Anchoring Element

Abstract

In particular, a foundation for an offshore structure is disclosed. The foundation includes: a tower having an anchoring section which is anchorable in the seabed and a connection section arranged at the opposite end of the tower. An electricity generation device arrangable above the water surface is connectable with the connection section of the tower. A natural frequency of the offshore structure is below an excitation from a single revolution number 1P of at least one exciting component. Further disclosed is an offshore structure.

Claims

1. An offshore structure, comprising: a tower having an anchoring section which is anchorable in the seabed and a connection section arranged at the opposite end of the tower, and an electricity generation device arranged and connected with the connection section of the tower above the water surface; wherein a natural frequency of the offshore structure is below an excitation from a single revolution number 1P of at least one exciting component; wherein the anchoring section engaging the seabed has one or more anchoring elements which counteract a torsional force about an axis in the longitudinal direction of the tower; wherein in a tilted position of the tower the anchoring section of the tower engaging the seabed is movable in the seabed.

2. The offshore structure according to claim 1, wherein the anchoring section engaging the seabed comprises an inner anchoring section and an outer anchoring element at least partially enclosing the inner anchoring section, wherein the inner anchoring section is insertable into the outer anchoring element, and wherein one or more torsional forces are transmittable from the inner anchoring section to the outer anchoring element.

3. The offshore structure according to claim 1, wherein the one or more anchoring elements protrude radially inwardly and/or outwardly from an inner and/or outer surface of the anchoring section.

4. The offshore structure according to claim 1, wherein the one or more anchoring elements extend substantially in the longitudinal extension direction of the tower beyond the seabed-engaging end of the anchoring section into the seabed.

5. The offshore structure according to claim 1, wherein the one or more anchoring elements comprise a reactive material or are filled with a reactive material.

6. The offshore structure according to claim 5, wherein in the course of installation of the foundation the reactive material hardens and/or expands after water saturation, and/or in the course of installation of the foundation expands radially and/or downwardly out of the anchoring section.

7. The offshore structure according to claim 1, wherein the one or more anchoring elements are each formed as sheet metal, hollow section, solid section, tube, or a combination thereof.

8. The offshore structure according to claim 1, wherein at least three anchoring elements are comprised by the foundation.

9. The offshore structure according to claim 1, wherein the one or more anchoring elements are fixedly connected to the anchoring section of the tower.

10. The offshore structure according to claim 1, wherein the foundation further comprises a plate-like element which, in the arranged state of the foundation, rests on the seabed and is in particular frictionally connected to the tower.

11. (canceled)

12. The offshore structure according to claim 1, wherein an upper section of the tower is movable relative to the anchoring section of the tower, wherein when the tower is tilted, the anchoring section in the seabed remains substantially in position.

13. The offshore structure according to claim 12, wherein the upper section of the tower is substantially torsionally stiff and/or torsionally force transmitting supported in the anchoring section of the tower.

14. The offshore structure according to claim 12, wherein the upper section of the tower is at least partially movably supported within and in a receiving region of the anchoring section of the tower, wherein a formed space between the receiving region of the anchoring section and the upper section of the tower is filled with a filling material.

15. The offshore structure of claim 14, wherein the filler material is or comprises an elastomer.

16. The offshore structure according to claim 1, wherein the anchoring section of the tower, at least at its end engaging the seabed, is substantially formed with a base surface deviating from a circular base surface, in particular is formed with an oval-shaped, rectangular, square, polygonal or semicircular base surface.

17. (canceled)

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0089] In the drawing shows

[0090] FIG. 1 schematic representation of an offshore structure comprising a present foundation;

[0091] FIG. 2 another schematic sectional view of an offshore structure comprising a present foundation;

[0092] FIG. 3a-d a respective schematic sectional representation of exemplary embodiments of present anchoring elements; and

[0093] FIG. 4 a frequency spectrum diagram.

DESCRIPTION OF THE INVENTION

[0094] FIG. 1 shows a schematic representation of an offshore structure 1, which is at least partially founded on or in the seabed M by means of a present foundation.

[0095] The offshore structure 1 is in the present case an offshore wind turbines comprising a tower 2 having at its upper end an electricity generation device 8 (e.g. a turbine, not shown in the schematic drawing according to FIG. 1) with three exciting components, in the present case three rotor blades 9. At the upper end of the tower 2, for example, a connection section 5 (e.g. a flange connection) is formed in order to arrange, for example, the schematically illustrated electricity generation device 8 on the tower 2.

[0096] The tower 2 is divided into an anchoring section 3 and an overlying upper section 4. In the present case, the anchoring section 3 is anchored in the seabed M or at least partially engages therein. Furthermore, the tower 2 or the anchoring section 3 comprises anchoring elements 7, which are presently formed as metal sheets and project radially or laterally from the outer wall of the anchoring section 3 into the seabed substantially in a horizontal direction. These can be formed alternatively or additionally to the embodiments shown in FIGS. 3a-d.

[0097] Optionally, the anchoring section 3 engaging the seabed M comprises an outer anchoring element 16 at least partially enclosing the seabed M. The anchoring section 3 is, for example, partially insertable or presently inserted into this outer anchoring element 16. Torsional forces T may then be transferable or presently transferred from the inner part to the outer anchoring element 16, for example.

[0098] The offshore structure 1, which is founded with a present foundation 1, has a natural frequency below an excitation from a single revolution number 1P from the three rotor blades 9 of the electricity generation device.

[0099] The design of the low natural frequency of the offshore structure 1 is made possible by the fact that the offshore structure 1 is anchored in the seabed M with a lower embedment depth.

[0100] The anchoring elements 7 counteract a torsional force which runs or acts radially around the longitudinal extension direction L of the tower 2 shown schematically in FIG. 1.

[0101] FIG. 2 shows another schematic sectional view of an offshore structure 1, wherein an upper portion 4 of the tower 2 of the offshore structure 1 is movable in the direction of at least two degrees of freedom within the anchoring section 3 of the tower 2. At the upper end of the tower 2, for example, a connection section 5 (e.g. a flange connection) is formed for arranging, for example, an electricity generation device 8 (not shown in FIG. 2) on the tower 2.

[0102] The upper section 4 of the tower 2 engages, by means of a conically tapering (inner) connection section 15 surrounded by the latter, in a receiving region 6 of the anchoring section 3. For this purpose, the anchoring section 3 comprises in the present case an outer anchoring element 16. The intermediate space formed between the inner connecting section 15 and the outer anchoring element 16 may, for example, be filled (illustrated schematically by means of the dotted area), for example with an elastic filling material 13, such as an elastomer, polymer, sand-clay, sand-clay mixture, to name but a few non-limiting examples.

[0103] Furthermore, the anchoring section 3 of the tower 2 comprises optional damper and spring elements 14 which act as restoring elements. The damper and spring elements 14 cause, for example, a tilted position of the tower 2, wherein the upper section 4 is tilted relative to the anchoring section 3, to be damped or sprung. Furthermore, by means of the optional damper and spring elements 14, a restoring tensile and/or compressive force can be effected in case of a tilted position of the upper section 4 of the tower 2, which can lead to an erection of the upper section 4 of the tower 2 after a tilted position of the upper section 4 of the tower has been effected.

[0104] The anchoring section 3 of the tower 2 may be open towards the bottom, as designed in the present case, so that anchoring of the anchoring section 3 in the seabed M can be safely effected.

[0105] Analogous to the offshore structure 1 of FIG. 1, the exemplary embodiment of a foundation illustrated in FIG. 2 also has anchoring elements 7 at the anchoring section. These can be designed analogously to the shown anchoring elements 7 of FIG. 1.

[0106] It is understood that both the anchoring elements 7 of FIG. 1 and the anchoring elements 7 of FIG. 2 may also be formed according to one or more of the embodiments shown in FIGS. 3a-d.

[0107] The anchoring section 3 of the tower 2 may, for example, form a so-called cofferdam in which a pile (the upper section 4 of the tower 2) is then at least partially arranged. A rotation of the upper section 4 of the tower 2 may then, for example, be restrained in such a way that the upper section 4 of the tower 2 cannot rotate within the excavated cofferdam or the anchoring section 3 of the tower 2. Alternatively, such an anchoring section may comprise a dynamic joint which also realizes the functions described above. Then, for example, torsional forces T occurring from, for example, the upper section 4 of the tower 2 formed as an inner pile are transmitted via such a joint to the anchoring section 3 of the tower 2 formed as an outer pile.

[0108] The foundation of FIG. 2 further comprises a plate-like element 11 which, in the arranged state of the foundation (i.e., for example, after its installation in the seabed M), substantially (in particular directly) rests on the seabed M and, in particular, is non-positively connected to the tower 2. In the present case, this connection is implemented via a screw connection of the plate-like element 11 to the tower 2.

[0109] In the present case, the plate-like element 11 is a ring plate which completely surrounds the tower 2. The plate-like element 11 has, for example, a scour-reducing effect. The plate-like element 11 may comprise one or more additional elements (e.g. piles) extending vertically into the seabed M from the plate-like element 11 (not shown in FIG. 2). This may further increase the torsional strength and/or torsional stiffness.

[0110] FIGS. 3a-d each show a schematic sectional representation of exemplary embodiments of present anchoring elements which can be used, for example, as anchoring elements on one of the foundations shown in FIGS. 1 and 2, instead of or in addition to the anchoring elements 7 formed as metal sheets.

[0111] Such anchoring elements are also referred to as torsion anchors, or torsion foundation anchors, in the sense of the subject matter.

[0112] The anchoring elements 7 of FIGS. 3a-d may, for example, either be arranged (e.g. welded or screwed on, to name but a few non-limiting examples) at the corresponding anchoring section already ex factory, i.e. during the manufacture of at least a section of the tower of a present foundation. Alternatively or additionally, one or more of these anchoring elements may be arranged offshore (or at a quay edge) only during installation of a present foundation. In the latter case, this may, for example, include appropriate support plates.

[0113] FIG. 3a shows anchoring elements 7, which in the present case are arranged on an anchoring section 3 having a circular base surface 12. Each of the anchoring elements 7 is arranged on the outer surface of the anchoring section 3. The anchoring elements 7 each have an identical spacing from one another.

[0114] FIG. 3b shows anchoring elements 7, which in the present case are arranged on an inner surface of the anchoring section 3. The anchoring elements protrude beyond the end of the anchoring section 3 that is lowest after installation. The anchoring elements 7 form a cross-shaped structure, and moreover a pointed structure which can facilitate, for example, the insertion of the foundation or the anchoring section 3 into the seabed. The anchoring section 3 shown in FIG. 3b also has a circular base 12.

[0115] FIG. 3c shows anchoring elements 7, which are presently arranged on an outer surface of the anchoring section 3. In the present case, the anchoring elements 7 are each tubular, for example in the form of small stakes. The anchoring elements 7 each have openings, for example holes. The anchoring elements 7 are hollow on the inside, so that they can be filled with a reactive material 10. After contact with water or water saturation, e.g. after insertion of the anchoring section 3 into the seabed, this reactive material 10 can escape from the openings, e.g. expand and subsequently harden. This increases, for example, the strength of the foundation in the seabed.

[0116] FIG. 3d shows an anchoring element 7 comprised by the anchoring section 3, extending it in a semicircular shape.

[0117] FIG. 4 shows a frequency spectrum diagram in which excitation frequencies are shown during operation of a wind turbine.

[0118] As already described, for the determination of a natural frequency of an overall system (offshore structure, in particular wind turbine) consisting of a foundation consisting of a tower and a power generation device (e.g. with one or more rotor blades), ranges within a frequency spectrum can be defined in advance in which the natural frequency should lie.

[0119] For example, a wind turbine experiences a (dynamic) excitation during operation, in particular from wind loads, from a periodic excitation with the single number of revolutions (rotor frequency, 1P excitation; for example, caused by imbalances that occur during the rotation of the rotor blades), as well as from a further periodic excitation from the rotor blade passage with three times a number of revolutions (3P excitation; for example, by an inflow of wind to the rotor blade, whereby the rotor blade is located directly in front of the tower).

[0120] Furthermore, FIG. 4 shows the so-called JONSWAP spectrum, which represents the wave energy spectrum due to the sea state in offshore structures and which can also cause excitation of the offshore structure.

[0121] The closer the natural frequency of the wind turbine is to these exciting frequencies, the higher the stress on the mechanical components and the tower can be.

[0122] If the first natural frequency of the offshore structure is below the frequency from three times the rotor revolution number 3P, the design of the offshore structure is referred to as “soft-stiff”. If the design of the offshore structure is also above the frequency from three times the rotor revolution number 3P, the design is also referred to as “stiff-stiff”. If, on the other hand, the first natural frequency of the offshore structure is below the frequency from the single rotor revolution number 1P, the design is referred to as “soft-soft”.

[0123] It is understood that when designing the natural frequency of an offshore structure, a natural frequency design that is within the 1P and/or 3P frequency band should be avoided to prevent premature material fatigue and wear.

[0124] The embodiments of the present invention described in this specification and the optional features and characteristics indicated in each case with respect thereto are also intended to be understood as disclosed in all combinations with each other. In particular, the description of a feature encompassed by an embodiment example—unless explicitly stated to the contrary—is also not to be understood herein as meaning that the feature is indispensable or essential for the function of the embodiment example. The sequence of the process steps described in this specification in the individual flowcharts is not mandatory, alternative sequences of the process steps are conceivable. The process steps can be implemented in various ways, for example, implementation in software (by program instructions), hardware or a combination of both is conceivable for implementing the process steps.

[0125] Terms used in the patent claims such as “comprising”, “having”, “including”, “containing” and the like do not exclude further elements or steps. The phrase “at least in part” includes both the case “in part” and the case “in full”. The phrase “and/or” is intended to be understood to disclose both the alternative and the combination, so “A and/or B” means “(A) or (B) or (A and B)”. The use of the indefinite article does not preclude a plurality. A single device may perform the functions of multiple units or devices recited in the claims. Reference signs indicated in the patent claims are not to be considered as limitations of the means and steps employed.

LIST OF REFERENCE SIGNS

[0126] 1 Offshore structure

[0127] 2 Tower

[0128] 3 Anchoring section

[0129] 4 Upper section

[0130] 5 Connection section

[0131] 6 Receiving region of the anchoring section

[0132] 7 Anchoring element

[0133] 8 Electricity generation device

[0134] 9 Rotor blade

[0135] 10 Reactive material

[0136] 11 plate-like element

[0137] 12 Base surface

[0138] 13 Filling material

[0139] 14 Restoring element

[0140] 15 inner anchoring section

[0141] 16 external anchoring element

[0142] M Seabed

[0143] S Water surface

[0144] L Longitudinal direction of the tower

[0145] T Torsion force