Truss cable semi-submersible floater for offshore wind turbines and construction methods   

Abstract: Truss cable semi-submersible floater for offshore wind turbines and construction methods are provided. A floating system includes a hull, a tensioned cable system, and a tower. The hull includes vertical buoyant columns with one column at the center of the pattern, larger size column base tanks, and a truss system, all of which are coupled to each other for supporting the tower and wind turbines. The column can be made of hybrid materials, including steel and composite-concrete. The steel section and the composite-concrete section of the column can be connected by grouting. The tensioned cable system including upper, lower, and diagonal tensioned cables to connect the column, the column base, and the tower to reduce the bending moments and improve stability, strength and dynamic performance of the hull structure.

CROSS-REFERENCE TO RELATED APPLICATIONS

This present application claims the benefits of priority from the United States of America provisional application No. 61/407,730, entitled “TRUSS CABLE SEMI-SUBMERSIBLE FLOATER FOR OFFSHORE WIND TURBINES AND CONSTRUCTION METHODS”, filed on Oct. 28, 2010.

Not applicable.

(1) U.S. Pat. No. : 4,702,321, Filing date: Sep. 20, 1985, Issue date: Oct. 27, 1987 (2) U.S. Pat. No. : 6,263,824, Filing date: Dec. 23, 1997, Issue date: Jul. 24, 2001 (3) U.S. Pat. No. : 7,819,073, Filing date: Jun. 2, 2006, Issue date: Oct. 26, 2010 (4) U.S. Pat. No. : 7,612,462, Filing date: Apr. 24, 2008, Issue date: Nov. 3, 2009

Embodiments of present invention relate generally to the field of floating offshore wind turbines for offshore wind power generation. More particularly, embodiments of present invention relate to the field of a semi-submersible floater with a truss system for connecting the columns and a tensioned cable system for connecting the main structural components to improve structural strength and integrity, and associated methods for construction and installation. Furthermore, the invention also relates to the use of composite materials for the whole or part of the semi-submersible wind turbine floater construction.

Conventionally, semi-submersible floaters used in deepwater offshore oil and gas exploration and production are built with columns and pontoons which are enclosed buoyant structures using steel material as shown in FIG. 1. This kind of oil and gas steel structure and hull form are large and costly. The present invention aims to provide an innovative semi-submersible floater with unique configuration connected by truss and cables which enables a floating wind turbine to be constructed, towed vertically and installed offshore at significantly lower cost than a conventional semi-submersible floater.

SUMMARY

Truss cable semi-submersible floater for offshore wind turbines and construction methods are provided to provide more cost and weight efficient floater with better stability and structural strength and dynamic performance for offshore wind turbines. Parts of the structure can be made of composite materials.

FIG. 1 illustrates a prior art of a semi-submersible floater used in oil and gas production according to some embodiments of the present invention.

FIG. 2 illustrates a front view of a truss cable semi-submersible floater for a wind turbine according to some embodiments of the present invention.

FIG. 3 illustrates a front view of a tower sleeve with special contact pads according to some embodiments of the present invention.

FIG. 4 illustrates a front view of a tensioned cable system for a semi-submersible floater for a wind turbine according to some embodiments of the present invention.

FIG. 5 illustrates a perspective view of construction of a column with composite donut ring according to some embodiments of the present invention.

FIG. 6 illustrates a perspective view of a typical column and base steel and composite-concrete system according to some embodiments of the present invention.

DETAILED DESCRIPTION

With reference to FIG. 2, a truss cable semi-submersible floater (hereinafter referred as “floater”) includes a hull, a tower, and a tensioned cable system. The hull mainly includes 3 components: columns, including a center column 1a and outer columns 1b, trusses coupled to the columns, including an upper truss 2a and a lower truss 2b, and column bases coupled to the columns and the trusses, including a center base 3a and outer bases 3b. The hull can have multiple outer columns for stability, typically 3 columns (as shown in FIG. 2), but also can have 4 columns or more. The hull has an in-service draft in the order of 60 ft to 80 ft depending on metocean conditions of the deployed area. The columns are most buoyant to provide the buoyancy for the wind turbine and rotor blades, which can be coupled with the floater and located above the water surface. The column bases, which can be tanks, provide stability for wet tow and hold ballast (sold or water ballast) for inplace conditions. The upper and lower trusses can be welded to the columns.

The tower 6 extends from the top of the center column 1a to the rotor for supporting the turbine and rotor blades. The tower 6 can be formed as a column structure. In some embodiment, as shown in FIG. 3, a tower sleeve 4 can be used with the tower 6. The tower sleeve 4 is a specially designed structure to allow the tower 6 to penetrate it without rigid connection. In some embodiment, the tower sleeve 4 is designed to contact the base of the tower 6 at certain points through specially designed contact pads to merely transmit forces without transmitting moments. This design feature will reduce the load into the upper truss 2a to give more efficient structural design.

With reference to FIG. 4, the tensioned cable system can have multiple tensioned cables to connect the tower and the hull together to improve the dynamic performance of the floater structure. In some embodiments, the tensioned cable system includes lower tensioned cables 7a for connecting outer bases 3b at the bottom of the columns. In some embodiments, the tensioned cable system includes upper tensioned cables 7b for connecting the topside of the outer columns 1b. In some embodiments, the tensioned cable system includes diagonal tensioned cables 7c for diagonally connecting the mid lower tower 6 to the end of the upper truss 2a, which is at the top of the outer column 1b, to reduce the bending moment at the bottom of the tower 6. The tensioned cables are preferably made of steel wire or similar materials.

In some embodiment, the floater can include a mooring line 5. The hull with three outer columns 1b can have 3 mooring lines 5, which can be pre-installed with drag anchor, suction anchor, or pile anchor for stabilizing the floater.

With reference to FIG. 5, the columns can be made of hybrid materials, including steel and composite materials, for reducing cost and weight. The upper and lower columns 8b are preferably made of steel, and the middle column 8a is made of a series of composite donut rings, which are made of composite tubes filled with concrete inside. The upper and lower columns 8b can be connected to the middle column 8a by grouting. In some embodiments, a watertight composite membrane 8c can be glued to the inside of the composite donut ring or the outside of the composite donut ring, even throughout the entire column to ensure that the column is watertight.

With reference to FIG. 6, a column includes a deck, a girder, and composite donut rings. The composite donut rings are placed on each other vertically to form a composite column section. The girder is substantially placed at 90 degrees inside the column. The deck is to be used to divide the column into two watertight compartments. Both the deck and the girder are preferably made of steel. A column base, as a column, also includes a deck, a girder and composite donut rings.

In some embodiments, a method of constructing a column with composite materials includes providing composite donut-shaped rings, placing multiple composite donut rings on each other vertically to form a composite section of a column, providing a steel section of the column and connecting it to the composite section of the column by grouting, attaching a watertight composite membrane to the inside or outside of the composite donut rings for connecting the composite donut rings and ensuring water tightness, placing a substantially vertical girder into the column, placing a deck into the column to divide the column into two watertight compartments. All or parts of the methods described above can be done on the land. Besides, a method of constructing a floater can further include installing a column base, a tensioned cable system, a tower, and a tower sleeve to the column, and coupling upper and lower trusses to the upper and lower ends of the columns. Then, the assembly of the columns can be loaded into water. The installation of turbine tower and assembly can be done in sequence in the water at quayside. Finally, the entire assembly of the floating system can be towed to the sea preferably at a draft within the depth of the column base, towered to in-service draft and fixed at the seabed with pre-set mooring lines.