JP2024088267A - Jacket structure for offshore wind turbine and welding method of the same - Google Patents

Abstract

To provide a jacket structure for an offshore wind turbine which can secure sufficient fatigue strength in a connection part, and to provide a welding method of the jacket structure for the offshore wind turbine.SOLUTION: A jacket structure 100 for an offshore wind turbine includes: a first oblique brace 40 which is a cylindrical member; a second oblique brace 50 which is a cylindrical member and intersects with the first oblique brace 40; and a pedestal 20 in which an offshore wind turbine 300 is installed and which is supported by the first oblique brace 40 and the second oblique brace 50. At an intersection between the first oblique brace 40 and the second oblique brace 50, double side welding is performed.SELECTED DRAWING: Figure 1

Description

The present invention relates to a jacket structure for an offshore wind turbine and a welding method for a jacket structure for an offshore wind turbine.

2. Description of the Related Art In order to place structures such as wind turbines used for wind power generation offshore, a jacket structure made of steel pipes may be used.
Patent Document 1 discloses a structure for reducing stress concentration at joints between steel pipes, in which steel pipes of different diameters are overlapped to form a joint and grout is poured into the joint.
Patent Document 2 discloses a structure in which, in order to reduce the amount of steel used in revetment structures, which are offshore structures, a wall is formed by arranging sheet piles in rows of piles and filling the wall with backfill material.

JP 2015-55045 A JP 2004-308328 A

In conventional jacket structures, when steel pipes are welded at grid points, welding is generally performed only from the outside of the steel pipes (one-side welding).
However, when a wind turbine is installed on the ocean (offshore wind turbine), the offshore wind turbine is placed in a severe fatigue environment, so it is impossible to provide sufficient fatigue strength to the welded portion with the above-mentioned one-sided welding.

The present invention was made in consideration of the above-mentioned circumstances, and aims to provide a jacket structure for an offshore wind turbine and a welding method for the jacket structure for an offshore wind turbine that can ensure sufficient fatigue strength at the connection.

<1> The jacket structure for an offshore wind turbine according to aspect 1 of the present invention is a jacket structure for an offshore wind turbine comprising a first diagonal brace that is a cylindrical member, a second diagonal brace that is also a cylindrical member and that intersects with the first diagonal brace, and a base on which an offshore wind turbine is installed and that is supported by the first diagonal brace and the second diagonal brace, characterized in that the intersection between the first diagonal brace and the second diagonal brace is welded on both sides.

According to this invention, the intersection between the first diagonal brace and the second diagonal brace is welded on both sides. This ensures sufficient fatigue strength at the connection between the first diagonal brace and the second diagonal brace.

<2> The jacket structure for an offshore wind turbine according to aspect 2 of the present invention is characterized in that in the jacket structure for an offshore wind turbine according to aspect 1, the outer diameter of the first diagonal brace is larger than the outer diameter of the second diagonal brace.

According to this invention, the outer diameter of the first diagonal brace is larger than the outer diameter of the second diagonal brace. This makes it easier to perform double-sided welding of the intersection between the first diagonal brace and the second diagonal brace.

<3> The jacket structure for an offshore wind turbine according to aspect 3 of the present invention is the jacket structure for an offshore wind turbine according to aspect 1 or aspect 2, characterized in that the base is supported by the first diagonal brace and the second diagonal brace via a plurality of legs, and the plate thickness of a first leg can portion, which is one part of the plurality of legs, and which includes an intersection point between the one leg and an end of the first diagonal brace, is thinner than the plate thickness of a second leg can portion, which is one part of the one leg, and which includes an intersection point between the one leg and an end of the second diagonal brace.

According to this invention, the plate thickness of the first leg can portion including the intersection of one of the multiple legs and the end of the first diagonal brace is thinner than the plate thickness of the second leg can portion including the intersection of one of the multiple legs and the end of the second diagonal brace. This makes it possible to reduce the plate thickness of the first leg can portion, and therefore the material cost of the legs.

<4> The jacket structure for an offshore wind turbine according to aspect 4 of the present invention is a jacket structure for an offshore wind turbine according to any one of aspects 1 to 3, characterized in that the base is supported by the first diagonal brace and the second diagonal brace via a plurality of legs, and the strength of the steel material in the first leg can portion, which is one part of the plurality of legs and includes the intersection between the one leg and the end of the first diagonal brace, is weaker than the strength of the steel material in the second leg can portion, which is one part of the plurality of legs and includes the intersection between the one leg and the end of the second diagonal brace.

According to this invention, the strength of the steel material in the first leg can portion, which includes the intersection between one of the multiple legs and the end of the first diagonal brace, is weaker than the strength of the steel material in the second leg can portion, which includes the intersection between one of the multiple legs and the end of the second diagonal brace. This allows a cheaper material to be used in the first leg can portion, thereby reducing the material costs of the legs.

<5> The jacket structure for an offshore wind turbine according to aspect 5 of the present invention is the jacket structure for an offshore wind turbine according to aspect 3 or 4, characterized in that the steel material of the first leg can portion is SM490Y or SM520, and the steel material of the second leg can portion is SA440.

According to this invention, the steel material of the first leg can portion is SM490Y or SM520, and the steel material of the second leg can portion is SA440. This allows the strength of the steel material of the first leg can portion to be weaker than the strength of the steel material of the second leg can portion. This allows the material cost of the legs to be reduced.

<6> The jacket structure for an offshore wind turbine according to aspect 6 of the present invention is characterized in that in the jacket structure for an offshore wind turbine according to any one of aspects 3 to 5, the length of the first leg can portion along the one longitudinal direction is longer than the length of the second leg can portion along the longitudinal direction.

According to this invention, the length of the first leg can portion along one longitudinal direction is longer than the length of the second leg can portion along one longitudinal direction. This makes it possible to reduce the length of the second leg can portion while keeping the length of the first leg can portion sufficient, for example, when the outer diameter of the first diagonal brace is larger than the outer diameter of the second diagonal brace. This makes it possible to reduce the material costs of the legs.

<7> The jacket structure for an offshore wind turbine according to aspect 7 of the present invention is the jacket structure for an offshore wind turbine according to any one of aspects 1 to 6, further comprising a third diagonal brace, the base being supported by the first diagonal brace, the second diagonal brace, and the third diagonal brace via a plurality of legs, a first leg can portion being one of the plurality of legs, the first leg can portion including the intersection of the one leg and an end of the first diagonal brace, the third diagonal brace being connected to the first leg can portion, and the outer diameter of the third diagonal brace being larger than the outer diameter of the second diagonal brace.

According to this invention, a third diagonal brace is connected to a first leg can portion including an intersection point between one of the multiple legs and an end of the first diagonal brace, and the outer diameter of the third diagonal brace is larger than the outer diameter of the second diagonal brace. This allows the cross sections of the first diagonal brace and the third diagonal brace connected to the first leg can portion to be unified, for example, when the outer diameter of the first diagonal brace and the outer diameter of the third diagonal brace are made the same. This makes it easier to manage parts when manufacturing the jacket structure. It also makes it easier to perform structural calculations for the jacket structure.

<8> The jacket structure for an offshore wind turbine according to aspect 8 of the present invention is the jacket structure for an offshore wind turbine according to any one of aspects 1 to 7, further comprising a fourth diagonal brace, the base being supported by the first diagonal brace, the second diagonal brace, and the fourth diagonal brace via a plurality of legs, the second leg can portion being one of the plurality of legs, the second leg can portion including the intersection between the one leg and an end of the second diagonal brace, the fourth diagonal brace being connected to the second leg can portion, and the outer diameter of the fourth diagonal brace being smaller than the outer diameter of the first diagonal brace.

According to this invention, a fourth diagonal brace is connected to a second leg can portion including an intersection point between one of the multiple legs and an end of the second diagonal brace, and the outer diameter of the fourth diagonal brace is smaller than the outer diameter of the first diagonal brace. This allows the cross sections of the second diagonal brace and the fourth diagonal brace connected to the second leg can portion to be unified, for example, when the outer diameter of the second diagonal brace and the outer diameter of the fourth diagonal brace are made the same. This makes it easier to manage parts when manufacturing the jacket structure. It also makes it easier to perform structural calculations for the jacket structure.

<9> The jacket structure for an offshore wind turbine according to aspect 9 of the present invention is a jacket structure for an offshore wind turbine according to any one of aspects 1 to 8, characterized in that a cylindrical portion of the second diagonal brace within a predetermined range including the intersection of the first diagonal brace and the second diagonal brace is a second nearby portion, a cylindrical portion of the second diagonal brace that is farther from the intersection than the second nearby portion is a second remote portion, the outer diameter of the second nearby portion is equal to or greater than the outer diameter of the second remote portion, and the inner diameter of the second nearby portion is equal to or less than the inner diameter of the second remote portion.

According to this invention, the outer diameter of the second nearby portion is equal to or larger than the outer diameter of the second remote portion, and the inner diameter of the second nearby portion is equal to or smaller than the inner diameter of the second remote portion. Therefore, the plate thickness of the second nearby portion is at least equal to or larger than that of the second remote portion. This ensures the strength of the intersection of the second diagonal brace. In addition, if the plate thickness of the second nearby portion is increased, the second nearby portion can be more easily welded on both sides at the intersection with the first nearby portion. This improves the fatigue strength.
Furthermore, by making the plate thickness of the second remote portion smaller than that of the second nearby portion, it is possible to prevent the weight of the entire second diagonal brace from increasing more than necessary while ensuring sufficient strength against bending moments, etc. in the second nearby portion.

<10> The jacket structure for an offshore wind turbine according to aspect 10 of the present invention is characterized in that the jacket structure for an offshore wind turbine according to aspect 9 further includes a tapered portion provided between the inner surface of the second nearby portion and the inner surface of the second remote portion.

According to this invention, a tapered portion is provided between the inner surface of the second nearby portion and the inner surface of the second remote portion. This allows the second nearby portion and the second remote portion to be connected by continuously changing the distance between them. This makes it possible to suppress stress concentration at the connection between the second nearby portion and the second remote portion.

<11> The jacket structure for an offshore wind turbine according to aspect 11 of the present invention is the jacket structure for an offshore wind turbine according to aspect 10, characterized in that the tapered portion and the second remote portion are welded on one side from the inside of the second diagonal brace.

According to this invention, the tapered portion and the second remote portion are welded on one side from the inside of the second diagonal brace. Here, if the inner diameter of the second nearby portion is equal to or smaller than the inner diameter of the second remote portion, stress concentration is likely to occur on the inner surface of the second diagonal brace at the boundary between the tapered portion and the second remote portion. Weld defects are particularly likely to occur at the root portion of the weld. By performing one-sided welding from the inside of the second diagonal brace, the root portion can be positioned on the outside of the second diagonal brace. Therefore, the root portion of the weld can be separated from the location where stress concentration is likely to occur at the boundary between the tapered portion and the second remote portion. This makes it possible to suppress a decrease in fatigue life at the boundary.

<12> The jacket structure for an offshore wind turbine according to aspect 12 of the present invention is a jacket structure for an offshore wind turbine according to any one of aspects 1 to 8, characterized in that a cylindrical portion of the second diagonal brace within a predetermined range including an intersection point between the first diagonal brace and the second diagonal brace is a second nearby portion, a cylindrical portion of the second diagonal brace that is farther from the intersection point than the second nearby portion is a second remote portion, an outer diameter of the second remote portion is equal to or greater than an outer diameter of the second nearby portion, and an inner diameter of the second remote portion is equal to or less than an inner diameter of the second nearby portion.

According to this invention, the outer diameter of the second remote portion is equal to or greater than the outer diameter of the second nearby portion, and the inner diameter of the second remote portion is equal to or less than the inner diameter of the second nearby portion. Therefore, the plate thickness of the second remote portion is at least the same as that of the second nearby portion, or is greater than that of the second nearby portion. This ensures that the second remote portion has sufficient strength against bending moments, etc.

<13> The jacket structure for an offshore wind turbine according to aspect 13 of the present invention is characterized in that the jacket structure for an offshore wind turbine according to aspect 12 further includes a tapered portion provided between the outer surface of the second nearby portion and the outer surface of the second remote portion.

According to this invention, a tapered portion is provided between the outer surface of the second nearby portion and the outer surface of the second remote portion. This allows the second nearby portion and the second remote portion to be connected by continuously changing the distance between them. This makes it possible to suppress stress concentration at the connection between the second nearby portion and the second remote portion.

<14> The jacket structure for an offshore wind turbine according to aspect 14 of the present invention is the jacket structure for an offshore wind turbine according to aspect 13, characterized in that the tapered portion and the second adjacent portion are welded on one side from the outside of the second diagonal brace.

According to this invention, the tapered portion and the second nearby portion are welded on one side from the outside of the second diagonal brace. Here, if the outer diameter of the second remote portion is equal to or larger than the outer diameter of the second nearby portion, stress concentration is likely to occur at the boundary between the tapered portion and the second nearby portion on the outer surface of the second diagonal brace. Weld defects are particularly likely to occur at the root portion of the weld. By performing one-sided welding from the outside of the second diagonal brace, the root portion can be positioned on the inside of the second diagonal brace. Therefore, the root portion of the weld can be separated from the location where stress concentration is likely to occur at the boundary between the tapered portion and the second nearby portion. This makes it possible to suppress a decrease in fatigue life at the boundary.

<15> The jacket structure for an offshore wind turbine according to aspect 15 of the present invention is a jacket structure for an offshore wind turbine according to any one of aspects 1 to 14, characterized in that the outer diameter of the first diagonal brace is the same throughout the entire length of the first diagonal brace.

According to this invention, the outer diameter of the first diagonal brace is the same throughout its entire length. This makes it easier to provide, for example, a rust-resistant stainless steel plate or the like on the outer peripheral surface of the first diagonal brace.

<16> The jacket structure for an offshore wind turbine according to aspect 16 of the present invention is a jacket structure for an offshore wind turbine comprising a plurality of cylindrical legs, a first diagonal brace which is a cylindrical member and connected to the legs, a second diagonal brace which is a cylindrical member and connected to the legs and intersects with the first diagonal brace, and a base supported by the legs, the first diagonal brace, and the second diagonal brace and on which the offshore wind turbine is installed, wherein the outer diameter of the first diagonal brace is larger than the outer diameter of the second diagonal brace, and the double-sided welds are provided at the intersections of the first diagonal brace and the second diagonal brace and at the intersections of the second diagonal brace and one of the legs, and the cylindrical portion of the second diagonal brace The brace proximal portion is a cylindrical portion within a predetermined range including the intersection of the second diagonal brace and the first diagonal brace, and the brace remote portion is a cylindrical portion of the second diagonal brace that is farther from the intersection of the second diagonal brace and the first diagonal brace than the brace proximal portion. The leg proximal portion is a cylindrical portion of the second diagonal brace within a predetermined range including the intersection of the second diagonal brace and the first diagonal brace, and the leg remote portion is a cylindrical portion of the second diagonal brace that is farther from the intersection of the second diagonal brace and the first diagonal brace than the leg proximal portion.

According to this invention, double-sided welds are provided at the intersection between the first diagonal brace and the second diagonal brace and at the intersection between the second diagonal brace and one of the legs. In other words, the intersection between the first diagonal brace and the second diagonal brace and the intersection between the second diagonal brace and one of the legs are both welded. This ensures sufficient fatigue strength at the intersection between the first diagonal brace and the second diagonal brace and the intersection between the second diagonal brace and one of the legs.

One-sided welds are provided between the brace proximal portion and the brace distal portion, and between the leg proximal portion and the leg distal portion. In other words, one-sided welds are provided between the brace proximal portion and the brace distal portion, and between the leg proximal portion and the leg distal portion. This makes it possible to avoid, for example, workers being left behind inside the jacket structure by double-sided welding each welded portion in the jacket structure.

<17> The welding method for a jacket structure for an offshore wind turbine according to aspect 17 of the present invention is a welding method for a jacket structure for an offshore wind turbine comprising a plurality of cylindrical legs, a first diagonal brace that is a cylindrical member and is connected to the legs, a second diagonal brace that is a cylindrical member and is connected to the legs and intersects with the first diagonal brace, and a base that is supported by the legs, the first diagonal brace, and the second diagonal brace and on which the offshore wind turbine is installed, the outer diameter of the first diagonal brace being larger than the outer diameter of the second diagonal brace, and the welding method includes a double-sided welding process for double-sided welding an intersection between the first diagonal brace and the second diagonal brace and an intersection between the second diagonal brace and one of the legs, and a double-sided welding process for double-sided welding the second diagonal brace after the double-sided welding process. The method is characterized by comprising a one-sided welding process for performing one-sided welding between a brace proximal portion, which is a cylindrical portion of the brace within a predetermined range including the intersection of the second diagonal brace with the first diagonal brace, and a brace remote portion, which is a cylindrical portion of the second diagonal brace that is farther from the intersection of the second diagonal brace with the first diagonal brace than the brace proximal portion, and a leg proximal portion, which is a cylindrical portion of the second diagonal brace within a predetermined range including the intersection of the second diagonal brace with the first diagonal brace, and a leg remote portion, which is a cylindrical portion of the second diagonal brace that is farther from the intersection of the second diagonal brace with the first diagonal brace than the leg proximal portion.

According to this invention, the method includes a double-sided welding process for double-sided welding the intersection between the first diagonal brace and the second diagonal brace and the intersection between the second diagonal brace and one of the legs, and a single-sided welding process for single-sided welding between the portion near the brace and the portion far from the brace after the double-sided welding process, and single-sided welding between the portion near the leg and the portion far from the leg.

Here, if the first diagonal brace is an integral cylindrical member, it is impossible to double-sided weld both ends of the first diagonal brace to the legs, as this would leave the worker inside the first diagonal brace after the welding work. In contrast, by performing a single-sided welding process after the double-sided welding process, it is possible to double-sided weld the intersection between the first diagonal brace and the second diagonal brace and the intersection between the second diagonal brace and one of the legs while avoiding the worker being left inside. This ensures the weld strength of each intersection that is double-sided welded.

The present invention provides a jacket structure for an offshore wind turbine that can ensure sufficient fatigue strength at the connection and a welding method for the jacket structure for an offshore wind turbine.

FIG. 2 is a front view of the jacket structure for an offshore wind turbine according to the present embodiment. FIG. 2 is an enlarged cross-sectional view of a portion II shown in FIG. FIG. This is the positional relationship between the first diagonal brace and the second diagonal brace, or the third diagonal brace and the fourth diagonal brace, when viewed from the axial direction of the leg. FIG. 2 is an enlarged cross-sectional view of a V portion shown in FIG. FIG. 2 is an enlarged cross-sectional view of a portion VI shown in FIG. This shows the positional relationship between the second proximal portion and the second distal portion when viewed from the axial direction of the second diagonal brace. 13 shows the positional relationship between the portion near the second leg and the portion remote from the second leg when viewed from the axial direction of the second diagonal brace. FIG. FIG. 13 is a cross-sectional view of an intersection between a first diagonal brace and a second diagonal brace as viewed from the axial direction of the first diagonal brace. FIG. 11 is an enlarged cross-sectional view of a V portion shown in FIG. 1 in a second embodiment. FIG. 6 is an enlarged cross-sectional view of a portion VI shown in FIG. 1 in a second embodiment. FIG. 2 is an enlarged cross-sectional view of a modified example of the V portion shown in FIG. 1 .

First Embodiment
Hereinafter, an offshore wind turbine jacket structure 100 and a welding method for the offshore wind turbine jacket structure 100 according to one embodiment of the present invention will be described with reference to the drawings.
The jacket structure 100 for an offshore wind turbine is installed offshore via piles L driven into the ground such as the seabed. As shown in FIG. 1 , the jacket structure 100 for an offshore wind turbine is used to support an offshore wind turbine 300.

(Regarding the offshore wind turbine jacket structure 100)
As shown in FIG. 1 , a jacket structure 100 for an offshore wind turbine includes a leg 10, a base 20, a skirt sleeve 30, a first diagonal brace 40, a second diagonal brace 50, a third diagonal brace 60, and a fourth diagonal brace 70.

The legs 10 are provided in a plurality of legs in the jacket structure 100 for an offshore wind turbine. In this embodiment, the number of legs 10 is four. As shown in FIG. 1, the legs 10 extend, for example, in the vertical direction. The pipe axis of the legs 10 is, for example, inclined with respect to the vertical direction. The upper end of the legs 10 is connected to the base 20. The lower end of the legs 10 is connected to the pile L via a skirt sleeve 30. For example, a steel pipe is preferably used for the legs 10. A first diagonal brace 40, a second diagonal brace 50, a third diagonal brace 60, and a fourth diagonal brace 70 are connected to the legs 10.

In this embodiment, a double-sided welded portion BW is provided at the intersection between the second diagonal brace 50 and one of the multiple legs 10, as shown in Fig. 2. In other words, the second diagonal brace 50 and one of the multiple legs 10 are welded on both sides. This ensures sufficient fatigue strength at the connection between the second diagonal brace 50 and the leg 10. At this time, the double-sided welded portion BW has, for example, a double-sided groove or a K-shaped groove K, as shown in Fig. 3.
As shown in FIG. 1 , the leg 10 includes a first leg can portion 11 , a second leg can portion 12 , and a straight pipe portion 13 .

The first leg can portion 11 is one of the multiple legs 10. The first leg can portion 11 includes an intersection between one of the multiple legs 10 and the end of the first diagonal brace 40. In other words, the first leg can portion 11 is connected to the first diagonal brace 40. In addition, the first leg can portion 11 is connected to the third diagonal brace 60 (details will be described later). In this embodiment, the length of the first leg can portion 11 along the longitudinal direction of one of the legs 10 is, for example, 1.5 to 2.5 times the outer diameter of the first diagonal brace 40.

The second leg can portion 12 is one of the multiple legs 10. The second leg can portion 12 includes an intersection between one of the multiple legs 10 and an end of the second diagonal brace 50. That is, the second leg can portion 12 is connected to the second diagonal brace 50. In addition, the second leg can portion 12 is connected to a fourth diagonal brace 70 (details will be described later). In this embodiment, the length of the second leg can portion 12 along the longitudinal direction of one of the legs 10 is, for example, 1.5 to 2.5 times the outer diameter of the second diagonal brace 50.
The straight pipe portion 13 is a portion of the leg 10 other than the first leg can portion 11 and the second leg can portion 12. The straight pipe portion 13 is located between the first leg can portion 11 and the second leg can portion 12, for example.

In this embodiment, the first leg can portion 11 and the second leg can portion 12 in one of the legs 10 have the following relationship.
For example, the length of the first leg can portion 11 along one longitudinal direction of the leg 10 is longer than the length of the second leg can portion 12 along one longitudinal direction of the leg 10. This corresponds to the diameter of the first diagonal brace 40 connected to the first leg can portion 11 being larger than the diameter of the second diagonal brace 50 connected to the second leg can portion 12 (details will be described later).

For example, the strength of the steel material of the first leg can portion 11 is weaker than the strength of the steel material of the second leg can portion 12. Specifically, the above-mentioned relationship is ensured as follows.
For example, the plate thickness of the first leg can portion 11 is made thinner than the plate thickness of the second leg can portion 12. For example, the first leg can portion 11 is made of a steel material having a lower strength than the second leg can portion 12. In this case, the steel material of the first leg can portion 11 is, for example, SM490Y or SM520. The steel material of the second leg can portion 12 is, for example, SA440.
As described above, when different steel materials are used for the first leg can portion 11 and the second leg can portion 12, the first leg can portion 11, the second leg can portion 12, and the straight pipe portion 13 are connected by, for example, welding.

In addition, the outer diameters of the first leg can portion 11 and the second leg can portion 12 of the leg 10 are preferably larger than the outer diameters of the first leg vicinity portion 43 of the first diagonal brace 40 and the second leg vicinity portion 54 of the second diagonal brace 50, which will be described later. With this configuration, for example, as shown in FIG. 4, when the first leg vicinity portion 43 or the second leg vicinity portion 54 is aligned with the side of the first leg can portion 11 or the second leg can portion 12, respectively, that is, when the axial end of the first diagonal brace 40 or the axial end of the second diagonal brace 50 is abutted against the outer peripheral surface of the leg 10, the radial end of the first diagonal brace 40 or the second diagonal brace 50 is located closer to the axial center of the leg 10 than the radial end of the first leg can portion 11 or the second leg can portion 12.

For example, as shown in FIG. 4, in a direction perpendicular to both the axial direction of the first diagonal brace 40 and the axial direction of the leg 10, the angle A between the radial end of the first diagonal brace 40 and the outer peripheral surface of the first leg can portion 11 is closer to a right angle when the outer diameter of the first diagonal brace 40 and the outer diameter of the first leg can portion 11 are equal to 180°. In a direction perpendicular to both the axial direction of the second diagonal brace 50 and the axial direction of the leg 10, the angle A between the radial end of the second diagonal brace 50 and the outer peripheral surface of the second leg can portion 12 is closer to a right angle when the outer diameter of the second diagonal brace 50 and the outer diameter of the second leg can portion 12 are equal to 180°. By adopting such an embodiment, it becomes easier to provide a double-sided groove or a K-shaped groove K at the end of the first diagonal brace 40 or the second diagonal brace 50.

As shown in FIG. 1, the offshore wind turbine 300 is installed on the base 20. The base 20 is supported by a first diagonal brace 40, a second diagonal brace 50, a third diagonal brace 60, and a fourth diagonal brace 70 via a number of legs 10. The base 20 is a so-called transition piece in a known jacket structure used as an offshore structure.

The skirt sleeve 30 is provided at the lower end of the leg 10 and is used to connect the leg 10 to the pile L. This allows the jacket structure 100 for an offshore wind turbine to be installed offshore via the pile L driven into the ground, such as the seabed.

The first diagonal brace 40 is a cylindrical member. For example, a steel pipe is preferably used for the first diagonal brace 40. In this embodiment, the outer diameter of the first diagonal brace 40 is the same throughout the entire length of the first diagonal brace 40. The first diagonal brace 40 includes a first proximal portion 41, a first remote portion 42, a first leg proximal portion 43, and a first leg remote portion 44 (see Figures 2 and 5).

5, the first vicinity portion 41 is a cylindrical portion of the first diagonal brace 40, and is a cylindrical portion within a predetermined range including an intersection point between the first diagonal brace 40 and the second diagonal brace 50. The predetermined range refers to a range in the longitudinal direction of the first diagonal brace 40. The predetermined range is preferably about 1.5 to 2.5 times the outer diameter of the first vicinity portion 41.
The first remote portion 42 is a cylindrical portion of the first diagonal brace 40 that is farther from the intersection than the first proximal portion 41 .

As shown in Fig. 2, the first leg vicinity portion 43 is a cylindrical portion of the first diagonal brace 40, and is a cylindrical portion within a predetermined range including an intersection point between the first diagonal brace 40 and one of the legs 10. The predetermined range refers to a range in the longitudinal direction of the first diagonal brace 40. The size of the predetermined range can be appropriately set based on the cross-sectional force distribution and the brace diameter. Taking into account the ease of welding work, the predetermined range is preferably set to 2.0 m or less.
The first leg remote portion 44 is a cylindrical portion of the first diagonal brace 40 that is farther from the intersection of the first diagonal brace 40 with one of the legs 10 than the first leg proximal portion 43 .

The second diagonal brace 50 is a cylindrical member and intersects with the first diagonal brace 40. For example, a steel pipe is preferably used for the second diagonal brace 50. As shown in FIG. 1 and FIG. 5, the second diagonal brace 50 includes two cylindrical members. In other words, the second diagonal brace 50 is divided into two. As shown in FIG. 1, the first diagonal brace 40 and the second diagonal brace 50 are arranged in an X-shape. The X-shape may be provided in only one stage in the jacket structure 100 for an offshore wind turbine, for example. In this embodiment, the X-shape is provided in two stages in the vertical direction (details will be described later). The X-shape may also be provided in three or more stages in the vertical direction. In this embodiment, a double-sided welded portion BW is provided at the intersection between the first diagonal brace 40 and the second diagonal brace 50, as shown in FIG. 5. That is, the first diagonal brace 40 and the second diagonal brace 50 are welded on both sides. More specifically, each of the cylindrical members of the second diagonal brace 50 is joined to the first diagonal brace 40 at the intersection by double-sided welding. This ensures sufficient fatigue strength at the connection between the first diagonal brace 40 and the second diagonal brace 50. The double-sided welded portion BW has, for example, a double-sided groove or a K-shaped groove K, as shown in FIG. 3.

The second diagonal brace 50 includes a second proximal portion 51, a second remote portion 52, a tapered portion 53, a second leg proximal portion 54, a second leg remote portion 55, and a leg tapered portion 56 (see Figures 5 and 6).
The second vicinity portion 51 is a cylindrical portion of the second diagonal brace 50, and is a cylindrical portion within a predetermined range including the intersection of the second diagonal brace 50 and the first diagonal brace 40. The predetermined range refers to a range in the longitudinal direction of the second diagonal brace 50. The size of the predetermined range can be appropriately set based on the cross-sectional force distribution and the brace diameter. In consideration of the workability of welding, the predetermined range is preferably 2.0 m or less, and more preferably 1.5 m or less.

The second remote portion 52 is a cylindrical portion of the second diagonal brace 50, and is a cylindrical portion farther from the intersection of the second diagonal brace 50 and the first diagonal brace 40 than the second nearby portion 51. In this embodiment, a one-sided weld OW is provided between the second nearby portion 51 and the second remote portion 52. That is, the second nearby portion 51 and the second remote portion 52 are connected by one-sided welding (details will be described later).
The relationship between the outer diameter and the inner diameter of the second proximal portion 51 and the second remote portion 52 is as follows.
That is, the outer diameter of the second nearby portion 51 is equal to or larger than the outer diameter of the second remote portion 52. That is, the outer diameter of the second nearby portion 51 is equal to or larger than the outer diameter of the second remote portion 52. The outer peripheral surface of the second nearby portion 51 is flush with the outer peripheral surface of the second remote portion 52, or is located radially outward of the outer peripheral surface of the second remote portion 52. Here, being flush means that the outer peripheral surface of the second nearby portion 51 is not located outward of the outer peripheral surface of the second remote portion 52, and is not located inward of the outer peripheral surface of the second remote portion 52.

The inner diameter of the second nearby portion 51 is at least equal to or smaller than the inner diameter of the second remote portion 52. The inner circumferential surface of the second nearby portion 51 may be flush with the inner circumferential surface of the second remote portion 52. Here, flush means that in the radial direction of the second diagonal brace 50, the inner circumferential surface of the second nearby portion 51 is not located inside the inner circumferential surface of the second remote portion 52, and is not located outside the inner circumferential surface of the second remote portion 52. In other words, it means that the inner diameter of the second nearby portion 51 is equal to the inner diameter of the second remote portion 52. The inner circumferential surface of the second nearby portion 51 may be located radially inside the inner circumferential surface of the second remote portion 52.

5, in this embodiment, the outer peripheral surface of the second nearby portion 51 is flush with the outer peripheral surface of the second remote portion 52. The inner peripheral surface of the second nearby portion 51 is located radially inward of the inner peripheral surface of the second remote portion 52. With such a relationship, the orthogonal projection of the second nearby portion 51 projected onto a plane perpendicular to the longitudinal axis of the second diagonal brace 50 covers the orthogonal projection of the second remote portion 52 projected onto the plane. In other words, as shown in FIG. 7, when viewed from the axial direction of the second diagonal brace 50, the cross section of the second remote portion 52 is located inside the cross section of the second nearby portion 51. Therefore, the cross-sectional area of the second nearby portion 51 in the plane perpendicular to the longitudinal axis of the second diagonal brace 50 is larger than the cross-sectional area of the second remote portion 52. In addition, the plate thickness of the second nearby portion 51 is larger than the plate thickness of the second remote portion 52.

The tapered portion 53 is provided between the inner surface of the second nearby portion 51 and the inner surface of the second remote portion 52. More specifically, as shown in FIG. 5, the tapered portion 53 is a portion that is provided in an inclined manner so as to connect between the inner surface of the second nearby portion 51 and the inner surface of the second remote portion 52. The tapered portion 53 connects the second nearby portion 51 and the second remote portion 52 by continuously changing the distance between the second nearby portion 51 and the second remote portion 52.

In this embodiment, the tapered portion 53 is formed integrally with the second nearby portion 51. The second nearby portion 51 and the second remote portion 52 are connected by welding the tapered portion 53 and the second remote portion 52. The tapered portion 53 and the second remote portion 52 are welded on one side from the inside of the second diagonal brace 50. As shown in FIG. 9, a V-shaped groove SB or a V-shaped groove is provided between the inner surface of the tapered portion 53 and the inner surface of the second remote portion 52. If the difference between the plate thickness of the second nearby portion 51 and the plate thickness of the second remote portion 52 is small, the second nearby portion 51 and the second remote portion 52 may be directly welded. In this case, the welded portion may be the tapered portion 53.

As shown in FIG. 6, the portion 54 near the second leg is a cylindrical portion of the second diagonal brace 50, and is a cylindrical portion within a predetermined range including the intersection of the second diagonal brace 50 and one of the legs 10. The predetermined range refers to the range in the longitudinal direction of the second diagonal brace 50. The dimensions of the predetermined range can be set appropriately based on the cross-sectional force distribution and the brace diameter. Taking into account the ease of welding, it is preferable that the predetermined range be 1.5 m or less.

The second leg remote portion 55 is a cylindrical portion of the second diagonal brace 50 that is farther from an intersection between the second diagonal brace 50 and one of the legs 10 than the second leg proximal portion 54. In this embodiment, a one-sided weld OW is provided between the second leg proximal portion 54 and the second leg remote portion 55. That is, the second leg proximal portion 54 and the second leg remote portion 55 are connected by one-sided welding (described in detail later).
The relationship between the outer diameter and the inner diameter of the second leg proximal portion 54 and the second leg remote portion 55 is as follows.
That is, the outer circumferential surface of the second leg proximate portion 54 is located radially outward of the outer circumferential surface of the second leg remote portion 55. That is, the outer diameter of the second leg proximate portion 54 is larger than the outer diameter of the second leg remote portion 55.

The inner diameter of the second leg vicinity portion 54 is at least equal to or smaller than the inner diameter of the second leg remote portion 55. The inner peripheral surface of the second leg vicinity portion 54 may be flush with the inner peripheral surface of the second leg remote portion 55. Here, flush means that in the radial direction of the second diagonal brace 50, the inner peripheral surface of the second leg vicinity portion 54 is not located inside the inner peripheral surface of the second leg remote portion 55, and is not located outside the inner peripheral surface of the second leg remote portion 55. In other words, it means that the inner diameter of the second leg vicinity portion 54 is equal to the inner diameter of the second leg remote portion 55. The inner peripheral surface of the second leg vicinity portion 54 may be located radially inside the inner peripheral surface of the second leg remote portion 55.

For example, as shown in FIG. 6, in this embodiment, the outer peripheral surface of the second leg vicinity portion 54 is located radially outward from the outer peripheral surface of the second leg remote portion 55. The inner peripheral surface of the second leg vicinity portion 54 is flush with the inner peripheral surface of the second leg remote portion 55. With such a relationship, the orthogonal projection of the second leg vicinity portion 54 projected onto a plane perpendicular to the longitudinal axis of the second diagonal brace 50 covers the orthogonal projection of the second leg remote portion 55 projected onto the plane. In other words, as shown in FIG. 8, when viewed from the axial direction of the second diagonal brace 50, the cross section of the second leg remote portion 55 is located inside the cross section of the second leg vicinity portion 54. Therefore, the cross-sectional area of the second leg vicinity portion 54 in the plane perpendicular to the longitudinal axis of the second diagonal brace 50 is larger than the cross-sectional area of the second leg remote portion 55. Additionally, the thickness of the portion 54 near the second leg is greater than the thickness of the portion 55 remote from the second leg.

As shown in FIG. 6, the leg taper portion 56 is an inclined portion that connects the outer surface of the second leg proximal portion 54 and the outer surface of the second leg remote portion 55. The leg taper portion 56 connects the second leg proximal portion 54 and the second leg remote portion 55 by continuously changing the distance between the second leg proximal portion 54 and the second leg remote portion 55.

In this embodiment, the leg taper portion 56 is formed integrally with the second leg nearby portion 54. The second leg nearby portion 54 and the second leg remote portion 55 are connected by welding the leg taper portion 56 and the second leg remote portion 55. The leg taper portion 56 and the second leg remote portion 55 are welded on one side from the outside of the second diagonal brace 50. As shown in FIG. 9, a V-shaped groove SB or a V-shaped groove is provided between the outer surface of the leg taper portion 56 and the outer surface of the second leg remote portion 55. When the difference between the plate thickness of the second leg nearby portion 54 and the plate thickness of the second leg remote portion 55 is small, the second leg nearby portion 54 and the second leg remote portion 55 may be directly welded. In this case, the welded portion may be the leg taper portion 56.

As described above, the intersection between the first diagonal brace 40 and the second diagonal brace 50 is welded on both sides. This ensures sufficient strength at the connection between the first diagonal brace 40 and the second diagonal brace 50. At this time, as shown in FIG. 3, a double-sided groove or K-shaped groove K is provided at the intersection between the first diagonal brace 40 and the second diagonal brace 50.

As shown in FIG. 5, the outer diameter of the first diagonal brace 40 is larger than the outer diameter of the second diagonal brace 50. In other words, the outer diameter of the first diagonal brace 40 is larger than the outer diameter of at least the second nearby portion 51 of the second diagonal brace 50. With this configuration, when the second nearby portion 51 is aligned with the side of the first nearby portion 41, as shown in FIG. 10, the radial end of the second diagonal brace 50 (i.e., the vertical direction of the paper) is located closer to the axial center of the first nearby portion 41 than the radial end of the first nearby portion 41.

As a result, for example, as shown in FIG. 10, when viewed along the axial direction of the first diagonal brace 40, the angle B between the radial end of the second diagonal brace 50 and the outer peripheral surface of the first nearby portion 41 becomes closer to a right angle when the outer diameter of the second diagonal brace 50 and the outer diameter of the first nearby portion 41 are equal, which is 180°. This configuration makes it easier to provide a double-sided groove or a K-shaped groove K at the end of the second diagonal brace 50.

As shown in FIG. 4, the third diagonal brace 60 is a cylindrical member. For example, a steel pipe is preferably used for the third diagonal brace 60. As described above, the third diagonal brace 60 is connected to the first leg can portion 11 of the leg 10 together with the first diagonal brace 40 as shown in FIG. 4. As described above, in this embodiment, the number of legs 10 in the jacket structure 100 for an offshore wind turbine is four. Therefore, for example, as shown in FIG. 4, the third diagonal brace 60 and the first diagonal brace 40 are approximately perpendicular when viewed from the axial direction of the leg 10. For example, in FIG. 1, when the first diagonal brace 40 is located in the left-right direction of the paper, the third diagonal brace 60 is located in the depth direction of the paper.

As shown in FIGS. 1 and 4 , a third diagonal brace 60 is connected to the first leg can portion 11 to which the first leg vicinity portion 43 of the first diagonal brace 40 is connected.
The configuration of the third diagonal brace 60 is, for example, similar to the configuration of the first diagonal brace 40 described above. For example, in this embodiment, the outer diameter of the third diagonal brace 60 is larger than the outer diameter of the second diagonal brace 50. The outer diameter of the third diagonal brace 60 may be the same over the entire length of the third diagonal brace 60.

The fourth diagonal brace 70 is a cylindrical member. For example, a steel pipe is preferably used for the fourth diagonal brace 70. As described above, the fourth diagonal brace 70 is connected to the second leg can portion 12 of the leg 10 together with the second diagonal brace 50. As described above, in this embodiment, the number of legs 10 in the jacket structure 100 for an offshore wind turbine is four. Therefore, for example, as shown in FIG. 4, when viewed from the axial direction of the leg 10, the fourth diagonal brace 70 is perpendicular to the second diagonal brace 50. For example, in FIG. 1, when the second diagonal brace 50 is located in the left-right direction of the paper, the fourth diagonal brace 70 is located in the depth direction of the paper.

As shown in FIGS. 1 and 4 , a fourth diagonal brace 70 is connected to the second leg can portion 12 to which the second leg vicinity portion 54 of the second diagonal brace 50 is connected.
The configuration of the fourth diagonal brace 70 is, for example, similar to the configuration of the above-described second diagonal brace 50. For example, in this embodiment, the outer diameter of the fourth diagonal brace 70 is smaller than the outer diameter of the first diagonal brace 40. The fourth diagonal brace 70 includes two cylindrical members. In other words, the fourth diagonal brace 70 is divided into two.
The above-mentioned components constitute the jacket structure 100 for an offshore wind turbine according to this embodiment.

As described above, according to the jacket structure 100 for an offshore wind turbine of this embodiment, the intersection between the first diagonal brace 40 and the second diagonal brace 50 is welded on both sides. This ensures sufficient fatigue strength at the connection between the first diagonal brace 40 and the second diagonal brace 50.

The outer diameter of the first diagonal brace 40 is larger than the outer diameter of the second diagonal brace 50. This makes it easier to perform double-sided welding of the intersection between the first diagonal brace 40 and the second diagonal brace 50.

In addition, the plate thickness of the first leg can portion 11, which includes the intersection between one of the multiple legs 10 and the end of the first diagonal brace 40, is thinner than the plate thickness of the second leg can portion 12, which includes the intersection between one of the multiple legs 10 and the end of the second diagonal brace 50. This makes it possible to reduce the plate thickness of the first leg can portion 11. Therefore, the material cost of the leg 10 can be reduced.

In addition, the strength of the steel material of the first leg can portion 11, which includes the intersection of one of the multiple legs 10 and the end of the first diagonal brace 40, is weaker than the strength of the steel material of the second leg can portion 12, which includes the intersection of one of the multiple legs 10 and the end of the second diagonal brace 50. This allows the first leg can portion 11 to use a cheaper material. This makes it possible to reduce the material cost of the leg 10.

The steel material of the first leg can portion 11 is SM490Y or SM520, and the steel material of the second leg can portion 12 is SA440. This allows the strength of the steel material of the first leg can portion 11 to be weaker than the strength of the steel material of the second leg can portion 12. This allows the material cost of the leg 10 to be reduced.

In addition, the length of the first leg can portion 11 along one longitudinal direction is longer than the length of the second leg can portion 12 along one longitudinal direction. This makes it possible to reduce the length of the second leg can portion 12 while keeping the length of the first leg can portion 11 sufficient, for example, when the outer diameter of the first diagonal brace 40 is larger than the outer diameter of the second diagonal brace 50. This makes it possible to reduce the material cost of the leg 10.

A third diagonal brace 60 is connected to the first leg can portion 11, which includes the intersection between one of the multiple legs 10 and the end of the first diagonal brace 40, and the outer diameter of the third diagonal brace 60 is larger than the outer diameter of the second diagonal brace 50. This allows the cross sections of the first diagonal brace 40 and the third diagonal brace 60 connected to the first leg can portion 11 to be unified, for example, when the outer diameter of the first diagonal brace 40 and the outer diameter of the third diagonal brace 60 are made the same. This makes it easier to manage parts when manufacturing the jacket structure. It also makes it easier to perform structural calculations for the jacket structure.

A fourth diagonal brace 70 is connected to the second leg can portion 12 including the intersection between one of the multiple legs 10 and the end of the second diagonal brace 50, and the outer diameter of the fourth diagonal brace 70 is smaller than the outer diameter of the first diagonal brace 40. This allows the cross sections of the second diagonal brace 50 and the fourth diagonal brace 70 connected to the second leg can portion 12 to be unified, for example, when the outer diameter of the second diagonal brace 50 and the outer diameter of the fourth diagonal brace 70 are made the same. This makes it easier to manage parts when manufacturing the jacket structure. It also makes it easier to perform structural calculations for the jacket structure.

Moreover, the outer diameter of the second nearby portion 51 is equal to or larger than the outer diameter of the second remote portion 52, and the inner diameter of the second nearby portion 51 is equal to or smaller than the inner diameter of the second remote portion 52. Therefore, the plate thickness of the second nearby portion 51 is at least equal to or larger than the second remote portion 52. This ensures the strength of the intersection of the second diagonal brace 50. Furthermore, when the plate thickness of the second nearby portion 51 is increased, the second nearby portion 51 can be more easily welded on both sides at the intersection with the first nearby portion 41. This improves the fatigue strength.
Furthermore, by making the plate thickness of the second remote portion 52 smaller than that of the second nearby portion 51, it is possible to ensure sufficient strength in the second nearby portion 51 against bending moments, etc., while preventing the weight of the entire second diagonal brace 50 from increasing more than necessary.

The second proximal portion 51 also includes a tapered portion 53 provided between the inner surface of the second proximal portion 51 and the inner surface of the second remote portion 52. This allows the second proximal portion 51 and the second remote portion 52 to be connected by continuously changing the distance between them. This makes it possible to suppress stress concentration at the connection between the second proximal portion 51 and the second remote portion 52.

The tapered portion 53 and the second remote portion 52 are welded on one side from the inside of the second diagonal brace 50. Here, if the inner diameter of the second nearby portion 51 is equal to or smaller than the inner diameter of the second remote portion 52, the boundary between the tapered portion 53 and the second remote portion 52 is prone to stress concentration on the inner surface of the second diagonal brace 50. Weld defects are particularly likely to occur at the root portion of the welded portion. By performing one-sided welding from the inside of the second diagonal brace 50, the root portion can be positioned outside the second diagonal brace 50. Therefore, the root portion of the weld can be moved away from the location where stress concentration is likely to occur at the boundary between the tapered portion 53 and the second remote portion 52. This makes it possible to suppress a decrease in fatigue life at the boundary.

The outer diameter of the first diagonal brace 40 is the same throughout the entire length of the first diagonal brace 40. This makes it easier to provide, for example, a stainless steel plate or the like for rust prevention on the outer peripheral surface of the first diagonal brace 40.

In addition, double-sided welds BW are provided at the intersection between the first diagonal brace 40 and the second diagonal brace 50 and at the intersection between the second diagonal brace 50 and one of the legs 10. In other words, the intersection between the first diagonal brace 40 and the second diagonal brace 50 and the intersection between the second diagonal brace 50 and one of the legs 10 are both welded. This ensures sufficient fatigue strength at the intersection between the first diagonal brace 40 and the second diagonal brace 50 and the intersection between the second diagonal brace 50 and one of the legs 10.

One-sided welds OW are provided between the portion near the brace and the portion far from the brace, and between the portion near the leg 10 and the portion far from the leg 10. In other words, one-sided welding is performed between the portion near the brace and the portion far from the brace, and between the portion near the leg 10 and the portion far from the leg 10. This makes it possible to avoid, for example, workers being left behind inside the jacket structure by double-sided welding each welded portion in the jacket structure.

Second Embodiment
Next, a second offshore wind turbine jacket structure 200 according to a second embodiment of the present invention will be described with reference to Figs. 11 and 12 .
In the second embodiment, the same components as those in the first embodiment are denoted by the same reference numerals, and their description will be omitted, with only the differences being described.

The second offshore wind turbine jacket structure 200 differs from the offshore wind turbine jacket structure 100 particularly in the configuration of the second diagonal brace 50 .
Specifically, in the second diagonal brace 50 of the second offshore wind turbine jacket structure 200, the outer diameter of the second remote portion 52 is equal to or larger than the outer diameter of the second nearby portion 51, and the inner diameter of the second remote portion 52 is equal to or smaller than the inner diameter of the second nearby portion 51. That is, for example, as shown in FIG. 11 , the outer peripheral surface of the second nearby portion 51 is located inside the outer peripheral surface of the second remote portion 52. The inner peripheral surface of the second nearby portion 51 is flush with the inner peripheral surface of the second remote portion 52. The tapered portion 53 is provided between the outer surface of the second nearby portion 51 and the outer surface of the second remote portion 52. The tapered portion 53 is formed integrally with the second remote portion 52. In these respects, the second diagonal brace 50 of the offshore wind turbine jacket structure 100 is different. The second proximal portion 51 and the second remote portion 52 are connected by one-sided welding of the tapered portion 53 and the second proximal portion 51 from the outside of the second diagonal brace 50 .

In accordance with this, the second diagonal brace 50 of the second offshore wind turbine jacket structure 200 has an outer diameter of the second leg remote portion 55 that is equal to or larger than the outer diameter of the second leg proximal portion 54, and an inner diameter of the second leg remote portion 55 that is equal to or smaller than the inner diameter of the second leg proximal portion 54. That is, for example, as shown in FIG. 12, the outer peripheral surface of the second leg proximal portion 54 is located radially inward from the outer peripheral surface of the second leg remote portion 55. The inner peripheral surface of the second leg proximal portion 54 is flush with the inner peripheral surface of the second leg remote portion 55. In addition, the leg taper portion 56 is formed integrally with the second leg remote portion 55. The second leg proximal portion 54 and the second leg remote portion 55 are connected by one-sided welding of the leg taper portion 56 and the second leg proximal portion 54.

As described above, according to the second offshore wind turbine jacket structure 200 of this embodiment, the outer diameter of the second remote portion 52 is equal to or greater than the outer diameter of the second nearby portion 51, and the inner diameter of the second remote portion 52 is equal to or less than the inner diameter of the second nearby portion 51. Therefore, the plate thickness of the second remote portion 52 is at least the same as that of the second nearby portion 51, or is greater than that of the second nearby portion 51. This ensures that the second remote portion 52 has sufficient strength against bending moments, etc.

The second proximal portion 51 also has a tapered portion 53 between the outer surface of the second proximal portion 51 and the outer surface of the second remote portion 52. This allows the second proximal portion 51 and the second remote portion 52 to be connected by continuously changing the distance between them. This makes it possible to suppress stress concentration at the connection between the second proximal portion 51 and the second remote portion 52.

The tapered portion 53 and the second nearby portion 51 are welded on one side from the outside of the second diagonal brace 50. Here, if the outer diameter of the second remote portion 52 is equal to or greater than the outer diameter of the second nearby portion 51, the boundary between the tapered portion 53 and the second nearby portion 51 is prone to stress concentration on the outer surface of the second diagonal brace 50. Weld defects are particularly prone to occur in the root portion of the weld. By welding on one side from the outside of the second diagonal brace 50, the root portion can be positioned inside the second diagonal brace 50. Therefore, the root portion of the weld can be moved away from the location where stress concentration is likely to occur at the boundary between the tapered portion 53 and the second nearby portion 51. This makes it possible to suppress a decrease in fatigue life at the boundary.

(Method of welding the jacket structure 100 for an offshore wind turbine)
Next, a description will be given of a welding method for the offshore wind turbine jacket structure 100 according to the above-mentioned first and second embodiments. The welding method described below prevents a worker from being left behind inside the offshore wind turbine jacket structure 100.
Hereinafter, a cylindrical portion of the second diagonal brace 50 within a predetermined range including the intersection of the second diagonal brace 50 and the first diagonal brace 40 will be referred to as a proximal brace portion. In other words, the second proximal portion 51 will be referred to as a proximal brace portion.
A cylindrical portion of the second diagonal brace 50 that is farther from the intersection of the second diagonal brace 50 and the first diagonal brace 40 than the brace proximate portion is referred to as a brace remote portion. In other words, the second remote portion 52 is referred to as the brace remote portion.

A cylindrical portion of the second diagonal brace 50 within a predetermined range including an intersection point between the second diagonal brace 50 and one of the legs 10 is referred to as a portion near the leg 10. In other words, the second leg vicinity portion 54 is referred to as a portion near the leg 10.
A cylindrical portion of the second diagonal brace 50 that is farther from the intersection of the second diagonal brace 50 and one of the legs 10 than the leg 10 proximal portion is referred to as the leg 10 remote portion. In other words, the second leg remote portion 55 is referred to as the leg 10 remote portion.

The welding method according to the present embodiment includes a double-sided welding step and a single-sided welding step.
In the double-sided welding process, an intersection between the first diagonal brace 40 and the second diagonal brace 50 is welded on both sides. Also, an intersection between the second diagonal brace 50 and one of the legs 10 is welded on both sides.
The single-sided welding process is performed after the double-sided welding process. In the single-sided welding process, single-sided welding is performed between the brace proximal portion and the brace distal portion, and also between the leg proximal portion and the leg distal portion.
Through the above steps, the jacket structure 100 for an offshore wind turbine according to this embodiment is constructed.

As described above, the welding method for the jacket structure 100 for an offshore wind turbine according to this embodiment includes a double-sided welding process for double-sided welding the intersection between the first diagonal brace 40 and the second diagonal brace 50 and the intersection between the second diagonal brace 50 and one of the legs 10, and a single-sided welding process for single-sided welding between the portion near the brace and the portion remote from the brace after the double-sided welding process, and for single-sided welding between the portion near the leg 10 and the portion remote from the leg 10.

Here, if the first diagonal brace 40 is an integral cylindrical member, it is impossible to double-sided weld both ends of the first diagonal brace 40 to the leg 10, because this would leave a worker inside the first diagonal brace 40 after the welding work. In contrast, by performing a single-sided welding process after the double-sided welding process, it is possible to double-sided weld the intersection between the first diagonal brace 40 and the second diagonal brace 50 and the intersection between the second diagonal brace 50 and one of the legs 10 while avoiding the worker being left inside. This ensures the weld strength of each intersection that is double-sided welded.

The technical scope of the present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the spirit of the present invention.
For example, although the outer diameter of the first diagonal brace 40 has been described as being constant over the entire length of the first diagonal brace 40, this is not limited thereto. For example, the outer diameter of the first nearby portion 41 may be equal to or greater than the outer diameter of the first remote portion 42. The outer diameter of the first remote portion 42 may be equal to or greater than the outer diameter of the first nearby portion 41.
Furthermore, each steel pipe member constituting the offshore wind turbine jacket structure 100 is not limited to being cylindrical, but may also be rectangular.
Furthermore, the outer diameters of the first leg can portion 11 and the second leg can portion 12 of the leg 10 may be the same as that of the straight pipe portion 13, for example. The outer diameters of the first leg can portion 11 and the second leg can portion 12 of the leg 10 may be larger than that of the straight pipe portion 13, for example.
13 , the tapered portion 53 may be provided between the outer surface of the second nearby portion 51 and the outer surface of the second remote portion 52. That is, for example, as shown in FIG. 13 , the outer circumferential surface of the second nearby portion 51 may be located radially outward of the outer circumferential surface of the second remote portion 52, and the inner circumferential surface of the second nearby portion 51 may be flush with the inner circumferential surface of the second remote portion 52.
In addition, the outer diameter of the second leg proximal portion 54 may be the same as the outer diameter of the second leg remote portion 55 .
Additionally, the leg tapered portion 56 may be provided between the inner surface of the second leg proximal portion 54 and the inner surface of the second leg remote portion 55 .

In addition, the components in the above embodiment may be replaced with well-known components as appropriate without departing from the spirit of the present invention, and the above-mentioned modifications may be combined as appropriate.

10 Leg 11 First leg can portion 12 Second leg can portion 13 Straight pipe portion 20 Base 30 Skirt sleeve 40 First diagonal brace 41 First proximal portion 42 First remote portion 43 First leg proximal portion 44 First leg remote portion 50 Second diagonal brace 51 Second proximal portion 52 Second remote portion 53 Tapered portion 54 Second leg proximal portion 55 Second leg remote portion 56 Leg tapered portion 60 Third diagonal brace 70 Fourth diagonal brace 100 Jacket structure for offshore wind turbine 200 Jacket structure for second offshore wind turbine 300 Offshore wind turbine BW Double-sided welded portion K K-shaped groove L Pile OW One-sided welded portion SB R-shaped groove

Claims (17)

A first diagonal brace that is a cylindrical member;
A second diagonal brace that is a cylindrical member and intersects with the first diagonal brace;
a base on which the offshore wind turbine is installed and supported by the first diagonal brace and the second diagonal brace;
A jacket structure for an offshore wind turbine comprising:
The intersection between the first diagonal brace and the second diagonal brace is welded on both sides.
A jacket structure for an offshore wind turbine. The outer diameter of the first diagonal brace is larger than the outer diameter of the second diagonal brace.
The jacket structure for an offshore wind turbine according to claim 1 . The base is supported by the first diagonal brace and the second diagonal brace via a plurality of legs,
a plate thickness of a first leg can portion which is one of the plurality of legs and includes an intersection between the one leg and an end of the first diagonal brace is thinner than a plate thickness of a second leg can portion which is one of the plurality of legs and includes an intersection between the one leg and an end of the second diagonal brace;
The jacket structure for an offshore wind turbine according to claim 2 . The base is supported by the first diagonal brace and the second diagonal brace via a plurality of legs,
a strength of a steel material of a first leg can portion which is one of the plurality of legs and includes an intersection between the one leg and an end of the first diagonal brace is weaker than a strength of a steel material of a second leg can portion which is one of the plurality of legs and includes an intersection between the one leg and an end of the second diagonal brace;
The jacket structure for an offshore wind turbine according to claim 2 . The steel material of the first leg can portion is SM490Y or SM520,
The steel material of the second leg can portion is SA440.
The jacket structure for an offshore wind turbine according to claim 4. The length of the first leg can portion along the one longitudinal direction is longer than the length of the second leg can portion along the longitudinal direction.
The jacket structure for an offshore wind turbine according to any one of claims 3 to 5. 3rd diagonal brace,
Further comprising:
The base is supported by the first diagonal brace, the second diagonal brace, and the third diagonal brace via a plurality of legs;
A first leg can portion is one of the plurality of legs, and the first leg can portion includes an intersection point between the one leg and an end of the first diagonal brace, and the third diagonal brace is connected to the first leg can portion,
The outer diameter of the third diagonal brace is larger than the outer diameter of the second diagonal brace.
The jacket structure for an offshore wind turbine according to claim 2 . 4th diagonal brace,
Further comprising:
The base is supported by the first diagonal brace, the second diagonal brace, and the fourth diagonal brace via a plurality of legs;
A second leg can portion is one of the plurality of legs, and the second leg can portion includes an intersection point between the one leg and an end of the second diagonal brace, and the fourth diagonal brace is connected to the second leg can portion,
The outer diameter of the fourth diagonal brace is smaller than the outer diameter of the first diagonal brace.
The jacket structure for an offshore wind turbine according to claim 2 . A cylindrical portion of the second diagonal brace, the cylindrical portion being within a predetermined range including an intersection point between the first diagonal brace and the second diagonal brace, is defined as a second vicinity portion;
A cylindrical portion of the second diagonal brace that is farther from the intersection than the second proximal portion is a second remote portion;
an outer diameter of the second proximal portion is equal to or greater than an outer diameter of the second remote portion;
an inner diameter of the second proximal portion is equal to or smaller than an inner diameter of the second remote portion;
The jacket structure for an offshore wind turbine according to claim 2 . a tapered portion between an inner surface of the second proximal portion and an inner surface of the second distal portion;
The jacket structure for an offshore wind turbine according to claim 9. The tapered portion and the second remote portion are welded on one side from the inside of the second diagonal brace.
The jacket structure for an offshore wind turbine according to claim 10. A cylindrical portion of the second diagonal brace, the cylindrical portion being within a predetermined range including an intersection point between the first diagonal brace and the second diagonal brace, is defined as a second vicinity portion;
A cylindrical portion of the second diagonal brace that is farther from the intersection than the second proximal portion is a second remote portion;
an outer diameter of the second remote portion is equal to or greater than an outer diameter of the second proximal portion;
an inner diameter of the second remote portion is equal to or smaller than an inner diameter of the second proximal portion;
The jacket structure for an offshore wind turbine according to claim 2 . a tapered portion between an outer surface of the second proximal portion and an outer surface of the second distal portion;
The jacket structure for an offshore wind turbine according to claim 12. The tapered portion and the second adjacent portion are welded on one side from the outside of the second diagonal brace.
The jacket structure for an offshore wind turbine according to claim 13. The outer diameter of the first diagonal brace is the same throughout the entire length of the first diagonal brace.
The jacket structure for an offshore wind turbine according to any one of claims 1 to 5 and 7 to 14. A plurality of cylindrical legs;
A first diagonal brace is a cylindrical member and is connected to the leg; and
A second diagonal brace is a cylindrical member connected to the leg and intersects with the first diagonal brace;
a base supported by the leg, the first diagonal brace, and the second diagonal brace, and on which an offshore wind turbine is installed;
A jacket structure for an offshore wind turbine comprising:
The outer diameter of the first diagonal brace is larger than the outer diameter of the second diagonal brace,
An intersection point between the first diagonal brace and the second diagonal brace;
an intersection of the second diagonal brace with one of the legs;
a double-sided weld provided on the
Between a brace proximate portion, which is a cylindrical portion of the second diagonal brace, within a predetermined range including an intersection point between the second diagonal brace and the first diagonal brace, and a brace remote portion, which is a cylindrical portion of the second diagonal brace, which is farther from the intersection point between the second diagonal brace and the first diagonal brace than the brace proximate portion;
Between a leg proximate portion of the second diagonal brace, the leg proximate portion being a cylindrical portion within a predetermined range including an intersection point between the second diagonal brace and the one of the legs, and a leg remote portion of the second diagonal brace, the leg proximate portion being a cylindrical portion farther from the intersection point between the second diagonal brace and the one of the legs than the leg proximate portion;
a one-sided welded portion provided on the
A jacket structure for an offshore wind turbine comprising: A plurality of cylindrical legs;
A first diagonal brace is a cylindrical member and is connected to the leg; and
A second diagonal brace is a cylindrical member connected to the leg and intersects with the first diagonal brace;
a base supported by the leg, the first diagonal brace, and the second diagonal brace, and on which an offshore wind turbine is installed;
A welding method for an offshore wind turbine jacket structure comprising:
The outer diameter of the first diagonal brace is larger than the outer diameter of the second diagonal brace,
An intersection point between the first diagonal brace and the second diagonal brace;
an intersection of the second diagonal brace with one of the legs;
a double-sided welding process for welding the
After the double-sided welding process,
A brace vicinity portion that is a cylindrical portion of the second diagonal brace and is a cylindrical portion within a predetermined range including an intersection point between the second diagonal brace and the first diagonal brace;
A brace remote portion is a cylindrical portion of the second diagonal brace that is farther from an intersection point between the second diagonal brace and the first diagonal brace than the brace proximate portion;
The area is welded on one side,
A cylindrical portion of the second diagonal brace, the cylindrical portion being within a predetermined range including an intersection point between the second diagonal brace and the one leg adjacent portion;
a leg remote portion, the leg remote portion being a cylindrical portion of the second diagonal brace that is further from an intersection of the second diagonal brace with the first diagonal brace than the leg proximal portion;
a one-sided welding process for performing one-sided welding between
A welding method for a jacket structure for an offshore wind turbine, comprising:

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