Login| Sign Up| Help| Contact|

Patent Searching and Data


Title:
WIND ENERGY CONVERTER COMPONENTS MADE OF ULTRA HIGH PERFORMANCE CONCRETE
Document Type and Number:
WIPO Patent Application WO/2013/108079
Kind Code:
A1
Abstract:
A cast ultra high performance concrete wind energy converter mainframe (50) is configured to be used under multi-directional dynamic loading conditions. The mainframe (50) is a hollow, multi-walled structure and includes reinforcing members (90) extending linearly within the walls. The reinforcing members (90) are bonded to the concrete of the article and apply a compressive stress to the article via the bond. The reinforcing members (90) are arranged within the walls so that the compressive stress is incorporated along multiple nonparallel planes (P1,P2,P3) within the article. Other structural components (90) of the wind energy converter, such as the hub (16'), can be similarly formed.

More Like This:
Inventors:
KRAUSE MARKUS RUDOLF (AT)
Application Number:
PCT/IB2012/050251
Publication Date:
July 25, 2013
Filing Date:
January 18, 2012
Export Citation:
Click for automatic bibliography generation   Help
Assignee:
APAMSC AUSTRIA GMBH (AT)
KRAUSE MARKUS RUDOLF (AT)
International Classes:
B28B7/16; B28B7/22; B28B23/04; B28B23/12; F03D11/04
Foreign References:
US2255022A1941-09-02
GB602153A1948-05-20
US20090232659A12009-09-17
US20070125017A12007-06-07
US2561581A1951-07-24
Other References:
None
Download PDF:
Claims:
What is claimed is,

1. Method of manufacturing a pre-stressed concrete article for use in a multi-directional dynamic loading application, the method comprising: providing a form comprising

a first outer wall

a first inner wall parallel to and spaced apart from the first outer wall such that an intermediate space is defined between the first inner wall and the first outer wall, providing

a first elongated reinforcing member disposed in the intermediate space extending in a first direction that is parallel to a first plane,

a second elongated reinforcing member disposed in the intermediate space extending in a second direction that is angled relative to the first direction and parallel to the first plane,

a third elongated reinforcing member disposed in the intermediate space extending in a third direction that is angled relative to the first direction and the second direction, and parallel to a second plane that is angled relative to the first plane; applying a tensile force to each of the reinforcing members; introducing fresh concrete into the intermediate space so as to at least partially embed each of the reinforcing members while under the applied tensile force; curing the fresh concrete within the intermediate space with the at least partially embedded reinforcing members under the applied tensile force ; releasing the tensile force applied to each of the reinforcing members so as to introduce a pre-stress into the cured concrete, and removing the cured-concrete article from the form.

2. The method of claim 1, wherein the article is removed from the form after the releasing step.

3. The method of claim 1, wherein the first plane is parallel to the first outer wall.

4. The method of claim 1, wherein the form further comprises

a second outer wall that adjoins, and is non-parallel to, the first outer wall, and a second inner wall parallel to and spaced apart from the second outer wall, the second inner wall adjoining the first inner wall, the vacancy between the second inner wall and second outer wall defining a second intermediate space, the second intermediate space communicating with the intermediate space between the first inner wall and the first outer wall, and

wherein the third reinforcing member extends within the second intermediate space.

5. The method of claim 1, wherein the third direction is transverse to both the first direction and the second direction.

6. The method of claim 1 , wherein the providing step further includes providing a fourth reinforcing member disposed within the second intermediate space extending in a fourth direction that is angled relative to the first, second and third directions.

7. The method of claim 1, wherein the fourth direction extends in parallel to the second plane.

8. The method of claim 1 , wherein the reinforcing members are linear and pass through corresponding openings provided in the form.

9. The method of claim 1 , wherein the concrete is an ultra high performance concrete having a compressive strength of at least 100 N/mm 2.

10. The method of claim 1, wherein the concrete is an ultra high performance concrete having a Young's Modulus of at least 45,000 N/mm2.

11. The method of claim 1 , wherein the amount of the applied tensile force is greater in at least one region of the form than in other regions of the form.

12. The method of claim 1, wherein the method further comprises providing a nonuniform density of reinforcing members such that higher numbers of reinforcing members are provided in regions of expected higher stress.

13. The method of claim 1 , wherein the forms are configured to provide the article with a monolithic hollow shape.

14. The method of claim 1 , wherein the forms are configured to provide the article with a monolithic hollow shape having openings formed in at least one side.

15. The method of claim 1, wherein the article comprises multiple walls, with at least one wall being spaced from another wall with a vacancy formed between the one wall and the another wall, and the article is formed as a monolithic structure in a single casting.

16. The method of claim 1, wherein the first reinforcing member comprises a first set of reinforcing members, and each reinforcing member of the first set extends in parallel to, and is spaced apart from, the other reinforcing members of the first set,

the second reinforcing member comprises a second set of reinforcing members, and each reinforcing member of the second set extends in parallel to, and is spaced apart from, the other reinforcing members of the second set, and the third reinforcing member comprises a third set of reinforcing members, and each reinforcing member of the third set extends in parallel to, and is spaced apart from, the other reinforcing members of the third set.

17. The method of claim 1 , wherein each reinforcing member comprises a single -wire filament.

18. The method of claim 1, wherein each reinforcing member comprises a multi-strand wire.

19. The method of claim 1 , wherein each reinforcing member comprises a cylindrical rod.

20. The method of claim 1, wherein the reinforcing members are formed of metal.

21. The method of claim 1, wherein the method comprises the following additional step: machining the article.

22. A cast concrete article configured to be used under multi-directional dynamic loading conditions, the article comprising:

a first sidewall defining a first plane;

a second sidewall defining a second plane that is angled relative to the first plane, the second sidewall adjoining the first sidewall along an edge of the first sidewall, and reinforcing members extending linearly within the article, the reinforcing members being bonded to the concrete of the article and applying a compressive stress to the article via the bond,

wherein

a first portion of the reinforcing members extend in parallel to the first plane, a second portion of the reinforcing members extend in parallel to the second plane, at least one of the first portion of the reinforcing members and the second portion of the reinforcing members is arranged in a grid pattern, and

the compressive pre stress is incorporated along multiple nonparallel planes via the reinforcing members disposed within the article.

23. The cast concrete article of claim 22, wherein each of the first portion of the reinforcing members and the second portion of the reinforcing members is arranged in a grid pattern.

24. The cast concrete article of claim 22, wherein the grid is Cartesian.

25. The cast concrete article of claim 22, wherein each reinforcing member of the first portion of reinforcing members extends in parallel to, and is spaced apart from, the other reinforcing members of the first portion, and each reinforcing member of the second portion of reinforcing members extends in parallel to, and is spaced apart from, the other reinforcing members of the second portion.

26. The cast concrete article of claim 22, wherein the article is formed monolithically.

27. The cast concrete article of claim 22, wherein the bond which provides the compressive stress is achieved during casting of the article.

28. The cast concrete article of claim 22, wherein the internal compressive stress is configured to accommodate external loads applied to the machine part in any direction.

29. The cast concrete article of claim 22, wherein the reinforcing members are configured to provide an internal compressive stress to the corresponding sidewall of at least 40 MPa.

30. The cast concrete article of claim 22, wherein the reinforcing members comprise single -wire filaments having a diameter of 6 mm or less.

31. The cast concrete article of claim 22, wherein the reinforcing members comprise multi-strand wires, each wire having a diameter of up to 13 mm.

32. The cast concrete article of claim 22, wherein the reinforcing members comprise rods having a diameter of up to 30 mm.

33. The cast concrete article of claim 22, wherein the reinforcing members are formed of metal.

34. The cast concrete article of claim 22, wherein the article includes a hollow interior space that is at least partially defined by interior surfaces of the first sidewall and the second sidewall, and the reinforcing members do not reside within the interior space.

35. The cast concrete article of claim 22, wherein the first sidewall further comprises an opening extending between an interior surface of the first sidewall and an exterior surface of the first sidewall, the opening spaced apart from, and surrounded by, a periphery of the first sidewall, and

the reinforcing members are arranged within the first sidewall so that they do not reside within the opening after the article has been finished.

36. The cast concrete article of claim 22, wherein the article further comprises an insert configured to permit connection of the article to another structure, wherein the insert is at least partially embedded in one of the sidewalls.

Description:
WIND ENERGY CONVERTER COMPONENTS MADE OF ULTRA HIGH

PERFORMANCE CONCRETE

BACKGROUND OF THE INVENTION

[001] Power generation continues to be an important application of rotating electrical machines. Wind energy is one of the fastest growing sources of electricity around the world, and wind turbines employing rotating electrical machines are used to convert wind energy to usable power. Some conventional wind turbines include a turbine rotor having turbine blades and an output shaft which drive an electrical machine that can supply 3-5 Megawatts of power to the utility power network. However, increased power demand is leading to increased power requirements for each wind turbine. To obtain a wind turbine that can deliver 10 Megawatts or more, a mere scaling up of the size of the conventional power train and corresponding support structures becomes impractical, due at least in part to the size, weight and cost of some components that accommodate these requirements.

[002] Referring to Fig. 1, a power train in an exemplary conventional wind turbine 10' includes a turbine rotor 20 having blades (not shown) connected to a hub 16'. The wind turbine 10' also includes an electrical generator 30 which is driven by the rotor 20 via a gearbox 26 and a drive shaft (not shown). The generator 30, gearbox 26 and drive shaft are housed in a nacelle 14, shown in outline to permit visualization of the components therein. As will be described in greater detail below, the rotor 20, gearbox 26 and generator 30 are supported on the wind turbine tower 12 using a conventional, cast iron mainframe 50'. In the wind turbine 10', the mainframe 50' is configured to support the rotor 20, the gearbox 26 and the generator 30 in their relative positions on the top of the tower 12. The conventional mainframe 50', when adapted for use in a 2 Megawatt wind turbine, is formed of cast iron and weighs about 28 tons. When the cast iron mainframe 50' is scaled up for use in a 5 Megawatt wind turbine, it will weigh about 70 tons, and the cost of materials is about three times more than for the 2 Megawatt machine. For these and other reasons, providing a wind turbine that can deliver 10 Megawatts or more without merely scaling up of the size of the conventional power train and corresponding support structures would be beneficial. SUMMARY

[003] In some aspects, a method of manufacturing a pre-stressed concrete article for use in a multi-directional dynamic loading application is provided. The method includes providing a form comprising a first outer wall, and a first inner wall parallel to and spaced apart from the first outer wall such that an intermediate space is defined between the first inner wall and the first outer wall. The method includes providing a first elongated reinforcing member disposed in the intermediate space extending in a first direction that is parallel to a first plane, a second elongated reinforcing member disposed in the intermediate space extending in a second direction that is angled relative to the first direction and parallel to the first plane, and a third elongated reinforcing member disposed in the intermediate space extending in a third direction that is angled relative to the first direction and the second direction, and parallel to a second plane that is angled relative to the first plane. The method includes applying a tensile force to each of the reinforcing members, and introducing fresh concrete into the intermediate space so as to at least partially embed each of the reinforcing members while under the applied tensile force. In addition, the method includes curing the fresh concrete within the intermediate space with the at least partially embedded reinforcing members under the applied tensile force; releasing the tensile force applied to each of the reinforcing members so as to introduce a pre-stress into the cured concrete, and removing the cured-concrete article from the form.

[004] The method may include one or more of the following features and/or method steps: The article is removed from the form after the releasing step. The first plane is parallel to the first outer wall. The form further comprises a second outer wall that adjoins, and is non-parallel to, the first outer wall, and a second inner wall parallel to and spaced apart from the second outer wall, the second inner wall adjoining the first inner wall, the vacancy between the second inner wall and second outer wall defining a second intermediate space, the second intermediate space communicating with the intermediate space between the first inner wall and the first outer wall, and the third reinforcing member extends within the second intermediate space. The third direction is transverse to both the first direction and the second direction. The providing step further includes providing a fourth reinforcing member disposed within the second intermediate space extending in a fourth direction that is angled relative to the first, second and third directions. The fourth direction extends in parallel to the second plane. The reinforcing members are linear and pass through corresponding openings provided in the form.

[005] The method may include one or more of the following additional features and/or method steps: The concrete is an ultra high performance concrete having a compressive strength of at least 100 N/mm 2 . The concrete is an ultra high performance concrete having a Young's Modulus of at least 45,000 N/mm . The amount of the applied tensile force is greater in at least one region of the form than in other regions of the form. The method further comprises providing a non-uniform density of reinforcing members such that higher numbers of reinforcing members are provided in regions of expected higher stress. The forms are configured to provide the article with a monolithic hollow shape. The forms are configured to provide the article with a monolithic hollow shape having openings formed in at least one side. The article comprises multiple walls, with at least one wall being spaced from another wall with a vacancy formed between the one wall and the another wall, and the article is formed as a monolithic structure in a single casting. The first reinforcing member comprises a first set of reinforcing members, and each reinforcing member of the first set extends in parallel to, and is spaced apart from, the other reinforcing members of the first set, the second reinforcing member comprises a second set of reinforcing members, and each reinforcing member of the second set extends in parallel to, and is spaced apart from, the other reinforcing members of the second set, and the third reinforcing member comprises a third set of reinforcing members, and each reinforcing member of the third set extends in parallel to, and is spaced apart from, the other reinforcing members of the third set. Each reinforcing member comprises a single -wire filament. Each reinforcing member comprises a multi- strand wire. Each reinforcing member comprises a cylindrical rod. The reinforcing members are formed of metal. The method comprises the following additional step: machining the article. [006] In some aspects, a cast concrete article is provided that is configured to be used under multi-directional dynamic loading conditions, the article comprising a first sidewall defining a first plane; a second sidewall defining a second plane that is angled relative to the first plane, the second sidewall adjoining the first sidewall along an edge of the first sidewall, and reinforcing members extending linearly within the article, the reinforcing members being bonded to the concrete of the article and applying a compressive stress to the article via the bond. A first portion of the reinforcing members extend in parallel to the first plane, a second portion of the reinforcing members extend in parallel to the second plane, and at least one of the first portion of the reinforcing members and the second portion of the reinforcing members is arranged in a grid pattern, whereby the compressive pre stress is incorporated along multiple nonparallel planes via the reinforcing members disposed within the article.

[007] The cast concrete article may include one or more of the following features: Each of the first portion of the reinforcing members and the second portion of the reinforcing members is arranged in a grid pattern. The grid is Cartesian. Each reinforcing member of the first portion of reinforcing members extends in parallel to, and is spaced apart from, the other reinforcing members of the first portion, and each reinforcing member of the second portion of reinforcing members extends in parallel to, and is spaced apart from, the other reinforcing members of the second portion. The article is formed monolithically. The bond which provides the compressive stress is achieved during casting of the article. The internal compressive stress is configured to accommodate external loads applied to the machine part in any direction. The reinforcing members are configured to provide an internal compressive stress to the corresponding sidewall of at least 40 MPa.

[008] The cast concrete article may include one or more of the following additional features: The reinforcing members comprise single-wire filaments having a diameter of 6 mm or less. The reinforcing members comprise multi-strand wires, each wire having a diameter of up to 13 mm. The reinforcing members comprise rods having a diameter of up to 30 mm. The reinforcing members are formed of metal. The article includes a hollow interior space that is at least partially defined by interior surfaces of the first sidewall and the second sidewall, and the reinforcing members do not reside within the interior space. The first sidewall further comprises an opening extending between an interior surface of the first sidewall and an exterior surface of the first sidewall, the opening spaced apart from, and surrounded by, a periphery of the first sidewall, and the reinforcing members are arranged within the first sidewall so that they do not reside within the opening after the article has been finished. The article further comprises an insert configured to permit connection of the article to another structure, wherein the insert is at least partially embedded in one of the sidewalls.

[009] By using non-traditional materials in combination with improved structures to form at least some of the component parts of the power train support structures, a wind turbine that can deliver at least 10 Megawatts can be provided having reduced weight and cost. Of course, these techniques have application to, and provide corresponding benefits for, smaller wind turbines as well.

[010] Structures formed of concrete have conventionally been made in simple shapes and are used in well-defined compressive loading conditions. This is due at least in part to the material properties of cement. In particular, cement has very high compressive strength, but relatively low tensile or bending strength. For concrete structures to be used in simple, known, non-compressive loading conditions, it is possible to compensate for low tensile or bending strengths in concrete by providing the concrete structure with reinforcing members and/or a pre-stress. In general, concrete is not considered as a material for use in applications where loading is complex (e.g, is applied in more than one direction) and of unknown or varying strength.

[011] Ultra High Performance Concrete (UHPC) is a type of concrete characterized by its very high compressive strength (at least 150 N/mm2 as compared to 10-60 N/mm2 for standard concrete). When appropriately pre-stressed, an article formed of UHPC can advantageously be used to form an article having a complex structure and that is suitable for use in dynamic, multidirectional loading conditions. [012] By forming the structural components of wind energy converters of pre-stressed UHPC, it is possible to replace components previously formed of cast iron. This has many advantages in material costs, manufacturing, and finish product characteristics.

[013] Material costs for using UHPC are much lower than those of cast iron, even taking into consideration the larger volume of material required to form a UHPC structure having the same strength characteristics of the cast iron version. For example, at current market prices, it is estimated that a wind energy converter mainframe made of iron costs about three times the cost of a corresponding UHPC mainframe.

[014] Manufacture of UHPC articles has many advantages relative to manufacture of cast iron articles, particularly when the article is very large in size (e.g., a wind energy converter mainframe, hub or tower). For example,

• Large amounts of energy are required to heat cast iron before it can be poured into the casting mould. This requirement makes it difficult to form cast iron mainframes or hubs on sites with poor supply of electrical power. In contrast, pouring UHPC, which is self compacting, does not require much energy.

• The casting form for a cast iron structure is destroyed after each casting cycle and has to be made new for the next part to be casted. Formworks for UHPC can be used several times and only have to be cleaned before pouring the next part.

• Large cast iron parts have to cool down a long time before they can be machined. For example, a 5.0 MW mainframe must cool for about 4 weeks before it can be machined. In contrast, UHPC structures can be stripped from the mold in about five hours after pouring, and a few days later the UHPC structures can placed in loading conditions.

• It is not necessary to expensively optimize shapes of UHPC structures due to the relative low cost of UHPC material as compared to cast iron. As a result, simpler shapes can be used, reducing complexity and thus also time of manufacture.

[015] An article formed of UHPC has characteristics that provide further advantages over an article formed of cast iron. For example,

• Because of its dense structure, UHPC is highly resistant to corrosion, even to chloride. For this reason, it doesn't have to be protected from the environment with expensive coatings.

• UHPC has no unfavorable material properties at cold temperatures up to - 40 degrees Celsius.

• Strength values of UHPC do not have to be reduced with increasing part thickness like steel structures.

• UHPC, particularly with fiber mixtures, is more ductile than conventional cements, and can be used in dynamic and/or fatigue loading conditions. This quality can be enhanced by adding fiber mixtures to the UHPC.

• The damping properties of UHPC are higher than that of steel or cast iron, providing further advantages when used to form wind energy components, machines or machine components.

• UHPC is less dense than cast iron. Although a UHPC structure may sometimes have to be manufactured with bigger wall thicknesses than a corresponding cast iron structure to achieve the same strength characteristics as the corresponding cast iron structure, the UHPC structure is not heavier than the cast iron structure because of its lower density.

BRIEF DESCRIPTION OF THE FIGURES

[016] Fig. 1 is a perspective view of a power train of a conventional wind turbine.

[017] Fig. 2 is a UHPC main frame that replaces the conventional mainframe within the wind turbine of Fig. 1.

[018] Fig. 3 is an isolated front perspective view of the mainframe of Fig. 2.

[019] Fig. 4 is an isolated rear perspective view of the mainframe of Fig. 2.

[020] Fig. 5 is a schematic side cross sectional view of the mainframe of Fig. 3. [021] Fig. 6 is a schematic bottom cross sectional view of the mainframe of Fig. 3.

[022] Fig. 7 illustrates the calculated stresses in MPa within the sidewalls of the mainframe of Fig. 2 under load.

[023] Fig. 8 is a side view of a conventional wind turbine hub.

[024] Fig. 9 is a schematic side cross sectional view of a UHPC wind turbine hub.

[025] Fig. 10 is a flow diagram illustrating a method of manufacturing a UHPC article.

[026] Fig. 11 is a rear perspective view of a UHPC mainframe within a form that is shown schematically using broken lines, illustrating an arrangement of reinforcing members.

[027] Fig. 12 is a front perspective view of the UHPC mainframe of Fig. 11 with the form omitted and portions of the reinforcing members within the front sidewall opening and bottom sidewall opening removed.

DETAILED DESCRIPTION

[028] Referring to Figs. 2, 3 and 4, a UHPC mainframe 50 is a monolithic, hollow structure that is configured to be used in the place of the conventional cast iron mainframe 50' in a wind energy converter 10. The mainframe 50 includes a front sidewall 52, and a rear sidewall 54 opposed to the front sidewall 52. The front sidewall 52 is formed having a front sidewall opening 64. The front sidewall opening 64 is generally circular in shape and extends through the thickness of the sidewall 52 between an interior surface 62 of the mainframe 50 and an exterior surface 65 of the mainframe 50. The front sidewall opening 64 is generally centered within the periphery of the front sidewall 52.

[029] The mainframe 50 includes mutually-spaced lateral sidewalls 56, 58 that extend between the front sidewall 52 and the rear sidewall 54. The lateral sidewalls 56, 58 extend normally from respective side edges of the front sidewall 52 and the rear sidewall 54. Although the front sidewall 52 and rear sidewall 54 have the same width, the front sidewall 52 is greater in height than the rear sidewall 54. In the illustrated embodiment, the front sidewall 52 has a height that is about three times the height of the rear sidewall 54. Accordingly, the height of the lateral sidewalls 56, 58 varies linearly from the front to the rear sides of the mainframe 50.

[030] The mainframe 50 includes a top sidewall 60 that closes a portion of the upper side of the mainframe 50. In particular, the top sidewall 60 adjoins the front sidewall 52 and extends between the lateral sidewalls 56, 58 in the region adjacent to the front sidewall 54. The upper side of the mainframe 50 is open between the top sidewall 60 and the rear sidewall 54. This configuration permits access to the interior space of the mainframe 50, whereby power train components can be assembled within the mainframe 50.

[031] The mainframe 50 includes a bottom sidewall 62 that closes the lower side of the mainframe 50. The bottom sidewall 62 is formed having a bottom sidewall opening 66. The bottom sidewall opening 66 is generally circular in shape and extends through the thickness of the sidewall 62 between the interior surface of the mainframe 50 and the exterior surface of the mainframe 50. The bottom sidewall opening 66 is generally centered within the periphery of the bottom sidewall 62. When the mainframe 50 is assembled on the tower 12, the opening 66 in the bottom sidewall is a throughway that provides access between the interior of the tower 12 and the interior of the mainframe 50.

[032] An outwardly protruding flange 68 is provided on each lateral sidewall 56, 58 of the mainframe 50. In particular, each flange 68 is located along the lower edge of each sidewall 56, 58 at a location generally midway between the front sidewall 52 and the rear sidewall 54 on an outward facing surface of the corresponding sidewall 56, 58. Each flange 68 includes several flange through-openings 70 arranged along an arc that is parallel to the outer periphery of the tower 12.

[033] The six mainframe sidewalls (front sidewall 52, rear sidewall 54, lateral sidewalls 56, 58, top sidewall 60 and bottom sidewall 62) are formed as a monolithic structure in a single casting from UHPC (discussed further below). The mainframe 50 includes a hollow interior space that is at least partially defined by interior surfaces 63 of the respective plate-like sidewalls 52, 54, 56, 58, 60, 62. In use, some components of the power train of the wind energy converter 10 are received within the interior space and supported by the mainframe sidewalls. Although in the illustrated embodiment, each sidewall 52, 54, 56, 58, 60, 62 is of uniform thickness and has the same thickness as the other sidewalls, the sidewalls 52, 54, 56, 58, 60, 62 are not limited to this configuration.

[034] Referring also to Figs. 5 and 6, each of the six sidewalls 52, 54, 56, 58, 60, 62 includes reinforcing members 90 that extend linearly within the mainframe 50. In some embodiments, the reinforcing members 90 are formed of single -wire metal filaments having a diameter of 10 mm. In other embodiments, the filaments have a diameter of 8 mm. In still other embodiments, the filaments have a diameter of 6 mm or less. The reinforcing members 90 are long relative to their diameter, in that they have a length that generally corresponds to the dimension of the sidewall in the direction corresponding to the orientation of the reinforcing member 90 within the sidewall.

[035] The reinforcing members 90 are cast within the sidewalls 52, 54, 46, 58 60, 62 while under a tensile load as discussed further below, and thus are bonded to the concrete while in a stretched configuration. When released from the applied tensile load after casting, the reinforcing members 90 exert a compressive stress to the concrete which forms the mainframe 50 via the bond between the reinforcing members 90 and the UHPC. Thus, the sidewalls of mainframe 50 are provided with an internal compressive stress (a "pre-stress") by the reinforcing members 90 in directions corresponding to the orientation of the reinforcing members 90. By careful arrangement of the reinforcing members 90 within the sidewalls 52, 54, 56, 58, 60, 62, each sidewall 52, 54, 56, 58, 60, 62 is provided with a pre-stress that is configured to accommodate external loads applied to the mainframe 50 in any direction. In the illustrated embodiment, the reinforcing members are configured to provide an internal compressive stress to the corresponding sidewall in a range of about lOMPa in some locations to about 40 MPa or more in other locations.

[036] Referring to Fig. 5, a schematic side sectional view of the mainframe 50 illustrates an exemplary arrangement of the reinforcing members 90 disposed within the front sidewall 52, the bottom sidewall 62, the rear sidewall 54 and the top sidewall 60. For explanation purposes, the reinforcing members 90 are illustrated here as extending beyond the outer surface 65 of the mainframe 50. Although this configuration occurs during casting of the mainframe 50, it will be understood that after the mainframe 50 has been cast and then released from the casting forms, the reinforcing members 90 reside entirely within the periphery of the outer surface of the finished article.

[037] In the illustrated embodiment, a first set 90a of the reinforcing members 90 extend generally in parallel to a plane PI defined by the first sidewall 52. The first set 90a is an array in which each reinforcing member 90 of the first set 90a extends linearly in a first direction Dl, and is parallel to and spaced apart from the other reinforcing members 90 of the first set 90a.

[038] A second set 90b of the reinforcing members 90 is an array in which each reinforcing member 90 of the second set 90b extends linearly in a second direction D2 that is angled relative to the first direction D 1 and is parallel to the first plane PI . In the illustrated embodiment, the second direction D2 is transverse to the first direction Dl , but is not limited to this configuration. Each reinforcing member 90 of the second set 90b is spaced apart from the reinforcing members of the first set 90a, and is parallel to and spaced apart from the other reinforcing members 90 of the second set 90b.

[039] In some embodiments, a third set 90c of elongated reinforcing members 90 is disposed within the sidewalls. The third set 90c is an array in which each reinforcing member 90 of the third set 90c extends linearly in a third direction D3 that is angled relative to the first direction Dl and the second direction D2. In addition, the third direction D3 extends parallel to a second plane P2 that is angled relative to the first plane PI . In the illustrated embodiment, the second plane P2 is parallel to the lateral sidewalls 56, 58. The third direction D3 also extends in parallel to a third plane P3, which in turn is parallel to the top and bottom sidewalls 60, 62. In the illustrated embodiment, the third direction D3 is transverse to both the first and second directions Dl, D2, but is not limited to this configuration. In addition, the second plane P2 is transverse to both the first and third planes PI , P3 but is not limited to this configuration. Each reinforcing member 90 of the third set 90c is spaced apart from the reinforcing members of the first set 90a and second set 90b, and is parallel to and spaced apart from the other reinforcing members 90 of the third set 90c.

[040] Referring to Fig. 6, in some embodiments, additional sets of elongated reinforcing members 90 can be disposed in the sidewalls. For example, a fourth sets 90d and a fifth set 90e can be included. The fourth set 90d extends in a fourth direction D4, and the fifth set 90e extends in a fifth direction D5. The fourth and fifth directions D4, D5 are each angled relative to the first direction D 1 , the second direction D2 and the third direction D3, and extend in parallel to the third plane P3. Like the previous sets, the reinforcing members 90 within the fourth and fifth sets 90d, 90e form an array in which each reinforcing member 90 of the set extends linearly, and is parallel to and spaced apart from the other reinforcing members 90 of the set.

[041] In the illustrated embodiment, the first set 90a and second set 90b reside within the first sidewall 52 and, in combination, effectively form a Cartesian grid pattern. The combined effect of all sets provides a compressive pre-stress that is incorporated along multiple non parallel planes that enable the mainframe 50 to be used under multidirectional dynamic loads.

[042] It should be noted that the reinforcing members 90 do not pass through or reside within the interior space 67 defined by the interior surfaces 63 of the sidewalls 52, 54, 56, 58, 60, 62, and also do not pass through or reside within the sidewall openings 64, 66, of the finished article.

[043] In most areas of the mainframe 50, the amount of pre-stressed strands 90 used is about one to five percent in volume of the whole structure. In addition, the pre-stressed strands 90 are not uniformly distributed throughout the wall structure, but instead are provided in higher concentrations in areas of higher tension stress. [044] In some embodiments, the sidewalls 52, 54, 56, 58, 60, 62 of the mainframe 50 may also be provided with an insert (not shown) configured to permit connection of the mainframe 50 to another structure. For example, an insert may be a plate, flange, anchor bolt, bracket or similar structure. In some embodiments, the insert is cast with the mainframe 50 so that the insert is at least partially embedded in one of the sidewalls 52, 54, 56, 58, 60, 62. In other embodiments, the insert is attached to the mainframe 50 subsequent to casting.

[045] The mainframe 50 is used, for example, to support the rotor 20, the gearbox 26, and the generator 30 on the top of the wind turbine tower 12. In particular, the rotor 20 is mounted to an outward facing surface 51 of the front sidewall 52 of the mainframe 50 via a coupling 28 that houses bearings (not shown) that support the driveshaft. The gearbox 26 is disposed within the mainframe 50. In some embodiments, the gearbox 26 at least partially rests on, and is fixed to, the mainframe bottom sidewall 62 and/or the left and the right lateral sidewalls 56, 58. In addition, a portion of the gearbox 26 extends through the front sidewall opening 64 and is secured to the mainframe front sidewall 52 via the coupling 28. The generator 30 is supported on a platform (not shown) that is cantilevered from an outward facing surface 53 of the rear sidewall 54. Yaw drive engines 32 are used to rotate the mainframe 50 relative to the tower 12 about a vertical axis and are supported on the flanges 68. In particular, a yaw drive engine 32 is disposed in each flange opening 70, and includes gearing configured to engage a gear wheel 34 mounted to the top of the tower 12.

[046] Referring to Fig. 7, the principal stress distribution within the mainframe 50 was calculated for expected maximum loads. In the figure, it can be seen that the highest stress is localized in the vicinity of the front wall opening 64, which corresponds to location at which the mainframe 50 is connected to the rotor 20. In addition, it can be seen that there are large regions of relative low stress, for example at locations distant from the front wall opening 64. In low stress regions, less pre-stress is required, whereby a lower density of reinforcing members 90 can be used. In addition, or alternatively, wall thicknesses can be reduced whereby the weight of the mainframe 50 can be reduced. Clearly, by providing sufficient levels of compressive pre-stresses in an appropriate arrangement within the mainframe 50, complex loads of high and varying strength can be accommodated.

[047] Referring to Figs. 8 and 9, other portions of the wind energy converter 10 can be formed of UHPC. For example, the cast iron hub 16' illustrated in Fig. 8 can be replaced with a hub 16 formed of UHPC and provided in the shape of a hollow triangular prism. Fig. 9 illustrates a schematic cross-sectional view of the UHPC hub 16, and shows reinforcing members 90 disposed within each prism sidewall 110, 112, 114. In the illustrated embodiment, a first set 90w of the reinforcing members 90 extends within the first prism sidewall 110 in parallel with a fourth plane P4 defined by the first prism sidewall 110. A second set 90z of the reinforcing members 90 extends within the second prism sidewall 112 in parallel with a fifth plane P5 defined by the second prism sidewall 112. A third set 90y of the reinforcing members 90 extends within the third prism sidewall 114 in parallel with a sixth plane P6 defined by the third prism sidewall 114. In the illustrated embodiment, each of the first set 90w, the second set 90z, and the third set 90y also extend in parallel to a seventh plane P7 that is transverse to each of the fourth plane P4, the fifth plane P5 and the sixth plane P6, but are not limited to this. In addition, a fourth set 90x of the reinforcing members 90 extends in parallel to a plane transverse to the seventh plane P7. The fourth set 90x extends within the apex regions 116 formed by the intersections between the first prism sidewall 110 and third prism sidewall 114, the first prism sidewall 110 and the second prism sidewall 112, and the second prism sidewall and the third prism sidewall 114. Together, the first set 90w and the fourth set 90x together form a grid arrangement within the first prism sidewall 110. Likewise, the second set 90z and the fourth set 90x together form a grid arrangement within the second prism sidewall 112, and the third set 90y and the fourth set 90x together form a grid arrangement within the third prism sidewall 114. In some embodiments, the grid may be Cartesian. Since the sidewalls 110, 112, 114 are arranged to form a triangle, the respective grids within each of the sidewalls 110, 112, 114 are angled relative to the other grids. [048] Referring to Figs. 10-12, a method of manufacturing a pre-stressed UHPC article for use in the multi-directional, dynamic loading conditions will now be described. As an example, a method of manufacturing a pre-stressed UHPC mainframe 50 that is formed as a monolithic structure in a single casting, and is suitable for use in the multidirectional, dynamic loading conditions found within a wind energy converter 10, will be described.

[049] At step 250, the method includes providing a form 200 that is configured to provide a monolithic manufactured article. In some embodiments, the manufactured article is hollow. In the illustrated example, the form 200 , shown partially and schematically using broken lines in Fig. 11 , is provided in a shape that generally corresponds to the mainframe's 50 hollow, multi-walled shape. In particular, for each sidewall 52, 54, 46, 58, 60, 62, the form includes an outer wall 202, and an inner wall 204 that is parallel to and spaced apart from the outer wall 202 such that an intermediate space 210 is defined between the inner wall and the outer wall.

[050] For example, with respect to the first sidewall 52, the form 200 includes a first outer wall 202a, and a first inner wall 204a that is parallel to and spaced apart from the first outer wall 202a such that a first intermediate space 210a is defined between the first inner wall 204a and the first outer wall 202a. With respect to the adjoining, second sidewall 56, the form 200 further includes a second outer wall 202b that adjoins, and is non-parallel to, the first outer wall 202a, and a second inner wall 204b that is parallel to and spaced apart from the second outer wall 202b. The second inner wall 204b adjoins the first inner wall 204a. The vacancy between the second inner wall 204a and second outer wall 202b defines a second intermediate space 210b. The second intermediate space 210b communicates with the first intermediate space 210a. The form 200 further includes similar structures for the remaining sidewalls 54, 58, 60 and 62.

[051 ] In the illustrated embodiment, in the front wall of the form 200, a curved surface 216 corresponding to the front wall opening 64 is provided that extends between the inner wall 204a and the outer wall 202a of the form 200. In addition, in the bottom wall of the form 200, a curved surface 218 corresponding to the bottom wall opening 66 is provided that extends between the inner wall 202 and the outer wall 204 of the form 200. In addition, the form 200 includes edge surfaces 220 that extend between the inner wall 204 and the outer wall 202 at the peripheries of the sidewalls so as to provide a closed form.

[052] At step 252, once a form 200 is provided, reinforcing members 90 are arranged within the form 200 in a configuration that is determined by the expected loading conditions of the mainframe 50 as discussed further below.

[053] A first set 90a of elongated reinforcing members 90 is disposed in the first intermediate space 210a. The first set 90a extends linearly in the first direction D 1 which is parallel to the first plane PI . In the illustrated embodiment, the first plane PI is parallel to the outer wall 202a, and thus is also parallel to the outer surface of the first sidewall 52, but is not limited to this configuration. Each reinforcing member 90 of the first set 90a is parallel to and spaced apart from the other reinforcing members 90 of the first set 90a.

[054] A second set 90b of elongated reinforcing members 90 is disposed in the first intermediate space 210a. The second set 90b extends linearly in the second direction D2 that is angled relative to the first direction D 1 and in parallel to the first plane PI . In the illustrated embodiment, the second direction D2 is transverse to the first direction Dl , but is not limited to this configuration. Each reinforcing member 90 of the second set 90b is spaced apart from the reinforcing members of the first set 90a, and is parallel to and spaced apart from the other reinforcing members 90 of the second set 90b.

[055] In some embodiments, the method includes providing a third set 90c of elongated reinforcing members 90 disposed both in the first intermediate space 210a and in the second intermediate space 210b. The third set 90c extends linearly in the third direction D3 that is angled relative to the first direction Dl and the second direction D2. In addition, the third direction D3 extends parallel to a second plane P2 that is angled relative to the first plane PI . In the illustrated embodiment, the second plane P2 is parallel to the form walls corresponding to the lateral sidewalls 56, 58. The third direction D3 also extends in parallel to a third plane P3, which in turn is parallel to the form walls corresponding to the top and bottom sidewalls 60, 62. In the illustrated embodiment, the third direction D3 is transverse to both the first and second directions Dl, D2, but is not limited to this configuration. In addition, the second plane P2 is transverse to both the first and third planes P 1 , P3 but is not limited to this configuration. Each reinforcing member 90 of the third set 90c is spaced apart from the reinforcing members of the first set 90a and second set 90b, and is parallel to and spaced apart from the other reinforcing members 90 of the third set 90c.

[056] Although not illustrated in Fig 11 and 12, additional sets of elongated reinforcing members 90 can be disposed in the first intermediate space 210a as discussed above with respect to Fig. 6.

[057] As shown in Fig. 11 , the reinforcing members 90 extend through the respective intermediate space 210 and pass through corresponding openings 214 provided in opposed outer walls 202 of the form 200. In addition, the reinforcing members 90 extend through the front sidewall opening 64 and the bottom sidewall opening 66, although only a subset of reinforcing members 90 are shown extending through the front and bottom sidewall openings 64, 66 to enhance clarity of the illustration.

[058] The reinforcing members 90 are provided in the remaining portions of the form 200 in a similar manner, and the description is therefore omitted.

[059] At step 254, once the reinforcing members 90 have been arranged within the intermediate space 210, then a tensile force is applied to each of the reinforcing members 90. In some embodiments, this is achieved by hydraulic or mechanical devices connected to the reinforcing members 90. For example, the reinforcing members may be connected to and tensioned by threaded spindles. In the illustrated embodiment, a uniform tensile force may be applied to all reinforcing members 90. In other embodiments, higher tensile forces may be applied to a subset of reinforcing members 90 that are located in regions of the sidewall that are expected to experience higher loads. As a result, the amount of the applied tensile force is greater in at least one region of the form than in other regions of the form.

[060] At step 256, when the reinforcing members have been placed under tension, fresh concrete is introduced into the intermediate space 210 so as to at least partially embed each of the reinforcing members 90 while under the applied tensile force. As used here, the term "fresh concrete" refers to mixed batch, non-cured concrete in its wet form. In particular, fresh UHPC is introduced into the intermediate space 210. In some embodiments, the UHPC has a compressive strength of at least 100 N/mm . In other embodiments, the UHPC has a compressive strength of at least 120 N/mm . In still other embodiments, the UHPC has a compressive strength of at least 180 N/mm 2 . In some embodiments, the UHPC has a Young's Modulus of at least 45,000 N/mm 2 . In other embodiments, the UHPC has a Young's Modulus of at least 55,000 N/mm 2 . In still other embodiments the UHPC has a Young's Modulus of at least 60,000 N/mm 2 . In the illustrated embodiment, the intermediate space is completely filled with the UHPC.

[061] At step 258, the fresh concrete within the intermediate space is then permitted to cure while the at least partially embedded reinforcing members 90 remain under the applied tensile force.

[062] As discussed above, the compressive pre-stress provided in the finished main frame 50 is achieved via a bond between the reinforcing members 90 and the concrete. The bond is established during the casting and curing steps 256, 258. The bond accrues by adhesion of the cement with the reinforcing members 90. In some embodiments, the adhesion is enhanced by providing the reinforcing members with ribs (not shown).

[063] At step 260, after the fresh concrete has cured to an extent that the concrete is a solid mass having a predetermined stiffness (i.e., sufficient to withstand the desired compressive pre-stress), and the reinforcing members 90 have bonded to the concrete, the tensile force previously applied to each of the reinforcing members 90 is released. As a result, a compressive pre-stress is introduced into the cured concrete by the reinforcing members 90 via the bond between the reinforcing members 90 and the concrete. The extent of the compressive pre-stress within the concrete is determined by the density of the reinforcing members 90 and the extent of the applied tensile force. In addition, the direction of the compressive pre-stress is determined by the direction of the reinforcing members within the concrete.

[064] The portions of the reinforcing members 90 extending beyond the outer surface 51 of the mainframe 50 are removed. As seen in Fig. 12, the portions of the reinforcing members 90 extending through the front sidewall opening 64 and the bottom sidewall opening 66 are also removed (the portions of the reinforcing members 90 extending beyond the outer surface 51 of the sidewalls 52, 54, 56, 58, 60, 62 have not yet been removed in this illustration).

[065] At step 262, the cured-concrete mainframe is removed from the form 200.

Although the method is described such that the step of removing the mainframe 50 from the form 200 occurs after the step of releasing the tensile force applied to the reinforcing members 90, the method is not limited to this ordering.

[066] In some embodiments, the released mainframe 50 can receive additional finishing steps. For example, the mainframe 50 can be machined to provide surface finishing, accurate placement of bolt holes, etc.

[067] A selected illustrative embodiment of the UHPC mainframe 50 for use in the wind energy converter 10 is described above in some detail. While this working example of the present invention has been described above, the present invention is not limited to the working example described above, but various design alterations may be carried out without departing from the present invention as set forth in the claims.

[068] Although the reinforcing members 90 are disclosed as being single-wire filaments, other types of reinforcing members 90 may be used. For example, in some embodiments, multi-strand wires may be used as reinforcing members, each wire having a diameter of up to 13 mm. In other embodiments, rods having a diameter of up to 30 mm may be used as reinforcing members. In addition, although the reinforcing members are disclosed as being formed of metal, other materials may be used to form the reinforcing members, such as carbon fiber, fiberglass, and other synthetic materials.

[069] It is advantageous to build several structural components of wind energy converters of UHPC. For example, it is possible to build the mainframe, hub, nacelle frame, generator cantilever, tower and foundations of UHPC. Of course, the inventive features can be applied to other machine components, with particular benefits for large machines or machine parts such as ships and mining machines.

[070] The mainframe 50 is an example of a hollow polyhedron, which is defined here as a geometric solid whose faces are each fiat polygons. In general, articles having this shape are well suited to be formed of UHPC and pre-stressed as described above since the reinforcing members extend linearly through the walls of the article. However, cast concrete articles configured to be used under multi-directional dynamic loading conditions are not limited to a being a polyhedron, and can have curvilinear surfaces.

[071] In addition, it should be understood that only structures considered necessary for clarifying the present invention have been described herein. Other conventional structures, and those of ancillary and auxiliary components of the system, are assumed to be known and understood by those skilled in the art.