Abstract:
A wind turbine including an article, article, and method of forming an article for distributing stress are disclosed. The article includes a flange for securing an upper tower section and a lower tower section of a wind turbine and includes a first arm extending in a first direction, a second arm extending in a second direction substantially perpendicular to the first direction, a relief region disposed between the first arm and the second arm, the relief region maintaining or improving the distribution of stress on wind turbine components selected from the group consisting of the first arm of the flange, the second arm of the flange, a fastener of the flange, and combinations thereof.

Description:
FIELD OF THE INVENTION 
       [0001]    The present disclosure generally relates to wind turbine components and, more particularly systems and methods for relieving stress on wind turbine components. 
       BACKGROUND OF THE INVENTION 
       [0002]    Wind turbines are continuously being designed and produced to be larger, to be more complex, and to have increased strength. One such structure is a wind turbine. Wind turbines can include a plurality of blades rotationally coupled to a generator rotor through a hub. The generator rotor can be mounted within a housing or nacelle, which may be positioned on top of a tubular tower or a base. The housing or nacelle has significant mass which is fatigue loaded on the tower or base. Movement of the housing due to wind or other forces may result in loads, such as reversing fatigue loads on the tower or base or on the nacelle or the housing. 
         [0003]    Fatigue loaded structures or portions of structures may be subjected to numerous physical forces. Physical forces may result from factors including, but not limited to, environmental effects (such as sunlight being on only a portion of the structure at a time), operational effects, and/or exposure to changing conditions. For example, a wind turbine tower can sway due to changes in wind speed, thereby subjecting the tower to tensile and compressive forces on the metal structures making up the tower. The nacelle may be exposed to similar forces from the rotation of the blades. Likewise, a generator housing or other portions of the wind turbine can be subjected to these and other forces. Over time, the tensile and compressive forces can form cracks. Upon being formed, the cracks can propagate with continued cycling of tensile and compressive forces. Ultimately, the cracks can lead to failure of the structure. 
         [0004]    To reduce, retard, or eliminate cracking, fillets having stress relief properties (for example, distribution of tensile and compressive forces) can be fastened to structures at locations where the structure is susceptible to cracking or experiences tensile and/or compressive forces. 
         [0005]    Fillets used for stress relief require a significant amount of material and require significant labor to install. 
       BRIEF DESCRIPTION OF THE INVENTION 
       [0006]    In an aspect, a flange for securing an upper tower section and a lower tower section of a wind turbine includes a first arm extending in a first direction, a second arm extending in a second direction substantially perpendicular to the first direction, a relief region disposed between the first arm and the second arm. 
         [0007]    In another aspect, a wind turbine includes at least one blade operably mounted on a tower, the at least one blade attached to a rotor having a rotor shaft, the rotor shaft in rotational communication with a generator, the tower including an upper tower section and a lower tower section, a first flange, and a second flange. Each flange includes a first arm extending in a first direction, a second arm extending in a second direction, the second direction being substantially perpendicular to the first direction, a relief region disposed between the first arm and the second arm. 
         [0008]    In another aspect, a method of distributing stress in flanges securing an upper tower section and a lower tower section of a wind turbine includes forming a first flange, forming a second flange, and securing the first flange to the second flange with the fastener. Each flange includes a first arm extending in a first direction, a second arm extending in a second direction, the second direction being substantially perpendicular to the first direction, a relief region disposed between the first arm and the second arm. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]      FIG. 1  is a perspective view of an exemplary embodiment of a wind turbine in accordance with the present disclosure. 
           [0010]      FIG. 2  shows a part of an exemplary flange between an upper tower section and lower tower section of a wind turbine. 
           [0011]      FIG. 3  shows an exemplary fastener for securing a first flange to a second flange. 
           [0012]      FIG. 4  shows a part of an exemplary flange between an upper tower section and lower tower section of a wind turbine. 
           [0013]      FIG. 5  shows a part of a flange having a fastener and no relief region. 
       
    
    
       [0014]    Wherever possible, the same reference numbers will be used throughout the drawings to represent the same parts. 
       DETAILED DESCRIPTION OF THE INVENTION 
       [0015]      FIG. 1  is a perspective view of an exemplary wind turbine  10  in accordance with an embodiment of the present disclosure. The embodiments of the present disclosure may include decreased material costs by decreasing the amount of material desired, maintained or improved distribution of stress, increased machine life, and/or decreased size of parts thereby generating cost savings, such as reduced labor costs and reduced material costs. Other features and advantages of the present disclosure will be apparent from the following more detailed description of the preferred embodiment, taken in conjunction with the accompanying drawings which illustrate, by way of example, the principles of the disclosure. 
         [0016]    Wind turbine  10  described and illustrated herein is a wind generator for generating electrical power from wind energy. However, in some embodiments, wind turbine  10  may be, in addition or alternative to a wind generator, any type of wind turbine, such as, but not limited to, a windmill (not shown). Moreover, wind turbine  10  described and illustrated herein includes a horizontal-axis configuration. However, in some embodiments, wind turbine  10  may include, in addition or alternative to the horizontal-axis configuration, a vertical-axis configuration (not shown). Wind turbine  10  may be coupled to an electrical load (not shown), such as, but not limited to, a power grid (not shown) for receiving electrical power therefrom to drive operation of wind turbine  10  and/or its associated components and/or for supplying electrical power generated by wind turbine  10  thereto. Although only one wind turbine  10  is shown in  FIG. 1 , in some embodiments a plurality of wind turbines  10  may be grouped together, sometimes referred to as a “wind farm.” 
         [0017]    Wind turbine  10  includes a body  16 , sometimes referred to as a “nacelle,” and a rotor (generally designated by  18 ) coupled to body  16  for rotation with respect to body  16  about an axis of rotation  20 . In the exemplary embodiment, nacelle  16  is mounted on a tower  14 . The height of tower  14  may be any suitable height enabling wind turbine  10  to function as described herein. Rotor  18  includes a hub  22  and a plurality of blades  24  (sometimes referred to as “airfoils”) extending radially outward from hub  22  for converting wind energy into rotational energy. Each blade  24  has a tip  25  positioned at the end thereof which is distant from the hub  22 . Although rotor  18  is described and illustrated herein as having three blades  24 , rotor  18  may have any number of blades  24 . Blades  24  may each have any length (whether or not described herein). 
         [0018]    Despite how rotor blades  24  are illustrated in  FIG. 1 , rotor  18  may have blades  24  of any shape, and may have blades  24  of any type and/or any configuration, whether or not such shape, type, and/or configuration is described and/or illustrated herein. Another example of a type, shape, and/or configuration of rotor blades  24  is a darrieus wind turbine, sometimes referred to as an “eggbeater” turbine. Yet another example of a type, shape, and/or configuration of rotor blades  24  is a savonious wind turbine. Even another example of another type, shape, and/or configuration of rotor blades  24  is a traditional windmill for pumping water, such as, but not limited to, four-bladed rotors having wooden shutters and/or fabric sails. Moreover, wind turbine  10  may, in some embodiments, be a wind turbine wherein rotor  18  generally faces upwind to harness wind energy, and/or may be a wind turbine wherein rotor  18  generally faces downwind to harness energy. Of course, in any embodiments, rotor  18  may not face exactly upwind and/or downwind, but may face generally at any angle (which may be variable) with respect to a direction of the wind to harness energy therefrom. 
         [0019]    Tower  14  can include an upper tower section  30  and a lower tower section  40  secured by flanges welded together. As shown, lower tower section  40  can support upper tower section  30 . Upper tower section  30  and/or lower tower section  40  can be arcuate, cylindrical or some portion thereof. In one embodiment, upper tower section  30 , lower tower section  40 , and other portions form tower  14  having a conical or frusto-conical geometry. In other embodiments, tower  14  may have other suitable geometries. 
         [0020]      FIG. 2  illustrates a part of a flanged joint between upper tower section  30  and lower tower section  40 . The flanged joint can be in turbine  10  between upper tower section  30  and lower tower section  40 . 
         [0021]    A lower region  37  of upper tower section  30  includes a flange  32 . Flange  32  includes a first arm  36  and second arm  38 , wherein first arm  36  and second arm  38  extend in a generally perpendicular arrangement. First arm  36  extends generally vertically along upper tower section  30 , and second arm  38  extends generally horizontally into the interior of tower  14  (see  FIG. 1 ). As used herein, the term “L-flange” refers to a flange having the generally perpendicular arrangement of two arms. Between first arm  36  and second arm  38  is region  37  and a relief region  39 . Region  37  includes material consistent with first arm  36  and second arm  38 . Region  37  connects first arm  36  and second arm  38 . Region  37 , first arm  36 , and second arm  38  may be formed as a unitary article. In one embodiment, region  37  may be part of upper tower section  30  of tower  14  (see  FIG. 1 ). Relief region  39  may be a relief region extending between an lower portion of first arm  36  and an lower portion of second arm  38 . The unitary article may be formed having relief region  39  or relief region  39  may be formed subsequent to the forming of the unitary article. For example, relief region  39  may be formed by machining. 
         [0022]    An upper region  47  of lower tower section  40  includes a flange  42 . Flange  42  includes a first arm  46  and second arm  48 , wherein the first arm  46  and second arm  48  extend in a generally perpendicular arrangement. First arm  46  extends generally vertically along tower section  40 , and second arm  48  extends generally horizontally into the interior of tower  14 . Between first arm  46  and second arm  48  is region  47  and a relief region  49 . Region  47  includes material consistent with first arm  46  and second arm  48 . Region  47  connects first arm  46  and second arm  48 . Region  47 , first arm  46 , and second arm  48  may be formed as a unitary article. Relief region  49  may be a relief region extending between an lower portion of first arm  46  and a lower portion of second arm  48 . The unitary article may be formed having relief region  49  or relief region  49  may be formed subsequent to the forming of the unitary article. 
         [0023]    First and second flange  32 ,  42  meet along arms  38 ,  48  extending horizontally into the interior of tower  14 . Each flange  32 ,  42  includes at least one opening  50  (the section portion of  FIG. 2  shows only one opening  50 ). For example, one arrangement of openings  50  includes openings spaced apart by the substantially same distance in the respective flanges. First flange  32  and second flange  42  are fastened to each other by fasteners  52  (for example a bolt sized to fit within opening  50  as shown in  FIG. 3 ). The fasteners and/or weld  44  can secure first flange  32  to second flange  42 . 
         [0024]      FIG. 3  shows an exemplary fastener for securing flange  32  and flange  42  together. Fastener  52  is a bolt having an elongated generally cylindrical portion  54  configured to extend through opening  50  of both flange  32  and flange  42  as well as a bolt head  56  on one end and a nut  58  on the other end. Generally cylindrical portion  54  and/or other suitable portions of fastener  52  may include threading for tightening nut  58  thereby further securing flange  32  and flange  42 . Additionally or alternatively, opening  50  may also include threading. Fasteners  52  may be positioned within tower  14  or, in an alternate embodiment, outside of tower  14  if flange arms  38 ,  48  extend outward from tower  14 . 
         [0025]    Relief regions  39 ,  49  of flanges  32 ,  42  can reduce or eliminate a desire for including excess material, thus avoiding excess material machining and providing cost savings without adversely affecting the stress resistance. Relief regions  39 ,  49  may result in fillet  60  being positioned below the surface instead of being positioned on a surface  62  of flange  64  as is shown in  FIG. 5 . In one embodiment, relief regions  39 ,  49  may permit use of the same fillet  60  as may be used in flange  64 . Depending on the geometry of flanges not including relief regions  39 ,  49 , the geometry of relief regions  39 ,  49  can be adapted accordingly to decrease material use and maintain or improving stress distribution while permitting use of similar fillets  60 . Additionally or alternatively, relief regions  39 ,  49  may have larger or smaller dimensions than those shown so long as in including relief regions  39 ,  49 , the stress distribution in flanges  32 ,  42  and/or fastener(s)  52  remains the same or improves in comparison to flange  64 . 
         [0026]    In an exemplary embodiment, flanges  32 ,  42  may include relief regions  39 ,  49  of a predetermined size and/or in a predetermined position. The predetermined size may be based upon the size of the flange. For example, flanges  32 ,  42  may have a predetermined height  100 . In relation to predetermined height  100 , a predetermined amount of material may be present between relief region  39  and relief region  49 . For example, between relief region  39  and relief region  49  may be a predetermined distance  102  (with ½ of predetermined distance  102  being the distance between an end of the flange and the relief region). Predetermined distance  102  may be greater than about 70% of predetermined height  100 . A predetermined amount of material may be present between each relief region  39 ,  49  and hole  50  of fastener  52 . For example, a predetermined distance  104  may be between relief region  39 ,  49  and hole  50  and/or nut  58  of fastener  52 . Predetermined distance  104  may be greater than about 10% of predetermined height  100 . A predetermined amount of space may be present in relief region  39 ,  49 . For example, relief region  39 ,  49  may have a predetermined width  106 . Predetermined width  106  may be greater than about 10% of predetermined height  100 . In one embodiment, a depth  108  of relief regions  39 ,  49  in flanges  32 ,  42  may be about 36% of predetermined height  100  and/or a radial length of fillet  60  may be about 16% of predetermined height  100 . 
         [0027]    The predetermined size and/or predetermined position of flanges  32 ,  42  may result in equivalent or improved stress resistance, as determined through extracting equivalent stress results from a simulation on a finite element computer program. Elastic measurements of the exemplary embodiment may be improved in comparison to flange  64  not having relief regions  39 ,  49 . Elastic measurements of an exemplary embodiment of first arm  36 ,  46  may be improved by at least 9%. Elastic measurements of an exemplary embodiment of second arm  38 ,  48  may be improved by at least 3%. Elastic measurements of an exemplary embodiment of fastener  52  may be improved by at least 1%. 
         [0028]    While the disclosure has been described with reference to a preferred embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the disclosure. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the disclosure without departing from the essential scope thereof. Therefore, it is intended that the disclosure not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this disclosure, but that the disclosure will include all embodiments falling within the scope of the appended claims.