negatively affect the support structure of the soil and therefore its ability to fix the monopile in the soil.

[0014] Preferably, the injection nozzle is directed to the lower end at an angle between zero and 90 degrees to the horizontal and preferably between 30 and 60 degrees to the horizontal. The direction may also have a small inward or outward radial component.

[0015] The method for installing a monopile into soil covered by a body of water may be performed for installing the monopile on the seabed. The body of water may also be a lake. The depth of the water (i.e., the height of the body of water) is preferably between 5 m and 100 m and more preferably between 10 m and 50 m. When the height of the body of water is below 5 m, preferably below 10 m, the column of suspension created within the monopile may exert excessive pressure on the soil as present at the lower end of the monopile during installation. The method may then comprise pumping the suspension from the interior. The soil may be sandy silt, soft clay, very hard clay or Boom clay or any combination of the above. The monopile and the method are particularly suitable for installation in sand.

[0016] A monopile for a wind turbine is suitably the portion of the wind turbine that extends just above the water level. By just extending is suitably meant extending between 5 m and 20 m above the water level when installed. On top of the monopile, the mast and wind turbine generator are typically mounted. The penetration distance of the monopile in the soil is suitably between 20 m and 50 m and preferably between 25 m and 40 m.

[0017] It has been found that the optimum distance at which the nozzle is positioned above the lower end is related to the type of soil and the ability of the water jet leaving the nozzle to penetrate the soil. Optimally, the water jet penetrates the soil to the level of the lower end of the monopile. In this way, optimal disturbance and soil suspension formation are achieved in this area to enhance the penetration of the monopile into the soil, while avoiding that a large amount of water can leak out to the surroundings of the monopile, as explained above. For easily penetrated soil types (such as sand), this distance will be higher, and for difficult to penetrate soil types (such as clay), this distance will be lower. The distance will also depend on the diameter of the lower end portion of the monopile. For larger monopiles, the distance may be higher, because more water may need to be injected to result in a higher penetration length. In addition, the angle at which the water is injected will affect this distance. When the direction is close to zero degrees with the horizontal, a relatively small distance will be selected, while when the direction becomes more downward, a larger distance will be selected. In the soil type for which the monopile is to be designed, the distance is easily determined by measuring the single penetration depth of the jet leaving the nozzle under the design conditions. The distance will then vary depending on the angle and measured penetration depth. Therefore, the monopile is preferably designed for the specific type of soil in which the monopile is to be positioned, with the distance between the nozzle and the lower end being determined by the type of soil, the orientation of the nozzle and the diameter of the lower end portion of the monopile.

[0018] Therefore, in the method of the present invention, it is preferred that the injected water does not substantially penetrate the soil to a level below the lower end of the monopile.Furthermore, it is preferred that more than 90 vol% of the water injected from the injection nozzle is discharged to a body of water via one or more openings.

[0019] Preferably, the pressure of the water as supplied to the water injection nozzle is at least 5 bar, and preferably between 20 and 300 bar. The pressure may depend on the type of soil. Suitably, for a sand type soil, this pressure is between 5 and 50 bar, and for a clay type soil, this pressure is between 50 and 300 bar. The water pressure of a mixture of sand and clay may overlap these preferred ranges.

[0020] The amount of water as sprayed at the lower end portion of the monopile will appropriately depend on the soil type and the size of the monopile. For sand type soils, high flow and low water pressure are preferred, while for clay type soils, low flow and high pressure are preferred. This results in that for sand type soils, substantially all of the soil in the monopile is present as a volume of fluidized soil (i.e., suspension). For clay type soils, the suspension will be present in an annulus against the inner wall and a denser clay core will be present in the center of the monopile. To give an indication, for a monopile with a diameter of the lower end portion between 6 meters and 15 meters, the water flow is preferably between 10000 l / min and 100000 l / min. For an 8 meter diameter monopile, this flow may be between 10000 l / min and 30000 l / min.

[0021] For the preferred soil type sand, the distance at which the nozzle is positioned above the lower end is suitably at least 0.01 m, preferably 0.1 m and even more preferably 0.25 m. For monopiles with larger diameters, the optimal distance suitably increases. This is because the required higher water flow will be higher than the increase in available water nozzles. Therefore, more water will flow per nozzle, resulting in a greater penetration length and therefore a greater distance at which the nozzle is preferably positioned above the lower end. For larger diameter monopiles, the distance at which the nozzle is preferably positioned above the lower end will suitably not exceed 5 m, preferably not exceed 3 m and more preferably not exceed 2 m. The optimal distance will further be affected by the penetration depth of one or more specific soil types as described above and the angle of the nozzle. This may result in the monopile design for each project being potentially different. The distance is defined as the axial distance between the lower end and the outlet opening for the water of the nozzle.

[0022] The nozzles may be positioned in any manner inside the tubular lower portion. Preferably, the nozzles are positioned in a circle so that each nozzle is approximately the same distance from the lower end. Optionally, two or more rows of these circular rows of nozzles may be positioned above each other. Preferably, the nozzles are fluidly connected to a circular conduit that is connected to the inner wall of the tubular lower portion. This conduit serves as a common header for the plurality of nozzles. The circular conduit is fluidly connected to one or more fluid supply conduits extending upward. The circular conduit may have any shape and cross-section, for example, a circular, square or triangular cross-section. Preferably, the conduit does not have a large size such that the remaining opening is large enough for the soil suspension moving upward.

[0023] The circular conduits are preferably welded to the inner wall of the tubular lower part. The supply conduits may be high pressure conduits suspended from an elevated position, preferably the upper end of the monopile. These conduits may extend free of the wall of the monopile. Preferably, one or more fluid supply conduits are welded to the inner wall of the tubular lower part.

[0024] The nozzle is preferably a high pressure injection nozzle suitably connected to a pump via a high pressure water conduit. Such a pump is preferably located from outside the pile, for example on a floating vessel. For example, the high pressure conduit may extend upwards to the upper end of the monopile where it is connected to the welded supply conduit.

[0025] The monopile preferably has a lower region, which is surrounded by the soil mass when positioned in the soil mass, and an upper region, which extends above the soil mass. One or more openings are present in the upper region. These openings may be one or more openings, which are also used to pass power cables and other connections required for the wind turbine when the monopile is installed. In order for a suspension of water and soil to flow from the lower end of the monopile to these openings, there is a fluid connection between the lower end and the one or more openings.

[0026] The upper region may comprise a tubular portion having a smaller diameter than the tubular portion of the lower region. A transition portion having a truncated cone shape may then be positioned below the tubular portion having the smaller diameter. This shape of monopiles for wind turbines is well known.

[0027] The monopile has a lower region and wherein the lower region preferably has a cylindrical and flush outer surface and a cylindrical and flush inner surface. This simplifies the design. It has been found that the penetration of the monopile according to the invention does not require a specifically designed toe as in prior art publications EP3464734B1, WO2020 / 207903 and WO2019 / 206690.

[0028] In the method of the invention, it is preferred to use a vibratory hammer also at the upper end of the monopile. The applicant has found that by providing a water jet at the lower part of the monopile according to the invention and providing vibrations to the upper end of the monopile, advantageous penetration of the monopile is achieved in many types of soil. The water jet achieves a 70% strain reduction as compared to when the monopile is driven into the soil using only a vibratory hammer. The reduction in strain is also a measure of noise reduction. It is believed that the water jet achieves a significant reduction or even removal of friction on the inside of the monopile. The vibratory hammer is suitably present to reduce the friction between the soil and the outer surface of the monopile and the soil resistance below the tip of the pile wall.

[0029] A vibratory hammer may be used as a connection between the upper flow end of the supply conduit and a high pressure conduit extending from a pump positioned from outside the foundation pile, for example on a floating vessel or jack-up vessel. Preferably, the vibratory hammer and the connected high pressure conduit may be positioned on the upper end of the monopile, resulting in a fluid connection between the high pressure conduit and the supply conduit within the monopile. It is also possible to have the supply conduit extend directly through one of the holes in the upper portion of the pile. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Will borrow from the following Figures 1 to 3To illustrate the present invention. DETAILED DESCRIPTION

[0031] Figure 1 A cross-sectional view of a monopile for a wind turbine according to the invention is shown. The monopile (1) has an upper end (2) and a lower end (3) when positioned. A tubular lower part (4) extends upwardly from the lower end (3). An injection nozzle (6) is present at the inner side (5) of the tubular lower part (4). The monopile (1) is provided with an opening (7) at a higher elevation (8) in an upper region (9). As shown, the injection nozzle (6) is positioned at a distance (10) from the lower end (3) and is directed to inject a water flow towards the lower end (3) in at least a tangential and axial direction. The nozzle (6) is shown directed to the lower end (3) at an angle of 45 degrees to the horizontal (11). The lower tubular part (4) has a cylindrical and flush outer surface (12) extending from the lower end (3). Furthermore, the inner side (5) of the lower tubular part (4) is a cylindrical and flush surface, except for the circular conduit (13) from which the nozzle (6) extends. The circular conduit (13) is welded to the inner side (5) of the lower tubular part (4). Figure 1 The circular duct (13) in the monopile has a triangular cross section and acts as a manifold for supplying water to the nozzles (6). The water is supplied by a fluid supply duct (14) welded to the inner wall (5). There is no pumping system for extracting fluid from the monopile.

[0032] Figure 2 A monopile (1) according to the invention is shown mounted on a seabed (15). The upper region (9) of the monopile (1) comprises a tubular portion (19) having a smaller diameter than the tubular portion (20) of the lower region (21) and a transition portion (22), the tubular portion (19) having a smaller diameter than the tubular portion (20) of the lower region (21), and the transition portion (22) having a truncated cone shape positioned below the tubular portion (19) having a smaller diameter. A vibratory hammer (23) is attached to the upper end (2) of the monopile (1). A pump (24) is positioned on a floating vessel (25) from outside the monopile (1). A high pressure conduit (26) delivers high pressure water to the upper end (2) of the monopile (1), where the high pressure conduit (26) is connected to a welded supply conduit (14). A further hydraulic conduit (27) for operating the vibratory hammer (23) is shown.

[0033] Single pile (1) Figure 2The monopile is installed in soil which is located below a body of water (18) consisting of a layer of sand (29), a layer of clay (30) and a deeper layer of sand (31). At the seabed, there is a scour protection (32) to prevent the sand around the monopile from being washed away by the local water current. At the inner side (5) of the tubular lower part (4), there is an injection nozzle (6) which injects water into the soil at an injection distance which does not extend beyond the lower end (3) of the monopile, as shown by the arrows and crosses. In this way, substantially all of the injected water remains in the monopile to form a suspension (28) consisting of sand and clay as well as water and having a suspension water level (16) just above the water level of the body of water (18). Due to this difference in water level, the suspension (28) will be continuously discharged through an opening (7) located below the water level (17) of the body of water (18).

[0034] Figure 3 Show according to Figure 1 Experimental results of laboratory tests of the penetration velocity of a monopile in a sandy soil type riverbed. The length of the monopile is 2 m.

[0035] Version V1 is provided with a ring of injection nozzles at a distance of 25 cm from the lower end of the monopile. The ring has injection nozzles directed vertically downwards and upwards. The nozzles directed upwards have a tangential direction.

[0036] Version V2 is as Version V1 except that all nozzles are directed to inject water streams towards the lower end at an angle of 30 degrees to the horizontal in at least the tangential and axial directions.

[0037] Version V3 is the same as Version V2 except that all nozzles are directed to inject the water stream at an angle of 45 degrees to the horizontal.

[0038] like Figure 3 It can be seen in the graph that the penetration speed increases when all the water is injected towards the lower end in at least the tangential and axial directions. The best results are achieved when the angle is 45 degrees. A vibratory hammer was not used in order to measure the effect of the water jet only. It is understood that the penetration speed will be significantly higher when a vibratory hammer is used.

Claims

1. A monopile for a wind turbine, the monopile having an upper end and a lower end when positioned and comprising a tubular lower portion extending upwardly from the lower end, and wherein an injection nozzle is present inside the tubular lower portion, The monopile is provided with one or more openings at a higher elevation, and Wherein the injection nozzle is positioned at a distance from the lower end and is directed to inject water flow in at least tangential and axial directions towards the lower end.

2. A monopile according to claim 1, wherein the injection nozzle is directed to the lower end at an angle of between 30 and 60 degrees to the horizontal.

3. A monopile according to any one of claims 1 to 2, wherein the injection nozzle is located at a distance of between 0.25 m and 2 m from the lower end.

4. The monopile according to any one of claims 1 to 3, wherein the monopile has a lower region and an upper region, the lower region being surrounded by the soil mass when positioned in the soil mass, the upper region extending above the soil mass, and wherein the one or more openings are present in the upper region.

5. The monopile according to claim 4, wherein the upper region comprises a tubular portion having a smaller diameter than the tubular portion of the lower region and a transition portion having a truncated cone shape located below the tubular portion having the smaller diameter.

6. A monopile according to any one of claims 1 to 5, wherein the lower tubular portion has a cylindrical and flush outer surface.

7. Monopile according to claim 6, wherein the lower region and the lower end of the monopile have the shape of a tube, inside which the ring of the nozzle is arranged at an injection distance from the lower end.

8. The monopile according to any one of claims 1-7, wherein the monopile is designed for a specific type of soil in which the monopile is to be positioned by varying the injection distance.

9. A monopile according to any one of claims 1 to 8, wherein the nozzle is fluidly connected to a circular conduit connected to the inner wall of the tubular lower portion, and wherein the circular conduit is fluidly connected to one or more fluid supply conduits extending upwardly.

10. A monopile according to claim 9, wherein the one or more fluid supply conduits are welded to the inner wall of the tubular lower portion.

11. A monopile according to any one of claims 1 to 10, wherein there is no pumping system for extracting fluid from within the monopile.

12. A method for installing a monopile for a wind turbine according to any one of claims 1 to 11 on a soil surface covered by a body of water, by positioning a lower end on the soil surface and by spraying water from an injection nozzle towards the lower end in a direction having at least a tangential and an axial direction, thereby causing the sprayed water to penetrate the soil at the lower end to cause a soil suspension of water and soil particles, the soil suspension swirling upwards within the monopile towards one or more openings, the soil suspension being discharged to the body of water through the one or more openings.

13. The method according to claim 12, wherein the diameter of the tubular lower part is between 6 m and 15 m and wherein between 10000 l / min and 100000 l / min of water is injected from the injection nozzle.

14. A method according to any one of claims 12 to 13, wherein the sprayed water does not substantially penetrate the soil to a level below the lower end of the monopile.

15. The method of claim 14, wherein more than 90 vol% of the water ejected from the injection nozzle is discharged to the body of water via the one or more openings.

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