Patent Application
20240059378
The present disclosure relates in general to wind turbines and more specifically to offshore wind turbine structures that support turbine replacement and near-shore maintenance.
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 are commonly pointed into the wind by a shaft and generator assembly within a nacelle, at the top of a tower that is yawed relative to the tower in order to align the rotor with the wind. The nacelle commonly s-s a direct drive generator or a transmission and generator combination.
Wind turbines used for offshore applications commonly Aude single-tower systems mounted to the sea bed. Some float, using shallow submersible or semi-submersible platforms employing spars or spar buoys, tension legs, or a large-area barge-type construction. Offshore turbines are usually connected to a local power grid. Produced electrical energy is transferred and conditioned by grid structures.
Spars are ballasted, elongate structures that float at the water line, placing the center of gravity lower than the center of buoyancy. A spar is moored to the sea floor.
Tension-leg platforms are permanently moored by tethers or tendons grouped at each of the structure's corners. A group of tethers is referred to as a tension leg. The design provides relatively high axial stiffness such that virtually all vertical motion of the platform is eliminated.
A large-area barge or “buoyancy-stabilized platform” is a heavy floating structure, moored to the sea bed, supporting a vertical axis turbine. Jack-up barges, similar to oil and gas platforms, are used as a base for servicing other structures such as offshore wind turbines. The state of the art emphasizes platforms that are immobilized against wave disturbance by mass, mooring, ballast and the like.
Many offshore wind fields are up to 100 miles from shore, with turbines that are not intended to be moved. For ballast and stability, heavy floating structures tend to be deeply placed, ruling out high-speed towing to shallow waters for maintenance. On-site, offshore installation, maintenance and repair is far more expensive and time-consuming than similar tasks conducted on land or in a near-land facility.
When conducted offshore, installation, maintenance and repair of offshore turbines is far more expensive and time-consuming than that conducted on land or on a near-land facility.
An apparatus for generating offshore wind energy is designed for passive yawing, employing shallow draft floats supporting a lattice tower with a wide base having a single-line anchoring. In some embodiments, dual-line anchoring may be used while still allowing passive yawing.
In an example embodiment, a lattice structure has four legs, each connected to a shallow float at the base. Each leg is joined at the top to a horizontal structure that is configured to support a wind-turbine rotor. The base of at least two of the lattice structure legs is connected to a V-shaped structure that is a mooring and towing point. The overall structure is an irregular pentagon with four vertices in a rectangular pattern, and a fifth vertex extending from the midpoint of two of the other vertices. The fifth vertex is configured with equipment appropriate to function as a mooring or towing point (it is also referred to as a hitch point). One skilled in the art is familiar with mooring points, towing apparatuses, and fifth wheels as used in towing and mooring. Mooring from a single point on the turbine lattice structure, in combination with shallow floats, allows the turbine to passively yaw into the wind, obviating the need for a mechanical yaw system in a nacelle. Shallow floats, in combination with a wide base and a single towing point, enable a turbine to be erected on or near land obviating the need for an ocean-based crane. The wide base may be used to accommodate a deck-level generator assembly with a belt drive, or the like, to the turbine rotor. One skilled in the art understands how mooring-line orientation, as described in the above example apparatus, may function to eliminate wind-thrust pitch or horizontal tower load as commonly occurs with monopole tower construction.
In an example embodiment, a turbine may be switched with one requiring maintenance or repair. In such a case, a tugged turbine is swapped with a moored turbine. A relatively small tug boat may be adapted to clasp the hitch point on a turbine to maneuver it to a mooring and again to clasp the hitch point of a turbine to be removed to tow it to land. One skilled in the art understands that electric connections would also be switched between the turbine being removed and the turbine being replaced. In some embodiments electric contacts are spring-energized and may be disconnected by way of a screw or pneumatic actuator. Mechanisms and devices for strain relief between cables and mooring lines are known in the art.
Shallow draft floats provide a low-cost solution that facilitates towing. To overcome the typical distance between shore and an offshore wind field, a towing speed close to 10 knots is necessary. The present disclosure describes innovations such as a broad base with shallow draft floats, a single towing/mooring point, and a low center of gravity to facilitate high-speed towing to land or shallow-water, near-land locations, for maintenance and repair. One skilled in the art understands that swapping out a turbine in a field is far more cost-effective than affecting repairs onsite.
In some embodiments, floats are hull-shaped to facilitate high-speed towing in less-than-optimal weather conditions. Other embodiments include hull-shaped adaptors that may be fitted to a shallow draft float for towing. One example includes adapters having fluid-dynamic forms that enable semi-planing of the floats to reduce drag while towing. Such adapters may include vertical, streamlined forms that are air-pressurized so as to raise the shallow draft floats above waves. One skilled in the art is familiar with inflatable hulls and streamlined forms.
In some embodiments, remote-controlled rudders or thrusters may be employed to orient the apparatus. In other embodiments, buoyancy may be controlled by partially inflating or deflating the shallow floats. In yet other embodiments blade-pitch tuning may be employed to negate wind-shadow loads.
The truss structure 116 supports a horizontal shaft 120 about which a turbine rotor 110 rotates. The structure 116 may be configured to support a shaft 120 at both ends. One skilled in the art understands the complexity of supporting a cantilevered shaft with a heavy rotor. In some embodiments, electrical-generation equipment is located on the base of the structure 126. Mechanical energy may be transferred from the rotor 110 to the electrical generation-equipment 122 by a drive mechanism 124. One skilled in the art understands that a drive mechanism 124 may be a belt, shaft, chain or the like. The overall structure obviates the need for a nacelle at the rotor axis 118, which obviates the need to perform high-altitude maintenance.
In some embodiments, electrical switchgear is mounted on the turbine structure and can suppress large currents in a power cable. In some embodiments the switchgear is operated remotely. One skilled in the art understands pneumatic, electric line or radio-signal-operated remote-switching technology. Other embodiments include an isolating switch below a cable connection to the turbine to enable safe switching. Strain relief in a cable may be achieved by pulling the turbine forward to slacken the line.
In an example switching operation, a tugged turbine is swapped with a moored turbine. A small boat 130 is adapted to clasp turbines to a hitch point 114 and move turbines about. In some embodiments, remote-controlled features include a remote-controlled mooring connection or removal, or remote-controlled rudders on wind turbine structures for straight-line towing or for rotation about the mooring point.
To facilitate quick towing, a turbine to be towed near to shore may be positioned over sunk air-cushion transporters, then winched onto land. One skilled in the art understands how a gin pole may be used to lift a turbine by its hub to move it to land. In other examples, a gantry crane may be erected near shore to assist in maintenance or movement to shore.
In an example scenario, each turbine is autonomously self-moving and self-connecting. Motors, propellers, rudders and a control unit enable simultaneous transport of more than one turbine to shore. In one example, all turbines in a field enter a protected anchorage and all are connected together to prepare for heavy weather.
In another example, automated boats, controlled from land, may be configured to move turbines, connect and disconnect electrical connections, and tow turbines to shore. To ease the switching of a mooring cable, it may be connected by a dovetail that allows horizontal sliding when not locked. Once a spare turbine is keyed to a moored turbine, hydraulic cylinders may push the mooring cable to the spare unit, even if the cable is still loaded.
| Number | Date | Country | |
|---|---|---|---|
| 63371664 | Aug 2022 | US |
