A wave energy absorbing device

Abstract

A wave energy absorbing device comprises a floating wave energy absorbing body (1) and a spring device (2), where the spring device is positioned inside the floating wave energy absorbing body. The spring device is designed to absorb sudden accelerations to mitigate excess forces that would otherwise affect the floating wave energy absorbing body and its connected components. The wave energy absorbing device comprises a self-regulating buoyancy control system comprising one or more ballast chambers and one or more accumulators and is attached to the spring device (2) to power the self-regulating buoyancy control system by forcing compressible fluid to flow between the one or more ballast chambers and the one or more accumulators, thereby ballasting the floating body and causing it to submerge under water in high waves.

Description

[0001] A wave energy absorbing device

[0002] Field of the invention

[0003] The present invention relates to the field of floating wave energy capture devices. More specifically, it relates to technology for protecting the device and associated machinery from destructive impacts from abrupt wave motions and high energy sea conditions.

[0004] Object of the invention

[0005] In cases where a wave energy-absorbing floating structure, e.g. a buoy, attached to a cable or rope or the like, experiences sudden jerks etc. or intense acceleration over a shorter time interval, great forces may arise. If the mass is significant and the time interval for the velocity change is small, the force induced can become so strong that it breaks something in the wave energy device, e.g. the cable. A spring device attached between the buoy and the cable will extend the time for the velocity change, thus reducing the acceleration, so that destructive forces don't arise.

[0006] A spring device, where resilient material, e.g. a coil spring or one or more elastomeric bodies, e.g. one or more lumps of rubber, or the like, is compressed when opposite parts of the containing structure are moved apart, may be preferred, due to durability and robustness. A disadvantage of such an assembly, however, is that it may have to be very large in the longitudinal direction, to be able to provide enough time for the speed change, for sufficient shock absorption during the most extreme wave incidents. By putting the spring device inside the buoy, the design of the wave energy-absorbing buoy with the spring device is improved, by greatly reducing the combined length of the buoy and spring device. This yields significant benefits, both in terms of the buoy with the spring device being more manageable and practical, in terms of reducing the number of moving parts, and in terms of lowered costs as less materials are required.

[0007] Also, the built-in self-regulating buoyancy control system aids to shelter the wave energy converter in periods of high-waves and during storms. That is because the wave movements gradually decrease when moving deeper into the water.Background and known technology on which the invention is based

[0008] Spring devices for ropes e.g. are common, and are used, among other things, for boat moorings. This is basically a tension spring, engineered to extend when a force is applied to pull it apart, and then return to its original shape when the applied force ceases. Similar spring devices made of elastomers are also well known.

[0009] The concept of putting an elastomer body inside a structure that reverses the direction of pressure, so that the elastomer is compressed instead of stretched when the device is extended (as shown on Figures 3A and 3B), is well known. An example from the patent literature is Figure 3 in WO 2011 / 067124, where an embodiment of a stretch-activated piston compressor pump is arranged inside two oppositely facing U-shaped brackets.

[0010] Designing a spring mechanism to absorb shocks from external forces acting on a wave energy-absorbing floating body of a wave energy converter is also well known, among others, from NO325878, where in one embodiment, between the cable and connecting point of the floating body, a shock-absorbing spring is inserted to absorb the load of heavy jerks in the cable during start-up, i.e. at the beginning of a wave cycle during periods of violent waves, where the shock-absorbing spring is designed to compensate for troublesome inertial forces in the system due to moving parts being accelerated at the start of each wave cycle.

[0011] US20130081388 presents a system and method for dynamically controlling the submersion of floating sections in wave power plants to protect them from extreme wave conditions, where a wave-powered pump transfers a compressible fluid from a ballast chamber to an accumulator, enabling seawater to enter the ballast chamber, thereby adjusting the buoyancy of the floating sections to comfortably match the prevailing wave conditions at any given time. This is precisely what is achieved by the submersion system integrated with the spring and the shock absorbing device, as described herein. However, as opposed to US20130081388, the present disclosure highlights the notion that the compressive pumping activity should occur when the spring returns to its resting position after being activated by impact from the waves, which is more efficient.JP5738043 presents a wave power generation apparatus which includes a floating body, a vibrator mounted to the floating body through a spring and linearly reciprocated according to the fluctuation of the water surface, and a power generator driven based on the linear reciprocating motion of the vibrator.

[0012] AU2013203488 presents yet another example of prior art wave energy apparatus.

[0013] Summary of the invention

[0014] The object of the invention is to provide a wave energy absorbing device that improves prior art technology.

[0015] The object of the invention is achieved by means of the patent claims.

[0016] This invention regards a shock-absorbing spring device mounted longitudinally inside an ocean wave energy absorbing floating body. The invention provides an improved mechanism for mitigating sudden acceleration forces, while also integrating a selfregulating submersion system for wave energy converters.

[0017] A wave energy absorbing device comprises in one configuration a floating wave energy absorbing body and a spring device, where the spring device is positioned inside the floating wave energy absorbing body. The spring device may be designed to absorb sudden accelerations to mitigate excess forces that would otherwise affect the floating wave energy absorbing body and its connected components, and the wave energy absorbing device may comprise a self-regulating buoyancy control system comprising one or more ballast chambers and one or more accumulators and may be attached to the spring device to power the self-regulating buoyancy control system by forcing compressible fluid to flow between the one or more ballast chambers and the one or more accumulators, thereby ballasting the floating body and causing it to submerge under water in high waves.

[0018] The one or more ballast chambers and one or more accumulators may be arranged within the floating body.

[0019] The spring device may be designed to reverse the direction of the applied force, to increase the force acting from the spring as any external agents cause the device toextend, thereby transforming compressive forces into tensile forces to enhance the durability and increase the lifespan of the device and its internal parts.

[0020] The self-regulating buoyancy control system may be activated upon release of the spring device, i.e. when the spring is being returned to its resting position.

[0021] There may further be provided a shock absorbing device integrated with the spring device, wherein the shock absorbing device includes a cylinder chamber with fluid inlets and outlets, a check valve allowing free inflow of fluid during the extension of the spring, and narrow fluid outlets forcing the trapped fluid to be expelled through one or more narrow fluid outlets, thereby converting the kinetic energy into heat and dissipating it into the surrounding fluid during the spring's return motion, where it provides damping only during the release of the spring.

[0022] At the bottom end connection point of the spring there may be arranged a universal joint, connecting the floating body to its mooring.

[0023] The universal joint at one or both shafts may have a swivel inserted, wherein the swivel permits independent rotational movement about the shaft between connected parts.

[0024] The universal joint and the swivel may be replaced by a ball-and-socket joint, resembling the human hip- or shoulder joint.

[0025] In one embodiment, elastic elements are compressed, when the spring device is stretched i.e. extended in the longitudinal direction. This is achieved by designing the structure to reverse the direction of the applied external force, causing the elastomer elements to undergo compression instead of extension when the spring device is extended. At the bottom of the floating body, an end mount point of the spring device extends, where a mooring may be attached. When the floating body, e.g. a buoy, is subjected to strong impacts, the spring device will extend in the longitudinal direction, ensuring that the mooring, or the like, attached to the end mount point doesn't experience accelerations so great that destructive forces arise. For the spring to be able to dampen high accelerations for a long enough duration, it must be considerably large in the longitudinal direction. Thus, integrating it into the floating body to reduce the overall size of the floating body and the spring device combined, as described, is highly advantageous.In one embodiment of the invention, the spring has a built-in shock absorber that also powers a self-regulating buoyancy control system allowing the floating body to submerge underwater in high waves.

[0026] What is described herein relates to protecting a wave energy converter from damaging mechanical stresses during high-energy wave events. It comprises a shock-absorbing spring mechanism that reduces forces arising from sudden jerks and intense accelerations, and, in connection therewith, a self-regulating buoyancy control system, acting to submerge the floating sections of the wave energy converter to safe depths below the sea surface adjusted to the prevailing wave conditions.

[0027] The spring mechanism, installed longitudinally inside a floating wave energy absorbing body, e.g. a buoy, allows for significant reduction in the overall size of the assembly without sacrificing performance.

[0028] By incorporating one or more compressible resilient bodies into the spring device, so that the resilient material is compressed when the spring device is extended longitudinally, and then mounting it inside the buoy, the overall length of the buoy and spring assembly is reduced. Thus, a cost-effective and practical solution is provided, to manage high-impact forces for wave energy converters, by facilitating ease of handling, enhancing durability by means of fewer moving parts, and reducing material costs. This approach ensures effective damping of high accelerations and preserves structural integrity during extreme wave events, while maintaining a compact design in which the combined size of the buoy and spring mechanism is minimized.

[0029] In one embodiment, the invention incorporates a system for controlling submersion of the floating structure, to protect the wave energy converter from suffering damage or excess wear in high waves, by means of a shock absorbing device, i.e. some form of a damper, a snubber or the like, in conjunction with the spring, which, in addition to handling shocks, constitute a wave powered compressor pump to remove compressible fluid, e.g. air, from one or more ballast chambers inside the floating structure, allowing seawater to enter the ballast chambers, weighing down the floating structure and decreasing the buoyancy of the structure. The compressible fluids from the ballast chambers are stored in one or more high-pressure accumulators, from which a narrow by-pass flow passage provides a controlled leakage, allowing the compressed fluid to slowly escape returning to its corresponding ballast chamber, thus displacing seawaterback into the ocean, increasing buoyancy. These two double-acting opposite processes constitute a self-regulating mechanism enabling the structure to submerge during storms, reducing its exposure to violent surface waves, and resurface as conditions normalize, thereby enhancing the durability and operational efficiency of the wave energy converter.

[0030] Brief description of the drawing

[0031] Fig. 1 shows one embodiment of a wave energy converter according to prior art, like the one described in NO346597, with a spring device 2 attached between the floating body 1 and the pulley 3B that connects the floating body to the winch cable 4.

[0032] Figure 2 provides a detailed view of a section from Figure 1, schematically illustrating the arrangement of elastomer cushions 9 within the spring device 2, i.e. the internal structure of the spring device.

[0033] Fig. 3A presents one embodiment of the spring device 2, uncompressed, where several elastomer cushions 9 are stacked inside a cylinder chamber, pierced by a piston rod, and trapped between the crown 8 of the piston and the cylinder chamber's end mount 12.

[0034] Fig. 3B is the same as Fig. 3A, but with the spring device extended, so that the elastomer cushions 9 are compressed, accordingly.

[0035] Fig. 4 shows one embodiment of the present invention, with the spring device 2 built into the floating body 1 and at the piston rod end mount 10 a universal joint 13 connecting the piston rod 6 of the spring device to an underwater pulley 3B.

[0036] Fig. 5 zooms in on a section of Fig. 4, revealing details 14, 15, 16 and 17 of one embodiment of a shock absorbing device at the top.

[0037] Fig. 6 illustrates the details of one version of the shock absorbing device acting as a compressor pump.

[0038] Fig. 7 shows the floating structure complete with self-regulating submersion system.Fig. 8 shows a zoomed in section of one embodiment of the present invention, where the universal joint 13 and the swivel 25 are replaced by a ball-and-socket joint 26.

[0039] Detailed description of the invention

[0040] When a wave energy converter, for example the one illustrated in figure 1 and 2, comprising a floating body 1 and a mooring structure, which in one embodiment may include a winch cable 4 and one or more underwater pulleys 3A-C, experiences a significant difference between the velocity of the floating body and the velocity of the mooring structure or parts of the mooring structure, e.g. the underwater pulley 3B and the winch cable, tremendous forces will arise, unless the device includes some kind of means to sufficiently dampen the acceleration of the connected parts as they move to catch up with each other. One example of when such a situation can occur is when cable is slack, and the floating body reaches high speed with the cable still slack, at the very moment the cable tightens.

[0041] Connecting the floating body to the mooring structure through a spring device 2, will adequately deal with this problem, provided that the spring has the appropriate spring characteristics and the capacity to extend sufficiently.

[0042] A spring designed to increase force when compressed, can be incorporated into a device that extends when the spring is compressed. This can be achieved by mounting the spring inside an arrangement of two opposing U-shaped brackets, as shown in Figure 3 of WO 2011 / 067124. The same principle of reversing the direction of the applied force can also be applied to a gear lever mechanism, as demonstrated in Figure 7 of WO 2011 / 067124. Reversing the direction of force, by allowing the spring device to extend when the spring itself compresses, may enable designs to enhance the spring's durability and increases its lifespan, particularly when it's made from elastomeric materials, such as rubber.

[0043] The elastic elements that are being compressed as the spring device is extended may in various embodiments be made of elastomeric materials, compressible gas trapped inside one or more chambers or cushions or the like, one or more springs made of resilient material, or magnets that repel each other.In one embodiment of the present invention, transformation of compressive force in the spring into tensile force is accomplished by enclosing the spring elements in a cylinder between two surfaces in a structure designed to force the surfaces closer together when the structure's end mounts are pulled apart. An example of such a structure is shown in figures 3A and 3B, where the bottom plate 12 and the piston crown 8 constitute the opposing end mounts. The space between the bottom plate and the piston crown, i.e. the cylinder chamber 7 in Figures 3A and 3B, is occupied by elastomer cushions 9. The cushions may be separated by washers serving as wear pads to extend the lifespan of the cushions. When a force is applied to pull the piston rod end mount 10 away from the cylinder chamber end mount 11, the distance between the cylinder chamber's bottom plate 12 and the piston crown 8 decreases, thus compressing the elastomeric elements inside the cylinder chamber.

[0044] Now, in the configuration illustrated in figure 4, the cylinder chamber 7 is incorporated into the floating body, thereby achieving a more compact design, with the piston rod 6 and its end mount 10 extending out of the bottom. Thus, the only moving part of the floating body and spring device combined, aside from the elastomer cushions, is the piston, which consists of the piston crown 8, the rod 6, and the end mount 10.

[0045] So far, the technical description addresses the same type of problem as an automotive suspension, which in the case of a car can be described as follows: When the vehicle's wheel hits a bump in the road, the spring absorbs the impact and prevents damage. However, the energy absorbed by the spring may cause trouble shortly after, when the spring bounces back and returns the energy.

[0046] Therefore, just as a car suspension system includes not only resilient springs but also shock absorption and dissipation of energy absorbed from shocks, it would be smart to equip the present invention with an equivalent or something similar. One or more shock absorbing devices, such as snubbers used in car suspensions or other functionally similar components, may thus be connected to the spring in the present invention.

[0047] In a car, a snubber is a device that controls unwanted spring motion through damping, converting the kinetic energy of suspension movement into heat, which is dissipated through a flowing fluid, thereby reducing the magnitude of vibratory spring motions. Typically, a snubber in an automotive suspension system works to control and dissipate energy both when the spring is compressed and when it is released. Duringcompression, e.g. when the vehicle hits a bump, the spring compresses to absorb the energy of the impact. The snubber resists this motion by absorbing some of the energy and converting it into heat, preventing the spring from compressing too quickly or too much. During release, after the spring is compressed, the snubber again absorbs and dissipates energy during this rebound phase, preventing the spring from releasing its energy too quickly and ensuring a smooth return to its original state.

[0048] The proposed shock absorbing device connected to said spring, dissipates, in a controlled manner, the energy absorbed by the spring. It is not necessarily required, and may not even be preferable, to design it to absorb energy when the spring assembly is being tensioned. In one or more embodiments, therefore, the device absorbs energy only upon release of the spring.

[0049] The spring device primarily mitigates acceleration forces, while the shock absorbing device controls rebound energy dissipation to prevent oscillations.

[0050] Figure 5 shows an embodiment of this shock absorbing device, integrated with the floating body 1 and the spring device 2. The upper part of the cylinder chamber 7 is filled with air from a fluid inlet 15 when the spring device extends. A check valve 16 allows the air to pass freely into the chamber from the outside. When the spring assembly is idle, the valve remains closed, maintained by a small spring 17 that provides sufficient force to seal the valve passage. However, when the spring device is extended and a lower pressure forms inside the chamber, the valve will open and let in air through the fluid inlet 15. As the spring returns, the valve 16 closes, so that no air can escape back through the fluid inlet. Then, the only way out for the air trapped inside the cylinder chamber is the one or more fluid outlets 14. These are narrow holes, forcing the air to be squeezed through, thereby converting energy into heat, which dissipates into the exhausting air.

[0051] In slightly different versions of the same embodiment, the air is replaced with another fluid, e.g. seawater.

[0052] In other similar embodiments, the fluid may be hydraulic fluid in a closed loop system.

[0053] In one embodiment of the invention, the shock absorbing device mentioned above is designed to use the absorbed energy to do some useful work, rather than just disposingit off by dissipating it into heat, namely to power a buoyancy control system built on the same principle as in a submarine.

[0054] In one embodiment, as illustrated in figure 6 and 7, the floating structure comprises one or more ballast chambers 18, which during calm waves are filled entirely with compressible fluid, e.g. air. As abrupt wave motions cause the spring device to extend, after which the spring returns to its resting position activating the shock absorbing device, it will drain compressible fluid from the ballast chambers through one or more flow passages 19, into the cylinder chamber 7, as a check valve 16 opens allowing the fluid to pass through, then, upon return of the spring to its resting position, the fluid is expelled from the cylinder chamber, whereby valve 16 closes while one or more valves 22A, 22B open, directing the fluid through one or more flow passages 20A, 20B into one or more accumulators 21A, 21B.

[0055] Each time compressible fluid, e.g. air, is drained from the ballast chambers this way, an amount of seawater will seep into the ballast chambers from below, through a seawater inlet and outlet 24A, 24B. This ballasts the floating structure, gradually causing it to sink more and more.

[0056] If it were only for this, the structure would eventually sink to the bottom of the sea. However, from each accumulator 21A, 21B, there is a narrow by-pass flow passage 23A, 23B, allowing trapped compressed fluid to flow back into the corresponding ballast chamber, where the fluid expands due to the relatively lower pressure, displacing seawater already in the ballast chamber, exiting seawater back into the sea through the seawater inlet and outlet 24A, 24B.

[0057] Thus, two processes are at play: One that pumps compressible fluid from the ballast cambers into the accumulators, causing the floating structure to sink further, and one that lets the fluid flow back from the accumulators into the ballast chambers, causing the floating structure to ascend. These opposing processes counteract each other.

[0058] In one embodiment of this self-regulating wave powered submersion control system the ballast chambers 18 may include a surface that separates the compressible fluid from the seawater below. This surface may be a movable plate, like the top of a piston, or it may be a device made of elastic material, such as a membrane. Alternatively, the parts of the ballast chamber containing the compressible fluid may be contained in abladder, or other means well known to engineers could be provided, to prevent any contact between the compressible fluid and the seawater. One purpose of this will be to prevent corrosion.

[0059] In one embodiment of the invention, illustrated in figure 4, the piston rod end mount 10, pointing down, is a universal joint 13. At the bottom end of this universal joint, the floating body is connected to its mooring, e.g. a pulley 3B holding the cable 4 attached to the winch 5. The upper or lower shaft of the universal joint, or both, may have inserted a swivel 25, i.e. a coupling between the two parts enabling one to revolve without turning the other. The universal joint and swivel(s) allow the floating body to tilt in any direction and to rotate about its own vertical axis without forcing other parts to move with it, like a shoulder joint or hip joint.

[0060] The shoulder and hip joints of the human body are ball-and-socket joints allowing movement in multiple directions, just like the universal joint and swivel(s) described above. Alternatively, in one embodiment of the invention, the swivel(s) and the universal joint may be replaced with a ball-and-socket joint 26, in principle the same as a shoulder or hip joint of a mammal skeleton.

[0061] Furthermore, at or near the piston rod end mount 10, on the outside, facing the water, a galvanic sacrificial anode can be attached, in electrical contact with the piston rod and the surrounding seawater, as a corrosion protection means.List of drawing references

[0062] 1. floating wave energy absorbing body

[0063] 2. spring device

[0064] 3. (A, B, C) underwater pulleys

[0065] 4. winch cable

[0066] 5. winch

[0067] 6. piston rod

[0068] 7. cylinder chamber

[0069] 8. piston crown

[0070] 9. elastomer cushions

[0071] 10. piston rod end mount

[0072] 11. cylinder chamber end mount

[0073] 12. cylinder chamber bottom plate

[0074] 13. universal joint

[0075] 14. fluid outlet

[0076] 15. fluid inlet

[0077] 16. check valve

[0078] 17. check valve spring

[0079] 18. (A, B) seawater ballast chamber

[0080] 19. (A, B) flow passage from ballast chamber to shock absorbing device 20. (A, B) flow passage from shock absorbing device to accumulator tank 21. (A, B) accumulator tank for compressible fluid

[0081] 22. (A, B) check valve

[0082] 23. (A, B) by-pass flow passage

[0083] 24. (A, B) seawater inlet and outlet

[0084] 25. swivel

[0085] 26. ball-and-socket joint

Claims

Patent claims1.A wave energy absorbing device comprising a floating wave energy absorbing body (1) and a spring device (2), c h a r a c t e r i z e d i n t h a t the spring device is positioned inside the floating wave energy absorbing body, wherein the spring device is designed to absorb sudden accelerations to mitigate excess forces that would otherwise affect the floating wave energy absorbing body and its connected components, a n d that the wave energy absorbing device comprises a selfregulating buoyancy control system comprising one or more ballast chambers and one or more accumulators and is attached to the spring device (2) to power the selfregulating buoyancy control system by forcing compressible fluid to flow between the one or more ballast chambers and the one or more accumulators, thereby ballasting the floating body and causing it to submerge under water in high waves.2.The wave energy absorbing device according to claim 1, wherein the one or more ballast chambers and one or more accumulators are arranged within the floating body.3.The wave energy absorbing device according to claim 1, c h a r a c t e r i z e d i n t h a t the spring device is designed to reverse the direction of the applied force, to increase the force acting from the spring as any external agents cause the device to extend, thereby transforming compressive forces into tensile forces to enhance the durability and increase the lifespan of the device and its internal parts.4.A device according to claims 1, 2 and 3, c h a r a c t e r i z e d i n t h a t the self-regulating buoyancy control system is activated upon release of the spring device, i.e. when the spring is being returned to its resting position.5.A device according to claims 1, 2 and 3, which is a shock absorbing device integrated with the spring device, wherein the shock absorbing device includes a cylinder chamber with fluid inlets and outlets, a check valve allowing free inflow of fluid during the extension of the spring, and narrow fluid outlets forcing the trapped fluid to be expelledthrough one or more narrow fluid outlets, thereby converting the kinetic energy into heat and dissipating it into the surrounding fluid during the spring's return motion, c h a r a c t e r i z e d i n t h a t it provides damping only during the release of the spring.6.A device according to claim 1 where at the bottom end connection point of the spring is a universal joint, connecting the floating body to its mooring.7.A device according to claims 1 and 6, where said universal joint at one or both shafts has a swivel inserted, wherein the swivel permits independent rotational movement about the shaft between connected parts.8.A device according to claims 1, 6 and 7, where the universal joint and the swivel are replaced by a ball-and-socket joint, resembling the human hip- or shoulder joint.

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