TECHNICAL FIELD

[0001] The present disclosure relates in general to wind turbines and more specifically to shallow floats supporting offshore wind turbines and increasing the speed of towing at sea.

BACKGROUND

[0001] A wind turbine is a rotating machine that converts kinetic energy from wind into mechanical energy that is converted to electricity. Utility-scale, horizontal-axis wind turbines have horizontal shafts that drive a generator assembly within a tower-top nacelle, that is yawed relative to the tower in order to align the rotor with the wind. Either a transmission and generator combination or a larger direct drive generator are commonly used.

[0002] The state of the art includes offshore wind turbines that rest on the ocean bottom and are neither designed nor intended to be moved. In waters shallower than 60m, wind turbines used for offshore applications commonly include single-tower systems mounted to the sea bed. In deeper waters the turbines must float, using spar-buoy or semi-submersible platforms, tension legs, or a large-area barge-type construction. Offshore turbines are usually connected to an onshore power grid and electrical energy produced is transferred by ocean-floor grid structures.

[0003] The hull shape of a leg-supporting float is commonly dependent on considerations such as strength, weight, displacement, wave motion, and behavior when towed. Hull shapes range from a square end, in the case of a scow barge, to the pointed surface of a sailboat racing hull, to the cylindrical shape of a harbor buoy.

[0004] A hydrofoil is commonly a wing-like structure mounted below the waterline of a hull or across structures such as the keels of a catamaran. Like the wing of an aircraft, a hydrofoil provides lift. It is usually employed to lift most of the hull out of the water in order to reduce drag and increase speed. SUMMARY

[0005] A floating structure for supporting an offshore wind turbine, particularly during towing, uses shallow draft floats of various configurations. These must provide stable buoyant support in all ocean conditions, with least material cost and easiest manufacturing. The structure enables launching of an offshore wind turbine in a shallow port, and towing to a mooring. The optimized floats are designed in varying iterations to prevent the shallow floats from swamping during towing at differing speeds, and to assist in aligning the floating structure when moored in a current or when towed. Floats may be optimized to meet the needs of various oceanic conditions.

[0006] In an example embodiment, a floating structure enabling towing of a floating wind turbine employs a plurality of legs, each with a shallow float at the base. At least two of the floats are connected to a V-shaped hitch point for mooring and towing. One skilled in the art is familiar with mooring points, towing apparatuses, fifth wheels and the like as are used in towing and mooring. Mooring from a single point enables the turbine to passively yaw into the wind, eliminating the need for a mechanical yaw system in a nacelle. The structure is built so that during towing, the shallow floats do not dive as they move through the water. Floats are optimized to align the turbine with a current of wave when the turbine is moored or towed by the hitch point.

[0007] The overall floating structure is an irregular pentagon with four vertices in a rectangular pattern and a fifth vertex extending from the mid-point of two of the other vertices. The fifth vertex is configured with equipment appropriate to function as a mooring or towing (hitch) point, and electric export cable connection point.

[0008] In one embodiment a hydrofoil extends between the front two floats, and another hydrofoil extends between the two rear shallow floats. The hydrofoil is designed to partially lift the floats, to reduce towing drag and keep them from diving. The hydrofoil has a cross-section designed to create lift at slow speeds sufficient to keep the floats from diving. One skilled in the art understands that a high angle of attack designed for slow-speed lift of a relatively low height is considerably different than a hydrofoil designed for high-speed operation with the hull entirely out of the water. [0009] In another embodiment the forward shallow floats are bow-shaped to reduce drag during towing. In another embodiment, the floats have relatively flat hydroplaning surface that can provide dynamic lift at relatively low speeds. In some embodiments ballast may be added or removed from floats. In one example embodiment, floats down-current of the hitch point may be partially filled with ballast to lower the down-current portion of the floating structure, thus partially raising the bow-shaped portion of the up-current floats out of the water, optimizing the effect of the bow-shape. One skilled in the art understands that removing ballast from downcurrent floats will lower the up-current floats in the water.

[0010] In yet another embodiment an inflatable collar is used to reduce hull draft and increase planing area, to facilitate faster towing, hull is inflated and fastened to shallow draft floats to facilitate towing. The inflatable form may be stowed when the turbine is not being towed.

[0011] Drawings are designed to illustrate rather than define the limits of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] FIG. 1 is a perspective and a detail view of an example embodiment of the present disclosure;

[0013] FIG. 2 is a side and detail view thereof;

[0014] FIG. 3 is a perspective view of an iteration of the embodiment.

[0015] FIG. 4 is a side view of the detail of FIG. 3.

[0016] FIG. 5 includes a perspective view and a detail view of an iteration of the embodiment.

[0017] FIG. 6A is a perspective view of a detail in FIG. 5, with an inflatable member shown inflated. [0018] FIG. 6B is a perspective view of a detail in FIG. 5, with an inflatable member shown deflated and stored.

[0019] FIG. 7 includes a perspective view and a detail view of an iteration of the embodiment.

[0020] FIG. 8 A is a perspective view of a detail in FIG. 7.

[0021] FIG. 8B is a side view of a detail in FIG. 7.

DESCRIPTION

[0022] Referring to FIGs. 1 and 2: FIG. 1 shows a perspective view of an example embodiment 100 and FIG. 2 shows a side cross-section detail view thereof. A wind turbine 110 is supported by a structure 115 that can be towed and moored from a hitch point 113. One skilled in the art understands that such a structure will align the wind turbine 110 with the wind as it pivots about the hitch point 113. When its rotor is stopped, the turbine 110 can be towed at hitch point 113 in the direction shown by arrow 120. Shallow floats 112 in the form of two buoyant frusto-conical shapes are joined at their bases to form an equatorial plane 114. This equatorial plane is designed to reside somewhat above the water line of the float 112. In one embodiment, four shallow floats 112 support the wind turbine 110 on the surface of the water. A hydrofoil 116 joins two floats 112 at a pivot point 118. In some embodiments a king-post-and- cable assembly 119 provides rigidity to the slender hydrofoil form 116. The hydrofoil 116 is designed to provide sufficient lift to raise the equatorial plane 114 well above the water line when the wind turbine 110 is towed at the hitch point 113 in the direction denoted by arrow 120.

[0023] Referring to FIGs. 3 and 4; FIG. 3 shows a perspective, detail view of an example embodiment 200 and FIG. 4 shows a side view of a shallow float that has a bow configuration optimized as a displacement hull. A wind turbine 210 is supported by a structure 215 that can be towed and moored from a hitch point 213 in the direction of arrow 220. One skilled in the art understands that such a structure will align the wind turbine 210 with the wind as it pivots about the hitch point 213. Shallow floats 212 in the form of two buoyant frusto-conical shapes are joined at their bases to form an equatorial plane 214. This equatorial plane is designed to reside at the water line of the float 212. In one embodiment, four shallow floats 212 support the wind turbine 210 on the surface of the water. A bow 222 is formed in the front end of at least two of the shallow floats 212. The bow 222 is designed to reduce drag when the wind turbine 210 is towed at the hitch point 213 in the direction denoted by arrow 220.

[0024] Referring to FIGs. 5, 6A and 6B: FIG. 5 shows a perspective, detail view of an example embodiment 300. FIG. 6A shows a perspective view of a shallow float 312 with an inflatable form 324 joined to it. FIG. 6B shows the shallow float 312 without the inflatable form. The float 312 is optimized as a semi-displacement hull both with the inflatable form 324 inflated and deflated. A wind turbine FIG. 5, 310 is supported by a structure 315 that can be towed and moored from a hitch point 313 in the direction shown by arrow 320. One skilled in the art understands that such a structure will align the wind turbine 310 with the wind as it pivots about the hitch point 313. A shallow float 312 is a pair of frusto-conical sections joined at their bases forming an equatorial plane 314 (FIG. 6B). The equatorial plane 314 is designed to be at the water line of the float 312. In one embodiment, four shallow floats 312 support the wind turbine 310 on the surface of the water (FIG. 5). Inflatable forms 324 are joined to the front end of at least two of the shallow floats 312. These inflatable forms 324 are designed to keep the equatorial plane 314 at or above the water line when the wind turbine 310 is towed at the hitch point 313 in the direction of arrow 320. One skilled in the art understands that an inflatable form 324 may be deflated and stowed when the turbine 310 is not being towed.

[0025] Referring to FIGs. 7, 8A and 8B: FIG. 7 shows a perspective, detail view of an example embodiment 400. FIG. 7A shows a perspective view of a shallow float 712 with a planing hull design 424. FIG. 7B shows a side view of the shallow float 412 with a planing hull design 424. One skilled in the art is familiar with hull designs configured to provide lift when moving through the water.

[0026] These embodiments should not be construed as limiting.