U.S. patent application number 13/998626 was filed with the patent office on 2014-09-04 for construction and installation process to deploy a wind turbine "wtg" on a tension leg platform/spar in medium to deep water.
The applicant listed for this patent is Andrew M. Filak, Fontain M. Johnson, JR.. Invention is credited to Andrew M. Filak, Fontain M. Johnson, JR..
Application Number | 20140248091 13/998626 |
Document ID | / |
Family ID | 51421009 |
Filed Date | 2014-09-04 |
United States Patent
Application |
20140248091 |
Kind Code |
A1 |
Johnson, JR.; Fontain M. ;
et al. |
September 4, 2014 |
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.
Inventors: |
Johnson, JR.; Fontain M.;
(Santa Claus, IN) ; Filak; Andrew M.; (Redondo
Beach, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Johnson, JR.; Fontain M.
Filak; Andrew M. |
Santa Claus
Redondo Beach |
IN
CA |
US
US |
|
|
Family ID: |
51421009 |
Appl. No.: |
13/998626 |
Filed: |
November 18, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61796656 |
Nov 16, 2012 |
|
|
|
61797360 |
Dec 6, 2012 |
|
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Current U.S.
Class: |
405/205 |
Current CPC
Class: |
B63B 2021/505 20130101;
B63B 2035/446 20130101; B63B 21/502 20130101; B63B 21/26 20130101;
E02B 2017/0078 20130101 |
Class at
Publication: |
405/205 |
International
Class: |
E02B 17/02 20060101
E02B017/02; E02B 17/00 20060101 E02B017/00 |
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.
Description
RELATED APPLICATIONS
[0001] 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
[0002] 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
[0003] 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.
[0004] 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.
[0005] 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
[0006] 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.
[0007] 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.
[0008] 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.
[0009] 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.
[0010] 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.
[0011] 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.
[0012] 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.
[0013] 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.
[0014] 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.
[0015] 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.
[0016] 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.
[0017] 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.
[0018] 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.
[0019] 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
[0020] 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:
[0021] FIG. 1 shows the installed WTG foundation with the WTG,
tension legs and gravity anchors;
[0022] FIG. 2 is a top view showing the concrete cylindrical spar
buoy WTG foundation with transition stem;
[0023] FIG. 3 is a side view showing the concrete cylindrical spar
buoy WTG foundation with transition stem;
[0024] FIG. 4 shows the construction barge supporting the wind
turbine WTG, and WTG foundation disposed between wing walls;
[0025] 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;
[0026] FIG. 6 is an elevational view showing the construction barge
supporting the wing walls, WTG, positioned upon the barge for
transport and deployment;
[0027] FIG. 7 is an plan view showing the construction barge
supporting the wing walls and spar in dry dock;
[0028] 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);
[0029] 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;
[0030] 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;
[0031] FIG. 11 is a elevational view of the gravity anchor is
depicted in FIG. 10;
[0032] FIG. 12 shows a clevis attached to the anchor block;
[0033] FIG. 13 shows a clevis attached to the anchor block;
[0034] FIG. 14 shows an enlargement of the anchor block of FIG.
12;
[0035] 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;
[0036] 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;
[0037] FIG. 17 shows a split hull scow with closed section;
[0038] FIG. 18 shows a split hull scow section when open;
[0039] FIG. 19 shows a split hull hydraulic dump scow; and
[0040] FIG. 20 shows the deck plane and hopper of a split hull
hydraulic scow.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0041] 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.
[0042] 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.
[0043] 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.
[0044] 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: [0045] Guidelines for Design
of Wind Turbines, Det Norske Veritas, Copenhagen and Riso National
Laboratory, Denmark, 2002. [0046] Hau, E.,
Windturbines--Fundamentals, Technologies, Application, and
Economics, Springer Verlag, Berlin Heidelberg, 2000. [0047]
Eggleston, D., Stoddard, F., Wind Turbine Engineering Design, Van
Nostrand Reinhold, N.Y., 1987. [0048] Burton, T., Sharpe, D.,
Jenkins, N., Bossanyi, E., Wind Energy Handbook, John Wiley &
Sons, West Sussex England, 2001. [0049] Gasch, R., Twele, J., Wind
Power Plants--Fundamentals, Design, Construction, and Operation,
Solarpraxis AG, Germany, 2002. [0050] Freris, L., Wind Energy
Conversion Systems, Prentice Hall International Ltd., London,
1990.
[0051] 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.times.W.times.H) 15100.times.6500.times.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.times.W) 75000.times.5000 mm Hub--approx. 104.7 s. tons,
(W.times.H) 7900.times.5500 mm It is premised that the hub height
is--295 feet and the blades about--43 feet above still water
level.
WTG Foundation
[0052] The WTG foundation is a vertical concrete cylinder designed
uniquely with geometry and weight distribution to:
Support the 6 MW WTG;
[0053] 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
[0054] 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.
[0055] 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.
[0056] 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.
[0057] 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
[0058] 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:
TABLE-US-00001 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
[0059] 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.
[0060] 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.
[0061] 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
[0062] 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
[0063] 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.
[0064] 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.
[0065] 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.
[0066] 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.
[0067] 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
[0068] 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.
[0069] 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/ft 3, each anchor would have a
volume of--54,871 ft 3.
[0070] 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.times.22.25 ft.times.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
[0071] 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
[0072] 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.
[0073] 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.
[0074] 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.
[0075] The scow has preliminary principal dimensions as
follows:
TABLE-US-00002 Length overall .240 Breadth .46 ft Depth @ side 25.5
ft. Hopper volume -55136 ftA3
[0076] 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.
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