Construction of offshore wind power foundations

Abstract

Methods for constructing foundations 10 for offshore wind turbine power plants, the methods comprising: positioning a crane 12 at a construction site 11, the crane being rotatable about a vertical axis; providing a plurality of workspaces 15,15a-d disposed about the crane; at each of a plurality of construction spaces 19,19a-d disposed about the crane and arranged between two of a plurality of workspaces, constructing a foundation by moving at least two elongate foundation parts 16,25a-h into two workspaces adjacent the construction space, pivoting each of the two foundation parts to a vertical or substantially vertical orientation, and interconnecting the two foundation parts at the construction space such as to form part of the foundation. An alternative method comprises positioning three first floater columns 20a,21a,22a about the crane, for each of the three first floater columns positioning two further floater columns 20b-c,21b-c,22b-c distally away from the crane, installing side connection members 16 between the first floater column and each of the two further floater columns;

Description

The present disclosure relates to foundations for use offshore, and particularly to construction of foundations for wind power plants. BACKGROUND Offshore wind plants for electric power generation are under development by a number of players, and the installation of offshore wind power plants is projected to continue to grow over the coming years. Some examples of publications which may be useful to understand the field of technology include WO 2020 / 167137 A1; WO 2023 / 009010 A1; WO 2009 / 131826 A2; EP 3 262 296 A1; and EP2 511 423 A1. A challenge with offshore wind power compared to land-based solutions is the cost level for construction and installation. There is consequently a need for more efficient solutions for the construction of offshore foundations and offshore wind power plants, as well as a need for solutions which are suitable for scaling-up to enable serial and / or mass production. The present disclosure has the objective to provide improved technology for offshore wind power plants, or at least to provide useful alternatives to the state of the art. SUMMARY In an aspect, there is provided a method for constructing a plurality of foundations for an offshore wind turbine power plant, the method comprising: positioning a crane at a construction site, the crane being rotatable about a vertical axis; providing a plurality of workspaces disposed about the crane, each workspace within operative reach of the crane; providing a plurality of construction spaces disposed about the crane, each construction space having or forming a base for temporarily positioning a foundation under construction, each construction space being within operative reach of the crane, and each construction space arranged between two of the plurality of workspaces; for each construction space, constructing a foundation at the respective construction space by: (i) moving at least two elongate foundation parts into two workspaces adjacent the construction space, (ii) pivoting each of the two foundation parts to a vertical or substantially vertical orientation, and (iii) interconnecting the two foundation parts at the construction space such as to form part of the foundation. In an aspect, there is provided a method of constructing a plurality of foundations for a floating wind turbine power plant, the method comprising: positioning a crane at a construction site, the crane being rotatable about a vertical axis; positioning three first floater columns about the crane and within an operational reach of the crane; for each of the three first floater columns, positioning two further floater columns distally away from the crane, wherein each first floater column and associated two further floater columns make up a set of columns for one floating foundation; wherein a workspace is defined between each pair of sets; and for each of the three first floater columns, installing side connection members between the first floater column and each of the two further floater columns; wherein the step of installing side connection members between the first floater column and each of the two further floater columns is carried out at least partly from the workspaces. The detailed description below and the appended claims outline further inventive aspects and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS The above and other characteristics will become clear from the following description of illustrative, non-restrictive examples, with reference to the attached drawings, in which: Fig. 1 is a top view of a construction site for constructing a plurality of foundations for a floating wind turbine power plant. Fig. 2 is a perspective view of a construction site similar to that illustrated in Fig. 1. Figs 3-6 illustrate steps in the construction of a foundation for a floating wind turbine power plant. Fig. 7 schematically illustrates a construction site for constructing four three-legged foundations. Fig. 8 schematically illustrates a construction site for constructing four four-legged foundations. Figs 9-11 schematically illustrate steps of a method for constructing an offshore wind power plant. Figs 12-13 illustrate steps of another example of a method for constructing an offshore wind power plant. Fig. 14 schematically illustrates a construction site for constructing foundations. DETAILED DESCRIPTION Fig. 1 is a top view of a construction site 11 for constructing a plurality of foundations for a floating wind turbine power plant. Fig. 2 is a perspective view of a construction site similar to that illustrated in Fig. 1. The construction site 11 enables the use of an efficient method for constructing foundations 10 (see Fig. 6) for a floating wind turbine power plant. Such foundations 10 can be configured to carry a wind turbine tower and generator on a column forming part of the foundation 10, for example in the manner described in the abovementioned publications. (See BACKGROUND, above.) A crane 12 is positioned at the construction site 11, in a central position thereof. The crane 12 is rotatable, for example having a rotatable base and / or rotatable crane arm. The crane 12 may, for example, be a tower crane. Three tower columns 20a,21a,22a are positioned about the crane 12 and within an operational reach of the crane 12. Each tower column 20a,21a,22a is configured for holding a wind turbine tower and generator, for example extending upwardly from the tower column 20a,21 a,22a and rigidly fixed to the tower column 20a,21 a,22a by means of a transition piece or equivalent. (Such wind turbine tower and generator may be installed onto the tower column 20a,21 a,22a after construction of the foundation 10, and optionally at a location which is different from the construction site 11.) For each of the three tower columns 20a,21a,22a, two further floater columns 20b-c, 21b-c, 22b-c are positioned distally away from the crane 12. Distally away as used here means farther away from the crane 12 compared with the respective tower column 20a,21a,22a. As can be seen in Fig. 1, the further floater columns 20b-c, 21b-c, 22b-c are in this manner also positioned and arranged about the crane 12. The further floater columns 20b-c, 21b-c, 22b-c are arranged relative to the respective tower column 20a,21 a,22a such as to enable the construction of a substantially triangular floater foundation, as will be described further below. Alternatively, the tower column(s) 20a,21a,22a can be positioned distally away from the crane and one of the further floater columns 20b-c,21b-c,22b-c for the respective foundation(s) be positioned closest to the crane 12 during construction. (I.e., one or more of the tower column(s) 20a,21a,22a switched with one of the other floater columns 20b-c,21b-c,22b-c in the arrangement as shown in Fig. 1, so that one of the other floater columns 20b-c,21b-c,22b-c is closest to the crane 12.) The arrangement and method may otherwise be the same. The tower columns 20a,21a,22a and associated further floater columns 20b-c, 21b-c, 22b-c are positioned about the crane 12 with workspaces 15 therebetween. (See Fig. 1.) The workspaces 15 provide space between each of the floater foundations (or, during construction, the parts being assembled at each construction space 19 to form the floater foundations) during construction. Fig. 1 indicates only one such workspace 15, however the skilled reader will understand that three such workspaces 15 are provided, between each pair of foundations under construction, located at respective construction spaces 19. The workspaces 15 provides access to a side of each floater foundation during construction, and also access to the crane 12. This is illustrated in Fig. 1 by crane supply area 31, to which access is provided through one workspace (the lowermost as illustrated in the figure), as indicated via the double arrow 32. In this manner, items for the crane 12 can be provided, for example scaffolding, equipment or heavy items for installation onto the tower column(s) 20a,21a,22a or elsewhere in relation to the floater foundation under construction. Further equipment and / or machines (indicated generally with reference 33) used in the construction of the floater foundations can also be positioned and used at (or from) the workspaces 15, for example additional crane units, etc. After positioning the tower column 20a,21 a,22a and the two further floater columns 20b-c, 21b-c, 22b-cfor one or more floater foundation, side connection members 16 are installed between the tower column 20a,21 a,22a and each of the two further floater columns 20b-c, 21b-c, 22b-c. This operation is carried out at least partly from the workspaces 15. The construction method may also comprise installing side connection members 16 between the two further floater columns 20b-c, 21b-c, 22b-c. The side connection members 16 can be pontoons, truss structures, beams, or other rigid structures (or combinations thereof) for interconnecting the columns. In the illustrated example, the connection members 16 are truss structures made up of cylindrical beams and the columns 20a-c,21a-c,22a-c are polygonal columns, however the skilled reader will appreciate that other structures and shapes (such as round columns or flat plate connection members) may equally well be used with the methods described herein. Machines 33, for example crawler cranes as illustrated here, can be used for installing the side connection members 16 onto the columns 20a-c,21a-c,22a-c. The machines 33 may, for example, hold the connection members 16 in place while welding or otherwise fixing the connection members 16 to the columns. In some examples, the side connection members 16 comprise a truss or interconnected beam structure, and the method comprises moving the side connection members into the workspaces 15 in a horizontal or substantially horizontal orientation, temporarily connecting the side connection members 16 to two columns 20a-c, 21a-c, 22a-c, pivoting the side connection members 16 to a horizontal orientation and fixing the side connection members 16 to the respective columns 20a-c, 21a-c, 22a-c. The temporary connection may, for example, be a pivoting connection formed by a hang-off point, a cradle or the like, while the fixed connection may be a welded connection, a bolted connection, or another type of permanent or semi-permanent connection. This is illustrated in further detail in Figs 3-6 in relation to one of the floater foundations. In Fig. 3, the columns 20a-c have been positioned as described above at one construction space 19 (see Fig. 1). A first side connection member 16a has been installed. A second side connection member 16b has been brought into position adjacent columns 20b and 20c and temporarily connected to columns 20b and 20c at two lower connection points on these columns. By means of a suitable machine 33, such as a moveable crane as illustrated here, the second side connection member 16b is subsequently pivoted upwardly into a vertical orientation (Fig. 4). The side connection member 16b is then fixed, such as welded or bolted, to the columns 20b and 20c. Fig. 5 illustrates the third side connection member 16c being moved horizontally into a workspace 15 and adjacent the respective columns 20a,b, and temporarily connected to these. Fig. 6 illustrates the third side connection member 16c having been pivoted to the vertical orientation and fixed to the columns 20a,b. Fig. 6 thus illustrates the substantially finished foundation 10, onto which further components, particularly a wind turbine tower and generator, can be mounted. With reference to Figs 1 and 2, a smallest distance between any two tower columns 20a,21 a,22a may advantageously be greater than the height of the side connection members 16. In this manner, sufficient space at the workspace 15 is provided to bring the side connection members 16 into the workspace 15 and to handle the side connection members, for example by means of equipment and / or machines 33. Illustrated in Fig. 1, the two further floater columns 20b-c,21b-c,22b-c for each floater foundation may be arranged at opposite sides of an (imaginary) axis, illustrated here as a first axis x only in relation to the uppermost floater foundation, extending through the crane 12 and the respective tower column 20a,21a,22a. The skilled reader will recognise that corresponding second and third axes exist through the crane 12 and each of columns 21a and 22a, respectively. The further floater columns 20b-c, 21b-c, 22b-c may advantageously be arranged symmetrically at opposite sides of the respective axis. The method may involve positioning exactly three tower columns 20a,21a,22a about the crane 12, with each of the three tower columns 20a,21 a,22a having the same or substantially the same distance to the crane 12 and the same distance between them such as to be evenly and symmetrically distributed about the crane 12. Alternatively, or additionally, the three tower columns 20a,21 a,22a about the crane 12 may be positioned such that an angle between any two of the first, second and third axes is at least 100 degrees or 110 degrees. Preferably, the angle is substantially 120 degrees or 120 degrees, i.e. such that the three floater foundations are positioned with rotational symmetry about the crane 12. The method may be used for constructing more than three floater foundations, and / or for constructing floater foundations having more than three columns 20a c,21a-c,22a-c. Fig. 7 schematically illustrates a construction site 11 for constructing four three-legged foundations 10a-d (i.e., four foundations each having three columns). Fig. 8 schematically illustrates a construction site 11 for constructing four four-legged foundations 10e-h (i.e., four foundations each having four columns). The method may otherwise be similar to that described in relation to Figs. 1-6. In any of the embodiments described here, the floater foundations 10,10a-h may comprise a plurality of columns 20a-c,21a-c,22a-c and a plurality of connection members 16, and have a substantially polygonal horizontal cross-section. The cross-section may be substantially triangular (as illustrated in Figs 1-7) or substantially rectangular (as illustrated in Fig. 8). One edge of the substantially polygonal horizontal cross-section for each floater foundation 10,10a-h under construction may be arranged towards (i.e., facing) the crane 12. The construction of floater foundations may be time-shifted, such that different operations / different steps are carried out in parallel at the different (partially constructed) floater foundations. In this manner, successive construction of floater foundations may be done, with better optimized utilization of equipment (e.g., welding equipment), machines (e.g., crawler cranes) and personnel (e.g., welders). For example, the crane 12 may carry out lifting and installation operations in relation to one (partially constructed) floater foundation, before moving to the next to carry out the same operation there, and the equipment and / or machines 33 may be moved between floater foundations under construction according to which construction step is being carried out at any one of these. When one floater foundation 10,10a-h is finalized, it may be moved away from the construction site 11, for example by multi-wheelers or skids, and three new columns 20a-c,21a-c,22a-c may be brought into position for constructing another floater foundation in the same place. By means of the shared workspaces 15, space is provided for carrying out the construction work, such as for the installation of connection members 16. A time-shifted construction may provide for optimized use of the shared workspaces 15. The columns 20a-c,21a-c,22a-c may be circular, polygonal, for example rectangular, pentagonal or hexagonal, or have another (e.g. irregular) shape. The connection members 16 may be truss structures (such as pre-assembled truss structures, as illustrated) made up of tubulars, box beams, other forms of elongate rigid structures, or a combination thereof. Alternatively, the connection members 16 may, for each connection between two columns, comprise several individual structural members of the beforementioned type(s), e.g. tubular beams or box beams. The connection between the connection members 16 and the columns may be at an upper part of the columns, at a lower part of the columns, both at upper and lower parts of the columns, or elsewhere on the columns. By means of the arrangement of columns 20a-c,21a-c,22a-c according to the methods described here, the floater foundations 10,10a-h being constructed may be positioned closer to the crane 12 and may utilize the crane 12 more efficiently, for example for installing scaffolding or moving tools and equipment. The crane 12 may, for example, be arranged with an operational reach which spans most or all of the columns 20a-c,21a-c,22a-c and / or most or all of the floater foundations 10,10a-h under construction. Further, space at the construction site 11 can be utilized more efficiently. Further inventive examples and embodiments are outlined in the following numbered clauses. A1. A method of constructing a plurality of foundations (10) for a floating wind turbine power plant, the method comprising: positioning a crane (12) at a construction site (11), the crane (12) being rotatable about a vertical axis; positioning three first floater columns (20a,21 a,22a) about the crane (12) and within an operational reach of the crane (12); for each of the three first floater columns (20a,21 a,22a), positioning two further floater columns (20b-c,21b-c,22b-c) distally away from the crane (12), wherein each first floater column (20a,21a,22a) and associated two further floater columns (20b-c,21b-c,22b-c) make up a set of columns (20a-c,21a-c,22a-c) for one floating foundation (10,10a-f); wherein a workspace (15) is defined between each pair of sets (20a-c,21a-c,22a-c); and for each of the three first floater columns (20a,21 a,22a), installing side connection members (16) between the first floater column (20a,21a,22a) and each of the two further floater columns (20b-c,21b-c,22b-c); wherein the step of installing side connection members (16) between the first floater column (20a,21 a,22a) and each of the two further floater columns (20b-c,21b-c,22b-c) is carried out at least partly from the workspaces (15). A2. The method of any preceding clause, wherein the three first floater columns (20a,21a,22a) are tower columns configured for holding a wind turbine tower. A3. The method of any preceding clause, wherein the step of positioning the two further floater columns (20b-c,21b-c,22b-c) distally away from the crane (12) comprises positioning the two further floater columns (20b-c,21b-c,22b-c) within the operational reach of the crane (12). A4. The method of any preceding clause, wherein the step of positioning two further floater columns (20b-c,21b-c,22b-c) distally away from the crane (12) comprises positioning the two further floater columns (20b-c,21b-c,22b-c) at opposite sides of an axis (x) extending through the crane (12) and the respective first floater column (20a,21a,22a). A5. The method of any preceding clause, wherein the step of positioning two further floater columns (20b-c,21b-c,22b-c) distally away from the crane (12) comprises positioning the two further floater columns (20b-c,21b-c,22b-c) symmetrically at opposite sides of the axis (x). A6. The method of any preceding clause, wherein the method comprises positioning exactly three or exactly four first floater columns (20a,21a,22a) about the crane (12). A7. The method of any preceding clause, wherein each of the first floater columns (20a,21 a,22a) having the same distance to the crane (12). A8. The method of any preceding clause, wherein the sets of columns (20a-c,21a-c,22a-c) are positioned with rotational symmetry about the crane (12). A9. The method of any preceding clause, wherein the method comprises positioning exactly three first floater columns (20a,21a,22a) about the crane (12) and a first axis (x) extends through a first of the exactly three first floater columns (20a,21 a,22a) and the crane (12), a second axis extends through a second of the exactly three first floater columns (20a,21 a,22a) and the crane (12), and a third axis extends through a third of the exactly three first floater columns (20a,21 a,22a) and the crane (12), and wherein the step of positioning the first floater columns (20a,21a,22a) about the crane (12) comprises positioning the first floater columns (20a,21 a,22a) such that an angle between any two of the first, second and third axes is at least 100 degrees, preferably at least 110 degrees, more preferably substantially 120 degrees or 120 degrees. A10. The method of any preceding clause, wherein the method comprises positioning exactly four first floater columns (20a,21a,22a) about the crane (12) and a first axis (x) extends through a first of the exactly four first floater columns (20a,21 a,22a) and the crane (12), a second axis extends through a second of the exactly four first floater columns (20a,21 a,22a) and the crane (12), a third axis extends through a third of the exactly four first floater columns (20a,21 a,22a) and the crane (12), and a fourth axis extends through a fourth of the exactly four first floater columns (20a,21 a,22a) and the crane (12), and wherein the step of positioning the first floater columns (20a,21a,22a) about the crane (12) comprises positioning the first floater columns (20a,21 a,22a) such that an angle between any two of the first, second, third and fourth axes is at least 70 degrees, preferably at least 80 degrees, more preferably substantially 90 degrees or 90 degrees. A11. The method of any preceding clause, comprising: moving the side connection members (16) into the workspaces (15) with the side connection members (16) in a horizontal orientation, a substantially horizontal orientation, or an orientation less than 45 degree off the horizontal orientation; temporarily connecting the side connection members (16) to the respective columns (20a-c,21a-c,22a-c); pivoting the side connection members (16) to a vertical orientation; fixing the side connection members (16) to the respective columns (20a-c,21a-c,22a-c). A12. The method of any preceding clause, wherein the step of pivoting the side connection members (16) to a vertical orientation is carried out by a movable crane (33). A13. The method of any preceding clause, wherein the step of pivoting the side connection members (16) to a vertical orientation is carried out by a movable crane (33) positioned in the workspace (15). A14. The method of any preceding clause, wherein the step of fixing the side connection members (16) to the respective columns (20a-c,21a-c,22a-c) is carried out while supporting the side connection members (16) by a movable crane (33). A15. The method of any preceding clause, wherein the step of fixing the side connection members (16) to the respective columns (20a-c,21a-c,22a-c) is carried out while supporting the side connection members (16) by a movable crane (33) positioned in the workspace (15). A16. The method of any preceding clause, comprising installing side connection members (16) between each pair of two further floater columns (20b-c,21b-c,22b-c). A17. The method of any preceding clause, wherein a smallest distance between any two first floater columns (20a,21a,22a) is greater than a height of each side connection member (16). In another example, illustrated in relation to Figs 9-11, a method for constructing a plurality of foundations 10 for an offshore wind turbine power plant may comprise positioning a crane 12 at a construction site 11, with the crane 12 being rotatable about a vertical axis. The crane 12 may, for example, be a tower crane. A plurality of workspaces 15a-d are disposed about the crane 12, where the crane 12 and each workspace 15a-d are arranged such that the workspaces 15a-d are within operative reach of the crane 12. The workspaces 15a-d are accessible, for example a side access at its outer edges which do not face the crane 12, to allow moving components and equipment into the workspaces 15a-d. Such side access may, for example, be suitable for crawler cranes, transport trolleys, multi-wheelers, or other types of transport equipment to move into and out of the respective workspace 15a-d. Optionally, components and equipment can be lifted into the workspaces 15a-d by means of a crane. The workspaces 15a-d may be a prepared area at the construction site 11, for example having a hard surface and prepared for moving and handling components and equipment for the construction of offshore foundations 10. A plurality of construction spaces 19a-d are disposed about the crane 12, where each construction space 19a-d has or forms a base for temporarily positioning a foundation 10 while the foundation 10 is under construction. The construction spaces 19a-d may be a prepared area at the construction site 11, for example having a hard surface and prepared for construction of offshore foundations 10 thereon. The construction spaces 19a-d may, optionally, have a base or support(s) onto which the foundation 10 can rest during construction, for example to support the legs of a jacket structure or the columns of a floater foundation. Each construction space 19a-d is within operative reach of the crane 12, and each construction space 19a-d is arranged between two of the plurality of workspaces 15a-d. In this example, there are exactly four workspaces 15a-d and exactly four construction spaces 19a-d. In the example in Figs 9-11, a first construction space 19a is arranged between and adjacent first and second workspaces 15a,b; a second construction space 19b is arranged between and adjacent second and third workspaces 15b,c; a third construction space 19c is arranged between and adjacent third and fourth workspaces 15c,d; and a fourth construction space 19d is arranged between and adjacent first and fourth workspaces 15a,d. The same arrangement is used in the examples of Figs 7 and 8. Alternatively, as in the example of Figs 1 and 2, there may be exactly three workspaces and exactly three construction spaces. This is illustrated schematically in Fig. 14, with a first construction space 19a arranged between and adjacent first and second workspaces 15a,b; a second construction space 19b arranged between and adjacent second and third workspaces 15b,c; and a third construction space 19c arranged between and adjacent first and third workspaces 15a,c. Illustrated in Fig. 10, a foundation 10 can be constructed at construction spaces 19a-d by first moving at least two horizontally or substantially horizontally oriented foundation parts 25a-d into two workspaces 15a-d adjacent the respective construction space 19a-d. Optionally the foundation parts 25a-d can be constructed in the two workspaces 15a-d. In Fig. 10, foundation parts 25a-d for constructing a foundation 10 at constructions spaces 19a and 19c are shown. The foundation parts 25a-d are suitably positioned in the workspaces 15a-d in relation to the respective adjacent construction space 19a,c, and subsequently pivoted to a vertical or substantially vertical orientation. The two foundation parts, in this example the two parts in each of the pairs 25a,b and 25c,d, are subsequently interconnected at the construction space 19a,c to form (at least part of) the foundation 10. Fig. 11 illustrates the foundation parts 25a,b having been interconnected to form (at least part of) a foundation 10 at the construction space 19a, and the foundation parts 25c,d having been interconnected to form (at least part of) a foundation 10 at the construction space 19c. Further work may be carried out on, and further parts may be connected to, the foundations 10 at the construction spaces 19a,c. The foundations 10 can then be moved away from the construction spaces 19a,c. (The skilled reader will understand that yet further work may be carried out at the foundations 10 elsewhere, for example at a quayside.) Fig. 11 further illustrates further foundation parts 25e-h having been moved into workspaces 15a-d and prepared for construction of foundations 10 at construction spaces 19b and 19d. The method of construction can follow the same principles as described above, where the foundation parts 25e-h are suitably positioned and thereafter pivoted into a vertical or substantially vertical orientation at the construction spaces 19b and 19d for interconnection. Advantageously, the steps of moving the foundation parts 25a-h into the workspaces 15a-d (or constructing the foundation parts 25a-h in the workspaces 15a-d) and / or pivoting the foundation parts 25a-h are carried out non-simultaneously and time-shifted between the construction spaces 19a-d which are adjacent the same workspace 15a-d. For example, with reference to Fig. 11, interconnecting foundation parts 25a / 25b and 25c / 25d, and / or moving the completed foundations 10 away from the construction spaces 19a,c, can be carried out concurrently with moving foundation parts 25e-h into the workspaces 15a-d or constructing foundation parts 25e-h in the workspaces 15a-d, and / or concurrently with pivoting foundation parts 25e-h into position. This allows for an efficient use of the construction site 11, crane 12, and other equipment, also with concurrent operations in workspaces 15a-d and construction spaces 19a-d which are adjacent one another. As in the examples described in relation to Figs 1-8 above, further equipment and / or machines (such as crawler cranes, and indicated generally in Figs 9-11 with reference 33) can be used in the construction of the foundations. As illustrated in Figs 9-11, the steps of moving the foundation parts 25a-h into the workspaces 15a-d or constructing the foundation parts 24a-h in the workspaces 15a-d and / or pivoting the foundation parts 25a-h can be carried out concurrently for two of the plurality of construction spaces 19a-d which are not adjacent the same workspace 15a-d. Thus, for this example, concurrent operations can be carried out in relation to construction spaces 19a and 19c (as illustrated in Fig. 10), and in relation to construction spaces 19b and 19d (as illustrated in Fig. 11). The foundations 10 may be foundation 10 for a floating wind turbine power plant as described above in relation to Figs 1-6. The foundation parts 25a-h may in such an example comprise the side connection members 16 to be installed between a pair of floater columns 20a-c,21a-c,22a-c, which can be arranged at the construction spaces 19a-d prior to installation of the foundation parts 25a-h. In another example, the foundation parts 25a-h may comprise elongate truss structures forming part of a jacket foundation configured to be installed on a sea floor. This is illustrated in relation to Figs 12-13. Fig. 12 illustrates a construction site having four workspaces 15a-d and four construction spaces 19a-d similarly as described above. Foundation parts 25a-h are in this example truss structures for making up parts of a jacket foundation. The foundation parts 25a-h may be pre-assembled offsite the workspaces 15a-d and moved into the workspaces 15a-d ready to be pivoted into place and interconnected, or the method may include carrying out steps of preparing the foundation parts 25a-h at the workspaces 15a-d while these are in a horizontal or substantially horizontal orientation. The latter is illustrated in relation to foundation part 25b in Fig. 12, where truss parts 26 are illustrated at the workspace 15b. The truss parts 26, for example beams or rods to form part of the jacket foundation, can be assembled together at the workspace 15b, e.g. by welding, prior to pivoting the two foundation parts 25a,b for interconnection at the construction space 19a. As can be seen, the foundation parts 25a-d may have a vertical extension while in the horizontal orientation, as illustrated in relation to foundation parts 25c and 25d in Fig. 12, for example in that part of the truss structure extends upwardly when the foundation parts 25a-d are in the horizontal orientation. Fig. 13 illustrates a subsequent step relative to Fig. 12, where the foundation parts 25a-d have been pivoted into a substantially vertical orientation at the construction spaces 19a and 19c to form parts of jacket foundations 10. Similarly as illustrated in Fig. 11, further foundation parts 25e-h have been moved into workspaces 15a-d for preparation and interconnection at construction spaces 19b and 19d (see Fig. 12). Concurrently, further work can be carried out at the foundations 10 at construction spaces 19a and 19c, for example mounting of further parts such as a transition piece 27 for mounting a wind turbine tower on the jacket foundation 10. The jacket foundations 10 can subsequently be moved from the construction spaces 19a and 19c for further work (if applicable), transport and installation offshore. Further inventive examples and embodiments are outlined in the following numbered clauses. B1. A method for constructing a plurality of foundations (10) for an offshore wind turbine power plant, the method comprising: positioning a crane (12) at a construction site (11), the crane (12) being rotatable about a vertical axis; providing a plurality of workspaces (15,15a-d) disposed about the crane (12), each workspace (15,15a-d) within operative reach of the crane (12); providing a plurality of construction spaces (19,19a-d) disposed about the crane (12), each construction space (19,19a-d) having or forming a base for temporarily positioning a foundation (10) under construction, each construction space (19,19a-d) being within operative reach of the crane (12), and each construction space (19,19a-d) arranged between two of the plurality of workspaces (15,15a-d); constructing a foundation (10) at each construction space (19,19a-d) by: (i) moving at least two elongate foundation parts (16,25a-h) into two workspaces (15,15a-d) adjacent the construction space (19,19a-d) or building at least two horizontally oriented, elongate foundation parts (16,25a-h) in the two workspaces (15,15a-d) adjacent the construction space (19,19a-d), (ii) pivoting each of the two foundation parts (16,25a-h) to a vertical or substantially vertical orientation, and (iii) interconnecting the two foundation parts (16,25a-h) at the construction space (19,19a-d) such as to form part of the foundation (10). B2. The method of any preceding clause, wherein step (i) comprises moving the elongate foundation parts (16,25a-h) into the workspaces (15,15a-d) with the elongate foundation parts (16,25a-h) in a horizontal orientation, a substantially horizontal orientation, or an orientation less than 45 degrees off the horizontal orientation. B3. The method of any preceding clause, wherein steps (i) and / or (ii) are carried out non-simultaneously and time-shifted between construction spaces (19,19a-d) which are adjacent the same workspace (15,15a-d). B4. The method of any preceding clause, wherein step (i) and / or step (ii) is carried out concurrently for two of the plurality of construction spaces (19,19a-d) which are not adjacent the same workspace (15,15a-d). B5. The method of any preceding clause, comprising providing exactly four workspaces (15,15a-d) and exactly four construction spaces (19,19a-d). B6. The method of the preceding clause, wherein a first (19a) of the exactly four construction spaces (19,19a-d) is arranged between and adjacent a first (15a) and a second (15b) of the exactly four workspaces (15,15a-d), a second (19b) of the exactly four construction spaces (19,19a-d) is arranged between and adjacent the second (15b) and a third (15c) of the exactly four workspaces (15,15a-d), a third (19c) of the exactly four construction spaces (19,19a-d) is arranged between and adjacent the third (15c) and a fourth (15d) of the exactly four workspaces (15,15a-d), and a fourth (19d) of the exactly four construction spaces (19,19a-d) is arranged between and adjacent the fourth (15d) and the first (15a) of the exactly four workspaces (15,15a-d). B7. The method of the preceding clause, comprising carrying out step (i) or step (ii) in relation to the first (19a) construction space (19,19a-d) concurrently with carrying out step (i) or step (ii) in relation to the third (19c) construction space (19,19a-d). B8. The method of any preceding clause, comprising providing exactly three workspaces (15,15a-d) and exactly three construction spaces (19,19a-d). B9. The method of the preceding clause, wherein a first (19a) of the exactly three construction spaces (19,19a-d) is arranged between and adjacent a first (15a) and a second (15b) of the exactly three workspaces (15,15a-d), a second (19b) of the exactly three construction spaces (19,19a-d) is arranged between and adjacent the second (15b) and a third (15c) of the exactly three workspaces (15,15a-d), and a third (19c) of the exactly three construction spaces (19,19a-d) is arranged between and adjacent the third (15c) and the first (15a) of the exactly three workspaces (15,15a-d). B10. The method of any preceding clause, comprising carrying out step (i) or step (ii) in relation to one of the plurality of construction spaces (19,19a-d) while concurrently: carrying out step (iii) in relation to another one of the plurality of construction spaces (19,19a-d), or moving a constructed foundation (10) out of the another one of the plurality of construction spaces (19,19a-d). B11. The method of the preceding clause, wherein the one of the plurality of construction spaces (19,19a-d) and the another one of the plurality of construction spaces (19,19a-d) are adjacent the same workspace (15,15a-d). B12. The method of any preceding clause, wherein the foundation (10) is a foundation (10) for a floating wind turbine power plant and step (iii) comprises installing side connection members (16) between a pair of floater columns (20b-c,21b-c,22b-c). B13. The method of any preceding clause, wherein the foundation (10) is a jacket foundation for positioning on a sea floor and step (iii) comprises interconnecting two elongate truss structures to form part of the jacket foundation. In all the examples and embodiments above, the methods can provide more efficient use of a construction site 11. Installed utilities at the site 11 (such as scaffolding, machines 33, welding equipment, etc.) and personnel (such as welders) can be used more efficiently, and / or the area use at or for the site 11 can be reduced. The methods described here may be particularly suitable for serial and / or mass production of foundations, for example for floating or bottom-fixed wind power plants, where construction efficiency is of importance. By utilizing methods as described herein for serial and / or mass production, the overall progress is less sensitive to errors or delays in the construction of individual foundations (compared to known “assembly line” methods in which subsequent processes may be held up and “bottlenecked” if one process step or work station experiences delays). In any of the examples or embodiments described herein, the term ‘space’ means an extent or area in two dimensions which is part of the construction site 11. In any 5 of the examples or embodiments described herein, the workspace(s) 15,15a-d and the construction spaces 19,19a-d are separate and non-overlapping extents or areas of the construction site 11. The invention is not limited by the embodiments described above; reference should be had to the appended claims. 10

Claims

1. A method for constructing a plurality of foundations (10) for an offshore wind turbine power plant, the method comprising:positioning a crane (12) at a construction site (11), the crane (12) being rotatable about a vertical axis;providing a plurality of workspaces (15,15a-d) disposed about the crane (12), each workspace (15,15a-d) within operative reach of the crane (12);providing a plurality of construction spaces (19,19a-d) disposed about the crane (12), each construction space (19,19a-d) having or forming a base for temporarily positioning a foundation (10) under construction, each construction space (19,19a-d) being within operative reach of the crane (12), and each construction space (19,19a-d) arranged between two of the plurality of workspaces (15,15a-d);for each construction space (19,19a-d), constructing a foundation (10) at the respective construction space (19,19a-d) by:(i) moving at least two elongate foundation parts (16,25a-h) into two workspaces (15,15a-d) adjacent the construction space (19,19a-d),(ii) pivoting each of the two foundation parts (16,25a-h) to a vertical or substantially vertical orientation, and(iii) interconnecting the two foundation parts (16,25a-h) at the construction space (19,19a-d) such as to form part of the foundation (10).

2. The method of claim 1, wherein step (i) comprises moving the elongate foundation parts (16,25a-h) into the workspaces (15,15a-d) with the elongate foundation parts (16,25a-h) in a horizontal orientation.

3. The method of any preceding claim, wherein steps (i) and / or (ii) are carried out non-simultaneously and time-shifted between construction spaces (19,19a-d) which are adjacent the same workspace (15,15a-d).

4. The method of any preceding claim, wherein step (i) and / or step (ii) is carried out concurrently for two of the plurality of construction spaces (19,19a-d) which are not adjacent the same workspace (15,15a-d).

5. The method of any preceding claim, comprising providing exactly four workspaces (15,15a-d) and exactly four construction spaces (19,19a-d).

6. The method of claim 5, whereina first (19a) of the exactly four construction spaces (19,19a-d) is arranged between and adjacent a first (15a) and a second (15b) of the exactly four workspaces (15,15a-d),a second (19b) of the exactly four construction spaces (19,19a-d) is arranged between and adjacent the second (15b) and a third (15c) of the exactly four workspaces (15,15a-d),a third (19c) of the exactly four construction spaces (19,19a-d) is arranged between and adjacent the third (15c) and a fourth (15d) of the exactly four workspaces (15,15a-d), anda fourth (19d) of the exactly four construction spaces (19,19a-d) is arranged between and adjacent the fourth (15d) and the first (15a) of the exactly four workspaces (15,15a-d).

7. The method of claim 6, comprising carrying out step (i) or step (ii) in relation to the first (19a) construction space (19,19a-d) concurrently with carrying out step (i) or step (ii) in relation to the third (19c) construction space (19,19a-d).

8. The method of any of claims 1-4, comprising providing exactly three workspaces (15,15a-d) and exactly three construction spaces (19,19a-d).

9. The method of claim 8, whereina first (19a) of the exactly three construction spaces (19,19a-d) is arranged between and adjacent a first (15a) and a second (15b) of the exactly three workspaces (15,15a-d),a second (19b) of the exactly three construction spaces (19,19a-d) is arranged between and adjacent the second (15b) and a third (15c) of the exactly three workspaces (15,15a-d), anda third (19c) of the exactly three construction spaces (19,19a-d) is arranged between and adjacent the third (15c) and the first (15a) of the exactly three workspaces (15,15a-d).

10. The method of any preceding claim, comprising carrying out step (i) or step (ii) in relation to one of the plurality of construction spaces (19,19a-d) while concurrently:carrying out step (iii) in relation to another one of the plurality of construction spaces (19,19a-d), ormoving a constructed foundation (10) out of the another one of the plurality of construction spaces (19,19a-d).

11. The method of claim 10, wherein the one of the plurality of construction spaces (19,19a-d) and the another one of the plurality of construction spaces (19,19a-d) are adjacent the same workspace (15,15a-d).

12. The method of any preceding claim, wherein the foundation (10) is a foundation (10) for a floating wind turbine power plant and step (iii) comprises installing side connection members (16) between a pair of floater columns (20b-c,21b-c,22b-c).

13. The method of any preceding claim, wherein the foundation (10) is a jacket foundation for positioning on a sea floor and step (iii) comprises interconnecting two elongate truss structures to form part of the jacket foundation.

14. A method of constructing a plurality of foundations (10) for a floating wind turbine power plant, the method comprising:positioning a crane (12) at a construction site (11), the crane (12) being rotatable about a vertical axis;positioning three first floater columns (20a,21 a,22a) about the crane (12) and within an operational reach of the crane (12);for each of the three first floater columns (20a,21 a,22a), positioning two further floater columns (20b-c,21b-c,22b-c) distally away from the crane (12), wherein each first floater column (20a,21a,22a) and associated twofurther floater columns (20b-c,21b-c,22b-c) make up a set of columns (20a-c,21a-c,22a-c) for one floating foundation (10,10a-f);wherein a workspace (15) is defined between each pair of sets (20a-c,21a-c,22a-c); andfor each of the three first floater columns (20a,21 a,22a), installing side connection members (16) between the first floater column(20a,21a,22a) and each of the two further floater columns (20b-c,21b-c,22b-c);wherein the step of installing side connection members (16) between the first floater column (20a,21 a,22a) and each of the two further floater columns (20b-c,21b-c,22b-c) is carried out at least partly from the workspaces (15).

15. The method of claim 14, wherein the three first floater columns (20a,21a,22a) are tower columns configured for holding a wind turbine tower.

16. The method of any of claims 14-15, wherein the step of positioning the two further floater columns (20b-c,21b-c,22b-c) distally away from the crane (12) comprises positioning the two further floater columns (20b-c,21b-c,22b-c) within the operational reach of the crane (12).

17. The method of any of claims 14-16, wherein the step of positioning two further floater columns (20b-c,21b-c,22b-c) distally away from the crane (12) comprises positioning the two further floater columns (20b-c,21b-c,22b-c) at opposite sides of an axis (x) extending through the crane (12) and the respective first floater column (20a,21a,22a).

18. The method of claim 17, wherein the step of positioning two further floater columns (20b-c,21b-c,22b-c) distally away from the crane (12) comprises positioning the two further floater columns (20b-c,21b-c,22b-c) symmetrically at opposite sides of the axis (x).

19. The method of any of claims 14-18, wherein the method comprises positioning exactly three or exactly four first floater columns (20a,21a,22a) about the crane (12).

20. The method of any of claims 14-19, wherein the method comprises positioning exactly three first floater columns (20a,21a,22a) about the crane (12) anda first axis (x) extends through a first of the exactly three first floater columns (20a,21 a,22a) and the crane (12),a second axis extends through a second of the exactly three first floater columns (20a,21 a,22a) and the crane (12), anda third axis extends through a third of the exactly three first floater columns (20a,21 a,22a) and the crane (12),and wherein the step of positioning the first floater columns (20a,21a,22a) about the crane (12) comprises positioning the first floater columns (20a,21 a,22a) such that an angle between any two of the first, second and third axes is at least 100 degrees, preferably at least 110 degrees, more preferably substantially 120 degrees or 120 degrees.

21. The method of any of claims 14-19, wherein the method comprises positioning exactly four first floater columns (20a,21a,22a) about the crane (12) anda first axis (x) extends through a first of the exactly four first floater columns (20a,21 a,22a) and the crane (12),a second axis extends through a second of the exactly four first floater columns (20a,21 a,22a) and the crane (12),a third axis extends through a third of the exactly four first floater columns (20a,21 a,22a) and the crane (12), anda fourth axis extends through a fourth of the exactly four first floater columns (20a,21 a,22a) and the crane (12),and wherein the step of positioning the first floater columns (20a,21a,22a) about the crane (12) comprises positioning the first floater columns (20a,21 a,22a) such that an angle between any two of the first, second, third and fourth axes is at least 70 degrees, preferably at least 80 degrees, more preferably substantially 90 degrees or 90 degrees.

22. The method of any of claims 14-21, comprising:moving the side connection members (16) into the workspaces (15) with the side connection members (16) in a horizontal orientation;temporarily connecting the side connection members (16) to the respective columns (20a-c,21a-c,22a-c);pivoting the side connection members (16) to a vertical orientation; fixing the side connection members (16) to the respective columns (20a-c,21a-c,22a-c).

23. The method of any of claims 14-22, wherein the step of pivoting the side connection members (16) to a vertical orientation is carried out by a movable crane (33) positioned in the workspace (15).

24. The method of any of claims 14-23, wherein the step of fixing the side connection members (16) to the respective columns (20a-c,21a-c,22a-c) is carried out while supporting the side connection members (16) by a movable crane (33) positioned in the workspace (15).

25. The method of any of claims 14-24, wherein a smallest distance between any two first floater columns (20a,21a,22a) is greater than a height of each side connection member (16).

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