CROSS-REFERENCE TO RELATED APPLICATION

[0001] Pursuant to 35 U.S.C. § 119(e), this application claims the benefit of provisional U.S.

Patent Application No. 61/719,252, filed October 26, 2012, and entitled "Method and System for Harnessing Hydrokinetic Energy", which is hereby incorporated by reference in its entirety.

TECHNICAL FIELD

[0002] The present disclosure is directed at methods, systems, and techniques for harnessing hydrokinetic energy.

BACKGROUND [0003] Reliance on non-renewable fossil fuels for energy results in a number of problems.

One problem is climate change resulting from greenhouse gases that are discharged into the atmosphere when the fossil fuels are burned. Another problem is the escalating price of oil, which is the source of much of the world's fossil fuels. Renewable energy accordingly continues to be the subject of significant research and development efforts; one type of renewable energy is hydrokinetic energy, which is energy manifested in the form of moving water.

SUMMARY

[0004] According to one aspect, there is provided a method for harnessing hydrokinetic energy. The method comprises during a traction phase, orienting a hydrofoil in moving water to produce a lift force that moves the hydrofoil and applies tension to a tether connected to the hydrofoil; using the tension in the tether to perform work; and during a recovery phase, orienting the hydrofoil to reduce the lift force and reduce tension in the tether.

[0005] The tether may be extendable and performing work may comprise extending the tether during the traction phase and retracting the tether during the recovery phase.

[0006] The tether may be connected to a base floating in the water, which in turn may be connected to an anchor in the water via an extendable anchor line. In this aspect, performing work may comprise extending the anchor line during the traction phase and retracting it during the recovery phase.

[0007] Orienting the hydrofoil may comprise adjusting one or more of the angle of attack, pitch, roll, and yaw of the hydrofoil. [0008] The hydrokinetic energy harnessed using the tether may be stored.

[0009] Storing the hydrokinetic energy may comprise mechanically storing the hydrokinetic energy.

[0010] Storing the hydrokinetic energy may comprise converting the hydrokinetic energy to electricity and storing the electricity. [0011] The hydrokinetic energy that has been stored may be used to retract the tether during the recovery phase.

[0012] The hydrokinetic energy that has been harnessed may be converted into salable energy.

[0013] Converting the hydrokinetic energy that has been harnessed into salable energy may comprise generating electricity by operating an electrical generator using the hydrokinetic energy.

[0014] Orienting the hydrofoil to produce the lift force may comprise orienting the hydrofoil such that it has a non-zero crosscurrent velocity by adjusting the angle of attack of the hydrofoil to be non-zero relative to the direction of the velocity of the water. Orienting the hydrofoil may also comprise adjusting one or more of the pitch, yaw, and roll to maintain stability and enhance performance by using techniques such as limiting induced drag or stall.

[0015] After the recovery phase, additional traction and recovery phases may be performed.

For each of the additional traction phases the angle of attack of the hydrofoil may be adjusted such that the hydrofoil has a non-zero crosscurrent velocity while the tether is extending and the crosscurrent velocity of the hydrofoil during any one of the additional traction phases may be of an opposite direction than of the hydrofoil during an immediately preceding one of the traction phases.

[0016] The hydrofoil may be oriented such that during the traction phase the hydrofoil moves in a pattern selected from a group consisting of: a line, a circle, a figure eight, and an ellipse. [0017] Fins may extend from the hydrofoil, and the method may further comprise, during the recovery phase, adjusting the fins such that between 40% and 60% of the hydrofoil is out of the water. The fins may also control the depth of the hydrofoil such that it moves below the surface.

[0018] The method may also comprise receiving an indication that the level of the water or rate of flow of the water exceeds a flood threshold; and when the flood threshold is exceeded, reducing flow resistance by reducing the angle of attack of the hydrofoil.

[0019] The method may also comprise detecting a change in presence of debris; determining a risk score from the change; when the risk score exceeds a risk threshold, determining an avoidance maneuver to perform to cause the hydrofoil and tether to avoid the debris; and performing the avoidance maneuver.

[0020] Determining the risk score may comprise any one or more of using a Bayesian learning process; using blob detection; detecting non- water objects entering an operational area of the system and increasing the risk score when the non-water objects are detected; when the sensors detect the debris entering the operational area of the system, projecting the trajectory of the debris, determining whether the debris will impact the hydrofoil or the tether, and increasing the risk score when the debris will impact the hydrofoil or the tether.

[0021] The avoidance maneuver may comprise any one or more of a modified sweep pattern; sheltering the tether and hydrofoil from the debris; removing the hydrofoil from the water; and submerging the hydrofoil. [0022] According to another aspect, there is provided a system for harnessing hydrokinetic energy. The system comprises a hydrofoil; a tether connected to the hydrofoil; an actuation system mechanically or electrically coupled to the tether such that the tether is extendable and retractable; an energy transfer system mechanically coupled to the actuation system and operable to transfer the hydrokinetic energy harnessed using the tether; and a control system communicatively coupled to the actuation system. The control system comprises a processor; and a memory communicatively coupled to the processor and having encoded thereon statements and instructions to cause the processor to (1) during a traction phase, orient the hydrofoil in moving water to produce a lift force that moves the hydrofoil and extends the tether; and (2) during a recovery phase, orient the hydrofoil to reduce the lift force and retract the tether. [0023] The hydrofoil may comprise a foil body having top and bottom surfaces; a load mounting point on each of the top and bottom surfaces to which the load tether is connected; and a cambered surface extending between the top and bottom surfaces. Alternatively, the hydrofoil may comprise a foil body having top and bottom surfaces, a pair of load mounting points on the foil body to which the load tether is connected; and a cambered surface extending between the top and bottom surfaces.

[0024] The tether may be a load tether and the system may further comprise control tethers connected to the actuation system. The hydrofoil may accordingly comprise control tether points on opposite sides of the cambered surface to which the control tethers are connected. The tether may have integrated or attached communication cables.

[0025] The foil body may be ballasted such that the center of mass of the foil body is lower than the center of buoyancy of the foil body when the system is in use.

[0026] The chord of the foil body and the mean camber of the foil body may be identical.

[0027] The trailing edge of the foil body may comprise an adjustable rudder.

[0028] The foil body may comprise horizontal stabilizers extending from the cambered surface.

[0029] The foil body further may comprise horizontal stabilizers extending from and parallel to the top and bottom surfaces.

[0030] The hydrofoil may further comprise a tail spar having one end attached to the foil body and extending away from the trailing edge of the foil body; and one or more adjustable control surfaces attached to another end of the tail spar.

[0031] The hydrofoil may comprise a foil body having top and bottom surfaces; a load mounting point on the top surface to which the load tether is connected; and a cambered surface extending between the top and bottom surfaces.

[0032] The hydrofoil may comprise a foil body have top and bottom surfaces; a cambered surface extending between the top and bottom surfaces; a tail spar having one end attached to the foil body and extending away from the trailing edge of the foil body; horizontal and vertical control surfaces attached to another end of the tail spar; and independently adjustable control surfaces extending along the trailing edge of the foil body.

[0033] The independently adjustable control surfaces may comprise an upper control surface located on one side of the tail spar and a lower control surface located on another side of the tail spar.

[0034] The statements and instructions may further cause the processor to adjust the upper and lower control surfaces for roll control and to increase lift regardless of which side of the hydrofoil is used to generate lift.

[0035] The hydrofoil may further comprise an anti-rotation tail comprising a tail spar having one end attached to the foil body and extending away from the trailing edge of the foil body; a horizontal spar and a vertical control surface attached to another end of the tail spar, wherein the horizontal spar comprises two ends and is attached to the tail spar between its two ends; and an anti- rotation lift surface attached to each of the ends of the horizontal spar.

[0036] The hydrofoil may comprise a foil body having top and bottom surfaces; a cambered surface extending between the top and bottom surfaces of the foil body; a floating hull having top and bottom surfaces, the bottom surface of the floating hull attached to the top surface of the foil body; a load mounting point attached to the top surface of the floating hull to which the load tether is connected; and a rudder attached to the bottom surface of the floating hull between the tailing edge of the foil body and the tailing edge of the floating hull. [0037] The hydrofoil may further comprise an outrigger hull located on one side of the cambered surface and another outrigger hull located on another side of the cambered surface; and a bridging spar connected to the top surface of the floating hull and extending in a direction transverse to the mean camber of the foil body, the bridging spar comprising one end connected to one of the outrigger hulls and another end connected to the other of the outrigger hulls. [0038] The hydrofoil may comprise two foil bodies each comprising a top surface, a bottom surface, a cambered surface extending between the top and bottom surfaces, and an adjustable rudder at the trailing edge of the foil body; two floating hulls, one of which is attached to the top surface of each of the foil bodies; and a bridging spar connecting the two floating hulls such that the mean cambers of the foil bodies are parallel. [0039] The energy transfer system may be mechanically coupled to the actuation system.

[0040] The actuation system may comprise a load frame connected to the load tether; a traction actuator connected to the load frame to move the load frame in a traction direction; a recovery actuator connected to the load frame to move the load frame in a recovery direction; control actuators mounted to the load frame and connected to the control tethers; and lead-out sheaves over which extend the load and control tethers.

[0041] The control actuators may comprise a belt-drive actuator.

[0042] The actuation system may comprise a load frame connected to the load tether; an electrically powered actuator connected to the load frame operable to move the load frame in a traction and a recovery direction; control actuators mounted to the load frame and connected to the control tethers; and lead-out sheaves over which extend the load and control tethers.

[0043] The electrically powered actuator may comprise a linear motor.

[0044] The electrically powered actuator may comprise a rotary motor linearized by one of a winch, belt drive, and lead-screw. [0045] The actuation system may comprise a traction actuator and a recovery actuator each of which is connected to the load tether; and control actuators connected to the control tethers.

[0046] Each of the actuators may comprise a winch.

[0047] The actuation system may comprise a pivotable load arm; a traction actuator connected to the load arm to pivot the load arm in a traction direction; a recovery actuator connected to the load arm to move the load arm in a recovery direction; control actuators mounted to the load arm and connected to the control tethers; and sheaves mounted to the load arm over which extend the control tethers.

[0048] The actuation system may comprise a pivotable load arm connected to the load tether; a rotary motor connected to the load arm to pivotably move it; control actuators mounted on the load arm and connected to the control tethers and sheaves mounted to the load arm over which extend the control tethers. [0049] The actuation system may comprise a pivotable load arm connected to the load tether; a traction actuator connected to the load arm to pivot the load arm in a traction direction; a recovery actuator connected to the load arm to move the load arm in a recovery direction; pivotable control arms each of which is connected to one of the control tethers; and control actuators connected to the control arms to move each of the control arms about its pivot point.

[0050] The actuation system may comprise a pivotable load arm; a cam; a load bar connecting the cam to the load arm such that rotation of the cam results in pivoting of the load arm; control actuators mounted to the load arm and connected to the control tethers; and sheaves mounted to the load arm over which extend the control tethers. [0051] The actuation system may comprise a winch drum around which are wound the control tethers and the load tether; lead-out sheaves over which the control and load tethers extend; a load actuator connected to the winch drum to rotate the winch drum; control sheaves located between the winch drum and the lead-out sheaves over which the control tethers extend; and control actuators connected to the control sheaves such that actuation of the control sheaves extends or retracts the control tethers relative to the load tether.

[0052] The actuation system may comprise a frame; a hydraulic cylinder have a base and an opposing rod end, wherein the base is affixed to the frame; a linear slide affixed to the frame; a pulley attached to the rod end of the hydraulic cylinder attached to the linear slide such that its motion is constrained to be along the linear slide; and a tension line that passes over the pulley that is attached to the tether.

[0053] The actuation system may comprise a hydraulic traction actuator and a hydraulic recovery actuator each of which is connected to the load tether, and the energy transfer system may comprise an accumulator hydraulically coupled to the traction and recovery actuators; a hydraulic fluid reservoir hydraulically coupled to the traction and recovery actuators; a generator/motor hydraulically coupled to the traction and recovery actuators; and an electrical generator mechanically coupled to the generator/motor.

[0054] The electrical generator may comprise a DC generator, and the energy transfer system may further comprise a DC/ AC inverter electrically coupled to the DC generator; and a DC energy storage device electrically coupled between the DC generator and the DC/ AC inverter. [0055] The energy transfer system may be electrically coupled to the actuation system.

[0056] The actuation system may comprise a linear electric motor.

[0057] The system may further comprise an anchor driven into the bed of a watercourse and the actuation system may be secured to the anchor above water. [0058] The system may further comprise a collision avoidance system communicatively coupled to the actuation system and secured to the anchor, which comprises a collision avoidance processor; debris sensors communicatively coupled to the collision avoidance processor; and a memory communicatively coupled to the collision avoidance processor and having encoded thereon statements and instructions to cause the collision avoidance processor to perform a method comprising (i) determining whether the sensors detect change in presence of debris; (ii) determining a risk score from the change; (iii) when the risk score exceeds a risk threshold, determining an avoidance maneuver to perform to cause the hydrofoil and tether to avoid the debris; and (iv) performing the avoidance maneuver.

[0059] Determining the risk score may comprise any one or more of using a Bayesian learning process; using blob detection; detecting non- water objects entering an operational area of the system and increasing the risk score when the non-water objects are detected; when the sensors detect the debris entering the operational area of the system, projecting the trajectory of the debris, determining whether the debris will impact the hydrofoil or the tether, and increasing the risk score when the debris will impact the hydrofoil or the tether. [0060] The avoidance maneuver may comprise any one or more of a modified sweep pattern; sheltering the tether and hydrofoil from the debris; removing the hydrofoil from the water; and submerging the hydrofoil.

[0061] The system may further comprise a vertically translating positioner on which the actuation and energy transfer systems are mounted, the positioner operable to vertically translate the actuation and energy transfer systems to adjust an angle the tether makes with the surface of the water.

[0062] The system may further comprise a pivotable lead-out arm on which the actuation and energy transfer systems are mounted and a sheave positioned on the lead-out arm over which the tether extends, and pivoting the lead-out arm may adjust an angle the tether makes with the surface of the water.

[0063] The control system may be contained within the hydrofoil.

[0064] The control system may be outside of the hydrofoil. [0065] According to another embodiment, there is provided a hydrofoil, comprising a foil body have top and bottom surfaces; a cambered surface extending between the top and bottom surfaces; a tail spar having one end attached to the foil body and extending away from the trailing edge of the foil body; horizontal and vertical control surfaces attached to another end of the tail spar; and an upper control surface and a lower control surface extending along the trailing edge of the foil body, wherein the upper and lower control surfaces are independently adjustable and wherein the upper control surface is located on one side of the tail spar and the lower control surface located on another side of the tail spar.

[0066] The hydrofoil may further comprise a control system, located within the foil body, comprising a processor and a memory communicative with the processor having statements and instructions encoded thereon to cause the processor to control the upper and lower control surfaces.

[0067] According to another aspect, there is provided a system for harnessing hydrokinetic energy that comprises a hydrofoil; a tether connected to the hydrofoil; a floating base connected to the tether; an anchor line connected to the floating base; an actuation system mechanically coupled to the anchor line such that the anchor line is extendable and retractable; an energy transfer system mechanically coupled to the actuation system and operable to transfer the hydrokinetic energy harnessed using the anchor line; and a control system communicatively coupled to the actuation system. The control system comprises a processor; and a memory communicatively coupled to the processor and having encoded thereon statements and instructions to cause the processor to (1) during a traction phase, orient the hydrofoil in moving water to produce a lift force that moves the hydrofoil and applies tension to the tether and extends the anchor line; and (2) during a recovery phase, orient the hydrofoil to reduce the lift force and reduce tension in the tether, and retract the anchor line.

[0068] According to another aspect, there is provided a method for harnessing hydrokinetic energy, the method comprising placing a hydrofoil assembly in moving water; determining the angle of attack of the hydrofoil assembly relative to the water; and when the angle of attack differs from an optimal angle of attack at which the lift-to-drag ratio of the hydrofoil assembly is at a maximum, adjusting the angle of attack of the hydrofoil assembly to approach the optimal angle of attack. [0069] The hydrofoil assembly may comprise a hydrofoil and a tether attached to the hydrofoil.

[0070] Determining the angle of attack of the hydrofoil assembly may comprise using measurements obtained using an inertial motion unit affixed to the hydrofoil.

[0071] Determining the angle of attack of the hydrofoil assembly may comprise using measurements obtained using an acoustic long-baseline system.

[0072] Determining the angle of attack of the hydrofoil assembly may comprise using measurements obtained using a sonar system.

[0073] Determining the angle of attack of the hydrofoil comprises using an acoustic long- baseline system or a sonar system to obtain an initial position; resetting an integration constant of an inertial motion unit affixed to the hydrofoil based on the initial position; using the inertial measurement unit to obtain a differential position relative to the initial position; and determining the angle of attack of the hydrofoil from the initial and differential positions.

[0074] According to another aspect, there is provided a system for harnessing hydrokinetic energy, the system comprising a hydrofoil having control surfaces adjustable to control the angle of attack of the hydrofoil; a tether connected to the hydrofoil; an actuation system mechanically coupled to the tether such that the tether is extendable and retractable; an energy transfer system mechanically or electrically coupled to the actuation system and operable to transfer the hydrokinetic energy harnessed using the tether; a position determining system configured to measure position and velocity of the hydrofoil; a control system communicatively coupled to the actuation system and the position determining system, the control system comprising a processor; and a memory communicatively coupled to the processor and having encoded thereon statements and instructions to cause the processor to determine the angle of attack of the hydrofoil assembly relative to the water; and when the angle of attack differs from an optimal angle of attack at which the lift-to-drag ratio of the hydrofoil assembly is at a maximum, adjust the angle of attack of the hydrofoil assembly to approach the optimal angle of attack.

[0075] The control system may be contained within the hydrofoil.

[0076] The control system may be outside of the hydrofoil. [0077] The position determining system may comprise an inertial motion unit affixed to the hydrofoil.

[0078] The position determining system may comprise an acoustic long-baseline system.

[0079] The position determining system may comprise a sonar system.

[0080] The position determining system may comprise an inertial motion unit affixed to the hydrofoil; and an acoustic long-baseline system or a sonar system, and wherein the statements and instructions further cause the processor to obtain an initial position using the acoustic long-baseline or sonar systems; reset an integration constant of the inertial motion unit based on the initial position; use the inertial measurement unit to obtain a differential position relative to the initial position; and determine the angle of attack of the hydrofoil from the initial and differential positions.

[0081] According to another aspect, there is provided a control system for use in a system for harnessing hydrokinetic energy. The control system comprises a processor; and a memory communicatively coupled to the processor and having encoded thereon statements and instructions to cause the processor to perform any of the foregoing methods. [0082] According to another aspect, there is provided a non-transitory computer readable medium having encoded thereon statements and instructions to cause a processor to perform any of the foregoing methods.

[0083] This summary does not necessarily describe the entire scope of all aspects. Other aspects, features and advantages will be apparent to those of ordinary skill in the art upon review of the following description of specific embodiments.

BRIEF DESCRIPTION OF THE FIGURES [0084] In the accompanying drawings, which illustrate one or more exemplary embodiments:

[0085] FIGS. 1 through 3, 23, 24, 28, and 30 depict different embodiments of a system for harnessing hydrokinetic energy. [0086] FIG. 4 depicts an exemplary hydrofoil for use with the embodiments of the system of

FIGS. 1 through 3, 23, 24, 28, and 30.

[0087] FIG. 5 depicts an exemplary tether sheathed in a fairing for use with the embodiments of the system of FIGS. 1 through 3, 23, 24, 28, and 30.

[0088] FIG. 6 depicts an exemplary actuation system for use with the embodiments of the system of FIGS. 1 through 3, 23, 24, 28, and 30.

[0089] FIGS. 7 through 13 and 29 depict exemplary hydrofoils for use with the embodiments of the system of FIGS. 1 through 3, 23, 24, 28, and 30.

[0090] FIGS. 14 through 22 depict exemplary actuation systems for use with the embodiments of the system of FIGS. 1 through 3, 23, 24, 28, and 30. [0091] FIG. 25 depicts a collision avoidance system for use with embodiments of the system of FIGS. 1 through 3, 23, 24, 28, and 30.

[0092] FIG. 26 depicts a block diagram of the collision avoidance system of FIG. 25.

[0093] FIG. 27 depicts an exemplary method for operating the collision avoidance system of

FIG. 25. DETAILED DESCRIPTION

[0094] Directional terms such as "top," "bottom," "upwards," "downwards," "vertically," and "laterally" are used in the following description for the purpose of providing relative reference only, and are not intended to suggest any limitations on how any article is to be positioned during use, or to be mounted in an assembly or relative to an environment. Furthermore, use of the indefinite article to refer to an item refers to one or more of those items unless otherwise expressly noted. [0095] The embodiments described herein are directed at methods, systems, and techniques for harnessing hydrokinetic energy. The system includes a hydrofoil that is connected via one or more tethers to an actuation system. The actuation system directs motion of the hydrofoil as it is moved by water. The hydrokinetic energy of the moving water moves the hydrofoil, which applies tension to the one or more tethers; this transfers hydrokinetic energy to the system, which optionally can then convert it to a form of salable energy such as electricity.

[0096] Referring now to FIG. 1, there is shown one embodiment of a system 100 for harnessing hydrokinetic energy. The system 100 includes an anchor 101 that is located in a waterway and that is securely affixed to the bed of the waterway. In an alternative embodiment (not depicted), the anchor 101 is affixed to the shore. Affixed to the anchor 101 above the water surface is an enclosure 103 and affixed to the anchor 101 within the waterway is a collision avoidance system 500. Within the enclosure is an actuation system 200 (not shown in FIG. 1, but shown in FIG. 6) that controls movement of a load tether 105 and a pair of control tethers 106. The tethers 105,106 are attached to a hydrofoil 400 that is positioned in the waterway and moved by the current. As discussed in further detail below, the actuation system 200 converts hydrokinetic energy from the waterway harnessed via the hydrofoil 400 into mechanical energy. Also within the enclosure is an energy transfer system 300 (not shown in FIG. 1, but shown in FIGS. 23 and 24) that subsequently transfers hydrokinetic energy that has been harnessed to another system, such as to a device for mechanically storing energy such as an accumulator, a device for electrically storing energy such as a battery or a capacitor, or to a generator for generating salable energy such as electricity. When the mechanical energy is converted into salable energy such as electricity, the electricity may be conducted off the anchor 101 to shore via a cable 104. Also as discussed in more detail below, the collision avoidance system 500 communicates with the actuation system 200 to provide the actuation system 200 with sufficient information to position the hydrofoil 400 to avoid debris while harnessing hydrokinetic energy.

[0097] The system 100 harnesses hydrokinetic energy by alternating operating in a traction phase and in a recovery phase.

[0098] During the traction phase, one of the control tethers 106 is retracted which rotates the hydrofoil 400, increasing the angle of attack the hydrofoil 400 makes relative to the water velocity. The resultant hydrodynamic forces on the hydrofoil 400 cause the hydrofoil 400 to move transversely to the water velocity, and parallel to the water surface. The component of the hydrofoil's 400 velocity that is orthogonal to the velocity of the water is known as the crosscurrent velocity. The crosscurrent velocity will be approximately equal to the water velocity multiplied by the lift-to-drag ratio of the foil. The apparent-velocity is the vector summation of the water velocity and the crosscurrent velocity and is much larger in magnitude than the velocity of the water relative to the earth. This increased velocity causes the hydrofoil 400 to produce significantly more lift- force than would be possible if the hydrofoil 400 were stationary. The majority of this lift-force is transferred to the tethers 105,106.

[0099] The actuation system 200 allows the tethers 105,106 to be drawn out using the lift- force from the hydrofoil 400, when the hydrofoil has a non-zero crosscurrent velocity. This motion of the tethers 105,106, which are under a tension-force, and the motion of the portion of the actuation system 200 mechanically coupled to the tethers 105,106, are mechanical work. The mechanical power of this motion is the product of the tension-force and the speed at which they are drawn out. The mechanical energy extracted is the product of the tension-force and the distance the tethers were drawn out. The energy transfer system 300 transfers this mechanical energy away from the actuation system 200 for use elsewhere; for example, the energy transfer system 300 may convert the mechanical energy into electricity using a generator, or may transfer the mechanical energy to an accumulator for storage. Some of this energy is stored within the energy transfer system 300 and some is converted into electricity or other forms of salable energy.

[00100] The traction phase completes when the tethers have been drawn out a certain amount, as determined by a control system 110 (not shown in FIG. 1, but shown in FIGS. 23 and 24) communicatively coupled to the actuation system 200. Following completion of the traction phase, the recovery phase commences. During the recovery phase, the control tether 106 that was retracted during the traction phase is released. The release of the control tether 106 and the specific arrangement of the tethers 105,106, which is discussed in further detail below, cause the hydrodynamic forces to reduce the angle of attack of the hydrofoil 400. Reducing the angle of attack reduces the lift-force acting on the hydrofoil 400. The actuation system 200 then applies a force to the tethers 105,106, drawing them back by approximately the distance the tethers 105,106 were extended during the traction phase. The energy required to draw in the tethers during the recovery phase is much less than the energy extracted during the traction phase because the distance the tethers move is the same in both phases, but the tension-force during the recovery phase is much smaller than the tension-force during the traction phase. The energy required to draw in the tethers during the recovery phase is provided by the energy that was stored within the energy transfer system 300 during the traction phase. The excess energy stored within the energy transfer system 300 during the traction phase that is not used to retract the tethers 105,106, is used to produce electricity or other forms of salable energy. [00101] The recovery phase completes when the tethers 105,106 have been drawn in by approximately the amount they were drawn out during the traction phase. After the completion of the recovery phase, the traction phase begins again with the hydrofoil 400 moving transversely to the water velocity, but in the opposite direction as the previous traction phase, such that it returns to the original side of the waterway. [00102] Many bodies of moving water are natural rivers, streams, channels or straits (natural waterways). Debris such as logs can be relatively common in natural waterways and this debris can cause damage to structures and devices placed within the waterway. The damage caused by debris can make operation of in- water devices relatively expensive. The interaction of in-water devices with marine wildlife may have negative environmental or ecological consequences. The interaction of in-water devices with watercraft or other anthropogenic users of the waterway could cause safety concerns. It is advantageous for the system 100 to have a mechanism that avoids collisions and interactions with debris, marine wildlife, watercraft and humans. This mechanism is termed the collision avoidance system 500.

[00103] The collision avoidance system 500 uses any one or more of acoustic, electromagnet, and optical sensors to detect the presence of debris, marine-wildlife, watercraft or humans (each an "intruding entity") within the system's 100 operational area. The control system 110 then uses characteristics of the sensor data such as return strength, shape and speed to identify the entity. Extrapolating the entity's path from observed data, the collision avoidance system 500 determines if the entity will likely come in contact with the hydrofoil 400 or tethers 105,106. If a collision is probable, the collision avoidance system initiates an avoidance maneuver. Avoidance maneuvers include altering the angle of attack of the hydrofoil 400 and tether draw rate to change the rate and direction of crosscurrent motion; drawing in the tethers 105,106 significantly, thereby pulling the hydrofoil 400 into the shelter of the anchor 101 ; or submerging the hydrofoil 400 by altering its ballast condition. [00104] The collision avoidance system 500 receives observations of the position and velocity of the intruding entity. When the entity is no longer in the operational area of the system 100, the collision avoidance system 500 ends the avoidance maneuver and the system returns to normal operation of traction and recovery cycles. The operation of the collision avoidance system 500 is further discussed below with respect to FIGS. 25 through 27.

[00105] Some natural waterways are subject to flood events where the water level in waterway is undesirably high. During these flood events, it is desirable to reduce the flow resistance in order to lower upstream water levels and allow higher flood conveyance. The flood event procedure may be triggered by measurements, including high water level or water velocity or by command from a remote authority. To respond to a flood event, the actuation system 200 alters angle of attack of the hydrofoil 400 to a minimum, which reduces the lift and drag forces. In the event of an extreme flood event where the reduction of flow resistance by changing angle of attack is insufficient, the tethers 105,106 and hydrofoil 400 may be completely retracted by winding the tethers onto a storage drum 270 (depicted and described below in respect of FIG. 6).

Applications

[00106] One of the systems 100, or several of the systems 100 that form an array, can be used in a variety of applications, including but not limited to:

(a) for production of electricity for sale on an electricity grid in conjunction with other electricity generators;

(b) as the sole producer of electricity to meet an isolated load;

(c) for production of useful mechanical or thermal energy. These uses include pumping water or other fluids, desalination, hydrogen or ammonia production, providing building or process heat, compressing gas, and driving other machinery;

(d) as a portable unit for production of electricity or other energy in camps or other temporary installations;

(e) as a portable unit for production of electricity or other energy in the course of disaster relief; and (f) installed in a boat, ship or vessel to produce auxiliary power while the vessel is anchored in a current.

[00107] Installation and operation of many of the systems 100 in an array may be advantageous as this configuration reduces undesirable frequency characteristic of the output energy.

Alternative Configurations and Operations

[00108] The anchor 101 shown in FIG. 1 is a piling; however, in alternative embodiments

(not depicted), the anchor 101 may take other forms. For example, the anchor 101 may alternatively comprise a gravity base that sits on the bottom of the waterway; a pier of a bridge or other marine structure; or a floating buoy affixed to the bottom of the waterway or to the shore using an anchor line.

[00109] Referring now to FIG. 2, there are shown two embodiments of the system 100,100A.

The anchor 101 in one embodiment of the system 100 is within a waterway, as depicted in FIG. 1. The other embodiment of the system 100 A has the anchor 101 A, enclosure 103 and the actuation and collision avoidance systems 200,500 (not depicted in FIG. 2) affixed to the river shore or an island, and the tethers 105,106 extend outward over the waterway. This embodiment of the system 100A is relatively advantageous over the other embodiment of the system 100 shown in FIG. 2 in that no structure is needed in the middle of the waterway and the cable 104 does not need to interact with the water. The system 100A has the relative disadvantage compared to the system 100 in that 101 A will produce less energy because the tethers are not, on-average, parallel with the water velocity.

[00110] Referring now to FIG. 3, there is shown an embodiment of the system 100B which includes a floating base 120, on which the enclosure 103 and the actuation and collision avoidance systems 200,500 (not depicted in FIG. 3) are affixed. The hydrofoil 400A is affixed to the actuation system 200 via tethers 105A,106A. An anchor line 121 is affixed to the anchor 101 and the energy transfer system (not depicted).

[00111] During the traction phase, the actuation system 200 changes the angle of attack of the hydrofoil 400A by actuating the tethers 105A,106A, inducing a crosscurrent velocity and a large tension-force. The tension-force on the tethers 105A,106A causes the anchor line 121 to be drawn out and the floating base 120 to move downstream. The energy transfer system 300 converts and stores the mechanical energy inherent in the anchor line 121 being drawn out.

[00112] During the recovery phase, the actuation system 200 reduces the angle of attack of the hydrofoil 400A, which reduces the tension-force. The energy transfer system 300 draws in the anchor line 121 and the floating base 120 moves upstream to near its original position. The energy required to draw in the anchor line 120 is provided by energy stored during the traction phase.

[00113] This embodiment of the system 100B has the relative advantages over the embodiments depicted in FIGS. 1 and 2 in that actuation of the foil 400 A is mechanically separated from the energy conversion, which reduces the mechanical complexity of the system 100B. Additionally, the floating base 120 may have longer traction and recovery phases than would be feasible using the embodiments depicted in FIGS. 1 and 2, which reduces parasitic losses associated with component acceleration. This embodiment of the system 100B has the relative disadvantages compared embodiments depicted in FIGS. 1 and 2 in that there may be lower efficiency because the floating structure produces parasitic drag during the recovery; and the cable 104 would need to accommodate an energy transfer system that is mounted on the floating base 120, which is continually moving relative to the shore.

[00114] Alternatively to the above, the embodiments depicted in FIGS. 1 , 2 and 3 may be operated where an angle of attack is commanded causing the hydrofoil 400 to move transversely across the waterway, parallel to the water surface. When the hydrofoil 400 reaches its maximum transverse distance, the angle of attack is reduced to zero and then increased in the opposite pitching angle. This causes a reversal of the lift-force and causes the hydrofoil 400 to move transversely in the opposite direction. After the hydrofoil 400 has performed two or more transverse sweeps, the system transitions to the recovery phase.

[00115] Alternatively to the above, the system depicted in FIGS. 1 , 2 and 3, during the traction phase, a control surface (not depicted) may produce hydrodynamic forces that causes the hydrofoil 400 to move vertically, relative to the water surface. Through actuation of the control surfaces and the control tethers 106, the hydrofoil 400 may transit through a path that, when projected on a cross section of the water way taken transverse to the flow of the water way (e.g. looking into the flow of the waterway), resembles a circle, figure-of-eight, ellipse, or other regular or irregular patterns. [00116] Alternatively to the above, during the recovery phase, a control surface (not depicted) may produce hydrodynamic forces that cause the hydrofoil 400 to substantially rise out of the water. This is relatively advantageous because there will be lower parasitic drag on the hydrofoil 400 in air than in water. [00117] Referring now to the embodiment of the system lOOC shown in FIG. 30, the hydrofoil 400 is connected to one end of the tether 105. The actuation system 200C comprises a linear electric motor that is controlled by a linear motor drive system (not depicted). The end of the tether 105 not connected to the hydrofoil 400 is connected to the linear electric motor. The linear electric motor is affixed via a structure to the river bottom, a pylon, a bridge pier, or another structure.

[00118] During the traction phase, the hydrofoil 400 applies a force on the tether 105, which causes the linear electric motor to move along its primary axis. The linear motor drive system is configured such that the motion of the linear electric motor produces electrical power that is transmitted to the energy transfer system 300C by means of an electrical cable 175. [00119] During the recovery phase, the linear motor drive system draws electrical power from the energy transfer system 300C. This electrical power energizes the linear electric motor, which provides a force that retracts the tether 105.

[00120] In this embodiment, the energy transfer system 300C comprises a generator, energy storage device, and an electrical converter. During the generation phase, electrical power is transmitted to the energy transfer system 300C from the actuation system 200C. A portion of the energy is stored in the energy storage device, and a second portion is transferred to the electrical converter. The electrical converter transforms the relatively low-quality energy from the linear electric motor to high-quality saleable electricity. Examples of the electrical converter are a Siemens™ SINAMICS SI 20™ and a motor driver with an SI 20™ Line Module. [00121] During the recovery phase, the energy storage device discharges electrical energy of which a portion is delivered to the actuation system 200C and a portion is delivered to the electrical converter. The energy that is delivered to the actuation system 200C is used to retract the hydrofoil 400. The energy that is delivered to the electrical converter is used to produce saleable electricity. [00122] By balancing the relative portion of electrical energy provided to the energy storage device as a function of the performance of the hydrofoil 400, a constant amount of saleable electricity can be produced over both generation and recovery phases.

[00123] The embodiment of FIG. 30 can be used when the tether 105 is anchored in the middle of the river and not on shore; this may be required when the tether 105 is kept relatively short. If using a hydraulic system, the hydraulics would either be on a pylon or barge or in a submerged container, none of which is ideal. Using a submerged linear electric motor as opposed to a hydraulic system and smoothing the power on shore is an alternative to using a hydraulic system.

Energy Extraction [00124] Referring now to FIG. 4, in which is shown an embodiment of the hydrofoil 400, which includes the foil body 401 having the profile of a symmetric foil such as the NACA 0012. Affixed to the top and bottom of the foil body 401 at load mounting points 404 is the load tether bridal 403. The connections of the load tether bridal 403 at the load mounting points 404 permit the foil body 401 to rotate along its longitudinal axis. The end of the load tether bridal 403 that is opposing the foil body 401 is affixed to the load tether 105. The load mounting points are located between the leading edge of the foil body 401 and the center-of-pressure of the foil body 401. This configuration means that if the foil body 401 interacts with a current while tension is applied only through the load tether 105, the balance of forces will cause the leading edge of the foil body 401 to orient itself towards the apparent-velocity of the surrounding fluid. [00125] For the purpose of the present disclosure, the terms port and starboard mean the left and right sides of the foil body 401 , respectively, as identified when looking towards the leading edge of the foil body 401 from the trailing edge of the foil body 401.

[00126] The control tethers 106 are affixed to each side of the foil body 401 at control tether points 405. The control tether points 405 are positioned between the center of pressure and the trailing edge of the foil body 401. With this configuration, a tension-force on one of the control tethers 106 while the foil body is subjected to a current, will, in conjunction with the resultant hydrodynamic forces, rotate the foil body 401 about the load mounting points 404. For the purpose of the description below, rotation about this axis is referred to as pitching. The foil body 401 can be pitched to starboard by applying tension to the port control tether and can be pitched to port by applying tension to the starboard control tether.

[00127] The majority of the volume of the foil body 401 is comprised of material that is significantly less dense than that of water. Affixed to the bottom section of the foil body 401 is a ballast weight 402 of sufficient mass that the overall density of the foil body 401 is only very slightly less than the density of the surrounding water so that a portion of the foil body 401 is above the surface of the water when the foil body 401 is at equilibrium in the water. In one embodiment, the overall density of the foil body 401 is at least 80% the density of the water. This amount and arrangement of mass will cause the majority of the foil body 401 to be submerged with the top load mounting point 404 above the water surface when not being actively controlled; i.e., when the vertical control surfaces aren't causing the hydrofoil 400 to rise or dive, and the hydrofoil 401 consequently floats with neutral control input. Additionally and advantageously, the hydrofoil 400 will be buoyantly stable. If the foil body 401 is perturbed from a vertical position, the gravity and buoyancy forces will produce a restoring moment to return the foil body to vertical. [00128] The transverse motion of the tethers 105,106 through the water during the traction phase causes parasitic drag, which acts to reduce the lift-to-drag ratio of the hydrofoil 400 and reduces energy production. It is advantageous to reduce the effect of this tether drag by making relatively minimal the portion of each tether that is submerged in water, the diameter of each tether and the coefficient of drag of each tether. The load-bearing component of the tether is a high- strength metal or synthetic line such as Amsteel-Blue, which facilitates manufacture of a relatively narrow tether.

[00129] Referring now to FIG. 5 there is shown a depiction of a tether fairing 480, which surrounds the load tether bridal 403 and the submerged portions of the tethers 105,106. The fairings 480 reduce the hydrodynamic drag of the tethers 105,106 and the load tether bridal 403 as they move transversely across the waterway by reducing the drag coefficient of the tether relative to that of a cylindrical profile. The fairings 480 are comprised of sections that may freely rotate about the line. The nature of the cambered shape cause the fairings 480 to rotate to the optimal orientation, relative to the apparent velocity of the surrounding fluid.

[00130] Referring now to FIG. 6, there is shown one embodiment of the actuation system 200 which includes one or more lead-out sheaves 204, over which the tethers 105,106 are passed. The control tethers 106 are passed over sheaves 271 which are affixed to the control actuators 202. The control actuators 202 are hydraulic cylinders that apply tension to the control tethers 106 upon command of the control system 110. The control actuators 202 are instrumented such that the control system 110 has continuous measurements of tether force and control actuator position (not depicted). The translation of a control actuator 202 causes the movement of the respective control tether 106 relative to the load tether 105 and the other control tether 106.

[00131] The control actuators 202 are affixed to a load frame 203 that translates parallel to the incoming tethers. The load frame 203 is affixed to and actuated by a traction actuator 201 and a recovery actuator 205. The traction actuator 201 and recovery actuator 205 are each comprised of one or more hydraulic cylinders. The load tether 105 is passed over sheaves 271 which are affixed to the load frame 203. The translation of the load frame 203 results in the movement of the tethers 105,106 simultaneously.

[00132] The tethers 105,106 are affixed to a storage drum 270. Rotating the storage drum 270 causes the tethers 105,106 to be wound onto the storage drum 270 and the hydrofoil 400 to be retracted. This may be advantageous for collision avoidance or in the case of a flood event.

[00133] Energy is captured from the moving water in the recovery phase through the translation of the traction actuator 201. During the traction phase, the tension-force of the tethers 105,106 causes hydraulic fluid to be pushed out of the traction actuator 201 cylinder. This pressurized fluid is converted to salable energy by the energy transfer system 300. During the recovery phase, the load frame 203 is returned to its original position by the recovery actuator 205. Fluid pumped by the control and recovery actuators 202,205 may also be used for power generation.

Alternative Configurations

[00134] Referring now to FIG. 7, in which is shown one embodiment of the hydrofoil 400A, which includes a foil body 401A. Affixed to the trailing edge of the foil body 401A is a rudder 406 that acts as a control surface. The rudder 406 is actuated by mechanisms (not depicted) within the foil body 401 A under command from the control system 110. When actuated, the rudder produces a hydrodynamic force to be produced that will pitch the foil body 401 A, changing the angle of attack allowing control without the use of the control tethers 106. The actuator of the rudder 406 is controlled through wired or wireless communication from the control system 110. The power provided to the rudder actuator is provided by an electrical cable to the actuation system 200; a wireless power transmission system from the energy transfer system 300; batteries or another energy storage integrated into the foil body 401 A; or generated on the foil body 401 A from the movement of water, solar power, wind power, or fuel combustion. [00135] This embodiment is advantageous over the embodiment depicted in FIG. 6 because it reduces the parasitic tether drag by eliminating the need for control tethers 106 and simplifies the actuation system 200 by eliminating the need for steering actuators 202. This alternate configuration is disadvantageous relative to the embodiment depicted in FIG. 6 because it requires that actuators 201, 205 be installed in the relatively hostile environment within the foil body 401 A and requires one or both of power and communication between the hydrofoil 400 and the energy transfer system 300.

[00136] Referring now to FIG. 8, in which is shown one embodiment of the hydrofoil 400B which includes a foil body 401 to which is affixed one or more fins 407. The fins 407 are actuated or static control surfaces and maintain stable and controllable motion of the hydrofoil 400 through the water. This embodiment is advantageous as it provides increased hydrodynamic stability. This embodiment is disadvantageous as it increases the cost and complexity of the hydrofoil 400B fabrication and increases the potential negative effect of fouling or damage.

[00137] Referring now to FIG. 9, there is shown one embodiment of the hydrofoil 400C which includes a tail spar 408 affixed to a foil body 401. Affixed to the tail spar 408 is one horizontal control surface 409, and two vertical control surfaces 410. Actuation of the vertical control surfaces 410 causes the hydrofoil 400 to pitch and change its angle of attack. Actuation of the horizontal control surface 409 causes the hydrofoil 400C to yaw. Yaw is defined as rotation about the axis that orthogonal to the pitching axis and chord of the foil body 401. While FIG. 9 depicts one horizontal control surface 409 and two vertical control surfaces 410, in alternative embodiments any suitable number of horizontal and vertical control surfaces may be affixed to the tail spar 408. For example, in an alternative embodiment (not depicted), there may be two independently adjustable horizontal control surfaces and only a single adjustable vertical control surface. As used herein with respect to the hydrofoil 400, "horizontal" refers to the plane parallel with the flat surfaces of the foil body 401, while "vertical" refers to the plane that is orthogonal to this horizontal plane. [00138] The horizontal and vertical control surfaces 409, 410 are controlled through actuators installed in the foil body 401C or the tail spar 408. Coordinated actuation of the horizontal and vertical control surfaces by the control system 110 enables the hydrofoil 400C to be steered in the controllable way through the water body. This embodiment is advantageous because it permits greater control of the foil in the horizontal and vertical dimensions and eliminates the need for control tethers 106. It is disadvantageous because it adds complexity to the hydrofoil 400C, requires installation of actuators in a relatively hostile environment, and increases the drag of the hydrofoil 400C. Alternatively, the control surfaces 409,410 may be controlled by an additional control system (not depicted) that is embedded in the hydrofoil 400 that is communicative with the control system 110 outside the hydrofoil 401. This additional control system may comprise, for example, a processor and memory (not shown) mounted on to a printed circuit board, with statements and instructions encoded on to this memory to cause this processor to coordinate with the external control system 110. The processor may be, for example, an ARM Cortex M3™ processor.

[00139] Referring now to FIG. 29, there is shown another embodiment of the hydrofoil 400H that is similar to the embodiment shown in FIG. 9 except the trailing edge of the foil body 401 comprises two control surfaces: an upper control surface 475A and a lower control surface 475B. Each of these control surfaces 475A,B is vertically extending in that they extend along the trailing edge of the foil body 401. Each of the upper control surface 475 A and the lower control surface 475B are movable by actuators located within the foil body 401 (not depicted), which cause the upper control surface 475A and lower control surface 475B to pivot about a vertically extending axis.

[00140] When the upper control surface 475A and the lower control surface 475B are pivoted in the same direction, they act to change the effective shape of the hydrofoil 400H and increase its coefficient of lift. In this state, the hydrofoil 400H is asymmetrical. This is advantageous because it increases the performance of the hydrofoil 400H by improving its ratio of lift to drag.

[00141] When the upper control surface 475A and the lower control surface 475B are rotated in opposite directions from each other, they have the effect of producing a moment that induces the hydrofoil 400H to roll. This is advantageous because it allows the roll of the hydrofoil 400H to be controlled during times when it is not constrained by the tether bridal 403. [00142] When being swept from side to side across a river, the hydrofoil 400H, the pitch, yaw, and roll of the hydrofoil 400H are controlled. The pitch and yaw (angle of attack) are controlled by the tail spar 408 and the roll is constrained by the tether 105. When turning, however, the tether bridal is unable to constrain the hydrofoil 400H in roll as it projects perpendicularly from the front of the hydrofoil 400H. The upper and lower control surfaces 475A,B allow some roll control during turns. As an added benefit, they can also be used to increase the lift-coefficient of the hydrofoil 400H during sweeps, effectively making it a higher performing, asymmetric foil. That is, adjusting the lift-coefficient of the hydrofoil 400H enhances the ability of both curved sides of the hydrofoil 400H to generate lift, as opposed to a single side as is the case with asymmetric foils. This better enables the hydrofoil 400H to harness hydrokinetic energy as it is turning in the water regardless of which side is facing upstream and is being used to generate lift.

[00143] Referring now to FIG. 10, in which is shown one embodiment of the hydrofoil 400D which includes the load tether 105 affixed to the top of the foil body 401 at a single mounting point, such that the load tether 105 is kept above the water surface. Affixed to the foil body 401 is the tail spar 408. Affixed to the tail spar 408 is a horizontal spar 411 and a vertical control surface 41 OA. Affixed to the horizontal spar 411 are two or more lift surfaces 412. The lift surfaces 412 are actuated in opposing directions which causes the production of an upwards force at one surface and a downwards force at the opposing surface. These forces combined produce a rotational moment about the axis of the foil body 401 chord and balance the rotational moment caused by the tension- force and the lift-force. The vertical control surface 41 OA is actuated to control the angle of attack of the hydrofoil 400D.

[00144] This embodiment is advantageous because it reduces the parasitic drag caused by the control tethers 106 while preventing the hydrofoil 400D from rolling due to a rotational moment caused by the load tether 105 tension force and the lift-force that acts through the center of pressure of the foil body 401. This configuration is disadvantageous because it increases the mechanical complexity and parasitic drag of the hydrofoil 400E relative to that of the embodiment depicted in FIG. 4.

[00145] Referring now to FIG. 11, there is shown one embodiment of the hydrofoil 400E which includes a floating hull 414 to which is affixed a rudder 415. The load tether 105 is affixed to an above-water mounting point 413E, which is in turn affixed to the hull. Ballast weight (not depicted) is installed in the bottom of the foil body 40 IE such that the hull 414 is floating and the foil body 40 IE is fully submerged. During the traction phase, the tension-force applied to the mounting point 413E causes a rolling moment. As the hydrofoil 400E rolls, a vertical misalignment will develop between the center of mass (dominated by the ballast weight at the bottom of the foil body 40 IE) and the center of buoyancy (dominated by the volume of the hull 414). This misalignment causes a restoring moment that counters the rolling moment caused by the tension and lift forces.

[00146] The rudder 415 is actuated using mechanisms enclosed within the hull 414 or foil body 40 IE. Actuating the rudder causes the hydrofoil 400E to pitch, changing the angle of attack. Power and communications for the rudder actuators is transmitted through wires or wirelessly from the energy transfer system 300.

[00147] Referring now to FIG. 12, there is shown one embodiment of the hydrofoil 400F, which includes two or more foil bodies 401F, each affixed to a floating hull 414F. The hulls affixed to each other by means of one or more bridging spars 416. The load tether 105 is affixed above the water surface to a mounting point 413F, which is in turn affixed to a bridging spar 416 or the hull 414F.

[00148] Pitching control of the hydrofoil 400F is by means of one or more rudders or control surfaces affixed to the hulls 414F or foil bodies 40 IF in a manner similar to the hydrofoil 400E as depicted in FIG. 11.

[00149] During the traction phase, the combination of the lift-forces and the tension-force will cause the hydrofoil 400F to roll. As the hydrofoil 400F rolls, a difference in buoyancy forces develops between two or more hulls 414F. This difference in buoyancy forces results in a counter- rolling moment that balances the rolling moment created by the lift and tension forces.

[00150] Referring now to FIG. 13, there is shown one embodiment of the hydrofoil 400G, which includes a floating hull 414G to which is affixed one or more outrigger hulls 417 via one or more bridging spars 416G. Affixed to the hull are one or more foil bodies 401G. The foil bodies 401G are ballasted such that the hull 414G is buoyantly stable. The outrigger hulls 417 are arranged such that if the floating hull 414G is in an upright position, the outrigger hulls 417 do not touch the water. The load tether 105 is affixed to the hull 414G via a mounting point 413G. During the traction phase, the hydrofoil 400G generates a rolling moment due to the tension and lift forces. As the hydrofoil 400G rolls, one or more outrigger hulls 417 descends into the water and experiences an upward buoyancy force. The combination of the ballast weight and the buoyancy forces creates a counter-rolling moment that keeps the hydrofoil 400G close to upright.

[00151] Pitching control of the hydrofoil 400G is implemented by means of one or more rudders 415G or control surfaces (not depicted) affixed to the hulls 414G, outrigger hulls 417, or foil bodies 401G. They are actuated in a manner similar to that described in the embodiment of the hydrofoil 400E depicted in FIG. 11.

[00152] Alternatively to the above, in all the embodiments, one or more of the hydraulic actuators (including 201,202,205) may be powered by compressed gas instead of pressurized hydraulic fluid (not depicted).

[00153] Referring now to FIG. 14, there is shown an alternative embodiment of the actuation system 200A. This embodiment is similar to the embodiment depicted in FIG. 6 with the exception of the control actuators 202A and recovery actuator (not depicted) being electrically powered linear actuators. [00154] Referring now to FIG. 15, there is shown an alternative embodiment of the actuation system 200B. This embodiment is similar to the embodiment depicted in FIG. 6 with the exception of the control actuators 202A and recovery actuator (not depicted) being a belt-drive actuator.

[00155] Referring now to FIG. 16, there is shown an alternative embodiment of the actuation system 200C, which includes lead-out sheaves 204, over which the tethers 105,106 are passed. The load tether 105 is affixed to the traction actuator 201C and a recovery actuator 205C via a sheave (not depicted). The control tethers 106 are each affixed to the control actuators 202C via a sheave (not depicted). The tethers 105,106, after passing over the sheaves, are affixed to a storage drum (not depicted) in a manner similar to that described in the embodiment depicted in FIG. 6. Translation of an actuator 201C,202C,205C causes the tether 105,106 affixed to that actuator to change in length.

[00156] Referring now to FIG. 17, there is shown an embodiment of the actuation system

200D, which includes lead out sheaves 204 over which the tethers 105,106 are passed. The control tethers 106 are affixed to control winches 202D, which when rotated cause the control tethers 106 to be wound on or off. The load tether 105 is affixed to the load winch 20 ID, which when rotated causes the load tether 105 to be wound on or off. The angle of attack of the hydrofoil 400 is controlled by rotating the winches 201D,202D at different speeds such that more of the port tether is drawn off faster or slower than the starboard tether, or vice versa. The winches 201D,202D are actuated by electric or hydraulic motors (not depicted), which can both source or receive power to or from the energy transfer system 300 and control the rotational position of the winches 201D, 202D.

[00157] Referring now to FIG. 18, there is shown an embodiment of the actuation system

200D, which includes a load arm 220, affixed to the base of the system 100 at a pivot 225. The load tether 105 is affixed to the load arm 220 at the end opposite the pivot 225. Affixed to the load arm 220 are two sheaves 222 over which the control tethers 106 are passed and two control actuators 202E. Each control tether 106 is affixed to a control actuator 202E, the translation of which changes the length of the respective control tether 106 affixed to that control actuator relative to the other tethers 105,106.

[00158] Affixed to the load arm 220 are a traction actuator 201E and a recovery actuator 205E, both being hydraulically or electrically powered linear actuators. The actuation of either the traction actuator 20 IE or the recovery actuator 202E causes the load arm 220 to rotate about the pivot 225. Rotation of the load arm 220 causes the tethers 105,106 to be drawn in or drawn out.

[00159] Referring now to FIG. 19, there is shown an embodiment of the actuation system

200F, which includes a load arm 220A. This embodiment is the same in configuration and operation as the embodiment of the actuation system 200E, depicted in FIG. 18 except with respect to the actuation of the load arm 220 A. A hydraulically or electrically powered motor 20 IF is affixed, via a gearbox or continuously variable transmission (not depicted), to the load arm 220A. Rotation of the motor 201F causes the load arm 220A to pivot, drawing in or drawing out the tethers 105,106. The motor 20 IF is able to absorb power and act as a pump/generator. [00160] Referring now to FIG. 20, there is shown an embodiment of the actuation system

200G, which includes a load arm 220G and a pair of control arms 221. The load tether 105 is affixed to one end of the load arm 220G and each control tether 106 is affixed to one end of each control arm 221. Each arm 220G,221 rotates about a pivot point 225G that is located at its end opposite where the tether 105,106 is affixed. The rotation of an arm 220G,221 about its pivot 225 allows for the corresponding tether 105,106 to be drawn in or drawn out. The load arms 220G are actuated by traction actuators 201G and recovery actuators 205G which are hydraulic cylinders or electrically powered linear actuators. The control arms 221 are actuated by control actuators 202G, which are hydraulic cylinders or electrically powered linear actuators.

[00161] Not depicted is an embodiment of the actuation system 200 that includes load and control arms. This embodiment is the same in configuration and operation as the embodiment of the actuation system 200G depicted in FIG. 20, except with respect to the actuation of the arms 220G,221. A hydraulically or electrically powered motor is affixed, via a gearbox or continuously variable transmission, to each arm 220G,221. Rotation of the motor causes the arm 220G,221 to pivot, drawing in or drawing out the tethers 105,106. The motor is able to absorb power and act as a pump/ generator.

[00162] Referring now to FIG. 21, there is shown an embodiment of the actuation system

200H, which includes a load arm 220H, affixed to the base of the system 100 at a pivot 225. The load tether 105 is affixed to the load arm 220H at its end opposite the pivot 225. Affixed to the load arm 220H are two sheaves 222, over which the control tethers 106 pass, and two control actuators 202H. Each control tether 106 is affixed to a control actuator 202E, the translation of which changes the length of the control tether 106 attached to that actuator relative to the other tethers 105,106. The control actuators are electrically powered linear actuators or belt drives.

[00163] A load bar 231 is affixed through a pivot to a cam 230 at one end and to the load arm

220H through a pivot at the opposing end. The cycles of the system 100 will cause the load arm 220H to rotate in one direction during the traction phase and then the opposite direction during the recovery phase. The load bar 231 and cam 230 are arranged such that as the load arm 220H pivots in either direction, the cam 230 rotates only in a single direction (counterclockwise in FIG. 21). The cam 230 is mechanically coupled, via a gearbox or continuously variable transmission (not depicted), to a hydraulic motor/pump or electrical motor/generator (not depicted) that transfers power to or from the energy transfer system 300.

[00164] Referring now to FIG. 22, there is shown an embodiment of the actuation system

2001, which includes three or more lead out sheaves 204 over which the tethers 105,106 are passed before being affixed to a winch drum 240. Rotation of the winch drum 240 allows all tethers 105,106 to be drawn in or drawn out an equal amount. Between the lead out sheaves 204 and the winch drum 240, each control tether 106 passes over two or more control sheaves 241. The control sheaves 241 are positioned with one closer to the winch drum 240 and one further from the winch drum 240. The control tether 106 travels from the lead out sheaves 204 and passes over the control sheave 241 closer to the winch drum 240 and then over the control sheave 241 that is further away from the winch drum 240. One of the control sheaves 241 is actuated by the control actuator 2021, which is a hydraulically or electrically powered linear actuator. Translating the control sheaves 241 such that they are closer together pays out (extends) that control tether 106. Translating the control sheaves 241 such that they are further apart draw in (retracts) that control tether 106.

[00165] The winch drum 240 is mechanically coupled to one or more load actuators 2011 which are hydraulic pumps/motors or electrical motors/generators. During the traction phase, the tethers 105,106 are drawn out and the winch drum 240 rotates in one direction, driving the load actuator 2011. During the recovery phase, the load actuator 2011 rotates the winch drum 240, drawing in the tethers 105,106.

[00166] In an alternative embodiment (not depicted), the system 100 uses the same tethers to both control the hydrofoil 400 and to harness the hydrokinetic energy of the water. In such an embodiment, the load and control tethers 105,106 are replaced with tethers that can simultaneously be used to control the hydrofoil 400 by orienting it in the water and to harness hydrokinetic energy by bearing tension applied when the hydrofoil 400 is moved by current. For example, in the embodiment of FIG. 1, the load tether 105 may be removed to result in an alternative embodiment in which the remaining tethers, which are labeled the control tethers 106 in FIG. 1, would simultaneously both control the hydrofoil 400 and transfer hydrokinetic energy to the actuation system 200.

[00167] Additionally to the above, sheaves may incorporated into the path of the tethers

105,106 such that the tethers are directed in a desirable manner.

[00168] Additionally to the above, sheaves may be may incorporated into the path of the tethers 105,106 such that the hydrofoil 400 or the actuation system 200 is provided with a mechanical advantage.

[00169] Alternatively to the above, the traction actuators 201 and recovery actuators 205 may be combined into a single component.

Energy Transfer [00170] Referring now to FIG. 23, there is shown an embodiment of the energy transfer system 300, which transfers the mechanical energy that was captured by the hydrofoil 400 away from the actuation system 200 and, in the embodiment of FIG. 23, converts the mechanical energy into salable energy in the form of electricity. The energy transfer system 300 also provides energy to the actuation system 200 during the recovery phase to allow the tethers 105,106 and hydrofoil 400 to be drawn in.

[00171] Within the energy transfer system 300 is a high-pressure hydraulic bus 314, which is hydraulically coupled to one or more accumulators 307. The accumulators 307 act as energy storage devices such that if more fluid is injected into the high-pressure hydraulic bus 314 than is being withdrawn, the accumulator 307 absorbs the excess fluid. Similarly, if the volume of fluid being withdrawn from the high-pressure hydraulic bus 314 exceeds what is injected, the accumulator 307 discharges into the high-pressure hydraulic bus 314. The ability of the accumulator 307 to store and discharge energy is limited by its volumetric capacity. Parallel to the high-pressure hydraulic bus is the low-pressure hydraulic bus 315, to which is hydraulically coupled a hydraulic fluid reservoir 304 which supplies and receives excess hydraulic fluid.

[00172] The hydraulic components 201,202,205 of the actuation system are coupled to the hydraulic buses 314,315 via valving 305 which controls the flow of hydraulic fluid between the energy transfer system 300 and the actuation system 200.

[00173] An electrically powered charge pump 309 is hydraulically coupled to the hydraulic buses 314,315.

[00174] Hydraulically coupled to the hydraulic buses 314,315 is a generator motor 301 , which is a variable or digital displacement hydraulic pump/motor. Mechanically coupled to the generator motor 301 is an induction generator 302. Mechanically coupled between the generator motor 301 and the generator 302 is a flywheel 310. Electrically coupled to the generator 302 is a variable frequency generator drive 308. Electrically coupled to the variable frequency generator drive 308 is a AC bus 313, which may be the electrical grid.

[00175] During the traction phase, the traction actuator 201 injects hydraulic fluid at high pressure into the high-pressure hydraulic bus 314. The fluid is simultaneously or alternatively delivered to the accumulator 307, generator motor 301, or control actuators 202 via valve components 305.

[00176] Fluid is discharged from the accumulator 307 and is simultaneously or alternatively delivered via valve components 305 to the generator motor 301, control actuators 202, and recovery actuators 205. The fluid energy delivered to the recovery actuators 205 is the primary energy for drawing in the tethers 105,106 and returning the hydrofoil 400 to its position at the beginning of the traction phase.

[00177] Fluid from the high-pressure hydraulic bus 314 turns the generator motor 301, after which the fluid is discharged to the low-pressure hydraulic bus 315 and returns to the hydraulic fluid reservoir 304. The generator motor 301 turns the induction generator 302, which converts the mechanical power from the rotating generator motor's 301 shaft into alternating current (AC) electricity. The flywheel 310 acts as a mechanical energy storage device and has the effect of reducing unwanted accelerations of the motor/generator 301,302,310 linkage.

[00178] The induction generator 302 requires the input of an AC excitation voltage to establish and maintain a magnetic field. Additionally, the rotational speed of the generator 302 is kept approximately proportional to the frequency of the excitation current. AC buses, such as the electrical grid, often are kept at a relatively constant frequency of either 50Hz or 60Hz depending on location. In order to allow the generator motor 301 and induction generator 302 to operate at variable speeds, the variable frequency generator drive 308 supplies a controllable frequency excitation voltage. The generator drive 308 also converts the frequency of the current produced by the induction generator 302 such that it matches the frequency of the AC bus 313. The AC bus 313 delivers electricity to the electrical grid or provides power for equipment. Electricity on the AC bus 313 is salable.

[00179] At system 100 startup and when there is insufficient system pressure, hydraulic fluid may be injected into the high-pressure hydraulic bus 314 from the low-pressure hydraulic bus 315 by the charge pump 309. The charge pump 309 is powered by an AC motor which draws power from the AC bus 313 or an external source. An additional charge pump (not depicted) may be powered by an internal combustion engine. [00180] Electricity from the AC bus 313 may be converted to high-pressure fluid by reversing the direction of energy flow through the generator drive 308, generator 302 and generator motor 301 and may be used to draw in the hydrofoil 400 and actuate the control actuators 202.

[00181] Additional hydraulic equipment (not depicted) may be hydraulically coupled to the hydraulic buses 314,315 to produce salable energy that is not electricity. This may include mechanical shaft work, pumping fluid, desalinating water, compressing gas, producing hydrogen, generating heat, or powering cooling equipment.

Alternative Configurations

[00182] Referring now to FIG. 24, there is shown an embodiment of the energy transfer system 300A, which is similar in configuration and operation to that depicted in FIG. 23 except with respect to the generator 302 and generator drive 308. A direct current (DC) generator 302A is mechanically coupled to the generator motor 301 and flywheel 310. The generator 302 A is electrically coupled to a DC bus 311, to which is also electrically coupled a DC/ AC inverter 308A, capacitor-based storage 312 and battery based storage 316. The inverter 308A is electrically coupled to the AC bus 313.

[00183] Fluid energy provided to the generator motor 301 is transferred to the DC generator

302 A. The DC generator outputs direct current electricity to the DC bus 311. DC generators do not require an excitation voltage and the ability to generate electrical power is relatively simple. The inverter 308 withdraws power from the DC bus 311 and converts it to the AC electricity [00184] The capacitor or battery storage 312,316 has the capability to store and discharge DC electricity. This is advantageous because it allows energy generated by the system 100 to be sold when the AC or electrical grid is in most need of it.

[00185] Energy may be stored in the capacitor or battery storage 312,316 during the traction phase and offset the DC electricity produced by the generator 302 during the recovery phase. This is advantageous because it reduces the amount of fluid capacity needed in the accumulator 307 in order to retract the tethers 105,106.

[00186] Energy may be stored in the capacitor or battery storage 312,316 during the traction phase and transferred to the high-pressure hydraulic bus 314 during the recovery phase via the generator 302 A and the generator motor 301. This hydraulic energy is used to retract the tethers and advantageously reduces or eliminates the need for hydraulic fluid storage in the accumulator 307.

[00187] Referring now to FIG. 23, there is shown an embodiment of the energy transfer system 300B, which is similar in configuration and operation to that depicted in FIG. 23 except for the presence of a motor 318 used to drive the charge pump 309, modifications to the valving 305, and the use of an actuation system 200 that is designed to be used with the load tether 105 but not the control tethers 106. Because the actuation system 200 in FIG. 23 is designed to be used without the control tethers 106, it is used in conjunction with the hydrofoils 400 that are able to control their own movement, such as the hydrofoil 400 of FIG. 29. The motor 318 permits the speed of the charge pump 309 to be controlled.

[00188] The actuation system 200 used in FIG. 28 comprises a pulley, a linear slide, a roller chain, and a hydraulic cylinder. The linear slide and the base of the hydraulic cylinder are affixed to the frame of the actuation system 200 and are accordingly fixed relative to each other. The pulley is affixed to the rod-end of the hydraulic cylinder and to the linear slide such that its motion is linearly constrained to the path of the linear slide. In this configuration, actuating the hydraulic cylinder causes the pulley to move along the linear slide. The tether 105 is attached to one end of the roller chain, which passes over the pulley. The other end of the roller chain is affixed to the actuation system's 200 frame. This configuration gives mechanical advantage to the tether 105, compared to the hydraulic cylinder. Extending the hydraulic cylinder one unit of length will cause the tether 105 to retract by two units of length.

[00189] The piston-end port of the hydraulic cylinder is hydraulically coupled through the valving 305 to the high-pressure hydraulic bus 314. The charge pump's 309 inlet is hydraulically coupled to the low-pressure hydraulic bus 315 and its outlet is hydraulically coupled through the valving 305 to both the piston-end port and the rod-end port of the hydraulic cylinder. The rod-end port and the piston-end port of the hydraulic cylinder are hydraulically coupled through the valving 305.

[00190] The charge pump 309 can be variable or fixed displacement type. The motor 318 driving the charge pump 309 is a variable speed type. [00191] During the traction phase, the tension in the tether 105 resulting from the hydrofoil's

400 movement results in a force being applied to the hydraulic cylinder via the roller chain. The valving 305 is adjusted such that the piston-end of the hydraulic cylinder is connected to the high- pressure hydraulic bus 314. The tension causes the hydraulic cylinder to retract, forcing fluid to flow into the high-pressure hydraulic bus 314. Concurrently, the charge pump 309 provides hydraulic fluid to the piston-end of the hydraulic cylinder. The pressure imparted to the hydraulic fluid by the charge pump 309 acts to limit the effects of fluid cavitation and provides additional pressure to the high-pressure hydraulic bus 314. Adjusting the displacement of the charge pump 309 and the speed of the motor 318 driving the charge pump 309 controls the flow rate and pressure of the pumped hydraulic fluid.

[00192] During the recovery phase, the valving 305 is changed such that the rod-end and the piston-end of the hydraulic cylinder are connected, and both ends of the hydraulic cylinder are disconnected from the high-pressure hydraulic bus 314. The charge pump 309 then injects fluid into both the rod-end and the piston-end. The piston-end of the hydraulic cylinder has a larger area than the rod-end of the hydraulic cylinder, and consequently a net force results that extends the hydraulic cylinder. Extending the hydraulic cylinder acts to retract the tether 105. The speed and displacement of the charge pump 309 is adjusted to control the retraction speed.

[00193] In the embodiment of FIG. 28, the charge pump 309 is used to both retract the piston in the actuation system 200 and to prevent cavitation. Without the charge pump 309, it is difficult to provide sufficient fluid to the low-pressure side of the piston while it is moving without the hydraulic fluid cavitating. While a roller chain is used in FIG. 28, in alternative embodiments (not depicted) any suitable tension line, such as a roller belt or rope, may be used.

[00194] Not depicted is an embodiment of the energy transfer system 300 that is similar in configuration and operation to that depicted in FIG. 23 and 24 except with respect to the coupling of the retraction actuator 205. The recovery actuator 205 in this alternative embodiment is hydraulically coupled to the discharge terminal of the generator motor 301. The discharged medium-pressure hydraulic fluid is used to retract the hydrofoil 400. This is advantageous because the medium-pressure fluid is less valuable than the high-pressure fluid because it does not contain as much energy. [00195] In alternative embodiments (not depicted), any one or more of the traction, recovery, and control actuators 201,202,205 are electrically powered. Any of these actuators 201,202,205 that are electrically powered are electrically coupled to either the DC or AC bus 311, 313 to receive power. [00196] Not depicted is an embodiment of the energy transfer system 300 where all actuators

201,202,205 are electrically powered and the energy transfer system forgoes the hydraulic components 301,304,305,307, and 309.

[00197] Not depicted is an embodiment of the energy transfer system 300 similar to the embodiment depicted in FIG. 23 except the induction generator 302 and generator drive 308 are replaced with a synchronous generator. The synchronous generator is electrically coupled to the AC bus 313 and mechanically coupled to the generator motor 301.

[00198] Not depicted is an embodiment of the energy transfer system 300 similar to the embodiment depicted in FIG. 23 except the generator drive 308 is eliminated and the generator 302 is electrically coupled to the AC bus 313. This configuration is relatively advantageous as it eliminates the parasitic loss caused by the generator drive 308. This configuration is relatively disadvantageous because it reduces the range of rotational speed at which the induction generator 302 can operate.

[00199] Not depicted is an embodiment of the energy transfer system 300 similar to the embodiments depicted in FIGS. 23 and 24 except a gearbox or continuously variable transmission (CVT) is mechanically coupled between the generator motor 30 land the generator 302,302A. The gearbox or CVT acts to improve efficiency by allowing different rotational speeds by at the induction generator and the generator motor.

Collision Avoidance

[00200] Referring now to FIG. 25, there is shown one embodiment of the collision avoidance system 500. The system 100 interacts with waterways that may have a variety of human uses, be subject to debris, and be habitat for marine wildlife. It is advantageous that the system 100, especially the hydrofoil 400, does not strike or impact entities 590 that have entered the system's 100 operational area. The position of the hydrofoil 400 is measured and controlled by the actuation system 200. If the location, velocity and other information about the entities is known or can be predicted, the hydrofoil 400 may be moved such that a collision is avoided. The mechanisms involved are discussed in further detail below.

[00201] Referring now to FIG. 26, there is shown a block diagram of an embodiment of the collision avoidance system 500, which includes a collision avoidance processor 501. Connected to the collision avoidance processor 501 are a multitude of debris sensors including cameras/machine vision 506, RADAR 505, sonar 502, metrological sensors 503 and river flow rate sensors 504. Additionally coupled to the collision avoidance processor 501 via wired or wireless communication channels 508 are other data systems 509 such as databases and remote sensing devices such as satellites. The collision avoidance processor 501 is connected to the control system 110 via two- way communication channels.

[00202] Referring now to FIG. 27, there is shown a flow chart describing the operation of the collision avoidance system 500. The collision avoidance processor 501 monitors the change from the sensors 506,505,502 and determines if a change in conditions has occurred. If no change has occurred, the system 100 continues to operate normally. If a change has occurred, the collision avoidance processor 501 determines if the change in measurements represents a risk to the system 100. If there is no risk or the risk is negligible, the system 100 continues normal operation.

[00203] If the risk is significant, the collision avoidance processor 501 determines what operational mode would best protect the system 100 from that risk. The collision avoidance processor 501 sends a command to the control system 110 to execute a specific avoidance maneuver.

[00204] A number of different detection methods are simultaneously employed by measuring reflected acoustic or electromagnetic waves in a passive or active setting as measured by the sensors 502-506. Each of these signals represents the reflectivity of an object at a particular spatial and temporal location. A change of one of these signals beyond a calibrated threshold triggers a determination of risk. The sensors' 502-506 scan frequency and horizon are calibrated to the stream flow conditions at the time of installation.

[00205] The collision avoidance processor 501 identifies the difference between safe and risky changes in stream flow using any one or more of a multitude of methods. Each method provides a risk score and characteristic, which is aggregated by the collision avoidance processor 501 to determine a final risk determination. The risks are categorized as passive and sparse; passive and dense; and active, each with an associated severity score.

[00206] One method employed for identifying and determining a risk score in this embodiment is a Bayesian learning process, which improves its skill through continual use. The initial calibration is trained by an operator. Recording of the sensors and risk identification and response modes are used to update the learning process. The identification process is further enhanced by determining minimum acceptable signal to noise ratio.

[00207] Another method employed for identifying and determining a risk score in this embodiment is blob detection, which detects the number of signals that have experienced change and determines a corresponding size of the changed area. The area changed is related the change in signal return and compared to a predefined lookup-table.

[00208] Another method employed for identifying and determining a risk score in this embodiment is to detect if a substance that is not water passes through a cross-section upstream of the system 100. [00209] Another method employed for identifying and determining a risk score in this embodiment to generate the projected trajectory of the entity through the system's 100 operational area. The predicted trajectory of the entity is generated from data sources including the sensors 502- 506 and environmental measurements such as river velocity sensors 504 and meteorological sensors 503. Additionally, the processor may incorporate data from remote sensors 507 or other data sources 509 via wired or wireless communication systems 508. The method to generate the projected trajectory is an aggregated prediction based on linear or higher order extrapolation of position, artificial neural network processes and look-up tables generated for a particular location.

[00210] If the aggregated risk score is above a determined risk threshold, the collision avoidance processor 501 determines and implements an avoidance maneuver to prevent damage to the system 100. The determination of a specific mode is by aggregated score from any one or more of a lookup table, Bayesian process and artificial neural network.

[00211] Another avoidance maneuver in this embodiment is a modified sweep pattern. The speed and direction of the hydrofoil 400 are altered by changing the angle of attack and the rate that the tethers 105,106 are drawn in or drawn out. Reversing the angle of attack causes the hydrofoil to move in the opposite direction and can be positioned such that it does not intersect with the projected trajectory of the intruding entity.

[00212] Another avoidance maneuver in this embodiment of is to take shelter. In this mode, the tethers 105,106 are reeled in significantly by rotating the storage drum 270. The hydrofoil 400 remains in the shadowed region downstream of the anchor 101. Not depicted is an embodiment of the system 100 that has a housing affixed to the anchor 101 such that additional protection is afforded to the hydrofoil 400.

[00213] Another avoidance maneuver in this embodiment of is to remove the foil from the water. In this mode, the tethers 105,106 are reeled in significantly by rotating the storage drum 270 and lifting the hydrofoil 400 out of the waterway.

[00214] Another avoidance maneuver in this embodiment of is to submerge the hydrofoil

400. Not depicted is an embodiment of the hydrofoil 400, which contains a mechanism that substantially changes the density of the hydrofoil 400 such that it will sink to the bottom of the waterway. The signaling to the hydrofoil 400 is by acoustic or electromagnetic signals. [00215] Once the avoidance maneuver is determined, the collision avoidance processor 501 commands the control system 110 to execute the corresponding, pre-programmed maneuver.

[00216] While the avoidance maneuver is being executed, the collision avoidance processor

501 receives signals from the sensors 502-506, and continuously performs the determination and categorization of risk as described above. Once the risk score is below a predetermined threshold, the control system 110 is commanded to resume normal operations.

[00217] While various embodiments of the system 100 and components thereof are described above and depicted in the figures, alternative embodiments, which are not depicted, are also possible. For example, in one alternative embodiment that is not depicted, the system 100 includes a load frame 203 to which the control actuators 202 and the load tether 105 are affixed, similar to the manner depicted in FIG. 6. The load frame 203 is translated by an electrically powered actuator that can absorb or discharge mechanical energy. The electrically powered actuator may be a linear motor or a rotary motor linearized by a winch, belt drive or lead-screw. The electricity generated by the electrically powered actuator is discharged or sourced from the DC bus 311 or AC bus 313. [00218] In another non-depicted alternative embodiment, the system 100 is affixed to a vertically translating positioner, which is in turn affixed to the anchor 101. When the positioner is activated, the enclosure 103 and the enclosed systems 200,300 move up or down relative to the anchor 101 and the angle the tethers 105,106 make with the water surface accordingly changes. There is an optimal angle for the tethers 105,106 to make with the water surface. If the angle is small, significant portions of the tethers 105,106 are submerged, which decreases the lift to drag ratio of the hydrofoil 400 and accordingly decreases power production. If the angle is large, the magnitude of the water velocity vector projected on the tether vector is relatively small, which results in lower power production. The ability to move the enclosure 103 and change the angle of the tethers 105,106 is advantageous because it allows the system 100 to maintain a relatively optimal tether angle despite varying water levels. Additionally, the ability to move the enclosure 103 up allows the system 100 to be in a safer position during flood events and reduces potential damage due to water inundation.

[00219] In an additional alternative embodiment that is not depicted, the system 100 includes a lead-out arm affixed via a pivot to the enclosure 103. At the end opposite the pivot are three sheaves over which the tethers 105,106 are passed. Actuating the arm moves the sheaves relatively closer or further from the surface of the water and changes the angle the tethers 105,106 make with the water surface. The ability to change the angles the tethers 105,106 makes relative to the water surface is advantageous because it allows the system 100 to maintain a relatively optimal tether angle despite varying water levels.

[00220] In an additional alternative embodiment, the functionality of the collision avoidance processor and the processor used in the control system 110 are combined into a single processor that controls both the actuation system 200 and the collision avoidance system 500.

Determining Hydrofoil Position [00221] In order to determine the angle of attack at which to orient the hydrofoil 400, the control system 110 acquires the position and velocity of the hydrofoil 400 relative to known reference frames, such as the position of the anchor 101 and the velocity of the water in which the hydrofoil 400 is immersed, respectively. From these raw inputs the control system 110 is able to determine the hydrofoil's 400 orientation as described below. [00222] The control system 110 may analyze measurements made using one type of position determining system, which is an inertial motion unit ("IMU") comprising gyroscopes and accelerometers. The IMU is installed on the hydrofoil 400 and measures its acceleration and rotation. The hydrofoil 400 transmits raw or processed outputs from the IMU to the control system 110. By performing mathematical integrations and transformations on the output from the IMU, the control system 110 can determine the position, orientation, velocity, and acceleration of the hydrofoil 400.

[00223] The control system 100 may also determine the hydrofoil's 400 position by using another type of position determining system, which is an acoustic long-baseline system. One or more acoustic emitters are affixed at known locations in the water in the operational region of the system 100. These emitters output a pulse of sound of a known frequency at either a predetermined time or upon command of the control system 110. One or more acoustic receivers is affixed to the hydrofoil 400, and these receivers receive the sound pulse. An electronic processing system records the time at which the one or more pulses are received and, using the physical properties of water, determines the distance between the hydrofoil 400 and the acoustic emitters. The control system 110 combines these distances to determine the position, velocity, and acceleration of the hydrofoil. Alternatively, the acoustic emitters may be affixed to the hydrofoil 400 while the receivers are positioned in known locations in the water. Alternatively, one or both of recording when the pulses are received and determining the distance travelled by the acoustic waves can be performed outside of the hydrofoil 400, such as at the control system 110. At the control system 110, dedicated amplification circuitry is used to amplify the signals prior to processing them to determine the hydrofoil's 400 position. The control system 110 may determine the orientation of the hydrofoil 400 from measurements obtained using the acoustic long-baseline system in conjunction with measurements obtained using the IMU. [00224] Another method used to determine the hydrofoil's 400 position is to use another type of position determining system, which is one or more single beam, multi-beam or side-scan sonar systems affixed to the hydrofoil 400. The output from the sonar system measures bathymetric and surface features, relative to the hydrofoil 400. The control system 110 matches these features to known bathymetry to calculate the position of the hydrofoil 400. The control system 110 may determine orientation using readings from the sonar system alone, or from the sonar system in conjunction with the IMU. [00225] Another method used to determine the hydrofoil's 400 position is to use another type of position determining system, which is one or more single beam, multi-beam or side-scan sonar systems at known locations in the water. The sound pulses emitted by the sonar system are reflected by the hydrofoil 400. The control system 110 can use the output from the sonar systems and their locations to calculate the position of the hydrofoil 400. The control system 110 may determine orientation using readings from the sonar system alone, or from the sonar system in conjunction with the IMU.

[00226] Each of these methods has benefits and drawbacks. Position determination based on

IMUs have very fast response time, which is advantageous as it enables high-speed control of the hydrofoil 400. The IMU measures acceleration and integrates this signal to determine position. Detrimentally, errors in measurement are amplified and the accuracy of the IMU can degrade quickly after a short period of time. Alternatively, the control system 1 10 may integrate acceleration to determine position.

[00227] Sonar and acoustic long-baseline based systems beneficially have good absolute spatial accuracy that does not degrade over time because it is based on known timings, positions, and water properties, and aggregate errors do not compound. Detrimentally, sonar and acoustic long-baseline systems have low update rates due to the travel time of a sound pulse through water.

[00228] An IMU and a sonar or acoustic long-baseline system can be combined to provide accurate and high-speed position response. At the time a sonar or acoustic long-baseline pulse is received, the control system 110 uses the sonar or acoustic long-baseline position as an initial position. The sonar or acoustic long-baseline system has a relatively low update rate of 0.5 to 10 Hz, therefore the control system 100 will not have a position update for 100 to 2,000 ms. For this period of time, the control system 110 relies on the IMU to provide a differential position relative to the initial position, which is the most recent sonar or acoustic long-base position. This is accomplished by using the initial position from the sonar or acoustic long-baseline to reset the integration constant of the inertial motion unit position system.

[00229] Additionally, sensor fusion methods such as Kalman filters and Bayesian learning algorithms can be used to further improve position accuracy. [00230] The control system 110 may be used to maintain a relatively high level of energy production based on the hydrofoil's 400 angle of attack, as determined using any of the foregoing sensors or combinations thereof. The control system 110 attempts to maintain the angle of attack of the hydrofoil 400 at an optimal angle of attack that produces the greatest lift-to-drag ratio for the assembly comprising the hydrofoil 400 and the tethers 105,106. The particular angle in any given case is determined the hydrofoil's 400 size, the shape of the foil body 401, and the size and drag coefficient of the tethers 105,106. In practice, the control system 110 may determine the angle of attack of the hydrofoil 400 and compare it to the optimal angle of attack. When these angles differ, the control system 110 may adjust the angle of attack of the hydrofoil 400 to approach the optimal angle of attack with the goal of ideally matching the optimal angle of attack.

System Control

[00231] The system 100 is controlled by a control system 110 that comprises a non-transitory computer readable medium that has stored on statements and instructions to cause the system 100 to perform any of the foregoing embodiments of methods described herein or depicted in the figures and a controller that is communicatively coupled to the computer readable medium and that can execute the statements and instructions stored on the medium. Any suitable controller may be used, such as a processor, microprocessor, microcontroller, programmable logic controller, field programmable gate array. Alternatively, the controller may be implemented in hardware using, for example, an application-specific integrated circuit. For example, the control system 110 may include a programmable logic controller having one or both of an internal and an external memory that either individually or collectively encoded thereon statements and instructions to cause the control system 110 to execute any of the foregoing embodiments of methods. Exemplary computer readable media include disc-based media such as CD-ROMs and DVDs, magnetic media such as hard drives and other forms of magnetic disk storage, semiconductor based media such as flash media, random access memory, and read only memory.

[00232] The control system 110 is communicatively coupled to and receives data from a multitude of sensors and controls components of the system 100 including traction actuators 201, control actuators 202, and recovery actuators 205. [00233] The control system 1 10 is also communicatively coupled to the collision avoidance processor 501 and can, for example, activate, deactivate, and override the collision avoidance system 500.

[00234] The control system 1 10 also provides bidirectional or unidirectional communication outside of the system 100 for operations, monitoring and maintenance.

[00235] While the control system 1 10 is shown as being outside of the hydrofoil 400 in

FIGS. 23, 24, and 28 (e.g. it may be located on shore), it may also be contained within the hydrofoil 400, such as within the foil body 401.

[00236] It is contemplated that any part of any aspect or embodiment discussed in this specification can be implemented or combined with any part of any other aspect or embodiment discussed in this specification.

[00237] For the sake of convenience, the exemplary embodiments above are described as various interconnected functional blocks. This is not necessary, however, and there may be cases where these functional blocks are equivalently aggregated into a single logic device, program or operation with unclear boundaries. In any event, the functional blocks can be implemented by themselves, or in combination with other pieces of hardware or software.

[00238] While particular embodiments have been described in the foregoing, it is to be understood that other embodiments are possible and are intended to be included herein. It will be clear to any person skilled in the art that modifications of and adjustments to the foregoing embodiments, not shown, are possible.