Systems, apparatus and methods for motion damping of floating offshore structures and uses of such systems

Abstract

A system (10), an apparatus (1) and a method for damping motion of a floating offshore structure (12). Uses of the system are also disclosed. The system comprises at least one damping device (20) configured to damp motion in one direction and allow motion in the opposite direction, and a suspension device (30) with a respective wire (32) configured to suspend the at least one damping device from the floating offshore structure at a suspension depth in the water, the damping devices (20) being oriented such that a damping force induced by the damping device is exerted upon elongation of the wire. Also, each damping device (20) is a passive damping device with a valve structure (62) configured to damp motion in one direction and allow motion in the opposite direction substantially without damping interaction.

Description

[Technical field]

[0001] The present invention relates to a system, an apparatus and a method for motion damping of a floating offshore structure.The present invention also relates to the use of the system for motion damping of a floating offshore structure. [Background technology]

[0002] Prior art systems for motion damping of floating offshore structures are used to keep the floating offshore structure relatively stable when subjected to waves and wind, for example by reducing the heel and pitch motions of an offshore wind power plant, thereby improving power generation efficiency.

[0003] A problem with prior art systems for motion damping of floating offshore structures is that in the event of unusually severe weather conditions, the damping devices of the system and the system as a whole can be highly stressed, potentially leading to permanent failure of the system. It has proven difficult to provide a system capable of withstanding such unusually severe weather conditions. Summary of the Invention [Problem to be solved by the invention]

[0004] The present invention is now disclosed, the object of which is to ameliorate or reduce at least one of the disadvantages of the known prior art, or at least to provide a useful alternative to the known prior art. In particular, it is an object of the present invention to provide a system for motion damping of floating offshore structures with improved resistance to unusually severe weather conditions. This object is achieved by the features set out in the following description and in the appended claims. The invention is defined by the independent claims, the dependent claims defining advantageous embodiments of the invention. [Means for solving the problem]

[0005] According to one aspect of the present invention, there is provided a system for motion damping of a floating offshore structure, the system comprising: at least one damping device configured to damp motion in one direction and allow motion in an opposite direction substantially without damping interaction; a suspension system comprising a respective wire configured to suspend at least one damping device suspended from the floating offshore structure at a suspension depth in the water, the at least one damping device being oriented such that a damping force induced by the at least one damping device is exerted upon elongation of the wire; Equipped with.

[0006] Also, each damping device is a passive damping device comprising a valve structure configured to damp motion in one direction and allow motion in the opposite direction substantially without damping interaction, the valve structure configuration being provided with slits configured to prevent water from passing in one direction and substantially allow water to pass in the other direction.

[0007] At least one damping device performs the function of a check valve, i.e., the damping device damps motion in one direction by preventing or substantially preventing water from passing through the damping device, and allows motion in the opposite direction substantially without damping interaction by allowing water to pass through the damping device. Passive damping devices also have the advantage that they function without being controlled.

[0008] The suspension arrangement of the system is configured to suspend at least one damping device in the water by wires from the floating offshore structure, the at least one damping device being connected such that an induced damping force is exerted on the wires upon elongation, thereby damping motion of the floating offshore structure. The system ensures that the floating offshore structure remains relatively stable when subjected to waves and wind.

[0009] The suspension system may include a wire control device configured to control a suspension depth of the at least one damping device in the water. The forces on the at least one damping device depend on the depth of the damping device in the water. At greater depths, wave interactions and turbulent water motions are less than when the damping device is located closer to the water surface. This results in a damping force induced by the at least one damping device being greater at a deeper location compared to a location closer to the water surface. Correspondingly, however, stresses on the at least one damping device are also greater at a deeper location compared to a location closer to the water surface. By adjusting the depth of the at least one damping device by the wire control device, the forces and stresses on the system can be reduced by raising the at least one damping device in the case of abnormally severe weather conditions. This provides a system for motion damping of a floating offshore structure with less forces and stresses on the system in the case of abnormally severe weather conditions.

[0010] According to one embodiment of the present invention, the suspension device comprises a control unit configured to receive information regarding the motion of the floating offshore structure and to control the suspension depth of at least one damping device in water by means of a wire control device depending on said information.

[0011] The control unit is configured to receive information regarding the motion of the floating offshore structure and determine a desired depth of the at least one damping device based on the information, and based on the determined desired depth of the at least one damping device, the control unit is configured to transmit control information to the wire control device.

[0012] The control unit comprises computing means, for example a central processing unit (CPU), and further comprises means for receiving information on the motion of the floating offshore structure, such as sensor information from a motion sensor, and means for generating control information for controlling the suspension depth of the at least one damping device in the water.

[0013] According to one embodiment of the present invention, the suspension device comprises at least an upper position and a lower position of at least one damping device, and the control unit is configured to determine at least the upper position and the lower position based on information on the motion of the floating offshore structure and to transmit control information to the wire control device based on the determined at least the upper position or the lower position.

[0014] According to one embodiment of the invention, the control unit is configured to determine at least an upper position and a lower position such that the stress on the system does not exceed a threshold value, the threshold value being related to a stress the system is configured to withstand.

[0015] According to one embodiment of the invention, the control unit is configured to continuously determine at least the upper and lower positions.

[0016] According to one embodiment of the invention, the control unit is configured to determine at least the upper and lower positions at intermittent intervals.

[0017] According to an embodiment of the present invention, the wire control device comprises a respective remotely controllable winch for at least one damping device configured to control said suspension depth of at least one damping device in water, and a control unit configured to transmit control information to the respective winch based on information about the movement of the floating offshore structure for setting said suspension depth of at least one damping device in water. The winch is configured to be attached to the floating offshore structure and comprises a wire drum around which a wire is wound or unwound.

[0018] According to one embodiment of the invention, the information relating to the motion of the floating offshore structure includes information relating to the heave and pitch of the floating offshore structure, and the control unit is configured to determine at least the upper and lower positions based on a function of the heave and pitch information of the floating offshore structure.

[0019] According to one embodiment of the invention, the information relating to the motion of the floating offshore structure further includes information relating to swell, roll, roll and yaw, and the control unit is configured to determine at least the upper and lower positions based on a function of the heave and pitch information of the floating offshore structure together with at least one of the information relating to the swell, roll, roll and yaw of the floating offshore structure.

[0020] According to one embodiment of the invention, the suspension device comprises a motion sensor at or in the vicinity of the floating offshore structure configured to provide said motion information to a control unit, the control unit being configured to determine a desired suspension depth of the at least one damping device based on said motion information.

[0021] According to one embodiment of the invention, the motion sensor is one of an angular rate sensor and a gyroscope.

[0022] According to one embodiment of the present invention, the suspension system includes continuous positions between at least an upper position and a lower position of the at least one damping device, and the control unit is configured to determine any position between and including the upper and lower positions of the at least one damping device.

[0023] The upper, lower and further positions in between keep the damping sufficiently high without exceeding threshold stresses on the system, thus allowing the system to use higher damping depending on weather conditions.

[0024] According to one embodiment of the invention, the suspension device comprises a spacer element connected to the floating offshore structure and configured to hold the at least one damping device at a distance from the floating offshore structure.

[0025] According to one embodiment of the invention, the system comprises two or more damping devices arranged symmetrically around the floating offshore structure. The use of multiple damping devices provides uniform motion damping of the floating offshore structure.

[0026] According to one embodiment of the invention, each damping device comprises a parabolic support structure including a valve structure and a plurality of openings.

[0027] According to another aspect of the invention there is provided an apparatus for motion damping of a floating offshore structure, the apparatus comprising a floating offshore structure and a system according to any of the above embodiments mounted on the floating offshore structure.

[0028] According to one embodiment of the present invention, the floating marine structure is a spar structure.

[0029] According to one embodiment of the invention, a floating offshore structure comprises a tower supporting a wind turbine.

[0030] According to a further aspect of the present invention there is provided a method for motion damping of a floating offshore structure using a system according to any of the above embodiments, the method comprising: receiving information relating to a motion of the floating offshore structure; determining a suspension depth of at least one damping device based on said information; setting at least one damping device to the determined depth by a wire control device; Includes.

[0031] According to another aspect of the invention there is provided a use of a system according to any of the above embodiments for motion damping of a floating offshore structure.

[0032] Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which: [Brief description of the drawings]

[0033] [Figure 1a] 1 is a perspective view of an apparatus and system for motion damping of a floating offshore structure according to one embodiment of the present invention; FIG. [Figure 1b] FIG. 1b is a schematic side view of the device and system of FIG. [Figure 2a] FIG. 2 is a perspective view of a damping device for the device and system of FIGS. 1a and 1b. [Figure 2b] FIG. 2b is a side view of the damping device of FIG. 2a. [Diagram 3] 1 is a flow diagram of a method for motion damping of a floating offshore structure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0034] The drawings are shown in a schematic and simplified manner, and features that are not necessary to explain the invention may be omitted. The same reference numbers refer to the same or similar features in the drawings. The various features shown in the drawings may not necessarily be drawn to scale.

[0035] Figures 1a and 1b show an apparatus 1 and a system 10 for motion damping of a floating offshore structure 12. The apparatus 1 comprises a floating offshore structure 12 and a system 10 mounted to the floating offshore structure 12.

[0036] The floating offshore structure 12 may comprise, for example, a tower for supporting a wind turbine. In the embodiment disclosed in Figures 1a-b, the floating offshore structure 12 comprises a spar structure. However, it should be understood that the system 10 may be used for motion damping of various types of floating offshore structures.

[0037] The system 10 is configured to damp the motion of the floating offshore structure 12 when subjected to waves and wind, thereby reducing heel and pitch motions and maintaining the floating offshore structure 12 in a relatively stable upright position, which is advantageous for the power generation efficiency of, for example, a wind power plant.

[0038] The system 10 includes at least one damping device 20, such as a passive damping device, configured to damp motion in one direction and allow motion in the opposite direction substantially without damping interaction. In the disclosed embodiment, six damping devices 20 are symmetrically positioned about the floating offshore structure 12. By symmetrically positioning multiple damping devices 20 about the floating offshore structure 12, motion damping is evenly distributed around the floating offshore structure 12.

[0039] It should be understood that any number of damping devices 20 is applicable, however, in continuing the description of the present invention, damping devices 20 will be described in plural.

[0040] The system 10 further comprises a suspension arrangement 30 for suspending the damping device 20 in the water. The suspension arrangement 30 comprises respective wires 32 and spacer elements 34 for holding the damping device 20 suspended at a distance from the floating offshore structure 12. The wires are, for example, steel wires configured for marine use. In the disclosed embodiment, the spacer elements 34 comprise ring-shaped elements attached to the floating offshore structure 12.

[0041] A damping device 20 is attached to the end of each wire 32 such that a damping force is induced upon stretching of the wire 32. Thus, upward motion is damped, while downward motion is substantially free of interaction with the damping device 20. In this way, the system 10 improves the stability of the floating offshore structure 12.

[0042] The suspension system 30 further comprises a wire control device 40 configured to control the suspension depth of the damping device 20 in water between at least an upper position and a lower position. Preferably, the wire control device 40 is configured to set the damping device 20 in an upper position, a lower position, and a position between the upper and lower positions.

[0043] The wire control device 40 comprises, for example, a respective remotely controllable winch 42 for the damping device 20 configured to control the suspension depth of the damping device 20 in water.

[0044] The suspension system 30 further comprises a control unit 50 and a motion sensor 52 of the floating offshore structure 12 configured to provide motion information to the control unit 50. The control unit 50 is configured to determine a desired suspension depth of the damping system 20 based on the motion information. In the disclosed embodiment, the control unit 50 and the motion sensor 52 are located in close proximity to each other. However, it should be understood that the control unit 50 and the motion sensor 52 may be located at different locations. The motion sensor 52 is configured to transfer the sensor information to the control unit 50.

[0045] The motion sensor 52 is configured to sense the heave and pitch of the floating offshore structure 12 or any entity dependent thereon. Preferably, the motion sensor 52 is further configured to sense the swell, roll, roll and yaw of the floating offshore structure 12 or any entity dependent thereon. The motion sensor 52 is, for example, an angular rate sensor or a gyroscope.

[0046] The forces on the damping device 20 depend on the depth to which it is suspended in the water. At greater depths, wave interactions and turbulent water motion are less than closer to the water surface. Thus, the damping device 20 provides a higher degree of damping when placed at greater depths compared to closer to the water surface. However, correspondingly, the greater depth of the damping device 20 also results in higher stresses on the system 10 compared to when the damping device 20 is placed closer to the water surface.

[0047] According to one embodiment of the present invention, the control unit 50 is configured to determine a desired suspension depth of the damping device 20 in water based on the motion information such that the stress on the system 10 does not exceed a threshold. The threshold corresponds, for example, to a design allowable stress level on the system 10. Based on the determined desired suspension depth of the damping device 20, the control unit 50 generates control information to the wire control device 40.

[0048] Figures 2a and 2b show an example of a damping device 20 for the device 1 and system 10 of Figures 1a and 1b. The damping device 20 is a passive damping device and has the function of a check valve.

[0049] The damping device 20 includes a parabolic support structure 60 including a valve structure 62 and a plurality of openings 64. The valve structure 62 includes slits configured to prevent water from passing in one direction and substantially allow water to pass in the other direction. The support structure 60 further includes a shaft 66 configured to be attached to each of the wires 32 of the system 10.

[0050] FIG. 3 discloses a flow diagram of a method for motion damping of a floating offshore structure 12.

[0051] The method includes, at step 110, receiving information relating to the motion of the floating offshore structure 12. The information may be generated by, for example, the motion sensor 52 and received by the control unit 50.

[0052] In step 120, the method includes determining a desired suspension depth of the damping device 20 based on the received information. The information may be, for example, the heave and pitch of the floating offshore structure 12. Alternatively, the information may include information regarding the swell, roll, roll, and yaw of the floating offshore structure 12.

[0053] In step 130, the method includes setting the attenuation device 20 to the determined depth by the wire control device 40. The steps of the method are configured to be repeated continuously.

[0054] Generally, terms used in the present specification and claims are to be interpreted according to their ordinary meaning in the art unless expressly defined otherwise. Nevertheless, the terms "comprises" and "comprising" and variations thereof mean that the specified features, steps or integers are included. These terms are not to be interpreted to exclude the presence of other features, steps or integers. Furthermore, the indefinite article "a" or "an" is openly interpreted as introducing at least one instance of an entity unless expressly stated otherwise. An entity introduced by an indefinite article is not excluded from being interpreted as a plurality of entities.

[0055] The features disclosed in the foregoing description, or in the following claims, or in the accompanying drawings, and expressed in their specific form, or as means for performing a disclosed function, or as methods or processes for obtaining a disclosed result, can, where appropriate, be utilized separately or in any combination of such features to realize the invention in diverse forms thereof.

[0056] Although the present invention has been described in relation to the above-mentioned embodiments, many equivalent modifications and variations will become apparent to those skilled in the art given this disclosure. Accordingly, the above-described embodiments of the present invention are considered to be illustrative and not limiting. Various changes can be made to the described embodiments without departing from the scope of the present invention, as defined in the appended claims.

Claims

1. A system (10) for motion damping of a floating offshore structure (12), comprising: at least one damping device (20) configured to damp motion in one direction and allow motion in the opposite direction without damping interaction; a suspension system (30) comprising respective wires (32) configured to suspend the at least one damping device (20) suspended from the floating offshore structure (12) at a suspension depth in the water, the at least one damping device (20) being oriented such that a damping force induced by the at least one damping device (20) is exerted upon elongation of the wires (32); A system (10) comprising: a passive damping device, each damping device (20) comprising a valve structure (62) configured to damp motion in one direction and allow motion in the opposite direction without damping interaction, characterized in that the valve structure (62) is provided with slits configured to prevent water from passing in one direction and to allow water to pass in the other direction; System (10).

2. 2. The system (10) of claim 1, wherein the suspension device (30) comprises a wire control device (40) configured to control the suspension depth of the at least one damping device (20) in water.

3. 3. The system (10) of claim 2, characterized in that the suspension device (30) comprises a control unit (50) configured to receive information regarding the motion of the floating offshore structure (12), determine a desired depth of the at least one damping device (20), and transmit control information to the wire control device (40) such that the suspension depth of the at least one damping device (20) in the water is controlled by the wire control device (40) based on the determined desired depth.

4. 4. The system (10) of claim 3, wherein the suspension device (30) includes at least an upper position and a lower position of the at least one damping device (20), and the control unit (50) is configured to determine the at least upper and lower positions based on information about the motion of the floating offshore structure (12) and to transmit control information to the wire control device (40) based on the determined at least upper or lower position.

5. 5. The system (10) of claim 4, wherein the control unit (50) is configured to determine the at least upper position and the lower position such that a stress on the system (10) does not exceed a threshold value.

6. 6. The system (10) according to claim 4 or 5, characterized in that the control unit (50) is configured to continuously determine the at least upper and lower positions.

7. 7. The system (10) according to any one of claims 3 to 6, wherein the wire control device (40) comprises a respective remotely controllable winch for the at least one damping device (20) configured to control the suspension depth of the at least one damping device (20) in water, and the control unit (50) is configured to transmit control information to the respective winch based on the information regarding the movement of the floating offshore structure (12) for setting the suspension depth of the at least one damping device (20) in water, The system (10) is configured to be attached to the floating marine structure (12), the winch comprising a wire drum about which the wire (32) is wound or unwound.

8. 8. The system (10) according to any one of claims 3 to 7, characterized in that the information relating to the motion of the floating offshore structure (12) comprises information about heave and pitch of the floating offshore structure (12), and the control unit (50) is configured to determine the at least upper and lower positions based on a function of the heave and pitch information of the floating offshore structure (12).

9. 9. The system (10) according to any one of claims 3 to 8, characterized in that the information relating to the motion of the floating offshore structure (12) further comprises information on swell, roll, roll and yaw, and the control unit (50) is configured to determine the at least upper and lower positions based on a function of heave and pitch information of the floating offshore structure (12) together with at least one of information on swell, roll, roll and yaw of the floating offshore structure (12).

10. 10. The system (10) according to any one of claims 3 to 9, characterized in that the suspension device (30) comprises a motion sensor (52) on the floating offshore structure (12) configured to provide information regarding the motion of the floating offshore structure (12) to the control unit (50), and the control unit (50) is configured to determine a desired suspension depth of the at least one damping device (20) based on the information regarding the motion of the floating offshore structure (12).

11. 11. The system (10) of claim 10, wherein the motion sensor (52) is one of an angular rate sensor and a gyroscope.

12. 12. The system (10) according to any one of claims 3 to 11, characterized in that the suspension (30) includes continuous positions between at least an upper position and a lower position of the at least one damping device (20), and the control unit (50) is configured to determine any position of the at least one damping device (20) between the upper position and the lower position, including the upper position and the lower position.

13. 13. The system (10) according to any one of claims 1 to 12, characterized in that the suspension device (30) comprises a spacer element (34) connected to the floating offshore structure (12) and configured to maintain the at least one damping device (20) at a distance from the floating offshore structure (12).

14. 14. The system (10) according to any one of claims 1 to 13, comprising two or more damping devices (20) symmetrically arranged around the floating offshore structure (12).

15. 15. The system (10) of any one of claims 1 to 14, wherein each damping device (20) comprises a parabolic support structure (60) including the valve structure (62) and a plurality of openings (64).

16. 16. An apparatus (1) for motion damping of a floating offshore structure (12), characterized in that it comprises a system (10) according to any one of claims 1 to 15 mounted on said floating offshore structure (12).

17. 17. The apparatus (1) according to claim 16, characterized in that the floating offshore structure (12) is a spar structure.

18. 18. Apparatus (1) according to claim 16 or 17, characterized in that the floating offshore structure (12) comprises a tower carrying a wind turbine.

19. A method for motion damping of a floating offshore structure (12) by a system (10) according to any one of claims 2 to 12, comprising the steps of: receiving information relating to the movement of the floating offshore structure (12); determining a suspension depth of the at least one damping device (20) based on the information; setting said at least one attenuation device (20) to said determined depth by said wire control device (40); A method comprising:

20. Use of a system (10) according to any one of claims 1 to 15 for the damping of motions of a floating offshore structure (12).

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