How to design a polygonal cylindrical structure

Abstract

According to the present invention, a cross-sectional shape in the horizontal direction is formed by the same number of corners, and a polygonal columnar body (1) is formed by steel flat plate members (10) being coupled by welding in the circumferential direction and column axis direction. The polygonal columnar body (1) forms a polygonal cross-section with a cross-sectional shape having 6-24 squares, and the plate thickness of the flat plate members (10) is 40-250 mm. The ratio of the outer diameter D to plate thickness t (outer diameter D / plate thickness t) of the polygonal cross-section is 200 or lower.

Description

[Technical field]

[0001] The present invention relates to How to design a polygonal cylindrical structure Regarding. This application claims priority based on Japanese Patent Application No. 2022-199328, filed on December 14, 2022, the contents of which are incorporated herein by reference. [Background technology]

[0002] Conventionally, wind turbines and the towers and foundations that support them have become larger in size in order to secure the amount of power generation from offshore wind power. Generally, circular structures made of cylindrical tubes are widely used for towers and foundations, and it is expected that cylindrical tubes with a large diameter, for example, an outer diameter of more than 10 m, will be adopted as foundations in the future. As the size of the equipment increases, the strength and rigidity must be increased, and the outer diameter and wall thickness must also be increased. Usually, as shown in Patent Document 1, for example, short tubes are manufactured by bending steel plates and welding the curved plates in the circumferential direction, and the towers and foundations are constructed by further welding the short tubes together in the column axis direction. In this case, there is a problem that the bending equipment has a limited capacity, cannot handle thicker walls or larger diameters, and costs also increase.

[0003] In contrast, a structure that does not involve bending is known in which a polygonal cross section is constructed by connecting multiple flat steel plates circumferentially by welding in a columnar float that constitutes a floating offshore wind power generation facility (see, for example, Patent Document 2). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 4708365 [Patent Document 2] Patent Publication No. 2022-1474 Summary of the Invention [Problem to be solved by the invention]

[0005] However, the above-mentioned structure having a polygonal cross section has the following problems. That is, in Patent Document 2, a polygon is constructed by connecting flat steel plates in the circumferential direction by welding, but there is a risk of the cost increasing due to the excessive increase in the number of corners. Furthermore, in order for a polygonal structure to exhibit bending performance equivalent to that of a circle under the same cross-sectional area, it is generally thought that the outer diameter should be increased to increase the second moment of area. However, as the perimeter increases, the plate thickness becomes relatively smaller, and the local buckling strength of the plate decreases. In addition, by changing from a circular shape to a polygonal shape, the buckling mode that determines the limit state changes from elephant foot buckling that occurs in circular members to local buckling of plates, so it is necessary to increase the number of corners of the polygon and reduce the width-thickness ratio of one side to improve the local buckling strength.However, increasing the number of corners increases the welding line length and assembly labor, which increases costs, and there was room for improvement in this regard.

[0006] The present invention has been made in consideration of the above-mentioned problems, and is capable of achieving a good balance between exhibiting bending performance equivalent to that of a circular pipe and reducing costs by omitting bending processes and reducing welding processes. How to design a polygonal cylindrical structure The purpose is to provide. [Means for solving the problem]

[0007] <1> A first aspect of the design method for a polygonal cylindrical structure according to the present invention is a design method for a polygonal cylindrical structure whose horizontal cross-sectional shape is formed with the same number of corners, and is configured by connecting steel flat plate members by welding in the circumferential direction and the column axial direction, and the cross-sectional shape is a polygonal cross-section having a hexagon or more and a 24-sided or less side, and the plate thickness of the flat plate members is 40 mm or more and 250 mm or less, When the circumferential length is the sum of the circumferential lengths at the thickness center in the cross section, and the outer diameter is the diameter at the thickness center of a cylinder having the same circumferential length in the cross section, the outer diameter at least at the base end of the polygonal cylindrical structure is 8 m or more and 40 m or less, The polygonal cross section has a ratio of the outer diameter to the plate thickness (outer diameter / plate thickness) More than 40 along the entire length of the column axis 200 or less The number of corners n of the polygonal cross section satisfies formula (1) or formula (2). The design is characterized by the following: 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), and n: number of corners (natural number).

[0008] In the present invention, in a polygonal tubular structure having a horizontal cross-sectional shape of a polygonal cross-section that is 6 to 24 sides, the plate thickness of the flat plate member is 40 to 250 mm, and the ratio of the outer diameter to the plate thickness (outer diameter / plate thickness) is 200 or less, thereby making it possible to suppress local buckling and to select a specification for the number of corners that has a cross-sectional area equivalent to that of a circle and exhibits bending performance equivalent to that of a circle, and a polygonal tubular structure can be manufactured in which the weld line length can be shortened. In this way, the present invention allows the arrangement of the flat plate members to be constructed by merely adjusting the geometry, and it is possible to omit the bending process and reduce the costly assembly and welding process. Therefore, the present invention can achieve a good balance between improving the bending performance to be equivalent to that of a circle and suppressing increases in costs. Furthermore, the present invention can provide a low-cost polygonal cylindrical structure because reinforcing members such as ribs are not required.

[0011] Also, In this case, the minimum number of corners n that results in the same cross-sectional area and same bending performance as a circle is determined according to the diameter-to-thickness ratio D / t using equation (1) or (2), making it possible to manufacture a polygonal tubular structure with the minimum weld line length.

[0012] <2> Aspect 1 of the design method for a polygonal cylindrical structure of the present invention To Subordinate Aspects 2 The polygonal cross section is preferably a regular polygon.

[0013] In this case, since the cross-sectional shape approaches a circle, it is possible to more precisely manufacture a polygonal tubular structure set to the specifications 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. Effect of the Invention

[0015] The present invention How to design a polygonal cylindrical structureAccording to this, it is possible to achieve a good balance between exhibiting bending performance equivalent to that of a circular tube and reducing costs by omitting the bending process and reducing the welding process. [Brief description of the drawings]

[0016] [Figure 1] FIG. 2 is a perspective view showing a polygonal column according to an embodiment of the present invention. [Diagram 2] 2 is a horizontal cross-sectional view of a portion of the polygonal column shown in FIG. 1 in the height direction. [Diagram 3] 4 is a horizontal cross-sectional view showing a welding state between circumferentially adjacent flat plate members. FIG. [Figure 4] FIG. 1 is a diagram showing an analytical model according to an embodiment. [Diagram 5] 4(a) to 4(d) are diagrams showing an example of contours of the distribution of equivalent plastic strain at maximum bending load according to the analysis results of an embodiment. [Figure 6] FIG. 13 is a diagram showing the relationship between the number of corners and the bending performance of a polygonal tubular structure according to an embodiment. [Figure 7] FIG. 13 is a diagram showing the relationship between the number of corners and the diameter-to-thickness ratio that provides performance equivalent to that of a circular cylinder according to an embodiment. [Figure 8] FIG. 2 is a perspective view showing a polygonal column according to an embodiment of the present invention. [Figure 9] FIG. 2 is a perspective view showing a polygonal column according to an embodiment of the present invention. [Figure 10] FIG. 2 is a perspective view of a cylinder for explaining the structure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a polygonal cylindrical structure according to an embodiment of the present invention will be described with reference to the drawings.

[0018] As shown in Figure 1, the polygonal cylindrical structure of this embodiment is exemplified by a tower (not shown) for fixing a rotor made of blades, etc., or a foundation structure (hereinafter referred to as polygonal columnar body 1) of a wind power generation facility that supports the tower from below.

[0019] Here, in the polygonal columnar body 1, the direction parallel to the central axis O is called the column axis direction, the direction going around the central axis O is called the circumferential direction, and the direction perpendicular to the central axis O is called the radial direction. Additionally, the radial direction toward the central axis O is called the inner side, and the direction away from the central axis O is called the outer side.

[0020] As shown in Figs. 1 and 2, the polygonal columnar body 1 is a polygonal cylindrical structure whose horizontal cross-sectional shape is formed by the same number of corners (here, octagonal). The polygonal columnar body 1 is formed by connecting steel flat plate members 10 in the circumferential direction and the column axial direction by welding. The horizontal cross-sectional shape of the polygonal columnar body 1 perpendicular to the column axial direction forms a regular polygonal cross section of a regular octagon. The flat plate member 10 may be a single steel plate, or may be a steel plate formed by welding multiple plates in the circumferential direction or the column axial direction.

[0021] The cross-sectional shape of the polygonal columnar body 1 may be a polygonal cross section having a hexagon or more and a 24-sided or less side. In addition, the cross-sectional shape is not limited to a regular polygon having equal side lengths, and it is possible to adopt a polygon having a part or all of different side lengths. In addition, the cross-sectional shape is not limited to a polygonal or regular polygonal cylindrical structure having equal thickness in the column axis direction, and it is possible to adopt a polygonal or regular polygon having different thickness 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 toward the top (upper part of the cylindrical structure). The predetermined height position may be, for example, any position above the lower end of the polygonal columnar body 1. In the portion where the plate thickness changes in this way, the plate thickness of a certain flat plate member 10 is thinner than that of another flat plate member 10 adjacent to the upper side. In addition, the flat plate members 10 are not limited to being of a polygonal or regular polygonal cylindrical structure in which the lengths in the column axis direction are all equal, and it is also possible to adopt a polygonal or regular polygonal structure in which the lengths in the column axis direction of each ring body 10A are different. For example, the length of the flat plate members 10 in the column axis direction may be increased from a predetermined height position in the column axis direction toward the top (upper part of the cylindrical structure). In such a portion where the length changes, the length in the column axis direction of a certain flat plate member 10 is longer than the length in the column axis direction of another flat plate member 10 adjacent to the upper side. Furthermore, the plate thickness of the flat plate member 10 may be thinner and the length in the column axis direction may be longer toward the top (upper part of the cylindrical structure) in the column axis direction. For example, the plate thickness and length of the flat plate member 10 do not need to gradually change toward the top (upper part of the cylindrical structure) in the column axis direction, and may change from any height position in the column axis direction. In this case, the plate thickness and length in the column axis direction of another flat plate member 10 adjacent to the upper side are thinner and longer than the plate thickness and length in the column axis direction of a certain flat plate member 10.

[0022] Here, the following cases are treated as regular polygons in the present invention. The circumferential dimensions of all flat plate members 10 fall within ±2% of the average value. When angles with adjacent flat plate members 10 (inner angles of a regular polygon, all inner angles fall within ±2% of (180×(n-2)) / n).

[0023] The polygonal columnar body 1 is a long body that is installed with the column axis direction parallel to the vertical direction, and has a cylindrical shape with a hollow interior. Devices that do not contribute to structural performance may be installed in the hollow part of the polygonal columnar body 1. The polygonal columnar body 1 is also made to have a truncated pyramid shape (tapered shape) in which the cross-sectional shape is gradually reduced only in the upper part or as it goes upward. In other words, the cross-sectional shapes at any height in the column axis direction are similar. The polygonal body 1 does not have to be tapered in the column axis direction.

[0024] The flat plate member 10 constituting the polygonal column 1 is a thick plate member in which no curved or bent parts are formed. The plate thickness t of the flat plate member 10 is 40 mm or more and 250 mm or less. The polygonal cross section of the polygonal column 1 having bending performance equivalent to that of a circle is preferably set to have a ratio of the outer diameter D (mm) to the plate thickness t (mm) (outer diameter D / plate thickness t) of 200 or less. If it exceeds 440, it becomes difficult to exhibit bending performance equivalent to that of a circle, even if the polygonal cross section has a 24-sided polygon. 10 shows a cylinder 100 whose perimeter is the same as the perimeter of the cross section of polygonal column 1. The outer diameter D of polygonal column 1 corresponds to the diameter D100 at the center line of flat plate member 110 of cylinder 100 whose perimeter is the same in cross section.

[0025] The number of corners n (natural number) of the polygonal cross section of polygonal columnar body 1 satisfies formula (1) or formula (2).

[0026] 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), and n: number of corners (natural number). When the unit of the outer diameter D is meters (m), the unit must be changed to millimeters (mm) before calculating D / t.

[0027] The flat plate members 10 connected in the circumferential and column axis directions are formed by connecting them together through welding. The symbol W in Fig. 1 indicates a welded portion (welded portion). The welded portion W has a horizontal welded portion W1 extending along the circumferential direction and a vertical 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.

[0028] The polygonal columnar body 1 of this embodiment is formed by connecting ring bodies, each of which is made of eight flat plate members 10 connected in the circumferential direction, in one or more stages (six stages are shown in FIG. 1) in the column axis direction. The vertical welds W2 of each of the ring bodies 10A connected in the column axis direction are continuous with each other in the column axis direction. The horizontal welds W1 of each of the ring bodies 10A may be continuous with each other in the circumferential direction. Furthermore, if the arrangement heights of circumferentially adjacent flat plate members 10 in the column axis direction are not the same, i.e., if a so-called staggered arrangement is used, the horizontal weld W1 will be discontinuous in the circumferential direction, but the vertical weld W2 will be continuous in the column axis direction.

[0029] Next, a method for manufacturing 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 serving as a 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 when the polygonal columnar body is constructed, which is 1.0 m or more and 5.0 m or less, and a length corresponding to the column axis direction, which is 2.0 m or more and 15.0 m or less. In this cutting process, a necessary number of flat plate members 10 for constructing the polygonal columnar body 1 are cut out. However, the large steel plate serving as the base material may be used as the flat plate member 10 as it is without going through the cutting process. The flat plate member 10 may be a cut plate piece or a single steel plate used without cutting, or may be a steel plate formed by welding the cut plate piece or the steel plate used without cutting in the circumferential direction or the column axis direction. In this way, when the flat plate member 10 is formed by welding a plurality of plate pieces in the circumferential direction or the column axis direction, the plate pieces can be treated as the same flat plate member 10 if the angle between adjacent plate pieces in the circumferential direction is within 1.0°.

[0030] Thereafter, the flat plate members 10 are arranged, for example, on a stand (not shown). At this time, two flat plate members 10 adjacent in the circumferential direction are arranged so as to butt against each other at a predetermined crossing angle. Here, the predetermined crossing angle is an angle (i.e., an interior angle of a polygon) at which the cross-sectional shape (polygon) of the intended polygonal columnar body 1 is completed by the flat plate members 10, and in the case of a regular octagon as shown in FIG. 1, the crossing angle that is a right angle to each side of the two adjacent flat plate members 10 is 135°. In this arrangement process, the flat plate members 10 are arranged as they are, without bending the flat plate members 10 as in the conventional technology. It is preferable that the flat plate members 10 arranged on the stand are arranged with the side to be welded facing upward, and are welded in a state in which the welding torch faces downward. On the other hand, there is also a case where a plurality of flat plate members 10 are arranged vertically while maintaining a predetermined interior angle, and welding is performed in a state where the welding torch faces sideways or downward. In this case, it is not necessary to use a stand.

[0031] When placing the flat plate members 10 on the stand, for example, a placement jig (not shown) having an abutment surface set at the above-mentioned specified intersection angle can be used, and the flat plate members 10 can be placed by abutting them against the abutment surface of this placement jig, thereby easily positioning adjacent flat plate members 10 relative to each other.

[0032] Next, a groove shape is formed at the butt joint between the adjacent flat plate members 10, and the groove is welded to connect the flat plate members 10 to each other via the weld W. The flat plate members 10 are assembled, for example, into the above-mentioned ring body 10A or a partial cross-sectional ring body obtained by dividing the cross section of the ring body 10A. The ring body 10A or the partial cross-sectional ring body is then welded and connected to the upper side in the column axis direction at a predetermined installation position of the polygonal columnar body 1, thereby constructing the polygonal columnar body 1. As shown in FIG. 2, the butt joint between the adjacent flat plate members 10 may be a natural groove or a V-shaped groove, and the weld W may be formed by welding from the outside of the cross section, and is not limited to welding from one side (inside or outside), and the weld W may be formed from both sides. Also, as shown in FIG. 3, X-shaped grooves 10c, 10d may be provided in advance at the ends of the respective circumferentially adjacent flat plate members 10, and the portions where the X-shaped grooves 10c, 10d are butted together may be welded from both the outer and inner sides of the cross section to form the welded portion W. Welding is not limited to being from one side (inner or outer side), and the welded portion W may be formed from both sides.

[0033] The divided ring bodies 10A etc. may be manufactured in a factory or yard near the installation location of the polygonal column 1, or they may be manufactured in a processing factory away from the installation location of the polygonal column 1 and then transported by truck, ship, etc. to the installation location of the polygonal column 1.

[0034] According to the polygonal columnar body 1, which is a polygonal cylindrical structure described above, the horizontal cross-sectional shape is formed with the same number of corners. The polygonal columnar body 1 is formed by connecting steel flat plate members 10 in the circumferential direction and the column axial direction by welding. The polygonal columnar body 1 has a polygonal cross-sectional shape of at least 6 sides and at most 24 sides, and the plate thickness of the flat plate members 10 is at least 40 mm and at most 250 mm. The polygonal cross-section has a ratio of the outer diameter D to the plate thickness t (outer diameter D / plate thickness t) of 200 or less.

[0035] With this configuration, under the condition that the horizontal cross-sectional shape of the polygonal cross section in the polygonal columnar body 1 is a polygonal cross section having the same cross-sectional area as a polygonal cross section having a polygonal cross section of 6 to 24 sides, the plate thickness t of the flat plate member 10 is set to 40 to 250 mm and the ratio of the outer diameter D to the plate thickness t (outer diameter D / plate thickness t) is set to 200 or less, so that local buckling can be suppressed, and the polygonal columnar body 1 can be manufactured with the minimum weld line length by selecting the specifications for the minimum number of corners that exhibits the same cross-sectional area as a circle and bending performance as a circle. Note that the above "equivalent" is defined as, for example, a maximum strength ratio of the polygonal cross section to the circular cross section of 0.9 (90%) or more. Therefore, in this embodiment, the arrangement of the flat plate members 10 can be constructed only by geometric adjustment, the bending process can be omitted, and the increase in cost can be suppressed by minimizing the costly assembly welding process. Furthermore, in this embodiment, since reinforcing members such as ribs are not required, a low-cost polygonal columnar body 1 can be provided.

[0036] In this embodiment, the number of corners n of the polygonal cross section satisfies the above formula (1) or (2). In this case, the minimum number of corners n that results in the same cross-sectional area and same bending performance as a circle is determined according to the diameter-thickness ratio D / t using equation (1) or (2), making it possible to manufacture a polygonal columnar body 1 with the minimum weld line length.

[0037] The number of corners n (a natural number) of the polygonal cross section of polygonal column 1 may satisfy formula (3) or formula (4).

[0038] n ≧ 8 {when D / t ≦ 80} (3) n ≧ (D / t) / 20 + 4 {when D / t > 80} (4)

[0039] When the number of corners, n, of a polygonal cross section satisfies equation (3) or equation (4), the maximum strength ratio is 0.95 (95%) or more.

[0040] The number of corners n (a natural number) of the polygonal cross section of polygonal column 1 may satisfy formula (5) or formula (6).

[0041] n ≧ 10 {when D / t ≦ 80} (5) n≧(D / t) / 20+6 {when D / t>80} (6)

[0042] When the number of corners, n, of a polygonal cross section satisfies equation (5) or equation (6), the maximum strength ratio is 0.99 (99%) or more.

[0043] The number of corners n (a natural number) of the polygonal cross section of polygonal column 1 may satisfy formula (7) or formula (8).

[0044] 6≦n≦10 {when D / t≦80} (7) (D / t) / 20+2≦n≦(D / t) / 20+6 {when D / t>80} (8)

[0045] When the number of corners, n, of a polygonal cross section satisfies equation (7) or equation (8), the maximum strength ratio is 0.90 (90%) or more.

[0046] The number of corners n (a natural number) of the polygonal cross section of polygonal column 1 may satisfy formula (9) or formula (10).

[0047] 8≦n≦12 {when D / t≦80} (9) (D / t) / 20+4≦n≦(D / t) / 20+8 {when D / t>80} (10)

[0048] When the number of corners, n, of a polygonal cross section satisfies equation (9) or equation (10), the maximum strength ratio is 0.95 (95%) or more.

[0049] The number of corners n (a natural number) of the polygonal cross section of polygonal column 1 may satisfy formula (11) or formula (12).

[0050] 10≦n≦14 {when D / t≦80} (11) (D / t) / 20+6≦n≦(D / t) / 20+10 {when D / t>80} (12)

[0051] When the number of corners, n, of a polygonal cross section satisfies equation (11) or equation (12), the maximum strength ratio is 0.99 (99%) or more.

[0052] In the design method of a polygonal cylindrical structure according to the present embodiment, the polygonal cylindrical structure is designed. For example, in the design method of a polygonal cylindrical structure, the polygonal cross section is designed so that the ratio of the outer diameter D to the plate thickness t (outer diameter / plate thickness) is 200 or less. In addition, the number of corners n of the polygonal cross section is designed to satisfy formula (1) or formula (2). The polygonal cross section is designed to be a regular polygon.

[0053] Furthermore, in this 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, it is possible to more accurately manufacture the polygonal columnar body 1 set to the specifications 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. That is, considering that side length errors occur during manufacturing, a polygonal cylindrical structure can be manufactured more accurately by connecting flat plate members with the same side length rather than connecting flat plate members with different side lengths.

[0054] As described above, the polygonal columnar body 1 of the wind power generation facility according to this embodiment, the design method for the polygonal tubular structure, and the foundation structure for offshore wind power generation facility using the polygonal tubular structure can achieve a balanced combination of exhibiting bending performance equivalent to that of a circular structure and reducing costs by omitting the bending process and reducing the welding process.

[0055] The polygonal column 1 shown in FIG. 1 has a truncated pyramid shape (tapered shape) whose cross section gradually decreases toward the top. Each flat plate member 10 constituting the polygonal column 1 shown in FIG. 1 has a trapezoid shape that decreases toward the top when viewed from the front. As shown in FIG. 8, the polygonal column 1' may have a cylindrical shape. That is, the outer diameter of the cross section of the polygonal column 1' may be approximately the same in the height direction. Each flat plate member 10' constituting the polygonal column 1' shown in FIG. 8 has a rectangular shape when viewed from the front. By making the polygonal column 1' cylindrical, a process of cutting the flat plate member 10 into a trapezoid shape is not required. Regarding the welds W' of the polygonal columnar body 1' shown in Figure 8, similarly to the welds W of the polygonal columnar body 1 shown in Figure 1, the vertical welds W2' of each ring body 10A' connected in the column axis direction are continuous with each other in the column axis direction, and the horizontal welds W1' of each ring body 10A' may be continuous with each other in the circumferential direction or may be staggered. The polygonal cylindrical structure formed by the polygonal pillars 1' shown in FIG. 8 can also provide the same effects as those of the polygonal cylindrical structure formed by the polygonal pillars 1 shown in FIG. Also, as shown in Fig. 9, the polygonal columnar body 1B' may have a frustum shape only at a portion of the upper end, and a cylindrical shape below that. In Fig. 9, the upper two-stage ring body 10B' has a frustum shape. In this case, the welded part W' (W1', W2') is the same as the welded part W described above.

[0056] When the polygonal body 1 has a tapered shape, it is desirable that the bottommost part, which is most susceptible to buckling, satisfies formula (1) or (2). More desirably, as long as formula (1) or (2) is satisfied at any column axial height, the outer diameter D and plate thickness t may change in the column axial direction.

[0057] Next, examples carried out to verify the effects of the polygonal cylindrical structure according to the above-described embodiment will be described below.

[0058] (Example) In the embodiment, a horizontal load F was applied to the apex (top) of a cantilever beam model 2, which models the polygonal cylindrical structure shown in Figure 4, using a numerical simulation analysis (finite element analysis), and the strength of the polygonal cylindrical structure was evaluated.

[0059] As shown in Table 1, in the embodiment, a cantilever beam model 2 as shown in FIG. 4 was created for each of five analysis cases (CASE 1, CASE 2, CASE 3, CASE 4, CASE 5), and a numerical simulation analysis was performed by changing the diameter-to-thickness ratio (D / t) of the polygonal shape for each analysis case 1 to 5. The specific conditions for each analysis case 1 to 5 are as shown in Table 1. The diameter-to-thickness ratio (D / t) for the analysis cases is 40 for CASE 1, 80 for CASE 2, 120 for CASE 3, 160 for CASE 4, and 200 for CASE 5. In Table 1, "outer diameter" is the distance between the center of the thickness of the flat plate member 10 and the center line of a cylinder that has the same reference circumference in cross section. "Circumference" is the outer diameter (m) of a cylinder that has the same reference circumference in cross section times pi, that is, plate width x number of corners. "Area" is calculated by plate thickness (mm) x circumference (m), that is, circumference x plate thickness (plate width x number of corners x plate thickness).

[0060] [Table 1]

[0061] Table 2 also shows the side width B (m), plate thickness t (mm), and width-thickness ratio (B / t) for each of the seven patterns of number of corners n (number of corners n of the polygonal shape is 4, 6, 8, 10, 12, 16, and 24) in analysis CASEs 1 to 5. As a comparative example to the polygonal cylindrical structure in this embodiment, a model of a circular cylindrical structure with a circular cross section was created and a similar analysis was performed. The analysis conditions for the circular cylindrical structure were that a regular 256-sided polygonal cylindrical structure with a side width of 0.123 m was considered to be equivalent to a cylinder in analysis cases 1 to 5. The "side width" in Table 2 is the value of perimeter / number of corners n.

[0062] [Table 2]

[0063] In this example, the maximum stress (equivalent plastic strain, maximum strength) acting when a horizontal load (bending load) is applied to each polygonal cylindrical structure was obtained by analysis for each of the seven patterns of corner numbers n in analysis cases 1 to 5. Similarly, the maximum stress (strength) acting when a horizontal load is applied to the circular cylindrical structure of the comparative example was obtained by analysis.

[0064] Figures 5(a) to (d) each show a cross-sectional shape of a cylindrical structure on the left side of the page, and an example of the distribution of equivalent plastic strain at maximum bending load based on the analysis results shown as a contour diagram on the right side of the page. Figure 5(a) is an example of a quadrangular case with four corners. Figure 5(b) is an example of an octagonal case with eight corners. Figure 5(c) is an example of a dodecagonal case with twelve corners. Figure 5(d) is an example of a comparative example with a circular cross section. The symbol K shown in Figures 5(a) to (d) indicates the area (high stress area) where equivalent plastic strain occurs in each contour.

[0065] It can be seen that large stress acts on the installation part (base end) of the cylindrical structure in all of Figures 5(a) to (d). In addition, from the state of the contours, it can be confirmed that the number of corners of 8 in Figure 5(b) and the number of corners of 12 in Figure 5(c) have the same stress distribution and magnitude as the circular cross section of the comparative example in Figure 5(d). On the other hand, in the case of the number of corners of 4 in Figure 5(a), the range (area) of the stress distribution is wider than the circular cross section of the comparative example in Figure 5(d), and the stress range is significantly expanded especially in the vertical direction (column axis direction), which indicates that the strength is insufficient.

[0066] 6 and 7 show the analysis results. FIG. 6 shows the relationship between the number of corners n and the bending performance of the polygonal cylindrical structure, and shows the case where the diameter-thickness ratio D / t is 80 (CASE 2). In this embodiment, FIG. 6 shows only the representative case where the diameter-thickness ratio D / t is 80, but the graph shows roughly the same tendency in the cases where the diameter-thickness ratio D / t is 40 (CASE 1), 120 (CASE 3), 160 (CASE 4), and 200 (CASE 5). In FIG. 6, the horizontal axis is the number of corners n, and the vertical axis is the ratio (maximum strength ratio) of the maximum strength of the polygonal cylindrical structure (polygon) to the maximum strength of the circular cylindrical structure (cylinder). Here, as an evaluation criterion for the maximum strength ratio, it is defined that the polygonal cylindrical structure has the same cross-sectional area as the circular cylindrical structure and the maximum strength is 90% or more, and has the same strength (bending performance).

[0067] As shown in FIG. 6, it can be seen that the number of corners n at which the maximum strength ratio is 90% or more is 6 or more. Specifically, it was confirmed that the maximum strength ratio is 90% or more when the number of corners is 6 (hexagon) or more, the maximum strength ratio is 95% or more when the number of corners is 8 (octagon) or more, and the maximum strength ratio is 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 to obtain a maximum strength ratio of 90% or more equivalent to that of a circular cross section is 6 (hexagon). Here, for example, the target is a circular cylindrical structure with an outer diameter D of 8 to 12 m. Considering the range of diameter-thickness ratio D / t of 80 to 200 in which a polygonal cylindrical structure can exhibit bending performance equivalent to or greater than that of a circular cylindrical structure (90%), the plate thickness t required when the outer diameter D is 8 to 12 m is 40 mm or more. 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, or 80 mm or more. The upper limit of the plate thickness is set to 250 mm because of the increase in assembly cost due to the increase in the weight of the plate material. The upper limit of the plate thickness is preferably 200 mm, and more preferably 150 mm.

[0068] FIG. 7 shows the relationship between the number of corners n and the diameter-thickness ratio D / t at which the bending performance is equal to or greater than that of a circular cylindrical structure (90%). In FIG. 7, the horizontal axis is the number of corners n, and the vertical axis is the diameter-thickness ratio D / t. Furthermore, FIG. 7 plots the points at which the number of corners n is 90% or more, 95% or more, and 99% or more of the maximum strength ratio when the number of corners n is increased at a certain diameter-thickness ratio D / t. These show the region where bending performance equal to or greater than that of a circular cylindrical structure (circular equivalent region R1) can be realized, and the buckling strength insufficient region R2 and the cross-sectional performance insufficient region R3 among the regions where the maximum strength ratio is less than 90%. The buckling strength insufficient region R2 is a region where the bending strength is significantly reduced due to local buckling of the plate as the side width B becomes longer and the plate thickness t becomes thinner as the number of corners n becomes smaller. The cross-sectional performance insufficient region R3 is a region where the cross-sectional performance cannot be obtained when the number of corners n is small, because the second moment of area against the bending load becomes smaller.

[0069] As shown in Figure 7, when the number of corners is 6 (hexagonal), and the diameter-thickness ratio D / t is 80 or less, the maximum strength ratio is 90% or more, which is in region R1 equivalent to a circle, and it can be seen that performance equivalent to a circle can be obtained. On the other hand, when the number of corners is 6 (hexagonal) and the diameter-thickness ratio D / t is 120 (over 80), the maximum strength ratio is less than 90% and falls in region R2 where buckling strength is insufficient, indicating a significant decrease in strength due to local buckling of the plate. In the cases of 8 corners (octagonal) and 10 corners (decagonal), a maximum strength ratio of 90% or more can be secured even when the diameter-thickness ratio D / t increases to 120 compared to the case of 6 corners (hexagonal).

[0070] Furthermore, when the number of sides is 12 or more (12-sided), the maximum strength ratio is 90% or more for any diameter-thickness ratio D / t, and the circular equivalent region R1 is reached, and the maximum strength ratio for the diameter-thickness ratio D / t also becomes large. In particular, when the number of sides is 16 or more (16-sided), the maximum strength ratio is 99% or more for any diameter-thickness ratio D / t, and it can be seen that the bending performance is almost the same as that of a circular cross section. 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.

[0071] 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.

[0072] 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.

[0073] For example, in the above-mentioned embodiment, the foundation structure of a wind power generation facility is exemplified as the polygonal columnar body 1 (polygonal cylindrical structure), but another embodiment is a foundation structure for an offshore wind power generation facility using the above-mentioned polygonal columnar body 1 (polygonal cylindrical structure). In this case, the polygonal columnar body 1 becomes, for example, the foundation of the offshore wind power generation facility. Specifically, it may be used for a fixed-bottom type monopile type, gravity type, or jacket type foundation structure for offshore wind power, or a floating type TLP (Tension Leg Platform) type or semi-submerged (semi-submerged) type foundation structure, and it is also possible to make structures for other purposes into polygonal cylindrical structures.

[0074] In addition, in this embodiment, a tapered polygonal columnar body 1 is used, whose cross-sectional shape tapers upward in the column axis direction. However, the polygonal cylindrical structure may have the same cross-sectional shape and cross-sectional dimensions at any height in the column axis direction, that is, a polygonal cylindrical structure that does not taper overall.

[0075] In addition, in this embodiment, the number of corners n of the polygonal cross section of the polygonal columnar body 1 may be configured to satisfy the above formula (1) or (2), but is not limited to the number of corners n satisfying formula (1) or (2).

[0076] Furthermore, within the scope of the present invention, the components in the above-described embodiments can be appropriately replaced with well-known components. [Industrial Applicability]

[0077] According to the present invention, it is possible to achieve a good balance between exhibiting bending performance equivalent to that of a circular shape and reducing costs by omitting bending processes and reducing welding processes. [Explanation of symbols]

[0078] 1. Polygonal columnar body (polygonal cylindrical structure) 10 Flat plate members 10A Ring body W Welding

Claims

1. A method for designing a polygonal cylindrical structure whose horizontal cross-sectional shape is formed with the same number of corners, comprising the steps of: The column is constructed by connecting flat steel plate members in the circumferential direction and the column axial direction by welding. The cross-sectional shape is a polygonal cross section having 6 or more and 24 or less sides, The plate thickness of the flat plate member is 40 mm or more and 250 mm or less, The circumferential length is the sum of the circumferential lengths at the center of the plate thickness in the cross section, When the outer diameter is the diameter at the center of the thickness of a cylinder having the same circumferential length in cross section, The outer diameter at least at the base end of the polygonal cylindrical structure is 8 m or more and 40 m or less, The polygonal cross section has a ratio of outer diameter to plate thickness (outer diameter / plate thickness) of 40 to 200 over the entire length in the column axial direction, The method for designing a polygonal cylindrical structure includes designing the number of corners n of the polygonal cross section to satisfy formula (1) or formula (2). 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), and n: number of corners (natural number).

2. The method for designing a polygonal cylindrical structure according to claim 1 , wherein the polygonal cross section is designed to be a regular polygon.

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