Soft-soft foundation for offshore structures

Abstract

A foundation for an offshore structure is disclosed. The foundation includes a tower having an anchoring portion anchored in the seabed and a connecting portion arranged at the opposite end. The foundation also includes a power generation system arranged above the water surface connected to the connecting portion of the tower. A natural frequency of the offshore structure lies below an excitation component one times the rotational frequency 1P of at least one exciting component. The foundation also includes at least one restoring element connected to the tower via one or more transition pieces. The restoring element is designed such that, in a skewed position of the tower, tensile and/or compressive forces can be transferred to the tower by means of the restoring element such that the tower can be straightened up.

Claims

1. A foundation for an offshore structure, comprising: a tower, which has an anchoring portion that can be anchored in the seabed and a connecting portion arranged at the opposite end, a power generation system that can be arranged above the water surface being able to be connected to the connecting portion of the tower; and at least one restoring element, the at least one restoring element being able to be connected to the tower directly or indirectly via one or more transition pieces, wherein a natural frequency of the offshore structure lies below an excitation component one times the rotational frequency 1P of at least one exciting component, wherein the natural frequency of the offshore structure lies below a frequency of 0.15 Hz, in particular below a frequency of 0.10 Hz, and wherein the at least one restoring element is designed in such a way that, in the case of a skewed position of the tower, in which the direction of longitudinal extending axis of the tower extends outside of a vertically extending axis, tensile and/or compressive forces can be transferred to the tower by means of the at least one restoring element such that the tower can be straightened up.

2. The foundation according to claim 1, wherein the anchoring portion of the tower that can be anchored in the seabed, engages in the seabed, wherein in the skewed position of the tower the anchoring portion of the tower engaging in the seabed can be moved in the seabed.

3. The foundation according to claim 2, wherein the skewed position of the tower relative to the sea bed, which occurs in a limit state of the load-bearing capacity of the foundation, is greater than 0.10°, in particular greater than 0.20° and in particular greater than 0.5°, and the skewed position after a cyclic loading is greater than 0.05°.

4. The foundation according to claim 1, wherein an upper portion of the tower is movable relative to the anchoring portion of the tower, wherein in the case of a skewed position of the tower, the anchoring portion in the seabed remains substantially in its position.

5. The foundation according to claim 1, wherein the anchoring portion of the tower is essentially hollow cylindrical.

6. The foundation according to claim 4, wherein the upper portion of the tower is movably mounted at least partially within and in a receiving area of the anchoring portion of the tower, wherein in particular the anchoring portion of the tower in the receiving area is filled with a filling material.

7. The foundation according to claim 4, wherein the upper portion of the tower extends conically from the tower within the receiving area of the anchoring portion.

8. The foundation according to claim 4, wherein the receiving area of the anchoring portion of the tower has at least one spring and/or damping element, so that when the upper portion of the tower moves relative to the anchoring portion of the tower, the upper portion of the tower can be sprung and/or damped.

9. The foundation according to claim 1, wherein the at least one restoring element comprises at least one buoyancy body or is designed as at least one buoyancy body, wherein in particular the at least one buoyancy body has a substantially conical or curved geometry.

10. The foundation according to claim 9, wherein the at least one buoyancy body is arranged below the water surface and at least partly surrounding the tower in a horizontal plane.

11. The foundation according to claim 1, wherein the at least one restoring element comprises one or more anchors, the one or more anchors being connectable to the seabed and being connected to the tower in each case by means of a flexible connection, which, when the tower is in a skewed position, generate a restoring tensile and/or compressive force in the opposite direction to the skewed position by tightening the flexible connection.

12. The foundation according to claim 1, wherein the at least one restoring element comprises one or more stabilizing arrangements or is designed as one or more stabilizing arrangements, preferably the one or more stabilizing arrangements being extendable from the tower, or preferably being integrated gyro stabilizers.

13. The foundation according to claim 1, wherein the center of gravity of the offshore structure is designed in such a way that fractions of a ground dead weight and ground friction forces of the seabed to be overcome are below the center of gravity of a liquid displaced by the foundation.

14. An offshore structure comprising a foundation according to claim 1.

Description

BRIEF DESCRIPTION OF THE DRAWING

(1) In the figures:

(2) FIG. 1 is a schematic illustration of an offshore structure comprising a foundation according to example embodiments;

(3) FIG. 2 is a schematic and detailed illustration of an offshore structure comprising a foundation according to example embodiments;

(4) FIGS. 3a-d are respective further schematic and detailed illustrations of an offshore structure comprising a foundation according to example embodiments;

(5) FIG. 4 is a frequency spectrum diagram;

(6) FIG. 5 is a block diagram of an example embodiment of an apparatus, which in particular can execute an exemplary method according to the second aspect; and

(7) FIG. 6 provides different example embodiments of storage media on which an example embodiment of a computer program can be stored.

DETAILED DESCRIPTION OF SOME EXEMPLARY EMBODIMENTS

(8) FIG. 1 shows a schematic illustration of an offshore structure 1, which is at least partially founded on the seabed 2 by means of a foundation according to the invention.

(9) The offshore structure 1 is a wind turbine, comprising a tower 2, on which at its upper end a power generation system (e.g. a turbine, not shown in the schematic drawing in FIG. 1) with three exciting components, in this case three rotor blades 5, is arranged.

(10) Tower 2 is divided into an anchoring portion 3 and an upper portion 4 above it. Anchoring portion 3 is anchored in the seabed M in this case. Furthermore, the tower comprises a restoring element, in this case an essentially conical-shaped buoyancy body 6, which surrounds the cylindrical tower 2.

(11) In addition to its function of providing lift for the wind turbine, the buoyancy body 6 also ensures that, in the event of a skewed position of tower 2 outside a vertically extending axis V, tensile and/or compressive forces can be transferred to tower 2 by the buoyancy body 6, so that tower 2 straightens up again after a skewed position and thus the direction of longitudinal extending axis of tower 2 is again essentially on the vertically extending axis V. For this, the buoyancy body 6 is located below the water surface S.

(12) Tower 2 is partly founded in the seabed M, and partly it is floating by means of the buoyancy body 6, so it is a “half-floating foundation”.

(13) The offshore structure 1, which is founded with a foundation according to the invention, has a natural frequency that lies below an exciting component one times the rotational frequency 1P of the three rotor blades 5 of the power generation system.

(14) The design of the low natural frequency of offshore structure 1 is made possible by the fact that offshore structure 1 is anchored to the seabed M at a low integration depth. Correspondingly, the anchoring of anchoring portion 3 in the seabed M alone cannot completely guarantee the stability of the offshore structure against tipping. The same can happen if the seabed M in which the anchoring portion 3 is anchored is soft, e.g. if it is a (strongly) water-saturated ground. The tilting stability is guaranteed by the restoring element, in this case the buoyancy body 6 which surrounds the tower 2.

(15) FIG. 2 shows a and detailed illustration of an offshore structure 1, which in contrast to FIG. 1 comprises at least two buoyancy bodies 6, each of which is connected to the tower 2 of offshore structure 1 via a transition piece 10 (e.g. an arm). The buoyancy bodies 6 both float on the water surface S with an orientation of the tower 2, wherein the longitudinal direction of the tower 2 is essentially parallel to the vertical extending axis V.

(16) The anchoring portion 3 of tower 2 is movable within the seabed M when the tower is tilted, as shown schematically in FIG. 2 by the dotted tilting of Tower 2. In the tilted position, the longitudinal direction of tower 2 is outside the vertical extending axis V. If a skewed position of tower 2 occurs, at least one of the two buoyancy bodies at hand is immersed in the water surrounding the tower 2. The submerged buoyancy body 6 now generates a tensile and/or compressive force, which acts in the opposite direction of the skewed position of the tower 2. Tower 2 will then straighten up again.

(17) The anchoring portion 3 of the tower 2, which penetrates the seabed M, can move in the direction of two degrees of freedom within the seabed M. For example, if the tower 2 is in a skewed position, e.g. caused by tilting of the tower 2 or by sea and/or wind load in at least one rotor blade of a power generation system located at the top of the tower (not shown in FIG. 2), such a movement of the anchoring portion 3 of the tower 2 can occur in at least one direction within these two degrees of freedom.

(18) FIG. 3a shows a further schematic and detailed illustration of an offshore structure 1, wherein an upper portion 4 of tower 2 of the offshore structure can be moved in the direction of at least two degrees of freedom within the anchoring portion 3 of the tower 2.

(19) In addition, the upper portion 4 of tower 2 is rotatable relative to the anchoring portion 3 of the tower 2. This is indicated schematically by the double arrow D.

(20) The upper portion 4 of tower 2 engages with a tapered end 9 comprised by it in a receiving area of the anchoring portion 3. This receiving area can be filled, for example, with an elastic filling material 7, such as an elastomer, polymer, sand-clay, sand-clay mixture, to name but a few non-limiting examples.

(21) In addition, the anchoring portion 3 of the tower 2 comprises optional string and/or dampening elements 8 which can spring or damp a skewed position of the tower 2, wherein the upper portion 4 is e.g. tilted in relation to the anchoring portion 3. In addition, by means of the optional string and/or dampening elements 8, a restoring tensile and/or compressive force can be produced when the upper portion 4 of the tower 2 is tilted, which can lead to the upper portion 4 of the tower 2 straightening up after the upper portion 4 of the tower has been tilted.

(22) The anchoring portion 3 of the tower 2 can be open at the bottom, as shown here, so that the anchoring portion 3 can be safely anchored in the seabed M.

(23) FIG. 3b shows an anchor device 11, which is used as at least one restoring element in the present situation. A weight element 11a is located below the anchoring portion 3 in the seabed M. An anchor rope 11c connects the weight element 11a with a connecting element 11b located inside the upper portion 4 of the tower 2. In the event of a skewed position of the upper portion 4 of tower 2, the anchoring device 11 generates a restoring tensile and/or compressive force which causes the upper portion 4 of tower 2 to straighten up. A skewed position is shown schematically by the dotted tilted tower 2.

(24) In FIG. 3c the anchoring portion 3 is filled with a filled or grouted volume. This is, for example, a cement suspension enriched, for example, with heavy aggregates and/or comprising steel chips or the like, to name but a few non-limiting examples.

(25) In FIG. 3d the anchoring portion 3 of the tower 2 comprises one or more openings 12a. Through these openings 12a, which are located, for example, in a detached area surrounding the anchoring portion 3 in the seabed M, one or more restoring tensile and/or compressive forces can be generated by hydrostatic suction forces. These can be generated and/or amplified, for example, by active pumping, presently with pump 13. The pump 13 is connected to the openings 12a via one or more pump pipings 13a.

(26) By active pumping or by active pumping of ballast water, a shift of weight can be generated, so that the corresponding restoring forces can be generated if the tower 2 is tilted. Anchoring portion 3, for example, has openings 12a surrounding it at regular intervals. Depending on the skewed position, for example, ballast water can be pumped through one or more openings 12a (simultaneously), so that a corresponding restoring force can be generated by the following directional force, which counteracts the skewed position of tower 2.

(27) FIG. 4 shows a frequency spectrum diagram, in which exciting component frequencies during operation of a wind turbine are shown.

(28) As already described, for the determining of a natural frequency of an overall system (offshore structure, in particular wind turbine) comprising a foundation that comprises a tower and a power generation system (e.g. with one or more rotor blades), areas within a frequency spectrum can be defined in advance in which the natural frequency should be lying.

(29) For example, a wind turbine experiences a (dynamic) exciting component during operation, in particular from wind loads, from a periodic exciting component with one times the rotational frequency (rotor frequency, 1P exciting component; caused, for example, by imbalances which occur during the rotation of the rotor blades), as well as from a further periodic exciting component from the rotor blade passage with the three times the rotational frequency (3P exciting component; caused, for example, by an inflow of the rotor blade with wind, wherein the rotor blade is located directly in front of the tower).

(30) Furthermore, FIG. 4 shows the so-called JONSWAP spectrum, which represents the wave energy spectrum caused by the sea state in the case of offshore structures and which can also cause an exciting component which the offshore structure has to handle.

(31) The closer the natural frequency of the wind turbine is to these exciting component frequencies, the higher the stress on the mechanical components and the tower can be.

(32) If the first natural frequency of the offshore structure is below the frequency three times the rotational frequency 3P, the design of the offshore structure is referred to as “soft-stiff” (range “target frequency” in FIG. 4). If the design of the offshore structure is also above the frequency of three times the rotational frequency 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 one times the rotational frequency 1P, the design is called “soft-soft”.

(33) It will be understood that when designing the natural frequency of an offshore structure, a design of the natural frequency that lies within the 1P and/or 3P frequency band should be avoided to avoid premature material fatigue and wear.

(34) FIG. 5 shows a block diagram of an example embodiment of an apparatus 500, which can in particular execute an exemplary method according to the second aspect. For example, apparatus 500 is an apparatus according to the third aspect or a system according to the fourth aspect.

(35) Apparatus 500 can therefore be, for example, a computer, a desktop computer, a server, a thin client or a portable computer (mobile device), such as a laptop computer, a tablet computer, a personal digital assistant (PDA) or a smartphone. For example, the apparatus can perform the function of a server or a client.

(36) Processor 510 of the apparatus 500 is in particular designed as a microprocessor, microcontroller, microcontroller, digital signal processor (DSP), application specific integrated circuit (ASIC) or field programmable gate array (FPGA).

(37) Processor 510 executes program instructions stored in program memory 512 and stores, for example, intermediate results or the like in main or working memory 511. For example, program memory 512 is a non-volatile memory such as flash memory, magnetic memory, EEPROM (Electrically Erasable Programmable Read-Only Memory) and/or optical memory. Main memory 511 is for example a volatile or non-volatile memory, in particular a Random Access Memory (RAM) such as a static RAM memory (SRAM), a dynamic RAM memory (DRAM), a ferroelectric RAM memory (FeRAM) and/or a magnetic RAM memory (MRAM).

(38) Program memory 512 is preferably a local data carrier permanently connected to the apparatus 500. Examples of media that are fixed to the apparatus 500 are hard disks that are built into the apparatus 500. Alternatively, the data carrier may, for example, be a data carrier separable connectable to the apparatus 500, such as a memory stick, a removable data carrier, a portable hard disk, a CD, a DVD and/or a floppy disk.

(39) For example, program memory 512 contains the operating system of apparatus 500, which is at least partially loaded into main memory 511 when apparatus 500 is started and is executed by processor 510. In particular, when apparatus 500 is started, at least part of the core of the operating system is loaded into main memory 511 and executed by processor 510. For example, the operating system of apparatus 500 is a Windows, UNIX, Linux, Android, Apple iOS and/or MAC operating system.

(40) In particular, the operating system allows the use of apparatus 500 for data processing. For example, it manages resources such as main memory 511 and program memory 512, communication interface 513, input/output device 514, provides basic functions to other programs via programming interfaces and controls the execution of programs.

(41) Processor 510 controls communication interface 513, which can be a network interface, for example, and can be designed as a network card, network module and/or modem. The communication interface 513 is designed in particular to connect the apparatus 500 to other devices, in particular via a (wireless) communication system, such as a network, and to communicate with them. The communication interface 513 can, for example, receive data (via the communication system) and forward it to processor 510 and/or receive data from processor 510 and send it (via the communication system). Examples of a communication system are a Local Area Network (LAN), Wide Area Network (WAN), Wireless Network (for example, according to the IEEE 802.11 standard, the Bluetooth (LE) standard and/or the NFC standard), wired network, mobile network, telephone network and/or the Internet.

(42) Furthermore, processor 510 can control at least one input/output device 514. For example, input/output device 514 is a keyboard, mouse, display unit, microphone, touch-sensitive display unit, speaker, reader, drive and/or camera. For example, input/output device 514 can receive input from a user and forward it to processor 510 and/or receive and output information for the user from processor 510.

(43) Finally, FIG. 6 shows different examples of storage media on which an example of a computer program can be stored. The storage medium can be, for example, a magnetic, electrical, optical and/or other type of storage medium. The storage medium may be part of a processor (e.g. the processor 510 in FIG. 5), for example, a (non-volatile or volatile) program memory of the processor or a part of it (like program memory 512 in FIG. 5). Examples of a storage medium are a flash memory 610, an SSD hard disk 611, a magnetic hard disk 612, a memory card 613, a memory stick 614 (e.g. a USB stick), a CD-ROM or DVD 615 or a floppy disk 616.

(44) The following example embodiments should also be understood to be disclosed:

Embodiment 1

(45) A method for designing a foundation of an offshore structure, comprising: Determining a natural frequency of the offshore structure comprising a foundation (e.g. according to one of the methods described herein; and optionally e.g. a power generation system), such that the natural frequency lies below an exciting component one times the rotational frequency 1P of at least one exciting component; wherein the determining of the natural frequency is iteratively based at least partially on changing parameters of the foundation.

Embodiment 2

(46) The method according to embodiment 1, wherein the respectively changing parameters comprise one or more of the following parameters i) to viii):

(47) (i) water depth at the site of the offshore structure;

(48) (ii) weight of power generation system;

(49) (iii) weight of tower;

(50) (iv) total weight of the offshore structure;

(51) (v) vertical stability;

(52) (vi) Stability buoyancy;

(53) (vii) restoring forces; and

(54) (viii) costs of the offshore construction.

Embodiment 3

(55) The method according to embodiment 1 or embodiment 2, wherein the method is carried out by at least one apparatus.

Embodiment 4

(56) An apparatus which is arranged or comprises corresponding means for performing and/or controlling a method according to one of the embodiments 1 to 3.

Embodiment 5

(57) A computer program comprising program instructions which cause a processor to execute and/or control a method according to any one of embodiments 1 to 3 when the computer program is executed on the processor.

Embodiment 6

(58) A system, comprising:

(59) a plurality of apparatus which together perform a method according to one of the embodiments 1 to 3.

(60) The example embodiments of the present invention described in this specification and the optional features and characteristics mentioned in each case in this respect should also be understood as disclosed in all combinations with each other. In particular, unless explicitly stated otherwise, the description of a feature covered by an example embodiment should not be understood in the present case as meaning that the features is essential or essential for the function of the embodiment. The sequence of the method steps described in this specification is not mandatory, alternative sequences of method steps are conceivable. The method steps can be implemented in different ways, e.g. implementation in software (by program instructions), hardware or a combination of both to implement the process steps.

(61) Terms used in the claims such as “comprise”, “have”, “include”, “contain” and the like do not exclude further elements or steps. The expression “at least partially” covers both the “partially” and the “fully” case. The expression “and/or” should be understood as meaning that both the alternative and the combination should be disclosed, i.e. “A and/or B” means “(A) or (B) or (A and B)”. The use of the indefinite article does not exclude a plural. A single apparatus can perform the functions of several units or devices mentioned in the claims. Reference signs indicated in the claims are not to be regarded as limitations of the means and steps used.

(62) All references, including publications, patent applications, and patents cited herein are hereby incorporated by reference to the same extent as if each reference were individually and specifically indicated to be incorporated by reference and were set forth in its entirety herein.

(63) The use of the terms “a” and “an” and “the” and similar referents in the context of describing the invention (especially in the context of the following claims) is to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. The terms “comprising,” “having,” “including,” and “containing” are to be construed as open-ended terms (i.e., meaning “including, but not limited to,”) unless otherwise noted. Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., “such as”) provided herein, is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention unless otherwise claimed. No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the invention.

(64) Preferred embodiments of this invention are described herein, including the best mode known to the inventors for carrying out the invention. Variations of those preferred embodiments may become apparent to those of ordinary skill in the art upon reading the foregoing description. The inventors expect skilled artisans to employ such variations as appropriate, and the inventors intend for the invention to be practiced otherwise than as specifically described herein. Accordingly, this invention includes all modifications and equivalents of the subject matter recited in the claims appended hereto as permitted by applicable law. Moreover, any combination of the above-described elements in all possible variations thereof is encompassed by the invention unless otherwise indicated herein or otherwise clearly contradicted by context.