Construction and installation process to deploy a wind turbine "WTG" on a tension leg platform/spar in medium to deep water

Abstract

Method for installation of a wind turbine generator on a tension leg platform/spar (WTG foundation) using gravity anchors or suction anchors. A concrete WTG foundation is built with the ‘slip form’ method, a combination construction/deployment barge (barge) allows the WTG and WTG foundation to be delivered to the installation site as a complete unit and a split hull hydraulic dump scow facilitates the slip form construction and deployment of the gravity anchors. The barge is sunk as a dry dock to a draft that permits the WTG/WTG foundation to be floated off. The free floating WTG foundation is ballasted with sea water to its operating draft with 5 feet of freeboard. The tension legs from the gravity anchors are attached to the WTG foundation and snugged with equal tension. The sea water is then removed from the WTG foundation. This process tightens the tension legs to their design loads. The WTG/WTG foundation maintains a relatively large water plane and a 5 foot freeboard. The gravity anchors are constructed and deployed to the installation site, with tension legs attached, by means of a split hull hydraulic dump scow. Four gravity anchors are deployed for each WTG installation.

Description

RELATED APPLICATIONS

This application and claims priority from Provisional Application Ser. No. 61/796,656 filed on Nov. 16, 2012 and Provisional Application 61/797,360 filed on Dec. 6, 2012, both of which are hereby incorporated by reference in their entirety.

FIELD OF INVENTION

A process for installation of a wind turbine generator “WTG” on a tension leg platform/spar using gravity anchors by implementation of a concrete WTG foundation built using the “slip form” method whereby a combination construction/deployment barge allows the WTG and WTG foundation to be delivered to the installation site as a complete unit and stabilized using a gravity anchor comprising a rock filled concrete cylinder made by the slip form method.

BACKGROUND OF INVENTION

Islands such as Hawaii have some of the highest retail electric tariffs, for example (31 cper KWh) due to a dependency on diesel generation. Renewable energy is a viable option such as offshore wind, solar and biomass renewable resources.

An offshore wind farm could connect to existing 138 kV grid as an generator for FRP purposes. There are limited or no sites for utility scale wind or solar power installations. A direct connection into the 138 KV HECO system is less costly than an inter island VHDC cable. An offshore gearless WTG can provide the energy. Concrete slip form technology can be applied utilized with tension leg platforms and gravity anchors.

Conventional platforms are constructed in shallow waters because medium to deep water wind farms of subject to casualties from the elements. Few if any are able to survive the loss of a tension leg. Catenary restrained types or floaters are subject to too much motion such that the well-being of the WTG is compromised. Construction of deep water units are currently dependent upon large construction areas near the wind farm shoreline site which defaces the shoreline. Currently no economical means of building and deploying gravity anchors are available for deep water platforms.

SUMMARY OF THE INVENTION

The present invention provides a system which facilitates the construction and installation of a spar buoy foundation for offshore wind turbine generator (“WTG”) units. The tension leg platform/spar system includes a WTG foundation, gravity anchors and tension legs which collectively supports a WTG.

The system utilizes a WTG foundation comprising a concrete platform/spar with unique geometry and weight distribution that is specifically designed to be constructed on a barge. The WTG foundation includes a buoyant concrete platform/spar on which the WTG is installed and to which the tension legs are attached to concrete anchors which are weights that rest on or in the sea floor. The anchors in conjunction with the tension legs offset the buoyancy of the WTG foundation and mitigate its motion (restricts heave, roll, pitch, yaw and lateral motion). The anchors can be comprised of concrete, steel, rock, and combinations thereof. The horizontal cross section of the WTG foundation can be any geometrical shape that can be extruded.

The tension leg platform/spar system is stable when free floating with the WTG installed in all circumstances and is anchored to the sea floor by tension legs to secure the unit in place and prevent “heave”. The tension legs are flexible devices comprising high strength wire rope, steel cable, or the like that connect the WTG foundation to the concrete anchors and transmit the buoyant forces. The platform is permanently moored by means of tethers or tendons grouped at each of the structure's corners. A group of tethers is called a tension leg. A feature of the design of the tethers is that they have relatively high axial stiffness (elasticity) such that virtually all of the vertical motion of the platform is eliminated. It is designed to be stable in 50 foot waves without tension legs becoming slack. It is; partially constructed by economical “slip form” methods. Moreover, the unit is stable even with the loss of one or more tension leg(s), so that it will resist capsizing.

A construction barge assembly comprising a combination barge/dry dock which serves as the constructing platform, transport device and launch mechanism for the WTG foundation. It is designed to be the construction platform on which the spar is constructed and the WTG is installed thereon; transport the spar to the installation site by tugs; be stable in all phases of construction and installation of the spar; perform as a dry dock and be ballasted to a draft that allows the spar to float off; be de-ballasted by self contained pumping system; be built to ABS rules for ocean deck barges with a load line; meet required structrual strength for deck loads and longitudinal strength; and be re-used for multiple WTG installations or be converted to heavy duty deck barge.

The scow is a split hull hydraulic dump scow used as a construction and deployment mechanism for the concrete anchors. The concrete anchor is constructed din the hopper of the closed scow. The scow is then used to transport the anchor to the WTG installation site where the scow is opened and the anchor deployed to the sea floor in a controlled manner.

It is an object of the present invention to utilize gravity anchors designed to withstand the maximum design lift forces imparted by tension legs; be constructed of re-enforced concrete or combination of concrete, rock and steel; and be constructed in and deployed form the hopper of a split hull hydraulic scow.

It is an object of the present invention to employ a split hull hydraulic dump scow designed to comply with the ABS rules for offshore open hopper barges; allow gravity anchors to be constructed in the hopper when in the closed position; to transport the completed gravity anchor to the installation site by tugs, and lower the gravity anchor through an open hopper to position on the sea floor in a controlled manner.

It is an object of the present invention to provide a method for utilizing a “slip form” method to form a significant portion of the concrete WTG foundation. Slip forming, continuous poured continuously formed, or slip form construction is a construction method in which concrete is poured into a continuously moving form. Slip forming is used for tall structures (such as bridges, towers, buildings, and dams), as well as horizontal structures, such as roadways. Slip forming enables continuous, non-interrupted, cast-in-place “flawless” (i.e. no joints) concrete structures which have superior performance characteristics to piecewise construction using discrete form elements. Slip forming relies on the quick-setting properties of concrete, and requires a balance between quick-setting capacity and workability. Concrete needs to be workable enough to be placed into the form and consolidated (via vibration), yet quick-setting enough to emerge from the form with strength. This strength is needed because the freshly set concrete must not only permit the form to “slip” upwards but also support the freshly poured concrete above it. In vertical slip forming the concrete form may be surrounded by a platform on which workers stand, placing steel reinforcing rods into the concrete and ensuring a smooth pour. Together, the concrete form and working platform are raised by means of hydraulic jacks. Generally, the slip form rises at a rate which permits the concrete to harden by the time it emerges from the bottom of the form.

It is another object of the present invention to devise a method to construct and employ the gravity anchors using the split hull hydraulic dump scow to significantly enhance the economics of using gravity anchors.

It is an object of the present invention to provide A WTG foundation that when installed in the final position has a relatively large water plane to allow for greater stability when free floating. It also allows the economy of deploying the gravity anchors separately of the WTG foundation because the free floating stability of the WTG foundation permits the tension leg to be easily installed in this circumstance. Also the large water plane will keep the WTG stable if tension legs are lost aiding in the prevention of capsizing of the WTG.

A preferred method for installation of a wind turbine generator “WTG” on a tension leg platform/spar using gravity anchors by implementation of a concrete WTG foundation built using the “slip form” method uses a combination construction/deployment barge allowing the WTG and WTG foundation to be delivered to the installation site as a complete unit and stabilized using a gravity anchor comprising a rock filled concrete cylinder made by the slip form method according to the following steps. Construct the WTG foundation on a construction barge at a dock; form the gravity anchors in the split hull scow and deploy same to the installation site; complete the WTG foundation on the construction barge; install the WTG foundation on the barge before it leaves the dock; tow the construction barge to the installation site using tugs; sank the construction barge to a selected draft such that the WTG foundation with the WTG thereon floats off of the barge (dry dock mode), wherein the WTG foundation with the WTG thereon floats freely and is stable having a positive G'M; refloat the construction barge with its self-contained pumping system for return to dock; ballasting the WTG foundation with sea water until it reaches its operating draft (approximately five feet of freeboard) maintaining stability throughout the process; positioning the spar over the gravity anchors; attaching the tension legs; and removing the WTG foundation and establishing tension in the tension legs.

The process sets forth a method for installation of a wind turbine generator on a tension leg platform/spar (WTG foundation) which uses gravity anchors built by a slip form method or suction anchors. The process employs a concrete WTG foundation built with the ‘slip form’ method, a combination construction/deployment barge (barge) which allows the WTG and WTG foundation to be delivered to the installation site as a complete unit and a split hull hydraulic dump scow (scow) which facilitates the construction and deployment of the gravity anchors or perhaps suction anchors.

The concrete WTG foundation is built on a heavy duty combination deck barge/dry dock. The WTG is installed onto the WTG foundation before the barge leaves the staging dock. The barge transports the WTG/WTG foundation to the deployment site via ocean tug(s). The barge is sunk as a dry dock to a draft that permits the WTG/WTG foundation to be floated off in a stable condition. The barge is then raised and returned by tug to the staging dock for another construction cycle. At the installation site, the ‘free floating’ WTG foundation is ballasted with sea water to its operating draft with 5 feet of freeboard. The tension legs from the gravity anchors are attached to the WTG foundation and snugged with equal tension. The sea water is then removed from the WTG foundation. This process tightens the tension legs to their design loads. The WTG/WTG foundation maintains a relatively large water plane and a 5 foot freeboard. Concurrently with the construction of the WTG foundation, the gravity anchors are constructed and deployed to the installation site, with tension legs attached, by means of a uniquely designed split hull hydraulic dump scow. Four gravity anchors are made and deployed for each WTG installation. The designs of the WTG foundation, the construction/deployment barge, the gravity anchors and the split hull hydraulic dump scow are inextricably related and, collectively facilitate a simple and economic process. The installed WTG foundation will remain floating even in gail force winds and even if one or more of the tension cables breaks due to its self-righting design.

Other objects, features, and advantages of the invention will be apparent with the following detailed description taken in conjunction with the accompanying drawings showing a preferred embodiment of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

A better understanding of the present invention will be had upon reference to the following description in conjunction with the accompanying drawings in which like numerals refer to like parts throughout the several views and wherein:

FIG. 1 shows the installed WTG foundation with the WTG, tension legs and gravity anchors;

FIG. 2 is a top view showing the concrete cylindrical spar buoy WTG foundation with transition stem;

FIG. 3 is a side view showing the concrete cylindrical spar buoy WTG foundation with transition stem;

FIG. 4 shows the construction barge supporting the wind turbine WTG, and WTG foundation disposed between wing walls;

FIG. 5 is a top view of the construction barge showing the wing walls, WTG, and WTG blade positioned upon the barge for transport and deployment;

FIG. 6 is an elevational view showing the construction barge supporting the wing walls, WTG, positioned upon the barge for transport and deployment;

FIG. 7 is an plan view showing the construction barge supporting the wing walls and spar in dry dock;

FIG. 8 is a plan view showing the maximum moments about points ‘D’ (top of anchor) and ‘E’ (attachment of windward tension leg to foundation);

FIG. 9 is a plan view showing lateral displacement resulting from the maximum moments about points ‘D’ (top of anchor) and ‘E’ (attachment of windward tension leg to foundation) of FIG. 8;

FIG. 10 is a plan showing the dimensions and physical characteristics of the gravity anchor in the ‘float-off condition and the ‘submerged, fully installed’ condition;

FIG. 11 is a elevational view of the gravity anchor is depicted in FIG. 10;

FIG. 12 shows a clevis attached to the anchor block;

FIG. 13 shows a clevis attached to the anchor block;

FIG. 14 shows an enlargement of the anchor block of FIG. 12;

FIG. 15 is a plan showing the dimensions and physical characteristics of the gravity anchor in the ‘float-off condition and the ‘submerged, fully installed’ condition;

FIG. 16 is a plan showing the dimensions and physical characteristics of the gravity anchor in the ‘float-off condition and the ‘submerged, fully installed’ condition;

FIG. 17 shows a split hull scow with closed section;

FIG. 18 shows a split hull scow section when open;

FIG. 19 shows a split hull hydraulic dump scow; and

FIG. 20 shows the deck plane and hopper of a split hull hydraulic scow.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The concrete WTG foundation is built on a heavy duty combination deck barge/dry dock. The WTG is installed onto the WTG foundation before the barge leaves the staging dock. The barge transports the WTG/WTG foundation to the deployment site via ocean tug(s). The barge is sunk as a dry dock to a draft that permits the WTG/WTG foundation to be floated off in a stable condition. The barge is then raised and returned by tug to the staging dock for another construction cycle. At the installation site, the ‘free floating’ WTG foundation is ballasted with sea water to its operating draft with 5 feet of freeboard. The tension legs from the gravity anchors are attached to the WTG foundation and snugged with equal tension. The sea water is then removed from the WTG foundation. This process tightens the tension legs to their design loads. The WTG/WTG foundation maintains a relatively large water plane and a 5 foot freeboard.

Prior to the construction of each of the WTG foundations, the concrete part of the gravity anchors are constructed and deployed to the installation site, with tension legs attached. Once the concrete cylinders are sunk to the sea floor, they are filled with rock.

The designs of the WTG foundation, the construction/deployment barge and the gravity anchors are inextricably related and, collectively facilitate a simple and economic process. FIG. 1 shows the tension leg platform/spar 10 with the installed WTG foundation 12 with the WTG 14, tension legs 16 and gravity anchors 18.

As set forth in U.S. Pat. No. 7,075,189 by Heronemus et al., which is incorporated by reference herein, the term ‘wind turbine’ encompasses the drive train, gearbox, and generator for embodiments that include these elements. The word ‘rotor’ refers to the external rotating parts of a wind turbine, namely blades and a hub. Issues regarding loads, materials, structural dynamics, aerodynamics, controls, and power conversion must be taken into consideration in the construction of a wind turbine. The following reference provide guidance for wind turbine design, all of which are incorporated herein by reference:

• Guidelines for Design of Wind Turbines, Det Norske Veritas, Copenhagen and Riso National Laboratory, Denmark, 2002.
• Hau, E., Windturbines—Fundamentals, Technologies, Application, and Economics, Springer Verlag, Berlin Heidelberg, 2000.
• Eggleston, D., Stoddard, F., Wind Turbine Engineering Design, Van Nostrand Reinhold, N.Y., 1987.
• Burton, T., Sharpe, D., Jenkins, N., Bossanyi, E., Wind Energy Handbook, John Wiley & Sons, West Sussex England, 2001.
• Gasch, R., Twele, J., Wind Power Plants—Fundamentals, Design, Construction, and Operation, Solarpraxis AG, Germany, 2002.
• Freris, L., Wind Energy Conversion Systems, Prentice Hall International Ltd., London, 1990.

Off shore wind turbines have unique design considerations related to wave loading, dynamics that are different from onshore turbines, corrosion due to a salt-water environment, and other factors. As noted in the above patent Special chapters on design of offshore wind turbines can be found in Chapter 13 of the above reference entitled Wind Power Plants—Fundamentals, Design, Construction, and Operation and Chapter 16.6 of the above reference entitled Windturbines—Fundamentals, Technologies, Application, and Economics. The design of wind turbine rotors for a windship differs from land-based wind turbines in that the load specification will be different because at the platform tilts backward and forward, the relative wind speed that each rotor encounter varies and this dependence of loads on rotor dynamics is a factor.

TYPICAL 6 MW WTG DATA is as follows:
Data for A TYPICAL 6 MW WIG used in this scenario is as follows:
Nacelle—approx. 192.9 s. tons, (L×W×H) 15100×6500×7250 mm.
Tower—approx. 444 s. tons, (W) Top diameter: 4185 mm—bottom diameter 6000 mm, (H) 87740 mm Blades—approx. 33.1 s. tons, (L×W) 75000×5000 mm
Hub—approx. 104.7 s. tons, (W×H) 7900×5500 mm
It is premised that the hub height is—295 feet and the blades about—43 feet above still water level.

WTG Foundation

The WTG foundation is a vertical concrete cylinder designed uniquely with geometry and weight distribution to:

Support the 6 MW WTG;

Be constructed on the barge;
Be stable when free floated off of the barge;
Be stable through the entire tension leg attachment process;
Be stable in trough of 50 ft wave without tension legs becoming slack;
Be stable in crest of 50 ft wave without overloading tension legs;
Be stable with loss of a tension leg; and
Allow internal pressure for compressed air removal of sea water ballast; and

Preliminary design of one preferred WTG foundation has been completed to the extent that preliminary costing can be done. The lower 12.98 feet (3.96 in) of the cylinder is heavy concrete with steel re-enforcement. This part of the cylinder is referred to as the permanent ballast and lowers the vertical center of gravity. The vertical part of the cylinder between the permanent ballast and the top or lid is made by the economical ‘slip form’ method and is made of re-enforced lightweight concrete. The top, or lid, of the cylinder is also made of lightweight concrete. The geometry and thicknesses of the structure is designed to support the WTG to stand up to wind, waves and current and to withstand internal compressed air pressure >36 psi.

The weights, centers of gravity, free floating stability and total tension leg forces must be determined for the following scenario in order to deploy the foundation.

1) WTG/WTG foundation free floating off the barge/dry dock;
2) WTG/WTG foundation free floating; when ballasted down to operating w/o tension legs;
3) WTG/WTG foundation with tension legs attached in calm water;
4) WTG/WTG foundation with tension legs attached in trough of 50 ft wave; and
5) WTG/WTG foundation with tension legs attached in crest of 50 ft wave.

A unique aspect of this WTG foundation is that it has a relatively large water plane in all installation, operating and failure modes. This large water plane contributes significantly to stability. For example, it allows the gravity anchors to be deployed separately from the WTG foundation because its ‘free floating’ stability facilitates simple tension leg installation. Also, high wind, wave and current loads produce lateral displacement which causes vertical displacement which increases the buoyancy which increases the tension leg loads. This allows lower initial tension leg design loads when considering the possibility of slack tension legs under high loads. A preliminary check of wind, wave and current forces on the WTG/WTG foundation and tension leg system indicates that the larger water plane does not cause unacceptable loads.

FIGS. 2 and 3 show the concrete cylindrical spar buoy WTG foundation with transition stem wherein the tension leg 16 is shown as disposed within a triangular support structure formed by junction of the cylindrical slip wall 20 formed cross section 20 and intersecting wall 21. FIG. 3 shows the tension leg pathway 24 formed within the slip formed section 30 supported on a base of heavy concrete ballast 22 with the stem 26 extending vertically therefrom with a lid 28 covering the top of the spar buoy 11.

Construction Barge

The construction barge is a combination deck barge and dry dock. It is specifically designed not to exceed ABS Load Line draft with maximum WTG/WTG foundation load, to withstand local deck loads due to WTG/WTG foundation induced loads, withstand longitudinal bending stresses due to WTG/WTG foundation loads, transport the WTG/WTG foundation to the installation site, withstand pressures due to submergence as a dry dock, have adequate stability with WTG/WTG foundation load in transit mode, have adequate stability during submergence as a dry dock with WTG/WTG foundation have adequate stability when submerged and WTG foundation has floated off, submerge to a draft such that the WTG/WTG foundation can float off, and meet ABS Rules for offshore deck barges. Preliminary design of this barge has been completed to the extent that preliminary costing can be done.

Preliminary principle dimensions of the barge for a preferred embodiment are:

	Total length of wing walls, one side	270	ft
	Length overall	100	ft
	Breadth	108	ft
	Depth @ side	23.5	ft
	Height of wing walls above deck	66	ft
	Width of wing walls	34	ft

FIGS. 3-7 depict the construction barge in various views with the WTG/WTG foundation on board. FIG. 4 shows the construction barge 32 supporting the wind turbine WTG 14, WTG spar 12 disposed between wing walls 33. FIG. 5 is a top view of the construction barge 32 showing the wing walls 33, WTG 14, and WTG blades 34 positioned upon the barge for transport and deployment. FIG. 6 is an elevational view showing the construction barge supporting the wing walls, WTG, positioned upon the barge for transport and deployment. FIG. 7 is an plan view showing the construction barge supporting the wing walls and spar in dry dock.

Calculation are required to determine weights, centers of gravity and stability data for the following:

1) Barge in transit mode with completed WTG/WTG foundation unit on board;
2) Barge, as dry dock, submerged to deck level (lowest stability) with WTG/WTG foundation load onboard; and
3) Barge, as dry dock, submerged after WTG/WTG foundation floats off.

The barge and the concrete foundation will not deflect in the same manner due to bending. The barge is less rigid than the concrete foundation. This could cause the barge deck to incur large concentrated loads. To deal with this, a thin layer of selected timber will be placed under the concrete foundation. This timber will be selected to crush and, thus, to distribute the foundation load in an acceptable manner.

Tension Legs

This application will have four (4) pairs of tension legs (8 total tendons) which will connect the WTG/WTG foundation to the gravity anchors. Each tendon will have a design strength of 2000 s. tons (breaking strength of 2500 s. tons). The detail design of tension legs is a proven art and will be provided by others. The load to which the tension legs will be deigned is, however, determined by this process. In a preferred embodiment, the total tension load (for all 8 tension legs) for the foundation at operating draft in calm water is—8060 s. tons. This means each leg will endure a calm water load of—1008 s. tons. The maximum tension leg load for a single tendon is estimated as 2016 s. tons and occurs when one pair of tendons (2) are lost (broken). The tension legs will be attached, with tag lines and buoys, to, the gravity anchors as the gravity anchors are made.

Installed Stability

There are several aspects of stability to be considered for this process. The “free floating” stability of the WTG/WTG foundation permits float-off from the construction barge and final installation of tension legs. The stability of the construction barge during construction, delivery and off-loading of the WTG/WTG foundation is a factor. The installed stability of the WTG/WTG foundation, complete with tension legs and gravity anchors, must be adequate for the maximum anticipated wind, wave and current loads. There are sophisticated computer programs which offer a probability of what these loads and reactions might be. However, in this preliminary exercise, an approximate manual method is used. The input data is intended to be conservative.

The maximum horizontal wind load at the hub is premised to be 184 s. tons (1643 kn). This comes from multiplying the 124 s. tons (1100 kn) used in the NREL Report, NREL/SR-50046282, for a 5 MG WTG by a ratio of the rotor disc area of the 6 MW WTG to that of the 5 MW WTG. The wave and current forces are, together, estimated at 453 s. tons (in trough of a 50 wave) and act horizontally through the foundation center of buoyancy. This comes from estimating the drag on the underwater part of the cylinder using a combined current and wave mass transfer velocity of 15.3 ft./sec. It is premised in all calculations that the wind, wave and current forces act in the same direction.

This input established the maximum moments about points ‘D’ (top of anchor) and ‘E’ (attachment of windward tension leg to foundation). See FIG. 8-9. In response to the moment about ‘D’, the foundation experiences a lateral displacement which, simultaneously, causes vertical displacement. This vertical displacement increases the foundation buoyancy and, thus, the tension in the tension legs. In the trough of the 50 ft. wave where buoyancy is lowest, this added tension is significant benefit. In response to the moment about ‘E’, the tension in the tension legs change to offset this moment. Thus, these loads establish the likely maximum and minimum forces in the tension legs and establish the basis for the design of the gravity anchors.

Requisite calculations are necessary to show the effect of these loads for the following cases:

Case #1—The foundation in the trough of a 50 ft. wave in 300 ft. water with maximum wind, wave and current loads with wind normal to a square tension leg pattern.
Case #2—The foundation in the trough of a 50 ft. wave in 300 ft. water with a maximum wind, wave and current loads with wind normal to a diamond tension leg pattern.

From the above calculations, the maximum and minimum tension leg loads are determined for each case. The minimum forces occur when the foundation is in the trough of the largest wave and the maximum forces occur when the foundation is in the crest of the largest wave. From this, the maximum external loads, with lateral and, thus, vertical displacement, do not slacken a tension leg. In the event of the failure of a pair of tendons, at the operating draft of 88 ft, the WTG/WTG foundation remains upright and stable and can withstand an up-setting moment of 42,243 ft-tons about the point ‘E’ before the top of the foundation starts to submerge and water plane starts to diminish.

Gravity Anchor

A single gravity anchor, to which the eight tension legs (4 pairs) from the WTG platform are attached, is used for this application. This gravity anchor is a cylindrical concrete container similar to the WTG platform. It will be constructed at the staging dock on the construction/deployment barge, previously described, using the efficient and economical ‘slip form’ method.

It will be deployed to the installation site on the construction/deployment barge and floated off in the same manner that the WTG platform is deployed. After the concrete container part of the gravity anchor is floated off of the deployment barge and positioned, it is sunk by adding sea water. Once on the sea floor, rock is added to achieve the required weight in water of—12,000 s. tons. The gravity anchor is depicted in FIGS. 12-14. In one preferred embodiment four gravity anchors for each WTG foundation or one for each tension leg. Thus, each gravity anchor will be designed to resist a 2908 s. ton load in water. The gravity anchor will be made of heavy re-enforced (with steel) concrete. Preliminarily, the weight of each gravity anchor that must resist a 2908 s. ton vertical load in water will weigh—4664 s. tons in air. If we premise a density of 170 lb/ft̂3, each anchor would have a volume of—54,871 ft̂3.

These gravity anchors will be made in the hopper of a split hull hydraulic dump scow. The hopper will, in fact, be the form. Based on the size of the scow hopper, the anchor will be—14 ft×22.25 ft×177 ft. Each anchor will also be transported to the installation site and deployed by the scow. FIGS. 10-11 and 15-16 depict a sea floor arrangement for the gravity anchors

Staging Dock

A staging dock in the vicinity of the wind farm is required. At this date, a specific dock has not been selected. The selected dock will have to meet the following requirements: 800 ft dock frontage with minimum 25 ft water depth. Lay down area of about 8 acres

Split Hull Hydraulic Dump Scow

The scow is unique and specifically designed to produce the concrete gravity anchors required for this application. Its hopper conforms to the dimensions required for the gravity anchor given in the previous section. First, the steel re-enforcement will be placed in the scow hopper. The heavy weight concrete will then be poured or pumped into the hopper. Shortly thereafter, the scow will be towed by tug(s) to the installation site. At the site the scow will be opened and the anchor deployed in a controlled manner. GPS will be used to appropriately position each anchor.

Split hull hydraulic dump scows have been used in the dredging industries for many years to transport dredging spoils to specified disposal sites. Dump scow technology has, thus far, not been applied to produce and/or deploy gravity anchors (or any other type of concrete items). Preliminary design of this scow has been completed to the extent that preliminary costing can be done and is shown in FIGS. 15, 11, and 12.

An added feature for the scow in this application is the use of multiple strand jacks to lower the anchor to the sea floor in a controlled manner. This application will use approximately twenty-four (24) 220 S. ton jacks, ten (12) spaced on each side of the hopper at the hopper coaming. The jacks can be synchronized to lower the anchor in a controlled manner.

The scow has preliminary principal dimensions as follows:

Length overall .240
Breadth        .46 ft
Depth @ side   25.5 ft.
Hopper volume  -55136 ftA3

The foregoing detailed description is given primarily for clearness of understanding and no unnecessary limitations are to be understood therefrom, for modification will become obvious to those skilled in the art upon reading this disclosure and may be made upon departing from the spirit of the invention and scope of the appended claims. Accordingly, this invention is not intended to be limited by the specific exemplifications presented herein above. Rather, what is intended to be covered is within the spirit and scope of the appended claims.

Claims

1. Method for installation of a wind turbine generator “WTG” on a tension leg platform/spar, comprising the steps of:

constructing a WTG foundation on a construction barge at a dock using a slip form method;

forming the gravity anchors in the split hull scow using a slip form method and deploying same to the installation site;

install the WTG foundation on the barge before it leaves the dock;

tow the construction barge to the installation site using tugs delivering WTG and WTG foundation to installation site as a complete unit;

sank the construction barge to a selected draft such that the WTG foundation with the WTG thereon floats off of the barge (dry dock mode), wherein the WTG foundation with the WTG thereon floats freely and is stable having a positive GM;

refloat the construction barge with its self-contained pumping system for return to dock;

ballasting the WTG foundation with sea water until it reaches its operating draft (approximately five feet of freeboard) maintaining stability throughout the process;

positioning the spar over the gravity anchors; attaching the tension legs leading from the gravity anchors to the spar; and;

and removing the WTG foundation and establishing tension in the tension legs.