Floating wave energy conversion system to amplify pitch oscillations

Abstract

The present invention is in the field of systems for converting wave energy into electrical energy, in particular a floating wave energy conversion system (1) comprising a water duct (2), a pneumatic chamber (3), an air turbine (4), a flotation tank (6) and at least one oscillatory amplification chamber (5) of tubular shape with two closed ends, at least one of which has an internal volume occupied by a gas and a liquid. The floating wave energy conversion system (1) makes it possible to amplify the pitch oscillations under sea waves. This amplification is caused by the alternating flow of liquid in the oscillatory amplification chamber (5), that increases the oscillation of the water column and increases the amount of energy converted.

Description

[0001] DESCRIPTION

[0002] FLOATING WAVE ENERGY CONVERSION SYSTEM TO AMPLIFY PITCH

[0003] OSCILLATIONS

[0004] FIELD OF THE INVENTION

[0005] The present invention is in the field of systems that convert wave energy into electrical energy.

[0006] BACKGROUND TO THE INVENTION

[0007] Wave energy of oceans and seas is a renewable energy that is still little utilised, in contrast to more conventional renewable energies used for electricity production — hydro, wind and solar.

[0008] Since the end of the 1970s, various configurations and technological solutions have been proposed to capture wave energy to generate electricity. These devices can be categorised as follows: (i) devices located on the shoreline or in shallow waters, generally with a fixed structure; (ii) devices integrated into breakwaters; (iii) devices for offshore applications, in waters between 20 and 100 metres deep, suitable to be arranged in arrays, consisting in most cases of floating converters moored to the bottom. The offshore devices are the ones that can contribute most significantly to the global electricity supply.

[0009] In one class of converters, generically known as oscillating water column (OWC) converters, there is a hollow structure, fixed or floating, opened to the sea in its submerged part. Due to the action of the incident waves, the free surface of the water inside the converter has an oscillatory movement similar to that of a piston, resulting in an oscillating pressure of the air that occupies the upper part of the cavity. This effect is used to drive an air turbine that communicates the air inside the cavity (the pneumatic chamber) and the outside atmosphere. Due to the action of the waves, the pressure of the air inside the chamber oscillates, and the turbine is subject to a pressure difference that changes sign cyclically. This is why it is called a self-rectifying turbine (the direction of rotation remains invariable, independently of the direction of the air flow) . Various types of self-rectifying air turbines have been designed and used for applications in wave energy converters .

[0010] The oscillating water column design provides a simple and reliable way of energy conversion: basically, an air turbine that directly drives a conventional electrical generator .

[0011] Offshore oscillating water column converters generally are able of absorbing wave energy even if the oscillations of their structure are impeded in various degrees of freedom. This is particularly relevant for the 'Backward-Bent-Duct-Buoy' or BBDB converter, where the structure's oscillation modes are essentially pitching and heaving .

[0012] The 'Backward-Bent-Duct-Buoy' or BBDB converter was the subject of patents US 4,741,157 and EP 0 950 812. It is a rectangular barge with a flat bottom. Inside, and covering the entire width and length of the float, there is a moon-pool or oscillating water column with an 'L' shape, in which the horizontal section is longer than the vertical one. The end of the horizontal section open to the sea is submerged, facing the opposite direction to the incident waves (hence the name 'backward' given to the converter) . The inner free surface is located at the top of the vertical part of the water column. The pneumatic chamber, whose volume varies due to the effect of the incident wave, communicates with the atmosphere via a self-rectifying air turbine driving an electric generator. Patent PT2410170E 'Floating wave energy converter and process for improving the efficiency of a floating wave energy converter' differs from patent US 4,741,157 in the following points: (i) the existence of a front ballast tank, extending vertically; (ii) the existence of one or more so-called stabilisation submerged plates located at the front of the floater.

[0013] Recent studies[1] [2]found that heave oscillations affect negatively the energy performance of BBDB-type converters, while pitch oscillations increase the conversion of wave energy into electrical energy in this type of converter. However, existing converters do not have the means to take advantage of pitch oscillations, that would improve the conversion performance.

[0014] The present solution addresses this problem with the additional advantage of amplifying the pitch oscillations in BBDB-type converters in an innovative way.

[0015] REFERENCES

[0016] [1] - Z. Liu, X. Zhang, C. Xu. Hydrodynamic and energy-harvesting performance of a BBDB-OWC device in irregular waves: An experimental study. Applied Energy vol. 350 (2023) 121737 [2] - Z. Liu, X. Zhang, C. Xu. Experimental study on a back-bent duct buoy oscillating water column device in various degrees of freedom. Renewable Energy vol. 224 (2024) 120121

[0017] SUMMARY OF THE INVENTION

[0018] The object of the present invention is thus a floating wave energy conversion system (1) comprising a water duct (2) , a pneumatic chamber (3) , an air turbine (4) , a flotation tank (6) and at least one oscillatory amplification chamber (5) , wherein:

[0019] - the water duct (2) is submerged below the water level and consists of a vertical section and a horizontal section, whereby the vertical section and the horizontal section are arranged perpendicular to each other and are joined in such a way that the water duct (2) has an L-shape, whereby the vertical section of the water duct (2) is arranged on a vertical axis, and the horizontal section of the water duct (2) is arranged on a horizontal axis; where the free end of the vertical section of the water duct (2) communicates with the pneumatic chamber (3) and the free end of the horizontal section of the water duct (2) comprises an opening (8) located below the water level, so that the water duct (2) is completely filled with water and a column of water forms under the pneumatic chamber (3) in the vertical section of the water duct (2) ;

[0020] - the pneumatic chamber (3) contains air which communicates with the water column inside the vertical section of the water duct (2) and with the air turbine (4) ;

[0021] - the air turbine (4) is coupled to an electric generator to generate electrical energy from the mechanical energy produced by the air flow through the turbine and transmitted by a coupling shaft;

[0022] - the flotation tank (6) is located on the horizontal section of the water duct (2) and may be fully or partially submerged;

[0023] - at least one oscillatory amplification chamber (5) is arranged parallel to the horizontal section of the water duct (2) , where at least one oscillatory amplification chamber (5) has a tubular shape with two closed ends where the longitudinal axis of at least one oscillatory amplification chamber (5) is parallel to the longitudinal axis of the horizontal section of the water duct ( 2 ) ; and

[0024] - the internal volume of at least one oscillatory amplification chamber (5) is filled with a gas and a liquid ( 9 ) .

[0025] The buoyancy and stability of the system is ensured by the buoyancy tank (6) , so that, in the absence of sea waves, the longitudinal axis of the oscillatory amplification chambers (5) is approximately horizontal.

[0026] The submerged water duct (2) is completely filled with a column of water whose shape fits the L-shaped water duct, since the opening (8) is in communication with the sea water. This water column has a horizontal part and a vertical part, with the free surface of the water column facing the bottom of the pneumatic chamber (3) , where the vertical part of the water column acts like a piston oscillating according to the sea waves. The effect of the oscillation of the water column is the compression of the air in the pneumatic chamber (3) during upward movements of the water column, or the expansion of the air in the pneumatic chamber (3) during downward movements of the water column. The compression and / or expansion of the air causes air to flow through the air turbine (4) , which, being coupled to an electrical generator, converts the mechanical energy generated by the air flow in the air turbine (4) into electrical energy in the electrical generator.

[0027] The oscillatory amplification chambers (5) make it possible to amplify the pitch oscillation of the floating wave energy conversion system (1) , this oscillation being caused naturally by the waves. The pitch oscillations of the floating wave energy conversion system (1) cause a longitudinal flow of the liquid (9) that partially fills each oscillatory amplification chamber (5) , alternately in one direction and the other, resulting in an alternating longitudinal movement of the centre of mass of the liquid in the oscillatory amplification chambers (5) . In addition, the longitudinal flow of the liquid, alternately from one end of the oscillatory amplification chamber (5) to the other, also influences the centre of mass of the floating wave energy conversion system (1) under sea waves, with the centre of mass of the floating wave energy conversion system (1) being displaced like a pendulum as the liquid in the oscillatory amplification chambers (5) flows longitudinally from one end of the oscillatory amplification chamber (5) to the other.

[0028] This alternating movement increases the oscillatory amplitude of the water column inside the vertical section of the water duct (2) , which in turn increases the amplitude of the compression and expansion of the air in the pneumatic chamber (3) and increases the amplitude of the alternating air flow that passes through the turbine (4) , thus increasing the electrical energy generated. In a preferred embodiment of the present invention, the oscillatory amplification chambers (5) are submerged and arranged under the lower horizontal wall of the water duct (2) . In addition to increasing the electrical energy generated by the floating wave energy conversion system (1) , the air contained inside the oscillatory amplification chambers (5) contributes positively to make the submerged oscillatory amplification chambers (5) beneficial to the buoyancy of the floating wave energy conversion system (1) .

[0029] In a preferred embodiment of the present invention, the floating wave energy conversion system (1) comprises a plurality of oscillatory amplification chambers (5) , arranged side by side so that the longitudinal axis of each of the oscillatory amplification chambers (5) is parallel to the longitudinal axis of the horizontal section of the water duct (2) . The area occupied by the oscillatory amplification chambers (5) is equal to or less than the area of the lower horizontal wall of the water duct (2) where the oscillatory amplification chambers (5) are placed side by side. Preferably, the oscillatory amplification chambers (5) are rigidly connected to the lower wall of the horizontal section of the water duct (2) , in order to provide structural reinforcement of the floating wave energy conversion system (1) •

[0030] This invention provides several advantages, namely allowing the efficient conversion of wave energy into electrical energy, enhanced by the pitch oscillation of the system, and the incorporation of oscillatory amplification chambers (5) into the floating wave energy conversion system (1) is simple to implement, reliable and easy to maintain. In addition, this solution does not involve high maintenance costs, which contributes to greater sustainability of the floating wave energy conversion system (1) .

[0031] DESCRIPTION OF THE FIGURES

[0032] Figure 1 - representation of an embodiment of the floating wave energy conversion system (1) : a) longitudinal section of the floating wave energy conversion system (1) ; b) AA cross-section of the floating wave energy conversion system (1) . The seawater level outside the system and at the interface between the top of the vertical section of the water duct (2) and the pneumatic chamber (3) is marked by the dashed line, and the liquid level (9) inside the oscillatory amplification chambers (5) is also marked by a dashed line inside the oscillatory amplification chambers (5) . The water duct (2) has an internal wall (10) aligned with the longitudinal axis of the horizontal section of the water duct (2) , and is configured to divide the water flow inside the horizontal section into two channels to provide better guidance of the water flow along the duct and, at the same time, reinforce structurally the water duct (2) . The floating wave energy conversion system (1) has seven oscillatory amplification chambers (5) arranged side by side parallel to each other under the lower horizontal wall of the water duct (2) , thus being submerged, with each oscillatory amplification chamber (5) having a rectangular tubular shape with two closed ends and a longitudinal axis parallel to the longitudinal axis of the horizontal segment of the water duct (2) . The oscillatory amplification chambers (5) are preferably rigidly connected to the lower horizontal wall of the water duct (2) to reinforce the structure of the system and ensure that the oscillatory amplification chambers (5) follow the movements of the floating wave energy conversion system (1) .

[0033] The internal volume of each oscillatory amplification chamber (5) is occupied by a gas, preferably air, and a liquid, preferably water.

[0034] DETAILED DESCRIPTION OF THE INVENTION

[0035] The most general advantageous configurations of the present invention are described in the Summary of the invention. These configurations are detailed below, according to other advantageous and / or preferred ways of implementing the present invention.

[0036] In a preferred embodiment of the present invention, the oscillatory amplification chamber (5) has a prismatic shape so that the cross-section of the oscillatory amplification chamber (5) has a polygonal shape preferably rectangular, as represented in Figure 1 (b) . Alternatively, the oscillatory amplification chamber (5) can have a cylindrical shape so that the cross-section of the oscillatory amplification chamber (5) has a circular shape.

[0037] In another embodiment of the present invention, each of the oscillatory amplification chambers (5) has a shape in which the geometric location of the centres of the cross-sections of the oscillatory amplification chamber (5) is not a straight line, in which the centre point (Po) of the cross-section of the oscillatory amplification chamber (5) that is equidistant from the two closed ends is beneath the straight line (Re) that joins the centre points of the cross-sections of the two ends. Preferably, the distance from the centre point (Po) of the cross-section equidistant from the two ends of the oscillatory amplification chamber (5) to the aforementioned straight line (Re) joining the centre points of the cross-sections of the two ends is less than 5% of the length of the oscillatory amplification chamber (5) . This is to prevent the liquid inside the oscillatory amplification chamber (5) from being trapped near one of the ends of the oscillatory amplification chamber (5) when the floating wave energy system (1) is more tilted in pitch.

[0038] In another embodiment of the present invention, the oscillatory amplification chambers (5) have a non- uniform length, this length preferably being equal to or less than the length of the horizontal section of the water duct ( 2 ) .

[0039] In a preferred embodiment of the present invention, each oscillatory amplification chamber (5) has at least one inlet valve and at least one outlet valve, with at least one inlet valve being configured to add liquid to the interior of the oscillatory amplification chamber (5) and at least one outlet valve being configured to remove liquid from the interior of the oscillatory amplification chamber (5) , thus facilitating maintenance operations related with the liquid level (9) inside the oscillatory amplification chambers (5) .

[0040] In addition, each oscillatory amplification chamber (5) has an amount of liquid ranging between 35% and 65% of the internal volume of the oscillatory amplification chamber (5) , so that the longitudinal flow of the liquid, alternately from one end of the oscillatory amplification chamber (5) to the other, results in a pendulum displacement of the centre of mass of the floating wave energy conversion system ( 1 ) .

[0041] Preferably, the liquid contained in the oscillatory amplification chamber (5) is water.

[0042] In a preferred embodiment of the present invention, the oscillatory amplification chambers (5) are made of a rigid material, preferably metallic such as steel. Alternatively, the rigid material making up the oscillatory amplification chambers (5) can be a plastic material.

[0043] In another embodiment of the present invention, the floating wave energy conversion system (1) has a water duct (2) has a curved inner surface at the corners formed by the perpendicular union of the vertical section with the horizontal section of the water duct (2) , in order to minimise the energy losses due to the separation of the boundary layer in the seawater flow inside the water duct (2) .

[0044] In another embodiment of the present invention, the horizontal section of the water duct (2) has at least one internal wall (10) aligned with the longitudinal axis of the horizontal section of the water duct (2) , so that the flow of water inside the horizontal section of the water duct (2) is divided into more than one channel. This division guides the water flow inside the water duct (2) better. In addition, the internal walls of the water duct (2) reinforce structurally the system.

[0045] In an alternative embodiment of the present invention, the floating wave energy conversion system (1) comprises at least one mooring device (7) configured to minimise the restriction of the pitch oscillations of the floating wave energy conversion system ( 1 ) .

[0046] As will be clear to one skilled in the art , the present invention should not be limited to the embodiments illustrated herein, and various modi fications are possible which remain within the scope of the present invention .

[0047] The preferred embodiments presented above can be combined in di f ferent ways , but we will avoid repeating all these combinations here .

Claims

CLAIMS1. Floating wave energy conversion system (1) comprising a water duct (2) , a pneumatic chamber (3) , an air turbine (4) , a flotation tank (6) , wherein:- the water duct (2) is submerged below the water level and consists of a vertical section and a horizontal section, whereby the vertical section and the horizontal section are arranged perpendicular to each other and are joined in such a way that the water duct (2) has an L-shape, whereby the vertical section of the water duct (2) is arranged on a vertical axis, and the horizontal section of the water duct (2) is arranged on a horizontal axis; where the free end of the vertical section of the water duct (2) communicates with the pneumatic chamber (3) and the free end of the horizontal section of the water duct (2) comprises an opening (8) located below the water level, so that the water duct (2) is completely filled with water and a column of water forms under the pneumatic chamber (3) in the vertical section of the water duct (2) ;- the pneumatic chamber (3) contains air which communicates with the water column inside the vertical section of the water duct (2) and with the air turbine (4) ;- the air turbine (4) is coupled to an electric generator to generate electrical energy from the mechanical energy produced by the air flow through the turbine and transmitted by a coupling shaft;- the flotation tank (6) is located on the horizontal section of the water duct (2) and may be fully or partially submerged;the floating wave energy conversion system (1) being characterised by comprising at least one oscillatory amplification chamber (5) arranged parallel to the horizontal section of the water duct (2) , where:- at least one oscillatory amplification chamber (5) has a tubular shape with two closed ends where the longitudinal axis of at least one oscillatory amplification chamber (5) is parallel to the longitudinal axis of the horizontal section of the water duct (2) ; and- the internal volume of at least one oscillatory amplification chamber (5) is filled with a gas and a liquid ( 9 ) .

2. Floating wave energy conversion system (1) according to the preceding claim characterised in that at least one oscillatory amplification chamber (5) is submerged and arranged under the lower horizontal wall of the water duct ( 2 ) .

3. Floating wave energy conversion system (1) according to claim 1 or 2 characterised by comprising a plurality of oscillatory amplification chambers (5) wherein the oscillatory amplification chambers (5) are arranged side by side so that the longitudinal axis of each of the oscillatory amplification chambers (5) is parallel to the longitudinal axis of the horizontal section of the water duct ( 2 ) .

4. Floating wave energy conversion system (1) according to claims 2 and 3 characterised in that the oscillatory amplification chambers (5) are connected to the bottom wall of the horizontal section of the water duct (2) .

5. Floating wave energy conversion system (1) according to any of the preceding claims characterised in that at least one oscillatory amplification chamber (5) has a prismatic shape so that the cross-section of the oscillatory amplification chamber (5) has a polygonal shape.

6. Floating wave energy conversion system (1) according to any one of claims 1 to 4 characterised in that at least one oscillatory amplification chamber (5) has a cylindrical shape so that the cross-section of the oscillatory amplification chamber (5) has a circular shape.

7. Floating wave energy conversion system (1) according to any of the preceding claims characterised in that at least one oscillatory amplification chamber (5) has a shape in which the geometric location of the centres of the cross-sections of the oscillatory amplification chamber (5) is not a straight line, in which the centre point (Po) of the cross section of the oscillatory amplification chamber (5) which is equidistant from the two closed ends is arranged in a lower plane with respect to the straight line (Re) joining the centre points of the cross sections of the two ends .

8. Floating wave energy conversion system (1) according to claim 7 characterised in that at least one oscillatory amplification chamber (5) has a shape in which the distance between the centre point (Po) of the cross section equidistant from the two ends of the oscillatory amplification chamber (5) and the straight line (Re) joining the centre points of the cross sections of the two ends is less than 5% of the length of the oscillatory amplification chamber .

9. Floating wave energy conversion system (1) according to any of the preceding claims characterised in that at least one oscillatory amplification chamber (5) has a length equal to or less than the length of the horizontal section of the water duct (2) .

10. Floating wave energy conversion system (1) according to any of the preceding claims characterised in that at least one oscillatory amplification chamber (5) comprises at least one inlet valve and at least one outlet valve, with at least one inlet valve being configured to add liquid to the interior of the oscillatory amplification chamber (5) and at least one outlet valve being configured to remove liquid from the interior of the oscillatory amplification chamber (5) .

11. Floating wave energy conversion system (1) according to any of the preceding claims characterised by at least one oscillatory amplification chamber (5) comprising an amount of liquid ranging between 35% and 65% of the internal volume of the oscillatory amplification chamber (5) .

12. Floating wave energy conversion system (1) according to any of the preceding claims characterised in that at least one oscillatory amplification chamber (5) is made of a rigid material.

13. Floating wave energy conversion system (1) according to any of the preceding claims characterised in that the water duct (2) has a curved inner surface at the corners formed by the perpendicular union of the vertical section with the horizontal section of the water duct (2) .

14. Floating wave energy conversion system (1) according to any of the preceding claims characterised in that the horizontal section of the water duct (2) has at least one internal wall (10) aligned with the longitudinal axis of the horizontal section of the water duct (2) , so that the flow of water inside the horizontal section of the water duct (2) is divided into more than one channel.

15. Floating wave energy conversion system (1) according to any of the preceding claims characterised in that it comprises at least one mooring device (7) .

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