WO2012175547A2

WO2012175547A2 - Support structure

Info

Publication number: WO2012175547A2
Application number: PCT/EP2012/061810
Authority: WO
Inventors: Sigurd Ramslie
Original assignee: Seatower As
Priority date: 2011-06-20
Filing date: 2012-06-20
Publication date: 2012-12-27
Also published as: NO332863B1; NO20110888A1; WO2012175547A3

Abstract

A support structure for installation on a seabed, comprising a foundation (2), and a column (1) secured to and extending up from the foundation and capable of supporting at least an equipment unit, the foundation (2') comprising a circumferential skirt (7) which extends downwards, thereby defining at least one compartment underneath the foundation (2). The skirt comprises a corrugated material, and is preferably constructed of corrugated steel plates.

Description

SUPPORT STRUCTURE

The invention relates to structures for the support of offshore wind turbines and similar equipment. More specifically, the invention relates to a support structure for use in offshore windmill parks, as disclosed in the preamble of independent claim 1.

The growing demand for the exploitation of renewable energy sources is increasing the demand for wind power generation offshore where the wind conditions are more favourable than onshore and the environmental consequences are smaller. There is a growing need for structures capable of supporting heavy wind turbines at a substantial height above the sea surface. The support structure consists of a shaft/tower fixed in the seabed either directly by means of a foundation, or in that the structure floats and is connected to the seabed by an anchor system. The invention relates to the first-mentioned type, that is to say, support structures which, when installed and in operation, are bottom- fixed.

The typical bottom- fixed support structures for wind turbines in practical use, planned for use and described in publicly available sources have in general the following characteristics:

1. Demanding installation procedure where the tower is mounted on site on pre- installed foundation;

2. The foundation is secured to the seabed by drilled or driven piles.

WO 2009/154472 A2 describes a support structure for use in the offshore windmill sector, comprising a foundation for installation on a bottom below a body of water and a tower connected to and extending up from the foundation and which is capable of supporting at least an equipment unit. The foundation comprises a bottom plate element and a wall which extends up from the bottom plate element, thereby defining a first cavity capable of holding ballast and providing buoyancy during tow-out and installation. The foundation has a circumferential skirt extending down from the bottom plate element, which thus defines at least one compartment underneath the foundation. The compartment may be divided into further compartments by means of skirts which extend down from the bottom plate element and preferably extend radially from a central portion of the bottom plate element to respective areas of the circumferential skirt.

WO 2010/143966 A2 describes a foundation base having a circular plate which has a circumferential skirt extending down from the plate 5 in such a way as to form a main compartment defined by the plate and the skirt. Arranged at regular intervals around the plate is a plurality of outer compartments with separate skirts, which are disposed around the plate at angular spacing of 120° with respect to one another. The main compartment and the outer compartments are in effect "inverted cups", with skirts capable of penetrating the surface during the installation of the foundation base.

Both during installation of the foundation and when the plant is in operation, the skirts will be subjected to substantial loads that call for large material thickness or a substantial number of stiffeners. Large material thickness and/or a large number of stiffeners give reduced penetration ability and high production costs.

A support structure has therefore been produced for installation on a seabed, comprising a foundation and a column secured to and extending up from the foundation and capable of supporting at least one equipment unit, wherein the foundation comprises a circumferential skirt extending downwards, thereby defining at least one compartment underneath the foundation, characterised in that the skirt comprises a corrugated material.

In an embodiment, the support structure comprises a plurality of outer sub- foundations attached to the foundation, and having downward skirts, the skirts comprising a corrugated material.

The skirts are preferably constructed of corrugated steel plates.

The corrugated skirts according to the invention are better stiffened and therefore less prone to buckle or break during seabed penetration than conventional skirts. It is therefore possible to have thinner plate thickness with corrugated skirts and still ensure that the skirt has the necessary strength. The production of the skirts is also simpler (and thus cheaper) when corrugated plates are used. There is no need for ring stiffeners or the like, which are necessary stiffening components in the production of conventional skirts.

These and other characteristic features of the invention will be set forth in the following description of a preferred embodiment, given as a non-limiting example, with reference to the following figures, wherein:

Figure 1 is a side view of an embodiment of the foundation according to the invention; and

Figure 2 is a top view of the same embodiment as that shown in Figure 1.

The support structure comprises a column 1 , a foundation 2, an intermediate conical structure 3, and in the figures it is shown located in a body of water W and resting on a seabed B via the foundation 2. The column is adapted to support a tower and a wind turbine, or the like (not shown), mounted on top of the tower. The column further comprises a work platform 4, a boat mooring system and a ladder 5 which runs from the mooring system up to the work platform.

The conical structure 3 preferably comprises a lower part 3a of concrete and an upper part 3b of steel. The foundation 2 comprises a downward skirt 7 and a plurality of outer sub- foundations 6a-c which also have downward skirts 8a-c. In the illustrated embodiment, the sub-foundations 6a-c are disposed around the foundation at an angular spacing of 120° with respect to one another. The skirts 7, 8a-c form respective compartments (not shown), and the skirts are thus able to penetrate down into the seabed B during the installation of the support structure.

The skirts, which preferably are made of steel, are corrugated. This gives increased stiffness and better penetration ability, and hence a more stable installation on the seabed.

Although the invention is described and illustrated here as a structure having a circular cross-section in the horizontal plane, the invention will not will limited to such cross-sections, but will also comprise, for example, rectangular or octagonal cross-sections.

Claims

1. A support structure for installation on a seabed, comprising a foundation (2), and a column (1) secured to and extending up from the foundation and capable of supporting at least an equipment unit, the foundation (2) comprising a

circumferential skirt (7) which extends downwards, thereby defining least one compartment underneath the foundation (2), characterised in comprising a plurality of outer sub- foundations (6a-c) having downward skirts (8a-c) attached to the foundation, the skirts (8a-c) comprising a corrugated material.

2. A support structure according to claim 1 , the skirt (7) comprising a corrugated material.

3. A support structure according to claim 1 or claim 2, wherein the skirts are constructed of corrugated steel plates.