NL2036515B1

NL2036515B1 - Method and system for forming a section for a floating body for an offshore floating foundation

Info

Publication number: NL2036515B1
Application number: NL2036515A
Authority: NL
Inventors: Antoin Marie Kurstjens Michel
Original assignee: Sif Holding N V
Priority date: 2023-12-13
Filing date: 2023-12-13
Publication date: 2025-06-20
Also published as: TW202523971A; WO2025127929A1

Abstract

Method and system for forming a section for a ﬂoating body for an offshore ﬂoating foundation Abstract Method for forming a section for a ﬂoating body for an offshore ﬂoating foundation, comprising providing a metal sheet having a sheet length direction and a sheet Width direction, and bending said sheet, such that the sheet is curved in the sheet length direction, forming a concave side. Furthermore a stiffener is formed, having a stiffener length direction, wherein the stiffener is curved in said stiffener length direction, forming a convex side. Said curved stiffener is placed With the convex side against the concave side of the sheet and is pushed against the concave side of the sheet, such that a curvature of the concave side of the sheet matches a curvature of the convex side of the stiffener at least at the position Where the stiffener is placed. Then the stiffener is welded against the sheet.

Description

P135668NL00

Title: Method and system for forming a section for a floating body for an offshore floating foundation

The invention relates to a method for forming a section for a floating body for an offshore floating foundation. The invention further relates to a system for forming a section for a floating body for an offshore floating foundation.

Offshore constructions, such as offshore wind turbines are traditionally formed by driving a foundation pile into the water bedding of a body of water, such that an upper end of the foundation pile extends above the water level of the body of water. Then a further construction is mounted onto the foundation pile, such as for example a wind turbine, having a tower which can for example be bolted to and/or slid over the upper end of the foundation pile. In some constructions such further construction can also be supported by multiple foundation piles, such as for example a drilling platform.

With an increasing demand for off shore constructions, especially wind farms, and for larger wind turbines, such offshore constructions are to be provided in increasingly deeper bodies of water, which is becoming a problem for example for strength of the foundation piles, handling thereof and use of materials.

In order to overcome at least some of these problems it has been proposed to use floating foundations for offshore constructions. These comprise one or more, for example three floating bodies, connected to each other, wherein for example a wind turbine generator is mounted on top of one of the floating bodies or on elements connecting said bodies. In these known off shore floating foundations the floating bodies are made traditionally of relatively thick steel forming a tubular wall and closed ends, which wall may be reinforced by cross beams, trusses or the like, welded and/or bolted to the walls or end plates. The floating bodies may be filled with for example air and/or ballast fluid, or for example with foam. These floating bodies are elaborate to maintain, are relatively heavy and require relatively much material for providing the desired strength to withstand for example waves and wind. Moreover these known floating bodies are difficult and costly to manufacture.

It is an aim of the present disclosure to provide for an alternative method for forming sections for a floating body for an offshore floating foundation. It is an aim of the present disclosure to provide for a method for forming sections for a floating body for an offshore floating foundation which is easy to perform and/or with high accuracy. An aim of the present disclosure is to provide a method which can be automated to a high degree.

An aim of the present disclosure is to provide a method with which sections for floating bodies for offshore foundations can be manufactured which can easily be assembled for forming a floating body. An aim of the present disclosure is to provide for a system for forming sections for a floating body for an offshore floating foundation. An aim of the present disclosure is to provide a section for a floating body for an offshore foundation.

At least one of these and other aims are achieved at least in part by a method, system and/or section according to the disclosure, at least as defined in the claims.

In an aspect of the disclosure a method for forming a section for a floating body for an offshore floating foundation, comprising the following steps, which may be performed in the given order or in a different order. A metal sheet is provided having a sheet length direction and a sheet width direction, which sheet is bent, such that the sheet is curved in the sheet length direction, forming a concave side. Furthermore a stiffener is formed, having a stiffener length direction, wherein the stiffener is curved in said stiffener length direction, forming a convex side. Said curved stiffener is placed with the convex side against the concave side of the sheet, which stiffener is pushed against the concave side of the sheet, such that a curvature of the concave side of the sheet matches a curvature of the convex side of the stiffener at least at the position where the stiffener is placed. The stiffener is welded against the sheet.

By pushing the stiffener against the curved sheet, the curvature of the sheet will be aligned with the curvature of the stiffener, such that the stiffener and sheet will be properly in contact with each other for welding.

Preferably at least longitudinal side edges of the convex side of the stiffener will be in brought in full contact with the sheet, such that the longitudinal edges can be line welded along the full length in an easy and proper manner.

In advantageous embodiments the stiffener is placed against the sheet having the stiffener length direction parallel to the sheet length direction. Thus radial and axial strength of the section and thus of a floating body formed therewith can be increased.

Preferably in a method or section according to the disclosure a series of stiffeners is welded with their convex sides to the concave side of the sheet, in side by side relations.

In an aspect of the disclosure the sheet is positioned on a support, prior to welding the at least one stiffener to the sheet.

The support can be such that it provides a rigid surface having a shape defining a desired outer surface of the curved sheet after welding the stiffeners to the sheet. Alternatively the support can provide for a flexible support surface or for supporting the sheet in a series of separate positions, allowing the sheet to be pushed into a desired shape by pushing the stiffeners against the concave surface of the sheet.

In embodiments the support defines a concave real or imaginary surface, having a concave curvature desired for the sheet after welding said stiffeners to said sheet. The concave surface preferably faces upward while supporting the sheet. This allows welding “under the hand” in which gravity aids the welding process, as is known in the art.

In an aspect of the disclosure the sheet is pushed against the support by pushing against a concave side of at least one said stiffener, at least during part of the welding.

In an aspect of the disclosure the stiffener is pushed against the sheet by applying a pushing force at at least two spaced apart locations, preferably at least three spaced apart locations, which pushing forces are preferably exerted in radial direction relative to the concave side of the sheet and the stiffener.

In an aspect of the disclosure in embodiments the stiffener is pushed against the sheet, at least during part of the welding, by applying at least a first pushing force in at least a radial direction at a position between a central part of the stiffener and a first longitudinal end of the stiffener, and at least a second pushing force in at least a radial direction at a position between said central part and a second opposite longitudinal end of the stiffener.

By pushing the stiffener in at least a radial direction at at least two positions spaced apart from a central part of the stiffener, it can be assured that the stiffener is pushed properly against the sheet, forcing the sheet into the desired shape, at least during welding. A central part of the stiffener should be understood as a part of the stiffener central between opposite longitudinal ends of the stiffener, wherein part should be understood as meaning at least a section of the stiffener having a very short length in the direction between the longitudinal ends, such as for example but not limited to up to 5%, such as for example up to 3%, for example up to 1% of the longitudinal length of the stiffener, measured along the concave surface of the stiffener between said longitudinal ends. In advantageous embodiments the position of the first pushing force applied to the stiffener and the position of the second pushing force applied to the stiffener are spaced apart over a distance measured along said concave surface, which distance preferably is between one-fourth and nine-tenth of the longitudinal length of the stiffener, for example between one-fourth and three-fourth of the longitudinal length. By properly placing the pushing forces and especially the radial directions of the pushing forces on the curved stiffener it is even better assured that the stiffener and sheet are forced into the same 5 curvature and this can be properly welded in an easy manner.

In advantageous embodiments the stiffener is tack welded to the sheet while the stiffener is pushed against the sheet, such that the sheet with the stiffener can be moved relative to the pushing device while maintaining the specific position of the stiffener relative to the sheet. After tack welding then the stiffener is line welded to the sheet along at least one and preferably two opposite longitudinal edges of the stiffener.

In further elaboration in a method if the disclosure a series of sheets can be provided with a series of stiffeners as discussed, wherein each sheet of the series of sheets is welded to at least one further sheet along a side parallel to the length direction and to at least one further sheet along an edge parallel to the width direction, such that a tubular body is formed, preferably such that the tubular body will have said stiffeners at an inside of said tubular body. Preferably also longitudinal ends of stiffeners of adjacent sheets will be coupled to each other, especially by welding.

With a method according to the disclosure a tubular body can be formed, using relatively thin sheets, stiffened by stiffeners at least in a radial direction. By closing off opposite ends of the tubular body the body can be used as a floating body, having its longitudinal axis extending upward, especially vertically, and which is relatively light weight in view of its volume, and which is especially suitable as a floating support or foundation for an off shore construction, and which is especially sufficiently resistant against deformation by for example wind and waves exerting forces on an outer surface of the body in a radial direction.

In embodiments of a method of the disclosure the sheet is placed on a support after said bending, wherein the support supports the sheet at least in three spaced apart locations or over its convex surface, wherein at least one longitudinal end, seen in the length direction of the sheet, is placed against at least one stop element of the support, and/or at least one side edge, seen in the width direction of the sheet, is placed against at least one stop element of the support, for positioning of the sheet in and/or on said support.

By using stop elements for positioning the sheet on the support, it can easily be ensured that the sheet is positioned properly and that therefore the stiffeners can easily be placed in the proper position relative to the sheet.

In an aspect of the disclosure a system is disclosed for forming a section for a floating body for an offshore floating foundation. The system comprises a sheet supply for supplying curved metal sheets, said sheets having a convex side and an opposite concave side. The system furthermore comprises a stiffener supply for supplying curved stiffeners. Moreover the system comprises at least a first gantry. In a system of the disclosure at least one support is provided for supporting a sheet supplied from the sheet supply, the support supporting the sheet during use at a convex side thereof.

Furthermore a lifting and positioning system is provided for lifting and positioning at least one stiffener, supplied from the stiffener supply, onto the concave side of a sheet supported on the support, the stiffener being positioned with a convex side on the concave side of the sheet on the support. According to the disclosure the first gantry comprises at least one first arm for pushing the convex side of the stiffener against the concave side of the sheet.

By pushing the convex side of the stiffener against the concave side of the sheet, the sheet is pushed into a desired curvature, conform the curvature of the convex side of the stiffener, such that the stiffener can be welded to the sheet properly. This means that for example deviations in the curvature of the sheet, for example due to manufacturing tolerances,

temperature influences, relaxation or the like can be pushed out of the sheet prior to and/or during welding, such as tack welding or line welding. Thus with a system according to the disclosure in an easy way sections can be formed having a proper curvature for forming a tubular body for an offshore floating foundation.

In an advantageous further elaboration in a system according to the disclosure the first gantry comprises at least two first arms for pushing the convex side of the concave side of the sheet. In further advantageous embodiments the two first arms have pushing directions extending in a radial direction of the convex side of the stiffener, preferably in mutually diverging directions.

By providing pushing forces in radial directions it is even better ensured that the stiffener pushes the sheet into the desired shape.

Pushing a sheet in a desired curvature should be understood as at least meaning holding a sheet in a desired shape or deforming part of the sheet in order to bring the sheet into the desired shape, such that it can be held in such position during at least initial welding of the stiffener to the sheet.

In embodiments the arm is or the at least two arms are articulated arms, comprising or connected to at least one driving device for pushing a pushing end of the or each arm against the stiffener.

The first gantry preferably comprises at least one welding tool for welding, preferably at least tack welding, the stiffener to the sheet.

In advantageous embodiments a system of the disclosure comprises atleast a second gantry, comprising at least a welding tool for welding at least one edge portion of the stiffener to the sheet, preferably for line welding.

In advantageous embodiments of a system of the disclosure the at least one support has a concave supporting surface defining a desired shape of the sheet when it is pushed against said supporting surface. In such embodiments the supporting surface preferably is curved, concave facing upward, such that during use a convex side of the sheet is supported on the supporting surface, the or each stiffener being positioned on the concave side of the sheet, such that the or each stiffener can be welded to the sheet from above, commonly referred to as welding under the hand.

In advantageous embodiments the or each support 1s provided with end stops for engaging edge portions of a sheet, defining a desired position of the sheet relative to the support. Such end stops can for example be provided for engaging longitudinal edge portion at one end of the sheet or at opposite ends, and/or end stops for engaging side edge portions of the sheet at one longitudinal side of the side or both opposite sides of the sheet.

The stiffener supply in advantageous embodiments comprises a stiffener support rack, with a first positioning element, and at least one stiffener being provided in said support rack having a second positioning element, cooperating with the first positioning element, for defining a desired position of the stiffener relative to the support rack. This provides for an easy manner of ensuring a right position of the stiffener, in the stiffener supply and also after transferring the stiffener to a sheet.

The disclosure further relates to a section for a body of a floating offshore foundation element, comprising at least a sheet of metal, curved in one first direction, providing an inner concave surface and an outer convex surface, wherein on the inner concave surface a series of stiffeners has been welded, the stiffeners being curved in said first direction, such that a convex side of the stiffeners abuts the concave surface of the sheet. The stiffeners are spaced apart and extend parallel to each other, wherein the sheet and the stiffeners are of substantially the same length in said first direction.

In advantageous embodiments the at least one stiffener is positioned on the sheet such that at a first longitudinal side of the section, seen in said first direction, a first end of said stiffener extends beyond an adjacent first longitudinal edge of the sheet, whereas at an opposite second longitudinal side of the section, seen in said first direction, a second end of said stiffener ends short of an adjacent second longitudinal edge of the sheet. Thus when coupling sections at longitudinal edges for forming a ring, first ends of stiffeners of a first section will extend over an second edge portion of an adjacent second section, such that it can be coupled to said second section, for example by welding first ends of the stiffeners of the first section to second ends of the stiffeners of the second section and/or to the sheet thereof and/or vice versa.

The section preferably encloses an angle of between 60 and 180 degrees in said first direction and/or forms a section of a circle, such that as series of such sections can be coupled to each other at opposite ends in said first direction for forming a ring.

The invention will be further elucidated on the basis of exemplary embodiments which are represented in the drawings. The exemplary embodiments are given by way of non-limitative illustration of the invention. In the drawings shows schematically:

Fig. 1 in top view a system for forming sections for bodies of floating foundations for offshore constructions;

Fig. 2 in isometric view part of a system according to fig. 1;

Fig. 3 in top view the part of the system as shown in fig. 2;

Fig. 4 in front view a gantry, especially a first gantry for use in a system according to the disclosure;

Fig. 4A in front view a gantry as shown fig. 4, during pushing;

Fig. 5 in front view a gantry, especially a second gantry for use in a system according to the disclosure;

Fig. 6 in isometric view two supports, in side by side relation, each with a section supported thereon;

Fig. 7 in front view a gantry, as for example shown in fig. 3, with different sizes and differently curved sections;

Fig. 8 an overview of some of many possible angles enclosed by a section cq sheet and/or stiffener;

Fig. 9 side by side in isometric view a support with a section comprising a sheet and stiffeners, and a rack supporting stiffeners to be used for forming a section;

Fig. 9A a stiffener, seen from a longitudinal end, welded to a sheet;

Fig. 10 in isometric view, partly broken away, a tubular body for forming a floating body of a floating offshore foundation.

In this description embodiments of the invention will be described with reference to the drawings by way of example only. These embodiments should by no means be understood as limiting the scope of the disclosure. At least all combinations of aspects, elements and features of the embodiments shown and discussed are also considered to have been disclosed herein. In this description the same or similar elements and features will be referred to by the same or similar reference signs. The drawings are not to scale, and can show exaggerations in order to more clearly show features of the claimed invention.

In this description expressions of orientation such as top, bottom, vertical etcetera are used for convenience only and refer to the orientation of the foundation pile as seen in the accompanying drawings, especially fig. 1 and 2, the pile being placed vertically in the ground, off shore or on shore.

In this description wording like substantially and generally should be understood as meaning that relatively small deviations from the feature or value they refer to are also considered to be covered, for example deviations of 20% or less, such as 15% or less or 10% or less.

In this description embodiments of a system will be described for forming a section for a floating body for an offshore floating foundation.

Such system according to the disclosure comprises a sheet supply for supplying curved metal sheets, said sheets having a convex side and an opposite concave side. The sheets can for example be rolled into a shape of a cylinder section, being curved in a first direction and linear in a second direction. Alternatively the sheet can be shaped as part of a truncated conical shape or a different curved shape. A sheet should be understood as at least a sheet of metal having a length, a width and a thickness, wherein the thickness is significantly smaller than the thickness. A sheet can for example have, but is not limited to a length of several meters, a width of one or more meters and a thickness between a few millimeters and several centimeters. A sheet for use in a system or method of the disclosure, for forming a section according to the disclosure is preferably made of metal, especially steel or aluminum. A sheet can be a single piece or can be assembled from different pieces.

A system of the disclosure further comprises a stiffener supply for supplying curved stiffeners. Curved stiffeners should be understood as at least meaning profiles curved in a longitudinal direction, which when welded to a sheet will increase resistance against bending of the sheet, or a section formed with said sheet and stiffeners, at least in said longitudinal direction. A stiffener can be formed as an integral profile, for example extruded of metal, especially but not limited to steel, preferably the same material as is used for the sheet or at least a material weldable to the sheet.

A system according to the disclosure further comprises at least a first gantry. A gantry should be understood as at least meaning an overhead bridge like structure, supporting equipment such as but not limited to a crane, pusher equipment as will be described, welding equipment and the like, wherein a gantry preferably is movable relative to sheets and/or stiffeners used in the system, for example guided by rails.

A system according to the disclosure further comprises at least one support for supporting a sheet supplied from the sheet supply, at a convex side thereof. The at least one support can for example have a substantially rigid support structure, especially support surface, or can have a partly or entirely flexible, deformable support structure. Preferably the or each support is movable relative to at least the first gantry.

A system according to the disclosure further comprises a lifting and positioning system for lifting and positioning at least one stiffener onto the concave side of a sheet supported on the support. The lifting and positioning system can be provided by, for example supported from the first gantry or another gantry, or can for example be a system at least partly separate from the gantry, such as for example but not limited to a separate crane, pallet truck, transfer track system or the like. With at least the lifting and positioning system a stiffener or a series of stiffeners can be positioned with a convex side on the concave side of the sheet on the support, wherein the first gantry comprises at least one first arm for pushing the convex side of the stiffener against the concave side of the sheet.

In the embodiments shown in the drawings the sheet supply, stiffener supply, at least one support, first gantry and lifting and positioning system are provided in close proximity of each other, for example in a single plant. However it will be appreciated that at least some of these elements and systems, such as a sheet supply and/or a stiffener supply can be provided spaced apart further, for example at a different location. Sheets and/or stiffeners can be provided in curved configuration to the sheet supply or stiffener supply, prepared at one or more different locations, or can be manufactured at the sheet supply or stiffener supply.

Fig. 1 shows schematically in top view a plant 1 for forming sections 2 for forming a floating body 3, as for example schematically shown in fig. 10, for an offshore floating foundation. At the plant 1 comprises a sheet supply 4, schematically indicated in striped lines by rectangle 4, for supplying curved metal sheets 5. The sheets 5 have a convex side 6 and an opposite concave side 7 and have been rolled into the curved shape. In the embodiments shown the sheets have a longitudinal direction or length L, and a width direction or width W, perpendicular to the length L, and a thickness direction or thickness T, perpendicular to the length L and width

W. By way of example, a sheet can have a length L of between 10 to 20 meter, a width between 2 and 5 meter and a thickness of between 10 and 100 millimeter. As is schematically shown in fig. 7 and 8, the sheet 5 is curved in the longitudinal direction L and can have a desired radius R of curvature of for example between one (1) and fifteen (15) meters, such as for example between five (5) and ten (10) meters, and preferably is constant for the curvature between longitudinal first end 8 and opposite longitudinal second end 9. The radius R is preferably the same as a radius of the body 3.

An enclosed angle a between opposite first and second ends 8, 9 is preferably 360/k degrees, wherein k is an integer, preferably between 2 and 6. The angle a can for example be between 60 and 180 degrees, such as for example between 90 and 120 degrees. With an angle of 90 degrees, four such sections 2 will form a circle, whereas with an angel of 120 degrees only three such sections will form a full circle, when connected by longitudinal ends 8, 9.

The sheets 5 in the embodiment are curved in the longitudinal direction L only.

The plant 1 further comprises a stiffener supply 10, schematically indicated in striped lines by rectangle 10, for supplying curved stiffeners 11.

The stiffeners 11 also have a convex side 12 and a concave side 13 and have a bending radius Rs measured at the convex side 12, similar to or identical to the bending radius R of the sheet 5, measured at the concave side 7 thereof. In the embodiments shown the stiffeners 11 are formed of sheet or plate material, and have a longitudinal direction Lg, a height Hs and a thickness Ts, wherein the height H. is measured between the convex side 12 and the concave side 13. At the concave side 13 the plate or sheet material has been curled in order to form a stiffening edge 14, as shown schematically in more detail in fig. 9A. It will be directly apparent that the stiffeners 11 can be made differently, for example as extruded profiles, for example bent after extrusion, and can have different configurations, for example I-profiles or T-profiles or U-profiles, or tubular profiles, and can be assembled of various components.

The plant 1 further comprises an area 15, indicated by a rectangle 15 in striped lines, where stiffeners 11 can be placed on sheets 5 and be welded together, as will be described.

In the embodiment shown in said area 15 a first gantry 16 is shown, as well as a series of supports 17 supporting sheets 5 cq sections 2 formed. The sheets 5 have been supplied from the sheet supply 4. Fig. 2 provides an isometric view of the area 15, fig. 3 shows a top view of said area 15. Fig. 6 shows is more detail two supports 17, in side-by-side relation, each supporting a section 3 comprising a sheet 5 and a series of stiffeners 11, the stiffeners 11 having been welded to the sheet 5 and having their longitudinal direction L parallel to the longitudinal direction L of the relevant sheet 5, which longitudinal directions L, Ls are curved. As will be discussed, the sheets 5 of adjacent sections 2 are welded along their longitudinal edges, forming a welding seam 100, and in the body three sections are welded together along their ends 8, 9 forming welding seams 101.

In the embodiment shown the support 17 has a frame 18 supporting a supporting surface 19, which supporting surface 19 in these embodiment is shown as a curved surface which is concave at an upward facing support side 20. The surface 19 can in embodiments be substantially closed, or can have openings therethrough. In embodiments shown the support 19 is formed by or comprises beams, especially I-beams 19A, extending in the width direction of the supports and sheets 5. The support side 20 or surface 19 is curved having a radius Rdesired which 1s conform the desired radius of curvature Rs of the in use outward facing, convex side 6 of the sheet 5 as it is to be welded and is thus ideally equal to the sum of the radius of the concave side 7 of the sheet 5 and the thickness T of the sheet 5 (Raesired = R7 + T) and which is therefore equal to the sum of the radius Rs of the convex side of the stiffener 11 and the thickness T of the sheet 5 (Raesired = Rs + T). The stiffener 11 has been manufactured with high precision, such that the radius Rs is conform a desired radius R; of the concave side 7 of the sheet 5.

As can especially be seen in fig. 4 and 7 the first gantry 16 comprises at least one first arm 21 and preferably at least two first arms 21, 22 for pushing the convex side 13 of the stiffener 11 against the concave side 7 of the sheet 5 supported on the support surface 20 of the support 17. In fig. 4A this is schematically shown. In fig. 4A a sheet 5 is shown, in an initial position, as a curved, striped line 5A. In this fig. 4A the sheet 5 is shown having a radius of curvature Rs, at the convex side 7 which is slightly larger than the desired radius Raesired. This can for example be the result of the manufacturing process, such as a rolling process for forming the sheet 5, or due to thermal influences, relaxation or other reasons. As can be seen in fig. 4A, by way of example, due to the larger radius Rs5a the sheet 5 will not align properly with the surface 19, 20 of the support. In a method of the disclosure the first arms 21, 22 push against a concave side 13 of a stiffener 11 to be welded to the sheet 5, pushing the stiffener 11, especially the convex side 12 thereof against the inner or concave surface 6 of the sheet 5.

Since the support surface 19 has the desired radius Raesireg and the convex side 12 of the stiffener 11 has been accurately made, with the desired radius, the sheet 5 is being pushed against the surface 19, 20 by the stiffener 11, in order to adopt the proper configuration, especially the proper desired radius of curvature Ryesirea at the convex side 7.

Preferably a gantry 16 is provided with at least a first welding tool 23, preferably for tack welding the stiffener 11, while being pushed by the arms 21, 22, to the sheet 5. In fig. 4 and 4a the first welding tool 23 is shown as an automatic or semi-automatic tack welding tool as known in the art, mounted to the gantry by a column 24, such that the welding tool 23 can be moved along the stiffener and sheet, in their longitudinal directions, for tack-welding the stiffener 11 at spaced apart positions along said longitudinal direction, preferably at both opposite longitudinal edges 25 of the stiffener 11, as schematically shown in fig. 9A. It will be appreciated that the welding can be done differently, for example by hand. In embodiments the column 24 can also be or comprise a pusher for pushing a central portion of the sheet 5 against the surface 19, 20.

In the embodiments shown and as preferred according to the disclosure, each first arm 21, 22 is an articulated arm, comprising at least an upper portion 21A, 22A and a lower portion 21B, 22B, connected by respective pivot points 21C, 22C and hydraulic cylinders 21D, 22D. At the lower ends of the lower portions 21B, 22B pusher elements 25A, 25B are provided, which can for example be pivotably connected to the arms 21, 22 in order to adjust position depending on the orientation of the arm relative to the stiffener, such that the pusher element 25A, B can properly align with the stiffener 11 it engages.

In preferred embodiments the two first arms 21, 22 have pushing directions F extending in a radial direction of the convex side 12 of the stiffener, preferably in mutually diverging directions F21y and Fez. In embodiments in which the column 24 is also provided with a pushing element, preferably the pushing direction of said column is also radial to the convex side of the stiffener 11. Radial pushing forces are preferable in order to properly and effectively push the stiffener 11 against the sheet 5 and the sheet 5 against the surface 19, 20.

As is shown in the drawings the first gantry 16 can be supported on rails 26 provided parallel to each other and extending in a direction substantially perpendicular to the longitudinal axis of the sheets 5 when positioned below the gantry 16. Thus the first gantry 16 can move over the support or supports 17.

In preferable embodiments at least the arms 21, 22 are designed for lifting stiffeners 11 and positioning them onto a sheet 5 resting on a support 17. The arms 21, 22 and/or pusher elements 25A, 25B can to than end for example be magnetic, for example electromagnetic, or can comprise grippers, suction elements or the like for engaging a stiffener 11, for example in a stiffener supply, lifting the stiffener 11, positioning the stiffener 11 on a sheet 5 and subsequently pushing the stiffener 11 against the sheet 5. Preferably without releasing the stiffener 11 during such maneuvering.

In fig. 2 an embodiment, especially a lay out is shown of part of a system 1, in which the first gantry 16 is shown positioned over a support 17 with a sheet 5 and at least one stiffener 11 positioned thereon, the stiffener engaged by the pushing elements 25 of the arms 21, 22. In fig. 2 to the left of the first gantry 16 a rack 27 is shown, as is also depicted in fig. 9, supporting a series of stiffeners 11 in side-by-side positions. The rack 27 is positioned between the rails 26, such that the gantry 16 can move over said rack, for picking up one of the stiffeners 11 supported therein and moving the stiffener to the sheet 5 on the support 17.

In the embodiments shown the first gantry 16 thus provides for a lifting and positioning system for lifting and position stiffeners 11 onto the sheet 5.

As can for example be seen in fig. 2, 3, 6 and 9 a series of stiffeners 11 1s positioned on the sheet 5 in a side-by-side relation, extending parallel to each other. After tack welding a first stiffener 11 onto the sheet 5 (in fig. 2 the most righthand one under the first gantry 16) the first gantry 16 can be moved over the support 17 to the next stiffener, i.e. the stiffener directly adjacent said first stiffener 11, for tack welding. Thus all stiffeners 11, for example four, are tack welded to the sheet 5.

After having tack welded the stiffeners 11 to the sheet 5, whereby the sheet 5 is forced into the proper configuration, especially with the desired radius Raesired, the stiffeners 11 can be welded by line welding over their length to the sheet, as schematically shown in fig. 9A by welds 102,

using appropriate welding tools 23A, such as automatic line welding tools.

Obviously the stiffeners could also be directly line welded to the sheet while being pushed onto the sheet 5.

In a system 1 according to the disclosure preferably a second gantry 30 is provided, for example supported on the same rails 26, movable in the same direction M. The second gantry 30 comprises at least a welding tool 23A for welding at least one edge portion 25 of the stiffener 11 to the sheet 5, preferably for line welding, forming welds 102. The same or a similar welding tool can be used for welding sections 2 together by forming the welds 100 as shown in fig. 6. As shown for example in fig. 5 two or more welding tools 23, 23A can be provided on a gantry 16, 30, for example for performing different welds, welding at different sides of stiffeners, and/or for increasing welding speed or at least reducing time spent on welding each section 2. By providing a second gantry 30 line welding stiffeners 11 and sections 2 can be performed simultaneously with tack welding stiffeners 11 using the first gantry.

The first 16 and/or second gantry 30 can be moved in the direction

M along the supports 17 supporting the sheets 5 cq sections 2, or the supports 17 can be moved in said direction M under the first 16 and/or second gantry 30, or the supports and gantries can all be moved in said direction M, for e.g. positioning the stiffeners on the sheets, positioning supports with sections to be welded and/or after welding and/or proper positioning of the welding tools 23, 23A relative to the stiffeners and sheets and sections.

As can be seen in the drawings, for example in fig. 4, 4A, 5, 6 and and 9 the stiffeners can be placed on the sheets 5 such that a first end 11A of each stiffener 11 is placed on the sheet 5, spaced apart from the first end 8 of the sheet 5, whereas at the opposite second end 11B of the stiffener the stiffener extends over the second end 9 of the sheet 5. Thus when welding sections 2 along the first and second ends 8, 9 of the sheets, forming the welds 101 (fig. 10) the second ends 11B of stiffeners of a section 2 can rest on and be welded to at least the sheet 5 of an adjacent section, the stiffener extending over the welding seam 101 connecting said adjacent sections.

Preferably also the said second end 11B of the stiffener 11 is welded to the first end 11B of the adjacent stiffener 11 of the adjacent section 2.

Fig. 8 schematically shows a series of curved sheets, having different lengths and radiuses, which are only shown by way of example.

For example a first sheet 5A has a radius R of 10,000 mm (10 m), and encloses an angle of 90 degrees between opposite ends 8, 9. A second sheet 5B shown has a radius R of 7,500 mm (7.5 m) and also an enclosed of 90 degrees between opposite ends 8, 9. A third sheet 5C shown in fig. 8 has a radius of 6,000 mm (6 m), and an enclosed angle of 120 degrees between opposite ends 8, 9. The fourth sheet 5D shown has a radius R of 5,000 mm and again an enclosed angle of 120 degrees between opposite ends 8, 9. By way of example, four sections 2 formed using a first sheet 5A shown in fig. 8 will provide a cylindrical element for forming a buoyancy body 3 with a diameter of 20 meters. Whereas for example three sections 2 based on the fourth sheet 5D will form a cylindrical element for forming a buoyancy body 3 with a diameter of 10 meters. It will be clear that for each of these and otherwise dimensioned sheets a specific series of supports 17 will be provided.

In embodiments the support 17 has at least one end stop 31 for engaging an edge portion 8, 9 of a sheet 5, defining a desired position of the sheet 5 relative to the support 17. The pushing arms 21, 22 and/or pushing elements 25A, B can be designed for pushing the sheet 5 not only against the support surface 20 but also against the end stop or end stops 31.

In embodiments the stiffener supply 10 comprises a stiffener support rack 27, with at least a first positioning element 32. The or each stiffener 11 in these embodiments has a second positioning element 33, cooperating with the first positioning element 32, for defining a desired position of the stiffener 11 relative to the support rack 27. In the embodiment shown in fig. 9 the second positioning element 33 is defined by, by way of example, a notch in the convex side 7 of the stiffener 11, whereas the first positioning element 32 is provided by a cross beam of the rack 27.

In the embodiment shown the rack 27 further has a comb-like provision 34 provided with teeth 35 sticking up, such that a stiffener 11 can be supported between two adjacent teeth of each of said provisions 34. When placed in the rack 27 each stiffener 11 is placed with the first positioning element 32 connecting to the second positioning element 33, end portions 11A, 11B supported between said teeth 35, such that stiffeners 11 can be supported in the rack 27 in a position next to each other and in a position from which they can be securely transferred to a sheet 5 on a support 17, for example by the first gantry 16, such that the stiffeners are positioned properly, without a need to adjust the position. In other words, when a stiffener is provided in said support rack having a second positioning element, it will cooperate with the first positioning element, for defining a desired position of the stiffener relative to the support rack.

As can be seen in the drawings, a support 17 can be provided with stops 36 along at least one side edge 37 of the support 17, for defining a position of the sheet 5 on the support 17 in a sideways direction. By positioning a side edge of the sheet against the stops 36 the position if the sheet 5 on the support surface is well defined easily.

The disclosure is also directed to a method for forming a section for a floating body 3 for an offshore floating foundation, comprising the steps of providing a metal sheet 5 having a sheet length direction L and a sheet width direction W, and bending said sheet 5, such that the sheet 5 1s curved in the sheet length direction L, forming a concave side 7, opposite a convex side 6. In such method also at least one and preferably a series of stiffeners 11 is provided, having a stiffener length direction Lg, wherein the stiffener is curved in said stiffener length direction Lg, forming a convex side 12. These steps can be performed simultaneously and/or consecutively, and can be performed at the same and/or different locations. The sheet 5 has a thickness T which is significantly smaller than a height Hs of the stiffener, measured perpendicular to the sheet surface, such that the sheet 5 is more flexible than the stiffener in said height direction.

A stiffener 11 can be formed directly have a curved shape, for example by cutting a curved shape from metal plate material, or can be curved by deformation of an initial product. Both should be understood as providing a curved stiffener.

After supplying said curved stiffener 11 and said sheet the convex side 12 of the stiffener is placed against the concave side 7 of the sheet. The stiffener 11 is then pushed against the concave side 7 of the sheet, such that a curvature R of the concave side 7 of the sheet 5 matches a curvature R of the convex side 12 of the stiffener 11at least at the position where the stiffener 11 is placed. By pushing the stiffener 11 against the sheet 5 the sheet 5 is pushed into shape conform the stiffener. For example the curvature of the sheet 5 is adapted to the curvature of the stiffener. The stiffener is then welded to the sheet. Preferably the stiffener is welded to the sheet while being pushed against the sheet, thus ensuring that the proper shape of the sheet is maintained after welding.

The welding can for example first be tack welding during pushing of the stiffener to the sheet, where after the stiffener can be line welded to the sheet after releasing the pushing force. Each stiffener is preferably welded through over substantially the full length of the stiffener, preferably after removing the pushing forces on the stiffener being welded.

Preferably the stiffener1l1 is placed against the sheet 5 having the stiffener length direction Ls parallel to the sheet length direction L.

Preferably a series of stiffeners 11 is welded with their convex sides 12 to the concave side 7 of the sheet 5, in side by side relations.

Preferably in a method of the disclosure the sheet 5 is positioned on a support 17, prior to welding the at least one stiffener 11 to the sheet 5.

Wherein more preferably the support 17 defines a concave real or imaginary surface 20, having a concave curvature desired for the sheet 5 after welding said stiffeners 11 to said sheet 5. The concave surface 20 preferably faces upward while supporting the sheet 5.

In preferred embodiments of a method of the disclosure the sheet 5 is pushed against the support 17 by pushing against a concave side 13 of at least one said stiffener 11, at least during part of the welding. Preferably the stiffener is pushed against the sheet 5 by applying a pushing force F at at least two spaced apart locations, preferably at least three spaced apart locations, which pushing forces F are preferably exerted in radial direction relative to the concave side 7, 13 of the sheet 5 and the stiffener 11. The stiffener 11 can be pushed against the sheet 5, at least during part of the welding, by applying at least a first pushing force Fey in a radial direction at a position between a central part of the stiffener and a first longitudinal 11A end of the stiffener, and at least a second pushing force Fez in a radial direction at a position between said central part and a second opposite longitudinal end 11B of the stiffener 11. Thus pressure can be distributed properly in an easy manner.

For forming a tubular body 3, to be used as a buoyancy body, a series of sheets 5 is provided with a series of stiffeners 11, forming sections 2. Each sheet of the series of sheets 5 and hence each section 2, is welded to at least one further sheet 5 along a side parallel to the length direction L and to at least one further sheet 5 along an edge parallel to the width direction W, such that a tubular body 3 is formed having said stiffeners 11 at an inside of said tubular body 3. The tubular body 3 hence comprises multiple sections 2, connected by welding seams 100, 101, wherein the stiffeners 11 form circular rings, wherein ends 11A, 11B of the stiffeners in such ring are preferably also welded to each other and to an adjacent sheet

5. The rings extend preferably in planes perpendicular to a longitudinal axis

X — X of the body 3, as shown in in fig. 10.

In a method according to the disclosure the sheet 5 can be placed on a support 17 after said bending, wherein the support 17 supports the sheet at least in three spaced apart locations or, preferably, over most of its convex surface 6, wherein at least one longitudinal end 8, 9, seen in the length direction L of the sheet, 1s placed against at least one stop element of the support, and/or at least one side edge, seen in the width direction of the sheet, 1s placed against at least one stop element 31 of the support 17, for positioning of the sheet in and/or on said support 17.

When using a system 1 as described a sheet 5 rests on a support 17 placed below a first gantry 16 or at least in a position in which the first gantry 16 can move over the support 17 and sheet 5. Then a first stiffener 11 is lifted, preferably using the first gantry 16, to a position above the sheet, and lowered onto the sheet 5. Then the stiffener is pushed against the sheet 5 and tack welded to it. Next a second stiffener 11 is lifted onto the sheet 5, to a position next to the first stiffener 11, and tack welded to the sheet. In the same manner next stiffeners are tack welded to the sheet 5.

When an appropriate number of stiffeners 11 has been tack welded to the sheet 5, the sheet 5 with the stiffeners 11 is moved to a position under or at least accessible to the second gantry 30. To this end the sheet 5 with the stiffeners 11 can be lifted off the support 17 and repositioned on another support, or can be moved together with the support 17.

As is shown in fig. 1 — 3 the first gantry 16 with a first support 17 can be positioned in a first part 40 of area 15, whereas the first gantry and a series of further supports 17 can be placed in a second part 41 of said area 15. In a method of the disclosure a first section 2 can be prepared up to and including tack welding of the stiffeners 11 to the sheet in the first part 40, where after the first section 2 is moved to an end of the second part 41 furthest from the first part. Then a second section is prepared in the first part 40, by tack welding the stiffeners 11 to the sheet 5, which second section is moved towards said end of the second part 41, to be placed with a longitudinal edge against a longitudinal edge of the first section 2. In the same manner further sections can be positioned in the second part 41, forming a closed row of sections 2. The second gantry 30 can be moved over said row of sections 2, for line welding the stiffeners 11 to the sheets 5 and welding the longitudinal welding seams 100 for connecting the sections to each other.

With a system and method according to the disclosure sections can be made for a buoyancy body using relatively think sheets which are supported by stiffeners for providing the desired stiffness and strength to withstand forces acting thereupon during use, without the body becoming undesirably heavy. Since initially substantially flat and relatively thin sheets can be used for forming the sections, these can relatively easily be bent into a curved shape. In a buoyancy body 3 as disclosed an upper end and a lower end will be closed, in order to make the body water tight.

Additionally further floors and/or walls can be provided inside the body.

The invention is by no means limited to the embodiments disclosed herein by way of example only. Many amendments can be made within the concept of the disclosure, including combinations of some or all of the features of the methods and structures as disclosed.

For example, in the drawings all stiffeners extend parallel to each other. Stiffeners can however also be positioned differently, for example in intersecting directions, for example forming a grid of stiffeners. A liner can be provided against the concave sides 13 of the stiffeners 11, for forming a double wall structure. Buoyancy increasing systems and/or materials and/or ballast systems can be provided in the body 3. Moreover a frame can be provided inside the body, for example for mounting constructive elements of an off shore structure to be supported by the body or connecting means for connecting the body to other buoyancy bodies.

Claims

Conclusions

1. Method for forming a section for a floating body for an offshore floating foundation, comprising the following steps: - providing a metal plate having a plate lengthwise direction and a plate widthwise direction, and bending said plate so that the plate is bent in a plate lengthwise direction, forming a concave side; - forming a stiffener having a stiffener lengthwise direction, the stiffener being bent in said stiffener lengthwise direction, forming a convex side; - placing said bent stiffener with the convex side against the concave side of the plate; - pressing the stiffener against the concave side of the plate, so that a curvature of the concave side of the plate corresponds to a curvature of the convex side of the stiffener at least at the position where the stiffener is placed; and - welding the stiffener to the plate.

Method according to claim 1, wherein the stiffener is placed against the plate with the stiffener length direction parallel to the plate length direction.

3. A method as claimed in claim 1 or 2, wherein a series of stiffeners are welded with their convex sides against the concave side of the plate in side-by-side relationships.

4. A method according to any preceding claim, wherein the plate is placed on a support prior to welding the at least one stiffener to the plate.

5. A method as claimed in claim 4, wherein the support defines a concave real or imaginary surface having a concave curvature desired for the plate after welding said stiffeners to said plate, the concave surface preferably facing upwards while supporting the plate.

6. A method as claimed in claim 4 or 5, wherein the plate is forced against the support by pushing against a concave side of the at least one said stiffener, at least during a portion of the welding.

7. A method according to any one of the preceding claims 4 - 6, wherein the stiffener is pressed against the plate by applying a pushing force at at least two spaced apart locations, preferably at least three spaced apart locations, the pushing forces preferably being applied in a radial direction relative to the concave side of the plate and the stiffener.

8. A method according to any one of the preceding claims 4 to 7, wherein the stiffener is forced against the plate, at least during a portion of the welding, by applying at least a first pushing force in a radial direction at a position between a central portion of the stiffener and a first longitudinal end of the stiffener, and at least a second pushing force in a radial direction at a position between said central portion and a second, opposite longitudinal end of the stiffener.

9. A method according to any preceding claim, wherein each stiffener is first tack welded to the plate and then welded throughout substantially the entire length of the stiffener, preferably after removing the thrust forces on the stiffener being welded.

A method according to any preceding claim, wherein a series of plates is provided with a series of stiffeners, each plate of the series of plates being welded to at least one further plate along a side parallel to the lengthwise direction and to at least one further plate along an edge parallel to the widthwise direction, so that a tubular body is formed having said stiffeners on an interior of said tubular body.

A method according to any preceding claim, wherein the plate is placed on a support after said bending, the support supporting the plate at at least three spaced-apart locations or across the convex surface of the plate, wherein: - at least one longitudinal end, viewed in the lengthwise direction of the plate, is placed against at least one stop element of the support; and/or - at least one side edge, viewed in the widthwise direction of the plate, is placed against at least one stop element of the support, for positioning the plate in and/or on said support.

12. System for forming a section for a floating body for an offshore floating foundation, the system comprising a plate feeder for feeding curved metal plates, said plates having a convex side and an opposite concave side, the system comprising a stiffener feeder for feeding curved stiffeners and the system comprising at least a first gantry crane, the system comprising at least one support for supporting a plate fed from the plate feeder, on a convex side thereof, and a hoisting and positioning system for hoisting and positioning at least one stiffener onto the concave side of a plate supported on the support, the stiffener being positioned on the support with a convex side on the concave side of the plate, the first gantry crane comprising at least one first arm for pressing the convex side of the stiffener against the concave side of the plate.

13. The system of claim 12, wherein the first gantry crane comprises at least two first arms for pushing the convex side of the stiffener against the concave side of the plate.

System according to claim 13, wherein the first two arms have pushing directions extending in a radial direction from the convex side of the stiffener, preferably in mutually diverging directions.

A system according to any one of claims 12 to 14, wherein the arm or arms are a pivoting arm comprising or forming at least one actuating device for urging a push end of the or each arm against a stiffener.

16. System according to any of the preceding claims 12 - 15, wherein the first gantry crane comprises at least one welding tool for welding the stiffener to the plate, preferably at least by means of tack welding.

17. System according to any of the preceding claims 12 - 16, wherein a second gantry crane is provided, which comprises at least one welding tool for welding at least an edge portion of the stiffener to the plate, preferably for line welding.

A system according to any one of the preceding claims 12 to 17, wherein the at least one support has a concave support surface defining a desired shape of the plate when pushed against said support surface.

A system according to any one of claims 12 to 18, wherein the support has at least one end stop for engaging an edge portion of a plate, thereby defining a desired position of the plate relative to the support.

20. A system according to any one of the preceding claims 12 to 19, wherein the stiffener supply comprises a support rack for supporting the stiffener, having a first positioning element, and at least one stiffener provided in said support rack having a second positioning element cooperating with the first positioning element to define a desired position of the stiffener relative to the support rack.

21. A section for a body of a floating offshore foundation element, comprising at least one metal plate bent in a first direction to provide a concave inner surface and a convex outer surface, a series of stiffeners welded to the concave inner surface, the stiffeners being bent in said first direction so that a convex side of the stiffeners abuts the concave surface of the plate, the stiffeners being spaced apart and extending parallel next to each other, the plate and the stiffeners having substantially the same length in said first direction, such that the section preferably includes an angle between 60 and 180 degrees in said first direction and/or forms a section of a circle, so that a series of such sections can be coupled together with opposite ends in said first direction to form a ring.