Minimizing the movement of offshore wind turbines

Abstract

Disclosed herein are techniques for minimizing the motion of offshore wind turbines. Using the described techniques, wind turbines can be attached to offshore platforms that are constructed and positioned to reduce environmental loads (e.g., wind, waves, etc.) on the platform in both shallow and deep waters. In some configurations, a full restraining platform (FRP) is configured to support the wind turbine. According to some examples, moorings are attached to the FRP and / or the structure of the wind turbine structure to reduce six degrees of freedom motion.

Description

Technical Field

[0001] Cross - reference to Related Applications This application claims priority to U.S. Provisional Patent Application No. 63 / 104,695, filed on October 23, 2020, entitled "Stationary Offshore Wind Turbine", and claims priority to U.S. Patent Application No. 17 / 249,676, filed on March 9, 2021, entitled "Minimizing Movement of Offshore Wind Turbines", the entire contents of which are incorporated herein by reference. Technical Field The present invention relates to a technique for minimizing the movement of an offshore wind turbine.

Background Art

[0002] Background Deep - sea areas off the coastline offer great potential as wind energy resources. Ocean structures, generally called platforms, can be used to house wind turbines and related electrical equipment in these areas. However, it can be difficult to determine how to reduce the movement of an offshore platform in order to support a wind turbine. In the open ocean, wind, waves, and ocean currents often act simultaneously, applying forces to the ocean platform that cause it to move.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] Detailed Description The following detailed description is directed to a technique for minimizing the movement of an offshore wind turbine. [Means for solving the problem]

[0005] Using the technologies described herein, wind turbines are constructed and positioned to mitigate movement and / or environmental impacts (e.g., wind, waves, etc.) on the platform in both shallow waters (e.g., less than 120 meters) and deep waters (e.g., more than 40 meters), and mounted on offshore platforms. As used herein, the term fully restrained platform (FRP) refers to a platform having restrained movement with 6 degrees of freedom (DOF), FRP monopile refers to a platform containing a monopile, and FRP single-hull platform refers to a platform containing a buoyant structure.

[0006] For illustrative purposes, the main structural elements of a platform can be considered rigid bodies. Their motion is characterized by and measured within six degrees of freedom (DOF), including three translational (surge, sway, heave) and three rotational (roll, pitch, yaw). Environmental loads can impart forces to the platform, causing it to move within one or more DOFs. Some of these loads are inherently dynamic, such as loads from water waves, while others are largely stable, such as traction caused by ocean currents.

[0007] One example of a platform design philosophy is that in shallow waters, environmental loads are primarily resisted by the lateral rigidity of the platform, which is designed to be "fixed." One example is a lattice-structured jacket platform with legs extending into the ground. However, in deep waters, the amount of material required for a fixed platform is not economical. Therefore, the platform concept incorporates some or all of the six permitted DOF movements, such as a tension-leg platform (TLP) that allows surge, sway, and yaw movements, or a semi-submersible platform that allows all six DOFs.

[0008] In current wind engineering practices, fixed offshore platforms such as jackets are used in shallow waters with depths of less than 60 meters. However, areas with sufficient wind are often located in deeper oceans with depths exceeding 60 meters.

[0009] Offshore platforms in fairly deep waters (such as 1,000 meters) are installed by the offshore oil and gas industry. There are mainly four types of such offshore structures: (1) tension leg platforms (TLPs) as disclosed in Patent Document 1, (2) spar platforms as disclosed in Patent Document 2, (3) semi-submersible platforms, and (4) moored hull platforms. A common feature of these four types of structures is that, under environmental stress, they would all have a large range of motion of 5-8% of the water depth during storms and strong ocean currents.

[0010] For a wind turbine to function effectively, its mounting structure should ideally have as little movement as possible. According to the examples described herein, a wind turbine is supported by a platform that attempts to minimize movement in all six DOFs, resulting in more efficient power generation by the wind turbine compared to a platform that does not restrict movement in all six DOFs. Prior to the technology described herein, known platforms with such characteristics were not permanently installed in deep waters to mount wind turbines.

[0011] The loads of wind turbines are significantly less than those of typical offshore oil and gas applications, and the water depths of foreseeable future wind applications are not as great as those routinely faced by the offshore oil and gas industry. Disclosed herein are offshore structures that reduce / minimize the movement of wind turbines and associated structures and equipment underwater (e.g., at depths greater than 60 meters), as described herein.

[0012] Offshore wind turbines are wind turbines mounted on offshore platforms. Offshore wind turbines (e.g., in waters deeper than 60m) generally consist of four main components: (1) an anchor on the seabed, (2) mooring lines, (3) a floating structure (also called a "hull" or "air can") with a deck (or structure called a "transition piece") on top of it, and (4) a wind turbine with a tower, nacelle, and rotor hub with blades. The mooring equipment may be connected at one end to the anchor on the seabed and at the other end to the hull and / or wind tower. The anchor is attached to the seabed at a depth of approximately 20 to 200 meters below the surface. According to some examples, the first three components (seabed anchors, mooring lines, and floating structures) constitute an offshore platform. The base of the wind turbine is attached to the offshore platform, such as the deck of the offshore platform. In addition to the wind turbine, other structures and equipment may also be attached to the platform.

[0013] Using the techniques described herein, motion in all six DOFs of an offshore wind turbine can be reduced / suppressed. Motion as used herein refers to the movement of the hull caused by environmental loads. External forces causing motion include those from waves and currents to the hull, mooring equipment, and all parts of the turbine in contact with water, and from wind to all parts of the structure above the sea surface. Methods for the assembly, transport, installation, and development of adjacent wind turbine units are also disclosed. Additional details regarding minimizing the motion of offshore wind turbines will be presented below with reference to Figures 1–15. [Brief explanation of the drawing]

[0014] [Figure 1] This diagram shows an overview of the use of mooring devices to restrain a floating structure having a deck for supporting a wind turbine. [Figure 2] These are front and top views illustrating how the rotational motion of the shell is suppressed. [Figure 3]It is a diagram showing an overview 300 for constructing an offshore platform that supports a wind turbine. [Figure 4A] It is a diagram showing an overview of a fully suppressed platform (FRP) that supports a wind turbine. [Figure 4B] It is a diagram showing an overview of a fully suppressed platform (FRP) that includes an integral monopile and an air can for supporting a wind turbine. [Figure 5] It is a diagram showing connecting a mooring to a floating structure and a structure / equipment attached to the upper part. [Figure 6A] It is a diagram showing the six-degree-of-freedom (DOF) motion of the hull of an offshore platform and the natural vibration frequencies in the six-degree-of-freedom motion of a fully suppressed platform (FRP). [Figure 6B] It is a diagram showing a comparison of surge motions between an FRP and a tension leg platform (TLP). [Figure 7] Figure 7 is a diagram showing stiffness, damping, and frequency zones controlled by mass with respect to the response of a mechanical resonator. [Figure 8] It is a diagram showing that an offshore wind turbine has a mass, a spring, and a dashpot representing one of its natural vibration frequencies. [Figure 9] It is a diagram showing an eigenvalue formula for obtaining natural vibration frequencies. [Figure 10] It is a diagram showing the natural vibration frequencies of a simple pendulum and the natural vibration frequencies of a liquid sloshing in a rectangular tank. [Figure 11] It is a diagram showing a tuned mass damping system. [Figure 12] It is a diagram showing a wind turbine attached to a tuned mass damping system. [Figure 13] It is a diagram showing a vortex-induced vibration suppression device attached to the mooring and hull of an FRP. [Figure 14] It is a diagram showing an example of an offshore wind turbine that does not have attached moorings but has temporary structures and equipment during transportation and installation. [Figure 15]This diagram shows an offshore wind power plant with 16 turbine units arranged in a grid pattern. [Modes for carrying out the invention]

[0015] In the following detailed description, references are made to specific examples or illustrative drawings that form part of this specification. In this specification, drawings are not drawn to scale. Similar figures represent similar elements in several figures (which may be referred to herein as “Figures” or “(Planetary) Figures.”

[0016] Figure 1 shows a schematic 100 (referred to herein as the first method) using mooring devices to restrain a floating structure with a deck for supporting a wind turbine. According to some configurations, the mooring devices for restraining the hull are configured to minimize the movement of the structure, including the turbine. Schematic 100 shows an example of a single-hull FRP hull.

[0017] As shown in Figure 1, the floating structure 103 with a deck provides upward buoyancy, indicated by arrows within the area of ​​the floating structure 103. Mooring devices 102, some of which are vertical and others inclined at an angle from the vertical, pull the floating structure 103 downward. The other end of the mooring devices 102 is connected to the seabed anchor 101. According to some examples, the mooring devices may include conduits. For example, the mooring devices may be tubular (or of some other shape) and include conduits for the transport of fluids, cables (e.g., electrical, telecommunications, etc.), and the like. In other configurations, the mooring devices are tubular and may include vortex-induced vibration suppression hardware, such as helical side plates or fairings, which are attached to mitigate vortex-induced vibrations. To remove the mooring equipment from the seabed, it can be secured at half its length.

[0018] The weight of the wind turbine and / or other structures and equipment 104, referred to as the payload, also exerts a downward force. Equilibrium of the vertical forces is achieved by the buoyancy of the hull being equal to the tensile force from the moorings and the sum of the weights of the wind turbine, electrical equipment, and other structures and equipment. The above description is applicable to a still water scenario.

[0019] In the presence of disturbances, environmental loads will tend to move the shell 103 away from its hydrostatic position. In the vertical and horizontal directions, the mooring device 102 will stretch and therefore provide resistance to movement. The action of the mooring device 102 is well adapted to both static and dynamic loads. This helps to suppress translational motion, surge, sway, and heave of the shell.

[0020] Figure 2 shows elevation view 200 and plan view 250 illustrating how the rotational motion of the hull can be suppressed. In the example shown in Figure 2, there are a total of eight mooring devices 202, four at each height of the hull. In other examples, a different number of mooring devices may be used. The hull 203 is secured by the mooring devices 202. The other end of the mooring devices 202 is connected to an anchor 201 on the seabed.

[0021] The shell 203 has three rotational motions: two around the horizontal axis (roll and pitch) and one around the vertical axis (yaw). According to some configurations, to suppress the roll and pitch motion of the shell 203, a mooring device 202 is attached to the shell 203 at two different heights (shown in elevation view 200 of Figure 2).

[0022] Some of the mooring devices 202 are positioned lower (shown inside the water), while others are positioned higher (shown outside the water). As shown in Figure 2, by restricting movement, rotation around the horizontal axis will stretch the mooring devices 202 and will be limited by the axial stiffness of the mooring devices 202.

[0023] As shown in the plan view 250 of Figure 2, the mooring devices 202 at a lower height on the shell 203 are configured such that pairs of devices 180 degrees apart lie on the same line. Two mooring devices 202 are aligned along the X-axis, and two mooring devices 202 are aligned along the Y-axis. Thus, the four mooring devices at this height are at 0, 90, 180, and 270 degrees (other angles may be used). According to some examples, the virtual extension of each of them will pass through the origin of the XY coordinate system.

[0024] The installation of mooring devices 202 at higher heights can also be seen in the plan view 250 of Figure 2. For illustrative purposes, assume that the mooring attachments are originally located at 45, 135, 225, and 315 degrees (dashed lines). When a pair of mooring devices are connected 180 degrees apart, the line passes through the origin of the XY coordinate system. Now, around the attachment point in the horizontal plane, rotate each mooring line by approximately 10 degrees counterclockwise for mooring devices in quadrants I and III, and by approximately 10 degrees clockwise for mooring devices in quadrants II and IV.

[0025] After rotation, the mooring devices 202, mounted higher on the shell 203, are shown by solid lines. The two mooring devices, originally 180 degrees apart, are no longer on the same line, and their respective virtual extensions will not pass through the origin. Thus, moment arms are created. In the event of clockwise or counterclockwise yaw motion, a portion of the mooring devices 202 will be stretched, providing resistance. More specifically, the mooring devices in quadrants I and III provide resistance to clockwise yaw motion, and the mooring devices in quadrants II and IV provide resistance to counterclockwise yaw motion.

[0026] While vertically mounted mooring devices 202 also suppress translational heave and rotational roll and pitch, as in the case of TLP, inclined mooring devices mounted on the shell at different heights can also suppress surge and sway in addition to heave, roll, and pitch.

[0027] As described above, the shell 203 can be restrained by 6DOF. All of its 6DOF movements, namely surge, sway, heave, roll, pitch, and yaw, will be resisted by the axial stiffness of the mooring 202. The axial stiffness of the mooring line will depend on the Young's modulus of the mooring material, the cross-sectional area of ​​the mooring, and the length of the mooring. A mooring system of appropriate size can minimize the movement of the shell.

[0028] Figure 3 shows an outline 300 for constructing an offshore platform supporting a wind turbine. A mooring device 302 is connected at one end to a seabed anchor 301 and at the other end to the floating structure and deck 303. The wind turbine tower and / or electrical equipment such as a transformer 304 can be securely attached to the floating structure and deck 303. By using the techniques for designing and positioning the mooring device 302 described above in Figures 1 and 2, the floating structure and deck 303 can be restrained to minimize movement at 6DOF.

[0029] Figure 4A shows an outline of a fully suppressed platform (FRP) supporting a wind turbine. According to some examples, FRPs can be deployed in relatively shallow bodies of water (e.g., 60–120 meters deep). As briefly mentioned above, the pile is used to help suppress the movement of the hull, and therefore may be referred to herein as an FRP monopile.

[0030] As shown in the figure, the FRP monopile structure includes various components. In some configurations, the FRP monopile includes a monopile 401 driven into the seabed, a transition piece placed on top of the monopile, one or more mooring devices 404, and one or more mooring anchors 403.

[0031] This configuration of the FRP monopile can be adapted to meet specific design, transportation, and installation needs. For example, the monopile 401 may be separated into two segments along its longitudinal direction, with the upper segment having different dimensions from the lower segment, and the buoyancy of the structure may be designed to improve the structure's performance by pre-tensioning the mooring and optimizing the axial load of the monopile 401.

[0032] The floating structure and deck 402 may be designed to have different forms / shapes. As shown in Figure 4A, the floating structure and deck 402 may have different structural dimensions (for example, larger in this example but smaller), and may or may not include a deck at its upper end, also referred to as a “transition piece.” As shown in Figure 4B, the monopile 401 includes an integrated floating structure 422 or an air can. The buoyancy of the air can may exert a lift on the pile 401. Depending on the size of the payload, the upper part of the pile 401 may be stretched or compressed. According to some examples, vortex-induced vibration (VIV) suppression hardware may be used on the pile 401 and / or air can structure to mitigate VIVs.

[0033] As illustrated, one or more piles 401 are driven into the seabed and are pulled upward toward the sky by a floating structure and deck 402. The top of the piles 401, including the deck / transition piece, may be located slightly above the seabed. The wind turbine tower and / or electrical equipment 405 and / or other payloads may be securely attached to the top of the floating structure and deck 402. According to some configurations, mooring devices 404 are connected to a seabed anchor 403 at one end and to the tower 405 at the other end. The payload (including the weight of the wind turbine and / or electrical equipment) is supported by the floating structure and deck 402. According to other configurations, the mooring devices 404 are connected to a seabed anchor at one end and to the floating structure and deck 402 at the other end. According to yet another example, mooring devices may not be used to help restrain movement. For example, in shallow waters (e.g., depths of 0-60 meters, 0-120 meters), the FRP monopile may not require the use of mooring devices 404.

[0034] According to several examples, the mounting height of one end of the mooring device 404 attached to the wind turbine tower 405 is, in fact, as high as possible. For example, in the case of a wind turbine, the mooring device may be positioned at a height that does not interfere with the rotating blades (not shown). As shown in Figure 4, the pile 401, the floating structure and deck 402, as well as the wind turbine tower and / or equipment 405, structurally form a cantilever beam, and the mooring device 404 provides a bracing function. The structural members are sized such that the mooring device 404 remains under tension. By using the techniques described above with respect to Figures 1-3, the mooring device, the floating structure and deck 402, as well as the wind turbine tower 405, can be restrained in each of the DOFs.

[0035] The mooring devices 404 and anchors 403 can be arranged according to the design. As shown in Figure 4A, the mooring devices 404 and anchors 403 are arranged at equal intervals (e.g., 90 degrees). In the example in Figure 4B, three mooring devices 404 are shown with the mooring devices spaced at 120-degree intervals.

[0036] Various mooring systems can be used. For example, tension mooring systems using synthetic ropes, metal chains, or a combination of synthetic ropes / metal chains, and possibly other materials, can be secured to the seabed with vertical load anchors (VLAs). In another example, catenary mooring systems using metal chains, or a combination of synthetic ropes / metal chains, and possibly other materials, can be secured to the seabed with drag-embedded anchors.

[0037] In tension mooring systems, mooring devices are pulled so that their shape is essentially straight. In catenary mooring configurations, mooring devices are in a suspended shape (catenary) when free. Generally, in tension mooring systems, mooring lines are pre-tensioned until they are taut, and the mooring lines terminate at a certain angle on the seabed (e.g., between approximately 30 and 45 degrees). Therefore, the anchor points of tension mooring systems are loaded by both horizontal and vertical forces.

[0038] Diagram 475 illustrates the suppression of yaw motion of an FRP monopile structure by mooring devices. As shown in Diagram 475, there are two mooring devices 404 attached to each anchor 403 on the seabed. The other end of each mooring device 404 is attached to the FRP monopile structure (e.g., air can, monopile, deck / transition piece, etc.) at different positions. The mooring attachment points can be on the waterline, at the waterline, or below the waterline on the air can or the pile itself. In-line mooring hardware may be used to tighten the mooring lines in order to maintain the necessary pretension of the mooring lines. One such case is the loosening of tension in synthetic ropes due to creep and slack. Turbine utility and signal cables may also be attached to one or more mooring lines to minimize the movement of such cables. Moment arms are created because the extensions of the mooring lines do not pass through the center of a circular structure. This is another mechanism that suppresses the yaw motion of a structure.

[0039] If the water is not deep enough, a mooring system may not be necessary; that is, the pile structure alone may be able to withstand external loads. On the other hand, if the water is very deep (and the air can / pile structure is very long), additional level mooring (mooring at a different height) may be used to secure the air can / pile structure. In some examples, the mooring systems described herein may be added to existing pile structures to provide additional support to ensure the overall structure remains intact. Existing offshore wind turbine foundations with only a single pile (such as a monopile) have problems, and therein, concerns are heightened regarding their ability to withstand environmental loads.

[0040] According to some examples, the foundation of a wind turbine can be installed by setting up mooring anchors, laying mooring equipment, installing monopiles and air cans, attaching mooring equipment to pipes / air cans and pulling them in place, installing the turbine, installing cables, and making it operational.

[0041] Figure 5 illustrates the connection of the mooring device to the floating structure and the structures / equipment mounted on top. As shown in Figure 5, the mooring device 502 is connected at one end to the seabed anchor 501 and at the other end to the floating structure and deck 503 in some cases, and to the wind turbine tower and / or electrical equipment 504 in others. Thus, the mooring device 502 is attached to the structure at two heights. The wind turbine tower and / or electrical equipment 504 are securely mounted on the floating structure and deck 503. By designing the mooring device 502 using the techniques described above, the floating structure and deck 503, as well as the wind turbine tower and / or electrical equipment 504, can be restrained at 6DOF. In some examples, the mounting height of the wind tower and / or electrical equipment 504 is practically as high as possible, provided that the mooring device 502 does not interfere with the rotating blades (blades not shown) in the case of a wind turbine.

[0042] Figures 6A and 6B illustrate the differences between the tension leg platform described herein and FRP. Referring to Figure 6A, illustration 600 shows the 6DOF motion of the offshore platform hull. Plot 650 shows the natural frequencies in the 6DOF motion of the FRP described herein. Plot 675 in Figure 6B shows a comparison of surge motion between FRP and TLP.

[0043] Due to the high tension in the mooring device of the motion control system, all six natural frequencies—surge, sway, heave, roll, pitch, and yaw—are to the right of the significant wave frequency (the peak at plot 650 in Figure 6A), where the wave energy is maximum.

[0044] As shown in plot 675 of Figure 6B, a comparison of surge motion in a wave is made between the motion control system described herein and the TLP. As can be understood, the motion control system described herein is essentially immobile in a wave.

[0045] Figure 7 shows the stiffness, damping, and mass-controlled frequency zones for the response of a mechanical resonator. The motion control system described above uses the axial stiffness of the anchor to suppress motion in some examples, and both axial and lateral stiffness in others. This system has been found to work well when motion is controlled primarily by the stiffness of the system. A single-degree-of-freedom (SDOF) mechanical resonator can be used as a model to represent the motion of each degree of freedom (DOF) of the shell. This mechanical resonator consists of a mass, a spring, and a dashpot. How the mass responds to disturbances depends on the excitation frequency relative to the resonator's natural frequency. As shown in Figure 7, there are three frequency zones. A fully suppressed structure is designed so that the excitation frequencies fall within the stiffness-controlled zone, i.e., they are below the system's natural frequency. It should be noted that stiffness is important at each frequency, but its effect is more pronounced in the stiffness-controlled zone. If the excitation frequency is higher and falls within the damping-controlled zone, a phenomenon called resonance occurs, where the shell motion can become large and unacceptable.

[0046] One example is when an incoming wave has a sum frequency close to one of the platform's natural frequencies (as a spring-strained rigid body, the shell has six natural frequencies corresponding to its six DOF movements). A wave load of sum frequency could also excite the bending natural frequency of the wind turbine tower. Another example is the aerodynamic load when the blades rotate as they pass through the wind turbine tower. From this perspective, tuned mass dampers (TMDs) and tuned liquid dampers (TLDs), which have been successfully used in high-rise buildings, could be attached to wind turbines to reduce their dynamic motion. This relates to a second method of the present invention.

[0047] The operating principle of TMDs and TLDs is that the mass of these dampers is adjusted so that the natural frequency of the damper itself is close to the target frequency for the damper, so that the mass of the damper functions to absorb the vibrational energy of the main system. In this way, the amount of motion of the main system will be reduced to a lower level. A TLD can be considered a special case of a TMD, where the mass is the mass of the liquid. The shape of the liquid tank, the amount of liquid in the tank, and the actual liquid can be designed so that the desired function can be achieved.

[0048] Therefore, the fundamental idea of ​​the second method is to install a synchronized mass damping system on the offshore wind turbine to reduce the dynamic motion of the turbine and mitigate the dynamic forces in the system's moorings. This synchronized mass damping system includes a synchronized mass damper (TMD) and a synchronized liquid damper (TLD), and multiple frequencies may be addressed. Its mechanism is described below.

[0049] Figure 8 shows a system 800 for an offshore wind turbine, having a mass 801, a spring 802, and a dashpot 803 to represent one of its natural frequencies. The tuned mass damping system has a primary mass 804, a spring 805, and a dashpot 806. Mass 804, such as a spherical tank, contains a liquid (forming a secondary mass) represented by mass 807, a spring 808, and a dashpot 809. This mass-spring-dashpot system is mounted on a foundation 810.

[0050] As shown in Figure 8, the overall system has three natural frequencies: one for the entire system (indicated as f1) and two introduced by the tuned mass damping system (indicated as f2 and f3). The two natural frequencies of the damping system are tuned so that f2 (corresponding to the primary mass 804) is close to f1, and f3 is tuned to target the same frequency as, or a different frequency from, another natural frequency of the system, or the same frequency as, or a different frequency from, one of the excitation frequencies, such as the dominant wave frequency of a once-in-a-century hurricane in the Gulf of Mexico.

[0051] Tuning can be achieved by changing the masses (804 and 807), and / or the springs (805 or 808), and / or the dashpots (806 and 809). According to some examples, the optimized specifications for f2 and f3, and the damping values ​​from dashpots 806 and 809, can be found by computer simulation, which will give the most effective damping result, i.e., the minimum movement of the platform. When the platform is subjected to a disturbance, masses 804 and 807 will respond, activating the intentional dashpots 806 and 809 to dissipate the energy.

[0052] Figure 9 shows the eigenvalue equation 900 for obtaining the natural frequencies. The natural frequencies of the system shown in Figure 8 can be obtained by solving the eigenvalue equation 900 (determinant equal to zero) shown in Figure 9. The correspondence between the symbols in Figure 9 and Figure 8 is as follows: (1) M1, M2, and M3 in Figure 9 are the values ​​of masses 801, 804, and 807 in Figure 8, respectively, and (2) K1, K2, and K3 in Figure 9 are the stiffness values ​​of springs 802, 805, and 808 in Figure 8, respectively. The solution to the eigenvalue equation, which can be easily obtained with computer code, is the three natural frequencies ω1, ω2, and ω3, which are ω i =2πf i The values ​​(i=1, 2, 3) are related to f1, f2, and f3.

[0053] Referring to Figure 8, the TMD (represented by mass 804 together with mass 807, spring 805, and dashpot 806) can be either a simple pendulum or a physical pendulum. In the former case, its natural frequency is given by √g / L / 2π, where g is the acceleration due to gravity and L is the length of the cable supporting the mass. The TLD (represented by mass 807, spring 808, and dashpot 809) is formed by a sloshing liquid in a tank of any practical shape, such as a right prism or a sphere. The liquid is water or a mixture of water and a viscoelastic material. For a rectangular tank, the formula for the natural frequency is √gh / 2L, where g is the acceleration due to gravity, h is the depth of the liquid in the tank, and L is the length of the tank.

[0054] Figure 10 shows the natural frequencies of a simple pendulum and a liquid oscillating in a rectangular tank. Plots 1000 and 1050 show that TMD and TLD can be used to reduce the dynamic motion of a wind turbine, as the geometric dimensions (particularly cable length and tank size) for the target frequency are practical considering the dimensions of a wind turbine. For example, a pendulum with a 9-foot (2.7m) long cable would have a natural frequency of 0.3 Hz. An 80-foot (24.4m) long tank filled with 8 feet (2.4m) of liquid would give a natural frequency of 0.1 Hz. These frequency values ​​are analogous to the sum of the frequencies of ocean waves.

[0055] Plots 1000 and 1050, shown in Figure 10, along with the eigenvalue equations in Figure 9, can be used to size the TMD and TLD to a target frequency. The vertical motion frequency of the TMD can be given by f = √K / M / 2π, where K is the axial stiffness of the cable, AE / L (A is the total cross-sectional area of ​​the cable, E is Young's modulus, and L is the cable length), and M is the mass. Thus, both the pendulum motion and the vertical motion frequencies can be sized simultaneously. This tuned mass damping system can be mounted on a wind turbine in such a way that any movement of the structure activates the damping system.

[0056] Figure 11 shows a synchronized mass damping system. As shown, the illustrated synchronized mass damping system 1100 includes (1) a prismatic tank 1101 that generates inertial energy during motion, (2) a cable 1102 that supports the tank 1101 and provides rigidity, and (3) a hydraulic cylinder 1103 that dissipates energy. The tank 1101 contains a liquid 1104 that forms a TLD that can be synchronized. The other ends of the cable 1102 and the hydraulic cylinder 1103 are attached to an intermediate support structure 1107 at position 1105. A solid mass sphere 1106 is placed in the liquid 1104 to enhance the energy dissipation performance of the TLD. A retaining pin 1108 protruding from the side of the tank 1101 functions as a safety device to limit the movement of the tank 1101.

[0057] Figure 12 shows a wind turbine mounted on a tuned mass damping system. According to several configurations, the tuned mass damping system 11 in Figure 11 may be mounted inside and / or above and / or below the hull. As shown in Figure 12, the tuned mass damping system 1204 (represented by a dashed box) is mounted inside the hull and deck 1203 of the wind turbine in the water. The damper 1204 is positioned on a support 1205. The hull 1203 is secured by a mooring device 1202. A foundation anchor 1201 on the seabed, connected to the mooring device 1202, will support the mooring load. The wind turbine and / or electrical equipment 1206 are mounted on the hull and deck 1203.

[0058] Figure 13 shows a vortex-induced vibration suppression device. When ocean currents encounter tubular structures, vortices can form due to flow separation within the structure. Once released, these vortices exert dynamic forces on the structure, causing it to move and resulting in fatigue damage. This phenomenon is called vortex-induced vibration (VIV). Field experience in the offshore oil and gas industry indicates that mitigation hardware is needed to suppress VIV. Floating structures will not move much because their rigidity is controlled. Even in cases where the vortex generation force in the hull is large, mitigation measures are still justified in some cases. Long tubular mooring lines are very flexible. VIV in mooring equipment can affect the movement of hulls and any structures associated with offshore platforms, which have natural frequencies close to the VIV and / or vortex generation frequencies. For the same flowing fluid, an inclined cylinder will have less VIV than a vertically mounted cylinder. However, mitigation measures may still be necessary. The helical side plates and streamlined fairings of the VIV suppressor can be used in mooring devices to reduce movement. This is a third method for minimizing the movement of offshore wind turbines.

[0059] As shown in Figure 13, one end of the mooring device 1302 is connected to the seabed anchor 1301, and the other end is connected to the floating structure and deck 1303, some at one height and others at another height. The wind turbine tower and / or structure and equipment 1304 are securely attached to the top of the floating structure and deck 1303. The VIV suppression hardware 1305 is attached to the mooring device 1302 along its longitudinal direction. The mitigation device 1305 is also attached to the floating structure and deck 1303.

[0060] Figure 14 shows an example of an offshore wind turbine that does not have permanent mooring but is equipped with temporary structures and equipment during transport and installation. Significant cost savings can be achieved if the wind turbine can be attached to a platform around a dock. However, due to the high vertical center of gravity (VCG) after the wind turbine is attached to the platform, there is a high risk of capsizing when moving such structures to the installation site, such as by towing on the water. The environmental impact associated with movements caused by disturbances could cause the entire structure to capsize.

[0061] Furthermore, due to the high VCG, hydrostatic stability is a concern before the structure is secured with mooring equipment during installation. Depending on the configuration, temporary installation / transport tools and equipment may be used to mitigate the risk of capsizing. In some examples, temporary weights may be attached to the underside of the hull during transport and installation to lower the VCG. These weights can also serve as gravity anchors for the mooring equipment. In some examples, the entire offshore wind turbine may be towed to the installation site, either whole or in part, with the mooring equipment and anchors attached. Additionally, the horizontal surface area of ​​the hull may be reinforced with air cans (hollow, buoyant cans) and / or other floats attached around the hull at the waterline.

[0062] As shown in Figure 14, the floating structure and deck 1403 are fitted with air cans and / or floats 1404 at waterline level. One or more weights or gravity anchors 1401 may be fitted below the hull and deck 1403 and supported by truss members or mooring devices 1402. The buoyancy of a floating structure can be reduced, or partially increased.The wind turbine tower, along with the nacelle and rotor hub 1405, is securely mounted to the top of the floating structure and deck 1403. The entire structure can be towed to the installation site. Once mooring equipment (not shown) locks off the platform and turbine, temporary structures and equipment (air cans and / or floats 1404, weights 1401, and support structures 1402) will be removed for future use such as assembly, transport, and installation of other wind turbine units, maintenance of the operating unit, or decommissioning.

[0063] According to some configurations, the assembly procedure includes fabricating the hull, installing temporary structures, and installing the wind tower and rotating nacelle assembly (RNA). In some examples, the transport and installation procedure includes installing seabed anchors (including those used as temporary weights during transport and installation, if any), installing mooring equipment, towing the hull and deck together with the attached wind turbines to the site, securing the platform and turbines with pre-installed mooring equipment, and removing temporary transport and installation equipment.

[0064] Figure 15 shows an offshore wind farm 1500 in which 16 turbine units are arranged in a grid. In some configurations, when offshore wind turbines are selected as an offshore wind farm with multiple units, the design can be optimized at an overall level by sharing the same seabed anchor with multiple mooring devices from the same and / or adjacent units. As a result of this optimization, the number of anchors may be reduced, and significant cost savings may be achieved. As shown, mooring devices from the same and / or multiple units may be attached to the same anchor.

[0065] Referring here to Figure 15, an offshore wind farm 1500 having 16 turbine units (more or fewer may be used) is arranged in a grid. Mooring devices 1503 secure turbine units 1501 to seabed anchors 1502. In this example, there are 16 turbine units in a 4x4 arrangement. Assume that each unit is secured by 4 mooring devices. If the 4 mooring units were designed individually, 64 anchors would be required. If the mooring devices for adjacent units share the same anchors, as shown in Figure 15, only 25 anchors are required. A saving of 39 anchors is achieved. It should also be noted that each of the four corner anchors secures one mooring device, the side anchors secure two mooring devices, and the anchor in the center secures four mooring devices.

[0066] Based on the foregoing, it should be understood that techniques for minimizing the motion of offshore wind turbines are presented herein. The subject matter described herein is provided for illustrative purposes only and should not be construed as limiting. Furthermore, the claimed subject matter is not limited to implementations that resolve any or all of the defects described in any part of this disclosure. Various modifications and changes can be made to the subject matter described herein without following the examples and applications described herein and without departing from the true spirit and scope of the invention as described in the claims.

Claims

1. A system comprising a platform for mounting a floating structure, a wind turbine structure, and an offshore substation, wherein the platform is coupled to the floating structure, one or more anchors attached to the seabed, a plurality of mooring devices including a first end coupled to a plurality of attachment points on at least one of the floating structure, the platform, or the wind turbine structure, and a second end coupled to at least one of the one or more anchors, and a monopile coupled to the floating structure, wherein at least a portion of the monopile is embedded in the seabed, the plurality of mooring devices restrict the movement of the platform by six degrees of freedom, at least a first mooring device of the plurality of mooring devices is connected to a first attachment point at a first height, and at least a second mooring device of the plurality of mooring devices is connected to a second attachment point at a second height different from the first height.

2. The system according to claim 1, characterized in that one or more anchors are attached to the seabed at a depth of approximately 20 to 200 meters below the water surface.

3. The system according to claim 1, characterized in that the buoyancy of the floating structure can be reduced at least partially or increased partially.

4. A system according to claim 1, wherein the first mooring device and the second mooring device are rotated around the first mounting point and the second mounting point to suppress surge, sway, heave, roll, pitch, and yaw.

5. A system according to claim 1, characterized in that the first mounting point of the plurality of mounting points is outside the water, and the second mounting point of the plurality of mounting points is below the water surface.

6. The system according to claim 1, wherein the mooring device is tubular and includes vortex-induced vibration suppression hardware for reducing vortex-induced vibration.

7. A system, wherein the system is A structure including the first end embedded in the seabed, A deck for mounting at least one of a wind turbine structure and an offshore substation, the deck being connected to a floating structure, The floating structure connected to the aforementioned structure, and A synchronized damping system comprising at least one of a synchronized mass damper (TMD) and a synchronized liquid damper (TLD), wherein the synchronized damping system comprises the floating structure and the synchronized damping system installed inside one or more of the structure.

8. The system according to claim 7, further comprising vortex-induced vibration (VIV) suppression hardware used in the structure and at least one of the floating structures for mitigating vortex-induced vibration (VIV).

9. A system according to claim 7, comprising one or more anchors and one or more mooring devices, each having a first end connected to one or more attachment points on at least one of the floating structure, the deck, or the wind turbine structure, and a second end connected to at least one of the one or more anchors, wherein the one or more mooring devices restrict the movement of the deck by six degrees of freedom.

10. A method for restraining movement of a platform equipped with a wind turbine structure or an offshore substation, wherein at least a portion of a monopile coupled to the platform is embedded in the seabed, the method comprising attaching mooring devices to first and second heights of the platform, the second height being different from the first height, the mooring devices being coupled to anchors attached to the seabed, the method comprising attaching the devices and rotating the individual mooring devices by a certain angle around their respective attachment points so that the extension lines of the individual mooring devices do not pass through the center of the platform in order to generate moment arms, wherein attaching the mooring devices and rotating the individual mooring devices restrains surge, sway, heave, roll, pitch, and yaw movements.

11. A method according to claim 10, further comprising temporarily attaching one or more weights to a floating structure coupled to the platform during the transport of the platform, wherein the one or more weights lower the vertical center of gravity (VCG).

12. A method according to claim 10, further comprising fixing the mooring device between the platform and the seabed to half its length in order to remove the mooring device from the seabed.

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