11 TUBULAR-MEMBER FLANGE COUPLING Technical Field [0001) The present invention relates to a tubular-member flange coupling for connecting (coupling or joining) tubular members, for example, tubular members constituting a support tower of a wind turbine for wind turbine generator. Background Art [0002] As a tubular-member flange coupling for connecting tubular members constituting a support tower of a wind turbine for wind turbine generator, for example, there is the one disclosed in Patent Document 1. Patent Document 1: Japanese Translation of PCT International Application, Publication No. 2004-525293 [0003] However, in the tubular-member flange coupling disclosed in Patent Document 1, a tubular portion to be connected (coupled or joined) to the bottom or top end of a tubular member via a weld seam is produced by cutting. Therefore, there are problems in that the production process is prolonged and the manufacturing costs increase. [0004] Any discussion of documents, acts, materials, devices, articles or the like which has been included in the present 2 specification is not to be taken as an admission that any or all of these matters form part of the prior art base or were common general knowledge in the field relevant to the present invention as it existed before the priority date of each claim of this application. Throughout this specification the word "comprise", or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps. SUMMARY OF THE INVENTION [0005] According to the present invention, there is provided a tubular-member flange coupling in which a circumferential portion of a top or bottom surface of the flange coupling is mated to a bottom or top end of a tubular member to couple the tubular member to another tubular member. A recess having a substantially U-shaped cross-section is provided along an entire circumference in the top or bottom surface to be connected to the tubular member, at a position radially inward of the circumferential portion to be mated to the tubular member and an entirety of the top or bottom surface except the recess is substantially flat. [0006] According to an embodiment of the present invention, the 3 tubular-member flange coupling only requires machining of the recess having a substantially U-shaped cross-section, which is relatively easily machinable, in the surface to be connected to the tubular member. Because it is unnecessary to fabricate (machine) a tubular portion to be connected to the tubular member by cutting away a large part of the surface to be connected to the tubular member, as in the conventional case, the production process can be shortened and the manufacturing costs can be reduced. Because it is unnecessary to fabricate (machine) a tubular portion to be connected to the tubular member by cutting away a large part of the surface to be connected to the tubular member to reduce the thickness, as in the conventional case, the original thickness can be effectively maintained. This prevents the heat during welding of the tubular member and the flange coupling (welding heat) from being transmitted to a mating surface (contact surface) of the flange coupling, whereby deformation (distortion) of the mating surface can be prevented. Moreover, because the deformation (distortion) of the mating surface can be prevented, shaping for correcting the deformation of the mating surface can be made unnecessary. Thus, the production process can be further shortened and the manufacturing costs can be further reduced. [0007] In the above-described tubular-member flange coupling, it 4 is preferable that the radius of curvature of a radially inward bottom surface of the recess be formed to be smaller than the radius of curvature of a radially outward bottom surface of the recess. [0008] In an embodiment of the present invention, with such a tubular-member flange coupling, a large P.C.D. (pitch circle diameter: the diameter of a circle formed by connecting the centers of bolt holes (bolt-hole pitch circle)) can be provided. Thus, separation of the circumferential portions of the flange couplings can be prevented, and the mating surfaces (contact surfaces) of the flange couplings can be kept in closer contact with each other. [0009] A wind turbine for wind turbine generator may include the flange coupling capable of shortening the production process and reducing the manufacturing costs. [0010] According to an embodiment of the present invention, the wind turbine for wind turbine generator can shorten the production process of the entire wind turbine for wind turbine generator and can reduce the manufacturing costs. [0011] Embodiments of the present invention provide advantages in that the production process can be shortened and the manufacturing costs can be reduced. Brief Description of Drawings 5 [0012] [FIG. 1] FIG. 1 is a side view of a wind turbine for wind turbine generator having flange couplings according to an embodiment of the present invention. [FIG. 2] FIG. 2 is a longitudinal sectional view of a relevant part in FIG. 1. [FIG. 3] FIG. 3 is a longitudinal sectional view of relevant parts of flange couplings according to another embodiment of the present invention, similar to FIG. 2. [FIG. 4] FIG. 4 is a longitudinal sectional view of relevant parts of flange couplings according to another embodiment of the present invention, similar to FIGS. 2 and 3. [FIG. 5] FIG. 5 is a longitudinal sectional view of relevant parts of flange couplings according to another embodiment of the present invention, similar to FIGS. 2 to 4. [FIG. 6] FIG. 6 is a longitudinal sectional view of relevant parts of flange couplings according to another embodiment of the present invention. Explanation of Reference Signs: [00131 1: wind turbine for wind turbine generator 7: tubular member 8: flange coupling 16: recess 16a: recess 6 20: flange coupling 21: recess 30: flange coupling 31: recess Best Mode for Carrying Out the Invention [0014] A ring-shaped-member flange coupling (hereinafter, "flange coupling") according to an embodiment of the present invention will be described below with reference to FIGS. 1 and 2. FIG. 1 is a side view of a wind turbine for wind turbine generator having flange couplings according to this embodiment, and FIG. 2 is a longitudinal sectional view of a relevant part in FIG. 1. [00151 As shown in FIG. 1, the wind turbine for wind turbine generator 1 includes a support tower (also referred to as "tower") 2 installed upright on a foundation B, a nacelle 3 mounted on the top of the support tower 2, and a rotor head 4 mounted to the nacelle 3 so as to be rotatable about a substantially horizontal axis. A plurality of (for example, three) wind turbine rotor blades 5 are radially attached around the rotation axis of the rotor head 4. Thus, the force of the wind blowing in the rotation axis direction of the rotor head 4 against the wind 7 turbine rotor blades 5 is converted into motive power for rotating the rotor head 4 about the rotation axis. [0016] The support tower 2 has a structure in which a plurality of (for example, three) units 6 (refer to FIG. 2) are joined in the vertical direction. Each unit 6 has a tubular member 7 (refer to FIG. 2) and a flange coupling 8 (refer to FIG. 2). The tubular member 7 consists of a plurality of cylindrical segments (not shown) each having a cylindrical shape assembled together by fixing their ends by welding, or, consists of a plurality of circular-truncated-cone segments (not shown) each having a circular-truncated-cone shape with a diameter gradually decreasing upward, assembled by fixing their ends by welding, as shown in FIG. 2. The nacelle 3 is mounted on the top unit 6 of the units 6 constituting the support tower 2 and has a nacelle base plate (not shown) attached to the top end of the support tower 2 and a cover 9 for covering the nacelle base plate from above. [0017] The flange couplings 8 according to this embodiment are each a plate-like member having a ring shape (doughnut-shape) in plan view, in which a plurality of bolt holes 10 penetrating in the thickness direction (vertical direction in FIG. 2) are provided (formed) around the circumferential direction.
8 The top or bottom end of the circumferential portion of the flange coupling 8 and the bottom or top end of the tubular member 7 are connected (coupled or joined) via a weld seam 11 located radially inward and a weld seam 12 located radially outward. Reference numerals 13, 14, and 15 in FIG. 2 respectively denote a bolt, a nut, and a washer that connect (couple or join) the flange couplings 8 to each other. [0018] Furthermore, a recess (groove) 16 having a ring shape (doughnut-shape) in plan view and a substantially U-shape in cross-section is provided (formed) around the circumferential direction in the upper or lower surface of the flange coupling 8 to be connected to the tubular member 7. The outer circumferential edge of the recess 16 is formed so as to be located approximately just beneath or above the inner circumferential surface of the tubular member 7. That is, the outer circumferential edge of the recess 16 is formed (provided) so as to provide a connecting surface (coupling surface or mating surface) having a ring shape (doughnut shape) in plan view and having a width that is substantially the same as the thickness of the tubular member 7 at the circumferential portion of the flange coupling 8. On the other hand, the inner circumferential edge of the recess 16 is formed so as to be located approximately just 9 beneath or above the outer circumferential surface of the washer 15 for connecting the flange couplings 8 to each other. That is, the inner circumferential edge of the recess 16 is formed (provided) such that the lower or upper surface of the washer 15 is entirely in contact (close contact) with the upper or lower surface of the flange coupling 8. [0019] The flange coupling 8 according to this embodiment only requires machining of the recess 16 having a ring shape in plan view and a substantially U-shape in cross-section, which is relatively easily machinable, in the surface to be connected to the machine tubular member 7. Because it is unnecessary to fabricate (machine) a tubular portion to be connected to the tubular member by cutting away a large part of the surface to be connected to the tubular member, as in the conventional case, the production process can be shortened and the manufacturing costs can be reduced. [0020] Because it is unnecessary to fabricate (machine) a tubular portion to be connected to the tubular member by cutting away a large part of the surface to be connected to the tubular member to reduce the thickness, as in the conventional case, the thickness can be kept at substantially the original thickness. This prevents the heat (welding heat) for welding the 10 tubular member 7 and the flange coupling 8 from being transmitted to a mating surface (contact surface) 8a of the flange coupling 8, whereby deformation (distortion) of the mating surface 8a can be prevented. Moreover, because the deformation (distortion) of the mating surface Ba can be prevented, shaping for correcting the deformation of the mating surface 8a can be made unnecessary. Thus, the production process can be further shortened and the manufacturing costs can be further reduced. In addition, because the original thickness can be effectively maintained, the internal force coefficient of the bolt 13 can be lowered. Thus, a bolt with superior strength can be achieved. [0021] Referring to FIG. 3, flange couplings according to another embodiment of the present invention will be described. FIG. 3 is a longitudinal sectional view of relevant parts of flange couplings according to this embodiment, similar to FIG. 2. Flange couplings 20 according to this embodiment differ from those according to the above-described embodiment in that each has a recess 21 instead of the recess 16. Because other components are the same as those according to the above described embodiment, an explanation of such components will be omitted.
11 The same members as those according to the above described embodiment are denoted by the same reference numerals. [0022] The flange couplings 20 according to this embodiment are each a plate-like member having a ring shape (doughnut-shape) in plan view, in which the plurality of bolt holes 10 penetrating in the thickness direction (vertical direction in FIG. 3) are provided (formed) around the circumferential direction. The top or bottom end of the circumferential portion of the flange coupling 20 and the bottom or top end of the tubular member 7 are connected (coupled or joined) via the weld seam 11 located radially inward and the weld seam 12 located radially outward. [0023] Furthermore, a recess (groove) 21 having a ring shape (doughnut-shape) in plan view and a substantially U-shape in cross-section is provided (formed) around the circumferential direction in the upper or lower surface of the flange coupling 20 to be connected to the tubular member 7. The outer circumferential edge of the recess 21 is formed so as to be located approximately just beneath or above the inner circumferential surface of the tubular member 7. That is, the outer circumferential edge of the recess 21 is formed 12 (provided) so as to provide a connecting surface (coupling surface or mating surface) having a ring shape (doughnut shape) in plan view and having a width that is substantially the same as the thickness of the tubular member 7 at the circumferential portion of the flange coupling 20. On the other hand, the inner circumferential edge of the recess 21 is formed so as to be located radially outward (the left side in FIG. 3) of the inner circumferential surface of the recess 16 according to the above-described embodiment, i.e., formed such that the radius of curvature of the radially inward bottom surface of the recess 21 is smaller than the radius of curvature of the radially outward bottom surface of the recess 21, and so as to be located approximately just beneath or above the outer circumferential surface of the washer 15 for connecting the flange couplings 20 to each other. The inner circumferential edge of the recess 21 is formed (provided) such that the lower or upper surface of the washer 15 is entirely in contact (close contact) with the upper or lower surface of the flange coupling 20. [0024] With the flange couplings 20 according to this embodiment, a large P.C.D. (pitch circle diameter: the diameter of a circle formed by connecting the centers of the bolt holes 10 (bolt-hole pitch circle)) can be provided. Thus, the separation of the flange couplings 8 at the 13 circumferential portion can be prevented, and the mating surfaces (contact surfaces) 8a of the flange couplings 8 can be kept in closer contact with each other. The radius of curvature of the radially inward bottom surface of the recess 21 is set to be smaller than the radius of curvature of the radially outward bottom surface of the recess 21. Thus, the stress is concentrated on the radially inward bottom surface of the recess 21. However, higher compressive force (fastening force or clamping force) is exerted on the radially inward bottom surface of the recess 21 than on the radially outward bottom surface of the recess 21, which increases the apparent fatigue strength of the material of the radially inward bottom surface of the recess 21. The stress concentration on the radially inward bottom surface of the recess 21 is balanced out (covered) by the apparently improved fatigue strength. Thus, generation of cracks in the radially inward bottom surface of the recess 21 can be prevented. Because other advantages are the same as those according to the above-described embodiment, an explanation thereof will be omitted. [0025] Referring to FIG. 4, flange couplings according to another embodiment of the present invention will be described. FIG. 4 is a longitudinal sectional view of relevant parts 14 of flange couplings according to another embodiment of the present invention, similar to FIGS. 2 and 3. Flange couplings 30 according to this embodiment differ from those according to the above-described embodiment in that each has a recess 31 instead of the recesses 16 and 21. Because other components are the same as those according to the above-described embodiment, an explanation of such components will be omitted. The same members as those according to the above described embodiment are denoted by the same reference numerals. [0026] The flange couplings 30 according to this embodiment are each a plate-like member having a ring shape (doughnut-shape) in plan view, in which the plurality of bolt holes 10 penetrating in the thickness direction (vertical direction in FIG. 4) are provided (formed) around the circumferential direction. The top or bottom end of the circumferential portion of the flange coupling 30 and the bottom or top end of the tubular member 7 are connected (coupled or joined) via the weld seam 11 located radially inward and the weld seam 12 located radially outward. [0027] Furthermore, a recess (groove) 31 having a ring shape 15 (doughnut-shape) in plan view and a substantially U-shape in cross-section is provided (formed) around the circumferential direction in the upper or lower surface of the flange coupling 30 to be connected to the tubular member 7. The outer circumferential edge of the recess 31 is formed so as to be located approximately just beneath or above the inner circumferential surface of the tubular member 7. That is, the outer circumferential edge of the recess 31 is formed (provided) so as to provide a connecting surface (coupling surface or mating surface) having a ring shape (doughnut shape) in plan view and having a width that is substantially the same as the thickness of the tubular member 7 at the circumferential portion of the flange coupling 30. On the other hand, similarly to the inner circumferential edge of the recess 21, the inner circumferential edge of the recess 31 at the opening end (on the tubular member 7 side) is formed so as to be located radially outward of the inner circumferential surface of the recess 16 (the left side in FIG. 4) and so as to be located approximately just beneath or above the outer circumferential surface of the washer 15 for connecting the flange couplings 30 to each other. The inner circumferential edge of the recess 31 located at the opening end is formed (provided) such that the lower or upper surface of the washer 15 is entirely in contact (close contact) with the upper or lower surface of the flange coupling 30. The 16 inner circumferential edge of the recess 31 at a deep part (on the bottom surface side) is, similarly to the inner circumferential edge at a deep part (on the bottom surface side) of the recess 16, formed so as to be located radially inward of the inner circumferential edge of the recess 31 at the opening end. [0028] Because the advantages of the flange coupling 30 according to this embodiment are the same as those according to the above-described embodiment, an explanation thereof will be omitted. [0029] With the wind turbine for wind turbine generator 1 including the flange couplings 8, 20, or 30 that can shorten the production process and reduce the manufacturing costs, the whole production process of the wind turbine for wind turbine generator 1 can be shortened and the manufacturing costs can be reduced. Furthermore, with the wind turbine for wind turbine generator 1 including the flange couplings 20 or 30 that can prevent the separation of the flange couplings 8 at the circumferential portion and can keep the mating surfaces (contact surfaces) 8a of the flange couplings 8 in closer contact with each other, the reliability of the support tower 2 can be improved and the reliability of the whole wind 17 turbine for wind turbine generator 1 can be improved. [0030] In the above-described embodiment, it is more preferable that the recesses 16, 21, and 31 that are formed in the upper surface of the flange coupling 30 (that open upward) be filled with silicon, grease or the like. This can prevent water droplets running down the inner wall surface of the tubular member 7 from being collected in the recess 16, 21, or 31, and can thus prevent rust from forming in the recess 16, 21, or 31. [0031] The shape of the side surface of the flange couplings is not limited to a cylindrical shape as shown in FIGS. 2 to 4, but may be a circular-truncated-cone shape as shown in FIG. 5. This enables the side surfaces of the flange couplings and the side surfaces of the tubular members 7 to be substantially flush with each other. Thus, irregularities on the entire surface of the support tower 2 can be reduced and the appearance of the support tower 2 and the whole wind turbine for wind turbine generator 1 can be improved. [0032) Furthermore, the recesses 16 shown in FIG. 5 may each be a recess 16a having a cross-section as shown in FIG. 6, i.e., an inclined U shape that is cut along (so as to be parallel 18 with) the side surface of the flange coupling 8. Because the advantages provided by this configuration are the same as those according to the embodiment explained with reference to FIG. 2, an explanation thereof will be omitted.