Polygonal cylindrical structure, and foundation structure for offshore wind power generation facility

Abstract

To provide a polygonal cylindrical structure capable of achieving a good balance of exhibiting bending performance equivalent to that of a circular shape and reducing the cost by eliminating a bending step and reducing a welding step.SOLUTION: A cross-sectional shape in a horizontal direction is formed by the same number of angles, and a polygonal columnar body (1) is configured by connecting flat plate members (10) made of steel in a circumferential direction and a columnar axis direction by welding. The polygonal columnar body (1) has a polygonal cross-sectional shape of a hexagonal shape or more and a 24-sided polygonal shape or less, and the plate thickness of the flat plate member (10) is 40 mm or more and 250 mm or less. In the polygonal cross-sectional shape, the ratio of an outer diameter D to a plate thickness t (outer diameter D / plate thickness t) is 200 or less.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a polygonal cylindrical structure and a foundation structure for offshore wind power generation facilities. This application claims priority based on Japanese Patent Application No. 2022-199328 filed in Japan on December 14, 2022, and incorporates its content herein.

Background Art

[0002] Conventionally, in order to ensure the power generation amount by offshore wind power, the size of wind turbines and the towers and foundations supporting them has been increasing. Generally, a circular structure composed of cylindrical pipes is frequently used for towers and foundations, and as the cylindrical pipe of the foundation, for example, a large-diameter one with an outer diameter exceeding 10 m is expected to be adopted in the future. Along with the increase in the size of the equipment, it is necessary to increase the strength and rigidity, and it is also necessary to increase the outer diameter and wall thickness. Usually, for example, as shown in Patent Document 1, a short pipe is manufactured by bending a steel plate to form a curved plate and welding it in the circumferential direction, and further welding the short pipes in the column axis direction to construct a tower or a foundation. In this case, there is a problem that the capacity of the bending equipment has a limit, it cannot cope with thickening and large diameter, and the cost also increases.

[0003] On the other hand, as a structure that does not perform bending processing, in a columnar floating body constituting a floating-type offshore wind power generation facility, a structure is known in which a plurality of flat steel plates are connected by welding in the circumferential direction to construct a polygonal cross-section (see, for example, Patent Document 2).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, the polygonal cross-section structure described above had the following problems. That is, in Patent Document 2, a polygon is constructed by connecting flat steel plates by welding in the circumferential direction. However, since the number of corners increases excessively, the cost may increase. Furthermore, under the condition of the same cross-sectional area, in order for a polygonal structure to exhibit bending performance equivalent to that of a circular shape, it is generally considered to increase the outer diameter to increase the sectional second moment. However, as the perimeter increases, the plate thickness relatively decreases, and the local buckling resistance of the plate decreases. Also, by changing from a circular shape to a polygonal shape, the buckling mode that determines the limit state changes from the elephant foot buckling that occurs in circular members to the local buckling of the plate. Therefore, it is necessary to improve the local buckling resistance by increasing the number of corners of the polygon and reducing the width-thickness ratio of one side. However, when the number of corners increases, the welding line length and the assembly man-hours increase, resulting in an increase in cost. There was room for improvement in that regard.

[0006] The present invention has been made in view of the above-described problems, and aims to provide a polygonal cylindrical structure that can achieve both equivalent bending performance to that of a circular shape and cost reduction by omitting the bending process and reducing the welding process, and a foundation structure for an offshore wind power generation facility in a well-balanced manner.

Means for Solving the Problems

[0007] <1>Aspect 1 of the polygonal cylindrical structure according to the present invention is a polygonal cylindrical structure formed by the same number of corners in the horizontal cross-sectional shape, which is configured by connecting steel flat members by welding in the circumferential direction and the column axis direction. The cross-sectional shape is a polygonal cross-section of 6 to 24 sides. The plate thickness of the flat member is 40 mm or more and 250 mm or less. When the perimeter is the sum of the circumferential lengths at the plate thickness center in the cross-section and the outer diameter is the diameter at the plate thickness center of the cylinder with the same perimeter in the cross-section, at least the outer diameter at the base end of the polygonal cylindrical structure is 8 m or more and 40 m or less. In the polygonal cross-section, the ratio of the outer diameter to the plate thickness (outer diameter / plate thickness) is 40 or more and 200 or less over the entire length in the column axis direction. The number of corners n of the polygonal cross-section satisfies formula (1) or formula (2), which is a polygonal cylindrical structure. n ≧ 6 {when D / t ≦ 80} ···(1) n ≧ (D / t) / 20 + 2 {when D / t > 80} ···(2) Here, D: outer diameter (mm), t: plate thickness (mm), n: number of corners (natural number).

[0008] In the present invention, in the polygonal cross-section of the polygonal cylindrical structure where the horizontal cross-sectional shape is a polygonal cross-section of 6 to 24 sides, by setting the plate thickness of the flat member to 40 mm or more and 250 mm or less and the ratio of the outer diameter to the plate thickness (outer diameter / plate thickness) to 200 or less, local buckling can be suppressed, and it is possible to select the number of corners that can exhibit bending performance equivalent to that of a circle with an equivalent cross-sectional area. It can be manufactured with a polygonal cylindrical structure that can shorten the welding line length. In this way, in the present invention, the arrangement of the flat members can be constructed only by geometric adjustment, the bending process can be omitted, and the costly assembly welding process can be reduced. Therefore, in the present invention, it is possible to balance improving the bending performance to be equivalent to that of a circle and suppressing an increase in cost. Furthermore, in the present invention, since reinforcing members such as ribs are not required, a low-cost polygonal cylindrical structure can be provided.

[0009] In this case, by defining the minimum number of corners n having a cross-sectional area equivalent to a circle and equivalent bending performance according to the diameter-to-thickness ratio D / t by formula (1) or formula (2), a polygonal cylindrical structure can be manufactured with the minimum weld line length.

[0010] <2>Aspect 2, which is subordinate to Aspect 1 of the polygonal cylindrical structure of the present invention, is preferably such that the polygonal cross-section is a regular polygon.

[0011] In this case, since the cross-sectional shape approaches a circle, a polygonal cylindrical structure set to the specification of the minimum number of corners (i.e., the minimum weld line length) that exhibits bending performance equivalent to that of a circle as described above can be manufactured with higher accuracy.

[0012] <3>Aspect 3 of the foundation structure for an offshore wind power generation facility according to the present invention includes the polygonal cylindrical structure described in Aspect 1 or 2, and is characterized in that the polygonal cylindrical structure serves as the foundation of the offshore wind power generation facility.

Advantages of the Invention

[0013] According to the polygonal cylindrical structure and the foundation structure for an offshore wind power generation facility of the present invention, it is possible to achieve a good balance between exhibiting bending performance equivalent to that of a circle and reducing costs by omitting the bending process and reducing the welding process.

Brief Description of the Drawings

[0014]

Figure 1

Figure 2

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Figure 9

Figure 10

Mode for Carrying Out the Invention

[0015] Hereinafter, the polygonal cylindrical structure according to the embodiment of the present invention will be described with reference to the drawings.

[0016] As shown in FIG. 1, the polygonal cylindrical structure according to the present embodiment is, for example, a tower (not shown) for fixing a rotor composed of blades or the like, or a foundation structure of a wind power generation facility that supports the tower from below (hereinafter referred to as the polygonal columnar body 1) as an example.

[0017] Here, in the polygonal columnar body 1, the direction parallel to the central axis O is referred to as the column axis direction, the direction that circulates around the central axis O is referred to as the circumferential direction, and the direction orthogonal to the central axis O is referred to as the radial direction. Also, the direction toward the central axis O in the radial direction is referred to as the inner side, and the direction away from the central axis O is referred to as the outer side.

[0018] As shown in FIGS. 1 and 2, the polygonal columnar body 1 is a polygonal cylindrical structure formed by the same number of corners (here, an octagon) in the horizontal cross-sectional shape. The polygonal columnar body 1 is configured by connecting steel plate members 10 in the circumferential direction and the column axis direction by welding. The horizontal cross-sectional shape orthogonal to the column axis direction of the polygonal columnar body 1 forms a regular octagonal cross-section. Note that the flat plate member 10 may be a single steel plate, or may be a steel plate formed by welding a plurality of plates in the circumferential direction or the column axis direction.

[0019] Note that the cross-sectional shape of the polygonal columnar body 1 may be a polygon with 6 or more sides and 24 or less sides. Also, it is not limited to a regular polygon with all side lengths equal, and it is also possible to adopt a polygon in which some or all of the side lengths are different. Further, it is not limited to a cylindrical structure of a polygon or a regular polygon with equal plate thickness in the column axis direction, and it is also possible to adopt a polygon or a regular polygon with different plate thicknesses in the column axis direction. For example, the plate thickness of the flat plate member 10 may become thinner from a predetermined height position in the column axis direction upward (the upper part of the cylindrical structure). The predetermined height position may be, for example, an arbitrary position above the lower end of the polygonal columnar body 1. In such a portion where the plate thickness changes, another flat plate member 10 adjacent to the upper side has a thinner plate thickness than a certain flat plate member 10. Also, it is not limited to a cylindrical structure of a polygon or a regular polygon in which the lengths of the flat plate members 10 in the column axis direction are all equal, and it is also possible to adopt a polygon or a regular polygon in which the lengths of each ring body 10A in the column axis direction are different. For example, the length of the flat plate member 10 in the column axis direction may be increased from a predetermined height position in the column axis direction upward (the upper part of the cylindrical structure). In such a portion where the length changes, another flat plate member 10 adjacent to the upper side has a longer length in the column axis direction than a certain flat plate member 10. Further, the plate thickness of the flat plate member 10 may be made thinner and the length in the column axis direction may be increased upward (the upper part of the cylindrical structure) in the column axis direction. For example, it is not necessary for the plate thickness and the length of the flat plate member 10 to gradually change upward (the upper part of the cylindrical structure) in the column axis direction, and they may change from an arbitrary height position in the column axis direction. In this case, another flat plate member 10 adjacent to the upper side has a thinner plate thickness and a longer length in the column axis direction than a certain flat plate member 10 and its length in the column axis direction.

[0020] Here, the following cases are treated as regular polygons in the present invention. When, in the circumferential dimension of the flat plate member 10, the dimensions of all the flat plate members 10 are within ±2% of the average value. The angle with the adjacent flat plate member 10 (in the interior angle of the regular polygon, when all the interior angles are within ±2% of (180×(n - 2)) / n).

[0021] The polygonal columnar body 1 is an elongated body installed with its column axis direction parallel to the vertical direction, and has a cylindrical shape with a hollow interior. In the hollow portion of the polygonal columnar body 1, devices or the like that do not contribute to the structural performance may be installed. Also, the polygonal columnar body 1 has a frustum shape (taper shape) in which only a part of the upper portion or gradually as it goes upward, the cross-sectional shape shrinks. That is, the cross-sectional shapes at any height in the column axis direction are similar shapes. The polygonal columnar body 1 does not have to be tapered in the column axis direction.

[0022] The flat plate member 10 constituting the polygonal columnar body 1 is a thick plate member in which no curved portion or bent portion is formed. The plate thickness t of the flat plate member 10 is 40 mm or more and 250 mm or less. For the polygonal cross-section of the polygonal columnar body 1 having bending performance equivalent to that of a circle, it is preferable that the ratio of the outer diameter D (mm) to the plate thickness t (mm) (outer diameter D / plate thickness t) is set to 200 or less. When it exceeds 440, even if it is a 24-sided polygonal cross-section, it becomes difficult to exhibit bending performance equivalent to that of a circle. FIG. 10 shows a cylinder 100 having the same perimeter as the perimeter of the cross-section of the polygonal columnar body 1. The outer diameter D of the polygonal columnar body 1 corresponds to the diameter D100 on the center line of the flat plate member 110 of the cylinder 100 having the same perimeter in the cross-section.

[0023] The number of corners n (natural number) of the polygonal cross-section in the polygonal columnar body 1 satisfies formula (1) or formula (2).

[0024] n≧6 {when D / t≦80} ···(1) n≧(D / t) / 20 + 2 {when D / t>80} ···(2) Here, let D: outer diameter (mm), t: plate thickness (mm), and n: number of corners (natural number). When the unit of the outer diameter D is meter (m), when calculating D / t, the unit should be unified to millimeter (mm) before calculation.

[0025] The flat plate members 10 connected in the circumferential direction and the column axis direction are formed by connecting them by welding. The symbol W in Fig. 1 indicates the welding location (welded portion). The welded portion W has a transverse welded portion W1 extending along the circumferential direction and a longitudinal welded portion W2 extending along the column axis direction. In this embodiment, eight flat plate members 10 of the same shape are connected in the circumferential direction, so that the cross-sectional shape of the polygonal columnar body 1 is a regular octagon.

[0026] The polygonal columnar body 1 of this embodiment is formed by connecting a ring body in which eight flat plate members 10 are connected in the circumferential direction in one or a plurality of stages (six stages are shown in Fig. 1) in the column axis direction. Also, the longitudinal welded portions W2 of the respective ring bodies 10A connected in the column axis direction are continuous in the column axis direction. The transverse welded portions W1 of the respective ring bodies 10A may be continuous in the circumferential direction. Also, in the case of a so-called stagger arrangement where the arrangement heights of the flat plate members 10 adjacent in the circumferential direction in the column axis direction are not the same, the transverse welded portion W1 is discontinuous in the circumferential direction, but the longitudinal welded portion W2 is continuous in the column axis direction.

[0027] Next, the manufacturing method of the polygonal columnar body 1 shown in Figs. 1 and 2 will be described. First, a plate piece (flat plate member 10) of a predetermined size is cut out from a large steel plate as the base material. Here, the plate piece (flat plate member 10) of a predetermined size is, for example, a plate piece having a length corresponding to the circumferential direction of 1.0 m or more and 5.0 m or less and a length corresponding to the column axis direction of 2.0 m or more and 15.0 m or less when constructing a polygonal columnar body. In this cutting process, the required number of flat plate members 10 for constructing the polygonal columnar body 1 is cut out. However, the large steel plate as the base material may be used as it is without going through the cutting process as the flat plate member 10. Note that the flat plate member 10 may be a cut plate piece or a single steel plate used without cutting, or a steel plate formed by welding cut plate pieces or a steel plate used without cutting in the circumferential direction or the column axis direction. Thus, when the flat plate member 10 is formed by welding a plurality of plate pieces in the circumferential direction or the column axis direction, if the angle formed by the adjacent plate pieces in the circumferential direction is within 1.0°, they can be treated as the same flat plate member 10.

[0028] Thereafter, for example, the flat plate member 10 is placed on a pedestal (not shown). At this time, two flat plate members 10 adjacent in the circumferential direction are butted and arranged so as to form a predetermined crossing angle. Here, the predetermined crossing angle is an angle (that is, the inner angle of the polygon) for completing the cross-sectional shape (polygon) of the target polygonal columnar body 1 by a plurality of flat plate members 10. For example, in the case of the regular octagon shown in FIG. 1, the crossing angle that is perpendicular to the respective sides of two adjacent flat plate members 10 is 135°. In this arrangement step, the flat plate member 10 is arranged as it is without bending the flat plate member 10 as in the prior art. Incidentally, it is preferable that the flat plate member 10 arranged on the pedestal is arranged with the welding side facing upward and welded in a state where the welding torch faces downward. On the other hand, there may be a case where a plurality of flat plate members 10 are arranged vertically while ensuring a predetermined inner angle and welded in a state where the welding torch faces horizontally or downward. At this time, it is not necessary to use a pedestal.

[0029] Incidentally, when arranging the flat plate member 10 on the pedestal, for example, an arranging jig (not shown) having a contact surface set to the above-described predetermined crossing angle is used, and the flat plate member 10 is brought into contact with the contact surface of this arranging jig and arranged, whereby the positioning of adjacent flat plate members 10 can be easily performed.

[0030] Next, since a groove shape is formed at the butting portion of the arranged adjacent flat plate members 10, welding is performed on the groove portion, and the flat plate members 10 are connected to each other via the welded portion W. The flat plate member 10 is assembled, for example, into the above-described ring body 10A or a partial cross-sectional ring body obtained by cross-sectionally dividing the ring body 10A. Then, the ring body 10A or the partial cross-sectional ring body is sequentially welded and connected upward in the column axis direction at a predetermined installation position of the polygonal columnar body 1 to construct the polygonal columnar body 1. As shown in FIG. 2, the butting portion of the arranged adjacent flat plate members 10 may be a natural groove or a V-shaped groove, and the welded portion W may be formed by performing welding from the outside of the cross-section. It is not limited to welding from one side (inside or outside), and the welded portion W may be formed from both sides. Further, as shown in FIG. 3, X-shaped grooves 10c and 10d are provided in advance at the respective ends of the flat plate members 10 adjacent in the circumferential direction, and the butted portion of the X-shaped grooves 10c and 10d is welded and joined from both the outside and the inside of the cross-section to form the welded portion W. It is not limited to welding from one side (inside or outside), and the welded portion W may be formed from both sides.

[0031] Note that the work of manufacturing the ring body 10A etc. in a divided state may be carried out in a factory, yard, etc. near the installation position of the polygonal columnar body 1, or after manufacturing in a processing factory away from the installation position of the polygonal columnar body 1, it may be transported to the installation position of the polygonal columnar body 1 by a truck, ship, etc.

[0032] According to the polygonal columnar body 1 having the polygonal cylindrical structure described above, the horizontal cross-sectional shape is formed by the same number of corners. The polygonal columnar body 1 is configured by connecting steel flat plate members 10 by welding in the circumferential direction and the column axis direction. The polygonal columnar body 1 has a polygonal cross-section with a cross-sectional shape of 6 to 24 sides, and the plate thickness of the flat plate member 10 is 40 mm or more and 250 mm or less. For the polygonal cross-section, the ratio of the outer diameter D to the plate thickness t (outer diameter D / plate thickness t) is 200 or less.

[0033] By adopting such a configuration, under the condition that the horizontal cross-sectional shape of the polygonal cross-section in the polygonal column 1 is a polygonal cross-section with 6 to 24 sides and the same cross-sectional area, the plate thickness t of the flat plate member 10 is set to be 40 mm or more and 250 mm or less, and the ratio of the outer diameter D to the plate thickness t (outer diameter D / plate thickness t) is set to be 200 or less, local buckling can be suppressed. By selecting the specification of the minimum number of sides that has the same cross-sectional area as a circle and exhibits the same bending performance as a circle, the polygonal column 1 can be manufactured with the minimum weld line length. Here, the above "equivalent" is defined as, for example, when the maximum load-bearing capacity ratio of the polygonal cross-section to the circular cross-section is 0.9 (90%) or more. Therefore, in this embodiment, the arrangement of the flat plate member 10 can be constructed only by geometric adjustment, the bending process can be omitted, and an increase in cost can be suppressed by minimizing the costly assembly welding process. Furthermore, in this embodiment, since a reinforcing member such as a rib is not required, a low-cost polygonal column 1 can be provided.

[0034] Also, in this embodiment, the number of sides n of the polygonal cross-section satisfies the above formula (1) or (2). In this case, by defining the minimum number of sides n that has the same cross-sectional area as a circle and the same bending performance according to the diameter-thickness ratio D / t by formula (1) or (2), the polygonal column 1 can be manufactured with the minimum weld line length.

[0035] The number of sides n (natural number) of the polygonal cross-section in the polygonal column 1 may satisfy formula (3) or (4).

[0036] n≧8 {when D / t≦80} ···(3) n≧(D / t) / 20 + 4 {when D / t>80} ···(4)

[0037] When the number of sides n of the polygonal cross-section satisfies formula (3) or (4), the maximum load-bearing capacity ratio is 0.95 (95%) or more.

[0038] The number of sides n (natural number) of the polygonal cross-section in the polygonal column 1 may satisfy formula (5) or (6).

[0039] n ≥ 10 {when D / t ≤ 80} ···(5) n ≥ (D / t) / 20 + 6 {when D / t > 80} ···(6)

[0040] When the number of corners n of the polygonal cross-section satisfies equation (5) or (6), the maximum endurance ratio is 0.99 (99%) or more.

[0041] The number of corners n (natural number) of the polygonal cross-section in the polygonal column 1 may satisfy equation (7) or (8).

[0042] 6 ≤ n ≤ 10 {when D / t ≤ 80} ···(7) (D / t) / 20 + 2 ≤ n ≤ (D / t) / 20 + 6 {when D / t > 80} ···(8)

[0043] When the number of corners n of the polygonal cross-section satisfies equation (7) or (8), the maximum endurance ratio is 0.90 (90%) or more.

[0044] The number of corners n (natural number) of the polygonal cross-section in the polygonal column 1 may satisfy equation (9) or (10).

[0045] 8 ≤ n ≤ 12 {when D / t ≤ 80} ···(9) (D / t) / 20 + 4 ≤ n ≤ (D / t) / 20 + 8 {when D / t > 80} ···(10)

[0046] When the number of corners n of the polygonal cross-section satisfies equation (9) or (10), the maximum endurance ratio is 0.95 (95%) or more.

[0047] The number of corners n (natural number) of the polygonal cross-section in the polygonal column 1 may satisfy equation (11) or (12).

[0048] 10 ≤ n ≤ 14 {when D / t ≤ 80} ···(11) (D / t) / 20 + 6 ≤ n ≤ (D / t) / 20 + 10 {when D / t > 80} ···(12)

[0049] When the number of corners n of the polygonal cross-section satisfies the formula (11) or (12), the maximum load-bearing ratio is 0.99 (99%) or more.

[0050] In the design method of the polygonal cylindrical structure according to the present embodiment, the above-mentioned polygonal cylindrical structure is designed. For example, also in the design method of the polygonal cylindrical structure, the polygonal cross-section is designed such that the ratio of the outer diameter D to the plate thickness t (outer diameter / plate thickness) is 200 or less. Further, the number of corners n of the polygonal cross-section is designed to satisfy the formula (1) or (2). The polygonal cross-section is designed to be a regular polygon.

[0051] Also, in the present embodiment, since the polygonal cross-section is a regular polygon and the cross-sectional shape is closer to a circle than polygons with different side lengths, the polygonal columnar body 1 having the specification of the minimum number of corners (i.e., the minimum weld line length) that exhibits bending performance equivalent to that of a circle as described above can be manufactured with higher accuracy. That is, considering that a side length error occurs during manufacturing, it is possible to manufacture the polygonal cylindrical structure with higher accuracy by connecting flat plate members with the same side length rather than connecting flat plate members with different side lengths.

[0052] As described above, in the polygonal columnar body 1 of the wind power generation facility, the design method of the polygonal cylindrical structure, and the foundation structure for the offshore wind power generation facility using the polygonal cylindrical structure according to the present embodiment, it is possible to achieve a good balance between exhibiting bending performance equivalent to that of a circle and reducing costs by omitting the bending process and reducing the welding process.

[0053] The polygonal columnar body 1 shown in FIG. 1 has a frustum shape (taper shape) in which the cross-sectional shape gradually shrinks upward. Each flat plate member 10 constituting the polygonal columnar body 1 shown in FIG. 1 has a trapezoidal shape that shrinks upward in a front view. As shown in FIG. 8, the polygonal columnar body 1' may be cylindrical. That is, the outer diameter of the cross-section of the polygonal columnar body 1' may be substantially the same in the height direction. Each flat plate member 10' constituting the polygonal columnar body 1' shown in FIG. 8 has a rectangular shape in a front view. By making the polygonal columnar body 1' cylindrical, the process of cutting out the flat plate member 10 into a trapezoidal shape becomes unnecessary. Regarding the welded portion W' of the polygonal columnar body 1' shown in FIG. 8, similar to the welded portion W of the polygonal columnar body 1 shown in FIG. 1, the longitudinal welded portions W2' of the respective ring bodies 10A' connected in the column axis direction are continuous in the column axis direction, and the transverse welded portions W1' of the respective ring bodies 10A' may be continuous in the circumferential direction or may be staggered. Also, in the polygonal cylindrical structure formed by the polygonal columnar body 1' shown in FIG. 8, the same effects as those of the polygonal cylindrical structure formed by the polygonal columnar body 1 shown in FIG. 1 can be obtained. Further, as shown in FIG. 9, the polygonal columnar body 1B' may have a frustum shape only at a part of the upper end portion, and a cylindrical shape below that. In FIG. 9, the upper two-stage ring bodies 10B' have a frustum shape. The welded portion W' (W1', W2') at this time is the same as the welded portion W described above.

[0054] When the polygonal body 1 has a tapered shape, it is desirable to satisfy formula (1) or (2) at the bottom part that is most likely to buckle. More desirably, as long as formula (1) or (2) is satisfied at any column axis height, the outer diameter D and the plate thickness t may vary in the column axis direction.

[0055] Next, examples conducted to verify the effects of the polygonal cylindrical structure according to the above-described embodiments will be described below.

[0056] (Example) In the example, using numerical simulation analysis (finite element analysis), a horizontal load F was applied to the vertex (upper part) of the cantilever beam model 2 that modeled the polygonal cylindrical structure shown in Fig. 4, and the load-bearing capacity of the polygonal cylindrical structure was evaluated.

[0057] As shown in Table 1, in the example, for each of the five analysis CASES (CASE1, CASE2, CASE3, CASE4, CASE5), a cantilever beam model 2 as shown in Fig. 4 was created, and numerical simulation analysis was performed while changing the diameter-to-thickness ratio (D / t) of the polygonal shape for each of analysis CASES 1 to 5. The specific conditions for each of analysis CASES 1 to 5 are as shown in Table 1. The diameter-to-thickness ratio (D / t) in the analysis CASE is 40 for CASE1, 80 for CASE2, 120 for CASE3, 160 for CASE4, and 200 for CASE5. In Table 1, the "outer diameter" is the distance between the centers of the plate thickness of the flat plate member 10 on the center line of the cylinder that serves as the reference with the same perimeter in the cross section. The "perimeter" is the outer diameter (m) of the cylinder that serves as the reference with the same perimeter in the cross section × pi, that is, the plate width × the number of corners. The "area" is calculated as the plate thickness (mm) × the perimeter (m), that is, the perimeter × the plate thickness (plate width × the number of corners × the plate thickness).

[0058]

Table 1

[0059] Also, Table 2 shows the side width B (m), the plate thickness t (mm), and the width-to-thickness ratio (B / t) for each of the seven patterns of the number of corners n (the number of corners n of the polygonal shape is 4, 6, 8, 10, 12, 16, 24) in analysis CASES 1 to 5. Note that as a comparative example to the polygonal cylindrical structure in this example, a model of a circular cylindrical structure with a circular cross section was created and the same analysis was performed. The analysis conditions for the circular cylindrical structure were such that in analysis CASES 1 to 5, a regular 256-sided polygon, that is, a polygonal cylindrical structure with a side width of 0.123 m, was regarded as equivalent to a cylinder and the analysis was carried out. In Table 2, the "side width" is the value of the perimeter / the number of corners n.

[0060]

Table 2

[0061] In this embodiment, when a horizontal load (bending load) was applied to each polygonal cylindrical structure for each of the 7 patterns of the number of corners n in Analysis CASE1 to 5, the maximum stress (equivalent plastic strain, maximum allowable stress) acting was obtained by analysis. Similarly, the maximum stress (allowable stress) acting when a horizontal load was applied to the circular cylindrical structure of the comparative example was obtained by analysis.

[0062] Figs. 5(a) to (d) show an example in which the cross-sectional shape of the cylindrical structure is shown on the left side of the paper surface, and the distribution of the equivalent plastic strain at the time of the maximum bending load according to the analysis result is shown as a contour diagram on the right side of the paper surface. Fig. 5(a) is an example of a case of a quadrilateral with 4 corners. Fig. 5(b) is an example of a case of an octagon with 8 corners. Fig. 5(c) is an example of a case of a dodecagon with 12 corners. Fig. 5(d) is an example of a case of a circular cross-section in the comparative example. The symbol K shown in Figs. 5(a) to (d) indicates the part (high stress part) where the equivalent plastic strain occurs in each contour.

[0063] It can be seen that a large stress acts on the installation part (base end part) of the cylindrical structure in any of Figs. 5(a) to (d). Also, from the state of the contours, it can be confirmed that the number of corners 8 in Fig. 5(b) and the number of corners 12 in Fig. 5(c) have a stress distribution and stress magnitude equivalent to those of the circular cross-section of the comparative example in Fig. 5(d). On the other hand, in the case of the number of corners 4 in Fig. 5(a), compared with the circular cross-section of the comparative example in Fig. 5(d), the range (area) of the stress distribution is widened, and particularly in the vertical direction (column axis direction), the stress range is greatly expanded, indicating that the allowable stress is insufficient.

[0064] Figs. 6 and 7 show the analysis results. Figure 6 shows the relationship between the number of corners n and the bending performance of the polygonal cylindrical structure, and shows the case (CASE2) where the diameter-to-thickness ratio D / t is 80. In this embodiment, only the case where the diameter-to-thickness ratio D / t is 80 is typically shown in Figure 6, but in the cases where the diameter-to-thickness ratio D / t is 40 (CASE1), 120 (CASE3), 160 (CASE4), and 200 (CASE5), the graphs generally show the same tendency. In Figure 6, the horizontal axis is the number of corners n, and the vertical axis is the ratio of the maximum load-bearing capacity of the polygonal cylindrical structure (polygon) to the maximum load-bearing capacity of the circular cylindrical structure (cylinder) (maximum load-bearing capacity ratio). Here, as the evaluation criterion for the maximum load-bearing capacity ratio, it is defined that when the polygonal cylindrical structure has the same cross-sectional area as the circular cylindrical structure and the maximum load-bearing capacity is 90% or more, it has the same load-bearing capacity (bending performance).

[0065] As shown in Figure 6, it can be seen that the number of corners n at which the maximum load-bearing capacity ratio is 90% or more is 6 or more. Specifically, it was confirmed that the maximum load-bearing capacity ratio is 90% or more when the number of corners is 6 (hexagon) or more, 95% or more when the number of corners is 8 (octagon) or more, and 99% or more when the number of corners is 10 (decagon) or more. From this, it can be seen that the minimum number of corners n for obtaining a maximum load-bearing capacity ratio of 90% or more equivalent to that of a circular cross-section is 6 (hexagon). Here, for example, a circular cylindrical structure with an outer diameter D of 8 to 12 m is targeted. Considering the range where the diameter-to-thickness ratio D / t at which the polygonal cylindrical structure can exhibit bending performance equivalent to (90% or more) that of the circular cylindrical structure is 80 to 200, the required plate thickness t when the outer diameter D is 8 to 12 m is 40 mm or more. Also, the plate thickness t may be 50 mm or more, 60 mm or more, 65 mm or more, 70 mm or more, 75 mm or more, 80 mm or more. The upper limit of the plate thickness is set to 250 mm due to the increase in assembly cost due to the increase in the weight of the plate material. Note that the upper limit value of the plate thickness is preferably 200 mm, and more preferably 150 mm.

[0066] Figure 7 shows the relationship between the number of corners n and the diameter - thickness ratio D / t that results in bending performance equivalent to or better than (90% or more) that of a circular cylindrical structure. In Figure 7, the horizontal axis represents the number of corners n, and the vertical axis represents the diameter - thickness ratio D / t. Further, in Figure 7, at a certain diameter - thickness ratio D / t, when the number of corners n is increased, the points where the number of corners n reaches 90% or more, 95% or more, and 99% or more of the maximum load - bearing ratio are plotted respectively. These indicate the region (circular - equivalent region R1) where bending performance equivalent to or better than (90% or more) that of a circular cylindrical structure can be achieved, and among the regions where the maximum load - bearing ratio is less than 90%, the buckling strength - insufficient region R2 and the cross - section performance - insufficient region R3. The buckling strength - insufficient region R2 is a region where, as the number of corners n decreases, the side width B becomes longer and the plate thickness t becomes thinner, and the bending load - bearing capacity decreases significantly due to local buckling of the plate. The cross - section performance - insufficient region R3 is a region where, when the number of corners n is small, the second moment of the cross - section with respect to the bending load is small, and cross - section performance cannot be obtained.

[0067] As shown in Figure 7, when the number of corners is 6 (hexagon) and the diameter - thickness ratio D / t is 80 or less, and the maximum load - bearing ratio is 90% or more, it becomes the circular - equivalent region R1, indicating that circular - equivalent performance can be obtained. On the other hand, when the number of corners is 6 (hexagon) and the diameter - thickness ratio D / t is 120 (when it exceeds 80), since the maximum load - bearing ratio is less than 90% and it becomes the buckling strength - insufficient region R2, it can be seen that the decrease in load - bearing capacity due to local buckling of the plate is significant. In the cases of the number of corners 8 (octagon) and the number of corners 10 (decagon), even when the diameter - thickness ratio D / t becomes larger up to 120 compared to the case of the number of corners 6 (hexagon), a maximum load - bearing ratio of 90% or more can be ensured.

[0068] Also, when the number of corners is 12 (dodecagon) or more, for any diameter - thickness ratio D / t, the maximum load - bearing ratio is 90% or more and it becomes the circular - equivalent region R1, and furthermore, the maximum load - bearing ratio with respect to the diameter - thickness ratio D / t also increases. In particular, when the number of corners is 16 (hexadecagon) or more, for any diameter - thickness ratio D / t, the maximum load - bearing ratio is 99% or more, indicating that bending performance almost the same as that of a circular cross - section can be obtained. Furthermore, when the number of corners is 4 (quadrilateral), the maximum strength ratio is less than 90% regardless of the diameter-thickness ratio D / t, which falls into the section performance insufficient region R3. In other words, when only the number of corners n is small, the second moment of area against the bending load becomes small, and it is clear that the section performance cannot be obtained.

[0069] From the analysis results of this embodiment, when the diameter-thickness ratio D / t is 80 or less, the condition for the polygonal tubular structure to ensure 90% or more of the circular performance (maximum strength ratio) of a circular tubular structure is that the number of corners n is 6 or more. When the diameter-thickness ratio D / t is 80 or less, the condition for the polygonal tubular structure to ensure 95% or more of the circular performance (maximum strength ratio) of a circular tubular structure is that the number of corners n is 8 or more. When the diameter-thickness ratio D / t is 80 or less, the condition for the polygonal tubular structure to ensure 99% or more of the circular performance (maximum strength ratio) of a circular tubular structure is that the number of corners n is 10 or more. Furthermore, when the diameter-thickness ratio D / t is 120, the condition for the polygonal tubular structure to ensure 90% or more of the circular performance (maximum strength ratio) of a circular tubular structure is that the number of corners n is 8 or more. When the diameter-thickness ratio D / t is 120, the condition for the polygonal tubular structure to ensure 95% or more of the circular performance (maximum strength ratio) of a circular tubular structure is that the number of corners n is 10 or more. When the diameter-thickness ratio D / t is 120, the condition for the polygonal tubular structure to ensure 99% or more of the circular performance (maximum strength ratio) of a circular tubular structure is that the number of corners n is 12 or more. The number of corners n may be an even number. By rearranging these, the above-mentioned formula (1) or (2) can be obtained.

[0070] Although the embodiment of the polygonal cylindrical structure according to the present invention has been described above, the present invention is not limited to the above embodiment and can be modified as appropriate without departing from the spirit of the present invention.

[0071] For example, in the above-described embodiment, the polygonal columnar body 1 (polygonal cylindrical structure) is exemplified as the foundation structure of a wind power generation facility. However, in other embodiments, it is a foundation structure for an offshore wind power generation facility using the above-described polygonal columnar body 1 (polygonal cylindrical structure). In this case, the polygonal columnar body 1 serves as the foundation of the offshore wind power generation facility, for example. Specifically, it may be used for a fixed monopile type, gravity type, or jacket type foundation structure for offshore wind power, or a floating TLP (Tension Leg Platform) type or semi-submersible type foundation structure. It is also possible to use a structure for other purposes with a polygonal cylindrical structure.

[0072] In this embodiment, a polygonal columnar body 1 having a tapered shape in which the cross-sectional shape shrinks upward in the column axis direction is adopted. However, a polygonal cylindrical structure having the same cross-sectional shape and the same cross-sectional dimensions at any height in the column axis direction, that is, a polygonal cylindrical structure that is not reduced in diameter as a whole, may also be used.

[0073] In this embodiment, there is also a form in which the number of corners n of the polygonal cross-section of the polygonal columnar body 1 is configured to satisfy the above formula (1) or (2). However, it is not limited to the number of corners n that satisfies these formulas (1) or (2).

[0074] Also, within the scope not departing from the gist of the present invention, it is possible to appropriately replace the components in the above-described embodiment with well-known components.

Industrial Applicability

[0075] According to the present invention, it is possible to achieve a good balance between exhibiting bending performance equivalent to that of a circle and reducing costs by omitting the bending process and reducing the welding process.

Explanation of Reference Numerals

[0076] 1 Polygonal columnar body (polygonal cylindrical structure) 10 Flat plate member 10A Ring body W Welding part

Claims

1. A polygonal cylindrical structure formed by the same number of corners in the horizontal cross-sectional shape, composed of steel flat members connected by welding in the circumferential direction and the column axis direction, the cross-sectional shape is a polygonal cross-section of 6 to 24 sides, the plate thickness of the flat member is 40 mm or more and 250 mm or less, the perimeter is defined as the sum of the circumferential lengths at the center of the plate thickness in the cross-section, when the outer diameter is defined as the diameter at the center of the plate thickness of a cylinder with the same perimeter in the cross-section, at least the outer diameter at the base end of the polygonal cylindrical structure is 8 m or more and 40 m or less, for the polygonal cross-section, the ratio of the outer diameter to the plate thickness (outer diameter / plate thickness) is 40 or more and 200 or less over the entire length in the column axis direction, the number of corners n of the polygonal cross-section satisfies formula (1) or formula (2), a polygonal cylindrical structure. n ≥ 6 {when D / t ≤ 80}... (1) n ≥ (D / t) / 20 + 2 {when D / t > 80}... (2) Here, D: outer diameter (mm), t: plate thickness (mm), n: number of corners (natural number).

2. The polygonal cross-section is a regular polygon, the polygonal cylindrical structure according to Claim 1.

3. Comprising the polygonal cylindrical structure according to Claim 1 or 2, the polygonal cylindrical structure is a foundation structure for an offshore wind power generation facility that serves as the foundation of the offshore wind power generation facility.

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