BRIEF DESCRIPTION OF THE DRAWING
These and other features, aspects, and advantages of the present invention will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein:
FIG. 1 illustrates an exemplary tubular structure with flanged sections that are bolted together.
FIG. 2 illustrates a cross-sectional view of a properly aligned flange connection for modular sections of a tower;
FIG. 3 illustrates a process for bolting with a distorted flange;
FIG. 4 illustrates a side sectional view of an finger plate assembly;
FIG. 5 illustrates an isometric view of a typical finger plate;
FIG. 6 illustrates the relative stiffness of a finger plate assembly joint and a current short flange joint in response to tower sidesway;
FIG. 7 illustrates the flangeless joint utilizing finger plate assemblies uniformly distributed around the periphery of a tubular support structure;
FIG. 8 illustrates an axial cross section of a wind turbine support tower including flangeless joints connected with finger plate assemblies.
DETAILED DESCRIPTION OF THE INVENTION
The following embodiments of the present invention have many advantages, including avoidance of high tensile stresses on welds and bolts leading to a probability of weld cracking or bolt failure and the associated high maintenance costs.
One aspect of the present invention provides finger plate assemblies to join adjacent sections of a tubular assembly. FIG. 4 illustrates a side sectional view of a finger plate assembly 50 that overcomes the previously described problem, in tubular assemblies with welded flanged joints, of flange distortion after welding. The annular rings of two adjacent flangeless modular sections 52 and 54 of the tubular assembly (without flanges) are brought together in close proximity at point 56. An inner finger plate 57 is provided on an interior of the tubular assembly. The inner finger plate 57 may be provided with a curved outer diameter matched to the curved inner diameter of the flangeless modular sections 52 and 54. The inner finger plate 57 is provided for connecting the inner surfaces 58 and 60 of the adjacent flangeless sections. An outer finger plate 62 is provided on an exterior of the tubular assembly. The outer finger plate 62 may be provided with a curved inner diameter matched to the curved outer diameter of the modular sections 52 and 54. The outer finger plate 62 is provided for connecting the outer surfaces 64 and 66 of the adjacent flangeless modular sections. Fastening throughhole arrays are provided on each finger plate and are matched with the fastening throughhole array provided on the corresponding adjacent ends of the flangeless modular sections. The assembly further may further include bolts 47 and nuts 49 according to the throughhole array. However, other suitable fastening means may be utilized depending upon the particular application.
FIG. 5 illustrates an isometric view of a typical finger plate utilizing nut and bolt fastening. The typical finger plate 70 has an inner surface 72 and an outer surface 74. For an inner finger plate, its outer surface is matched to the curved outer surface of the adjacent tubular sections. For an outer finger plate, its outer surface matched to corresponding surface of adjacent tubular sections. A typical bolt throughhole array 76 is shown for connection with one tubular section and typical bolt throughhole array 78 is shown for connection with the adjacent tubular section. Finger plate design is according to standard design practice including spacing of bolt throughholes from the edge of the finger plate, spacing between adjacent bolt throughholes, thickness of the finger plate, surface dimension of the finger plate and plate material selection.
For the exemplary 80 m tower, the finger plate may have an arc dimension of about 2 m, a height of about 1 m, and a thickness of about 30-40 mm. The material for finger plates may preferably include ASTM A 572 Gr 50 steel plate. Bolt throughhole arrays 76 and 78 on the finger plates may be preferably configured in double rows applied to each adjacent section of tower for a total of about 48 bolt holes per finger plate. Diameter for the bolt throughholes may preferably be sized about 1.25 inch. Minimum spacing between the bolt throughholes may be about 5 inches. Typical bolts for the finger plates in the 80 m tower may preferably be M36 10.9 grade bolts that are torqued to a bolt prestress of about 510 Mpa (74 ksi).
In addition to eliminating the end flanges, the discrete nature accommodates slight aberrations in tower section geometry to speed up assembly and minimize expensive re-work. The finger plate assemblies are designed with sufficient thickness, length and width to provide acceptable local and overall stiffness to address tower side-sway and stability requirements. Standard bolt design practice will determine finger plate dimensions.
FIG. 6 illustrates the relative stiffness of a finger plate assembly joint and a current short flange joint in response to tower sidesway. Long curved finger plate assembly joint 80 of inner finger plate 57 and outer finger plate 62 provide increased joint stiffness for resisting bending due to tower sidesway. The finger plate assembly joint 80 distributes the bending moments over a longer curved surface L1 as compared to a short surface L2 of top closure flange 27 and bottom closure flange 29 available to absorb the sideway moment in the conventional flanged joint 85.
A typical flangeless joint with finger plate assemblies according to one aspect of the present invention uniformly distributes a plurality of finger plates around the periphery of adjacent sections of the tubular support structure.
FIG. 7 illustrates a flangeless joint 90 with finger plate assemblies 92 uniformly distributed around the periphery of a lower tubular section 96. The inner finger plates 93 and outer finger plates 94 and the lower tubular section 96 are shown for clarity. An upper tubular structure and fasteners are omitted for the sake of clarity. The tubular structure may be a support tower or a wind turbine support tower. For an exemplary wind turbine support tower of about 80 m, five finger plate assemblies may be distributed around the periphery of the adjacent sections of the wind turbine support tower. Further bolting may be employed as a fastening means for the wind turbine support tower. While a simplified scheme for bolting throughholes is shown, FIG. 5 illustrates a finger plate with a more typical throughhole array for the exemplary wind turbine support tower.
The curved nature of the finger plates contributes to joint stiffness. Appropriate design of the finger plate length, thickness, and width will stiffen the joint locally and provide prescribed over-all tower stiffness for side sway, stability, and tower-head eccentric loading in a much more structurally efficient manner compared to flanged joints of prior art. The thickness and spacing of the finger plates will also be a function of the prevailing standard practice for bolted joint design. The bolt hole diameter and spacing will be a function of service conditions.
The use of finger plate assemblies replaces welding flanges to the can assemblies as the means of joining modular sections of the tower. Consequently, the distortion and prestressing problems associated with these welds and the bolts is eliminated. Further, it is difficult to get an accurate assessment of weld integrity since prevailing inspection techniques rely on a calibrated, non-direct, detection procedure. Replacing the welds with bolts allows an inspector to check each bolt for allowable pre-load using a torque wrench.
According to yet another aspect of the present invention, a tubular structure is provided that includes a plurality of tubular sections and a plurality of flangeless joints employing finger plate assemblies for connecting the adjacent tubular sections. The finger plate assemblies are uniformly distributed around the periphery of the adjacent tubular sections. The tubular structure may define a support tower and more specifically a wind turbine support tower that utilizes the finger plate assemblies for joining modular sections of the tower. The modular sections of the tower are assembled by welding tubular segments to form tower sections.
FIG. 8 illustrates an axial cross section of a wind turbine support tower 105. The wind turbine support tower 105 incorporates flangeless joints 90 utilizing finger plate assemblies 120 for connecting tower sections 96. The wind turbine support tower 105 provides support for wind turbine generator 110 and wind turbine rotor 115. The exemplary wind turbine support tower 105 is about 80 m in height, incorporating three tower sections 96 and two flangeless joints 90.
In this exemplary wind turbine support tower, five finger plate assemblies may be uniformly distributed around the periphery of the flangeless joint. The tower sections may be cylindrical shaped or have a generally truncated right conical section to provide for overall reduction in cross section of tower sections at higher elevations. Further individual tubular segments may be individually tapered along the axial length to provide for the progressive reduction in cross section for each individual tower section along the axial length of the tower section.
While only certain features of the invention have been illustrated and described herein, many modifications and changes will occur to those skilled in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the invention.
Patent Application
20080041009
