Patent Publication Number: US-2009223164-A1

Title: Vertical rotating aerodynamic tower

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Patent Application Ser. No. 61/034,914, filed on Mar. 7, 2008, and also claims the benefit of U.S. Provisional Patent Application Ser. No. 61/039,084, filed on Mar. 24, 2008, both of which are incorporated by reference herein in their entirety for all purposes. 
    
    
     TECHNICAL FIELD 
     Embodiments of the present invention relate generally to tower structures, and more specifically to monopole structures with reduced air drag. 
     BACKGROUND 
     Current monopole structures often have an outer surface with a circular or polygonal cross section. Such a cross section often leads to a high drag coefficient, and thus a higher loading force for a given wind velocity. Such a high drag coefficient often requires stronger and heavier materials and/or foundations to withstand wind loading. 
     SUMMARY 
     Monopoles according to embodiments of the present invention include a base structure, and an aerodynamic shell structure mounted to a shaft. According to some embodiments of the present invention, the aerodynamic shell structure houses one or more antennae. According to other embodiments of the present invention, the aerodynamic shell structure rotates about a shaft according to the direction of the wind, such that the leading edge of the aerodynamic shell structure orients itself against the prevailing wind, the shaft being rigidly coupled to the base structure. The aerodynamic shell structure may include a ladder and/or be constructed with dimensions sufficient to permit a person to ascend the inside of the aerodynamic shell structure. 
     While multiple embodiments are disclosed, still other embodiments of the present invention will become apparent to those skilled in the art from the following detailed description, which shows and describes illustrative embodiments of the invention. Accordingly, the drawings and detailed description are to be regarded as illustrative in nature and not restrictive. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates a front perspective view of an aerodynamic monopole according to embodiments of the present invention. 
         FIG. 2  illustrates a front perspective view of the aerodynamic monopole of  FIG. 1  with a transparent outer shell, according to embodiments of the present invention. 
         FIG. 3  illustrates a side cross sectional elevation view of the aerodynamic monopole of  FIGS. 1 &amp; 2 , according to embodiments of the present invention. 
         FIG. 4  illustrates a top view of the aerodynamic monopole of  FIGS. 1-3 , according to embodiments of the present invention. 
         FIG. 5  illustrates a side elevation view of an aerodynamic monopole, according to embodiments of the present invention. 
         FIG. 6  illustrates an enlarged partial sectional view of the aerodynamic monopole of  FIG. 5 , according to embodiments of the present invention. 
         FIG. 7  illustrates an outer perimeter of an aerodynamic monopole, according to embodiments of the present invention. 
         FIG. 8  illustrates a cross-sectional view of an aerodynamic monopole with an enlarged partial cross-sectional view, according to embodiments of the present invention. 
         FIG. 9  illustrates another cross-sectional view of an aerodynamic monopole, according to embodiments of the present invention. 
     
    
    
     While the invention is amenable to various modifications and alternative forms, specific embodiments have been shown by way of example in the drawings and are described in detail below. The intention, however, is not to limit the invention to the particular embodiments described. On the contrary, the invention is intended to cover all modifications, equivalents, and alternatives falling within the scope of the invention as defined by the appended claims. 
     DETAILED DESCRIPTION 
       FIG. 1  illustrates a front perspective view of an aerodynamic monopole  100  according to embodiments of the present invention. Aerodynamic monopole  100  includes an aerodynamic shell structure  102 , a shaft  104 , and a base structure  106 , according to embodiments of the present invention. The aerodynamic shell structure  102  includes a vertical axis that is substantially aligned with the force of gravity, represented by arrow  300 . The shaft  104  also includes a central axis, which is substantially aligned with the vertical axis of the shell structure  102  and about which the shell structure rotates with respect to the shaft  104  and the base structure  106 . The base structure  106  is mounted on horizontal support beams  110  and/or caisson footing  112  on or within the ground  108  or other underlying surface, according to embodiments of the present invention. The aerodynamic monopole may also be connected directly to a large caisson, a spread-footing, or any other foundation design to resist overturning moments. According to some embodiments of the present invention, the aerodynamic monopole  100  extends to one hundred feet above ground level; according to other embodiments of the present invention, the aerodynamic monopole  100  extends to two hundred or more feet above ground level. 
       FIG. 2  illustrates a front perspective view of the aerodynamic monopole  100  with a transparent outer shell, revealing antennae  202  and inner shaft  104 , according to embodiments of the present invention.  FIG. 3  illustrates a side cross sectional elevation view of the aerodynamic monopole  100 , according to embodiments of the present invention. Antennae  202  may be mounted within the aerodynamic shell structure  102 , according to embodiments of the present invention. As such, mounting additional antennae  202  inside of the aerodynamic shell structure  102  does not increase the drag coefficient or the corresponding wind loading of the monopole  100 . An aerodynamic shell structure  102  with a substantially hollow interior permits a wide variety of AM pipe or tower antenna masts, FM, UHF, and/or cellular antennae, electronics, and/or other equipment to be mounted within the aerodynamic shell structure  102  while preserving a simple and aesthetically pleasing appearance for the aerodynamic monopole  100 . Using an aerodynamically-shaped structure  102  with a long chord length also increases banner or advertising space on an aerodynamic monopole  100  without adding additional wind drag, according to embodiments of the present invention. The base structure  106  may also include ports  204  to add additional shelter space. 
     According to some embodiments of the present invention, the aerodynamic shell structure  102  rotates about a shaft  104  according to the direction of the wind, such that the leading edge  304  of the aerodynamic shell structure (as seen in  FIGS. 4 and 7 ) orients itself against the prevailing wind, the shaft  104  being rigidly coupled to the base structure  106 . According to other embodiments of the present invention, the aerodynamic shell structure  102  is rigidly coupled with the shaft  104 , and the shaft  104  rotates within the base structure  106  to permit the leading edge  304  of the aerodynamic shell structure  102  to orient itself into the prevailing wind. According to yet other embodiments, the aerodynamic shell structure  102  rotates about the shaft  104  and the shaft  104  also rotates with respect to the base  106 . The aerodynamic shell structure  102  may include a ladder  404  and/or be constructed with dimensions sufficient to permit a person to ascend the inside of the aerodynamic shell structure  102 . 
     According to some embodiments of the present invention, the shaft  104  is substantially or partially hollow, and a coaxial or other cable or wire  302  may be inserted from the base, through the shaft  104  and extend up to the antennae  202  nearer the top of the monopole  100 , as illustrated in  FIG. 3 . According to some embodiments of the present invention, the aerodynamic shell structure  102  orients itself according to the prevailing wind by rotating to the position of least wind drag (e.g. the position with the leading edge  304  oriented toward the prevailing wind) similar to a weather vane. According to other embodiments of the present invention, a motor or other mechanical assembly is used to rotate the aerodynamic shell structure  102  and/or the shaft  104 . The motor or other mechanical assembly may be used to rotate the aerodynamic shell structure  102  and/or the shaft  104  to a position in which the leading edge  304  is oriented toward the prevailing wind based on a wind direction sensor, according to embodiments of the present invention. An advertisement or other visual information or display may be formed on the side and/or top of the aerodynamic shell structure  102 , according to embodiments of the present invention. In such cases, the motor or other mechanical assembly may be used to rotate the aerodynamic shell structure  102  according to a pre-programmed and/or random display or advertising orientation, according to embodiments of the present invention. 
       FIG. 5  illustrates a side elevation view of an aerodynamic monopole  100 , according to embodiments of the present invention. The aerodynamic monopole  100  may include a top cap  504  for additional drag reduction, according to embodiments of the present invention. According to some embodiments of the present invention, the aerodynamic shell structure  502  is coupled to a shaft  508  by a bearing assembly  506 , and rotates on the bearing assembly  506 . 
       FIG. 6  illustrates an enlarged partial cross sectional view of the aerodynamic shell monopole  100  of  FIG. 5 , according to embodiments of the present invention. A bearing assembly  604  may be coupled to the bottom  602  of the aerodynamic shell structure  502 , according to embodiments of the present invention. Bearing assembly  604  may be bolted to bottom  602  via bolts  608 , according to embodiments of the present invention. Bearing assembly  604  may also be coupled to a fixed base connection  606 , according to embodiments of the present invention. Rotational bearing assembly  604  bears the horizontal and axial loads of the aerodynamic shell structure  502  and permits the aerodynamic shell structure  502  to rotate about an axial centerline  610  of the bearing assembly  604 , according to embodiments of the present invention. The aerodynamic shell structure  502  and bearing assembly  604  rotate with respect to the axial centerline  610 , according to embodiments of the present invention. Bearing  604  may be a turntable-type bearing, similar to the bearings used in construction cranes or in the rotors of large wind turbines. A Kaydon 390 Series turntable bearing assembly by Kaydon Bearings may be used as bearing  604 , according to embodiments of the present invention. 
       FIG. 7  illustrates a geometrical configuration for an outer perimeter  704  of an outer surface of an aerodynamic shell structure  102 ,  502  according to embodiments of the present invention. The aerodynamic shell structure rotates about vertical axis  708 , according to embodiments of the present invention. The geometrical configuration for the outer perimeter  704  includes a leading edge  304  and a trailing edge  702 , according to embodiments of the present invention. Chord  706  is a straight line connecting the leading edge  304  with the trailing edge  702 . According to some embodiments of the present invention, the outer perimeter  704  is an airfoil shape. According to embodiments of the present invention, the aerodynamic shape of the outer perimeter  704  permits air to flow over the shell  102  with less drag; for example, the aerodynamic shape of the outer perimeter  704  permits wind to flow over the monopole shell  102  in an attached flow at normal, or all, wind speeds, instead of in a flow pattern that results in unattached flow or swirling, for example. The location of the vertical axis  708  along the chord  706  may depend upon the final shape of the aerodynamic shell structure  704 , and may be used to improve yaw of the shell. If the vertical axis  708  is closer toward the leading edge  304  from the aerodynamic center (along the chord  706 ), the aerodynamic shell will be more responsive with the leading edge  304  staying into the wind. If the vertical axis  708  is placed along the chord  706  behind the aerodynamic center, the aerodynamic structure  704  will be less responsive, reducing yaw. 
     According to some embodiments of the present invention, the chord  706  length L is longer than the width W of the outer perimeter  704 , where the width W is the maximum dimension of the outer perimeter  704  measured in a direction that is orthogonal to the chord  706  and the vertical axis represented by circles  708  (where the vertical axis  708  extends in a direction orthogonal to the plane of the view of  FIG. 7 ). As illustrated in  FIG. 7 , the distance along the outer perimeter  704  between the leading edge  304  and the trailing edge  702  is larger than the chord  706  length, according to embodiments of the present invention.  FIG. 7  also illustrates an outer perimeter  704  having a continuous curvature along the outer perimeter  704  from the leading edge  304  to the trailing edge  702 . The entire outer perimeter  704  includes a continuous curvature except for a single discontinuous edge at the trailing edge  702 , according to embodiments of the present invention. 
     According to some embodiments of the present invention, the shape of the outer perimeter  704  is determined by the following equation: 
     
       
         
           
             
               
                 
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                           0.35160 
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                           0.2843 
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     where x is the position along the chord  706  from leading edge  304  to trailing edge  702 , and y is the distance from the chord  706  to the outer perimeter  704  for a given value of x. Although  FIG. 7  illustrates an outer perimeter  704  that has bilateral symmetry about the chord  706 , other aerodynamic shapes may be used, including aerodynamic shapes that are not bilaterally symmetrical. However, bilateral symmetry may help ensure that the aerodynamic shell  102  reduces wind drag and lift, and orients itself into the prevailing wind. Based on the disclosure provided herein, one of ordinary skill in the art will recognize that numerous other geometries for the aerodynamic shell structure  102  are effective for reducing wind drag when compared to a circular and/or polygonal cross section, according to embodiments of the present invention. 
     According to some embodiments of the present invention, more than one aerodynamic shell structure  102  may be mounted on a shaft  104 . Each such aerodynamic shell structure  102  may rotate independently of the other aerodynamic shell structures  102 , according to embodiments of the present invention. Such a characteristic may permit optimized wind drag reduction along the height of a monopole  100  which experiences winds in different directions along its height, according to embodiments of the present invention. Each of multiple aerodynamic shell structures  102  may have separate bearings below each aerodynamic shell structure  102 , similar to the bearing arrangement shown in  FIG. 6 , according to embodiments of the present invention. Alternatively, each of multiple aerodynamic shell structures  102  may be configured to rotate in a synchronized manner, according to embodiments of the present invention. The aerodynamic shell structures  102  may be constructed in modular format, permitting easy addition and/or subtraction and/or substitution of discrete aerodynamic shell structures  102  from a new or existing monopole  100 , according to embodiments of the present invention. 
     According to some embodiments of the present invention, the aerodynamic shell  102  rotates about a shaft  104  that is rigidly fixed to a base structure  106 , as illustrated in  FIGS. 1-4 . According to other embodiments of the present invention, the aerodynamic shell  502  is a self-supporting structure without a supporting shaft, and the bearing assembly  604  coupled to the shell  502  and the shaft  508  bears not only the vertical forces of the shell  502  (e.g. the weight force of the shell), but also the lateral forces (e.g. the wind load) and resulting moments, as illustrated in  FIGS. 5 and 6 . In some cases, a shaft may be used in combination with a shell  502  similar to that illustrated in  FIGS. 5 and 6 , as an additional support and/or as a backup support for the monopole shell  502 . 
     According to some embodiments of the present invention, the aerodynamic shell structure  102  has the properties of being the main structural member, transparent to radio-frequency radiation, with the internal monopole  104  acting as the amplitude modulation (AM) device, with an insulator encased in the aerodynamic shell structure  102 , according to embodiments of the present invention. According to other embodiments of the present invention, antennae  202  are mounted within the aerodynamic shell structure  102 . According to some embodiments of the present invention, a cross-sectional aerodynamic shell outer surface  704  remains constant in shape and dimension from the base  106  up to the top of the monopole  100 . According to other embodiments of the present invention, the cross-sectional aerodynamic shell outer surface  704  changes in shape and/or decreases in dimensional scale from the base  106  up to the top of the aerodynamic monopole  100 . According to some embodiments of the present invention, the aerodynamic-shaped outer surface  704  has a coefficient of drag of less than 0.1, such as, for example, a coefficient of drag of approximately 0.05, as compared with the coefficient of drag of a perfectly circular cross section of 1.05, or the coefficient of drag of an octagonal cross section of up to 1.2. According to some embodiments of the present invention, a rotating shell  102  may be suitable for AM antenna applications, while a fixed shell  102  that does not rotate may be used for directional antenna applications such as cellular. The aerodynamic shell  102 ,  502  or sections thereof may be made of RF transparent materials, such that omnidirectional radiating elements can be encapsulated in such shells  102 ,  502  or may be a part of such structures, which may be well suited for top elements or for pylon applications using omnidirectional or collinear antennae, according to embodiments of the present invention. 
       FIG. 8  illustrates a cross-sectional view of an aerodynamic monopole shell  802  with an enlarged partial cross-sectional view  804 , according to embodiments of the present invention. The aerodynamic shell includes an inner layer  806  of fiberglass, an outer layer  808  of fiberglass, with an intermediate or core layer  810  of foam, according to embodiments of the present invention. The fiberglass layers  806 ,  808  may include a fiberglass with a biaxial weave, for example a biaxial weave at a forty-five degree angle for better stress transfer. The monopole shell  802  may include more or less layers, and/or may include one or more layers made of different materials, with or without a foam core, according to embodiments of the present invention. 
       FIG. 9  illustrates a cross-sectional view of a section of an aerodynamic monopole shell  902  having a shaft  104  interface assembly. The monopole shell  902  is configured to rotate about vertical axis  914 . The shaft  104  interface assembly includes front  912  and rear  910  shaft interface plates (which may also be a single shaft sleeve), as well as rear support braces  904 ,  906  coupling the shaft  104  interface assembly with the inside perimeter of the shell  902  and a front support brace  908  coupling the shaft  104  interface assembly with the inside perimeter of the shell  902  near the leading edge, according to embodiments of the present invention. More or less support braces may be used, and more or less or different support brace  904 ,  906 ,  908  placements and/or configurations may be used, according to embodiments of the present invention. According to some embodiments of the present invention, the shaft  104  interface assembly and support braces may be used in the monopole  100  embodiments illustrated in  FIGS. 1-4 . The support braces and/or shaft  104  interface structure of  FIG. 9  may be used along the entire length of the monopole shell  902  and/or may be used at discrete heights or portions along the vertical axis of the monopole shell  902 , such as, for example, every ten to twenty feet, according to embodiments of the present invention. 
     Various modifications and additions can be made to the exemplary embodiments discussed without departing from the scope of the present invention. For example, while the embodiments described above refer to particular features, the scope of this invention also includes embodiments having different combinations of features and embodiments that do not include all of the described features. Accordingly, the scope of the present invention is intended to embrace all such alternatives, modifications, and variations as fall within the scope of the claims, together with all equivalents thereof.