US20100327583A1 - Pitch, roll and drag stabilization of a tethered hydrokinetic device - Google Patents

Pitch, roll and drag stabilization of a tethered hydrokinetic device Download PDF

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US20100327583A1
US20100327583A1 US12789074 US78907410A US2010327583A1 US 20100327583 A1 US20100327583 A1 US 20100327583A1 US 12789074 US12789074 US 12789074 US 78907410 A US78907410 A US 78907410A US 2010327583 A1 US2010327583 A1 US 2010327583A1
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rotor
drag
device
configured
hydrokinetic
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US12789074
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Turner HUNT
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Hunt Turner
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    • BPERFORMING OPERATIONS; TRANSPORTING
    • B63SHIPS OR OTHER WATERBORNE VESSELS; RELATED EQUIPMENT
    • B63BSHIPS OR OTHER WATERBORNE VESSELS; EQUIPMENT FOR SHIPPING
    • B63B21/00Tying-up; Shifting, towing, or pushing equipment; Anchoring
    • B63B21/50Anchoring arrangements or methods for special vessels, e.g. for floating drilling platforms or dredgers
    • YGENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02EREDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E10/00Energy generation through renewable energy sources
    • Y02E10/20Hydro energy
    • Y02E10/28Tidal stream or damless hydropower, e.g. sea flood and ebb, river, stream
    • YGENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02EREDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E10/00Energy generation through renewable energy sources
    • Y02E10/30Energy from the sea
    • Y02E10/38Wave energy or tidal swell, e.g. Pelamis-type

Abstract

A hydrokinetic device is provided that extracts power from a water current. The device comprises a buoyant body and a rotor coupled to the buoyant body configured to drive a power generator. The buoyant body and the rotor jointly define a center of buoyancy and a center of gravity, the center of buoyancy being located above and upstream of the center of gravity.

Description

    CROSS REFERENCE TO PRIOR APPLICATIONS
  • This application claims priority and the benefit thereof from U.S. Provisional Application No. 61/221,676, filed on Jun. 30, 2009, and entitled OCEAN CURRENT TURBINE AND HYDROKINETIC POWER GENERATION APPARATUSES AND RELATED METHODS, ALONG WITH MOORING & YAW ARRANGEMENTS, FURLING ROTOR DEPTH CONTROL, AND MOORING HARNESSES FOR USE THEREWITH, the entirety of which is hereby incorporated herein by reference. This application also claims priority and the benefit thereof from U.S. Provisional Application No. 61/236,222, filed on Aug. 24, 2009, and entitled SELF-CONTAINED VARIABLE PITCH CONTROL ROTOR HUB; METHOD OF MAXIMIZING ENERGY OUTPUT AND CONTROLLING OPERATING DEPTH OF AN OCEAN CURRENT TURBINE; AND VARIABLE DEPTH HYDROPLANE SLED, the entirety of which is also hereby incorporated herein by reference. This application also claims priority and the benefit thereof from U.S. Provisional Application No. 61/328,884, filed on Apr. 28, 2010, and entitled FLOODED ANCHORING SYSTEM AND METHOD OF DEPLOYMENT, POSITIONING AND RECOVERY, the entirety of which is hereby incorporated herein by reference.
  • BACKGROUND OF THE DISCLOSURE
  • 1. Field of the Disclosure
  • The present disclosure relates to a method, a system and a device for generating power from the kinetic energy of a fluid current, including pitch, roll and drag stabilization of the device. More particularly, the disclosure relates to a method, a system and a device for generating power from the kinetic energy of an ocean or river current, including pitch, roll and drag stabilization of the device.
  • 2. Related Art
  • Kinetic energy of flowing ocean currents represents a significant source of clean renewable energy. The water in the world's oceans is constantly in motion, and in many locations there exist repeatable, consistent and rapidly moving ocean currents with speeds in excess of 1.5 meters-per-second (m/s). Such examples include the Gulf Stream, the Humboldt, the Kuroshio, the Agulhas and others. These currents have their origins in ocean thermal and salinity gradients, Coriolis forces, and other ocean thermal transport mechanisms.
  • These currents represent “rivers in the ocean” which lie predominantly in continental shelf areas with bottom depths in excess of 300 meters. Such depths necessitate mooring the hydrokinetic device with cables or tethers to upstream anchors fixed to the sea bed. Upstream mooring cables can introduce destabilizing pitching moments onto the hydrokinetic device that require opposing moments to maintain a level trim steady state attitude that provides for the alignment of the rotational axis of the rotor and the free stream current flow direction. Misalignment of the rotational axis and free stream current flow direction (“furl angle”) can rapidly degrade energy conversion performance of a horizontal axis rotor. An additional destabilizing rolling moment, or adverse torque, may be introduced by the rotation of a horizontal axis rotor. Further, it may be advantageous to provide a means to mimic or proxy the rotor drag force that disappears when the rotor ceases operation in order to maintain depth control and to prevent a surge forward in the position of the hydrokinetic device.
  • An upstream mooring cable tension, which has a vertical force component, referred to as the “drowning force,” acts as an apparent weight and tends to pull the hydrokinetic device to greater depths. Since it is generally advantageous to attach the mooring cable(s) near the nose of the hydrokinetic device to promote directional alignment with changes in the free-stream current direction, the drowning force also creates a nose down pitching moment referred to as the “drowning moment” and this moment must be opposed by restoring moments generated by the hydrokinetic device. As the angle of the mooring cable with the horizontal (mooring cable “intercept angle”) becomes steeper, the drowning force increases, thus increasing the drowning moment and requiring even greater restoring nose up moments to maintain a level trim steady state attitude for maximum energy conversion performance.
  • Various methods are known to oppose destabilizing pitching moments, including, for example, fore and aft hydroplane lifting surfaces, using a lever system by changing the mooring cable attachment point or causing the device to be semi submerged allowing a reserve of buoyancy above the waterline to counteract the drowning moment. These known solutions tend to trade device stability for a loss in energy conversion performance by increasing the furl angle or by creating an apparent furl angle, or wake, upstream of the rotor that drifts downstream and impinges upon the rotor swept area thereby introducing a flow inclination angle into the rotor swept area.
  • For example, in U.S. Pat. No. 7,291,936, issued to Robson, a hydrokinetic device is described that uses a leverage system, which alters the attachment point of the upstream mooring cable, and a supplementary system, which alters the location of the center of gravity fore and aft, to provide for pitch angle changes of the entire device, thereby changing the angle of attack of an attached hydroplane wing to create more (or less) lift to offset changes in the drowning force, such that the device remains at or near a constant depth of operation. The main axis of the rotors of the Robson device becomes furled with the oncoming flow direction by pitching the entire device nose up or nose down to achieve constant depth operation. Robson moves the center of gravity and alters the lever point location not to ensure alignment of the rotor axis with the free stream, but rather to pitch the entire device for constant depth operation. Robson also suggests that the mooring cable intercept angle “should be kept reasonably small.” Shallow mooring cable intercept angles imply lengthy, more costly and heavier mooring cables as well as a less efficient use of the natural resource in that a larger projected geographic area is required to deploy the same number of devices in a regular patterned array.
  • U.S. Patent Application Publication No. US2008/0050993 to Mackie proposes fore and aft trimming hydrodynamic surfaces, as well as above surface buoyant elements, to counteract undesirable pitching moments for “near level trim to ensure optimum performance from the horizontal axis marine turbine.” Both of these solutions compromise energy conversion performance of the horizontal axis rotor. Fore and aft trimming surfaces, while providing lift to create moments to maintain level trim, also create a flow downwash inclination angle, or wake, that drifts downstream and impinges on the rotor swept area, presenting an apparent furl angle to the rotor, thereby reducing its energy conversion performance. Further, above-surface buoyant elements subject the device to wind/wave action disturbances on the surface, which translate into periodic or sinusoidal bobbing action of the entire device and the rotor, further degrading energy conversion performance. Both Robson and Mackie state that the center of buoyancy is located directly above the center of gravity “ensuring stability of the device,” but do not offer additional information or teachings with respect to the relative locations of the center of gravity and the center of buoyancy.
  • Significant adverse rolling moments may be introduced by the rotation of the rotor, since diameter and torque of the rotor tend to be of large measure in comparison to the remainder of the hydrokinetic device. Adverse torque is the tendency of the entire hydrokinetic device itself to rotate in the same direction as the rotational direction of the rotor, and, in the case of a horizontal axis rotor, this translates to the presence of a rolling moment proportional to the amount of torque absorbed by the rotor. The hydrokinetic device may therefore present a restoring torque to counteract the adverse torque created by the rotor to remain in a preferred vertical orientation.
  • Known hydrokinetic devices, including those described in U.S. Pat. Nos. 6,091,161 and 7,291,936 and U.S. Patent Application Publication No. 2008/0018115, typically use a second rotor of equal size, but opposite directional rotation to provide a cancelling torque. Dual counter rotating rotors can be operationally problematic and require rotor torque synchronization, thereby reducing machine availability in the event of the unintentional stoppage of one rotor since that necessitates the intentional stoppage of the second functional rotor to prevent the risk of overturning.
  • U.S. Pat. No. 4,025,220, and patent application publication Nos. US 2007/023107 and WO 2009/004420A2 propose the use of a multi-point mooring scheme by adding additional mooring cables attached to certain points on the device to provide restraining forces and moments via cable tension for maintaining proper device attitude. Given depths of several hundred meters, additional mooring cables are lengthy, costly, increase system weight and provide greater entanglement risk as well as additional maintenance concerns.
  • Given that the drag force created by the operational rotor is nearly equivalent to a flat plate of equivalent swept area, the total drag force acting on the hydrokinetic device may change by, for example, several hundred percent between a rotor operational condition and a rotor non-operational condition. As a result, the upstream mooring cables may slacken to a catenary condition, causing the hydrokinetic device to surge forward in position, which may present a collision risk to other neighboring hydrokinetic devices moored in an ocean current farm array. Further, the disappearance of the rotor drag force may also cause a significant decrease in the drowning force and thus depth control of the hydrokinetic device may become problematic, potentially leading to a rapid uncontrolled ascent or at least deviation from a specified depth. Known tethered hydrokinetic devices have not generally been concerned with drag stabilization in the absence of rotor operation.
  • Therefore, a solution is needed for the pitch and roll stabilization of a tethered hydrokinetic device without the compromises to energy conversion performance of known devices. Further, a solution is needed to mimic or proxy the rotor drag in the absence of rotor operation to aid in depth control and avoid a rapid surge forward in the position of the device.
  • The present disclosure provides a hydrokinetic device that harnesses the kinetic energy of flowing water currents to provide clean, renewable energy, as well as a system and a method for stabilizing the pitch, roll and drag of the hydrokinetic device.
  • SUMMARY OF THE DISCLOSURE
  • A method, a system, and a hydrokinetic device are provided for harnessing the kinetic energy of flowing water currents to provide clean, renewable energy, as well as a system and a method for stabilizing the pitch, roll and drag of the hydrokinetic device.
  • According to an aspect of the disclosure, a hydrokinetic device is disclosed that extracts power from water current. The device comprises: a buoyant body; and a rotor coupled to the buoyant body configured to drive a power generator, wherein the buoyant body and the rotor jointly define a center of buoyancy and a center of gravity, the center of buoyancy being located above and upstream of the center of gravity. The hydrokinetic device may further comprise: a moveable counterweight that is configured to adjust the center of gravity; a variable ballast that is configured to adjust the center of gravity; a hydroplane wing with an elevator control surface; or a keel that is attached to the buoyant body, the keel comprising a deadweight attached to a distal end. The rotor may be configured to selectively engage or disengage a water current flow.
  • According to a further aspect of the disclosure, a hydrokinetic device is disclosed that extracts power from water current, the device comprises: a buoyant body; a rotor coupled to the buoyant body, the rotor being configured to drive a power generator; a keel coupled to the buoyant body; and a deadweight coupled to a distal end of the keel. The device may further comprise: a plurality of laterally separated ballast tanks that are configured to be alternately purged of water or filled with water; a hydrodynamic lifting surface that is configured to provide a rolling moment; a drag inducer that is configured to deploy a varying drag condition, wherein the varying drag condition comprises a high drag condition, a low drag condition, or an intermediate drag condition; or a drag inducer that is configured to deploy a high drag condition, a low drag condition, or an intermediate drag condition. The deadweight may be offset from a vertical plane of symmetry of the buoyant body. The deadweight may be movable between a fore position and an aft position, or between a port side position and a starboard side position.
  • According to a still further aspect of the disclosure, a hydrokinetic device is disclosed that extracts power from water current. The device comprises: a buoyant body; a rotor coupled to the buoyant body, the rotor being configured to drive a power generator; and a drag inducer that is configured to deploy a varying drag condition, the varying drag condition including a high drag condition, a low drag condition, or an intermediate drag condition. The device may further comprise: a keel that is attached to the buoyant body, the keel comprising a deadweight attached to a distal end; a variable ballast that is configured to adjust the center of gravity; or a hydroplane wing with variable incidence means or an elevator control surface. The rotor may be configured to engage or disengage a water current flow. The drag inducer may be configured to disengage when the rotor is engaged. The drag inducer may be further configured to engage when the rotor is disengaged.
  • Additional features, advantages, and embodiments of the disclosure may be set forth or apparent from consideration of the following detailed description and drawings. Moreover, it is to be understood that both the foregoing summary of the disclosure, the following detailed description and drawings are exemplary and intended to provide further explanation without limiting the scope of the disclosure.
  • BRIEF DESCRIPTION OF THE EXHIBITS
  • The accompanying attachments, including drawings, which are included to provide a further understanding of the disclosure, are incorporated in and constitute a part of this specification, illustrate embodiments of the disclosure and together with the detailed description serve to explain the principles of the disclosure. No attempt is made to show structural details of the disclosure in more detail than may be necessary for a fundamental understanding of the disclosure and the various ways in which it may be practiced. In the exhibits:
  • FIGS. 1A and 1B show perspective and side views, respectively, of an example of a hydrokinetic device according to principles of the disclosure;
  • FIG. 2A shows a side view of an example of a hydrokinetic device with a center of buoyancy (CB) and center of gravity (CG) at about the same longitudinal station;
  • FIG. 2B shows a side view of an example of a hydrokinetic device with a CB above the CG at the same longitudinal station;
  • FIG. 2C shows a side view of an example of a hydrokinetic device with a CB above and upstream of the CG;
  • FIG. 3A is a side view of an example of an ocean current farm array of hydrokinetic devices with shallow mooring cable intercept angles;
  • FIG. 3B is a side view of an example of an ocean current farm array of hydrokinetic devices with moderate mooring cable intercept angles;
  • FIG. 3C is a side view of an example of an ocean current farm array of hydrokinetic devices with steep mooring cable intercept angles;
  • FIG. 4A is a side view of the hydrokinetic device of FIG. 1A with a ballast and a counter-weight, wherein the CG of the hydrokinetic device is in an aft position;
  • FIG. 4B is a side view of the hydrokinetic device of FIG. 1A with a ballast and a counter-weight, wherein the CG of the hydrokinetic device is a forward position;
  • FIG. 5A is a front view of the hydrokinetic device of FIG. 1A with a rotor in an operational state and the hydrokinetic device rolled to a starboard side;
  • FIG. 5B is a front view of the hydrokinetic device of FIG. 1A with the rotor in a non-operational state and the hydrokinetic device rolled to a port side with a keel weight located in a position transverse to the device plane of symmetry;
  • FIG. 5C is a front view of the hydrokinetic device of FIG. 1A with the rotor in the operational state and the hydrokinetic device in a vertical orientation with the keel weight located in the position transverse to the device plane of symmetry;
  • FIG. 6A is a perspective view of the hydrokinetic device of FIG. 1A, with a drag inducer deployed to a high drag condition;
  • FIG. 6B is a front view of the hydrokinetic device of FIG. 1A, with a drag inducer deployed to the high drag condition;
  • FIG. 7 is a side view of an ocean current farm array comprising a plurality of the hydrokinetic devices of FIG. 1A in various stages of operation; and
  • FIG. 8 shows an example of a process for detecting and controlling pitch, roll and drag of a hydrokinetic device, according to principles of the disclosure.
  • The present disclosure is further described in the detailed description that follows.
  • DETAILED DESCRIPTION OF THE DISCLOSURE
  • The embodiments of the disclosure and the various features and advantageous details thereof are explained more fully with reference to the non-limiting embodiments and examples that are described and/or illustrated in the accompanying drawings and detailed in the following description. It should be noted that the features illustrated in the drawings are not necessarily drawn to scale, and features of one embodiment may be employed with other embodiments as the skilled artisan would recognize, even if not explicitly stated herein. Descriptions of well-known components and processing techniques may be omitted so as to not unnecessarily obscure the embodiments of the disclosure. The examples used herein are intended merely to facilitate an understanding of ways in which the disclosure may be practiced and to further enable those of skill in the art to practice the embodiments of the disclosure. Accordingly, the examples and embodiments herein should not be construed as limiting the scope of the disclosure, which is defined solely by the appended claims and applicable law. Moreover, it is noted that like reference numerals represent similar parts throughout the several views of the drawings.
  • A “computer”, as used in this disclosure, means any machine, device, circuit, component, or module, or any system of machines, devices, circuits, components, modules, or the like, which are capable of manipulating data according to one or more instructions, such as, for example, without limitation, a processor, a microprocessor, a central processing unit, a general purpose computer, a super computer, a personal computer, a laptop computer, a palmtop computer, a notebook computer, a desktop computer, a workstation computer, a server, or the like, or an array of processors, microprocessors, central processing units, general purpose computers, super computers, personal computers, laptop computers, palmtop computers, notebook computers, desktop computers, workstation computers, servers, or the like. Further, the computer may include an electronic device configured to communicate over a communication link. The electronic device may include, for example, but is not limited to, a mobile telephone, a personal data assistant (PDA), a mobile computer, a stationary computer, a smart phone, mobile station, user equipment, or the like.
  • A “network,” as used in this disclosure, means an arrangement of two or more communication links. A network may include, for example, the Internet, a local area network (LAN), a wide area network (WAN), a metropolitan area network (MAN), a personal area network (PAN), a campus area network, a corporate area network, a global area network (GAN), a broadband area network (BAN), any combination of the foregoing, or the like. The network may be configured to communicate data via a wireless and/or a wired communication medium. The network may include any one or more of the following topologies, including, for example, a point-to-point topology, a bus topology, a linear bus topology, a distributed bus topology, a star topology, an extended star topology, a distributed star topology, a ring topology, a mesh topology, a tree topology, or the like.
  • A “communication link”, as used in this disclosure, means a wired , wireless and/or acoustic medium that conveys data or information between at least two points. The wired, wireless or acoustic medium may include, for example, a metallic conductor link, a radio frequency (RF) communication link, an Infrared (IR) communication link, an optical communication link, or the like, without limitation. The RF communication link may include, for example, WiFi, WiMAX, IEEE 802.11, DECT, 0G, 1G, 2G, 3G or 4G cellular standards, Bluetooth, or the like.
  • The terms “including”, “comprising” and variations thereof, as used in this disclosure, mean “including, but not limited to”, unless expressly specified otherwise.
  • The terms “a”, “an”, and “the”, as used in this disclosure, means “one or more”, unless expressly specified otherwise.
  • Devices that are in communication with each other need not be in continuous communication with each other, unless expressly specified otherwise. In addition, devices that are in communication with each other may communicate directly or indirectly through one or more intermediaries.
  • Although process steps, method steps, algorithms, or the like, may be described in a sequential order, such processes, methods and algorithms may be configured to work in alternate orders. In other words, any sequence or order of steps that may be described does not necessarily indicate a requirement that the steps be performed in that order. The steps of the processes, methods or algorithms described herein may be performed in any order practical. Further, some steps may be performed simultaneously.
  • When a single device or article is described herein, it will be readily apparent that more than one device or article may be used in place of a single device or article. Similarly, where more than one device or article is described herein, it will be readily apparent that a single device or article may be used in place of the more than one device or article. The functionality or the features of a device may be alternatively embodied by one or more other devices which are not explicitly described as having such functionality or features.
  • A “computer-readable medium”, as used in this disclosure, means any medium that participates in providing data (for example, instructions) which may be read by a computer. Such a medium may take many forms, including non-volatile media, volatile media, and transmission media. Non-volatile media may include, for example, optical or magnetic disks and other persistent memory. Volatile media may include dynamic random access memory (DRAM). Transmission media may include coaxial cables, copper wire and fiber optics, including the wires that comprise a system bus coupled to the processor. Transmission media may include or convey acoustic waves, light waves and electromagnetic emissions, such as those generated during radio frequency (RF) and infrared (IR) data communications. Common forms of computer-readable media include, for example, a floppy disk, a flexible disk, hard disk, magnetic tape, any other magnetic medium, a CD-ROM, DVD, any other optical medium, punch cards, paper tape, any other physical medium with patterns of holes, a RAM, a PROM, an EPROM, a FLASH-EEPROM, any other memory chip or cartridge, a carrier wave as described hereinafter, or any other medium from which a computer can read.
  • Various forms of computer readable media may be involved in carrying sequences of instructions to a computer. For example, sequences of instruction (i) may be delivered from a RAM to a processor, (ii) may be carried over a wireless transmission medium, and/or (iii) may be formatted according to numerous formats, standards or protocols, including, for example, WiFi, WiMAX, IEEE 802.11, DECT, 0G, 1G, 2G, 3G or 4G cellular standards, Bluetooth, or the like.
  • According to an aspect of the disclosure, a hydrokinetic device 100 is disclosed that has a center of buoyancy (“CB”) above and upstream of the device's center of gravity (“CG”). The configuration of the hydrokinetic device 100 provides a restoring pitching moment, which may be referred to as the body pitching moment. The body pitching moment opposes a drowning moment and maintains the hydrokinetic device 100 in a level steady state trimmed operational attitude with substantially zero furl angle, providing for maximum energy conversion performance. With the introduction of the body pitching moment, the hydrokinetic device 100 may be configured to include smaller or substantially nonexistent fore and/or aft lifting surfaces. Further, the hydrokinetic device 100 may support steeper mooring cable intercept angles with shorter, less costly and lighter mooring cables, thereby allowing for deployment of larger numbers of hydrokinetic devices 100 per square kilometer and making more efficient use of the natural resources. Additionally, the pitch attitude of the hydrokinetic device 100 may be altered by moving counterweights fore and aft, or by flooding and evacuating fore and aft ballast tanks, or by altering the lift or down-force on fore and aft hydrodynamic surfaces.
  • According to a further aspect of the disclosure, a hydrokinetic device 100 is disclosed that creates a rolling moment in opposition to the adverse torque created by an operational rotor. The hydrokinetic device 100 may include a downwardly depending ventral keel structure with a dead weight attached to a distal end to create the rolling moment. In this regard, the ventral keel acts as a weighted pendulum that, when a roll angle deflection occurs, the weighted ventral keel is angularly displaced in the direction of rotation of the rotor and passively creates a restoring rolling moment to rotate the entire hydrokinetic device 100 back to a predetermined vertical orientation.
  • Additionally, the dead weight at the ventral keel distal end may be offset from the vertical plane of symmetry of the hydrokinetic device 100 such that when the rotor is in operation and rotor adverse torque is present, the ventral keel assumes a near vertical orientation; and, when the rotor is inoperative, the ventral keel assumes a slanted or angularly deflected orientation. The length of the ventral keel and the weight of the dead weight at the distant end may be configured so that a resulting opposing rolling moment substantially cancels any adverse torque created by the operational rotor.
  • According to a further aspect of the disclosure, a hydrokinetic device 100 is disclosed that deploys or extends a rotor drag proxy device, or drag inducer, in the absence of rotor operation to mimic the drag created by the operational rotor such that the upstream mooring cables do not slacken to a catenary condition causing the hydrokinetic device to surge forward in position and cause a collision or mooring cable entanglement risk to neighboring hydrokinetic devices that may be moored nearby in a patterned deployment farm array. In addition, the drag inducer provides a means to modulate a drag force acting on hydrokinetic device 100, thereby modulating the drowning force which may aide in maintaining depth control in the absence of rotor operation.
  • FIG. 1A shows an example of a hydrokinetic device 100 configured in accordance with the principles of the disclosure. FIG. 1B shows a side view of the hydrokinetic device 100.
  • The hydrokinetic device 100 includes a hull 101, a rotor 109, an aft mounted electrical generator (not shown), a keel 105, a keel cylinder 111, a hydrodynamic wing 106, and a harness 102. The hydrokinetic device 100 may include a computer (not shown) and a transceiver (not shown). The hydrokinetic device 100 may include one or more sensors for detecting ambient conditions, such as, for example, water temperature, pressure, depth, proximity of objects (such as, for example, of other hydrokinetic devices, mammals, fish, vessels, and the like), speed and/or direction of water current flow, and the like. Further, the rotor 109 may include an onboard hub controller (not shown) and a transceiver. The hull 101 may include a main pressure vessel which may provide the main source of buoyancy for the hydrokinetic device 100. Additionally, the hull 101 may include one or more interior ballast tanks (not shown) that can be alternately flooded or purged with water to adjust the weight (ballast), as well as the location of the center of gravity of the hydrokinetic device 100.
  • The rotor 109 may include a downstream horizontal axis rotor having a plurality of rotor blades 107 and a variable pitch control rotor hub 108. The variable pitch control rotor hub 108 may be connected to the aft mounted electrical generator (not shown), which is employed in the production of electricity.
  • The keel 105 may include a ventral keel structure having, for example, a moveable counter weight (not shown) that is capable of fore and aft movement. The keel 105 may be connected to the keel cylinder 111 and offset by a distance 117 from a vertical plane of symmetry of the hydrokinetic device 100. The keel cylinder 111 may include a dead weight. The keel 105 and/or keel cylinder 111 may provide a variety of purposes, including, for example, a natural rudder for passive yaw alignment, a weighted pendulum to aide in the cancellation of rotor adverse torque, a means to facilitate the CB above and upstream of the CG to facilitate production of the body pitching moment, a large surface for the mounting of one or more drag inducers 112 to facilitate drag modulation, a leading edge root extension (LERX) 114 to provide a forward attachment point for the mooring system, and the like, and other advantageous uses as described herein, or that will become readily apparent to one of ordinary skill in the art. The one or more drag proxy devices 112 may include, for example, split drag flaps. The hydrodynamic wing 106 may be generally mounted above the hull 101. Alternately, the hydrodynamic wing 106 may be mounted at par with the hull 101 or may be mounted below the hull 101. The LERX 14 may provide a nose-forward attachment point for a harness 102. Alternately, the harness 102 may be attached to the hull 101.
  • The hydrodynamic wing 106 may be configured to provide either variable angle incidence deflections or trailing edge elevator control surface deflections to create lift or down-force on the hydrokinetic device 100.
  • The harness 102 may include a universal joint mooring device. The harness 102 may be configured to allow the hydrokinetic device 100 to freely pivot in both pitch and yaw, as seen, for example, in FIG. 1B, shown by an arrow 120. The harness 102 may be attached to one or more mooring cables 103. The mooring cables 103 may be attached to anchors 104, which may be fixed to a surface 110, such as, for example, sea bed, a river bed, an underwater platform, and the like. The mooring cables 103 may be arranged to prohibit port or starboard translational movement as the hydrokinetic device 100 yaws about the harness 102. The mooring cables 103 form an intercept angle 121 with the horizontal or transverse component of the water current flow vector C, shown in FIG. 1B.
  • The hydrokinetic device 100 is configured to be deployed in patterened deployment arrays, or ocean current farm arrays, (shown, for example, in FIGS. 3A-3C). Neighboring hydrokinetic devices 100 in a given farm array may share anchors 104. Electricity created by each onboard generator (not shown) may be routed to, for example, neighboring hydrokinetic devices 100 or one or more electric stations (not shown) located in the water, or on land, to collect the electrical energy from each hydrokinetic device 100 prior to transmitting the electricity to, for example, a utility grid, which may be located on water or land. The electricity may be transmitted via electrical cables (not shown), which may be attached to, for example, the mooring cables 103 and routed to the neighboring devices 100, or to the one or more stations.
  • The hydrokinetic device 100 is configured to maintain a fully level steady state trimmed operational attitude with a free-stream current flowing in, for example, the direction shown by arrow C. In this regard, the hydrokinetic device 100 may maintain the rotational axis 115 of rotor 109 substantially parallel to the oncoming free-stream current flow C, thereby maximizing the conversion of the kinetic energy in the moving fluid to useable electrical power.
  • In the level steady state trimmed operational attitude, the hydrokinetic device 100 may maintain the CB above and upstream of the CG to create a body pitching moment to oppose a drowning moment. Fore and aft ballast tanks (not shown) interior to the hull 101 may be purged or flooded with water to alter the location of the CG relative to the location of the CB to adjust the magnitude of the body pitching moment to exactly cancel the drowning moment, which may fluctuate from time to time with changing free-stream current conditions. Further, a moveable counter weight, or keel weight (not shown), located interior to the keel cylinder 111 may be shifted fore and aft to alter the location of the CG relative to the location of the CB to also adjust the magnitude of the body pitching moment. Fore and aft trimming surfaces (not shown) may be used to trim out any excess pitching moments to remain in the level steady state trimmed operational attitude.
  • The rotor 109 may be configured to rotate, for example, in the direction shown by arrow 116 in FIG. 1A about the rotational axis 115 (counterclockwise as viewed from the front of the hydrokinetic device 100). The rotation 116 of the rotor 109 creates a rolling moment or adverse torque that is imparted to the hydrokinetic device 100, which is also in the direction of arrow 116. The rotor adverse torque may cause the keel 105 to angularly deflect to, for example, the port side, thereby causing the keel cylinder 111 (including, for example, a dead weight and counter weight contained therein) to traverse to the port side, thereby creating a restoring rolling moment to oppose the rotor adverse torque. As shown in FIG. 1A, the keel cylinder 111 may be offset from the vertical plane of symmetry of the hydrokinetic device 100 by the lateral distance 117.
  • The drag inducers 112 may include, for example, a pair of split drag flaps that are attached to the keel 105 near a trailing edge of the keel 105, as seen in FIG. 1A. The drag inducers 112 may mimic and proxy a drag force of the rotor 109 in the absence of operation of the rotor 109. To increase a drag force, the drag inducers 112 may be deflected substantially simultaneously in opposite directions, as shown, for example, in FIG. 6A. The drag inducers 112 may be progressively deflected, providing a progressively larger frontal area as the angle of deflection increases. To reduce a drag force, the drag inducers 112 may be retracted inward and moved toward each other at substantially the same time, providing a progressively smaller frontal area as the angle of deflection decreases. The drag inducers 112 may be deployed whenever the rotor 109 is not operating, or operating below a predetermined threshold, to prevent a surge forward in position of the hydrokinetic device 100, or to control and/or maintain a specified depth.
  • The computer (not shown) in the hydrokinetic device 100 may be configured to control the various mechanical aspects of the hydrokinetic device 100, according to the principles of the disclosure. The computer may control, for example, flooding or purging of water into the one or more interior ballast tanks (not shown), the operation of the rotor 109, the rotor blade pitch angles associated with the variable pitch control rotor hub 108, the operation of the drag inducers 112, the operation of the hydrodynamic wing 106, the trailing edge elevator control surface deflections, communication with the one or more stations (not shown) and/or power grid (not shown), the operation of the moveable counterweight, or keel weight located interior to the keel cylinder 111, and the like. Communication between the onboard computer and, for example, the station and/or grid may be carried out by means of the onboard transceiver (not shown) and communication links (not shown), as is known by those having ordinary skill in the art.
  • The station and/or grid may each include a computer (not shown) that is communicatively coupled via one or more transceivers, one or more communication links and, optionally, a network to a plurality of hydrokinetic devices 100. The computer may be configured to remotely monitor and control each of the hydrokinetic devices 100.
  • FIGS. 2A-2C show examples of three different hydrokinetic devices 200, 220, and 240, each having a different configuration than the other two. In particular, FIG. 2A shows a side view of a hydrokinetic device 200 with the center of buoyancy (CB) and center of gravity (CG) at about the same longitudinal station. FIG. 2B shows a side view of a hydrokinetic device 220 with a CB above the CG at the substantially the same longitudinal station. FIG. 2C shows a side view of a hydrokinetic device 240 with the CB above and upstream of the CG. FIGS. 2A-2C show some mechanical advantages gained by, for example, positioning the CB above and upstream of the CG.
  • FIG. 2A shows a hydrokinetic device 200 having a CB 219 and a CG 214 co-located at substantially the same longitudinal and waterline station, having a near zero longitudinal separation 215. The hydrokinetic device 200 may be restrained by a mooring cable 208. The mooring cable 208 may have, for example, a shallow intercept angle 207 with a horizontal reference plane. In this regard, the mooring cable 208 may transfer the vector forces 209, 210, 211 to the hydrokinetic device 200, including the drowning force 211.
  • Prior to the rotor 201 becoming operational, the hydrokinetic device 200 may assume a level attitude (not shown). When the rotor 201 becomes operational, the rotor 201 creates a large downstream drag force that is applied to the hydrokinetic device 200, causing the hydrokinetic device 200 to rotate nose down, as shown in FIG. 2A. The hydrokinetic device 200 may rotate nose down until the drowning moment resulting from the drowning force 211 of the hydrokinetic device 200 is substantially equal and opposite to the sum of a nose up moment caused by the wing 202 and the nose up moment caused by the drag force of the rotor 201 acting above the CG 214. The nose up moment caused by the wing 202 may be increased by a trailing edge up angular deflection 212 by elevator control surface 203. As a result of this nose down rotation of the hydrokinetic device 200, a furl angle 206 is introduced with regard to the rotational axis 204 of the rotor 201, thereby reducing the energy conversion performance by a factor approximately equal to a cube of the cosine of angle 206.
  • In order to return the hydrokinetic device 200 to a level trim attitude, the elevator control surface deflector 203 may be configured to deflect even further trailing edge up to an angle 212, thereby increasing the down-force on the wing 202 and causing a nose up moment of the hydrokinetic device 200. The resultant increased down-force on the wing 202 may cause a trailing edge downwash flow angularity (or wake) to drift downstream and impinge onto the rotor 201, thereby causing the rotor 201 to experience an apparent furl angle 212, which may be in addition to the already existing geometric furl angle 206, both of which conspire to degrade the energy conversion performance of rotor 201 At a shallow intercept angle 207, the mooring cables 208 must be lengthy, heavier and more costly.
  • At a steeper intercept angle 207, the magnitude of the drowning force 211 will increase, thereby increasing the drowning moment acting on hydrokinetic device 200. With steeper intercept angle 207, the rotor 201 will become increasingly furled, and less efficient, requiring a larger and more costly wing 202 to create the necessary restoring nose up moments to level the hydrokinetic device 200. If the mooring cable attachment point were moved aft toward the CG 214 location in an attempt to reduce the drowning moment by shortening the lever arm associated with drowning force 211, the hydrokinetic device 200 may sacrifice directional stability and the ability to align itself in yaw with the oncoming current direction.
  • FIG. 2B shows a hydrokinetic device 220 with a CB 239 and a CG 234 at substantially the same longitudinal station. However, the CB 239 is located directly above the CG 234 when the hydrokinetic device 220 is in a substantially level trim attitude (not shown). The hydrokinetic device 220 may be restrained by a mooring cable 228, which has a steeper intercept angle 227 with a horizontal reference plane than the hydrokinetic device 200 in FIG. 2A. The mooring cable 228 may transfer vector forces 229, 230, 231 to the hydrokinetic device 220, including the drowning force 231, as shown in FIG. 2B.
  • Prior to the rotor 221 becoming operational, the hydrokinetic device 220 may assume a level attitude (not shown). When the rotor 221 becomes operational, it may create a large drag force downstream that causes the hydrokinetic device 220 to rotate nose down, as shown in FIG. 2B. As the hydrokinetic device 220 rotates nose down, the CB 239 advances upstream of the CG 234. The nose down rotation of the hydrokinetic device 220 may stop when the drowning moment resulting from the drowning force 231 is substantially equal and opposite to the sum of the nose up moment caused by a wing 222, the nose up moment caused by the rotor drag force of the rotor 221 acting above the CG 234, and the nose up moment resulting from a longitudinal separation 235 between the CB 239 and the CG 234. The nose up moment caused by the wing 222 may be aided by a trailing edge up angular deflection 232 by elevator control surface 223. The longitudinal separation 235 may be solely a result of the nose down (or nose up) rotation of the hydrokinetic device 220. The CG 234 may have a height separation 236 with regard to the CB 239. With the additional contributing moment represented by the longitudinal separation 235 between CG 234 and CB 239, a furl angle 226 (with regard to the rotational axis 224 of the rotor 221) may be reduced relative to the furl angle 206 shown in FIG. 2A.
  • In order to return the hydrokinetic device 220 to a level trim attitude, it may be necessary to increase the deflection angle 232 of the trailing edge elevator control surface 223, thereby introducing or increasing flow angularity into the downstream rotor 221. The flow angularity may cause the rotor 221 to experience an apparent furl angle 232 in addition to the previously described geometric furl angle 226, thereby reducing the energy conversion efficiency of the rotor 221.
  • At a shallow intercept angle 227, mooring cable cables 228 must be lengthy, more costly and heavier. At a steeper intercept angle 227, the rotor 221 becomes even more furled and less efficient, requiring a larger, more costly wing 222 to create the necessary restoring nose up moments to the hydrokinetic device 220. If the mooring cable attachment point is moved aft toward the CG 234 location, in an effort to reduce the drowning moment by shortening the lever arm associated with drowning force 231, the hydrokinetic device 220 may sacrifice directional stability and the ability to align itself in yaw with the oncoming current direction.
  • FIG. 2C shows an example of a hydrokinetic device 240 (or 100), according to principles of the disclosure. The hydrokinetic device 240 has a CB 259 that may be located above and upstream of a CG 254 when the hydrokinetic device 240 is in a substantially level trim attitude. The CG 254 may have a height separation 256 with regard to the CB 259. The hydrokinetic device 240 may be restrained by a mooring cable 248, which may have a steeper intercept angle 247 (or 121 in FIG. 1B) than angles 207 or 227 of FIGS. 2A, 2B, respectively. The mooring cable 248 may transfer vector forces 249, 250, 251 to the hydrokinetic device 240, including a drowning force 251.
  • Prior to a rotor 241 (or 109) becoming operational, the hydrokinetic device 240 may assume a nose high attitude (not shown), where the nose of the hydrokinetic device 240 is rotated upward and a separation distance 255 between the CB 259 and CG 254 may be minimal. When the rotor 241 becomes operational, it may create a large downstream drag force that causes the hydrokinetic device 240 to rotate nose down from, for example, a nose high attitude. The hydrokinetic device 240 may cease to rotate nose down when the drowning moment resulting from drowning force 251 becomes substantially equal and opposite to the sum of the nose up moment caused by the rotor drag force acting on the hydrokinetic device 240 above the CG 254, and the body pitching moment resulting from the longitudinal separation 255 between the CB 259 and the CG 254. By locating the CB 259 above and upstream of the CG 254, the hydrokinetic device 240 may remain in a substantially level steady state trimmed operational attitude with a substantially zero geometric furl angle 246 with regard to the rotational axis 244 of the rotor 241. Since a trimming moment will not be necessary from a wing 242 (or 106) and trailing edge elevator control surface 243 may have zero deflection angle 252, flow angularity may be avoided or minimized and, therefore, not introduced into the rotor 241. Accordingly, the rotor 241 may remain in its most efficient operating condition providing maximum energy conversion performance.
  • As seen in FIG. 2C, the intercept angle 247 can be significantly steeper than the intercept angles 207, 227, shown in FIGS. 2A, 2B. Accordingly, the mooring cable 248 may be shorter, less costly and lighter than the mooring cables 208, 228 in FIGS. 2A, 2B. The hydrokinetic device 240 is configured to offset the larger drowning moments conveyed from mooring cable 248 by adjusting the longitudinal separation 255 between CB 259 and CG 254, without a loss in efficiency caused by a geometric or apparent furl angle of the rotor 241. Thus, energy conversion performance of the rotor 241 may be maximized while simultaneously ensuring pitch stability and a level trim operating attitude of hydrokinetic device 240.
  • As noted earlier, the keel cylinder 260 (or 111) may include a movable counterweight (not shown), and the hull 101 may include one or more ballast tanks (not tanks). By adjusting the counterweight in the keel cylinder 260 (for example, moving the counterweight fore or aft in the keel cylinder 260) and/or exchanging water ballast between a pair of fore and aft ballast tanks (in the hull 101), the position of the CG 254 may be adjusted. Furthermore, by adjusting the counterweight in the keel cylinder 260 and exchanging the water ballast between the fore and aft ballast thanks, the amount of longitudinal separation 255 between the CB 259 and the CG 254 may be adjusted so that the hydrokinetic device 240 remains in a level steady state trimmed operational attitude with substantially zero rotor furl angle 246 and substantially no lifting force created by the wing 242 (or 106), thereby avoiding any geometric or apparent furl angle experienced by the rotor 241. Accordingly, the pitch of the hydrokinetic device 240 may be stabilized and a level steady state trimmed operational attitude maintained without comprising the energy conversion performance of the rotor 241.
  • According to an embodiment of the disclosure, the wing 242 (or 106) may be eliminated entirely from the hydrokinetic device 240 (or 100). In this embodiment, pitch, roll and/or drag stabilization of the tethered hydrokinetic device 240 may be accomplished by the remaining means.
  • According to another embodiment of the disclosure, the wing 242 (or 106) may be located proximate the CG 254 and thus may be used solely to lift or down-force (drown) the hydrokinetic device 240. Alternatively (or additionally), the wing 242 may be located distant from CG 254 and may be used as both a trimming device and a lifting device.
  • According to principles of the disclosure, the harness 102 may be located reasonably far forward on the hydrokinetic device 240 to maximize the directional stability and yaw alignment capability of the device. The body pitching moment resulting from the longitudinal separation 255 of the CB 259 and CG 254 may assist in counter acting the increased drowning moment resulting from the drowning force acting at a reasonably far forward attachment point of the harness 102.
  • FIGS. 3A-3C show various examples of farm arrays of fully submerged operational hydrokinetic devices 300, 310 and 320 with free-stream current shown flowing in the direction of arrow C. In particular, FIG. 3A shows a side view of an example of an ocean current farm array of hydrokinetic devices 300 (or 200) with shallow mooring cable intercept angles 301 (or 207); FIG. 3B shows a side view of an example of an ocean current farm array of hydrokinetic devices 310 (or 220) with moderate mooring cable intercept angles 311 (or 227); and FIG. 3C shows a side view of an example of an ocean current farm array of hydrokinetic devices 320 (or 240, or 100) with steep mooring cable intercept angles 321 (or 121, or 247).
  • Referring to FIG. 3A, the hydrokinetic devices 300 generally correspond to the hydrokinetic device 200 shown in FIG. 2A. The hydrokinetic devices 300 are configured in a farm array, with each of the hydrokinetic devices 300 connected to a mooring cable having a shallow intercept angle 301. As seen in FIG. 3A, the shallow mooring cable intercept angles 301 require lengthy, costly and heavier mooring cables 303 than the farm arrays shown in FIGS. 3B or 3C. Additionally, a significant furl angle 305 may be introduced that causes a substantial reduction in energy conversion performance of the horizontal axis rotor. In addition to the increased cost and length of mooring cables 303, such cables tend to be heavier, requiring a larger and costlier hydrodynamic device, buoyant volume, or larger wing lifting surface to support the increased weight of the mooring cables 303.
  • A mooring overlap distance 302 denotes a distance between a location of an upstream hydrokinetic device 300 and a surface bed anchoring location 306 of the neighboring downstream hydrokinetic device 300. In order to increase the density of hydrokinetic devices 300 within a patterned deployment array of devices 300 and maximize the use of the natural resource by using the smallest overall geographic footprint, mooring overlap distances 302 may be increased so that successive rows of devices 300 in the downstream direction may be moved closer to the upstream row of devices 300. With lengthy mooring cables 303, it becomes more problematic to increase the overlap distance 302 given, for example, the possibility of mooring cable 303 entanglement, collisions between neighboring devices 300, increased difficulty of servicing an anchoring location 316 or a mooring cable 303 of a hydrokinetic device 300 that can only be accessed directly below an upstream neighboring operational hydrokinetic device 300.
  • Referring to FIG. 3B, the hydrokinetic devices 310 generally correspond to the hydrokinetic device 220 shown in FIG. 2B. In the farm array of hydrokinetic devices 310, a plurality of mooring cables 313 have steeper intercept angles 311 than the mooring cables 303 of the farm array shown in FIG. 3A. Accordingly, shorter, less costly and lighter mooring cables 313 may be used compared to the mooring cables 303 of the farm array shown in FIG. 3A. The mooring cable overlap distance 312 may be decreased compared to the overlap distance 302 of FIG. 3A, whilst still increasing the density of the hydrokinetic devices 310 in a given geographic area.
  • Furthermore, while smaller than the furl angle 305 introduced in the hydrokinetic devices 300 in FIG. 3A, the hydrokinetic devices 310 introduce a significant furl angle 315 that causes a substantial reduction in energy conversion performance of the horizontal axis rotor.
  • Referring to FIG. 3C, the hydrokinetic devices 320 generally correspond to the hydrokinetic device 240 shown in FIG. 2B, or the hydrokinetic device 100 shown in FIGS. 1A, 1B. With the CB 259 above and upstream of the CG 254, as described in FIG. 2C, the hydrokinetic devices 320 may use the resultant body pitching moments to allow for the steepest mooring cable intercept angles 321, thereby allowing for the shortest, lightest and least costly cables 323, whilst allowing the hydrokinetic devices 320 to maintain a level steady state trimmed operational attitude with substantially zero rotor furl angle 325 (geometric or apparent) that provides for maximum energy conversion performance. Furthermore, a greater number of hydrokinetic devices 320 may be deployed in a smaller geographic area, thereby maximizing use of the natural resource, while minimizing the mooring cable overlap distance 322 between a location of an upstream hydrokinetic device 320 and a surface bed anchoring location 326 of the neighboring downstream hydrokinetic device 300 to avoid cable entanglement risks and complications with servicing anchors or mooring cables of neighboring devices 320.
  • FIG. 4A is a side view of a hydrokinetic device 400 that is similar to, or substantially the same as the hydrokinetic device 100 shown in FIG. 1A, or the hydrokinetic device 240 shown in FIG. 2C. The hydrokinetic device 400 includes at least two mechanisms for moving a CG 404 (or 254) fore and aft in relation to a CB 416 (or 259) to alter the magnitude of a body pitching moment of the hydrokinetic device 400. For example, the hydrokinetic device 400 may include a pair of fore and aft located ballast tanks 401, 402. As seen in FIG. 4A, the forward located ballast tank 401 is shown as being near-empty and the ballast tank 402 is shown as being near-full. The hydrokinetic device 400 may further include a pump (not shown) that is configured to transfer water between the tanks 401 and 402. The hydrokinetic device 400 may further include a movable counterweight 403 in the keel cylinder 260 (or 111). The counterweight 403 may be configured to move longitudinally along a length of the keel cylinder 260, from a fore to an aft position, or from an aft to a fore position. The rotor axis is represented by 405.
  • The near-full aft ballast tank 402 and aft-most position of the counterweight 403 in the hydrokinetic device 400 may be representative of a maximum load condition. The maximum load condition may include, for example, where the CG 254 is located in a most aft-location 404, corresponding to the largest magnitude of a resultant body pitching moment on the hydrokinetic device 400.
  • FIG. 4B is a side view of the hydrokinetic device 400 (represented by 410) with a load condition where the CG 254 is located in a forward-most location 414, corresponding to a minimum magnitude of the resultant body pitching moment on the hydrokinetic device 400. As seen, the fore-located ballast tank 401 (represented by 411) is near-full and the aft-located ballast tank 402 (represented by 412) is near-empty. Further, the moveable counter weight 403 (represented by 413) is positioned in a forward position. The ballast tanks 401, 402 and/or the counterweight 403 may be employed to adjust the location of the CG 254 and, thereby, change the magnitude of the body pitching moment of the hydrokinetic device 400 to maintain a substantially level steady state trimmed operational attitude, so as to maximize energy conversion performance by the alignment of the rotational axis of the rotor 241 (or 109) and the free-stream current direction. The rotor axis is represented by 415.
  • FIG. 5A is a frontal view of the hydrokinetic device 500 that is similar to, or substantially the same as the hydrokinetic device 100 shown in FIG. 1A, or the hydrokinetic device 240 shown in FIG. 2C. Referring to FIG. 5A, the free-stream current C flows into the page with the horizontal axis rotor 501 (or 109, or 241) rotating in, for example, a counterclockwise direction 502 about an axis of rotation, which is perpendicular to the surface of the page. The hydrokinetic device 500 has a CB 259 (represented as 505) and a CG 254 (represented as 508).
  • During operation, the rotor 501 imparts a rolling moment, referred to as an adverse torque, to the hydrokinetic device 500 which tends to roll the hydrokinetic device 500, for example, counterclockwise in the direction 502. For example, the hydrokinetic device 500 may roll to a bank angle 507, at which the adverse torque is substantially offset by a restoring rolling moment created by the weight of a deadweight 503 and/or the counterweight 403 (represented by 503) acting thru a lever arm distance 506. The magnitude of the bank angle 507 is inversely proportional to the length of the keel 105 (represented by 510), the weight of the deadweight 503, and/or the weight of the counterweight 503. So, by using a longer keel 510, a heavier deadweight 503, and/or a heavier counterweight 503, a smaller bank angle 507 may be required to create the opposing rolling moment to offset the adverse torque created by the operational rotor 501. Thus, the weighted keel 510 may act as a righting pendulum.
  • However, as seen in FIG. 5A, the hydrokinetic device 500 may be angularly displaced from a vertical reference plane 509, leaning, for example, starboard and, therefore, not positioned in a preferred upright vertical orientation. The preferred upright vertical orientation occurs when the vertical plane of symmetry 504 of the hydrokinetic device 500 coincides with the vertical reference plane 509. In order to provide the rolling moment necessary to cancel the adverse torque from the rotor 501 and simultaneously achieve the preferred upright vertical orientation of the hydrokinetic device 500, a keel weight 513 may be laterally offset from the vertical plane of symmetry 504 of hydrokinetic device 500, as seen in FIG. 5B.
  • FIG. 5B is a front view of the hydrokinetic device 500, with the rotor 501 in a non-operational condition and the hydrokinetic device 500 rolled to a port side with a keel weight 513 located in a position transverse to the vertical plane of symmetry 504 of hydrokinetic device 500 and attached to, or integrally formed with the keel 510. The keel weight 513 may be configured to be laterally offset from the vertical plane of symmetry 504 of the hydrokinetic device 500 by a distance 516. As seen in FIG. 5B, with the rotor 501 not operational, the hydrokinetic device 500 will roll to the port side, thereby positioning a CB 515 and a CG 518 in vertical alignment with the vertical reference plane 509.
  • FIG. 5C is a front view of the hydrokinetic device 500 with the rotor 501 in the operational state and the hydrokinetic device 500 in a preferred vertical orientation with the vertical plane of symmetry 504 of hydrokinetic device 500 coincident with a vertical reference plane 509. The keel weight 513 may be located in a position substantially transverse to the vertical plane of symmetry 504 of the hydrokinetic device 500.
  • In FIG. 5C, with the rotor 501 operational and rotating in, for example, the direction 522, the hydrokinetic device 500 rolls to the starboard side from its prior port-side leaning position (shown in FIG. 5B), thereby righting the hydrokinetic device 500 to the preferred vertical orientation that is aligned with (or parallel to) the vertical reference plane 509. In this operational condition, the CG 528 is laterally displaced and located to, for example, the port side of the CB 525, thereby creating a persistent rolling moment to oppose the adverse torque created by the operational rotor 501.
  • As seen in FIG. 5C, the hydrokinetic device 500 may include one or more differential control surface deflectors 533, which may be provided on the wing 106 (represented as 531). The deflectors 533 may provide additional righting moments that oppose the adverse torque due to the operational rotor 501.
  • Further, the hydrokinetic device 500 may include a plurality of wing tanks 532 that may be attached to, or integrally formed with the wing 531. The wing tanks 532 may be provided at the distal ends of the wing 531 (for example, wing-tip tanks, shown in FIG. 5C), or at a position located between the distal end of the wing 531 and the hull 101. Additional righting moments may be provided by alternate purging or flooding of the wing tanks 532 to oppose the adverse torque due to the operational rotor 501.
  • Furthermore, the hydrokinetic device 500 may include a control surface deflector 535 that may be located on the distal end of the keel 524, as shown in FIG. 5C.
  • FIG. 6A shows a perspective view of a hydrokinetic device 600 that is similar to, or substantially the same as the hydrokinetic device 100 shown in FIG. 1A, or the hydrokinetic device 240 shown in FIG. 2C. In FIG. 6A, the hydrokinetic device 600 is shown with rotor blades 601 in a fully feathered, non-operational condition and with the drag inducer 602 located on the ventral keel 603 in a deflected position, thereby creating a high drag condition. The drag inducer 602 is shown as including, for example, a pair of split drag flaps.
  • FIG. 6B shows a front view of the hydrokinetic device 600, with the drag inducer 602 deployed to a high drag condition. In FIG. 6B, the split drag flaps of the drag inducer 602 may be deflected to provide a large frontal area, thereby imparting substantial drag under the force of the free-stream current flow C.
  • The mooring cable drowning force is proportional to the magnitude of the rotor drag force (for example, drowning force 251 in FIG. 2C). Accordingly, the presence or removal of the rotor drag force may cause large changes in the magnitude of the mooring cable drowning force and, hence, alter the vertical force balance required to maintain a specified depth of operation of the hydrokinetic device 600. The drag inducer 602 provides a proxy or substitute drag force for the rotor drag force, whenever the rotor drag force is absent or minimal. The drag inducer 602 provides a proxy for rotor drag force that prevents large fore and aft movement in position of the hydrokinetic device 600, which may occur during the transition of rotor blade pitch angles from a rotor operational condition to a rotor non-operational condition. Large fore and aft movements in position of the hydrokinetic device 600 may be very problematic, since the movements may slacken the upstream mooring cables, which may be of particular concern in a regularly spaced ocean current farm array where neighboring devices 600 may present a collision risk (see, for example, FIG. 7).
  • The drag inducer 602 may be deployed to a high drag condition anytime the rotor is not operating, and retracted to a low drag or no drag condition anytime the rotor is operational. Further, during a rotor blade 602 pitch angle engagement or disengagement sequence via, for example, the use of a variable pitch control rotor hub, the drag inducer 602 may retract or extend respectively in a manner and at a rate so as to keep the total drag force (or alternately total vertical force) acting on the hydrokinetic device 600 at a constant value, thereby providing a seamless transition between rotor operational and rotor non-operational conditions.
  • The drag inducer 602 may include a variety of deployable high drag devices, including, for example, the split drag flaps, deflectable body flaps or scales, deployable flaps located on wings or fore and aft trimming surfaces, pop-up or pop-out stall fences located on other surfaces of the hydrokinetic device 600, wing or trimming surfaces capable of about 90 degree incidence deflections, a tethered ballute or a tethered parachute that may be ejected from an interior cavity of the hydrokinetic device 600, or other high drag deployable devices that may be later retracted to a low drag or no drag condition.
  • FIG. 7 shows a side view of an ocean current farm array comprising a plurality of the hydrokinetic devices 700, 701, 702, 703 and 706 in various stages of operation. Each of the hydrokinetic devices 700, 701, 702, 703 and 706 may be similar to, or substantially the same as the hydrokinetic device 100 shown in FIG. 1A, or the hydrokinetic device 240 shown in FIG. 2C. For illustration, the hydrokinetic devices 700, 701, 702, 703 and 706 will be described below with reference to the example of the hydrokinetic device 100, shown in FIG. 1A.
  • The hydrokinetic devices 700, 701 and 702 may be operational in a substantially level trim steady state, at a depth at which a rated speed may occur and, thus, rated power may be produced by the onboard generators (not shown). The hydrokinetic device 703 may have its rotor 109 disengaged and, for the sake of illustration, the drag inducer 112 retracted to a non-drag, or low-drag condition. Accordingly, the hydrokinetic device 703 may be caused to surge forward in position with the mooring cables 705 in a catenary condition and pose a collision risk to the immediate upstream neighboring hydrokinetic device 701. By deploying the drag inducer 112 to the high drag condition, the hydrokinetic device 703 will pull the mooring cables 705 taught and recede downstream to a position 704, thereby alleviating any collision risk with the hydrokinetic device 701.
  • The hydrokinetic device 704 may have its rotor blades 107 fully feathered and its rotor 109 non-operational with the drag inducer 112 deployed to a high drag condition, and with the aid of the down-force on its wing 106 and increased sea water in the ballast tanks (for example, 401, 402 in FIG. 4A), the hydrokinetic device 704 may remain at the depth at which the rated speed may occur whilst at an idle power condition with the rotor non-operational (or substantially non-operational).
  • The hydrokinetic device 706 is shown in a semi-submerged surface condition, with its rotor 109 non-operational and the drag inducer 112 deployed to an intermediate deflection angle, thus creating an amount of drag sufficient to draw the mooring cables 705 taught, but yet not enough drag to increase the drowning force to a level that would pull the hydrokinetic device 706 to greater depths. In this condition, the hydrokinetic device 706 may be serviced and maintained by a crew from a surface vessel 707. In order to descend to an operating depth, the hydrokinetic device 706 may fully deploy the drag inducer 112 to a high drag condition, thereby increasing the drowning force and pulling the device 706 below the water surface. Once below the surface, the wing 106 may be rotated to negative incidence angles to create a down-force. Simultaneously (or at a different time), the ballast tanks (for example, shown in FIGS. 4A, 4B) may be filled with sea water to increase the weight of the hydrokinetic device 706 and descend the device 706 to a position 708, having a depth at which the rated speed may occur. At this depth, a drag force transition may occur between the drag inducer 112 that is progressively retracted towards the low drag condition and the actual rotor 109 now in the process of pitching the rotor blade pitch angles to an operational condition, thereby increasing the drag produced by the rotor 109 as it enters operation. This drag transition between rotor proxy (created by the drag inducer 112) and the actual rotor 109 at the specified depth occurs such that the vertical force balance acting on the entire hydrokinetic device 706 remains substantially zero and the device, along with the aid of the wing 106 which is relieving down-force as well as the ballast tanks 401, 402, which are offloading ballast during the rotor engagement transition process, remains at the specified depth at the rated speed at which rated power may be generated by hydrokinetic device 706. A similar but reverse drag force transition may occur as the rotor 109 is transitioned into a non-operational condition, wherein the drag force transference occurs from the rotor 109 to the drag inducer 112 prior to a controlled ascent of the hydrokinetic device 706. These two drag transition sequences, including, from a rotor 109 operational condition to a rotor 109 non-operational condition, and from a rotor 109 non-operational condition back to a rotor 109 operational condition, are referred to as a rotor disengage transition protocol and a rotor engage transition protocol, respectively, which are described in co-pending U.S. patent application Ser. No. ______ (Attorney Dkt. No. 2056997-5007US), filed on the same date as the instant application, entitled POWER CONTROL PROTOCOL FOR A HYDROKINETIC DEVICE INCLUDING AN ARRAY THEREOF, the entire disclosure of which is hereby incorporated herein by reference for all purposes as if fully set forth herein.
  • The hydrokinetic device 100 may be retained in the water by a mooring system, such as, for example, the mooring system described in co-pending U.S. patent application Ser. No. ______ (Attorney Dkt. No. 2056997-5006US), filed on the same date as the instant application, and entitled MOORING SYSTEM FOR A TETHERED HYDROKINETIC, the entire disclosure of which is hereby incorporated herein by reference for all purposes as if fully set forth herein.
  • The hydrokinetic device 100 may include a variable control rotor hub with a self-contained energy storage reservoir, such as, for example, described in co-pending U.S. patent application Ser. No. ______ (Attorney Dkt. No. 2056997-5005US), filed on the same date as the instant application, and entitled VARIABLE CONTROL ROTOR HUB WITH SELF CONTAINED ENERGY STORAGE RESERVOIR, the entire disclosure of which is hereby incorporated herein by reference for all purposes as if fully set forth herein.
  • FIG. 8 shows an example of a process 800 for detecting and controlling pitch, roll and drag of a hydrokinetic device, according to principles of the disclosure. Referring to FIGS. 1A and 8 concurrently, the process 800 includes sensing and determining a pitch of the hydrokinetic device 100 (Step 810), sensing and determining a roll (including vertical alignment) of the hydrokinetic device 100 (Step 814), and/or a drag force of the hydrokinetic device 100 (Step 818).
  • If a determination is made that the pitch angle of the hydrokinetic device 100 is outside of a predetermined range of pitch (YES at Step 820), then the pitch angle of the hydrokinetic device 100 may be adjusted by, for example, controllably, alternately filling and purging a plurality of longitudinally separated ballast tanks with water until the pitch angle of the hydrokinetic device 100 is returned to the predetermined range of pitch (Step 830), otherwise pitch angle adjustment is not carried out (NO at Step 820). Additionally (or alternatively), the pitch angle may be adjusted by controllably moving the counterweight in the keel cylinder 111 until the pitch angle of the hydrokinetic device 100 is returned to the predetermined range of pitch (Step 830). Additionally (or alternatively), the pitch angle may be altered by controllably adjusting portions of the hydrodynamic wing 106, including, for example, a variable incidence angle or one or more trailing edges, until the pitch angle of the hydrokinetic device 100 is returned to the predetermined range of pitch (Step 830).
  • If a determination is made that a vertical alignment position of the hydrokinetic device 100 is outside a predetermined range of vertical alignment positions (YES at Step 824), then the vertical alignment of the hydrokinetic device 100 may be adjusted by, for example, the methods indicated in reference to FIG. 5C which may include additionally (or alternatively) filling and/or purging wing tanks 532, deflecting an elevator control surface 533 or deflecting a rudder control surface 535 (Step 834), otherwise roll adjustment is not carried out (NO at Step 824).
  • If a determination is made that a drag force of the hydrokinetic device 100 is outside a predetermined range of drag force (YES at Step 828), then the drag of the hydrokinetic device 100 may be adjusted by, for example, controllably retracting or deploying the drag inducer 112 until the aggregate of the drag force due to the rotor 109 and the drag force due to the drag created by the drag inducer 112 is within the predetermined range of drag force (Step 838), otherwise drag adjustment is not carried out (NO at Step 828). Additionally (or alternatively), the drag force acting on the hydrokinetic device 100 may be adjusted by changes to the rotor blade 107 pitch angles, until the drag force is returned to an acceptable range (YES step 828). The aggregate of the drag force due to the rotor 109 and the drag force due to the drag created by the drag inducer 112 may be equal to the rotor drag force created by the rotor 109 alone during normal operating conditions.
  • Although shown as being carried out at substantially the same time, the sensing and determining Steps 810 and 818 may be carried out at different times. Similarly the decision Steps 820, 828, and the adjusting Steps 830, 838, may be carried out substantially simultaneously, or at different times.
  • According to an aspect of the disclosure, a computer readable medium may be provided that includes a computer program with a plurality of code sections (or segments) tangibly embodied therein. The computer program may include a code section for each of the Steps 810 through 838 in the process 800. When executed on, for example, the onboard computer (not shown) in the hydrokinetic device 100, the computer program may cause detection and control of pitch, roll and/or drag of the hydrokinetic device 100.
  • In accordance with various embodiments of the present disclosure, the methods described herein are intended for operation as software programs running on a computer. Dedicated hardware implementations including, but not limited to, application specific integrated circuits, programmable logic arrays and other hardware devices can likewise be constructed to implement the methods described herein. Furthermore, alternative software implementations including, but not limited to, distributed processing or component/object distributed processing, parallel processing, or virtual machine processing can also be constructed to implement the methods described herein.
  • Although the present specification describes components and functions implemented in the embodiments with reference to particular standards and protocols, the disclosure is not limited to such standards and protocols. Accordingly, replacement standards and protocols having the same functions are considered equivalent.
  • While the disclosure has been described in terms of exemplary embodiments, those skilled in the art will recognize that the disclosure can be practiced with modifications in the spirit and scope of the appended claims. These examples given above are merely illustrative and are not meant to be an exhaustive list of all possible designs, embodiments, applications or modifications of the disclosure.

Claims (20)

  1. 1. A hydrokinetic device for extracting power from water current, the device comprising:
    a buoyant body; and
    a rotor coupled to the buoyant body configured to drive a power generator,
    wherein the buoyant body and the rotor jointly define a center of buoyancy and a center of gravity, the center of buoyancy being located above and upstream of the center of gravity.
  2. 2. The device according to claim 1, further comprising:
    a moveable counterweight that is configured to adjust the center of gravity.
  3. 3. The device according to claim 1, further comprising:
    a variable ballast that is configured to adjust the center of gravity.
  4. 4. The device according to claim 1, further comprising:
    a hydroplane wing with an elevator control surface.
  5. 5. The device according to claim 1, further comprising:
    a keel that is attached to the buoyant body, the keel comprising a deadweight attached to a distal end.
  6. 6. The device according to claim 1, wherein the rotor is configured to selectively engage or disengage a water current flow.
  7. 7. A hydrokinetic device for extracting power from a water current, the device comprising:
    a buoyant body;
    a rotor coupled to the buoyant body, the rotor being configured to drive a power generator;
    a keel coupled to the buoyant body; and
    a deadweight coupled to a distal end of the keel.
  8. 8. The device according to claim 7, wherein the deadweight is offset from a vertical plane of symmetry of the buoyant body.
  9. 9. The device according to claim 7, wherein the deadweight is movable between a fore position and an aft position, or between a port side position and a starboard side position.
  10. 10. The device according to claim 7, further comprising:
    a plurality of laterally separated ballast tanks that are configured to be alternately purged of water or filled with water.
  11. 11. The device according to claim 7, further comprising:
    a hydrodynamic lifting surface that is configured to provide a rolling moment.
  12. 12. The device according to claim 7, further comprising:
    a drag inducer that is configured to deploy a varying drag condition, wherein the varying drag condition comprises a high drag condition, a low drag condition, or an intermediate drag condition.
  13. 13. The device according to claim 7, further comprising:
    a drag inducer that is configured to deploy a high drag condition, a low drag condition, or an intermediate drag condition.
  14. 14. A hydrokinetic device for extracting power from a water current, the system comprising:
    a buoyant body;
    a rotor coupled to the buoyant body, the rotor being configured to drive a power generator; and
    a drag inducer that is configured to deploy a varying drag condition, the varying drag condition including a high drag condition, a low drag condition, or an intermediate drag condition.
  15. 15. The device according to claim 14, wherein the rotor is configured to engage or disengage a water current flow.
  16. 16. The device according to claim 14, wherein the drag inducer is configured to disengage when the rotor is engaged.
  17. 17. The device according to claim 14, wherein the drag inducer is further configured to engage when the rotor is disengaged.
  18. 18. The device according to claim 14, further comprising:
    a keel that is attached to the buoyant body, the keel comprising a deadweight attached to a distal end.
  19. 19. The device according to claim 14, further comprising:
    a variable ballast that is configured to adjust the center of gravity.
  20. 20. The device according to claim 14, further comprising:
    a hydroplane wing with variable incidence mechanism or an elevator control surface.
US12789074 2009-06-30 2010-05-27 Pitch, roll and drag stabilization of a tethered hydrokinetic device Abandoned US20100327583A1 (en)

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US22167609 true 2009-06-30 2009-06-30
US23622209 true 2009-08-24 2009-08-24
US32888410 true 2010-04-28 2010-04-28
US12789074 US20100327583A1 (en) 2009-06-30 2010-05-27 Pitch, roll and drag stabilization of a tethered hydrokinetic device

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US12789074 US20100327583A1 (en) 2009-06-30 2010-05-27 Pitch, roll and drag stabilization of a tethered hydrokinetic device

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US12789159 Abandoned US20100326343A1 (en) 2009-06-30 2010-05-27 Mooring system for a tethered hydrokinetic device and an array thereof
US12789074 Abandoned US20100327583A1 (en) 2009-06-30 2010-05-27 Pitch, roll and drag stabilization of a tethered hydrokinetic device
US12788945 Abandoned US20100329866A1 (en) 2009-06-30 2010-05-27 Variable control rotor hub with self-contained energy storage reservoir
US12789192 Active 2031-01-06 US8219257B2 (en) 2009-06-30 2010-05-27 Power control protocol for a hydrokinetic device including an array thereof

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US12789192 Active 2031-01-06 US8219257B2 (en) 2009-06-30 2010-05-27 Power control protocol for a hydrokinetic device including an array thereof

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WO2011008353A2 (en) 2011-01-20 application
WO2011008351A1 (en) 2011-01-20 application
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CN102498286A (en) 2012-06-13 application
JP2012532274A (en) 2012-12-13 application
JP2012532267A (en) 2012-12-13 application
US20100332041A1 (en) 2010-12-30 application
WO2011008353A3 (en) 2011-06-09 application
US20100329866A1 (en) 2010-12-30 application
EP2449251A1 (en) 2012-05-09 application
WO2011008354A1 (en) 2011-01-20 application
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