Patent ID: 12247545

DETAILED DESCRIPTION OF THE INVENTION

FIG.1shows an exemplary embodiment of the wind turbine of the invention in isometric view. The turbine comprises a floating foundation1, a support structure2and a generator3. The foundation1in general comprises rolled tubular steel sections that form a general A-shape with a turret4at its apex, two first sections5,6extending from the turret with an angular separation of about 45°, two further sections7,8extending in parallel from the free end of each of the first sections5,6and a transverse tubular section9connecting the two further sections7,8.

The foundation1is airtight and will have sufficient buoyancy to support the support structure2and generator3. The interior of the foundation1may be divided into a multiple of compartments to allow for adjustment of the buoyancy.

The turret4accommodates a swivel (not shown) to which mooring lines10are to be attached. The mooring lines10are at the opposite ends attached to anchors (not shown). The anchors may be of any type suitable for long time mooring, such as suction anchors, piles, drag anchors, mushroom anchors, augers or dead-weights. The lines10extends in a catenary fashion between the anchor and the turret4. This allows for the foundation to move to somewhat relative to the seabed, both in horizontal and vertical directions. The mooring forces in this type of mooring will be lower than a tensioned mooring.

The support structure2comprises two truss beams11,12. Each beam11,12is attached to further sections7,8of the foundation1close to where the transverse section9is attached. The truss beams11,12extends to the generator3, which is fixedly attached to the beams11,12. The beams11,12may be attached to one another at their upper ends but may also be coupled via the generator3.

It is also conceivable within the ambit of the invention to use pipe sections instead of truss beams. As will be explained below, the support structure will substantially be subjected to compression forces only. Consequently, the pipe sections for the support structure2need not have the same diameter and wall thickness as the tubular sections of the floating foundation1.

The support structure2can also comprise a set of backstays, such as four backstays13,14,15,16. The backstays13,14,15,16extend from close to the upper end of the truss beams11,12to each end of the further tubular sections7,8.

In order for the generator rotor not to interfere with the backstays13,14,15,16, the truss beams11,12are leaning towards the turret4at an angle.

The generator3comprises a nacelle17that is fixedly attached to the upper ends of the beams11,12. A rotor18, preferably with three blades is rotatably attached to the nacelle. Both the nacelle and the rotor are standard mass-produced units.

FIG.2shows the turbine in a side elevation view. As can be seen in this view, the up-wind backstays13,16extend practically in a vertical plane and the rotor18is also arranged in a vertical plane, while the truss beams11,12form an angle of about 15° with the vertical plane. The down-wind backstays14,15form an angle of about 25° with the vertical plane. The foundation1is designed to float substantially horizontally.

FIG.3shows the turbine floating at sea and subjected to waves. Waves are allowed to wash over the tubular sections of the foundation1. Due to the relatively small diameter of the tube sections, it is expected that the forces from wave and current will be small. This reduces the mooring forces.

The truss beams may be of the same design as used for crane booms. These are known to be light weight but have a great strength.

FIG.4shows the substantial part of the foundation1in an exploded view. The turret4basically comprises a cylindrical part19with short tubular connection pieces20,21welded to the side thereof. The cylindrical part is open at the lower end (not shown) to receive the swivel (not shown) and closed at its upper end. The cylindrical part19may have a larger diameter than the connection pieces20,21, but is preferably made from the same tube as the remaining tubular parts of the foundation1.

The first sections5,6and the further section7,8are uniform rolled steel tubes having the same diameter. Consequently, these sections can be formed from a continuous length of tube that is cut into proper length.

To connect the first sections5,6with the further sections7,8connection pieces22,23have each been formed by two short tubular pieces that are cut at an angle and welded together to extend from one another at the angle intended for the joining of the first sections5,6and the further sections7,8.

The sections5,6,7,8is preferably connected to the connection pieces by bolts. This facilitates transport of the parts to an assembly site where the foundation1can be assembled using simple tools. It is however also possible to weld the parts together or use a combination of welds and bolts.

The transverse section9is not shown inFIG.4. This section is an option, which may be omitted if it is not proven necessary. The transverse section9will enhance the stiffness and buoyancy of the foundation1. Short connecting pieces may be welded to the further sections7,8to allow for a bolted connection of the transverse section9to the further sections7,8.

The tube sections are preferably made airtight, e.g., by welding a bulkhead (not shown) inside the sections, close to each end thereof. If it is desired to divide a section into further compartments, further bulkheads may be welded into the tubes. If it is desired to be able to adjust the buoyancy, holes (not shown) for valves can be made at appropriate places on the tube sections to allow for flowing air or/and water into or out of compartments in the tube sections.

The tube sections5-8should be pressure tested before assembly.

FIG.5shows a part of a truss beam11,12. These beams preferably have a uniform cross section along their length so that they can be manufactured from identical truss sections. Each truss section is preferably welded by welding robots in a line production operation. The truss sections are preferably connected to complete beams by bolts. As stated above, it is possible to use pipe sections instead of truss sections.

Although, a square cross-section with four corner rods24that are interconnected by a plurality of inclined rods25are shown for the truss beams, they may have any suitable cross section, such as triangular.

The truss beams are preferably bolted to the foundation, to one another and to the nacelle.

The assembly of the turbine can be done as follows:

The tube sections and truss sections are made short enough to facilitate transport by conventional ships and lorries, preferably in ISO containers.

At the assembly site, which conveniently is a port where the wind turbine can be transferred to an installation ship or barge, the parts are assembled by bolting the tube sections together. The swivel is installed in the turret cylinder part19. The assembly may be done on shore and the complete wind turbine subsequently lifted onto a ship or barge, or the assembly may be done on the deck of a ship or barge. In the latter case, the assembly may at least partly be done while the ship or barge is sailing to the installation site.

When the tube sections5-8have been bolted together, the truss sections11,12are assembled and connected to the foundation1.

The wires13-16are then connected at their lower ends to the foundation and at their upper ends to (or close to) the upper ends of the truss beams. The wires may alternatively be connected to the nacelle. The wires are tightened to a predetermined tension. The wires ensure that the truss beams are always kept in compression, as the wires will take up substantially all moments.

Mounting of the nacelle and the rotor may also take place while the foundation is afloat.

Cables for power and signal will be connected to the nacelle17and fed through the truss beams11,12. A coupling for the electric cables may conveniently be installed at the lower end of one of the truss beams11,12, so that a power line, that may have already been installed at the installation site, may easily be connected to the wind turbine upon installation.

The mooring lines, which have already been deployed, are coupled to the turret4upon installation.

The wind turbine is deployed either by lifting it from the deck and into the water or by de-ballasting a barge, upon which the wind turbine is situated, until the wind turbine is afloat.

When deployed, the wind turbine functions are tested, and the wind turbine is left to produce electric power.

The steel tube sections and truss beams are made of a selected steel grade that has been known for many years to endure harsh conditions and salt water in the offshore oil and gas industry. When the time for supervision and maintenance of these structures is reached, the wind turbine may be brought onto the deck of a vessel and either maintained on the deck or brought to the shore. It may also be towed to the shore.

Maintenance of the nacelle can be done by climbing a ladder (not shown) within the truss beams11,12. An elevator may also be installed inside the truss beams11,12to bring people and parts up to the nacelle.

When the rotor blades need to be changed, this can either be done by lifting the blades from the wind turbine while it is floating (as is common practice with most sea based wind turbines today) or by bringing the turbine onto the deck of a vessel.

FIG.6shows an alternative embodiment of the invention. This embodiment is very similar to the embodiment ofFIGS.1-5, but a few changes have been made.

Instead of the foundation1′ having five tubular sections, it has only two sections5′ and6′, extending at an angular separation from the turret4′. The support structure2′ is also made up of tubular sections instead of truss beams. Tubular sections11′ and12′ extend from a respective side of the foundation1′ to the generator3. Instead of the section9forming a part of the foundation shown inFIG.9, the embodiment ofFIG.6has a transverse section9′ extending between the support structure sections11′ and12′ at a location distant from the foundation1′. Two inclined tubular struts30,31extend from the tubular sections11′ and12′, respectively, to the transverse section9′.

Next the height of the turret4′ has been elongated. This enables the foundation to be ballasted to a lower position with respect to the water surface. As shown inFIG.6, the foundation sections5′ and6′ are situated completely below the water, while the turret4′ protrudes through the surface. This gives a very small water plane area, which is made up of the cross-sectional area of the turret and the support structure sections11′ and12′. A small water plane area results in an improved stability and makes the floating structure less influenced by wave actions.

It is indeed possible to combine features of the embodiment ofFIGS.1-5and6, such as using truss beams in the embodiment ofFIG.6, or elongating the turret4ofFIGS.1-5to enable the foundation to be ballasted to a position below the water surface.

With the above described designs, it is possible to manufacture a wind turbine by using standard components or at least components that are within the ambit of standardized production. The number of parts is also reduced. This lowers fabrication costs and time considerably.

The amount of material (steel weight), which is a significant part of costs, is also reduced compared to known designs. This also reduces the environmental impact.

The production can be done almost everywhere where these is an engineering industry. This facilitates production close to the deployment site, which has significance for the overall environmental impact.

The wind turbine design is scalable and only limited by the sizes of nacelle and rotor available.

Due to the turret, the foundation1will turn with the current and waves so that the turret will be facing the oncoming current and waves. As the currents, waves and wind generally comes from approximately the same direction, the wind will almost always be approximately up-wind of the rotor. In some situations, the wind direction may be slightly different from the direction of the current and waves, but the difference is seldom more than a few degrees. This has in total very little significance on the overall performance. Consequently, a yaw mechanism or any other active means to keep the rotor against the wind has been dispensed with.