Submersible cross-flow turbine device

Abstract

A submersible cross-flow turbine device for generating electricity from ocean or tidal currents is provided. The device includes a support member having a first end and a second end, and a plurality of foils that rotate in a single direction when exposed to fluid flow, where the plurality of foils is joined to the support member such that the rotating plurality of foils cause the support member to rotate. The device also includes a first buoyant structure positioned at the first end of the support member, and a second buoyant structure positioned at the second end of the support member. The first and second buoyant structures may be substantially disk-shaped.

Description

[0001] SUBMERSIBLE CROSS-FLOW TURBINE DEVICE

[0002] Related Applications

[0003] The present application claims the benefit under 35 U.S.C. §119(e) to U.S. Provisional Application No. 63 / 520.995 filed on August 22, 2023, the contents of which is incorporated by reference herein in its entirety.

[0004] Field

[0005] The present disclosure relates generally to cross-flow turbine devices that harness energy from a fluid flow to produce power.

[0006] Background

[0007] Various types of turbine devices exist to capture energy from fluid flow to produce power. Wind turbines are commonly used on land to capture energy from the wind. Hydrokinetic turbines capture ocean and tidal currents and are capable of providing an emission-free renewable energy.

[0008] Summary

[0009] According to one aspect, a submersible cross-flow turbine device for generating electricity from ocean or tidal currents is provided. The device includes a support member having a first end and a second end, and a plurality of foils that rotate in a single direction when exposed to fluid flow, where the plurality of foils is joined to the support member such that the rotating plurality of foils cause the support member to rotate. The device further includes a first buoyant structure positioned at the first end of the support member, and a second buoyant structure positioned at the second end of the support member.

[0010] According to another aspect, a submersible cross-flow turbine device for generating electricity from ocean or tidal currents is provided. The device includes a central shaft having a first end and a second end, and a plurality of foils that rotate in a single direction when exposed to fluid flow, where the plurality of foils is joined to the central shaft such that the rotating plurality of foils cause the shaft to rotate. The device also includes a first substantially disk-shaped buoyant structure positioned at the first end of the central shaft, and a second substantially disk-shaped buoyant structure positioned at the second end of the central shaft. Both the first buoyant structure and the second buoyant structure includes a fixed buoyancy portion and a variable buoyancy portion, where the buoyancy of the variable buoyancy portions can be adjusted to alter the overall buoyancy of the cross-flow turbine to position the cross-flow turbine at a desired water column location.

[0011] Brief Description of the Drawings

[0012] Figure 1 is a perspective view of a cross-flow turbine device according to one embodiment;

[0013] Figure 2 is a side view of the cross-flow turbine device illustrated in Figure 1;

[0014] Figure 3 is a front view of the cross-flow turbine device illustrated in Figure 1;

[0015] Figure 4 is a perspective view of the cross-flow turbine device illustrated in Figure 1 deployed in the ocean;

[0016] Figure 5 is a perspective view of a cross-flow turbine device according to another embodiment;

[0017] Figure 6 is a perspective view of a cross-flow turbine device according to another embodiment;

[0018] Figure 7 is a perspective view of a cross-flow turbine device according to yet another embodiment;

[0019] Figure 8 is a perspective view of a cross-flow turbine device according to another embodiment; and

[0020] Figures 9A-9C are perspective views of cross-flow turbine devices illustrating alternative anchoring arrangements.

[0021] Detailed Description

[0022] The technology of the present disclosure relates to a submersible cross-flow turbine device for transforming the energy associated with ocean or tidal currents into power. The present disclosure builds upon the technology7disclosed in Applicant s earlier patents directed to devices which are discussed in U.S. Patent No. 7.902,687 filed on October 19. 2007, U.S. Patent No. 8,393,853 filed November 19, 2007, U.S. Patent No. 7,849,596 filed November 19, 2007, U.S. Patent No. 8,096,750 filed March 20, 2009, and U.S. Published Application No. 2020 / 0400117A1 filed on August 25, 2020, all of which are incorporated by reference herein in their entirety. These earlier patents and published application disclose turbine technology and describe the internal components of the turbine in detail.

[0023] Applicant recognized that traditional tidal hydrokinetic systems are either surface mounted (i.e., device floats on the surface of the water) or bottom mounted (i.e., device rests on the ocean floor). Applicant further recognized that there were problems associated with both configurations. First, surface mounted systems leave a visual impact on the environment. Second, surface mounted systems are exposed to additional structural loading from ice and debris accumulation. Third, surface mounted systems can present a danger to mariners. High flow sites often exist in narrow straits, estuaries, and headlands. While these locations are desirable for their ocean or tidal currents, they also tend to be locations where marine traffic finds difficult to navigate. In contrast, bottom mounted devices present a much- reduced threat to marine traffic. However, bottom-mounted systems are located at a point in the water column that presents the lowest opportunity for energy extraction. This is undesirable as it may limit the amount of power produced by the turbine.

[0024] Aspects of the present disclosure are directed to a new turbine device which is configured to operate below an ocean depth that is a danger to marine traffic, while also being high enough to generate power within the high energy region of a water column. As set forth in more detail below, in one embodiment, the device may be configured to be positioned in mid-water column so that there is no visual indication of the presence of the device from the water surface during operation. In one embodiment, mid-water column maybe defined as being between about 3 and 30 meters below the water surface and / or between about 10% and 60% of the ocean depth at a specific location. In one particular embodiment, the device may be positioned between 20 meters - 100 meters below the water surface.

[0025] It should be recognized that in another embodiment, the device may be placed at any desired location within the water column, including at the water surface, and / or on the ocean floor, as the present disclosure is not so limited. As set forth in more detail below, aspects of the present disclosure are directed to a submersible cross-flow turbine device which includes a first buoyant structure positioned on a first end of the device, and a second buoyant structure positioned on a second end of the device. As discussed below, these buoyant structures may be configured so that the device may be placed in a desired water column location in the ocean.

[0026] In one illustrative embodiment, the first and second buoyant structures may each include a variable buoyancy portion. As discussed in more detail below, by adjusting the buoyancy of the variable buoyancy portion, the device can be raised or lowered in the ocean to the desired position in the water column. In one embodiment, the shape of the first and second buoyancy structures is designed to reduce pressure drag. Furthermore, as discussed in more detail below, in one embodiment, the buoyancy of the variable buoyancy portions may be adjusted to lower their buoyancy when the turbine is being transported through the ocean.

[0027] Turning now to the drawings, the embodiment disclosed in Figures 1-4 will now be more fully described. Figures 1-4 illustrate one embodiment of a submersible cross-flow turbine device 100 which includes a support member 20 having a first end 22 and a second end 24. A plurality of foils 40 rotate in a single direction when exposed to fluid flow and the plurality of foils 40 is joined to the support member 20 such that the rotating plurality of foils 40 cause the support member 20 to rotate. As shown, the device 100 also includes a first buoyant structure 60 positioned at the first end 22 of the support member 20. and a second buoyant structure 80 positioned at the second end 24 of the support member 20. As mentioned above, the first and second buoyant structures 60, 80 may be configured to provide sufficient buoyancy so that the device 100 can be configured to be positioned in mid- water column in the ocean.

[0028] As described in more detail below, in one embodiment, the support member 20 includes a central shaft 72, in another embodiment, the support member 20 may be a separate rotating component positioned over a central shaft 72, and in other embodiments, which also include shaftless turbine embodiments discussed below, the support member 20 may be configured differently where the support member 20 may, for example, include a beam extending between the first and second buoyant structures 60, 80 positioned in a different location. The specific arrangement of the plurality of foils will be discussed in more detail below, but at a high level, one of ordinary skill in the art will appreciate that the foils 40 (i.e., blades or hydrofoils) rotate in a single direction when exposed to fluid flow. In one embodiment, the foils 40 may trace a spiral wound path about a central axis of the device 100. As shown in Figure 3, a generator 30 may be provided to generate power based upon the rotational movement of the foils 40. In one embodiment, the device is configured to have a power output of 2MW at 3.5 m / s. Various types of foils 40 and generator 30 configurations are known to one having ordinary skill in the art, including, but not limited to those discussed in Applicant's earlier patents including U.S. Patent No. 7,902,687, U.S. Patent No. 8,393,853, U.S. Patent No. 7,849,596. U.S. Patent No. 8,096.750, and U.S. Published Application No. 2020 / 0400117A1.

[0029] As shown in Figures 1-4, in one embodiment, the first and second buoyant structures 60, 80 may include a fixed buoyancy portion 62, 82 and a variable buoyancy portion 64, 84. In one embodiment, the combination of a fixed buoyancy portion and a variable buoyancy portion may be desirable to reduce anchor loads during deployment and retneval operations.

[0030] It should be appreciated that ‘‘fixed buoyancy” is intended to define a static buoyant structure that is not configured to change its amount of buoyancy. In one embodiment, the fixed buoyancy portions 62, 82 of the first and second buoyant structures are made of a buoyant material, such as, but not limited to various foam materials, including but not limited to syntactic foam, or any material with a density less than that of water, or gas filled chambers. In one embodiment, the fixed buoyancy portions may be made with high-density syntactic foam, which may be ideal as it can be formed into a low-drag shape, further reducing the buoyancy requirement.

[0031] In contrast to “fixed buoyancy”, it should be recognized that “variable buoyancy” is intended to define a buoyant structure that is configured such that the buoyancy can be changed. For example, in one embodiment, the variable buoyancy portions 64, 84 of the first and second buoyant structures may each include a ballast tank, such as a steel, composite, or plastic vessel, that can be filled or emptied with a fluid, such as water, to vary the buoyancy of the overall turbine. By adjusting the amount of fluid in the ballast tank, the buoyancy is changed and the device 100 can be raised or lowered in the ocean to the desired position in the water column.

[0032] In one embodiment, the shape of the variable buoyancy portion 64, 84 is configured so that when filled with a fluid, the fluid collects at the bottom of the variable buoyancy portion 64, 84 and air fills the top of the variable buoyancy portion. Applicant recognized that this design reduces the risk of trapped air during maintenance and may contribute to a lower overall center of gravity. In one embodiment, the device 100 is configured to travel vertically through the water column with water in the ballast tanks, so the tanks will not have to sustain large differential pressures. However, when the device is operating with the tanks filled with air, they may have to endure large pressure differentials resulting from the inclining of the device 100, as well as tidal range.

[0033] In the embodiment disclosed in Figures 1-4, the first and second buoyant structures 60, 80 are substantially disc-shaped. Applicant recognized that the disk shape may help to reduce pressure drag. The device 100 inclines from side to side as the tide ebbs and floods. The substantially disc-shaped first and second buoyant structures 60, 80 maintain a constant coefficient of drag as the device 100 pitches. This simplifies analysis and aids stability’, as it does not require pitch control of the device. In general, a turbine device is agnostic to flow direction about the shaft axis. This system design allows the exploitation of this turbine characteristic while maintaining unimpeded inflow through the capture area during operation. As discussed in more detail below, the present disclosure also contemplates first and second buoyant structures having other shapes, as the disclosure is not so limited.

[0034] In one embodiment, the substantially disc-shaped first and second buoyant structures 60, 80 are designed to lower the center of gravity below the center of buoyancy of the surfaced device. This may cause the center of gravity to be vertically offset from the center of buoyancy when the system pitches which may enable a restoring moment and may ensure the surface stability of the turbine device.

[0035] As illustrated in Figures 1-4, in one embodiment, the device 100 has a helically twisted turbine design with at least one helical foil 40 and at least one strut 42 coupling the foils 40 to the support member 20. As shown, in one embodiment, three spaced apart substantially triangular shaped struts 42 couple the three foils 40 to the support member 20. However, the present disclosure is not so limited and one of ordinary skill in the art will appreciate that in other embodiments, other foil / strut configurations are contemplated. For example, straight foils 40 are also contemplated. As shown in Figure 2, the device 100 may include a generator 30 coupled to a central shaft 72, where the generator is configured to convert rotation of the central shaft into electricity. It should be appreciated that in a shaftless embodiment, a generator may be coupled directly to the foils 40 to convert rotation of the turbine into power and / or electricity.

[0036] As shown in Figures 1-4, in one embodiment, the disc-shaped first buoyant structure 60 includes a fixed buoyancy portion 62 located on an outside portion of its disk-shaped structure, and a variable buoyancy portion 64 located on an inside portion of the first buoyant substantially disc-shaped structure. In other words, the fixed buoyancy portion 62 is positioned along the periphery of the first buoyant structure, and the variable buoyancy portion 64 is positioned proximate the center of the first buoyant structure. Likewise, in one embodiment, the disc-shaped second buoyant structure 80 includes a fixed buoyancy portion 82 located on an outside portion of its disk-shaped structure, and a variable buoyancy portion 84 located on an inside portion of the second buoyant substantially disc-shaped structure.

[0037] As also shown in Figures 1-4, in one embodiment, the first buoyant structure 60 includes a notch 66. The notch 66 may provide stability to the device 100, making it less likely to roll. As shown in Figure 4. when the device 100 is deployed in the ocean, the notch 66 is upwardly facing. In one embodiment, the notch is a substantially V-shaped notch, but other notch shapes are also contemplated. In one embodiment, both the first and second buoyant structures 60, 80 include a notch.

[0038] As shown in Figures 1-4, the support member 20 extends between the first and second buoyant structures 60, 80. In one embodiment, the support member 20 may include a central shaft 72, and in one embodiment, the support member 20 may include at least one support beam 74. As shown in Figures 1-4, in one embodiment, the support member 20 includes a chassis 70 which includes a plurality of support beams 74 coupled to opposing end plates 76. As shown, the first and second buoyant structures 60. 80 may be coupled to the end plates 76. In one embodiment, the chassis 70 includes three support beams 74, a central shaft 72, and a substantially Y-shaped end plate 76 positioned at each end 22, 24. As shown, the central shaft 72 may be coupled to the center of each of the Y-shaped end plates 76, and the ends of the three support beams 74 may be coupled to one of the three outwardly extending tines of the Y-shaped end plate 76 at each end of the device 100. As mentioned above, a turbine device having a shaftless designs is also contemplated. In this shaftless embodiment, the support member 20 may include a chassis 70 without a central shaft 72. For example, the support member 20 may include one or more support beams 74. It should be recognized that in a shaftless design, rotation of the foils 40 cause the shaftless support member 20 to rotate.

[0039] The present disclosure also contemplates a third buoyant structure 50. In one illustrative embodiment, a third buoyant structure 50 is positioned on the rotating support member 20. In one embodiment, the support member 20 includes a central shaft 72 and the third buoyant structure 50 is positioned along the central shaft 72. Applicant recognized that this additional buoyant structure may reduce the bending moment on the shaft 72, and it may also reduce the buoyancy requirements of the first and second buoyancy structures 60, 80. In one embodiment, the third buoyant structure 50 may include at least one, or a plurality of syntactic foam pods positioned within the central shaft 72. It is contemplated that the shaft 72 may be filled with foam. In another embodiment, the shaft may be sealed to create an inside buoyant air-filled structure 50.

[0040] Aspects of the present disclosure are directed to providing an improved multimegawatt utility scale turbine device 100 which may increase efficiency and maximize system reliability. In one embodiment, the device 100 is designed in a manner that reduces the overall complexity of the device, which may also make the device more economical. As set forth in more detail below, in one embodiment, the device 100 is designed to minimize drag of the components that are not contributing to power capture, thus reducing anchor sizing. In one embodiment, the device can be easily station-kept on the water surface to allow for maintenance operations on the surface. In one embodiment, the device 100 has a modular design of sub-components which may reduce complex maintenance operations both offshore and onshore. In one particular embodiment, the device 100 is a 2MW cross-flow turbine device with at least 20% less drag than a baseline design. In one embodiment, there is a plurality of devices, which may be positioned in an array in the ocean. Applicant recognized that there are advantages associated with using a combination of a fixed buoyant structure with a variable buoyant structure. First, the use of a fixed buoyant structure, such as a syntactic foam, reduces the reliance on air-filled tanks, which may be subject to corrosion and leaks. A fixed buoyant structure eliminates those potential issues and also makes it easier to form the first and second buoyant structures 60, 80 into a desirable overall shape.

[0041] As illustrated in Figures 1 -4, in one embodiment, the cross-flow turbine device 100 includes one or more anchors 90. In one embodiment, one or more mooring lines 92, 94 are provided to couple the first and second buoyant structures 60, 80, the support member 20 and plurality of foils 40, to the anchor 90. In one particular embodiment, a mooring line 92 is coupled to the first end 22 of the support member 20, and a mooring line 94 is coupled to the second end 24 of the support member 20.

[0042] The turbine device 100 may be positioned within the water column using a taut mooring system. In order to stay at a reasonable inclination angle and depth at high flow speeds, a significant amount of net buoyant force may be required. It may also be favorable to reduce drag as much as possible. In one embodiment, the number of anchors 90 is kept to a minimum to reduce costs and complexity7when deploying and retrieving the device 100. Although one anchor 90 is illustrated in Figures 1-4, in another embodiment, 2-anchor, 3- anchor. and 4-anchor configurations are also contemplated, as the present disclosure is not so limited.

[0043] In one embodiment, a single cross-flow turbine device 100 has a minimum of 264 m2of frontal area which is buoyed by syntactic foam and the device may be secured with as few anchors as possible. As mentioned above, in one embodiment, substantially disc-shaped buoyant structures 60, 80 are desirable as they are free to pitch about the shaft axis. This has numerous benefits regarding the stability of the device. Furthermore, as the device pitches, the frontal area does not change, and the drag does not change appreciably. The center of drag, the center of gravity, and center of buoyancy all exist at approximately the same point, even when pitching. This minimizes the existence of moments being generated around restraints by either buoyant or hydrodynamic forces. Also, the line of action of the reaction force in the anchor lines closely pass these centers (in 2D). This improves the anchor’s efficiency in restraining the device and reduces internal stresses in the chassis 70. The Y- shaped chassis is designed such that there is never a spar within capture area of the turbine, while still allowing good stiffness. There may be a slight offset of the center of mass downwards, providing dynamic stability' when the device is surfaced and less than an approximately 65° pitch when no anchors are attached. When surfaced, the generator, brake, and much of the device is exposed for maintenance. While there is a large amount of wetted surface area, the catamaran-like arrangement may allow for tow with good towing stability7. In one embodiment, the arrangement of the buoyancy and structure is such that there is a positive righting moment about the shaft axis until approximately a 70° pitch.

[0044] To retrieve and deploy the device, it may be desirable for the buoyancy to be reduced. Variable buoyancy ballast tanks may be used to reduce the buoyancy to a level that can be manipulated by small to medium-sized vessels (15 tons per anchor). These can be closed ballast tanks (subject to pressure variations) or open ballast tanks (where the tanks are open to the environment and thus no pressure requirements). As there would be no pressure differential w ith open ballast tanks, the tank wall thickness can be significantly reduced, thus also reducing the weight. In other w ords, the variable buoyancy portions 64, 84 of the first and second buoyant structures 60, 80 can be filled with seawater to reduce the net buoyancy making it more feasible for the device to be towed by a smaller vessel.

[0045] In one embodiment, the variable buoyancy portions 64, 84 are ballast tanks that are shaped to encourage w ater to pool relatively low in the tank, and for air to collect near the top of the device. This aids stability7by low ering the center of gravity w hen the device is surfaced, particularly as water is being pumped out.

[0046] As mentioned above, the present disclosure contemplates a variety of desirable shapes for the first and second buoyant structures 60, 80. Figure 5 illustrates another embodiment of a cross-flow turbine device 200 with substantially7disc-shaped first and second buoyant structures 260, 280. In many respects, the device 200 is substantially similar to the abovedescribed device 100 shown in Figures 1-4, and accordingly, like reference numbers have been used. In particular, as shown in Figure 5, the cross-flow turbine device 200 includes a support member 20, and a plurality of foils 40 that rotate in a single direction when exposed to fluid flow and the plurality7of foils 40 is joined to the support member 20 such that the rotating plurality of foils 40 cause the support member 20 to rotate. As shown, the turbine device 200 also includes a first buoyant structure 260 positioned at the first end of the support member 20, and a second buoyant structure 280 positioned at the second end of the support member 20. The first and second buoyant structures 260, 280 may be configured to provide enough buoyancy so that the turbine device 200 can be positioned at a desired location in the water column in the ocean. As shown in Figures 5, the first and second buoyant structures 260, 280 are substantially disc-shaped, however, unlike the embodiment shown in Figures 1 - 4, the first and second buoyant structures 260, 280 do not include a notch 66. The designs illustrated in either Figures 1-4 or Figure 5 may be desirable for having a low and constant center of gravity, a strong chassis design, a low frontal area, and only two anchors.

[0047] In one embodiment, the device 200 illustrated in Figure 5 has a frontal area of about 80 m2, and the frontal area remains unchanged when the device pitches to a 45° angle. The drag coefficient for these disc-shaped buoyant structures 260, 280 is 0.29 per DNV-RP-H103 standard from Modeling and Analysis of Marine Operations, and the drag @ 3.5m / s is 142,100.

[0048] It should be appreciated that Figures 1-5 illustrate two different embodiments which both include substantially disc-shaped buoyant structures. It should be recognized that other disc-shapes are also contemplated, as the disclosure is not so limited. For example, in one embodiment, the disc-shaped buoyant structure 60, 80, 260, 280 may include a plate-like disk with flat end walls, in another embodiment, the buoyant structure may have a biconcave disk structure, and in another embodiment, the buoyant structure may have a biconvex disk structure and / or a combination of any of the above. Furthermore, it should be appreciated that disk shapes where there is not an equal radius are also contemplated.

[0049] Figure 6 illustrates another embodiment of a cross-flow turbine device 300. In many respects, the turbine device 300 is substantially similar to the above-described turbine device 100 shown in Figures 1-4, and accordingly, like reference numbers have been used. In particular, as shown in Figure 6, the device 300 includes a support member 20, and a plurality of foils 40 that are joined to the support member 20 such that the rotating plurality of foils 40 cause the support member 20 to rotate. As shown, the device 300 also includes a first buoyant structure 360 positioned at the first end of the support member 20, and a second buoyant structure 380 positioned at the second end of the support member 20. As shown in Figures 6, the first and second buoyant structures 360, 380 are substantially capsule-shaped. In one embodiment, these side pod buoyant structures 360, 380 include four anchors connected to the four mooring lines 92, 92’, 94, 94’, where the mooring lines 92, 92’ are positioned at each end of the first substantially capsule-shaped buoyant structure 360, and mooring lines 94, 94’ are positioned at each end of the second substantially capsule-shaped buoyant structure 380. The design illustrated in Figure 6 may be desirable for being stable at the water surface, having a low frontal area, and being easily towed.

[0050] In one embodiment, the turbine device 300 illustrated in Figure 6 has a frontal area of about 39.28 m2, and the frontal area remains unchanged when the device anchor line 94, 92 moves to a 45° angle. The drag coefficient for these capsule-shaped buoyant structures 360, 380 is 0.29 for a static unpitched shape per DNV-RP-H103 standard from Modeling and Analysis of Marine Operations, and the drag @3.5 m / s is 69,771 Newtons.

[0051] Figure 7 illustrates yet another embodiment of a cross-flow turbine device 400. In many respects, the turbine device 400 is substantially similar to the above-described turbine device 300 shown in Figures 6, and accordingly, like reference numbers have been used. As shown, the device 400 includes a first buoyant structure 460 positioned at the first end of the support member 20, and a second buoyant structure 480 positioned at the second end of the support member 20, and the first and second buoyant structures 460, 480 are substantially capsule-shaped. This embodiment further includes a ballast tank 410 which is rigidly coupled to the first and second buoyant structure 460, 480 by lower support beams 402, 404. As shown, the ballast tank 410 extends below the foils 40 to provide a righting moment to the device 400. In one embodiment, two anchors are provided. The design illustrated in Figure 7 may be desirable for being stable at the water surface and for having only two anchors.

[0052] In one embodiment, the device 400 illustrated in Figure 7 has a frontal area of about 172.48 m2, and the frontal area changes to 121.6 m2at a 45° angle. The drag coefficient for these capsule-shaped buoyant structures 460, 480 is 1 per DNV-RP-H103 standard from Modeling and Analysis of Marine Operations, and the drag @3.5m / s is 1,053,500 Newtons, and 741 ,125 Newtons at a 45° angle. Figure 8 illustrates another embodiment of a cross-flow turbine device 500 which is substantially similar to the above-described devices 300, 400 shown in Figures 6-7, and accordingly, like reference numbers have been used. As shown, the turbine device 500 includes a first buoyant structure 560 positioned at the first end of the support member 20, and a second buoyant structure 580 positioned at the second end of the support member 20, and the first and second buoyant structures 560, 580 are substantially capsule-shaped with a front end of the capsule having a tapered and / or conical end which provides extra buoyancy to provide a righting moment to the device 500. In one embodiment, two anchors are provided. The design illustrated in Figure 8 may be desirable for being stable at the water surface, easily towed, and for having only two anchors.

[0053] In one embodiment, the device 500 illustrated in Figure 8 has a frontal area of about 150 m2, and the frontal area changes to 106 m2at a 45° device pitch angle. The drag coefficient for these capsule-shaped buoyant structures 560, 580 is 1 per DNV-RP-H103 standard from Modeling and Analysis of Marine Operations, and the drag @3.5m / s is 918,750 Newtons, and 649,250 Newtons at a 45° device pitch angle.

[0054] Figures 9A-9C are perspective views of cross-flow turbine devices 100 illustrating alternative anchoring arrangements. In particular, the device 100 shown in Figure 9A includes Y-shaped mooring lines 92, 94 which are each coupled to an anchor (not shown). In Figure 9B, the device 100 includes a Y-shaped mooring line 94 with two additional mooring lines 92, 92’ providing three spaced apart locations coupled to an anchor on the ocean floor (not shown). Finally, Figure 9C illustrates a device 100 including mooring lines 92, 94 which provide four spaced apart locations coupled to an anchor. As described above, a variety of different mooring line and anchor configurations may be provided.

[0055] One of ordinary skill in the art will appreciate that the term “device” may be used to reference the full physical system floating in the water. Furthermore, the term “turbine”, may be the specific cross-flow turbine, which is a component of the device. Finally, the term "power system” may be the device integrated into a system that delivers power to the grid.

[0056] One of ordinary skill in the art will appreciate that the device may include additional conventional turbine sub-components, such as, but not limited to a power-take-off (PTO), a bearing system, and other power generation equipment. These sub-components may be designed to optimize their effect on the overall system weight, efficiency, and assembly. The PTO may include all of the components required to transmit the mechanical power of the turbine to the generation of power in the generator before transmission to shore. For example, the PTO may include the generator and gearbox, locating and non-locating bearing set, mechanical braking system, shaft coupling subcomponents, and sealing components. It should be appreciated that these sub-components may be designed to minimize the device’s frontal area to decrease the drag on the structure and thus the demands of the anchoring system. Various types of electrical generators may be employed as the disclosure is not limited in this respect. Permanent magnet generators (PMGs) and electrically excited synchronous generators (EESGs) are two types of generators which may be used. Furthermore, either direct drive or multi-stage generators may be used. In one particular embodiment, a radial flux permanent magnet generator is provided, and in another embodiment, a magnetic pseudo-direct drive (PDD) generator is provided which allows for a step up of rotation speed without the need for the many rotating parts of a conventional gearbox.

[0057] Although several embodiments of the present invention have been described and illustrated herein, those of ordinary skill in the art will readily envision a variety of other means and / or structures for performing the functions and / or obtaining the results and / or one or more of the advantages described herein, and each of such variations and / or modifications is deemed to be within the scope of the present invention. Those skilled in the art will recognize or be able to ascertain using no more than routine experimentation, many equivalents to the specific embodiments of the invention described herein. It is, therefore, to be understood that the foregoing embodiments are presented by way of example only and that, within the scope of the appended claims and equivalents thereto; the invention may be practiced otherwise than as specifically described and claimed. The present invention is directed to each individual feature, system, article, material, and / or method described herein. In addition, any combination of two or more such features, systems, articles, materials, and / or methods, if such features, systems, articles, materials, and / or methods are not mutually inconsistent, is included within the scope of the present invention. All definitions, as defined and used herein, should be understood to control over dictionary definitions, definitions in documents incorporated by reference, and / or ordinary meanings of the defined terms.

[0058] The indefinite articles “a” and “an,” as used herein in the specification and in the claims, unless clearly indicated to the contrary, should be understood to mean “at least one.” The phrase “and / or,” as used herein in the specification and in the claims, should be understood to mean “either or both” of the elements so conjoined, i.e., elements that are conjunctively present in some cases and disjunctively present in other cases. Other elements may optionally be present other than the elements specifically identified by the “and / or” clause, whether related or unrelated to those elements specifically identified, unless clearly indicated to the contrary.

[0059] All references, patents and patent applications and publications that are cited or referred to in this application are incorporated in their entirety herein by reference.

[0060] What is claimed is:

Claims

Claims1. A submersible cross-flow turbine device for generating electricity from ocean or tidal currents, the device comprising: a support member having a first end and a second end; a plurality of foils that rotate in a single direction when exposed to fluid flow, wherein the plurality of foils is joined to the support member such that the rotating plurality’ of foils cause the support member to rotate; a first buoyant structure positioned at the first end of the support member; and a second buoyant structure positioned at the second end of the support member.

2. The submersible cross-flow turbine device of claim 1, wherein the first buoyant structure includes a fixed buoyancy portion and a variable buoyancy portion.

3. The submersible cross-flow turbine device of claim 1. wherein the first buoyant structure is substantially disk-shaped.

4. The submersible cross-flow turbine device of claim 1, wherein the first buoyant structure is substantially capsule-shaped.

5. The submersible cross-flow turbine device of claim 3, wherein the first buoyant structure includes a fixed buoyancy portion located on an outside portion of the first buoyant substantially disk-shaped structure and a variable buoyancy portion located on an inside portion of the first buoyant substantially disk-shaped structure.

6. The submersible cross-flow turbine device of claim 3, wherein the first buoyant structure includes a notch.

7. The submersible cross-flow turbine device of claim 2, wherein the variable buoyancy portion includes a ballast tank which can be filled or emptied with water to adjust the overallbuoyancy of the cross-flow turbine to position the cross-flow turbine at a desired water column location.

8. The submersible cross-flow turbine device of claim 2, wherein the second buoyant structure includes a fixed buoyancy portion and a variable buoyancy portion.

9. The submersible cross-flow turbine device of claim 3, wherein the second buoyant structure is substantially disk-shaped.

10. The submersible cross-flow turbine device of claim 5. wherein the second buoyant structure is substantially disk-shaped; and wherein the second buoyant structure includes a fixed buoyancy portion located on an outside portion of the second buoyant substantially disk-shaped structure and a variable buoyancy portion located on an inside portion of the second buoyant substantially diskshaped structure.

11. The submersible cross-flow turbine device of claim 9, wherein the second buoyant structure includes a notch.

12. The submersible cross-flow turbine device of claim 1, wherein the plurality of foils includes at least one helical foil.

13. The submersible cross-flow turbine device of claim 1. further comprising at least one strut coupling the plurality of foils to the support member.

14. The submersible cross-flow turbine device of claim 1, wherein the support member includes a chassis extending from the first buoyant structure to the second buoyant structure.

15. The submersible cross-flow turbine device of claim 1 , wherein the support member includes a central shaft.

16. The submersible cross-flow turbine device of claim 15, further comprising a third buoyant structure positioned along the central shaft.

17. The submersible cross-flow turbine device of claim 15 in combination with a generator coupled to the central shaft, wherein the generator is configured to convert rotation of the central shaft into electricity.

18. A submersible cross-flow turbine device for generating electricity from ocean or tidal currents, the device comprising: a central shaft having a first end and a second end; a plurality of foils that rotate in a single direction when exposed to fluid flow, wherein the plurality of foils is joined to the central shaft such that the rotating plurality of foils cause the shaft to rotate; a first substantially disk-shaped buoyant structure positioned at the first end of the central shaft; a second substantially disk-shaped buoyant structure positioned at the second end of the central shaft, and wherein both the first buoyant structure and the second buoyant structure includes a fixed buoyancy portion and a variable buoyancy portion, wherein the buoyancy of the variable buoyancy portions can be adjusted to alter the overall buoyancy of the cross-flow turbine to position the cross-flow turbine at a desired water column location.

19. The submersible cross-flow turbine device of claim 18, wherein the both the first and second substantially disk-shaped buoyant structures include a notch.

20. The submersible cross-flow turbine device of claim 19, wherein the fixed buoyancy portions of the first and second buoyant structures are located on an outside portion of the substantially disk-shaped first and second buoyant structures, and the variable buoyancyportions of the first and second buoyant structures are located on an inside portion of the substantially disk-shaped first and second buoyant structures.

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