AND USING THE SAME FOR INSTALLATION OF A FLOATING OFFSHORE WIND TURBINE ASSEMBLY

FIELD OF THE INVENTION

This invention relates to the field of floating offshore wind turbines and, more particularly, to a technique for transporting and installing floating offshore wind turbines. BACKGROUND OF THE INVENTION

The world's demand for electrical energy is continuously increasing. A vast amount of electrical energy is currently generated by oil, gas, coal or nuclear plants. However, burning oil, gas and coal results in air pollution, and all of these fuel resources are rapidly diminishing. Nuclear energy requires the disposal of nuclear waste, which remains dangerous for centuries.

Wind energy conversion technology is today regarded as one of the most technically advanced technologies available that can effectively help develop a low carbon economy while ensuring a clean and secure supply of energy. The floating offshore wind turbine market is set to grow in the near future with various players entering this field of opportunity and using their significant resources to overcome critical barriers that will enable higher penetration levels of offshore wind energy technologies.

A key challenge is the process of installing large scale floating wind energy conversion systems at deep water offshore sites.

International Patent publication WO2011/083021 relates to a method of erecting a floating offshore wind turbine comprising a floatation element, one or more tower modules forming a tower, a nacelle and blades. The method includes providing at least one anchorage to the seabed and first and second connecting means connected thereto; and submerging a lower part of the wind turbine. The lower part comprises at least the floatation element. The method also includes connecting the first connecting means to a lower end of the lower part of the wind turbine, and connecting the second connecting means to one of the modules to be arranged above sea level when the wind turbine is in a fully-assembled condition. Finally, the method includes elevating the wind turbine to an operational level.

U.S. Pat. No. 8,770,126 describes a method of moving a floating wind turbine relative to a body of water. The floating wind turbine has a buoyant body with a nacelle at the upper end thereof. The method includes the steps of floating the floating wind turbine in a body of water, and towing the floating wind turbine while holding the buoyant body in an inclined position, whereby the nacelle and blades are held clear of the water. As the wind turbine is held in an inclined position, it can be towed through regions of shallower water than if it were towed in a vertical position.

U.S. Pat. No. 9,476,409 describes an offshore wind turbine apparatus that includes a platform and an equalizer with sealed internal volumes, a turbine mast connected to the platform, a turbine which is connected to the turbine mast, and turbine blades connected to the turbine. The apparatus is rotatably mounted on a barge via a trunnion. The apparatus may rotate from a substantially horizontal position to a substantially upright position when sufficient ballast material is inserted into the equalizer. The equalizer may rest on a sea floor. The platform may provide a restorative buoyant force that tends to cause the apparatus to return to the upright position when perturbed from the upright position.

GENERAL DESCRIPTION OF THE INVENTION

There is still a need in the art, and it would be useful to have a novel technique, for transporting and installing floating offshore wind turbines (FOWTs).

It would be advantageous to avoid the use of large floating cranes and a separate ballasting barge for erecting floating offshore wind turbines.

It would also be advantageous to have a technique that allows a FOWT configuration that assembles horizontally rather than vertically. This provision can reduce navigation problems for aircraft flying to and from nearby airports. It can also avoid the use of very large land-based cranes at the quayside.

02694690\4-01 It would be beneficial to tow a fully-assembled megawatt class FOWT assembly in horizontal orientation rather than in a vertical assembly. This can lower the center of gravity (CoG) and reduce towing drag, hence possibly widening the acceptable Metocean conditions window, reducing transportation time offshore, and also reducing the fuel consumed by tug boats.

It would be beneficial to have a technique for transporting and installing floating offshore wind turbines, which is not restricted to port facilities having a large draft.

The present invention improves on the prior art of a technique for transporting and installing floating offshore wind turbines, and proposes a novel transportation and installation technique using a reusable wind turbine transportation cradle (WTTC) to tow a fully-assembled megawatt class floating offshore wind turbine (FOWT) out of a port in a stable and low center of gravity (CoG) configuration, and to erect the FOWT into an upright position at a deep offshore installation site. The technique also leverages a compressed-air system integrated within the wind turbine transportation cradle (WTTC) for use during the installation process.

According to one general aspect of the present invention, a wind turbine transportation cradle (WTTC) is provided that can serve a dual function during transporting and installing FOWTs in deep waters. Specifically, the WTTC can act as a floating vessel to provide additional buoyancy to transport the entire floating wind turbine in an inclined orientation from the port to the installation site offshore. Moreover, the WTTC can transport and store compressed air and a ballasting slurry (if required), which can be used during the installation phase offshore.

The FOWT that can benefit from the use of the WTTC of the present invention includes a floating structure, a supporting tower mounted at a top end of the floating structure, and an electrical wind turbine system. The floating structure is configured to provide buoyancy for keeping the FOWT afloat in an upright stable position under different wind and wave conditions. The electrical wind turbine system is configured to harness wind energy and generate electricity.

According to the present invention, the WTTC also participates in installing a floating offshore wind turbine (FOWT) assembly at the offshore installation site. The (FOWT) assembly includes the FOWT and seabed securing components.

According to an embodiment of the present invention, the WTTC includes a plurality of buoyancy vessels providing buoyancy to the WTTC. The buoyancy vessels 02694690\4-01 are structurally interconnected to each other by a support structure and separated from each other by a predetermined distance required to provide floating stability to the WTTC. Each vessel of the plurality of the buoyancy vessels includes a corresponding chamber adapted to contain pressurized air. The buoyancy vessels are pneumatically interconnected to each other so that a uniform compressed air pressure can be maintained therebetween.

The WTTC also includes a support assembly integrated with the support structure to form a single floating structure. The support assembly includes a plurality of cradle support members arranged over the buoyancy vessels. The cradle support members are adapted to hold the upper part of the FOWT above sea water level during transportation.

According to some embodiments of the present invention, the chamber of at least one buoyancy vessel includes one or more WTTC air inlet valves configured to pressurize the chambers with compressed air. The chamber also includes one or more WTTC air outlet valves configured to provide compressed air from the chambers. The chamber also includes one or more WTTC pressure relief valves configured to protect the chambers from over-pressurization, in case the pressure of the compressed air exceeds the safety limit.

According to an embodiment of the present invention, the chamber of at least one buoyancy vessel further includes a WTTC slurry outlet valve arranged at the lower levels of the chamber. The WTTC slurry outlet valve is configured for providing slurry into the chamber. The slurry can be transported by the WTTC in the chamber and used for ballasting the floating structure during installation of the wind turbine (FOWT) assembly.

According to some embodiments of the present invention, each buoyancy vessel can include a front fairlead arranged at the front of the WTTC and a rear fairlead arranged at the rear of the WTTC. Moreover, each buoyancy vessel can include a side fairlead arranged on the corresponding external side of the WTTC.

According to some embodiments of the present invention, each buoyancy vessel can include a manhole adapted for routine maintenance work and inspection of the corresponding chamber.

According to an embodiment of the present invention, the WTTC further comprises at least one pair of floaters attached to the external sides of the buoyancy 02694690\4-01 vessels, correspondingly, via additional structural elements. The pair of floaters is configured to provide additional buoyancy to the WTTC.

According to an embodiment of the present invention, the WTTC further comprises a hull including walls surroundings the plurality of buoyancy vessels and the support assembly. The hull can be attached to the plurality of buoyancy vessels via additional structural elements. The hull is configured to provide additional buoyancy to the WTTC and safety to the plurality of buoyancy vessels in case of collisions of the WTTC with other structures at sea.

According to some embodiments of the present invention, the floating structure of the FOWT is a single structure.

According to some embodiments of the present invention, the floating structure of the FOWT includes a plurality of single structures which are interconnected structurally and pneumatically.

According to some embodiments of the present invention, the floating structure of the FOWT includes one or more ballasting valves located at the bottom of the floating structure, one or more purging valves located at the top of the floating structure to be above the sea water level during installation of the FOWT, and a FOWT inlet air valve.

The ballasting valves are configured for operating during controllable ballasting of the FOWT during installation of the FOWT assembly. The purging valves are configured for purging air trapped within the floating structure during the installation ballasting. The FOWT inlet air valves are configured for pressurizing the floating structure with compressed air.

According to some embodiments of the present invention, the seabed securing components of the FOWT assembly include a plurality of top fairleads arranged at the top of the floating structure, and at least one bottom fairlead arranged at the bottom of the floating structure. The top fairleads and said at least one bottom fairlead are configured for mooring the FOWT to the seabed. According to this embodiment, the seabed securing components of the FOWT assembly also include a plurality of catenary moorings linked to the floating structure via the plurality of the top fairleads. The catenary moorings are configured for anchoring the floating structure to the seabed by a plurality of side anchors located on the seabed. The seabed securing components of the FOWT assembly further include one or more tension tether(s) connected to bottom 02694690\4-01 fairlead(s) at the bottom of the floating structure. The tension tether is configured for anchoring the floating structure to the seabed by a main anchor located on the seabed.

According to some embodiments of the present invention, the seabed securing components of the FOWT assembly include a plurality of top fairleads arranged at the top of the floating structure, and a plurality of catenary moorings linked to the floating structure via the plurality of the top fairleads. The top fairleads are configured for mooring the FOWT assembly to the seabed. The catenary moorings are configured for anchoring the floating structure to the seabed by a plurality of side anchors located on the seabed. The seabed securing components of the FOWT assembly also include a slurry located in the lower part of the floating structure. The slurry is used for ballasting the FOWT assembly. Specifically, the slurry lowers the center of gravity of the FOWT, hence providing the necessary stability to keep the electrical wind turbine system in its correct vertical position over a wide range of operating wind and wave conditions.

According to some embodiments of the present invention, the seabed securing components of the FOWT assembly include a plurality of top fairleads arranged at the top of the floating structure, and a plurality of bottom fairleads arranged at the bottom of the floating structure. The top fairleads and the bottom fairleads are configured for mooring the FOWT assembly to the seabed. The seabed securing components also include a plurality of catenary moorings linked to the floating structure via the plurality of the top fairleads. According to this embodiment, the catenary moorings are configured for anchoring the floating structure to the seabed by a plurality of side anchors located on the seabed. The seabed securing components further include a plurality of tension tethers connected to the bottom fairleads and a ballast suspended from the bottom of the floating structure via the plurality of the tension tethers to lower the center of gravity of the entire structure and to provide the necessary stability required over a wide range of wind and wave conditions.

According to some embodiments of the present invention, the FOWT includes a plurality of arms attached to the floating structure. In this case, the seabed securing components of the FOWT assembly include arm fairleads arranged at the ends of the arm. The arm fairleads are configured for mooring the FOWT assembly to the seabed. According to this embodiment, the seabed securing components of the FOWT assembly include a plurality of tension tethers connected to the arm fairleads. The tension tethers

02694690\4-01 are configured for anchoring the floating structure to the seabed by a plurality of main anchors located on the seabed.

According to another general aspect of the present invention, there is provided a method for transporting a floating offshore wind turbine (FOWT) to an offshore installation site, and installing a floating offshore wind turbine (FOWT) assembly at the offshore installation site. As described above, the FOWT assembly includes the FOWT and the seabed securing components.

According to some embodiments of the present invention, the method includes providing a wind turbine transportation cradle (WTTC) configured for transporting the FOWT, and transferring the FOWT from the onshore hardstanding onto the nearby berthed floating WTTC in an inclined position, with the turbine tower resting on the cradle support members of the WTTC. Then, the FOWT is secured to the WTTC by tying the WTTC to the top of the supporting tower and to the top of the floating structure.

The method further includes charging the plurality of buoyancy vessels of the WTTC with compressed air. After the charging of the buoyancy vessels, the FOWT which rests on the WTTC, is towed to the offshore installation site.

The method further includes controllably ballasting the FOWT. Such ballasting is carried out by controllably providing a ballasting fluid inside of the floating structure, thereby allowing the center of gravity of the FOWT (100) to shift, and the FOWT to tilt upwards.

Then, the quantity of the ballasting fluid entering the floating structure is regulated until the FOWT achieves a vertical position.

The method further includes securing the floating structure to the seabed by the seabed securing components, thereby forming the FOWT assembly.

Then, the floating structure is disconnected from the WTTC, and the WTTC can be towed back to the shore. Thus, the WTTC can be ready to transport the next FOWT.

According to some embodiments of the present invention, the ballasting fluid is sea water. In this case, the controllable ballasting of the FOWT includes allowing the sea water to penetrate inside of the floating structure, while allowing internal air located inside of the floating structure to be purged to the atmosphere. The quantity of the sea water entering the floating structure is regulated until the FOWT assembly achieves the vertical position.

02694690\4-01 According to some embodiments of the present invention, the method includes pneumatically connecting the chambers of the buoyancy vessels of the WTTC to the inside of the floating structure to allow the compressed air stored in the chambers to flow into the inside of the floating structure, thereby purging the ballasting sea water out. The method further includes disconnecting the pneumatic connection of the chambers from the inside of the floating structure after the securing the floating structure to the seabed.

According to some embodiments of the present invention, the chamber of at least one buoyancy vessel of the WTTC is adapted to contain a slurry. In this case, the method comprises charging the chamber with the slurry before towing the FOWT to the offshore installation site. Thus, when the ballasting fluid is a slurry, the controllable ballasting of the FOWT assembly includes hydraulically connecting the chamber(s) (holding the slurry) to the inside of the floating structure, thus allowing the slurry to flow into the bottom of the floating structure under the influence of the compressed air in the chambers. The method also includes regulating quantity of the slurry entering the floating structure until the FOWT achieves the vertical position. Then, after the securing of the floating structure to the seabed, the hydraulic connection of the chambers disconnects from the floating structure.

According to some embodiments of the present invention, the securing of the floating structure to the seabed includes mooring the top of the floating structure to the seabed by a plurality of side anchors via a plurality of catenary moorings.

According to some embodiments of the present invention, the securing of the floating structure to the seabed includes anchoring the bottom of the floating structure to the seabed by a main anchor via at least one tension tether.

The technique for transportation of FOWT and installation of the FOWT assemblies of the present invention has many of the advantages of the prior art techniques, while simultaneously overcoming some of the disadvantages normally associated therewith.

The transportation and installation technique of the present invention eliminates the need for costly offshore floating cranes and barges and limits the complex transportation and installation processes in the open sea, such as attaching a turbine to a floating platform. This is crucial, since a study based on existing designs established that the offshore assembly of wind turbines can be four times more costly than inshore 02694690\4-01 assembly and towing of the complete structure. Apart from a significant cost reduction, other key advantages of this new concept include shorter installation times, lower dependency on Metocean conditions during transportation and at the installation site, and the possibility of using shallower water quays for inshore system assembly.

The transportation and installation technique of the present invention avoids the use of large floating cranes and a separate ballasting barge for erecting floating wind turbines offshore.

Towing of the FOWT is carried out in horizontal orientation instead of vertical transportation or assembly operations. This provision can lower the low center of gravity (CoG) and reduce the towing drag, hence possibly widening the acceptable Metocean conditions installation window, reducing transportation time offshore, and also reducing the fuel consumed by tug boats.

The transportation and installation technique of the present invention enables the ballasting process to be more efficient than existing methods using aggregates.

The transportation and installation technique of the present invention enables the FOWT to be assembled horizontally. This reduces navigation problems for aircraft flying to and from nearby airports. It also avoids the use of very large land-based cranes at the quayside.

The assembly process of the FOWT of the present invention is not restricted to port facilities having a large draft or to deep waters in their approaches.

Use of the WTTC for storing compressed air can avoid use of large compressed air machinery offshore.

There has thus been outlined, rather broadly, the more important features of the invention in order that the detailed description thereof that follows hereinafter may be better understood. Additional details and advantages of the invention will be set forth in the detailed description, and in part will be appreciated from the description, or may be learned by practice of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to understand the invention and to appreciate how it may be carried out in practice, embodiments will now be described, by way of non-limiting examples only, with reference to the accompanying drawings, in which:

02694690\4-01 Fig. 1A is a schematic front/rear cross-sectional view of a wind turbine transportation cradle (WTTC), according to one embodiment of the present invention;

Fig. IB is a schematic side view of a wind turbine transportation cradle (WTTC), according to an embodiment of the present invention;

Fig. 2 is a schematic front/rear cross-sectional view of a wind turbine transportation cradle (WTTC), according to another embodiment of the present invention;

Fig. 3 is a schematic front/rear cross-sectional view of a wind turbine transportation cradle (WTTC), according to a further embodiment of the present invention;

Figs. 4 through 7 schematically illustrate four configurations of floating offshore wind turbine (FOWT) assemblies that could benefit through the use of the wind turbine transportation cradle (WTTC) of the present invention;

Figs. 8A through 8D schematically illustrate placing the floating offshore wind turbine (FOWT) on the wind turbine transportation cradle (WTTC), according to several embodiments of the present invention;

Figs. 9A through 9C schematically illustrate towing a floating offshore wind turbine (FOWT) resting on a wind turbine transportation cradle (WTTC), according to several embodiments of the present invention;

Figs. 10A and 10B schematically illustrate ballasting of the FOWT assembly shown in Fig. 4, according to an embodiment of the present invention;

Figs. 11A and 11B schematically illustrate ballasting of the FOWT assembly shown in Fig. 5, according to an embodiment of the present invention;

Figs. 12A and 12B schematically illustrate ballasting of the FOWT assembly shown in Fig. 6, according to an embodiment of the present invention; and

Figs. 13A and 13B schematically illustrate ballasting of the FOWT assembly shown in Fig. 7, according to an embodiment of the present invention.

DETAILED DESCRIPTION OF EMBODIMENTS

The principles and operation of the wind turbine transportation cradle (WTTC) according to the present invention may be better understood with reference to the drawings and the accompanying description. It should be understood that these 02694690\4-01 drawings are shown for illustrative purposes only and are not meant to be limiting. It should also be noted that the figures illustrating various examples of the system of the present invention are not to scale, and are not in proportion, for purposes of clarity. It should be noted that the blocks as well other elements in these figures are intended as functional entities only, such that the functional relationships between the entities are shown, rather than any physical connections and/or physical relationships. The same reference numerals and alphabetic characters are utilized for identifying those components which are common in the wind turbine transportation cradle (WTTC), the floating offshore wind turbine (FOWT) assembly and their components, shown in the drawings throughout the present description of the invention. Examples of constructions are provided for selected elements. Those versed in the art should appreciate that many of the examples provided have suitable alternatives which may be utilized.

Referring to Figs. 1A and IB together, schematic cross-sectional front/rear and side views of a wind turbine transportation cradle (WTTC) 7 are illustrated, according to one embodiment of the present invention. The WTTC 7 is configured for transportation of a floating offshore wind turbine (FOWT) (not shown in Figs. 1A and IB) to an offshore installation site, and for installation of a FOWT assembly at the offshore installation site. In the present description, the term "FOWT assembly" refers to an assembly including a floating offshore wind turbine (FOWT) and seabed securing components configured for securing the FOWT to the seabed. Various examples of the FOWT assemblies that can be installed at the offshore installation site by using WTTC 7 are shown in Figs. 4 through 7, and are described in detail hereinbelow.

According to an embodiment of the present invention, the wind turbine transportation cradle (WTTC) 7 includes a plurality of buoyancy vessels 71 (two buoyancy vessels 71 are shown in Figs. 4 -7) having dimensions sufficient to provide buoyancy to the WTTC. The buoyancy vessels 71 are structurally interconnected to each other by a support structure 72 to form a single floating structure. The buoyancy vessels 71 are separated from each other by a predetermined distance required to provide stable operation of the WTTC 7, when it is exposed to harsh weather conditions, such as storms and strong waves. Each vessel 71 includes a corresponding chamber 710 adapted to contain pressurized air. The vessels 71 are pneumatically

02694690\4-01 interconnected to each other so that a uniform air pressure is maintained between the chambers 710 of the vessels 71.

The wind turbine transportation cradle (WTTC) 7 also includes a support assembly 750 integrated with the support structure 72 to form a single floating structure with the plurality of the buoyancy vessels 71. The support assembly 750 includes a plurality of cradle support members 75 arranged over the buoyancy vessels 71. The cradle support members 75 are adapted to hold an upper part of the floating offshore wind turbine (FOWT) above sea water level (not shown in Figs. 1A and IB) during transportation. As will be described hereinbelow in detail, a FOWT (not shown in Figs. 1A and IB) suitable for transportation and installation by the wind turbine transportation cradle (WTTC) 7 includes a floating hollow structure, a supporting tower mounted at the top end of the floating structure, and an electrical wind turbine system mounted on the supporting tower. Accordingly, the WTTC 7 is configured so that it can support the turbine supporting tower and the electrical wind turbine system in a horizontal (or inclined) position using the plurality of the cradle support members 75.

According to an embodiment of the present invention, the chamber 710 of at least one buoyancy vessel 71 of the plurality of the buoyancy vessels 71 includes one or more WTTC air inlet valves 76 configured to pressurize the chambers 710 with compressed air, and one or more WTTC air outlet valves 77 configured to provide compressed air from the chambers 71. The chamber 710 of at least one buoyancy vessel 71 can also include a pressure relief value 43 to protect the buoyancy vessels 71 and chambers 710 from over-pressurization in case the pressure of the compressed air exceeds the safety limit.

It should be understood that although the buoyancy vessels 71 shown in Figs. 1A and IB have a cylindrical shape, generally, the buoyancy vessels 71 can have any desired shape and be constructed of a suitable metal, plastic or composite material with thickness of the walls appropriate to withstand the strain on the walls caused by the air-hydraulic pressure inside the chambers 710.

According to an embodiment of the present invention, the chamber 710 of at least one buoyancy vessel 71 of the plurality of the buoyancy vessels 71 can include a WTTC slurry outlet valve 78 arranged at lower levels of the buoyancy vessel 71. It should be noted that having slurry inlet valve 78 above the waterline (not shown) can remove the need for diver operations when filling with slurry at the quayside.

02694690\4-01 The WTTC slurry outlet valve 78 is configured for providing slurry into the chamber 710. As will be described hereinbelow, the slurry can be used for ballasting the floating structure during the installation process of the FOWT assembly by using the slurry transported by the WTTC in the chamber 710 of the buoyancy vessels 71.

According to an embodiment of the present invention, each buoyancy vessel 71 includes a front fairlead 73a arranged at the front of the WTTC 7 and a rear fairlead 73b arranged at the rear of the WTTC 7. The front fairlead 73a and the rear fairlead 73b can be used to tie the floating offshore wind turbine (FOWT) to the WTTC 7 for transportation.

According to an embodiment of the present invention, each buoyancy vessel 71 includes a side fairlead 74 arranged on the corresponding external side of the WTTC 7. The side fairleads 74 can be used to tie the WTTC 7 to a tug boat (not shown in Figs. 1A and IB) used to tow the WTTC 7 with the floating offshore wind turbine (FOWT) to an offshore installation site.

According to an embodiment of the present invention, each buoyancy vessel 71 includes a manhole 47 adapted for routine maintenance work and inspection of the corresponding chamber 71.

Referring to Fig. 2, a schematic front/rear cross-sectional view of a wind turbine transportation cradle (WTTC) 70 is illustrated, according to another embodiment of the present invention. The WTTC 70 differs from the WTTC (7 in Fig. 1A) in that it additionally includes at least one pair of floaters 79 attached to external sides 712 of the buoyancy vessels 71, correspondingly, to provide additional buoyancy. The inner volume of the floaters 79 can be pneumatically connected with the chambers 710 of the buoyancy vessels 71. Accordingly, the WTTC 70 is able to carry a larger mass of compressed air than the WTTC (7 in Fig. 1A) and to support a larger floating wind turbine during assembly and transportation. Added structural elements 721 can be used to firmly attach the floaters 79 to the cradle 70. If desired, in this configuration, the front fairlead 73a and the rear fairlead 73b as well as the side fairleads 74, may be conveniently attached to the floaters 79 instead of to the buoyancy vessels 71.

Referring to Fig. 3, a schematic front/rear cross-sectional view of a wind turbine transportation cradle (WTTC) 700 is illustrated, according to a further embodiment of the present invention. The WTTC 700 differs from the WTTC (7 in Fig. 1A) in that it further includes a hull 711 including walls 713 surrounding the plurality of buoyancy

02694690\4-01 vessels 71 and the supporting assembly 750. In other words, the cradle 7 can be assembled in the hull 711, which serves to provide additional buoyancy. This configuration may also provide added safety in case of collisions with other structures at sea by minimizing the risk that the buoyancy vessel 71 suffer damages. The hull 711 can be optimized to serve as a stable vessel in a wide range of Metocean conditions.

According to an embodiment of the present invention, the hull 711 can be attached to the buoyancy vessels 71 via additional structural elements 722. If desired, in this configuration, the front fairlead 73a and the rear fairlead 73b, as well as the side fairleads 74, may be conveniently attached to the hull 711 instead of to the buoyancy vessels 71.

Figs. 4 through 7 illustrate four configurations of floating offshore wind turbine (FOWT) assemblies 101 through 104 that could benefit through the use of the wind turbine transportation cradle (WTTC) of the present invention. It should be noted that these four FOWT configurations are envisaged to operate in deep waters in which the water level 1 is usually at least 60 meters above the seabed 2. Each configuration of the FOWT assemblies shown in Figs. 4 through 7 includes a floating offshore wind turbine (FOWT) 100 and securing components 105 - 108 configured for securing the FOWT 100 to the seabed 2.

Generally, the FOWT 100 that can benefit from the technique of present invention includes a floating structure 5, a supporting tower 4 mounted at a top end of the floating structure 5, and an electrical wind turbine system 3 mounted on the supporting tower 4.

The floating structure 5 is hollow and is configured to accommodate compressed air and to provide buoyancy to keep the FOWT 100 afloat and stable under different wind and wave conditions. The floating structure 5 is also configured for anchoring the FOWT 100 to a seabed 2 via the securing components 105 - 108.

The floating structure 5 can, for example, be a single structure. Alternatively, the floating structure 5 can include a plurality of single structures interconnected structurally and pneumatically. It should be understood that the floating structure 5 can have a cylindrical or any other desired shape, and be constructed of any suitable metal or composite materials.

According to an embodiment of the present invention, the floating structure 5 includes one or more ballasting valves 55 located at the bottom of the floating structure

02694690\4-01 5. The ballasting valve(s) 55 is (are) configured for operating during controllable ballasting of the FOWT 100, as will be described hereinbelow. The floating structure 5 also includes one or more purging valves 56 located at the top of the floating structure 5 to be above the sea water level 1 during installation of the FOWT assemblies 101 - 104. The purging valve(s) 56 is (are) configured for purging air trapped within the floating structure 5 during the installation ballasting operation.

According to an embodiment of the present invention, the floating structure 5 includes one or more FOWT inlet air valve(s) 57 configured for controllable pressurizing of the floating structure 5 with compressed air.

The supporting tower 4 is mounted at a top end of the floating structure 5, and is configured for supporting the electrical wind turbine system 3 mounted on the supporting tower 4. The electrical wind turbine system 3 is configured to harness wind energy and generate electricity. The electrical wind turbine system 3 has a plurality of wind vanes disposed to intercept prevailing winds and an electrical generator driven by the wind to generate output electrical power. The electrical generator can, for example, be connected to an offshore electrical power grid.

Referring to Fig. 4, a schematic side view of the FOWT assembly 101 is illustrated, which is installed at an offshore installation site in accordance with one embodiment of the present invention. The FOWT assembly 101 includes the FOWT 100 secured to the seabed by using the securing components 105.

According to this embodiment of the present invention, the securing components 105 include a plurality of top fairleads 51 arranged at the top of the floating structure 5, and at least one bottom fairlead 52 arranged at the bottom of the floating structure 5. The top fairleads 51 and the bottom fairlead(s) 52 is (are) configured for mooring the floating offshore wind turbine (FOWT) 100 to the seabed 2.

The securing components 105 also include a plurality of catenary moorings 53 linked to the floating structure 5 via the plurality of the top fairleads 51. The catenary moorings 53 are configured for anchoring the floating structure 5 to the seabed 2 by a plurality of side anchors 63 located on the seabed. The side anchors 63 can, for example, include gravity anchors, in which the weight of the anchor itself can keep it in place, drag-type anchors, suction bucket anchors, and/or pile-driven anchors.

The floating structure 5 is also moored to the seabed via a tension tether 54 connected at one end to the bottom fairlead 52 at the bottom of the floating structure 5.

02694690\4-01 The tension tether 54 is a vertical link (e.g. wire, rope, or chain) configured for anchoring the floating structure 5 to the seabed 2 by using a main anchor 6 located on the seabed. The main anchor 6 includes an anchor fairlead 61 connected to the tension tether 54 at its another end. The main anchor 6 can include a gravity anchor, a suction bucket or a pile driven into the seabed 2. The floating structure 5 is configured such that it provides an upthrust that is larger than the combined weight of the electrical wind turbine system 3, the supporting tower 4 and the floating structure 5, thereby enabling the tether 54 to be in a permanent state of tension.

Referring to Fig. 5, a schematic side view of the FOWT assembly 102 is illustrated, which is installed at an offshore installation site in accordance with another embodiment of the present invention. The FOWT assembly 102 includes the FOWT 100 secured to the seabed by using the securing components 106.

According to this embodiment, the FOWT 100 includes a plurality of arms 58 attached to the floating structure 5, and the securing components 106 include arm fairleads 59 arranged at ends of the arms 58, and a plurality of tension tethers 54 (two tension tethers 54 are shown in Fig. 5) connected to the arm fairleads 59. The securing components 106 are configured for anchoring the floating structure 5 to the seabed 2 by a plurality of main anchors 6 (two main anchors 6 are shown in Fig. 5) located on the seabed 2. The arm 58 is used to adjust the distance between the tension tethers 54 to achieve the required system stability.

In this configuration, the floating structure 5 is moored to the seabed 2 via the plurality of the tension tethers 54. The tension tethers 54 can be either vertical or inclined links configured for mooring the FOWT 100 to the seabed 2.

Each tension tether 54 is connected to the corresponding end of the arm 58 via the corresponding fairlead 59. Each main anchor 6 includes an anchor fairlead 61 which is attached to the corresponding main anchor 6. Each tension tether 54 is also connected to the seabed 2 through the corresponding anchor fairlead 61. Each anchor 6 can include a gravity anchor, a suction anchor or a pile driven into the seabed 2.

The floating structure 5 is configured such that it provides an upthrust that is larger than the combined weight of the electrical wind turbine system 3, the supporting tower 4 and the floating structure 5, enabling the tethers 54 to be in a permanent state of tension, hence forming a tension-leg platform.

02694690\4-01 Referring to Fig. 6, a schematic side view of the FOWT assembly 103 is illustrated, which is installed at an offshore installation site in accordance with a further embodiment of the present invention. The FOWT assembly 103 includes the FOWT 100 secured to the seabed by using the securing components 107.

According to this embodiment, the securing components 107 include a plurality of top fairleads 51 arranged at the top of the floating structure 5, and a plurality of bottom fairleads 52 arranged at the bottom of the floating structure 5. The top fairleads 51 and the bottom fairleads 52 are configured for mooring the FOWT assembly 100 to the seabed 2.

The securing components 107 also include a plurality of catenary moorings 53 linked to the floating structure 5 via the plurality of top fairleads 51. The catenary moorings 53 are configured for anchoring the floating structure 5 to the seabed 2 by a plurality of side anchors 63 located on the seabed 2. The side anchors 63 can, for example, include gravity anchors, in which the weight of the anchor itself can keep it in place, of drag-type anchors, suction bucket anchors, and/or pile driven anchors.

The floating structure 5 is also stabilized via one or more tension tethers 54 (two tethers 54 are shown in Fig. 6) connected to the bottom fairlead 52 at the bottom of the floating structure 5.

The securing components 107 also include a ballast 141 suspended from the bottom of the floating structure 5 via the tethers 54. The ballast 141 is adapted to lower the center of gravity of the entire structure and to provide the necessary stability required over a wide range of wind and wave conditions. Each tether 54 is attached to the fairlead 52 on the floating structure 5 and to a fairlead 61 mounted on the ballast 141. The length of the tethers 54 and the draft of the floating structure 5 are configured such that the ballast 141 is never in contact with the seabed 2.

Referring to Fig. 7, a schematic side view of the FOWT assembly 104 is illustrated, which is installed at an offshore installation site in accordance with another embodiment of the present invention. The FOWT assembly 104 includes the FOWT 100 secured to the seabed by using the securing components 108.

According to this embodiment of the present invention, the securing components 108 include a plurality of top fairleads 51 arranged at the top of the floating structure 5. The top fairleads 51 are configured for mooring the floating offshore wind turbine (FOWT) 100 to the seabed 2.

02694690 4-01 The securing components 108 also include a plurality of catenary moorings 53 linked to the floating structure 5 via the plurality of the top fairleads 51. The catenary moorings 53 are configured for anchoring the floating structure 5 to the seabed 2 by a plurality of side anchors 63 located on the seabed. The side anchors 63 can, for example, include gravity anchors, in which the weight of the anchor itself can keep it in place, of drag-type anchors, suction bucket anchors, and/or pile-driven anchors.

The securing components 108 also include a slurry 14 introduced in the lower part of the floating structure 5 to act as a ballast by lowering the center of gravity of the FOWT assembly 100, hence providing the necessary stability to keep the wind turbine (3) in its correct position over a wide range of operating wind and wave conditions. The floating structure 5 is configured such that it provides enough buoyancy that is equal to the combined weight of the electrical wind turbine system 3, the supporting tower 4, the floating structure 5 and the slurry ballast 14.

According to another general aspect of the present invention, there is provided a method for transporting a floating offshore wind turbine (FOWT) to an offshore installation site, and installing a floating offshore wind turbine (FOWT) assembly including the FOWT and the seabed securing components. The method is based on the use of the wind turbine transportation cradle (WTTC) described above and shown in Figs. 1A, IB, 2 and 3.

The method can be adapted for each of the four configurations of the FOWT assemblies 101 - 104 described above and shown in Figs. 4 through 7, correspondingly. In all FOWT configurations, the electrical wind turbine system 3, the wind turbine tower 4 and the floating structure 5 of the floating offshore wind turbine (FOWT) are assembled together on land or in the water next to the quayside, with the entire assembly inclined horizontally. A land-based crane or a floating crane may be used for this operation.

The wind turbine transportation cradle (WTTC) 7 floats in the water by the quayside and a crane is used to place the entire FOWT on the floating WTTC to rest in an inclined position with the turbine tower 4 resting on the cradle support members 75. Figs. 8A through 8D illustrate placing the FOWT 100 on the WTTC 7 in an inclined position with the turbine tower 4 resting on the cradle support members 75 for various embodiments of the FOWT.

02694690\4-01 In the inclined position, the ballasting valves 55, purging valves 56 and inlet air valves 57 of the floating structure 5 are closed, to ensure no water ingress into the floating structure 5. The FOWT assembly which is oriented in an inclined position, is kept afloat through the combined buoyancy offered by the floating structure 5 and the cradle (WTTC) 7.

According to an embodiment of the present invention, the WTTC 7 is secured firmly to the top of the supporting tower 4 and to the top of the floating structure 5 of the FOWT. For example, it can be tied to the FOWT by front lines 8 connecting the front fairleads 73a of the cradle 7 to the top fairleads 51 of the floating structure 5, and by rear lines 81 connecting the rear fairleads 73b of the wind turbine transportation cradle 7 to fairleads 41 arranged at the tower top. The front lines 8 and the rear lines 81 can include ropes, chains, brackets and/or straps designed to keep the cradle secured to the tower 4 during towing.

In the case of FOWT configurations shown in Figs. 8A, 8B and 8C, the chambers 710 of the cradle 7 are charged with compressed air supplied by a compressor (not shown) at the quayside once the front lines 8 have been secured.

In the case of FOWT configuration shown in Figs. 8D, the cradle 7 is first partially filled with slurry 14. Then, compressed air provided by a compressor at the quayside is injected into the chambers 710 of the wind turbine transportation cradle (WTTC) 7 to retain the slurry 14 under pressure.

Referring to Figs. 9A through 9C, the assembly comprising the floating offshore wind turbine (FOWT) located on the wind turbine transportation cradle (WTTC) can be towed to the offshore installation site using a tug boat 10. Two additional tug boats 1010 are used to maintain the correct orientation and to compensate for any drift forces induced by the wind, sea currents and waves.

Fig. 9A shows the towing arrangement for installation of the FOWT assembly configurations 101 and 108, which are shown in Figs. 4 and 7, correspondingly. Fig. 9B shows the towing arrangement for installation of the FOWT assembly configuration (102 in Fig 5). Fig. 9C shows the towing arrangement for installation of the FOWT assembly configuration (103 in Fig. 6).

As shown in Fig. 9A, in the case of the FOWT assembly configurations 101 and 108, a single towing line 9 is used to connect tug boat 10 to the bottom fairlead 52 of the floating structure 5. In the case of the FOWT assembly configurations 102 and 103, 02694690\4-01 a plurality of towing lines 91 are used to connect the tug boat 10 to the arm fairleads 59 and to the bottom fairleads 52, as shown in Figs. 9A and 9C. For all the four FOWT configurations, two tug boats 1010 are connected to the side fairleads 74 of WTTC 7 via side towing lines 111. Tensioning front and rear lines 8 and 81 can keep the WTTC 7 secured to the wind turbine tower 4 through connections with the top fairleads 51 and 41, respectively.

Referring to Figs. 10A and 10B, ballasting of the FOWT assembly 101 is illustrated, according to an embodiment of the present invention.

On arrival at the installation site offshore, the towing line 9 is disconnected from the bottom fairlead 52, and is connected to one of the top fairleads 51 while retaining the connection with a tugboat 10 as shown in Fig. 10A. The tension tether 54 is connected to bottom fairlead 52 at one end, allowing it to hang freely in the water. The rear lines (81 in Fig. 8A) holding the cradle 7 to the top of the wind turbine tower (4 in Fig. 8A) are disconnected.

The ballasting valve 55 and the purging valve 56 of the floating structure 5 are then opened, allowing the ballasting fluid to enter the floating structure 5. According to the embodiment shown in Figs. 10A and 10B, the ballasting fluid is sea water. Thus, opening of the valves 55 and 56 allows the sea water 12 to penetrate the inside of the floating structure 5, while allowing internal air to be purged into the atmosphere.

This process allows the center of gravity of the FOWT including the electrical wind turbine system 3, the wind turbine tower 4 and the floating structure 5 to change, thus tilting the aforementioned FOWT upwards as shown in Fig. 10A. The quantity of the sea water 12 entering the floating structure 5 is regulated through the ballasting valve 55 until the FOWT is vertical, as shown in Fig. 10B.

The catenary moorings 53 are then interconnected to the top fairleads 51 and to the side anchors 63, which are arranged at the seabed. The tension tether 54 is then attached to anchor fairlead 61 of the anchor 6.

The purging valve 56 is then closed and a pneumatic cable 13 is connected between the FOWT inlet air valve 57 of the floating structure 5 and the WTTC air outlet valve (77 in Figs. 1A and IB) of one of the buoyancy vessels 71 of the WTTC 7. The WTTC air outlet valve 77 is then opened, allowing compressed air from the buoyancy vessels 71 of the cradle 7 to flow into the floating structure 5 and purge the ballasting water out through ballasting valve 55. Once the entire ballasting water is purged, the 02694690\4-01 ballasting valve 55 is closed. This process allows the entire FOWT assembly 101 to be installed in the position shown in Fig. 4.

Then, the towing line 9, front lines 8 and the pneumatic cable 13 are disconnected from the floating structure 5. Finally, the tugboats 1010 tow the WTTC 7 back to the shore.

Referring to Figs. 11A and 11B, ballasting of the FOWT assembly (102 in Fig. 5) is illustrated, according to an embodiment of the present invention.

On arrival at the installation site offshore, the towing lines 91 are disconnected from the arm fair leads 59 at the bottom of the floating structure 5, and are connected to one of the top fairleads 51, while retaining the connection with the tugboat 10 as shown in Fig. 11 A. The tension tethers 54 are connected to arm fairleads 59 at one end, allowing them to hang freely in the water. The rear lines (81 in Figs. 8A) holding the cradle 7 to the top of the wind turbine tower (4 in Fig. 8A) are disconnected.

The ballasting valve 55 and the purging valve 56 of the floating structure 5 are then opened, allowing the ballasting fluid to enter the floating structure 5.

According to the embodiment shown in Figs. 11A and 11B, the ballasting fluid is sea water. Thus, opening of the valves 55 and 56 allows the sea water 12 to penetrate the inside of the floating structure 5, while allowing internal air to be purged to the atmosphere.

This process allows the center of gravity of the FOWT 100 including the electrical wind turbine system 3, the wind turbine tower 4 and the floating structure 5 to change, thus tilting the aforementioned FOWT in an upward arc as shown in Fig. 11 A. The quantity of the sea water 12 entering the floating structure 5 is regulated through the ballasting valve 55 until the FOWT is vertical, as shown in Fig. 11B.

The tension tethers 54 are then connected to the side seabed anchors 6 via the anchor fairleads 61.

The purging valve 56 is then closed and a pneumatic cable 13 is connected between the FOWT inlet air valve 57 of the floating structure 5 and the WTTC air outlet valve (77 in Figs. 1A and IB) of one of the buoyancy vessels 71 of the WTTC 7. The WTTC air outlet valve 77 is then opened, allowing compressed air from the buoyancy vessels 71 of the cradle 7 to flow into the floating structure 5 and purge the ballasting water out from the floating structure 5 through ballasting valve 55. Once the entire amount of ballasting water is purged, the ballasting valve 55 is closed. This process 02694690\4-01 allows the tethers to be tensioned, hence keeping the FOWT stable in the required position. Accordingly, the entire FOWT assembly 102 is installed in the position shown in Fig. 5.

Then, the towing lines 91, front lines 8 and the pneumatic cable 13 are disconnected from the floating structure 5. Finally, the tugboats 1010 tow the WTTC 7 back to the shore.

Referring to Figs. 12A and 12B, ballasting of the FOWT assembly (103 in Fig. 6) is illustrated, according to an embodiment of the present invention.

On arrival at the installation site offshore, the towing lines 9 are disconnected from the bottom fairleads 52, and are connected to one of the top fairleads 51 while retaining the connection with the tugboat 10 as shown in Fig. 12A. The tension tethers 54 are connected to bottom fairleads 52 at one end, allowing them to hang freely in the water. The rear lines (81 in Fig. 8A) holding the cradle 7 to the top of the wind turbine tower (4 in Fig. 8A) are disconnected.

The ballasting valve 55 and the purging valve 56 of the floating structure 5 are then opened, allowing the ballasting fluid to enter the floating structure 5. According to the embodiment shown in Figs. 12A and 12B, the ballasting fluid is sea water. Thus, opening of the valves 55 and 56 allows the sea water 12 to penetrate the inside of the floating structure 5, while allowing internal air to be purged to the atmosphere.

This process allows the center of gravity of the FOWT including the electrical wind turbine system 3, the wind turbine tower 4 and the floating structure 5 to change, thus tilting the aforementioned FOWT in an upward arc as shown in Fig. 12A. The quantity of the sea water 12 entering the floating structure 5 is regulated through the ballasting valve 55 until the FOWT is vertical, as shown in Fig. 12B.

The catenary moorings 53 are then interconnected to the top fairleads 51 and to the side anchors 63, which are arranged at the seabed. The tension tethers 54 are then connected to the fairleads 61 mounted on the ballast 141 lying on the seabed.

The purging valve 56 is then closed and a pneumatic cable 13 is connected between the FOWT inlet air valve 57 of the floating structure 5 and the WTTC air outlet valve (77 in Figs. 1A and IB) of one of the buoyancy vessels 71 of the WTTC 7.

The WTTC air outlet valve 77 is then opened, allowing compressed air from the buoyancy vessels 71 of the cradle 7 to flow into the floating structure 5 and purge the ballasting water out from the floating structure 5 through ballasting valve 55. Once the 02694690\4-01 entire ballasting water is purged, the ballasting valve 55 is closed. This process allows the FOWT 100 to achieve more upthrust moving upwards and allowing the tethers 54 to be tensioned and the ballast (141) to detach from the seabed and become suspended. Thus, the entire FOWT assembly 103 is installed in the position shown in Fig. 6.

Then, the towing line 9, front lines 8 and the pneumatic cable 13 are disconnected from the floating structure 5. Finally, the tugboats 1010 tow the WTTC 7 back to the shore.

Referring to Figs. 13A and 13B, ballasting of the FOWT assembly (104 in Fig. 7) is illustrated, according to an embodiment of the present invention.

On arrival at the installation site offshore, the towing line 9 is disconnected from the bottom fairlead 52, and is connected to one of the top fairleads 51 while retaining the connection with the tugboat 10 as shown in Fig. 13A. The rear lines (81 in Fig. 8A) holding the cradle 7 to the top of the wind turbine tower (4 in Fig. 8A) are disconnected.

The ballasting valve 55 and the purging valve 56 of the floating structure 5 are then opened. An umbilical 131 is connected to the ballasting valve 55 of the floating structure 5 and to the WTTC slurry outlet valve 78 on the buoyancy vessels 71 of the cradle (WTTC) 7, allowing the ballasting fluid to enter the floating structure 5. According to the embodiment shown in Figs. 13A and 13B, the ballasting fluid is a slurry. Thus, opening of the valves 55 and 56 allows the slurry 14 to flow into the bottom of the floating structure 5 under the influence of compressed air in the buoyancy vessels 71 of the cradle 7, while allowing internal air to be purged to the atmosphere.

This process allows the center of gravity of the FOWT, including the electrical wind turbine system 3, the wind turbine tower 4 and the floating structure 5, to change, thus tilting the aforementioned FOWT in an upwards arc, as shown in Fig. 13A. The quantity of the slurry 14 entering the floating structure 5 is regulated through the ballasting valve 55 until the FOWT 100 is vertical, as shown in Fig. 13B.

The catenary moorings 53 are then interconnected to the top fairleads 51 and to the side anchors 63, which are arranged at the seabed.

The ballasting valve 55, the purging valve 56 and the WTTC slurry outlet valve 78 are then closed and the umbilical 131 is disconnected from the floating structure 5. The purging valve 56 is also closed.

This process allows the entire FOWT assembly 104 to be installed in the position shown in Fig. 7.

02694690\4-01 Then, the towing line 9, front lines 8 and the pneumatic cable 13 are disconnected from the floating structure 5. Finally, the tugboats 1010 tow the WTTC 7 back to the shore.

As such, those skilled in the art to which the present invention pertains, can appreciate that while the present invention has been described in terms of preferred embodiments, the concept upon which this disclosure is based may readily be utilized as a basis for the designing of other structures, systems and processes for carrying out the several purposes of the present invention.

Also, it is to be understood that the phraseology and terminology employed herein are for the purpose of description and should not be regarded as limiting.

Finally, it should be noted that the words “comprising”, “including” and “containing” as used throughout the appended claims are to be interpreted to mean “including but not limited to”.

It is important, therefore, that the scope of the invention is not construed as being limited by the illustrative embodiments set forth herein. Other variations are possible within the scope of the present invention as defined in the appended claims. Other combinations and sub-combinations of features, functions, elements and/or properties may be claimed through amendment of the present claims or presentation of new claims in this or a related application. Such amended or new claims, whether they are directed to different combinations or directed to the same combinations, whether different, broader, narrower or equal in scope to the original claims, are also regarded as included within the subject matter of the present description.

02694690\4-01