EP4600483A1

EP4600483A1 - Multiple resonance wave energy converter and respective method thereof

Info

Publication number: EP4600483A1
Application number: EP24398002.6A
Authority: EP
Inventors: Kourosh REZANEJAD
Original assignee: Frenesim Das Ondas Lda
Current assignee: Frenesim Das Ondas Lda
Priority date: 2024-02-07
Filing date: 2024-02-07
Publication date: 2025-08-13

Abstract

Multiple resonance wave energy converter comprising an L-shaped compartment (1), delimited by the flotation module (3), the bottom plate (9), the side plates (13) and (14), the rear plates (10) and (11) and connected to a turbine (8) at the top, a compartment (2), delimited by the flotation modules (4), (5) and (6) of trapezoidal shape, the front plate (12), the rear plate (10) and connected to a turbine (7) at the top, two Electrical generators (15) and (16) coupled with the Turbines (7) and (8), respectively, a control unit (17) that controls the rotational speed of the turbines (7) and (8) and a power-transmission substation (18) to transmit the generated power to the grid by using underwater cable (19)and a single mooring element (20) attached to an anchor (21) at seabed configured so that the device rotates naturally around the anchor point.

Description

Field of the invention

The present invention falls within the scope of wave energy converters (WEC), particularly Dual Chamber Floating Oscillating Water Column (DCFOWC).

Background of the invention

The present invention is most closely related to patent application WO 2018147753 . This patent application discloses wave energy converter with two columns of oscillating water, the anterior and the posterior, relative to the incident waves.
The solution of the present invention presents several differences:
The multiple resonance wave energy converter and respective method has a fully submerged buoyancy module which plays a vital role in improving performance compared to the WO 2018147753 . By practical observations in the laboratory, plate 5 in WO 2018147753 device cannot impose a desired Harbor resonance mechanism to the system, because of the high draft of the device (height of the submerged part of the device is called as draft in naval architecture). In this case, the plate cannot interact properly with water particles and therefore, has no constructive influence on the performance as it cannot impose any resonance condition. On the other hand, application of buoyancy module 4 in the present invention (Fig. 1a and 1b) instead of plate 5 in the WO 2018147753 , causes an appropriate interaction with the water particles and imposes proper resonance mechanism on the WEC leading to quite higher efficiency.
The buoyancy tank 3 in WO 2018147753 causes a kind of destructive effect on the performance leading to a decrease in the efficiency of the system. It is because tank 3 prevents a straightforward entrance of water flow inside Chamber 1 in WO 2018147753 . In the present application, the buoyancy tank is removed causing an increase in the performance. Instead of using buoyancy tank 3 in WO 2018147753 ), buoyancy modules (4), (5) and (6) are used in the present application to provide desired floatation for the system as well as interact with waves to enhance the energy absorption performance.
WO 2018147753 system has not a quite relevant stability in roll motions due to the relatively small size of buoyancy tank 3 (practically it was not possible to increase the size of this tank as it has a strong destructive effect on the performance of the system causing a significant drop in efficiency curve). In the present application, implementing side buoyancy modules (5) and (6) provides relevant stability in both pitch and roll motions. In addition, the trapezoid shape of those buoyancy modules causes accumulation of the wave energy flux on the entrance of the compartment (2) of the device.
In WO 2018147753 , the buoyancy tank 4 has a cubic shape which causes a significant drag force when the system interacts with waves leading to efficiency reductions. In present application, buoyancy module (3), preferably has a rounded shape that causes a significant reduction in wave forces, therefore leading to a significant increase in performance.
In another embodiment of the present invention, the buoyancy module (3), has a conical shape, elliptical shape or any other shape that can rip the water causing a certain reduction in wave-structure interaction forces.

Detailed description of the invention

A multiple resonance wave energy and respective method is, therefore, an object of the present invention.
The application of the present invention is to capture energy from waves and convert it into electricity (renewable energy production). As can be seen in Fig. 1a and 1b, the multiple resonance wave energy converter and respective method is mainly composed of two compartments. An L-shaped compartment (1)that typically is Backward Bent Duct Buoy (BBDB), delimited by the flotation module (3), the bottom plate (9), the side plates (13) and (14), the rear plates (10) and (11) and connected to a turbine (8) at the top, a compartment (2)that typically is a oscillating water column (OWC), delimited by the flotation modules (4), (5) and (6), the front plate (12), the rear plate (10) and connected to a turbine (7) at the top. Each of these compartments (1) and (2) has the role of harvesting a portion of wave energy and converting it into the pneumatic power in a specific range of wave frequency. Electrical generators (15) and (16) are connected (coupled) with the Turbines (7) and (8), respectively, to convert the mechanical power of the turbines to electrical power. Control unit (17) controls the rotational speed of the turbines to capture maximum power in various sea states. Power-transmission substation (18) is used to transmit the generated power to the grid (in the coastal area) by using underwater cable (19) or to any other energy demander (such as oil and gas offshore platforms). It should be noted that Control unit (17) and power-transmission substation (18) are located inside the same structure. A single mooring element (20) is attached to the multiple resonance wave energy (underneath the OWC part) to keep the multiple resonance wave energy converter in its position. The single mooring element (20) is attached to an anchor (21) at seabed.
When the WEC interacts with waves, the internal free surfaces inside compartments (1) and (2) start to have oscillatory motions in the vertical direction. In other words, water columns (22) and (23) (shown in Fig. 2) start to have oscillatory motions causing the air trapped inside the compartments (air pockets (24) and (25) in Fig. 2) to compress and expand. Compression and expansion of the air pockets imposes a kind of inhalation and exhalation air flow which allows the turbines (7) and (8) to convert the pneumatic power (energy of the air flow) to mechanical power. The electrical generators (15) and (16) coupled with the two turbines (7) and (8) generate clean electricity by using the mechanical power (extracted by the turbines). Therefore, the working principle of the WEC is to first convert energy of waves into pneumatic power, then from pneumatic power to mechanical power and finally generate electricity by using mechanical power. It should be noted that bi-directional turbines such as Wells or Bi-directional Impulse turbines should be used in this technology (for turbines (7) and (8)) to convert pneumatic power to mechanical power. The blades of the bi-directional turbines have a kind of symmetrical shape that allows the turbine to rotate always in one direction capturing the pneumatic energy irrespective of the air flow direction. To maintain the multiple resonance wave energy converter floating with having a proper hydrostatic and dynamic stability in waves, the buoyancy modules (3),(4),(5) and (6) provide the required buoyancy forces as well as restoring forces and moments in waves. Moreover, those buoyancy modules also play a prominent role in appropriately interacting with water particles in waves leading to a significant improvement in the performance of the device.
The multiple resonance wave energy converter and respective method has quite a high performance in terms of converting energy of waves into pneumatic power (and finally into electrical energy). This is due to the reason that various resonance mechanisms occur simultaneously that allows the capture of the energy from waves efficiently. It is noteworthy to remark that an oscillatory system has the highest tendency to capture energy of the excitation source in the resonance condition (Note: excitation source is an external resource such as sea waves that imposes excitation forces on an oscillatory system). In other words, when the natural damped frequency of the oscillatory system coincides with the frequency of the excitation source (such as waves in our case), the oscillatory mechanism captures maximum energy leading to amplified motions. Due to this reason, most of the existing wave energy converter technologies are designed in such a way to impose a natural resonance mechanism that allows to increase their performance in a specific wave frequency. However, by changing the frequency of waves in different sea states (due to the random nature of sea waves), the performance of those devices drops significantly as the resonance mechanism has no longer occurred. Therefore, the most existing technologies of wave energy converters have high performance only in a narrow range of wave frequencies and their performance drops significantly outside of this range. Due to the random nature of waves, those devices cannot efficiently capture energy of waves in a wide range of sea-states. Hence, their energy production costs (LCOE- Levelized Cost of Energy) become high, not allowing them to become a commercially viable energy production solution.
The novelty of the proposed multiple resonance wave energy converter and respective method is related to its geometrical shape that causes a multi-resonance mechanism with the dedicated various natural frequencies. In the wave frequencies that are relatively close to the natural frequency of the above-mentioned resonance mechanisms, the performance of the multiple resonance wave energy converter and respective method is maximized. Choosing the proper dimensions for the multiple resonance wave energy converter and respective method causes the natural frequencies of those resonance mechanisms to occur consecutively with a proper increment (difference) from each other. Therefore, a wide range of wave frequencies are covered by occurring several resonance frequencies successively causing the performance to remain at a high level in the whole range of typical wave frequencies. In other words, the efficiency bandwidth becomes maximized allowing the multiple resonance wave energy converter and respective method to efficiently capture energy of the random waves in a wide range of sea-states.
In this context, two resonance mechanisms occur in the OWC part of the device that includes compartment (2), buoyancy modules (4), (5) and (6) and Turbine (7), and three resonance mechanisms take place in the BBDB part that includes compartment (1), buoyancy module (3) and turbine (8).
These five resonance mechanisms cause the multiple resonance wave energy converter to maintain its tendency to capture maximum power in a wide range of wave frequencies. The OWC part of the device has the main contribution in capturing energy of waves in high and medium range frequencies. On the other hand, the BBDB part of the device has the main role of harvesting energy of waves in the low and medium frequencies of ocean waves. In this case, the five-resonance mechanism are as follows:

(I) The first resonance mechanism is dedicated to the case in which the frequency of the waves is relatively close to the natural frequency of Oscillating Water Column (22) in the BBDB part of the multiple resonance wave energy converter. As can be seen in Fig. 2, Oscillating Water Column (22) has an L-shaped geometry as it is surrounded by the buoyancy module (3). The relatively long length of the Oscillating Water Column (22), due to its L-shaped geometrical configuration, is causing a low natural frequency. Therefore, the BBDB part of the multiple resonance wave energy converter has the main contribution in capturing energy of waves in low frequencies. Moreover, in addition to provide the required buoyancy, the buoyancy module (3) has another role of shaping the L-shaped geomatical configuration in the BBDB part of the multiple resonance wave energy converter. Hence, it has a prominent effect in energy absorption mechanism.
(II) The second and third resonance mechanism (in the BBDB part) is related to the natural frequency of Heave and Pitch motions of the multiple resonance wave energy converter. When the frequency of waves occurs relatively close to the natural frequency of Heave or Pitch motions, those motions are amplified causing the internal free surface inside the two compartments, specifically compartment (1) to oscillate with large motions extracting energy from waves with high efficiency.
(III) The fourth resonance mechanism in OWC part, like the first resonance mechanism in BBDB, is related to the natural frequency of Oscillating Water Column (23). As it was indicated earlier, buoyancy modules (5) and (6) in addition of having the role of providing the required buoyancy for the multiple resonance wave energy converter, originate an energy concentration when the waves enter compartment (2). Therefore, they also have a prominent influence on the energy absorption mechanism of the multiple resonance wave energy converter.
(IV) The last (fifth) resonance mechanism in OWC part is related to the natural resonance frequency of the semi-confined water pocket (26) outside compartment (2) which is semi-confined above the buoyancy module (4) and between buoyancy modules (5) and (6). When the wave frequency occurs relatively close to the natural frequency of (horizontal motion of) the semi-confined water pocket (26), it starts to have amplified horizontal motions pushing the oscillating water column (23) to move with large motions which leads to a substantial increase in power capturing capacity of the multiple resonance wave energy converter. Hence, the submerged buoyancy module (4) plays a vital role in imposing this resonance mechanism in the energy production process.

The occurring of the above-mentioned resonance mechanisms consecutively causes the multiple resonance wave energy converter to maintain its high performance in almost whole range of ocean waves, so it can produce energy with high capacity, therefore with lower costs. This important feature makes this multiple resonance wave energy converter a commercially viable system to produce renewable energy from ocean waves.
The multiple resonance wave energy converter device has only a single line mooring system. In other words, the single mooring line (20) is attached to the multiple resonance wave energy converter (OWC part of the multiple resonance wave energy converter) in its top end and the other end is connected to an anchor (21) at seabed. This mooring line keeps the multiple resonance wave energy in the position. However, the multiple resonance wave energy converter is free to have oscillatory motions in 6 Degrees of Freedom (DOF). Furthermore, the multiple resonance wave energy with the attached mooring line can rigidly turn around the anchorage point depending on the dominant wave direction. In other words, by changing the wave direction, the device naturally turns around (rotates) the anchorage point in such a way that it always stays align with the dominant wave direction. This natural heading angle adjustment of the multiple resonance wave energy converter puts it in the exposes of receiving high wave energy flux which is a desirable condition for a multiple resonance wave energy converter. In this case, compartment (1) always stays downstream of waves and compartment (2) interacts with the waves directly.
Another object of the present invention is the method to produce energy with the multiple resonance wave energy converter. Said method being a method of capturing energy from waves and convert it into electricity when received at a multiple resonance wave energy converter, characterized in that said method includes:

a) interacting with waves, making the water columns (22) and (23) to start to have oscillatory motions causing the air pockets (24) and (25) inside the compartments (1) and (2) to compress and expand;
b) Utilizing the compression and expansion of air pockets (24) and (25) to create an inhalation and exhalation air flow, enabling turbines (8) and (7) to convert pneumatic power into mechanical power;
c) Amplifying the reciprocating motions of the Oscillating Water Column (22) within compartment (1) when the frequency of incoming waves coincides with or is relatively close to its natural frequency, resulting in increased wave energy absorption capacity;
d) Amplifying the heave motion of the multiple resonance wave energy converter device when the frequency of incoming waves coincides with or is relatively close to its natural frequency, leading to an increase in the reciprocating motions of Oscillating Water Columns (22) and (23) , resulting in increased wave energy absorption capacity;
e) Amplifying the pitch motion (rotational motion around the lateral axis) of the multiple resonance wave energy converter device when the frequency of incoming waves coincides with or is relatively close to its natural frequency, causing an increase in the reciprocating motions of Oscillating Water Column (22) resulting in increased wave energy absorption capacity;
f) Amplifying the reciprocating motions of the Oscillating Water Column (23) within compartment (2) when the frequency of incoming waves coincides with or is relatively close to its natural frequency, resulting in increased wave energy absorption capacity;
g) Amplifying the reciprocating horizontal motions of the semi-confined water pocket (26) outside compartment (1) when the frequency of incoming waves coincides with or is relatively close to its natural frequency, causing an amplified motion in the Oscillating Water Column (23) and leading to increased wave energy absorption capacity;

The method also comprising the steps of:

Converting mechanical power from turbines (7) and (8) to electrical power through mechanically coupled electrical generators (15) and (16);
Automatically controlling the rotational speed of turbines (7) and (8) via a control unit (17), by adjusting the rotational speed of generators (15) and (16) to maximize the captured power;
Transmitting the generated electrical power to an energy demander through a power-transmission substation (18) and an underwater cable (19).

The present disclosure is not to be limited to the specific implementations disclosed and that modifications and other implementations are intended to be included within the scope of the appended claims. Moreover, although the foregoing description and the associated drawings describe example implementations in the context of certain example combinations of elements and/or functions, it should be appreciated that different combinations of elements and/or functions may be provided by alternative implementations without departing from the scope of the appended claims. In this regard, for example, different combinations of elements and/or functions than those explicitly described above are also contemplated as may be set forth in some of the appended claims. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.

Brief description of the drawings

Fig. 1a illustrates the multiple resonance wave energy converter device with its apparatus (such as mooring line, underwater cable, control unit, etc.). In order to better indicate the components of the device, the longitudinal cross-section of the multiple resonance wave energy converter device with its apparatus are shown in Fig. 1b. As can also be seen in Fig. 1a, the compartment (2) (OWC part of the device) always interacts directly with waves and compartment (1) (BBDB part of the device) is located downstream of waves where it interacts with waves indirectly.
Fig. 2 represents the longitudinal cross-section of the multiple resonance wave energy converter device that is floating in water (water free surface level is also shown in this figure). Oscillating water columns, air pockets and semi-confined water pocket that are contributing to the energy harvesting mechanisms are shown in Fig. 2. It should be noted that the represented oscillating water columns, air pockets and semi-confined water pocket in Fig. 2 are not a part of the multiple resonance wave energy converter device, because they are belonging to the encompassed material in the surrounding environment.

Legend:

1-: Compartment
2-: Compartment
3-: flotation module
4-: flotation module
5-: flotation module
6-: flotation module
7-: Turbine
8-: Turbine
9-: Bottom plate
10-: Rear plate
11-: Rear plate
12-: Front plate
13-: Side plate
14-: Side plate
15-: Electrical generator
16-: Electrical generator
17-: Control unit
18-: Power transmission substation
19-: underwater cable
20-: mooring element
21-: Anchor
22-: water column
23-: water column
24-: Air pocket
25-: Air pocket
26-: Semi-confined water pocket

Claims

Multiple resonance wave energy converter comprising:
- an L-shaped compartment (1), delimited by the flotation module (3), the bottom plate (9), the side plates (13) and (14), the rear plates (10) and (11) and connected to a turbine (8) at the top;

- a compartment (2), delimited by the flotation modules (4), (5) and (6) of trapezoidal shape, the front plate (12), the rear plate (10) and connected to a turbine (7) at the top;

- two Electrical generators (15) and (16) coupled with the Turbines (7) and (8), respectively;

- A control unit (17) that controls the rotational speed of the turbines (7) and (8) and a power-transmission substation (18) to transmit the generated power to the grid by using underwater cable (19).
and

- a single mooring element (20) attached to an anchor (21) at seabed configured so that the device rotates naturally around the anchor point;
characterized in that
said compartment (1) being arranged contiguously with said compartment (2) by means of said rear plates (10) and (11) being configured to generate at least three different resonance frequencies from each other and said compartment (2) being configured to generate at least two different resonance frequencies from each other.
Multiple resonance wave energy converter according to the previous claim, characterized in that geometrical shape is configured to generate at least five resonance frequencies consecutively with a proper increment from each other.
Multiple resonance wave energy converter according to the previous claims, wherein one of the resonance frequencies is a low natural frequency due to the L-Shaped geometrical configuration of the Oscillating Water Column (22) and at least two another resonance frequencies are natural frequencies of Heave and Pitch motions of the Multiple resonance wave energy converter.
Multiple resonance wave energy converter according to the previous claims, wherein one of the resonance frequencies is related to the natural frequency of Oscillating Water Column (23) and at least another resonance frequency is related to the natural resonance frequency of the semi-confined water pocket (26) outside compartment (2).
Multiple resonance wave energy converter according to the previous claims, wherein air pockets (24) and (25) are forced to compress or expand by oscillatory motions in water columns (22) and (23).
Multiple resonance wave energy converter according to the claim 1, wherein the turbines (7) and (8) are bi-directional turbines such as Wells or Bi-directional Impulse.
A method of capturing energy from waves and convert it into electricity when received at a multiple resonance wave energy converter, characterized in that said method includes:
a) interacting with waves, making the water columns (22) and (23) to start to have oscillatory motions causing the air pockets (24) and (25) inside the compartments (1) and (2) to compress and expand;

b) Utilizing the compression and expansion of air pockets (24) and (25) to create an inhalation and exhalation air flow, enabling turbines (8) and (7) to convert pneumatic power into mechanical power;

c) Amplifying the reciprocating motions of the Oscillating Water Column (22) within compartment (1) when the frequency of incoming waves coincides with or is relatively close to its natural frequency, resulting in increased wave energy absorption capacity;

d) Amplifying the heave motion of the multiple resonance wave energy converter device when the frequency of incoming waves coincides with or is relatively close to its natural frequency, leading to an increase in the reciprocating motions of Oscillating Water Columns (22) and (23), resulting in increased wave energy absorption capacity;

e) Amplifying the pitch motion (rotational motion around the lateral axis) of the multiple resonance wave energy converter device when the frequency of incoming waves coincides with or is relatively close to its natural frequency, causing an increase in the reciprocating motions of Oscillating Water Column (22), resulting in increased wave energy absorption capacity;

f) Amplifying the reciprocating motions of the Oscillating Water Column (23) within compartment (2) when the frequency of incoming waves coincides with or is relatively close to its natural frequency, resulting in increased wave energy absorption capacity;

g) Amplifying the reciprocating horizontal motions of the semi-confined water pocket (26) outside compartment (1) when the frequency of incoming waves coincides with or is relatively close to its natural frequency, causing an amplified motion in the Oscillating Water Column (23) and leading to increased wave energy absorption capacity.
The method of claim 7 further comprising the steps of:
- Converting mechanical power from turbines (7) and (8) to electrical power through mechanically coupled electrical generators (15) and (16);

- Automatically controlling the rotational speed of turbines (7) and (8) via a control unit (17), by adjusting the rotational speed of generators (15) and (16) to maximize the captured power;

- Transmitting the generated electrical power to an energy demander through a power-transmission substation (18) and an underwater cable (19).