HK1225431B - Spar buoy platform - Google Patents

Description

cylindrical buoy platform

This application claims priority to U.S. Patent Application No. 14/144,272, filed December 30, 2013, which is hereby incorporated by reference in its entirety.

Background Art

Unless otherwise indicated herein, what is described in this section is not prior art to the claims in this application and is not admitted to be prior art by inclusion in this section.

Power generation systems can convert chemical and/or mechanical energy (eg, kinetic energy) into electrical energy for various applications, such as utility systems. As an example, a wind energy system can convert wind kinetic energy into electrical energy.

Wind turbines have been used for many years as a means of harnessing energy. Conventional wind turbines typically include large turbine blades atop a tower. The costs of manufacturing, erecting, repairing, and maintaining such wind turbine towers and wind turbines are considerable.

One alternative to expensive wind turbine towers that can be used to harness wind energy is to use an aircraft connected to a ground station with a conductive tether. Such an alternative may be called an airborne wind turbine or AWT.

Summary of the Invention

Now, offshore aerial wind turbine systems provide a viable method for utilizing wind energy in deep-sea applications that were previously unavailable. An aerial wind turbine system is arranged on a cylindrical buoy moored to the seabed. The aerial wind turbine system includes an aeroplane connected to a conductive tether that transmits the electricity generated by the aeroplane to a platform on the cylindrical buoy, where it is transmitted to shore via a cable and, in some cases, to a power grid. The electricity can also be used locally, for example, to reform aluminum or compress air into compressed air tanks on the seabed. This aerial wind turbine system, because it utilizes a floating buoy that can be simply moored to the seabed with a mooring line, does not require a large tower connected to the seabed and is therefore suitable for use in deep-sea locations.

In another aspect, an offshore airborne wind turbine system is provided that includes an aircraft; a conductive tether having a first end secured to the aircraft and a second end secured to a platform; a rotatable cable drum disposed on the platform; and an aircraft parking rack extending from the platform, wherein the platform is disposed on top of a spar buoy.

In another aspect, a spherical buoy is provided comprising: a vertically oriented main member, wherein the main member is configured to support an airborne wind turbine system disposed on an upper end of the main member; a ballast at a lower end of the main member, wherein a second end of a conductive tether is connectable to a platform, and wherein an aircraft is connectable to a first end of the tether.

These and other aspects, advantages and alternatives will become apparent to those of ordinary skill in the art by reading the following detailed description with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an offshore airborne wind turbine 10 including an aerial vehicle 20 connected to a spar buoy platform with a conductive tether 30 , according to an example embodiment.

FIG. 2 is a close-up perspective view of the aircraft 20 shown in FIG. 1 .

FIG3 is a side view of the offshore airborne wind turbine 10 according to an example embodiment, with the aircraft 120 positioned on the docking station 54 and the conductive tether 30 connecting the spar buoy platform 50 to the aircraft 120 .

FIG4 is a side view of the offshore airborne wind turbine 10 shown in FIG3 with the heave plate 64 positioned on the main member 50 of the spar buoy, according to an example embodiment.

FIG5 is a perspective view of the offshore airborne wind turbine 10 shown in FIG3 , wherein the spar buoy platform 50 is tilted toward the aircraft 120 , according to an example embodiment.

FIG6A is a side view of the offshore airborne wind turbine 10 shown in FIG5 , wherein the aircraft 120 is docked on the docking rack 54 of the spar buoy platform 50 , according to an example embodiment.

FIG6B is a side view of the offshore airborne wind turbine 10 shown in FIG6A , wherein the aircraft is unspooled from a rotatable cable drum 53 located on a spar buoy platform 50 , according to an example embodiment.

FIG6C is a side view of the offshore airborne wind turbine 10 shown in FIG6A and FIG6B , wherein the aircraft 120 is transitioned to crosswind flight, according to an example embodiment.

7A is a top view of the spar buoy platform 50 shown in FIGs. 6A-6C with the tether 30 extending from the rotatable cable drum 53 and the docking platform 95 in a first position relative to the biasing arm 58 of the spar buoy platform 50, according to an example embodiment.

7B is a top view of the spar buoy platform 50 shown in FIGs. 6A-6C with the tether 30 extending from the rotatable cable drum 53 and the docking platform 95 in a second position relative to the offset arm 58 of the spar buoy platform 50, according to an example embodiment.

7C is a top view of the spar buoy platform 50 shown in FIGs. 6A-6C with the tether 30 extending from the rotatable cable drum 53 and the docking platform 95 in a third position relative to the offset arm 58 of the spar buoy platform 50, according to an example embodiment.

FIG8A is a side view of an alternative spar buoy platform 150 with a cable drum 53 and a docking plate 54 disposed on top, according to an example embodiment.

FIG. 8B is a top view of the spar buoy platform 150 shown in FIG. 8A .

FIG9A is a side view of the spar buoy platform with the vehicle 120 in the parked position and the main member 52 tilted to the left.

FIG. 9B is a side view of the spar-buoy platform shown in FIG. 9A , with the vehicle 120 in flight and the primary member 52 tilted to the right toward the vehicle 120 .

DETAILED DESCRIPTION

Example methods and systems are described herein. Any example embodiment or feature described herein is not necessarily to be construed as preferred or superior to other embodiments or features. The example embodiments described herein are not meant to be restrictive. It will be readily understood that certain aspects of the disclosed systems and methods can be arranged and combined in a wide variety of different configurations, all of which are contemplated herein.

In addition, the specific arrangement shown in the figures should not be regarded as restrictive. It should be understood that other embodiments may include more or less of each element shown in the given figures. In addition, some of the elements shown may be combined or omitted. Moreover, example embodiments may include elements not shown in the figures.

1. Overview

Example embodiments relate to an aircraft that can be used in a wind energy system, such as an airborne wind turbine or AWT. Specifically, the illustrative embodiments may relate to or take the form of methods and systems using an aircraft that is connected to a ground station with a conductive tether.

Wind energy systems such as AWT can be used to convert wind energy into electrical energy. AWT is a wind-based energy generation device that may include an aircraft constructed of rigid wings with mounted turbines. The aircraft may be operable to fly above the ground (or water) in a path that crosses the wind, such as a substantially circular path, to convert the kinetic energy of the wind into electrical energy. In such crosswind flight, the aircraft flies across the wind in a circular pattern similar to the wingtips of a wind turbine. Rotors connected to the rigid wings can be used to generate electricity by slowing the wings. Specifically, the air moving across the turbine blades can push the blades to rotate, which drives a generator to generate electricity. The aircraft can also be connected to a ground station via a conductive tether that transmits the electricity generated by the aircraft to the ground station, and in some cases to the power grid, or for local use.

When it is desired to land the aircraft, the conductive tether can be wound onto a spool or cable drum in the ground station, which is then reeled in to pull the aircraft toward the docking station. Before landing on the docking station, the aircraft can transition from flight mode to hover mode. After the aircraft transitions to hover mode, the tether can be wound onto the cable drum until the aircraft returns to rest on the docking station.

Airborne wind turbines can offer significant advantages over conventional wind turbines. For example, an airborne wind turbine can fly up to 500 meters above the ground, where winds are significantly stronger than at closer ground locations (e.g., 70 meters) where conventional wind turbines operate. Wind at 500 meters can provide twice the power of wind at 70 meters. Furthermore, conventional wind turbines typically require large blades and large towers to support them. Manufacturing, transporting, and maintaining the blades and towers is prohibitively expensive compared to airborne wind turbines.

Furthermore, conventional wind turbines typically require a gearbox to increase the revolutions per minute ("rpm") of the rotating turbine blades to a useful speed for the generator. Gearboxes can be expensive and prone to failure. In an example AWT, the aircraft can fly at 100-150 miles per hour, with much smaller propellers spinning at 1000 rpm, eliminating the need for a gearbox. Furthermore, since a large tower and large turbine blade interior are not required, the material cost of an airborne wind turbine is one-tenth that of a conventional wind turbine.

However, when it comes to offshore power generation, airborne wind turbines can offer another significant advantage over conventional wind turbines. Specifically, strong, sustained winds can be found in deep-sea locations (e.g., in waters 30 meters deep or deeper). However, due to the large rotational loads caused by their rotating blades, the top of a conventional wind turbine may not be able to tolerate the swaying that can be caused by wind, currents, and waves. If a floating platform were used to support a conventional wind turbine, this would require an extremely large amount of ballast to prevent the top of the wind turbine from swaying due to wave action, currents, and/or wind. Therefore, a floating platform for a conventional platform may not be practical.

Therefore, for offshore applications, conventional wind turbines typically have a tower that extends downward from the sea surface to the seabed. Consequently, the deeper the water, the larger the tower size, and the greater the moment around the base of the tower caused by the rotating turbine blades. Consequently, the use of conventional wind turbines for deepwater applications may not be practical. Specifically, in many offshore locations, the cost of constructing and/or installing such a tower can be prohibitively expensive.

Example embodiments are directed to a spar-shaped buoy platform that can be anchored to the seafloor and used in an aerial wind turbine system at offshore locations. In an aerial wind turbine system, the aircraft is connected via a tether that extends to the top of the buoy platform near the sea level. This eliminates the significant moment caused by the aircraft in flight, unlike the moment around the base of a conventional wind turbine caused by the rotating blades at the top of the tower. Furthermore, this moment remains constant regardless of water depth because the tether extends to the platform just above sea level, rather than to the seafloor. This is particularly advantageous in deep-sea applications.

Furthermore, the spar buoy does not need to be a massive buoy like conventional wind turbines, as the airborne wind turbine system is insensitive to the swaying of the buoy's top caused by wave action or wind while the aircraft is in flight. In other words, it may not matter if the top of the buoy sways above the water during crosswind flight. However, the top of the buoy platform should be stable during landing of the aircraft.

Ballast or a mass can be provided at the bottom of the spherical buoy to help maintain the buoy in a vertical position and provide stability. The mass can be water, filler, steel, or concrete located at the bottom of the buoy to provide stability. The spherical buoy should be stable enough to remain upright during takeoff and landing of an aircraft.

The spar buoy can be connected to a mooring device anchored to the seafloor via a tether, which can advantageously be connected to an offset arm extending from the spar buoy. With this arrangement, when the aircraft flies in a crosswind, the aircraft pulls the top of the spar buoy toward the aircraft, causing the spar buoy to deflect and tilt toward the aircraft. Furthermore, through the offset arm, the aircraft's pulling force provides a more direct tension load extending through the tether, offset arm, and tether to the mooring device. Consequently, the moment caused by the aircraft's drag is reduced, and the spar buoy is not subjected to the large bending moments at the base of the tower found in conventional wind turbines.

The ability to tilt is also an advantage because the aircraft flies in a loop, where it climbs for part of the loop and descends for part of the loop. So by having a system where you're actually raising and lowering the entire spar, energy is stored. So, because the spar can tilt and is more compliant than a land-based design, potential energy can be stored, which helps stabilize the energy given off by the aircraft. As a result, the motors on the aircraft operate at a more consistent level.

Furthermore, when the vehicle is in circular flight, the oscillations of the buoy can lag behind the vehicle's motion, so that there are times when the vehicle is traveling upwards and the buoy is traveling downwards, and vice versa for downwards. This relative motion can dampen both the vehicle's motion and the oscillations of the buoy. The net result can be more stable energy generation, since there are typically oscillations (more power generation on the upward stroke, less power generation on the downward stroke). Advantageously, the vehicle can be constructed with a flight circle period that falls within the structural insensitivity zone of the structure, which also must be avoided in terms of structural excitation, as the period of a 50- or 100-year wave might be 17 seconds, the circle period of an AWT flight might be between 10 and 20 seconds, depending on wind speed, and the cylindrical buoy can be constructed to have the most significant resonance in terms of response to tension or wave action over a 35-second period.

Furthermore, the spar buoy provides a small cross-section at the waterline (and below) to minimize the transfer of wave energy, thereby minimizing the effects of wave action on the spar buoy.Another consideration is that it may be desirable to position the buoy where current and wave forces are in a different direction than the wind.

A spar buoy platform has an inherent resonance based on its mass and waterline diameter, causing it to bounce up and down in the water at a specific frequency while the wind can blow at different frequencies. Therefore, the spar buoy system should be relatively well damped so that it does not resonate strongly with either wave motion or the motion of the aircraft. Advantageously, the resonant frequency can be set outside those frequencies introduced by wave motion or by the flight of the aircraft and changes in the tension and direction of forces. The heave plate can be positioned horizontally with respect to the spar buoy to provide damping. The diameter of the structure at the waterline can be varied to achieve a beneficial response of the system. Advantageously, the heave plate can be configured to dampen heaving motion in the platform, but can be positioned horizontally to limit the damping of the platform's pitching motion, which can help store energy, during a flyaround by the aircraft, with only a partial loss of damping.

The cable drum can be used to store the tether while it is being reeled back toward the platform during the landing process. In one example, the cable drum can rotate about a horizontal axis. As the tether is wound onto the drum, the buoy can be tilted toward the aircraft so that the tether is at a perpendicular angle to the drum. The cylindrical buoy platform can include a docking frame extending from the top of the cylindrical buoy using docking supports. In some embodiments, the docking frame and docking supports can rotate around the top of the cylindrical buoy to allow for desired positioning of the docking frame during landing and takeoff. However, the present cylindrical buoy design advantageously allows for a non-rotating docking frame. Specifically, the cylindrical buoy can float in a manner that follows the wind. When the aircraft is reeled in, the docking frame can be positioned in the path of the tether wound onto the cable drum, and the cylindrical buoy and docking frame can simply float around and follow the aircraft as the aircraft is reeled in. In this way, the docking frame will always remain in a position suitable for landing the aircraft.

In this way, by rotating and following the aircraft, the spar-buoy platform can eliminate the yaw axis, which can allow movement of the spar-buoy platform tower about its moorings to stabilize movement of the dock along its yaw axis, such as movement in azimuth.

2. Illustrative offshore aerial wind turbines

As disclosed in Figures 1-2, according to an exemplary embodiment, an offshore airborne wind turbine system 10 is disclosed. The offshore airborne wind turbine system 10 is a wind-based energy generation device comprising an aircraft 20 constructed from rigid wings 22 having mounted turbines 40a, 40b, the aircraft 20 flying in a path across the wind, such as a substantially circular path. In an exemplary embodiment, the aircraft 20 can fly between 250 and 600 meters above the water surface to convert wind kinetic energy into electrical energy. However, the aircraft can fly at other altitudes without departing from the scope of the present invention. In crosswind flight, the aircraft 20 flies across the wind in a circular pattern similar to the wingtips of a wind turbine. Rotors 40a and 40b connected to the rigid wings 22 are used to generate electricity by slowing the wings 22. Air moving across the turbine blades causes them to rotate, which drives a generator to produce electricity. The aircraft 20 is connected to the spar buoy platform 50 via a conductive tether 30 , which transmits the electricity generated by the aircraft 20 to the spar buoy platform 50 and to the power grid.

1 , aircraft 20 may be connected to a tether 30, which may be connected to a spherical buoy platform 50. In this example, tether 30 may be connected to spherical buoy platform 50 at one location on spherical buoy platform 50 and connected to aircraft 20 at three locations on aircraft 20 using bridle lines 32a, 32b, and 32c. However, in other examples, tether 30 may be connected to any portion of spherical buoy platform 50 and/or aircraft 20 at multiple locations.

The cylindrical buoy platform 50 can be used to secure and/or support the aircraft 20 until it is in operational mode. The cylindrical buoy platform 50 can include a vertically oriented main member 52 that can extend approximately 15 meters above the water surface. The cylindrical buoy platform 50 can also include a cable drum 53 that can rotate about a cable drum axis 55. The cable drum 53 is used to retrieve the aircraft 20 by winding the tether 30 onto the rotatable cable drum 53. In this example, the cable drum 53 is oriented horizontally, although it can also be oriented vertically (or at an angle). Furthermore, the cylindrical buoy platform 50 can be further configured to receive the aircraft 20 during landing. For example, docking support members 56a and 56b are connected to a docking plate 54 and extend outward from the rotatable cable drum 53. When the tether 30 is wound onto the cable drum 53 and the aircraft 20 is reeled toward the cylindrical buoy platform 50, the aircraft 20 can return to dock on the docking plate 54. The spar buoy platform 50 may be formed of any material capable of properly maintaining the aircraft 20 connected to the spar buoy during hover flight, forward flight, or crosswind flight.

Tether 30 can transmit electrical energy generated by aircraft 20 to spar buoy platform 50, where it can then be transmitted via cables to shore and to the power grid. Furthermore, tether 30 can transmit electricity to aircraft 20 to power aircraft 20 during takeoff, landing, hovering flight, and/or forward flight. Tether 30 can be constructed in any form and using any material that allows for the transmission, transport, and/or utilization of electrical energy generated by aircraft 20 and/or the transmission of electricity to aircraft 20. Tether 30 can also be configured to withstand one or more forces acting on aircraft 20 when aircraft 20 is in operational mode. For example, tether 30 can include a core configured to withstand one or more forces acting on aircraft 20 when aircraft 20 is in hovering flight, forward flight, and/or crosswind flight. The core can be constructed from any high-strength fiber or carbon fiber strip. In certain examples, tether 30 can have a fixed length and/or a variable length. For example, in one example, the tether has a fixed length of 500 meters.

Aircraft 20 may include or take the form of various types of devices, such as a kite, helicopter, wing, and/or airplane, among other possibilities. Aircraft 20 may be formed from a solid structure of metal, plastic, and/or other polymers. Aircraft 20 may be formed from any material that allows for a high thrust-to-weight ratio and the generation of electrical energy that can be used for utility applications. Additionally, materials may be selected to allow for a rapidly hardening, redundant, and/or fault-tolerant design that can handle large and/or sudden changes in wind speed and direction. Other materials are also possible.

1 and in more detail in FIG2 , aircraft 20 may include a main wing 22, rotors 40a and 40b, a tail boom or fuselage 24, and an empennage 26. Any of these components may be shaped in any manner that allows for the use of lift components that resist gravity and/or move aircraft 20 forward.

The main wing 22 can provide the primary lift for the aircraft 20. The main wing 22 can be one or more rigid or flexible wings and can include various control surfaces, such as winglets, flaps, rudders, elevators, etc. The control surfaces can be used to stabilize the aircraft 20 and/or reduce the drag of the aircraft 20 during hovering flight, forward flight, and/or crosswind flight. The main wing 22 can be made of any material suitable for the aircraft 20 to perform hovering flight, forward flight, and/or crosswind flight. For example, the main wing 20 can be made of carbon fiber and/or alkali-free glass.

Rotor connector 43 may be used to connect upper rotor 40a to main wing 22, and rotor connector 41 may be used to connect lower rotor 40b to main wing 22. In some examples, rotor connectors 43 and 41 may take the form of, or be similar in form to, one or more external pylons. In this example, rotor connectors 43 and 41 are arranged so that upper rotor 40b is positioned above wing 22 and lower rotor 40a is positioned below wing 22.

Rotors 40a and 40b can be configured to drive one or more generators to generate electrical energy. In this example, rotors 40a and 40b can each include one or more blades 45, such as three blades. The one or more rotor blades 45 can rotate via interaction with the wind, which can be used to drive the one or more generators. In addition, rotors 40a and 40b can also be configured to provide thrust to aircraft 20 during flight. By this arrangement, rotors 40a and 40b can be used as one or more propulsion units, such as propellers. Although rotors 40a and 40b are shown as four rotors in this example, in other examples, aircraft 20 can include any number of rotors, such as less than four rotors or more than four rotors, for example six or eight rotors.

1 , when it is desired to land the aircraft 20, the cable drum 53 is rotated to reel the aircraft 20 toward the docking plate 54 on the spar buoy platform 50, and the conductive tether 30 is wound onto the cable drum 53. Before landing on the docking plate 54, the aircraft 20 transitions from the flight mode to the hovering mode. The cable drum 53 is further rotated to further wind the tether 30 onto the cable drum 53 until the aircraft 20 returns to rest on the docking plate 54.

3. Illustrative Example of a Spar Buoy Platform

FIG3 and FIG4 illustrate an example embodiment of an offshore airborne wind turbine 10, which includes an aircraft 120 having a fuselage 124. Aircraft 120 is shown docked on a docking plate 54 extending from a docking support 56a connected to a spar buoy platform 50. A conductive tether 30 is shown extending from a rotatable cable drum 53 that rotates about a horizontal drum axis 55. Rotatable cable drum 53 is disposed atop the upper end 52a of the spar buoy's main member 52. The spar buoy platform 50 is stabilized by ballast 53 located at the bottom of the spar buoy's main member 52. An offset arm 58 extends from the top 52a of the spar buoy's main member 52 to a connection point 60 located at the intersection of the offset arm 58 and a lower arm 59 connected to the bottom of the spar buoy's main member. A first end of a rope 70 is connected to mooring lines 72 and 74 anchored to the seafloor 80, and a second end of the rope 70 is connected to the connection point 60. The main member 52 of the spar buoy has a small cross-section 62 at the waterline (and below), which minimizes energy transfer from forces from waves or currents of water 90 passing over the main member 52 .

Ballast or mass 53 may be provided at the bottom of the main element 52 of the spherical buoy to help maintain the buoy in a vertical position and thus provide stability. The mass may be water, filler, steel, or concrete placed at the bottom of the buoy to provide stability. The spherical buoy should be stable enough to remain upright during takeoff and landing of the aircraft 20.

FIG5 illustrates the offshore airborne wind turbine system 10 shown in FIG1-4 , shown with the aircraft 20 in flight. In this example, the aircraft 20 is connected by a tether 30 extending to the top of a cylindrical buoy platform 50 near the sea level. Therefore, there are no significant moments caused by the aircraft 20 in flight, unlike the moments around the base of the tower caused by the rotating blades at the top of the tower in conventional wind turbines. Furthermore, this moment remains constant regardless of the depth of the water 90 because the tether 30 extends to the cylindrical buoy platform 50 just above sea level, rather than to the seafloor as in conventional wind turbines. This is particularly advantageous in deep-sea applications.

In FIG5 , the tension of the vehicle 20 and the attached tether 30 during flight exerts a force that tends to tilt the spur-buoy platform 50 toward the vehicle 20 at an angle α. The ability to tilt is also beneficial because the vehicle 20 flies in a loop, climbing for part of the loop and descending for part of the loop. Thus, by having a system that effectively lifts and lowers the entire spur-buoy platform 50, energy is stored. Thus, because the spur-buoy platform 50 can tilt and is more compliant than land-based designs, potential energy can be stored, which helps stabilize the energy released by the vehicle 20. Consequently, the motors on the vehicle 20 can operate at a more consistent level. This benefit must be balanced against the need to avoid strong resonances of the platform (which would increase loads), and there are preferred system parameters or preferred ranges of system parameters to achieve a certain amount of power balance while avoiding undesirable loads. For example, the wing frequencies on various excitation axes or along specific eigenmodes can significantly exceed or well ahead of the platform's resonant modes. However, if the system is made to have a different response in flight, both benefits can potentially be retained. For example, the larger waterline area of the buoy when tilted at a flight angle and placed at flight depth, or when the mooring line is under flight tension, can result in a significantly faster pitch response and less damping than when the buoy is more upright and the system is moored.

The spar buoy platform 50 can be connected to mooring lines 72 and 74 anchored to the seafloor by ropes 70, which can advantageously be connected to biasing arms 58 extending from the top 52a of the main element 22 of the spar buoy platform 50. With this arrangement, when the aircraft 20 flies in a crosswind, the aircraft 20 pulls the top of the spar buoy platform 50 toward the aircraft 20, causing the spar buoy platform 50 to tilt toward the aircraft 20. In addition, using the biasing arms 58, the pulling force of the aircraft 20 provides a straighter tension load that extends through the tether 30, the biasing arms 58, and the ropes 70 to the mooring lines 72 and 74. As a result, the moment caused by the pull of the aircraft 20 can be reduced, and the spar buoy platform 50 is not subjected to the large bending moments at the base of the tower found in conventional wind turbines.

Furthermore, the spar-buoy platform 50 does not need to be a large buoy, as is required for conventional wind turbines, because the airborne wind turbine system 10 is insensitive to the swaying of the top of the buoy caused by wave action or wind while the aircraft 20 is in flight. In other words, even if the top of the spar-buoy platform 50 sways above the water surface during crosswind flight, it is not a problem as long as the top of the spar-buoy platform 50 is stable during landing of the aircraft 20.

4, as described above, the spar buoy platform 50 may have a natural resonance based on its mass and waterline diameter, so that it will bob up and down in the water 90 at a specific frequency while the wind may blow at different frequencies. Therefore, the spar buoy platform 50 should be relatively well damped so that it exceeds a critical frequency at which the spar buoy generally follows the motion of the aircraft 20. To provide damping for the spar buoy platform 50, a heave plate 64 may be disposed horizontally around the main element 52 of the spar buoy.

Figures 6A-6C illustrate side views of the offshore airborne wind turbine 10 shown in Figure 5 , with the aircraft 120 shown in various positions. Figure 6A is a side view of the offshore airborne wind turbine 10, according to an example embodiment, with the aircraft 120 docked on a docking plate 54 of a spur buoy platform 50. The aircraft 120 is shown docked on the docking plate 54, which extends from a docking support 56a connected to the spur buoy platform 50. The conductive tether 30 is shown extending from a rotatable cable drum 53, which rotates about a horizontal drum axis 55, to the wings 122 of the aircraft 120. The rotatable cable drum 53 is positioned atop the upper end 52a of the main member 52 of the spur buoy. The spur buoy platform 50 is stabilized by ballast 53 located at the bottom of the main member 52 of the spur buoy. An offset arm 58 extends from the top 52a of the main member 52 of the spar buoy to a connection point 60 located at the intersection of the offset arm 58 and a lower arm 59, which is connected to the bottom of the main member 52 of the spar buoy platform 50. A first end of a rope 70 is connected to mooring lines 72 and 74 anchored to the sea floor 80, and a second end of the rope 70 is connected to the connection point 60. The main member 52 of the spar buoy has a small cross-section 62 at the waterline (and below) that minimizes energy transfer from waves passing through the water 90 of the main member 52.

FIG6B is a side view of the offshore airborne wind turbine 10 shown in FIG6A , with the aircraft 120 unwound from a rotatable cable drum 53 disposed on the spur buoy platform 50. The rotatable cable drum 53 can be used to store the tether 30 as it is reeled back toward the spur buoy platform 50 during the landing process. In a preferred embodiment, the cable drum 53 can rotate about a horizontal axis 55. As the tether 30 is wound onto the cable drum 53, the spur buoy platform 50 can be tilted toward the aircraft 120 so that the tether 30 is at an angle perpendicular to the axis 55 of the cable drum 53. The spur buoy platform 50 can include a docking plate 54 extending from the top of the spur buoy 52a using docking supports 56a (and 56b).

FIG6C is a side view of the offshore airborne wind turbine 10 shown in FIG6A and FIG6B , wherein the aircraft 120 transitions to crosswind flight, according to an example embodiment.

Figure 7A is a top view of the cylindrical buoy platform 50 shown in Figures 6A-6C according to an example embodiment, wherein the tether 30 extends from the rotatable cable drum 53 and the docking platform 95 is in a first position relative to the offset arm 58 of the cylindrical buoy platform 50, and the docking platform 95 is connected to the docking supports 56a and 56b, and the docking supports 56a and 56b are connected to the docking plate 54 and the docking rod 54a.

Figure 7B is a top view of the cylindrical buoy platform 50 shown in Figures 6A-6C according to an example embodiment, wherein the tether 30 extends from the rotatable cable drum 53 and the docking platform 95 is in a second position relative to the offset arm 58 of the cylindrical buoy platform 50, and the docking platform 95 is connected to the docking supports 56a and 56b, and the docking supports 56a and 56b are connected to the docking plate 54 and the docking rod 54a.

Figure 7C is a top view of the cylindrical buoy platform 50 shown in Figures 6A-6C according to an example embodiment, with the tether 30 extending from the rotatable cable drum 53, the docking platform 95 in a third position relative to the offset arm 58 of the cylindrical buoy platform 50, and the docking platform 95 connected to the docking supports 56a and 56b, and the docking supports 56a and 56b are connected to the docking plate 54 and the docking rod 54a.

7A-7C, the docking platform 95, docking supports 56a and 56b, and docking plate 54 can be rotated about the top 52a of the main element 52 of the spar buoy platform 50 to allow for desired positioning of the docking plate 54 during landing and takeoff.

However, the present spar buoy platform design can advantageously allow for a non-rotating docking plate 54. Specifically, the spar buoy platform 50 can float in the water 90 in a manner such that the spar buoy platform 50 follows the wind. When the aircraft 120 is reeled in, the docking plate 54 can be positioned in the path of the tether 30 as it is wound onto the cable drum 53. The spar buoy platform 50 (as shown in FIG. 7A ) and the docking plate 54 can simply float around on top of the spar buoy platform 50 and follow the aircraft 120 as it is reeled in. In this way, the docking plate 54 will always remain in a position suitable for landing the aircraft, and the need for a rotatable docking platform can be eliminated.

8A and 8B are views of a spare spar buoy platform 150 according to an example embodiment having a cable drum 53 rotatable about an axis 55 and a docking plate 54 disposed on a top 160. Downwardly extending legs 152, 154, and 156 extend below the top 160 and connect to cross members 158a, 158b, and 158c. Mooring lines 72, 74, and 76 are used to position the spar buoy platform in a desired location relative to wind, current, or wave action.

The cylindrical buoy platform shown in Figures 1-8 can have an oscillation frequency between 0.5 and 2 times the lap period of the aircraft. Specifically, the cylindrical buoy platform can have a dead zone between approximately 10 and 20 seconds. If the aircraft also flies with a lap period of 10-20 seconds (depending on the wind), the platform is suitable for both. Therefore, in some embodiments, the platform can have an oscillation frequency of 10-20 seconds, and the aircraft flies with a lap period of 10-20 seconds.

FIG9A is a side view of the spar-buoy platform with vehicle 120 in a parked position. With vehicle 120 parked on the spar-buoy platform, primary member 52 is shown tilted to the left in a first orientation. FIG9B is a side view of the spar-buoy platform shown in FIG9A , with vehicle 120 in flight, and primary member 52 tilted to the right and angled off-vertical toward the vehicle in a second orientation when the vehicle is in flight mode. Thus, the platform has a very different orientation when the vehicle is parked than when it is in a loop.

Furthermore, the spar-buoy platform can be configured so that the waterline in a first, parked orientation is lower (or higher) than the waterline in a second orientation when the vehicle is in flight. The response from the spar-buoy can be varied under flight loads to reduce damping and increase the energy stored by the vehicle through changes in waterline height, roll or pitch angle, or tether tension.

4. Conclusion

The above detailed description, with reference to the accompanying drawings, describes various features and functions of the disclosed systems, devices, and methods. Although many aspects and embodiments have been disclosed herein, other aspects and embodiments will be apparent to those skilled in the art. The various aspects and embodiments disclosed herein are for illustrative purposes only and are not intended to be limiting, with the true scope and spirit being indicated by the appended claims.

Claims (32)

1. A marine-aerial wind turbine system, comprising: Aircraft; A conductive tether having a first end fixed to the aircraft and a second end fixed to the platform; A rotatable cable reel is mounted on the platform; An aircraft parking rack extends from the platform; The platform is positioned on top of the cylindrical buoy; The bias arm extends downwards at an angle from the upper part of the cylindrical buoy; and The mooring cable is connected to the lower end of the bias arm, which extends downward and outward. 2. The system of claim 1, wherein the lower arm is connected to the lower end of the bias arm, which is also connected to the lower portion of the cylindrical buoy. 3. The system of claim 2, wherein the mooring cable is connected at the intersection of the bias arm and the lower arm. 4. The system of claim 3, wherein when the aircraft is flying in a crosswind, the top of the cylindrical buoy is tilted toward the aircraft. 5. The system of claim 3, wherein the connection point is located at the intersection between the lower end of the bias arm and the lower arm. 6. The system of claim 1, wherein when the aircraft is being pulled back and the conductive tether is being wound onto the rotatable cable reel, the aircraft parking rack is located in the path where the conductive tether is wound onto the rotatable cable reel. 7. The system of claim 6, wherein the rotatable cable reel has a horizontal axis of rotation. 8. The system of claim 1, wherein the platform has an oscillation period between 0.5 and 2 times the orbital period of the aircraft. 9. The system of claim 8, wherein the platform has an oscillation period of 10-20 seconds, and the orbital period of the aircraft is 10-20 seconds. 10. The system of claim 1, wherein the cylindrical buoy has a first orientation when the aircraft is parked on an aircraft parking rack, and has a second orientation when the aircraft is in flight mode. 11. The system of claim 10, wherein when the aircraft is in the flight mode, the cylindrical buoy deviates from the vertical and rotates toward the aircraft to the second orientation. 12. The system of claim 10, wherein the waterline height of the cylindrical buoy in the first orientation is different from the waterline height in the second orientation. 13. The system of claim 10, wherein the response from the cylindrical buoy changes under flight load to reduce attenuation and increase the energy stored in the aircraft by changes in waterline height, roll or pitch angle, or tether tension. 14. A marine-aerial wind turbine system, comprising: Aircraft; A conductive tether having a first end fixed to the aircraft and a second end fixed to the platform; A rotatable cable reel is mounted on the platform; An aircraft parking rack extends from the platform; The platform is positioned on top of the cylindrical buoy; The bias arm extends downward at an angle from the upper part of the cylindrical buoy; The lower arm is connected to the lower end of the bias arm and is also connected to the lower part of the cylindrical buoy. The bias arm includes a connection point at its lower end for connection to the mooring cable; and The aircraft's pull causes a tensile load to extend axially through the bias arm and the mooring cable, which is connected to the lower end of the bias arm. 15. An offshore aerial wind turbine system, comprising: Aircraft; A conductive tether having a first end fixed to the aircraft and a second end fixed to the platform; A rotatable cable reel is mounted on the platform; An aircraft parking rack extends from the platform; The platform is positioned on top of the cylindrical buoy; When the aircraft is parked on the aircraft parking rack, the cylindrical buoy has a first orientation; when the aircraft is in flight mode, the cylindrical buoy has a second orientation. When the aircraft is in the flight mode, the cylindrical buoy rotates toward the aircraft to the second orientation; and The cylindrical buoy is tilted in a direction opposite to the direction of the second orientation, which is the direction of the first orientation. 16. A cylindrical buoy, comprising: A vertically oriented main component, wherein the main component is configured to support an airborne wind turbine system platform disposed on the upper end of the main component; Ballast material, located at the lower end of the main component; The second end of the conductive tether can be connected to the platform; The aircraft can be connected to the first end of the conductive tether; and The bias arm extends downward at an angle from the upper part of the main component; and When the mooring cable is connected to the lower end of the bias arm, the aircraft's tension causes a tensile load to extend axially through the bias arm and the mooring cable. 17. The cylindrical buoy of claim 16, further comprising the airborne wind turbine system platform disposed on the upper end of the main component. 18. The cylindrical buoy of claim 17, further comprising a rotatable cable reel disposed on the platform. 19. The cylindrical buoy of claim 18, further comprising an aircraft parking rack extending from the platform. 20. The cylindrical buoy of claim 19, wherein the offset arm extends from the side of the main component of the cylindrical buoy, wherein the upper end of the cylindrical buoy is tilted toward the aircraft when the aircraft is flying in a crosswind. 21. The cylindrical buoy of claim 19, wherein the aircraft parking rack is rotatable about the top of the cylindrical buoy. 22. The cylindrical buoy of claim 19, wherein the biasing arm extends from the side of the main component of the cylindrical buoy, and wherein the aircraft parking rack is located in the path of the conductive tether being wound onto the rotatable cable reel when the aircraft is being pulled back and the conductive tether is being wound onto the rotatable cable reel. 23. The cylindrical buoy of claim 22, wherein the rotatable cable reel has a horizontal axis of rotation. 24. The cylindrical buoy of claim 16, wherein the lower arm is connected to the lower end of the bias arm and the lower arm is also connected to the lower portion of the main member. 25. The cylindrical buoy of claim 24, wherein the biasing arm includes a connection point at the lower end of the biasing arm for connection to a mooring cable. 26. The cylindrical buoy of claim 25, wherein the connection point is located at the intersection of the lower end of the bias arm and the lower arm. 27. The cylindrical buoy of claim 16, wherein the heave plate is disposed around the main component of the cylindrical buoy. 28. A cylindrical buoy, comprising: A vertically oriented main component, wherein the main component is configured to support an airborne wind turbine system platform disposed on the upper end of the main component; Ballast material, located at the lower end of the main component; The second end of the conductive tether can be connected to the platform; The aircraft can be connected to the first end of the conductive tether; and The bias arm extends downward at an angle from the upper part of the main component; The offset arm extends from the side of the main component of the cylindrical buoy, wherein, when the aircraft is flying in a crosswind, the upper end of the cylindrical buoy tilts towards the aircraft; and When the mooring cable is connected to the lower end of the offset arm, the tension of the aircraft causes a tensile load to extend axially through the offset arm and the mooring cable. 29. The cylindrical buoy of claim 28, wherein the mooring line is connected to the lower end of the bias arm. 30. The cylindrical buoy of claim 28, wherein the mooring line is connected to the intersection between the lower end of the bias arm and the lower arm, and the lower arm is connected to the lower portion of the bias arm and the main member. 31. A cylindrical buoy, comprising: A vertically oriented main component, wherein the main component is configured to support an airborne wind turbine system platform disposed on the upper end of the main component; Ballast material, located at the lower end of the main component; The second end of the conductive tether can be connected to the platform; The aircraft can be connected to the first end of the conductive tether; and The bias arm extends downward at an angle from the upper part of the main component; and The mooring cable is connected to the lower end of the bias arm. 32. The cylindrical buoy of claim 31, wherein the mooring cable is connected to the intersection between the lower end of the bias arm and the lower arm, the lower arm being connected to the bias arm and to the lower portion of the main member.