Hammer-on t flange for offshore wind turbines

Abstract

A tower assembly includes a tower and a pedestal. The assembly includes a T-flange for the pedestal including a first surface, a central impact zone for driving the pedestal into the ground; and a first plurality of bolt holes. The assembly also includes a T-flange for the tower including a second surface that comes in contact with the first surface, a recess for receiving the impact zone that leaves a gap above the impact zone, and a second plurality of bolt holes that align with the first plurality of bolt holes. Bolts can be used to secure the T-flange for the pedestal to the T-flange for the tower to secure the tower and the pedestal together.

Description

[0001] SP3164

[0002] 1

[0003] HAMMER-ON T FLANGE FOR OFFSHORE WIND TURBINES

[0004] Field of the Invention

[0005] The present application relates generally to tower installation, and more particularly to a T- flange design for a monopile having a central impact zone for installation . Background of the Invention

[0006] Today, more than 65 , 000 wind turbines across the country generate clean, reliable power . Wind power capacity today exceeds 125 Giga Watts , making it the third-largest source of electricity generation capacity in the country . Wind energy ( or wind power ) refers to the process of creating electricity using the wind or air flows that occur naturally in the earth' s atmosphere . Wind turbines capture kinetic energy from the wind and use it to generate electricity . Wind turbines are comprised of rotating blades that are driven by the wind . The rotating blades then turn a shaft connected to a gearbox that converts the blade rotor' s low speed, high- torque power into high-speed, low-torque power that is trans ferred to a generator to generate DC power . The DC power is then converted to AC electricity by power converters and trans ferred to cables that transmit the power to homes , businesses and other end-users through the power grid .

[0007] High amounts of force are exerted on the base of the wind turbine and its mount due to the wind force at the top of the turbine . Thus , the wind turbine must be anchored or mounted to a stable surface . Wind turbines must be mounted to a strong foundation, the underlying structure that trans fers the loads to the earth . Larger wind turbines call for taller towers and larger foundations that consume enormous amounts of concrete and rebar. Wind turbine towers can exceed 260 feet in height and the blades can exceed 150 feet in length. As the wind blows across the blades and tower, a tipping force is exerted against the base of the tower. The foundation must resist this force and be stiff enough to keep the tower from rocking or tilting. In off-shore installations, a pedestal or monopile is used to transfer the loads to the earth.

[0008] Larger wind towers capture more kinetic energy and thus produce more electricity. The longer the turbine blades the more energy a turbine can capture. Generally, doubling the rotor diameter produces a four-fold increase in energy output. Furthermore, the taller the tower is, the more energy it can capture because wind speeds increase with elevation. Therefore, the larger the wind tower, the more efficient it is at producing electricity. However, there are limitations to the size a wind tower can be and still be easily deployed.

[0009] A standard T-flange can be used to mate a T-flange of a tower with a T-flange of a pedestal. The pedestal is typically installed by a pile hammer that drives the pedestal or monopile into the earth. A regular T-flange is very strong and provides a robust connection but is not well suited for piling. Hammering across the enter diameter of the T-flange causes eccentric loading. Vibrations or "flange wobble" introduced into the flange during piling are problematic as this wobble greatly reduces the fatigue life or structural integrity of the weld below the flange. As such, the T-flange can get damaged, the weld can get damaged or that the piling operation is not successful due to excessive vibrations.

[0010] There are also practical limitations on the diameter and grade of steel that connect the tower to the pedestal. Larger turbines are beginning to push the limit on the practical limits of steel strength . L- flanges are commonly used but are limited by strength . Thus , as wind turbines become larger and larger, improvements to methods and apparatuses of mounting the wind tower to its foundation are desirable .

[0011] Summary of the Invention

[0012] In a first aspect of the present invention, a T- flange for a monopile is disclosed . The T- flange includes a first surface that comes in contact with a T- flange of a tower ; a central impact zone for driving the monopile into the ground; and bolt holes for securing the T- flange of the tower and the T- flange of the monopile together .

[0013] In a second aspect of the present invention, a tower assembly includes a tower and a pedestal . The assembly includes a T- flange for the pedestal including a first surface , a central impact zone for driving the pedestal into the ground; and a first plurality of bolt holes . The assembly also includes a T- flange for the tower including a second surface that comes in contact with the first surface , a recess for receiving the impact zone that leaves a gap above the impact zone , and a second plurality of bolt holes that align with the first plurality of bolt holes . Bolts can be used to secure the T- flange for the pedestal to the T- flange for the tower to secure the tower and the pedestal together .

[0014] In a third aspect of the present invention, a method of installing a monopile having an impact zone and a first surface on a T- flange of the monopile , the first surface designed to come in contact with and support a T- flange of a tower, is disclosed . The method includes applying a force to the impact zone and determining i f the monopile is suf ficiently driven, and i f not , applying the force to the impact zone repeatedly until the monopile is suf ficiently driven; and i f the monopile is suf ficiently driven, stop applying the force to the impact zone . The monopile can be driven into the ground by hammering on the impact zone without coming in contact with the first surface .

[0015] The foregoing has outlined rather broadly the features and technical advantages of the present invention in order that the detailed description of the invention that follows may be better understood . Additional features and advantages of the invention will be described hereinafter that form the subj ect of the claims of the invention . It should be appreciated by those skilled in the art that the conception and speci fic embodiment disclosed may be readily utili zed as a basis for modi fying or designing other structures for carrying out the same purposes of the present invention . It should also be reali zed by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims . The novel features that are believed to be characteristic of the invention, both as to its organi zation and method of operation, together with further obj ects and advantages will be better understood from the following description when considered in connection with the accompanying figures . It is to be expressly understood, however, that each of the figures is provided for the purpose of illustration and description only and is not intended as a definition of the limits of the present invention .

[0016] Brief Description of the Figures

[0017] For a more complete understanding of the disclosed system and methods , reference is now made to the following descriptions taken in conj unction with the accompanying drawings .

[0018] Figure 1 is a schematic drawing of a wind tower, according to one example embodiment of the present invention;

[0019] Figure 2 is a cross-sectional drawing of the wind tower of Figure 1 anchored to a pedestal by a standard T- flange , according to one example embodiment of the present invention;

[0020] Figure 3 is a cross-sectional view of a pedestal having an impact zone , according to one example embodiment of the present invention;

[0021] Figure 4 is a cross-sectional view of a tower anchored to a pedestal having an impact zone , according to one example embodiment of the present invention; and

[0022] Figure 5 is a flow diagram of a method of driving a monopile using an impact hump, according to one example embodiment of the present invention . Detailed Description of the Invention

[0023] In general , the present disclosure relates generally to tower installation, and more particularly to a flange design for a monopile having an impact zone for installation . The T- flange of the monopile is designed such that a region is defined that is dedicated as the impact zone for a piling hammer, i . e . , piling in order to install of fshore monopile foundations . A standard T- flange does not consist of a dedicated impact zone , but instead, the entire surface acts as the contact zones with the piling hammer causing problems in the monopile . The T- flange can be damaged and / or the weld below the T- flange can be damaged . There is also a risk of installation complexities when the T- flange is not speci fically designed to interface with a piling hammer . A central hump, such as an elevated or raised region on the T- flange , allows for energy or forces introduced into the hump or contact zone of the flange by the piling hammer to travel directly downwards into the steel shell of the monopile , thereby minimi zing vibrations due to eccentric loading . The hump is centered in the monopile and allows for a more concentrated trans fer of energy from the piling hammer directly with the primary load path into the shell of the monopile . Vibrations or flange wobble introduced into the flange during piling are problematic as this wobble greatly reduces the fatigue li fe , or structural integrity, of the weld below the flange ( that connects the T- flange with the steel tubular shell ) . A recess is also introduced into the top part or tower part of the T- flange connection, such that the hump and recess fit together without making contact once the T- flanges are assembled .

[0024] Referring to Figure 1 , a schematic of a wind tower 100 is shown . The wind tower includes rotating blades 102 connected to a generator 104 mounted to a tower 106 . The combination of the blades 102 and the generator 104 is also referred to as a wind turbine . The tower is anchored to a foundation (not shown) . As the wind 110 blows , it exerts a tipping force against the tower and rotates the blades 102 . A force 112 , including a tipping force from the wind 110 and the weight of the wind tower 100 are exerted against the foundation . The earth must resist this force 112 with a soil resistance force 114 such that the tower 100 can stand and not rock in the wind . Thus , the foundation and the mounting of the tower 106 to the foundation must be engineered to resist the force 112 and trans fer the loads to the earth . Referring to Figure 2 , a cross-sectional view of a typical T-flange mounting 200 of a tower 202 to a concrete pedestal 204 is shown . The wind tower 202 has a base or flange 206. The flange 206 sits on top of a flange 208 of the concrete pedestal or foundation 204 . Bolts 210 are placed to align with through-holes in the flange 206 of the tower 202 and through-holes in the flange 208 of the pedestal 204 . The tower 202 is placed on the pedestal 204 such that the bolts 210 extend through the through-holes . Nuts are then screwed onto the bolts 210 and tightened to secure the tower 202 to the pedestal 204 during installation .

[0025] Referring to Figure 3 , an installation 300 of a pedestal or monopile 302 is illustrated . The pedestal 302 includes a T- flange 304 . The T- flange 304 is typically welded to a hollow shell , or a steel tubular shell structure , 305 via a weld 307 . The T- flange 304 includes through holes 306 , 308 and an impact zone or hump 310 on the T- flange . During installation, a piling hammer 312 exerts a downward force 314 on the impact zone 310 . The pedestal 302 is driven into the ground by repeated pounding by the piling hammer 312 on the impact zone 310 until the pedestal is properly grounded . The piling hammer 312 only comes in contact with the impact zone 310 and not a first surface 317 of the T- flange 304 . As such, the energy or forces introduced on the pedestal by hammering by the piling hammer 312 travel directly downwards via a load path 316 , thereby minimi zing vibrations due to eccentric loading . This mitigates the introduction of unwanted moments and therefore minimi zes the fatigue damage in the weld 307 due to piling, and allows for a more ef ficient energy trans fer from the hammer into the monopile . Referring to Figure 4 , an installed tower 401 on a pedestal 402 is shown without the bolts . The tower 401 is typically of steel tubular construction, having a diameter of between six and nine meters . The pedestal 402 includes a T- flange 404 having an impact zone 410 , through bolt holes 406 , 408 and a first surface 417 . The tower 401 includes a T- flange 412 that comes in contact with and rests on the first surface 417 of the T- flange 404 of the pedestal 402 . A transition piece could also be used between the two T- flanges . The T- flange 412 of the tower 401 includes a recessed area 414 and a first surface 425 of the T- flange 412 of the tower 401 . The recessed area 414 is designed such that the impact zone 410 fits within the recess area 414 but does not come in contact with the T- flange 412 of the tower 401 . A gap 416 exists between the recessed area 414 of the T- flange 412 of the tower 401 and the impact zone 410 of the T- flange 404 of the pedestal 402 such that the impact zone 410 does not come in contact with the T- flange 412 of the tower 401 . The gap 416 can be approximately 5mm . The gap 416 can be larger or smaller as long as the surfaces in this region do not make contact with each other .

[0026] The T- flange 412 of the tower 401 also includes through bolt holes 418 , 420 that align with the bolt holes 406 , 408 , respectively, of the T- flange 404 of the pedestal 402 such that bolts can be placed through the bolt holes 406 , 418 and 408 , 420 to secure the tower to the pedestal . The bolt forces of the bolts compact the first area 417 of the T- flange 404 of the pedestal 402 with the first surface 425 of the T- flange 412 of the tower 402 around the bolt holes 406 , 408 , 418 , 420 and act as the load path once the wind turbine is operational , trans ferring loads from the tower 401 into the foundation 402. The gap 416 ensures that contact is not made with the impact zone such that full contact exists in the area of the bolt holes where contact is critical.

[0027] The impact zone 410 has a flat surface 420. Preferably, the flat surface 420 is about as wide as the steel shell 402 below it. The impact zone 410, or hump, can transition downwards from the flat surface 420 to the first surface 417 of the T-flange 404. The area of the T-flange around the first surfaces 417, 425 experience the compressive force of the bolts 424 that are under preload. This compressive force is generally in a cone like region, or pressure cone, 426. Preferably, this cone region 426 does not overlap with the impact zone 410. Alternatively, the cone region could overlap the impact zone 410, but this would reduce the structural robustness of the bolted joint.

[0028] Figure 5 is a flow diagram of a method 500 of installing a pedestal, such as the pedestal 302 of Figure 3. The method begins at 502. At 504, a force is applied to an impact zone, such as impact zone 310 of Figure 3, on the pedestal driving the pedestal into the ground. Preferably, the force is applied only to the impact zone and not the remainder of the T-flange. At 506, it is determined if the pedestal has been driven into the ground to its required depth. If it is determined that the pedestal is not sufficiently driven, flow branches "No" back to 504. The process continues until the pedestal is sufficiently driven into the ground to its required depth, typically in a hammering-type installation. If it is determined that the pedestal is sufficiently driven, flow branches "Yes" to 508 and the method ends . By allowing an impact zone of a T- flange of a pedestal to be hammered upon, the diameters of monopiles can be restricted . This reduces wave loading introduced into the monopile , reduces manufacturing complexity and reduces the amount of steel required, thereby reducing cost .

[0029] Although the present disclosure and its advantages have been described in detail , it should be understood that various changes , substitutions and alterations can be made herein without departing from the spirit and scope of the disclosure as defined by the appended claims . Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process , machine , manufacture , composition of matter, means , methods and steps described in the speci fication . As one of ordinary skill in the art will readily appreciate from the present invention, disclosure , machines , manufacture , compositions of matter, means , methods , or steps , presently existing or later to be developed that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein may be utili zed according to the present disclosure . Accordingly, the appended claims are intended to include within their scope such processes , machines , manufacture , compositions of matter, means , methods , or steps .

Claims

C L A I M S1. A T-flange for a monopile, the T-flange comprising: a first surface that comes in contact with a T-flange of a tower; a central impact zone for driving the monopile into the ground; and bolt holes for securing the T-flange of the tower and the T-flange of the monopile together.

2. The T-flange of claim 1, wherein the central impact zone is in line with the shell that is directly below the T- f lange .

3. The T-flange of claim 2, wherein the T-flange extends radially around the central impact zone.

4. The T-flange of claim 3, wherein the bolt holes are on both sides of the central impact zone.

5. The T-flange of claim 4, wherein the T-flange has a flange geometry symmetrical about the central impact zone and directly in line with a steel shell below the central impact zone such that a load path directly travels from the central impact zone to the steel shell below.

6. The T-flange of claim 1, wherein the central impact zone has a flat surface that is about as wide as the steel shell that is directly below the T-flange.

7. The T-flange of claim 6, wherein the flat surface is raised higher that a first surface of T-flange.

8. The T-flange of claim 1, wherein when bolts are secured in the bolt holes, a compression region is created, and wherein the central impact zone does not overlap with the pressure cone.

9. The T-flange of claim 1, wherein the impact zone is a rounded off or chamfered hump.

10. The T-flange of claim 1, further comprising a weld securing the T-flange to a steel tubular shell structure.

11. The T-flange of claim 3, wherein the central impact zone for driving the monopile into the ground reduces vibrations and more efficiently transfers the forces into the monopile for improved driving.

12. The T-flange of claim 1, further comprising a plurality of bolt holes.

13. A tower assembly including a tower and a pedestal, the assembly comprising: a T-flange for the pedestal including a first surface, a central impact zone for driving the pedestal into the ground; and a first plurality of bolt holes; and a T-flange for the tower including a second surface that comes in contact with the first surface, a recess for receiving the impact zone that leaves a gap above the impact zone, and a second plurality of bolt holes that align with the first plurality of bolt holes; wherein bolts can be used to secure the T-flange for the pedestal to the T-flange for the tower to secure the tower and the pedestal together.

14. The assembly of claim 13, wherein the first plurality of bolt holes surrounds the central impact zone.

15. The assembly of claim 13, wherein the T-flange for the pedestal has a flange geometry symmetrical about the central impact zone and directly in line with a steel shell below the central impact zone such that a load path directly travels from the central impact zone to the steel shell below.

16. The assembly of claim 13, wherein the central impact zone has a flat surface that is about as wide as a diameter of the pedestal.

17. The assembly of claim 13, wherein the central impact zone has a flat surface that is raised higher that the first surface .

18. The assembly of claim 13, wherein when bolts are secured, a pressure cone is created, and wherein the central impact zone does not overlap with the pressure cone.

19. The assembly of claim 13, wherein the central impact zone for driving the pedestal into the ground more efficiently transfers the forces into the pedestal for improved driving.

20. A method of installing a monopile having a central impact zone and a first surface on a T-flange of the monopile, the first surface designed to come in contact with and support a T-flange of a tower, the method comprising: applying a force to the impact zone; and determining if the monopile is sufficiently driven, and if not, applying the force to the impact zone repeatedly until the monopile is sufficiently driven, and if the monopile is sufficiently driven, stop applying the force to the impact zone ; wherein the monopile can be driven into the ground by hammering on the impact zone without coming in contact with the first surface.

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