WO2018039409A1 - Water turbine with torque compensation and adjustable components for shipping and deployment - Google Patents

Abstract

A platform for extracting energy from flowing fluid is provided. The platform includes: first and second lateral side members, the first lateral side member having an internal cavity; a fluid turbine disposed between and below the lateral side members; a support connecting each side member to the turbine; and a pump adapted to change buoyancy of the first lateral side member by pumping fluid from an external fluid environment into or out of the first lateral side member. Changes in buoyancy of the first lateral side member offsets torque from rotation of the fluid turbine.

Description

WATER TURBINE WITH TORQUE COMPENSATION

AND ADJUSTABLE COMPONENTS FOR SHIPPING AND DEPLOYMENT

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] The instant application claims priority to U.S. Patent Application 62/378,794 entitled WATER TURBINE WITH TORQUE COMPENSATION AND ADJUSTABLE COMPONENTS FOR SHIPPING AND DEPLOYMENT filed August 24, 2016. The instant application also relates to U.S. Provisional Application 62/333,983, filed May 10, 2016 entitled FLOATING ENERGY GENERATING PLATFORM WITH HORIZONTAL LIFT. The contents of the foregoing are expressly incorporated by reference herein in their entireties.

FIELD OF THE INVENTION

[0002] The various embodiments described herein relate generally to water energy capture devices. More specifically, various embodiments of the present invention relate to water energy capture devices that can compensate for torque generated by a submerged turbine. Various embodiments also relate to water energy capture devices that can collapse into a shipping container and then deploy to full operational size.

BACKGROUND

[0003] The generation of electricity from water today predominantly uses impoundments, such as dams.

[0004] To convert water currents into electricity without impoundments, in-stream energy conversion devices are placed in a flowing stream. According to the Electric Power Research Institute, such in-stream electricity generation without using impoundments remains a largely untapped potential. See, e.g., "North American Ocean Energy Status," Electric Power Research Institute, March 2007. This report states that the world's first marine renewable energy system of significant size to be installed in a genuinely offshore location was the Marine Current Turbine (MCT) 300 kw experimental SeaFlow unit installed off the coast of Devon, UK in May 2003. The MCT SeaFlow unit used a rotating, axial-flow turbine using hydrodynamic, generally planar blades as working members. (The term "working member" here refers to one or more members having a surface that functions to react with a working fluid, such as water, such that movement of a working fluid causes movement of the working member.) The report discusses other in-stream projects that use axial-flow turbines with generally planar blades. The Verdant Power 5.5 axial flow turbines were installed in the East River of New York beginning in December 2006. The Canadian Race Rocks British Columbia Tidal Project delivered electricity for the first time in December 2006.

[0005] Many prior art water generation in stream devices rely on partially or fully submerged elongated turbines with a helicoid working member (similar to screw threads). The turbine shapes are known to include cylinders and prolate casings. Water flow over the turbines interacts with the working member, causing the turbine to rotate. This rotation is transferred to an electrical generator that generates electricity.

[0006] Rotation of the above noted elongated turbine generates a torque that will tend to bias the turbine out of position, which can impact both its efficiency and stability of any supporting structure. To compensate, turbines are often provided in pairs, with each turbine in the pair has an opposite direction of the helicoid working member. One turbine will thus rotate clockwise while the other turbine rotates counterclockwise. The torque of each turbine offsets, thus neutralizing the tendency of the pair to move. A non-limiting example of such a configuration of paired turbines is shown in U.S. Patent 8,710,688, the contents of which are expressly incorporated by reference in its entirety.

SUMMARY OF THE INVENTION

[0007] It is accordingly an object of at least some embodiments of the invention to provide a water turbine platform that can compensate for the torque of a water turbine without requiring an offsetting pair of water turbines.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Various embodiments in accordance with the present disclosure will be described with reference to the drawings, in which:

[0009] Fig. 1 illustrates a perspective view of a platform according to an embodiment of the invention.

[0010] Fig. 2 illustrates a side view of the platform of Fig. 1.

[0011] Fig. 3 illustrates a top view of the platform of Fig. 1.

[0012] Fig. 4 illustrates a front view of the platform of Fig. 1.

[0013] Fig. 5 illustrates a rear view of the platform of Fig. 1.

[0014] Fig. 6 illustrates a rear perspective view of the platform of Fig. 1.

[0015] Fig. 7 illustrates a front view of the platform of Fig. 1 under influence of uncompensated torque from rotation of the platform' s turbine. [0016] Fig. 8 illustrates a block figure of a turbine with adjustable buoyancy according to an embodiment of the invention.

[0017] Fig. 9 illustrates a perspective view of a platform according to an embodiment of the invention.

[0018] Fig. 10 illustrates a side view of the platform of Fig. 9.

[0019] Fig. 11 illustrates a rear view of the platform of Fig. 9.

[0020] Fig. 12 illustrates a front view of the platform of Fig. 9.

[0021] Fig. 13 illustrates a front view of the platform of Fig. 9 under influence of torque from rotation of the platform' s turbine.

[0022] Figs. 14-16 are perspective, side and front views of another embodiment of a platform.

[0023] Figs. 17 and 18 are transparent perspective and front views of another embodiment of a platform of Fig. 14 within a shipping container.

[0024] Fig. 19 is a perspective view of a mobile carrier of a platform according to an embodiment of the invention.

[0025] Figs. 20-22 are perspective, side and front views of another embodiment of a platform in an array.

[0026] Fig. 23 is a perspective view of another embodiment of a platform in an array.

[0027] Fig. 24 is a perspective view of a platform according to another embodiment of the invention.

[0028] Fig. 25 is a perspective view of another embodiment of a platform in an array.

[0029] Figs. 26A-C are front views of another embodiment of a platform in which the working member is assembled.

[0030] Figs. 27A-D are side views of another embodiment of a platform in which the working member is assembled.

DETAILED DESCRIPTION

[0031] In the following description, various embodiments will be illustrated by way of example and not by way of limitation in the figures of the accompanying drawings.

References to various embodiments in this disclosure are not necessarily to the same embodiment, and such references mean at least one. While specific implementations and other details are discussed, it is to be understood that this is done for illustrative purposes only. A person skilled in the relevant art will recognize that other components and configurations may be used without departing from the scope and spirit of the claimed subject matter.

[0032] Several definitions that apply throughout this disclosure will now be presented. The term "substantially" is defined to be essentially conforming to the particular dimension, shape, or other feature that the term modifies, such that the component need not be exact. For example, "substantially cylindrical" means that the object resembles a cylinder, but can have one or more deviations from a true cylinder. The term "comprising" when utilized, means "including, but not necessarily limited to"; it specifically indicates open-ended inclusion or membership in the so-described combination, group, series and the like. The term "a" means "one or more" unless the context clearly indicates a single element and expressly excludes multiple elements. The term "connect," "connecting" or the like refers to direct and indirect connections between described points, and allows for the presence of other intervening components. "First," "second," third," etc. are labels to differentiate between components with like names, and does not imply any number or sequence.

[0033] As used herein, the term "front", "rear", "left," "right," "top" and "bottom" or other terms of direction, orientation, and/or relative position are used for explanation and convenience to refer to certain features of this disclosure. However, these terms are not absolute, and should not be construed as limiting this disclosure.

[0034] Shapes as described herein are not considered absolute. As is known in the art, surfaces often have waves, protrusions, holes, recess, etc. to provide rigidity, strength and functionality. All recitations of shape herein are to be considered modified by "substantially" regardless of whether expressly stated in the disclosure or claims, and specifically accounts for variations in the art as noted above.

[0035] Figs. 1-6 illustrate various views of a platform 100 for generating electricity from flowing fluid, such as water (water is referred to herein for simplicity of description, although the invention is not limited to any particular fluid flow). For purposes of description, the front end 120 of the platform 100 may be referred to as the "forward" end, while the opposite side (best seen in Fig. 3) may be referred to as the "aft" end. As viewed from the forward end looking aft (Fig. 3), the left side of the platform 100 may be referred to as the "port" side, while the right side may be referred to as the "starboard" side.

[0036] Platform 100 includes a frame having a starboard longitudinal side member 104 running forward and aft along the port side of platform 100 and a port longitudinal side member 106 running forward and aft along the port side of platform 100. Between and below side members 104 and 106 is a hydro turbine 108. Hydro turbine 108 may be any type of water energy extraction device, but is preferably an elongated structure that extends from the fore to aft of platform 100 in parallel with side members 104 and 106. A walkway (not shown in Fig. 1) may be supported by one or both of the lateral side members 104, 106 to support human occupants 900.

[0037] Side members 104 and 106 preferably provide a substantially majority of the buoyancy needed to keep the platform 100 afloat, although some buoyancy may be provided by other sources, including turbine 108 itself (discussed below). Under balanced conditions, the waterline relative to platform 100 is shown generally at 202.

[0038] Hydro turbine 108 preferably includes an internal shaft 116 (either part of the turbine and/or a mounting for the turbine 108), and a helicoid working member 110 coiling around a casing 112 (which may be multiple overlapping helicoids). The casing 112 provides structural support for turbine 108, and the working member 110 engages the water flow to rotate turbine 108. None-limiting examples of casing shapes include cylindrical, prolate, partially prolate, and combinations thereof.

[0039] Rotation of turbine 108 drives electrical generating components. Figs. 1-6 show a non- limited example of such components at the aft portion of platform 100, in the form of a sprocket 118 (which may have internal blades to also capture water flow), cable 122, a second sprocket 124, a shaft 126 and a generator 128. However, the invention is not limited to the manner in which electricity is generated by rotation of turbine 108, and other methodologies could be used.

[0040] A network of cross beams 134 and 136 connect the lateral side members 104 and 106 together. The network can be laid out in a manner as known in the art, for which the network as shown in the figures is a non- limiting example. The invention is not limited to any particular network, or even connection methodology. By way of example, the connections could be consistent with Applicants' US Provisional Patent FLOATING

ENERGY GENERATING PLATFORM WITH HORIZONTAL LIFT noted above. A mooring line 140 may be attached to cross beams 134 to anchor platform 100 to some external fixed structure (not shown).

[0041] A forward support 138 extends downward and rearward from the network of cross beams 134 to the front of turbine 108. A rear support 140 extends from the network of cross beams 136 to the rear of turbine 108.

[0042] The downward and rearward lie of forward support 138. Support 138 may form an angle with turbine 108. The angle may serve as a debris deflector, in that debris encountering the forward support 138 will under water flow tend to move along that angle downward in the water to beneath case 112. The motion of the working member 110 will further create a water flow that tends to direct debris below the entire turbine 108, flowing beneath and past platform 100 without becoming entangled or otherwise damaging the platform components. The overall fluid flow pathway is shown in Fig. 2 generally by 142. This differs from a perpendicular support, which would not direct debris below the platform, and for which instead such debris would tend to entangle a perpendicular forward support, turbine 108 and other components in the water pathway (the shape of turbine 108 may provide some limited deflection capability, but not as much as in combination with the angle of support 138).

[0043] The angle of forward support 138 relative to the axis of turbine 108 is preferably between about 45-75 degrees, particularly 50-70 degrees, and optimally about 60 degrees. Larger angles are viable, but will tend to have lesser impact on debris deflection as there will not be enough linear path to allow the debris to submerge below platform 100. Smaller angles are also viable, although they would require added length to the first support and side members 104 and 106 for which at some point the incremental improvement of the angle may be outweighed by the supporting structure needed for that angle, although this does not limit the scope of the invention.

[0044] Rear support 140 preferably has a cutting tool 160, such as a sharp edge or a chain saw like device. This will cut incoming debris into smaller pieces that has less of chance of becoming entangled or damaging the downstream components such as sprocket 118.

[0045] Referring now to Figs. 4 and 7, when floating in flowing water, rotation of turbine 108 will create a corresponding torque in a direction tangential to the direction of rotation. For example, in the embodiment of Fig. 1-6 working member 110 is a so-called right-handed spiral, and from the front perspective of Figs. 4 and 7 will rotate counterclockwise as shown at 702. This counterclockwise rotation in turn will in turn generate a starboard-directed torque 704. Absent compensation, this torque 704 rolls platform 100 from the rest position in Fig. 4 to a pitched position in Fig. 7.

[0046] To offset the platform pitch in Fig. 7 and substantially maintain the balanced position in Fig. 4, lateral side members 104 and/or 106 have an adjustable buoyancy, and specifically platform 100 can add water from the surrounding environment to an interior of lateral side member 104 to increase its weight compared to lateral side member 106. In the absence of torque 704, this weight/buoyancy imbalance would cause platform 100 to shift to port in the opposite direction of Fig. 7. In the presence of torque 704, an appropriate amount of additional weight on lateral side member 104 will offset that pitch from torque 704, resulting in a substantially balanced platform as shown in Fig. 4. However, the invention is not so limited, and less or more than complete offset that does not result in substantial balance may also be used.

[0047] Referring now to Fig. 8, a lateral side member 802 with adjustable buoyancy is shown. Side member 802 may be either side member 104 or 106 in platform 100. Side member 802 has an interior cavity 804 in fluid communication with a pump 806, which in turn is in fluid communication with the exterior water that the side member 802 floats on in the surrounding environment. Pump 806 is operated by a control 808, and can pump external water into cavity 804 to decrease buoyancy/ increase weight, or pump water out of cavity 804 to increase buoyancy/decrease weight. Pump 806 may be a single pump that pumps fluid both ways, or different pumps responsible for intake/outake of fluid.

[0048] One or more sensor sensors 810 on the platform 100 may provide information to control 808 for decision-making. One type of sensor would be a level or tilt sensor that detects roll of platform 100. Another type of sensor is a speed of rotation sensor that indicates how fast turbine 108 is rotating. Yet another type of sensor is a speed of water passing in the area of platform 100. The invention is not limited to any particular type of sensor or collection of sensors.

[0049] Control 808 may be manual and/or automatic. A non- limiting example of a manual implementation would be a switch that controls the direction (fill, empty) of the pump and/or the rate of water flow, for which a human operator manually activates the switch to stabilize platform 100. Data from sensors 810, if present, may provide direct sensor readouts or computer processed computer readouts that provide information for a human operator to make informed decisions on how to control the switch.

[0050] A non- limiting example of an automatic solution would be computer control that receives data from sensors 810 and automatically adjusts the buoyancy of side member 802 to compensate. By way of non- limiting example, in the case of a tilt sensor the computer could respond to a roll of platform 100 by pumping water into/out of cavity 804, and deactivating pump 804 when roll abates. Another non-limiting example would be based on speed of the rotation of turbine 108 and/or the water flow, determining how much offset is needed (e.g., table, real time calculations) and adjusting the buoyancy as necessary.

[0051] Combinations of manual and/or automatic options may thus be used as controller 808. The invention is not limited to the methodology by which the need for offsetting buoyancy is determined and/or controlled. [0052] Changes in the rate of water flow will change the rotating speed of turbine 108. Thus, just as buoyancy was decreased to prevent pitch of platform 100 in response to an increase of torque, so too can buoyancy can be increased to compensate for a decrease in torque.

[0053] In the above embodiments, the side member 104 had adjustable buoyancy to compensate for the right-hand spiral of working member 110, and side member 106 need not have an adjustable buoyancy. However, the invention is not so limited. Side member 106 could have an adjustable buoyancy and operate in the reverse manner of side member 104, i.e., increase buoyancy/decrease weight. Both side members 104 and 106 could have adjustable buoyancy and work collectively. The invention is not limited to which side members adjust buoyancy and/or the direction of spin of turbine 108.

[0054] Similarly, the embodiments may be symmetrical in that a left-hand spiral of working member 110 would result in a symmetrical implementation of the above

embodiments.

[0055] Referring now to Figs. 9-13, another embodiment of a platform 900 is shown. Platform 900 is similar to platform 100, in that it includes hydro turbine 108 and similar electrical generation options; like reference designators in the figures denote like elements. Where platform 100 had two buoyant side members, platform 900 uses only a single buoyant support member 904 that supports turbine 108 via a rear support 940. No forward support is shown, although the invention is not so limited and a forward support such as in Figs. 1-6 could also be provided.

[0056] Referring now to Figs. 12 and 13, hydro turbine 108 has a left-handed spiral working member 110. Because of this orientation, water flow over hydro turbine 108 will induce clockwise rotation 902 and corresponding port side torque 903. The torque will bias platform 900 from the position in Fig. 12 to Fig. 13, with turbine 108 moving toward water line 202 and support member 904 rotating to the starboard side.

[0057] Hydro turbine 108 is significantly heavier and less buoyant than support member 902. When torque 903 biases hydro turbine 108 upward past the water line 202, that bias would tend to push buoyant support member 904 down below water line 202. The natural buoyancy of support member 904 will resist that submersion, such that the buoyancy of support member 904 creates its own upward bias counter to the downward bias of torque 903. When the two biases match, platform 900 will reach a state of equilibrium and tend to hold the corresponding position under steady water flow conditions. [0058] If the water flow abates, the loss of torque 903 will remove the upward bias on hydro turbine 108. The weight of water turbine 108 will cause it to submerge, returning platform 900 to the position of Fig. 12.

[0059] Similarly, the embodiments are symmetrical in that a right-hand spiral of working member 110 would result in a symmetrical implementation of the above embodiment.

[0060] Referring now to Figs. 14-16, another embodiment of the invention is shown. A platform 1400 includes a frame having a port longitudinal side member 1404 running forward and aft along the port side of platform 1400 and a starboard longitudinal side member 1406 running forward and aft along the port side of platform 1400. Either or both of side members 1404 and 1406 may have adjustable buoyancy as discussed herein, although the invention is not so limited and non-buoyant or fixed buoyancy side members may be used. A debris deflector 1438 may be provided and operates in a manner discussed in embodiments above.

[0061] Between and below side members 1404 and 1406 is a hydro turbine 1408. Hydro turbine 1408 may be any type of water energy extraction device, but is preferably an elongated structure that extends from the fore to aft of platform 100 in parallel with side members 1404 and 1406. A walkway 1409 may be supported by one or both of the lateral side members 1404, 1406 to support human occupants 900.

[0062] A series of adjustable supports 1420 extend from the later side members 1404, 1406 to turbine 1408. Four such adjustable supports are shown in Fig. 14 all extending vertically, but the invention is not so limited to four supports and/or vertical extension. Any number or angle of supports may be used. Adjustable supports 1420 may be electrically or mechanical adjustable as is known in the art (e.g., pneumatic pistons under mechanical or electrical control).

[0063] The adjustable nature of supports 1420 allows the overall vertical height of platform 1400 to be adjustable between a fully deployed position such as shown in Fig. 14, and a fully retracted position, in which the turbine 1408 tucks beneath the platform 900. These two positions preferably do not change the overall width or length of platform 1400.

[0064] The fully deployed position, and partially deployed positions, allows the turbine 1408 to rotate in response to water flow and platform 1400 to convert the rotation into electricity in a known manner.

[0065] The fully retracted position sets the vertical height of platform 1400 to something that will fit within a prevalent intermodal shipping container 1700 as shown in Figs 17 and 18. Such shipping containers have handful of universal sizes, with a typical height of 8.5 or 9.5 feet, 8 foot width and 20 or 40 foot length. Platform 1400 already preferably has a maximum width and length that fits within container 1700, although they may in theory also be adjustable such as discussed below.

[0066] The adjustable size of platform 1400 provides a "plug and play" capability that avoids any significant need for assembly or disassembly between the point of manufacture and deployment. By contraction to the retracted position, platform 1400 can be loaded into container 1700 in a fully assembled or near fully assembled state, shipped via container to the point of delivery, unloaded and either dropped directly into the water or placed on a transport 1900 for delivery to the water for deployment. Once deployed, platform 1400 floats in the retracted position, and the supports 1420 are extended to lower turbine 1408 to the desired depth. No significant assembly, other than perhaps attaching deflector 1438 and/or working member extensions (discussed below), is needed between the point of manufacture and the point of deployment.

[0067] It may be desirable for the platform to utilize a hydro turbine with an outermost diameter that is larger than can be accommodated within a shipping container. Referring now to Figs. 26A-C and Figs. 27A-D, a no n- limiting example of a platform 2600 with a hydro turbine 2608 having a spiral working member 2610 is shown, and may have other features or configurations as discussed herein. Hydro turbine 2608 is shown as having a diameter that would fit inside the shipping container 1700 designated to ship it, and is mountable inside shipping container 1700 in the manner discussed with respect to Figs. 17 and 18.

[0068] Platform 2600 includes several sectional working member extensions 2670. Extensions 2670 can be stored in shipping container 1700 for transport, such that the entire platform 2600 can be stored and shipped in a single shipping container. When the platform 2600 is unloaded, the extensions 2670 are mounted to the working member 2610 around at least a portion of its periphery. Mounting is via known connection methods such as welding or nuts/bolts, although the invention is not so limited and other methods of connection as known in the art may be used.

[0069] Figs. 26A and 27A show the platform 2600 without extensions 2670. Figs. 26B and 27B show the platform 2600 with half of the extensions 2670 mounted. Fig. 27C shows three quarters of the extensions 2670 mounted. Figs. 26D and 27D show all of the extensions 2670 mounted.

[0070] When the extensions 2670 are mounted, the combination of working member 2610 and extensions 2670 define a new working member 2672 that may have a larger diameter than could have been accommodated in the shipping container 1700. The assembly can then be placed in water and the turbine section lowered to the desired depth as discussed in other embodiments herein.

[0071] In the embodiment of Figs. 26 and 27, working member extensions 2670 are in 90 degree segments. However, these need not be the case, and any size may be used (although 180 degrees may be the maximum size for installation purposes).

[0072] In the embodiment of Figs. 26 and 27, working member extensions 2670 run along the entire length of working member 2610. However, this need not be the case, as extensions 2670 may only run along a portion (or non consecutive portions) of working member 2610.

[0073] The invention is not limited to the particular shapes shown in Figs. 26 and 27 for working member 2610 and/or extensions 2670. Preferably the only potential limiting factors is that working member 2610 will be narrow enough to fit within shipping container 1700, and the assembled combination of working member 2610 and extensions 2670 will define the desired shape of new working member 2672. Extensions 2670 may all be the same size and shape, although the invention is not so limited and different shapes may be used (e.g., smaller extensions near the ends of the working member to establish an overall prolate profile).

[0074] Working member extensions 2670 are preferably unitary formed components. However, the invention is not so limited, and each could be defined by a series of connected subcomponents. This may be useful if unitary working member extensions 2670 would be too large or heavy to easily mount or transport.

[0075] Fig. 19 shows a mobile support for transporting any platform as discussed herein.

[0076] Figs. 20-22 show how several platforms 2000 can be connected together in parallel to lie across a fluid flow, such as perpendicular to the flow of a river. Each platform 2000 can be connected to an adjacent platform by a frame 2002. The connection may be adjustable/pivotable to allow for a degree of platform to platform movement to account for waves on the surface of the water. In the alternative, the connection may be fixed such that no adjustment for movement is allowed beyond any degree of flex provided by the material components of frame 2002. The fixed connection provides an anti- torque feature in that any tendency of an individual turbine to lift out of the water as described herein will be countered by the weight of the entire array of connected platforms 2000.

[0077] A lateral pontoon 2004 may be fixedly or adjustably connected via a frame 2002 to a particular platform for additional stability; such pontoon may have an adjustable buoyancy as discussed herein, or have a fixed buoyancy. Pontoon 2004 as shown on one end of the array, but may be provided on the other side as well. Platform 2000 is shown as the exemplary platform for such connections, and differs from platform 1400 in that only a single adjustable support is provided at the front of platform 2000. However, the invention is not so limited, and other platform designs can be so configured in parallel.

[0078] Fig. 23 shows another embodiment of the invention in the form of a platform 2300. Platform 2300 is similar to platform 2000, save that a single floating pontoon 2302 is used instead of lateral side members; floating pontoon 2302 may be variable buoyancy or fixed buoyance as disclosed herein, adjustable buoyancy may be based on internal chambers on the left and/or right sides of the pontoon 2302 to balance as discussed above. Fig. 23 also shows how debris deflector 2038 is attachable to platform 2300, preferably after the platform is deployed in water and lowered to the desired depth.

[0079] Fig. 24 shows another embodiment of the invention in the form of a platform 2400. Platform 2400 is similar to the embodiment discussed with respect to Fig. 9, save that it includes a debris deflector 2438. Fig. 25 shows platform 2400 in a parallel array.

[0080] It is to be understood that the disclosed platforms are floating and the positions described herein are not expected to be stable and the movements are not precise. Water flow and surface conditions can change unexpectedly.

[0081] The specification and drawings are, accordingly, to be regarded in an illustrative rather than a restrictive sense. It will, however, be evident that various modifications and changes may be made thereunto without departing from the broader spirit and scope of the invention as set forth in the claims.

Claims

CLAIMS What is claimed is:

1. A platform for extracting energy from flowing fluid, comprising:

first and second lateral side members, the first lateral side member having an internal cavity;

a fluid turbine disposed between and below the lateral side members;

a support connecting each side member to the turbine; and

a pump adapted to change buoyancy of the first lateral side member by pumping fluid from an external fluid environment into or out of the first lateral side member;

wherein when placed in the fluid environment, rotation of the turbine induces a torque that biases the platform to roll in a first direction;

wherein adjustment of the buoyancy of the first lateral side member changes the weight distribution of the platform to bias the platform to roll in a second direction different from the first direction; and

wherein a change in the weight distribution offsets the torque bias to limit overall roll of the platform.