The present disclosure relates to systems and methods for construction of wind power plants, and particularly for constructing offshore, bottom-fixed wind power plants.

BACKGROUND

Offshore wind power is growing in importance worldwide, with the recent years having seen a number of large development projects being planned or commissioned, among other places in the North Sea. At present, such development projects mainly utilize bottom-fixed wind turbine generators, i.e. wind turbine generators which are mounted on a bottom-fixed structure such as a piled or gravity- base foundation to form a power plant. While floating wind turbine generators are being investigated by various groups worldwide, bottom-fixed technology is currently the most competitive at shallower water depths. Bottom-fixed wind turbine generators are currently feasible at water depths of up to about 60 m, and with future advances in technology, it is likely that bottom-fixed systems will become suitable for even larger water depths.

Publications which may be useful to understand the field of technology include: W011 102738, WO03066427, W011028102, EP2251254, EP3170730, GB2580103, EP2505484, GB2479232, US2009217852, EP2307269, US2004262926,

W02006080850, W02006076920.

With a projected continued increase in the investments into wind power in the future, there is a need for further improved technology in this area, including but not limited to solutions for safe and efficient installation of such wind power plants. The present disclosure has the objective to provide such improvements, or at least alternatives, to the current state of the art.

SUMMARY

It is an object of the present disclosure to mitigate, alleviate or eliminate one or more of the above-identified deficiencies and disadvantages in the prior art and solve at least the above mentioned problem. According to a first aspect there is a method for installation of an offshore wind power generator on a base, the method comprising providing a wind turbine generator having a connection profile in the shape of a hollow frustum cone, moving the connection profile into the vicinity of a base having a tapered end section, establishing a connection between the connection profile and the base, lowering the connection profile onto the base, and securing the connection profile onto the base.

According to a second example, the step of lowering the connection profile onto the base may comprise bringing a top surface on the tapered end section into contact with a shoulder arranged in the connection profile.

According to a third example, the step of securing the connection profile onto the base may comprise arranging a wedge member between an outer surface of the tapered end section and an inner surface of the connection profile.

According to a fourth example, the step of securing the connection profile onto the base comprises arranging two vertically spaced wedge members between an outer surface of the tapered end section and an inner surface of the connection profile.

According to a second aspect, there is a connector assembly for securing an offshore wind power generator on a base, the connector assembly comprising a connection profile in the shape of a hollow frustum cone, the connection profile configured for being arranged at a lower end of a tower of a wind turbine generator, and a base having a tapered end section.

According to a second example of the second aspect, the tapered end section may comprise a top surface and the connection profile may comprise a shoulder, wherein the top surface may be configured for engagement with the shoulder for carrying at least a part of the, or preferably the full, weight of the wind power generator.

According to a third example of the second aspect, the connector assembly may comprise a wedge member configured for arrangement between an outer surface of the tapered end section and an inner surface of the connection profile.

According to a fourth example of the second aspect, the connector assembly may comprise two wedge members configured for vertically spaced arrangement between an outer surface of the tapered end section and an inner surface of the connection profile.

According to a fifth example of the second aspect, the connector assembly may comprise at least one damper arranged to provide a dampening force between the connection profile and the base.

According to a third aspect, there is an offshore wind power plant comprising an offshore wind power generator arranged on a base, the wind power generator being secured on the base by means of a connector assembly according to any preceding claim.

The present disclosure will become apparent from the detailed description given below. The detailed description and specific examples disclose preferred embodiments of the disclosure by way of illustration only. Those skilled in the art understand from guidance in the detailed description that changes and modifications may be made within the scope of the disclosure.

Hence, it is to be understood that the herein disclosed disclosure is not limited to the particular component parts of the device described or steps of the methods described since such device and method may vary. It is also to be understood that the terminology used herein is for purpose of describing particular embodiments only, and is not intended to be limiting. It should be noted that, as used in the specification and the appended claim, the articles "a", "an", "the", and "said" are intended to mean that there are one or more of the elements unless the context explicitly dictates otherwise. Thus, for example, reference to "a unit" or "the unit" may include several devices, and the like. Furthermore, the words "comprising", "including", "containing" and similar wordings does not exclude other elements or steps.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other characteristics will become clear from the following description of illustrative embodiments, given as non-restrictive examples, with reference to the attached drawings, in which: Fig. 1 shows a schematic illustration of the installation of a wind turbine onto an offshore foundation by a vessel.

Figs 2a-e illustrate the process of lowering a wind turbine generator onto a base during installation. Figs 3a-c illustrate the securing of a wind turbine generator on a base.

Fig. 4 shows further detail of a secured wind turbine generator.

Figs 5 to 8 illustrate a base comprising a dampening arrangement.

DETAILED DESCRIPTION OF THE DRAWINGS The following description may use terms such as “horizontal”, “vertical”, “lateral”, “back and forth”, “up and down”, ’’upper”, “lower”, “inner”, “outer”, “forward”, “rear”, etc. These terms generally refer to the views and orientations as shown in the drawings and that are associated with a normal use of the invention. The terms are used for the reader’s convenience only and shall not be limiting. Fig. 1 illustrates in a schematic manner two steps in an installation process for an offshore wind turbine generator 204. An installation vessel 205 carries the wind turbine generator 204, which may in the conventional way comprise a tower, a nacelle section and a plurality of blades, to an offshore location which forms an installation site 211. At the offshore location, a foundation structure 201 (e.g. a base or base structure) has been pre-installed and arranged on the sea floor 212. The foundation structure 201 may be a jacket-type structure, as illustrated in Fig. 1, or another type of structure such as a monopile. The installation vessel 205 carries the wind turbine generator 204 to the installation site 211 and to the prepared foundation structure 201 (illustrated at the left hand side of Fig. 1) and then positions the wind turbine generator 204 onto an installation part (not visible in Fig. 1 but shown below) of the foundation structure 201, as illustrated at the right hand side of Fig. 1. The installation part comprises a conical engagement member to receive a corresponding engagement member on the wind turbine generator 204, described in further detail below. The wind turbine generator 204 may then be secured to the foundation structure 201, and dismounted from the vessel. The vessel may then be moved and used to install a further wind turbine generator, or may be used for some other use.

Alternatively, the vessel 205 may install the wind turbine generator 204 in steps, for example first installing a tower part of the wind turbine generator 204 on the foundation structure 201, and thereafter installing the nacelle and blades such that the wind turbine generator 204 may be provided first as a tower, the nacelle and blades to be installed subsequently. The present disclosure relates to the interface between the tower part of the wind turbine generator 204 and the foundation structure 201.

Advantageously, with systems and methods according to the examples described herein, it may be possible to carry out various operations relating to the construction and installation of bottom-fixed, offshore wind power plants in a safer, more efficient and/or simpler manner.

Figures 2a-e illustrate an interface between the wind turbine generator 404 and the base 401 during the installation process, according to one geometry of a connector assembly 445 suitable for this purpose. In this example, the connector assembly is based on conical engagement members. The connection profile 404b is configured for being integrated in (e.g., being manufactured as part of) a tower 404a (see Figure 1 , for example) of a wind power generator or for being provided as a separate component fixed to the lower end of the tower 404a prior to installation.

The tower 404a and/or the installation method may otherwise be similar to those described above, or may be of different types.

Here it can be seen that the connection profile 404b comprises a flared profile 438, while the base 401 comprises a tapered end section 440. In providing this geometry, the operation of aligning and installing the connection profile 404b with the base 401 is eased. In addition, the geometry of the connection profile 404b is advantageous because it may require limited modification for integration with an existing base (which may be e.g. a monopile) to be used in the installation process.

In contrast to some other examples of wind turbine generator which may comprise a base connection profile in the form of a plate or bolted flange connection to a base, in this example the connection profile 404b comprises a protruding rib 446 around the periphery of the base connection profile. Here, the protruding rib 446 may permit or assist the base connection profile 404b to be connected to an installation member or structure. For example, cables (not shown), a bracket and/or hoisting member may be connected to the rib 446 to support and optionally lift the wind turbine generator.

As illustrated in Figure 2a, the wind turbine generator is moved into the vicinity of the base 401. Moving the wind turbine generator towards the base can, for example, be done by positioning the floating structure or vessel carrying the wind turbine generator adjacent the base. Movement of the turbine generator 404 may then be slowed as the turbine generator 404 is lowered onto the base 401. Lowering of the turbine generator 404 onto the base may be continued until it is apparent that there is some contact between the turbine generator 404 and the base 401 (e.g. between the flared profile 438 and the upper rim of the tapered end section 440), as is illustrated in Figures 2b and 2c. At this point, the turbine generator 404 may be more accurately aligned with the base 401. To assist in alignment, the flared profile 438 may comprise an additional flared collar 439 to increase the diameter of the flared profile 438 in the region of initial engagement with the base 401. Guide members 432,433 (see Fig. 4) may be arranged on an inner surface of the flared profile 438 in order to assist the alignment and positioning of the tapered end section 440 and flared profile 438 in relation to each other while lowering the wind turbine generator 404 onto the base 401. Guide members 432, 433 may, for example, be annular or semi-annular guide shoulders or ribs arranged on the inner surface of the flared profile 438.

Further lowering of the turbine generator 404 onto the base 401 may then be possible until the flared profile 438 of the turbine generator 404 engages fully with the tapered profile of the base 401. This “fully landed” position is illustrated in Figs 3a, b and 4. Indicated in Fig. 2e, and also visible in Figs 2a-d, the connection profile 404b may comprise an internal stop shoulder 430, for example in the form of an annular or semi-annular horizontal shoulder surface, to engage a top surface 431 of the base 401. As such, the final relative position between the connection profile 404b and the base 401 may be controlled, in that the two parts are prevented from moving further when the stop shoulder 430 engages the base 401. At this point, the turbine generator 404 is fully supported by the base 401. The turbine 404 may then be dismounted from the installation structure or vessel, and if necessary further steps may be taken to ensure that the turbine generator 404 is adequately secured to the base 401. Having a connection profile 404b and a tapered base 401 may provide a geometry that is easy to manufacture due to manufacturing tolerances being low, and detailed machining not being required. Further, the described profile may facilitate a robust load transfer from the wind turbine generator 404 to the base 401 , which is able to be quickly established, thereby also saving costs in terms of installation vessel time.

Figures 3a and 3b provide an illustration of a further embodiment which may be used to ensure that the turbine generator 404 is adequately secured to the base 401. Here, engagement between the connection profile 404b of the turbine generator 404 and the tapered section 440 of the base 401 is shown. Between the connection profile 404b and the tapered section 440 is a wedge member 442 having a wedge shaped profile in its cross-section, as illustrated. The wedge member 442 may be in the shape of a ring or an arc, and may extend fully or partly around the inner circumference of the connection profile 404b, particularly around the inner circumference of the flared profile 438 but the (or a) wedge member may be arranged in the connection profile 404b above the flared profile 438. The wedge member 442 may be arranged inside the connection profile 404b prior to the installation of the wind turbine generator. The wedge member 442 is movable relative to both the connection profile 404b and the tapered section 440.

Illustrated in Fig. 3b, a second wedge member 443 is shown. The second wedge member 443 may have the same properties as described above for wedge member 442, and may be used in addition to wedge member 442. The specific design of the wedge members 442,443 may be different; they may for example have different thicknesses and/or wedge angles. An example of a suitable semi-annular wedge profile design is shown in Fig. 5.

Movement of the wedge member 442,443 in a direction towards the opening of the flared profile 438 may be used to establish a tight mechanical connection between the connection profile 404b of the turbine generator 404 and the tapered section 440 of the base 401. The connector assembly 445 may be provided with two wedge members 442, 443 which are vertically spaced and arranged between the connection profile 404b of the turbine generator 404 and the tapered section 440 of the base 401. In this manner, two contact points can be provided, to allow for effective transfer of bending moment loads from the wind turbine generator to the base 401 when in operation. Optionally, only one wedge member 442,443 may be foreseen while a second such contact point is provided by design of the connection profile 404b of and the tapered section 440. For example, the stop shoulder 430 and the top surface 431 may be designed with an angled (e.g. conical- or wedge-type) interface such that when the tower 404a is fully landed onto the base 401 , the interface between the shoulder 430 and surface 431 also acts to prevent relative horizontal movement between the connection profile 404b and the tapered section 440. A wedge member 442,443 may subsequently be used at a position further down in order to provide two-point contact and enhanced bending moment support through the connector assembly 445.

The wedge member 442.443 may be arranged for actuation after landing the connection profile 404b on the base 401. For example, a hydraulic tool may be used to provide a force to drive, e.g. from above, the wedge member 442,443 downwardly and to achieve a tight fit between the connection profile 404b and the tapered section 440.

As illustrated in Figure 3a, there may be a rib 444 extending around the inner circumference of the flared profile 438 to prevent accidental movement of the wedge member 442 towards the opening of the flared profile, as well as guiding, before engagement with the base 401. After installation, the position of the wedge member(s) 442,443 may be monitored to ensure that there is still a tight connection between the turbine generator 404 and the base 401 (e.g. movement of the wedge members 442,443 may indicate a loose and/or unstable connection).

Advantageously, by providing one or two wedge members 442,443 to secure the connection profile 404b of the turbine generator 404 to the base 401 , manufacturing tolerances may be relaxed and manufacturing intensity reduced for the different components of the connector assembly 445. Moreover, offshore installation may be eased in that a larger gap between the connection profile 404b and the tapered section 440 can be allowed, and additional load-bearing contact can be obtained after landing the tower 404a by activating the wedge members 442,443. An example of a wedge member 442, 443 is illustrated in Figure 3c. Figure 3c may illustrate an entire wedge member 442, 443 in the case where the wedge member 442, 443 extends circumferentially around part of the inner circumference of the flared profile 438. In this case, there may be multiple wedge members 442, 443 located around varying sections of the flared profile 438.

Advantageously, the top surface 431 and shoulder 430 are configured for carrying the majority of the turbine weight. In any of the embodiments described herein, the surface 431 may be dimensioned for carrying at least 50%, at least 75% or at least 90% of the weight of the wind turbine generator 404 via the shoulder 430. In such an embodiment, the wedge members 442,443 may provide substantially horizontal support, not being required to carry any substantial part of the wind turbine generator weight.

In any of the embodiments herein, one or more dampers may be provided and adapted to engage either the connection profile 404b or the base 401 just prior to the final landing of the wind turbine generator 404 on the base 401. An example of such dampers are shown in Figs 5-8. In this example, four damper units 428 are disposed circumferentially adjacent the shoulder 430. The damper units 428 may be arranged in recesses 429 (see Fig. 2e) or the like arranged in either the connection profile 404b or the base 401. In Figs 5-8, the damper units comprise a piston- cylinder arrangement pre-mounted in the connection profile 404b. The piston- cylinder arrangement may be filled with a liquid (such as water) and arranged that a piston engages the top surface 431 , whereby the piston-cylinder arrangement is compressed as the wind turbine generator 404 is further lowered onto the base 401. A relatively small outlet for the liquid can be arranged such that the piston-cylinder arrangement provides a dampening force while slowly compressing until fully compressed, at which point the top surface 431 has engaged the shoulder 430. Other types of dampers may also be possible. Similarly, the damper(s) may equally well be arranged on the base 401.

In any of the embodiments or examples described herein, the floating structure may be an installation vessel, which may be self-propelled or non-self-propelled, such as a barge or towed floater. Advantageously, the installation vessel is a self-propelled vessel. By means of the embodiments described above, enhanced safety or operational reliability may be achieved for installing offshore wind power generators.

In any of the embodiments or examples described herein, the floating structure or installation vessel may be a monohull vessel. As will be appreciated when reading the disclosure herein, advantages of the methods described may be realised individually and by the use of only some of the method steps described above. The invention is not limited by the embodiments described above.