Inverted pendulum wave energy converting device

Abstract

An inverted pendulum wave energy converting device for floating structures, boats, and ships is disclosed. It comprises an inverted pendulum structure having a moment of inertia changing system, and an energy converting connection system that connects the inverted pendulum structure to a host vessel. The capability to control the moment of inertia of the inverted pendulum structure about the axis of oscillation of the host vessel, substantially minimizes the danger of capsizing in a survival mode, maximizes wave energy conversion into electric energy, and minimizes the host vessel oscillations amplitude. In boats and ships, the inverted pendulum structure may comprise a wind-assisted propulsion system for maximizing dean energy harvesting efficiency.

Description

[0001] INVERTED PENDULUM WAVE ENERGY CONVERTING DEVICE

[0002] TECHNICAL FIELD

[0003] The present invention relates to inverted pendulum wave energy converting devices which are installed on floating structures, boats, and ships for converting wave energy into electrical energy and for reducing oscillation amplitude.

[0004] BACKGROUND ART

[0005] A host vessel may be a floating structure, a boat, or a ship. Such host vessels absorb wave energy and convert it into oscillating energy. To convert part of this oscillating energy, and therefore wave energy, into electrical energy, swinging pendulum devices are installed on host vessels (Yong Ma, Shan Ai, Lete Yang, Aiming Zhang, Sen Liu, Binghao Zhou; Research on design and optimization of the pitching float wave energy converter; July 2020). Such pendulum wave energy converting devices comprise a pendulum structure, and an energy converting connection system that connects the pendulum structure to the host vessel. Usually, the pendulum structure is a rod with a lumped mass at its far end that is connected at the other end, via an energy converting connection system, to the host vessel. A number of different energy converting connection systems have been developed in recent years for converting motion energy into electrical energy, such systems may be hydraulic, electromagnetic, or mechanical but other technologies may also be utilized, similar systems are widely being utilized also in other engineering fields for example in car suspension. During operation, for maximizing wave energy conversion, the dynamic motion of the pendulum structure is usually controlled by controlling the stiffness and damping of the energy converting connection system.

[0006] However, such pendulum wave energy converting devices have the disadvantage that the moment of inertia of the pendulum structure about the axis of oscillation of the host vessel is quite small relative to the mass of the pendulum structure, since the centre of mass of the pendulum structure is close to the axis of oscillation of the host vessel. As a result, very heavy pendulum structures are required for converting relatively small amounts of wave energy into electrical energy and for reducing just slightly the amplitude of oscillations of the host vessel, which economically is not viable.

[0007] An improved wave energy converting device that solves this problem and it can be considered the current state of the art in this field replaces the pendulum structure with an inverted pendulum structure (Jinming Wu, Chen Qian, Siming Zheng, Hi Chen, Dan Xia, Malin Goteman; Investigation on the wave energy converter that reacts against an internal inverted pendulum; Volume 247, 15 May 2022, 123493, ELSEVIER), In those devices, the centre of mass of the inverted pendulum structure is far from the axis of oscillation of the host vessel, and therefore during operation such inverted pendulum structures can achieve very high moment of inertia relative to their mass, thereby enabling wave energy conversion and oscillation amplitude reduction to be economically viable.

[0008] However, such inverted pendulum wave energy converting devices have the disadvantage that in an emergency case where the energy converting connection system is broken down and ceased while the sea is very rough or in a survival mode when the waves are too high, the inverted pendulum structure can cause the host vessel to capsize. Furthermore, provided that the oscillations of the host vessel are quite chaotic, it would be desirable for improving the efficiency of the wave energy conversion, to have the capability to control more parameters of the dynamic motion in addition to having the capability to control the stiffness and damping of the energy converting connection system. Moreover, to make inverted pendulum wave energy converting devices even more viable from an economical point of view particularly for boats and ships, it would be desirable to combine them with wind energy systems.

[0009] SUMMARY OF INVENTION The objective of the present invention is to provide an inverted pendulum wave energy converting device, wherein the inverted pendulum structure is not dangerous for the host vessel in emergency or survival mode cases, more parameters of the dynamic motion can be controlled during operation, and parts of the device can be combined with wind energy systems.

[0010] In accordance with the present invention, there is provided an inverted pendulum wave energy converting device, comprising an inverted pendulum structure, and an energy converting connection system connecting the inverted pendulum structure to a host vessel, characterized by the fact that the inverted pendulum structure comprises a moment of inertia changing system. The host vessel may be a floating structure, a boat, or a ship. During operation, the moment of inertia changing system may change the moment of inertia of the inverted pendulum structure about the axis of oscillation of the host vessel by the following ways: first by increasing or reducing the mass of the inverted pendulum structure, second by increasing or reducing the perpendicular distance of the inverted pendulum structure centre of mass from the axis of oscillation of the host vessel, or third by a combination of them.

[0011] The moment of inertia changing system may comprise a folding mechanism which can raise or lower the inverted pendulum structure centre of mass. The folding mechanism can fold down the inverted pendulum structure in a short period of time. The inverted pendulum structure may comprise a water tank, and the moment of inertia changing system may comprise a water filling and emptying system. Furthermore, the moment of inertia changing system may further comprise an emergency water emptying door which can empty the water tank in a short period of time.

[0012] The inverted pendulum structure may comprise a column and a body which is connected to the column, and the moment of inertia changing system may comprise a guided connection between the column and the body and a motor mechanism which can move the body up and down the column. Furthermore, the moment of inertia changing system may further comprise an emergency decoupling mechanism which can decouple the motor mechanism so that the body can be lowered in a short period of time.

[0013] When the host vessel is a boat or a ship, the inverted pendulum structure may comprise a wind-assisted propulsion system. Also, the energy converting connection system may comprise a yaw rotating mechanism which can rotate the wind-assisted propulsion system. The wind-assisted propulsion system may comprise one or more of the following: a rotor sails system (Flettner rotor), a rigid wing sails system, a soft wing sails system, a soft sail system, or a ventilated foil system.

[0014] An inverted pendulum wave energy converting device, in accordance with the present invention, offers numerous advantages. In an emergency or a survival mode the moment of inertia changing system reduces in a short period of time the moment of inertia of the inverted pendulum structure about the axis of oscillation of the host vessel, down to a very small fraction, thereby reducing substantially the adverse effects of the inverted pendulum structure on the stability of the host vessel Furthermore, the moment of inertia of the inverted pendulum structure about the axis of oscillation of the host vessel is an important parameter of dynamics and therefore having the capability to control it during operation, in addition to having the capability to control the stiffness and damping of the energy converting connection system, enables maximization of the wave energy con version efficiency and minimization of the oscillations amplitude of the host vessel. Moreover, wave energy and wind energy technologies can be combined in devices of the present invention since the inverted pendulum structure may comprise a wind-assisted propulsion system. Such combined clean energy devices, by being very efficient, can be very attractive from an economical point of view and therefore quite more likely to be installed on boats and ships. BRIEF DESCRIPTION OF DRAWINGS

[0015] Some preferred embodiments of the present invention will now be described by way of example only and with reference to the accompanying drawings, in which:

[0016] Figure 1 shows a cross-section of a ship having an inverted pendulum wave energy converting device, in accordance with one embodiment of the present invention. The sea is wavy, the ship is shown in a vertical orientation, the inverted pendulum wave energy converting device is not in operation and therefore it is also in a vertical orientation.

[0017] Figure 2 shows a cross-section of a ship having an inverted pendulum wave energy converting device, in accordance with the embodiment of the present invention that is shown in Figure 1, during operation where the ship is rolling, and the device of the present invention oscillates. The sea is wavy, the ship is having a random rolling angle with the vertical, the inverted pendulum wave energy converting device is in operation and therefore it is having, in general, a different angle with the vertical compared to the angle that the ship is having with the vertical.

[0018] Figure 3 shows a longitudinal-section of a ship having an inverted pendulum wave energy converting device, in accordance with the embodiment of the present invention that is shown in Figures 1 and 2, where the inverted pendulum structure is folded-down on the ship deck. The sea is wavy, and the ship is shown in a vertical orientation.

[0019] Figure 4 shows a cross-section of a ship having an inverted pendulum wave energy converting device, in accordance with another embodiment of the present invention. The sea is wavy, the ship is shown in a vertical orientation, the inverted pendulum wave energy converting device is not in operation and therefore it is also in a vertical orientation.

[0020] Figure 5 shows a cross-section of a ship having an inverted pendulum wave energy converting device, in accordance with a further embodiment of the present invention in which all features are the same with those in the first embodiment (Figures 1, 2 and 3) and the inverted pendulum structure further comprises a rotor sails system (Flettner rotor). The sea is wavy, the ship is shown in a vertical orientation, the inverted pendulum wave energy converting device is not in operation and therefore it is also in a vertical orientation.

[0021] DESCRIPTION OF EMBODIMENTS

[0022] In accordance with the preferred embodiment of the present invention as shown in Figure 1, the host vessel is a ship 1, the inverted pendulum structure comprises a cylindrical water tank 2 which is perpendicular to the ship deck when the inverted pendulum wave energy converting device is not in operation, the energy converting connection system comprises a hydraulic connection system 3 that connects the circular base of the cylindrical water tank 2 to the ship 1. The hydraulic connection system 3 comprises hydraulic piston-cylinders, hydraulic accumulators, hydraulic motor-electric generator systems and a mechanical hinge support. During operation, spring stiffness constants are actively controlled by small electric motor-hydraulic pump systems, and damping coefficients are actively controlled by controlling the converting power. Many other hydraulic or non- hydraulic known configurations are possible for the energy converting connection system. The moment of inertia changing system comprises a water filling and emptying system. The water filling and emptying system comprises electric motor-hydraulic pump systems, valves, and PLCs for control. Furthermore, the moment of inertia changing system further comprises an emergency water emptying door which can empty the cylindrical water tank 2 in a very short time. During operation as shown in Figure 2, in case of emergency, for example, if the ship rolling angle threshold has been exceeded, the water filling and emptying system and the emergency water emptying door will empty the cylindrical water tank 2 in a very short time, thereby reducing the mass and therefore the moment of inertia of the cylindrical water tank 2 about the axis of oscillation of the ship 1, which substantially minimizes the adverse effects of the cylindrical water tank 2 on the stability of the ship 1. In addition, by having the capability to change the water mass and therefore the moment of inertia of the cylindrical water tank 2 about the axis of oscillation of the ship 1, the ability to control the dynamic motion during operation is enhanced, thereby enabling maximization of the converted wave energy and minimization of the ship oscillations amplitude. Moreover, the moment of inertia changing system further comprises a folding mechanism. The folding mechanism comprises a hinge-actuator system which is installed on the base of the cylindrical water tank 2 enabling the cylindrical water tank 2 to rotate until it is laid-down on the ship deck as shown in Figure 3. By rotating the empty, for example, cylindrical water tank 2 between its vertical position and its laid-down position, the perpendicular distance of the cylindrical water tank centre of mass from the axis of oscillation of the ship 1 changes, and therefore the cylindrical water tank moment of inertia about the axis of oscillation of the ship 1 also changes. This rotation, therefore, can be utilized for further controlling the cylindrical water tank moment of inertia about the axis of oscillation of the ship 1. As a result, the enhanced moment of inertia control can be utilized in emergency cases, in reducing the amplitude of the ship oscillations, and in maximizing the wave energy conversion efficiency.

[0023] In accordance with another preferred embodiment of the present invention as shown in Figure 4, the host vessel is a ship 1, the inverted pendulum structure comprises a steel column 4 which is perpendicular to the ship deck when the inverted pendulum wave energy converting device is not in operation and a water tank 5 which is connected to the steel column 4, the energy converting connection system comprises a hydraulic connection system 3 connecting the steel column base to the ship 1. The energy converting connection system is the same as that in the first embodiment. The moment of inertia changing system comprises all the three features that it comprises in the first embodiment, namely : the water filling and emptying system, the emergency water emptying door and the folding mechanism. The moment of inertia changing system further comprises a guided connection between the steel column 4 and the water tank 5, and a motor mechanism which can move the water tank 5 up and down the steel column 4. During operation, the moment of inertia of the inverted pendulum structure about the axis of oscillation of the ship 1, can be controlled further by controlling the up and down movement of the water tank 5, since this up and down movement changes the perpendicular distance of the inverted pendulum structure centre of mass from the axis of oscillation of the ship 1. This enhanced moment of inertia control enables maximization of the wave energy conversion efficiency and minimization of the ship oscillations amplitude. Moreover, the moment of inertia changing system further comprises an emergency decoupling mechanism which decouples the motor mechanism letting the water tank 5 roll down the steel column 4 in case the motor mechanism is broken down and ceased, so the adverse effects of the inverted pendulum structure on the stability of the ship 1 are minimized.

[0024] In accordance with a further preferred embodiment of the present invention as shown in Figure 5, all features are the same with those in the first embodiment (Figures 1, 2 and 3) and the inverted pendulum structure further comprises a wind-assisted propulsion system. The wind-assisted propulsion system comprises a rotor sails system (Flettner rotor) 6. The resulting clean energy device is very attractive from an economical point of view due to its high efficiency. Generally, the wind-assisted propulsion system comprises one or more of the following systems: a rotor sails system (Flettner rotor) 6, a rigid wing sails system, a soft wing sails system, a soft sail system, or a ventilated foil system, in case the wind-assisted propulsion system requires yaw rotation, the energy converting connection system further comprises a yaw rotating mechanism.

[0025] Although the invention has been explained in relation to its preferred embodiments as mentioned above, it is to be understood that many other possible modifications and variations can be made without departing from the scope of the present invention. It is, therefore, contemplated that the appended claims will cover such modifications and variations that fall within the true scope of the invention.

Claims

CLAIMS1. An inverted pendulum wave energy converting device, comprising an inverted pendulum structure, and an energy converting connection system connecting the inverted pendulum structure to a host vessel, characterized by the fact that the inverted pendulum structure comprises a moment of inertia changing system.

2. An inverted pendulum wave energy converting device, in accordance with claim 1, characterized by the fact that the moment of inertia changing system comprises a folding mechanism which can raise or lower the inverted pendulum structure centre of mass.

3. An inverted pendulum wave energy converting device, in accordance with claim 1, characterized by the fact that the inverted pendulum structure comprises a water tank, and the moment of inertia changing system comprises a water filling and emptying system.

4. An inverted pendulum wave energy converting device, in accordance with claim 3, characterized by the fact that the moment of inertia changing system further comprises an emergency water emptying door.

5. An inverted pendulum wave energy converting device, in accordance with claim 1, characterized by the fact that the inverted pendulum structure comprises a column and a body which is connected to the column, and the moment of inertia changing system comprises a guided connection between the column and the body and a motor mechanism which can move the body up and down the column.

6. An inverted pendulum wave energy converting device, in accordance with claim 5, characterized by the fact that the moment of inertia changing system further comprises an emergency decoupling mechanism which can decouple the motor mechanism.

7. An inverted pendulum wave energy converting device, in accordance with claim 1, characterized by the fact that the energy converting connection system comprises a yaw rotating mechanism.

8. An inverted pendulum wave energy converting device, in accordance with claim 1, characterized by the fact that the inverted pendulum structure comprises a wind-assisted propulsion system.

9. An inverted pendulum wave energy converting device, in accordance with claim 8, characterized by the fact that the wind-assisted propulsion system comprises a rotor sails system (Flettner rotor).

10. An inverted pendulum wave energy converting device, in accordance with claim 8, characterized by the fact that the wind-assisted propulsion system comprises a rigid wing sails system.

11. An inverted pendulum wave energy converting device, in accordance with claim 8, characterized by the fact that the wind-assisted propulsion system comprises a soft wing sails system.

12. An inverted pendulum wave energy converting device, in accordance with claim 8, characterized by the fact that the wind-assisted propulsion system comprises a soft sail system.

13. An inverted pendulum wave energy converting device, in accordance with claim 8, characterized by the fact that the wind-assisted propulsion system comprises a ventilated foil system.

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