Multi-frequency resonance point absorption type wave energy conversion device and control method

Abstract

The invention discloses a multi-frequency resonance point absorption type sea wave energy conversion device and a control method. The device comprises a fixed base, a sea wave energy absorption mechanism, an energy conversion mechanism, a variable stiffness mechanism and a power generation mechanism. An energy conversion mechanism, a variable stiffness mechanism and a power generation mechanism are mounted in the fixed base, and the variable stiffness mechanism and the power generation mechanism are connected with the energy conversion mechanism; one end of the sea wave energy absorption mechanism is arranged in the fixed base in a penetrating mode, and the end, arranged in the fixed base in a penetrating mode, of the sea wave energy absorption mechanism is connected with the energy conversion mechanism. According to the point absorption type sea wave energy conversion device, a new thought for improving the energy capture efficiency is provided, the spring force output by the spring is adjusted through the variable stiffness mechanism, and the stiffness of the whole sea wave energy capture device is changed through real-time adjustment of the spring force; therefore, the floater can be matched with the dominant frequency of the sea waves in a certain frequency band to generate resonance, and the capturing efficiency of the sea wave energy is further improved.

Description

Technical Field

[0001] This invention relates to a multi-frequency resonant point absorption wave energy conversion device and control method, belonging to the field of new energy equipment technology. Background Technology

[0002] To promote the development of wave energy and improve wave energy capture efficiency, various new wave energy conversion devices have been proposed, such as valve-type, pendulum-type, wave-surfing type, oscillating water column type, and point absorption type. The structure of these devices can be divided into three parts: wave energy absorption mechanism, energy conversion mechanism, and power generation mechanism. The difference lies in their absorption mechanism and energy conversion mechanism. Currently, the most commonly used point absorption type wave energy conversion device uses a hydraulic cylinder and a hydraulic motor for energy conversion. When wave force acts on the float, the float moves up and down, causing the working fluid in the hydraulic cylinder to form hydraulic pressure. This process converts the kinetic energy of the wave into hydraulic energy. After the hydraulic pressure is formed, it drives the hydraulic motor through a hydraulic circuit, which then converts the hydraulic energy back into kinetic energy, ultimately transmitting the power to the generator for power generation.

[0003] However, the aforementioned point-absorption wave energy conversion devices mostly use hydraulic oil as the working fluid. In practical applications, this requires significant costs to maintain the hydraulic system and address issues such as leaks. Furthermore, hydraulic oil can cause marine pollution. Simultaneously, current point-absorption wave energy conversion devices have relatively low power generation efficiency. Although numerous control strategies have been proposed to improve efficiency, these strategies rely on active power actuators such as electric motors, resulting in the overall wave energy conversion device's power generation efficiency remaining suboptimal. Summary of the Invention

[0004] This invention provides a multi-frequency resonant point-absorption wave energy conversion device and control method. Through the ingenious cooperation of a wave energy absorption mechanism, an energy conversion mechanism, a variable stiffness mechanism, and a power generation mechanism on a fixed base, the absorbed wave energy is converted from linear motion to rotational motion by the energy conversion mechanism and transmitted to the generator for power generation via a gear set. Furthermore, during this process, a suitable excitation current can be applied to the magnetorheological damper in the variable stiffness mechanism to adjust the spring force on the float, so that the float exhibits stiffness characteristics that match the dominant frequency of the waves during movement, enabling it to resonate with the waves and thereby improve the wave energy capture efficiency.

[0005] The technical solution of this invention is:

[0006] According to a first aspect of the present invention, a multi-frequency resonant point-absorbing wave energy conversion device is provided, comprising a fixed base, a wave energy absorption mechanism, an energy conversion mechanism, a variable stiffness mechanism, and a power generation mechanism; the energy conversion mechanism, the variable stiffness mechanism, and the power generation mechanism are installed inside the fixed base, and the variable stiffness mechanism and the power generation mechanism are connected to the energy conversion mechanism; one end of the wave energy absorption mechanism passes through the fixed base, and the end of the wave energy absorption mechanism passing through the fixed base is connected to the energy conversion mechanism.

[0007] Furthermore, the energy conversion mechanism includes two first drive shafts, and the power generation mechanism includes one second drive shaft; the axes of the two first drive shafts and the one second drive shaft are parallel, and the three axes extend along the axial direction to form a "triangular prism" space; the transmission gear installed on the first drive shaft meshes with the generator gear installed on the second drive shaft.

[0008] Furthermore, the energy conversion mechanism includes a positive threaded lead screw, a negative threaded lead screw, a thrust plate, a positive and negative threaded lead screw fixing seat, a positive and negative threaded lead screw nut, a positive and negative threaded lead screw support seat, a first coupling, a first transmission gear, a second transmission gear, a first overrunning clutch, and a second overrunning clutch, and also includes a lead screw drive shaft as a first drive shaft; the positive and negative threaded lead screws, arranged in parallel, pass through both ends of the thrust plate, and one end of the positive and negative threaded lead screws is fixed to one end of the fixed base, while the other end of the positive and negative threaded lead screws passes through the positive and negative threaded lead screw support seat fixed on the fixed base and is connected to one end of the first coupling, the other end of the first coupling is connected to one end of the lead screw drive shaft, and the other end of the lead screw drive shaft is connected to the other end of the fixed base; a first transmission gear is installed on the lead screw drive shaft connected to the negative threaded lead screw through a first overrunning clutch, and a second transmission gear is installed on the lead screw drive shaft connected to the positive threaded lead screw through a second overrunning clutch; the center of the thrust plate away from the lead screw drive shaft is connected to the wave energy absorption mechanism.

[0009] Furthermore, both the first overrunning clutch and the second overrunning clutch employ an inner ring that locks in direction A and unlocks in direction B; where direction A and direction B represent two opposite directions.

[0010] Furthermore, the wave energy absorption mechanism consists of a float and a drive shaft. One end of the drive shaft is connected to the float, and the other end of the drive shaft is connected to the energy conversion mechanism via a fixed base.

[0011] Furthermore, the variable stiffness mechanism includes a magnetorheological damper, a damper mounting base, a spring, and a spring mounting plate; one end of the spring is fixedly installed at the center of the thrust plate in the energy conversion mechanism on the side away from the wave energy absorption mechanism, the other end of the spring is fixed to the spring mounting plate, the spring mounting plate is connected to the piston shaft end of the magnetorheological damper, and the magnetorheological damper is connected to the damper mounting base fixed in the fixed base.

[0012] Furthermore, the power generation mechanism includes a generator gear, a generator, a second coupling, and a gear shaft serving as a second transmission shaft; the generator gear is fixed on the gear shaft, and one end of the gear shaft is mounted on a fixed base via a first bearing seat, while the other end of the gear shaft transmits power to the generator via the second coupling.

[0013] According to a second aspect of the present invention, a control method for a multi-frequency resonant point absorption wave energy conversion device is provided, comprising:

[0014] A mathematical model of a multi-frequency resonant point absorption wave energy conversion device was established.

[0015] This paper addresses a multi-frequency resonant point-absorbing wave energy conversion device, revealing that the variable stiffness mechanism in this device can achieve an equivalent stiffness K by adjusting the magnitude of the excitation current. n Adjustment; the output spring force F in the mathematical model of the point absorption wave energy conversion device. ks (t) is replaced with the equivalent stiffness K. n The relevant expressions are used to obtain a mathematical model of a point-absorbing wave energy conversion device based on variable stiffness. Based on the mathematical model of the point-absorbing wave energy conversion device based on variable stiffness, the relationship between the natural frequency of the float and the equivalent stiffness is defined, realizing that the natural frequency of the float is affected by the equivalent stiffness K. n adjust.

[0016] The beneficial effects of this invention are:

[0017] This invention provides a novel approach to improving energy capture efficiency in a point-absorption wave energy conversion device. The device utilizes a variable stiffness mechanism to adjust the spring force output. Real-time adjustment of the spring force changes the stiffness of the entire wave energy capture device, allowing the float to resonate with the dominant wave frequency within a specific frequency band, thereby enhancing wave energy capture efficiency. Specifically, this invention uses a variable stiffness mechanism composed of a magnetorheological damper and a spring to provide a range of adjustable equivalent stiffness for the traditional point-absorption wave energy conversion device. By adjusting the equivalent stiffness, the natural period of the wave energy conversion device is adjusted, enabling the float to resonate with the waves within a certain sea state frequency band, thus significantly improving the capture efficiency. Furthermore, the force actuator used in this invention is a magnetorheological damper. This semi-active force actuator consumes significantly less energy during control compared to using a motor as a force actuator, allowing the wave energy conversion device to operate with high efficiency in various sea conditions. Attached Figure Description

[0018] Figure 1 A three-dimensional structural diagram of a multi-frequency resonant point absorption wave energy conversion device provided in an embodiment of the present invention;

[0019] Figure 2 An equivalent physical model diagram of a variable stiffness mechanism for a multi-frequency resonant point absorption wave energy conversion device provided in an embodiment of the present invention;

[0020] Figure 3 This is an assembly diagram of a multi-frequency resonant point absorption wave energy conversion device provided in an embodiment of the present invention;

[0021] Figure 4 This is a structural cross-sectional view of a multi-frequency resonant point absorption wave energy conversion device provided in an embodiment of the present invention;

[0022] Figure 5 A transmission gear and generator gear meshing diagram of a multi-frequency resonant point absorption wave energy conversion device provided in an embodiment of the present invention;

[0023] Figure 6 A graph showing the relationship between the equivalent stiffness of the variable stiffness mechanism and the excitation current in a multi-frequency resonant point absorption wave energy conversion device provided in an embodiment of the present invention.

[0024] Figure 7 The free decay test diagram of a multi-frequency resonant point absorption wave energy conversion device under different excitation currents is provided for an embodiment of the present invention.

[0025] The main components in the diagram are labeled as follows: 1. Lead screw fixing seat; 2. Lead screw support seat; 3. Frame; 5. Fixing base; 6. Top plate; 7. Reverse thread lead screw; 8. Lead screw; 9. Lead screw nut; 10. First coupling; 11. First overrunning clutch; 12. Second overrunning clutch; 16. Spring; 20. Intermediate plate; 21. Lead screw drive shaft; 22. Generator; 23. Second coupling; 24. Gear shaft; 25. First bearing seat; 26. Magnetorheological damper; 27. Piston shaft; 28-1 first transmission gear; 28-2 second transmission gear; 29. ​​Generator gear; 30. Thrust plate; 32. Spring fixing plate; 33. Fixing shaft support; 35. Damper fixing seat; 37. Bottom plate; 38. Second bearing seat; 42. Drive shaft; 43. Float. Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. It should be noted that, unless otherwise specified, the embodiments and features in the embodiments of this application can be arbitrarily combined with each other.

[0027] like Figures 1-7 As shown, according to a first aspect of this embodiment, a multi-frequency resonant point-absorbing wave energy conversion device is provided, including a fixed base 5, a wave energy absorption mechanism, an energy conversion mechanism, a variable stiffness mechanism, and a power generation mechanism; the fixed base 5 houses the energy conversion mechanism, the variable stiffness mechanism, and the power generation mechanism, and the variable stiffness mechanism and the power generation mechanism are connected to the energy conversion mechanism; one end of the wave energy absorption mechanism passes through the fixed base 5, and the end of the wave energy absorption mechanism passing through the fixed base 5 is connected to the energy conversion mechanism.

[0028] For example: the fixed base 5 includes a frame 3 and a top plate 6, an intermediate plate 20 and a bottom plate 37 arranged in parallel and at intervals on the frame 3.

[0029] Furthermore, the energy conversion mechanism includes two first drive shafts, and the power generation mechanism includes one second drive shaft; the axes of the two first drive shafts and the one second drive shaft are parallel, and the three axes extend axially to form a "triangular prism" space; the transmission gear mounted on the first drive shaft meshes with the generator gear 29 mounted on the second drive shaft. Based on the above design, while achieving effective power transmission, it can further prevent the variable stiffness mechanism from interfering with the installation of the generator in the power generation mechanism.

[0030] Furthermore, the energy conversion mechanism includes a positive threaded lead screw 8, a negative threaded lead screw 7, a thrust plate 30, a positive and negative threaded lead screw fixing seat 1, a positive and negative threaded lead screw nut 9, a positive and negative threaded lead screw support seat 2, a first coupling 10, a first transmission gear 28-1, a second transmission gear 28-2, a first overrunning clutch 11, and a second overrunning clutch 12, and also includes a lead screw transmission shaft 21 as a first transmission shaft; the positive threaded lead screw 8 and the negative threaded lead screw 7, which are arranged in parallel, pass through both ends of the thrust plate 30, and one end of the positive threaded lead screw 8 and the negative threaded lead screw 7 is fixed to one end of the fixing base 5. The other end of the threaded screw 7 passes through the positive and negative threaded screw support 2 fixed on the fixed base 5 and is connected to one end of the first coupling 10. The other end of the first coupling 10 is connected to one end of the threaded screw drive shaft 21, and the other end of the threaded screw drive shaft 21 is connected to the other end of the fixed base 5. The first drive gear 28-1 is installed on the threaded screw drive shaft 21 connected to the negative threaded screw 7 through the first overrunning clutch 11, and the second drive gear 28-2 is installed on the threaded screw drive shaft 21 connected to the positive threaded screw 8 through the second overrunning clutch 12. The center of the thrust plate 30 is connected to the wave energy absorption mechanism on the side away from the threaded screw drive shaft 21.

[0031] Furthermore, both the first overrunning clutch 11 and the second overrunning clutch 12 employ an inner ring that locks in direction A and unlocks in direction B; where direction A and direction B represent two opposite directions.

[0032] Specifically: such as Figure 3 , Figure 4The energy conversion mechanism includes a positive threaded lead screw 8, a negative threaded lead screw 7, a fixed shaft support 33, a thrust plate 30, a positive and negative threaded lead screw fixing seat 1, a positive and negative threaded lead screw nut 9, a positive and negative threaded lead screw support seat 2, a first coupling 10, a lead screw drive shaft 21, a first transmission gear 28-1, a second transmission gear 28-2, a first overrunning clutch 11, a second overrunning clutch 12, and a second bearing seat 38. The top ends of the positive threaded lead screw 8 and the negative threaded lead screw 7 are connected to the positive and negative threaded lead screw fixing seat 1, which is fixed on the top plate 6. The fixed shaft support 33 is installed at the center of the thrust plate 30. Both ends of the thrust plate 30 are fixed to the positive and negative threaded lead screw nuts 9. The positive threaded lead screw 8 and the negative threaded lead screw 7 pass through the two ends of the thrust plate 30 and rotate with the positive and negative threaded lead screw nuts 9. The bottom end of the reverse threaded lead screw 7 is connected to one end of the first coupling 10 through the shaft hole on the intermediate layer plate 20. The journal part at the junction of the threaded and unthreaded parts at the bottom end of the positive and negative threaded lead screw is equipped with a positive and negative lead screw support 2. The positive and negative lead screw support 2 is fixed on the intermediate layer plate 20, so that the positive and negative threaded lead screw is fixed in the fixed base. The other end of the first coupling 10 is connected to the top end of the lead screw drive shaft 21. The bottom end of the lead screw drive shaft 21 is connected to the second bearing seat 38. The second bearing seat 38 is fixed on the bottom layer plate 37. A first overrunning clutch 11 is installed at the shaft hole of the first transmission gear 28-1, and a second overrunning clutch 12 is installed at the shaft hole of the second transmission gear 28-2. Both overrunning clutches are locked clockwise and unlocked counterclockwise. The inner ring of the overrunning clutch is fixed to the lead screw drive shaft 21.

[0033] Furthermore, the wave energy absorption mechanism consists of a float 43 and a drive shaft 42. One end of the drive shaft 42 is connected to the float 43, and the other end of the drive shaft 42 is fixedly connected to the fixed shaft support 33 in the energy conversion mechanism via a shaft hole at the center of the top plate 6 of the fixed base 5. In specific applications, the multi-frequency resonant point absorption wave energy conversion device, except for the float 43 and part of the drive shaft 42 connecting the float 43, is fully sealed and submerged underwater and fixed to the seabed by mooring.

[0034] Based on the above, the linear motion of the float is transmitted to the positive and negative lead screw nut 9 via the transmission shaft 42, fixed shaft support 33, and thrust plate 30. Then, the positive threaded lead screw 8 converts the motion into rotational motion, which is transmitted to the first transmission gear 28-1 via the first coupling 10 and the first overrunning clutch 11. The negative threaded lead screw 7 converts the motion into rotational motion, which is transmitted to the second transmission gear 28-2 via the first coupling 10 and the second overrunning clutch 12. The first transmission gear 28-1 / second transmission gear 28-2 transmit the motion to the generator gear 29.

[0035] Furthermore, the variable stiffness mechanism includes a magnetorheological damper 26, a damper mounting base 35, a spring 16, and a spring mounting plate 32. One end of the spring 16 is fixedly installed at the center of the thrust plate 30 in the energy conversion mechanism on the side away from the wave energy absorption mechanism. The other end of the spring 16 is fixed to the spring mounting plate 32. The spring mounting plate 32 is threadedly connected to the end of the piston shaft 27 of the magnetorheological damper 26. The magnetorheological damper 26 is threadedly connected to the damper mounting base 35 fixed in the fixed base 5. That is, the entire variable stiffness mechanism is mounted on the intermediate layer plate 20 of the fixed base 5 through the damper mounting base 35.

[0036] Furthermore, the power generation mechanism includes a generator gear 29, a generator 22, a second coupling 23, and a gear shaft 24 serving as a second transmission shaft; the generator gear 29 is connected to the gear shaft 24 by a key, and one end of the gear shaft 24 is mounted on the fixed base 5 via a first bearing seat 25, while the other end of the gear shaft 24 transmits power to the generator 22 via the second coupling 23.

[0037] Such as assembly relationships Figure 3 The bottom end of the gear shaft 24 of the power generation mechanism is connected to the first bearing seat 25, which is fixed to the bottom plate 37. (The gears mesh.) Figure 5 The generator gear 29 meshes normally with the two transmission gears.

[0038] According to a second aspect of this embodiment, a control method for a multi-frequency resonant point absorption wave energy conversion device is provided, comprising:

[0039] A mathematical model of a multi-frequency resonant point absorption wave energy conversion device was established.

[0040] This paper addresses a multi-frequency resonant point-absorbing wave energy conversion device, revealing that the variable stiffness mechanism in this device can achieve an equivalent stiffness K by adjusting the magnitude of the excitation current. n Adjustment; the output spring force F in the mathematical model of the point absorption wave energy conversion device. ks (t) is replaced with the equivalent stiffness K. n The relevant expressions are used to obtain a mathematical model of a point-absorbing wave energy conversion device based on variable stiffness. Based on the mathematical model of the point-absorbing wave energy conversion device based on variable stiffness, the relationship between the natural frequency of the float and the equivalent stiffness is defined, realizing that the natural frequency of the float is affected by the equivalent stiffness K. n adjust.

[0041] Specifically: Assuming that spring 16 in the variable stiffness mechanism is massless, piston rod 27 is considered a point mass, and magnetorheological damper 26 is considered a variable damping MRD, the variable stiffness mechanism described in this invention can be simplified to a spring-mass-variable damping series model. Please refer to [link to relevant documentation]. Figure 2 Let the spring constant of spring 16 be K. s The mass of the particle is M s The displacement produced by the particle is z s The input quantities of the variable stiffness mechanism are the excitation current of the magnetorheological damper 26 and the excitation displacement z at the top of the spring 16. b (The excitation displacement at the top of spring 16 is the float displacement). The external excitation displacement z... b Under the action of the spring 16, a portion of the spring force acts on the top of the piston shaft 27, that is, on the particle and produces a displacement z. s Part of it acts on the thrust plate 30 ( Figure 1 Simultaneously, the magnetorheological damper 26, also known as the variable damper MRD, generates a certain damping force to hinder the movement of the piston shaft 27 (mass point) and the bottom end of the spring 16. This damping force can be adjusted by controlling the current. According to the working principle of the magnetorheological damper 26, the damping force increases with the increase of the excitation current. Therefore, a larger damping force will produce a greater constraint effect, causing the mass point displacement z to increase. s The displacement decreases, meaning the displacement at the bottom of spring 16 decreases. Therefore, under the same external excitation displacement z... b Under these conditions, the larger the excitation current, the greater the particle displacement z. s The smaller the value, the greater the spring force F output by spring 16. ks The larger the value, the greater the effect. That is, the variable stiffness mechanism can change the displacement z of the mass point by adjusting the magnitude of the excitation current. s The constraint effect realizes the output spring force F ks The adjustment can therefore be understood as the same external excitation displacement z b Under the given conditions, the equivalent stiffness K of the variable stiffness mechanism n Adjusted, equivalent stiffness K n It can be defined by the following formula:

[0042] F ks (t)=K s ·(z b -z s )=-K n ·z b ;;

[0043] According to the well-known potential flow theory, the mathematical model of a point absorption wave energy conversion device can be given by the Cummins equation:

[0044]

[0045] In the formula, M and M(∞) are the buoy mass and the additional mass at infinite frequency, respectively, and K(t) is the impulse response function of the radiation load. ω For water purification and recovery, F exc (t), F PTO(t) represent the wave excitation force and the force exerted by the energy conversion mechanism, respectively; These are the float's displacement, velocity, and acceleration, respectively.

[0046] In the mathematical model of the point absorption wave energy conversion device, F ks (t) is replaced with the equivalent stiffness K. n The relevant expressions are used to obtain a mathematical model of a point-absorbing wave energy conversion device based on variable stiffness:

[0047]

[0048] From the mathematical model of the point-absorbing wave energy conversion device based on variable stiffness, it can be seen that the natural frequency f of the float is... s It can be defined as:

[0049]

[0050] At this point, the natural frequency of the float will be affected by the equivalent stiffness K. n Adjustment, that is, in a point absorption wave energy conversion device that can achieve multi-frequency resonance through excitation current, the natural frequency of the float resonates with the wave within a certain range, thereby improving the wave energy capture efficiency.

[0051] The working process of this embodiment will be described in detail below:

[0052] When wave force acts on float 43, the kinetic energy generated by float 43 is transmitted to thrust plate 30 via drive shaft 42. At the same time, the lead screw nut 9 and spring 16 connected to thrust plate 30 will be displaced by force. During this process, by applying a preset excitation current to magnetorheological damper 26, spring 16 can generate the required spring force F. ks The force is applied to the float 43 via the thrust plate 30 and the drive shaft 42, giving the float appropriate stiffness characteristics during its movement, matching the dominant frequency of the waves to achieve resonance. Simultaneously, the positive and negative threaded screw nuts 9, along with the positive threaded screw 8 and the negative threaded screw 7, convert the vertical linear motion of the float 43 into rotational motion.

[0053] When float 43 moves downward, the positive threaded screw 8 rotates clockwise, and the negative threaded screw 7 rotates counterclockwise. The second transmission gear 28-2, due to the second overrunning clutch 12 being locked, follows the positive threaded screw 8 in clockwise rotation. According to the transmission relationship, generator gear 29 rotates counterclockwise, while the first transmission gear 28-1, due to the first overrunning clutch 11 being unlocked, does not rotate counterclockwise with the negative threaded screw 7. According to the transmission relationship, the first transmission gear 28-1 and the second transmission gear 28-2 rotate in the same direction. Simultaneously, the first transmission gear 28-1 acts as an energy storage device, making the power output of generator 22 more stable.

[0054] When float 43 moves upward, the positive threaded screw 8 rotates counterclockwise, and the negative threaded screw 7 rotates clockwise. The first transmission gear 28-1, due to the first overrunning clutch 11 being locked, rotates clockwise along with the negative threaded screw 7. According to the transmission relationship, the generator gear 29 rotates counterclockwise, while the second transmission gear 28-2, due to the second overrunning clutch 12 being unlocked, does not rotate counterclockwise with the positive threaded screw 8. According to the transmission relationship, the second transmission gear 28-2 rotates in the same direction as the first transmission gear 28-1. Simultaneously, the second transmission gear 28-2 acts as an energy storage device, making the power output of the generator 22 more stable.

[0055] To verify the feasibility of the scheme, this invention tested the effect of different excitation currents on the equivalent stiffness of the variable stiffness mechanism under the condition of an external excitation signal of sin(2π*0.5) using Matlab software. Figure 6 It can be observed that the equivalent stiffness provided by the variable stiffness mechanism increases with the increase of the excitation current. Specifically, when the current increases from 0 to 4A, the equivalent stiffness increases from 14.026 kN / m to 104.02 kN / m, an increase of 7.4 times. This indicates that the stiffness characteristics of the variable stiffness mechanism can be adjusted by the current.

[0056] Furthermore, to verify the effect of the variable stiffness mechanism on the stiffness adjustment of the multi-frequency resonant point-absorbing wave energy conversion device described in this invention, a free decay test was conducted in the hydrodynamic simulation software Ansys / Aqwa. The natural frequency of the float can be determined by the oscillation period during free decay. The prototype parameters of the multi-frequency resonant point-absorbing wave energy conversion device in this invention are shown in Table 1. The water depth of the simulation pool was 15m, and the length and width were 80m each. During the free decay test, the initial position of the float's center of mass was 1m above the sea level. Due to the imbalance between gravity and buoyancy, the float would oscillate back and forth in the ocean. Figure 7 As shown in the figure, different excitation currents cause changes in the period of the float's reciprocating oscillation, i.e., changes in the float's natural frequency. To present the results more clearly, the dashed line in the figure measures the interval between two adjacent wave crests under a 0.1A current excitation condition, which is 3.226s. The float's natural frequency is the reciprocal of this interval. Similarly, the solid line measures the interval between two adjacent wave crests under a 0.6A current excitation condition, which is 2.956s. It can be observed that as the current increases, the float's natural period decreases, i.e., the float's natural frequency increases. This indicates that the variable stiffness mechanism can adjust the stiffness characteristics of the multi-frequency resonant point-absorbing wave energy conversion device.

[0057] Table 1

[0058] Float radius (m) Float mass (kg) Draft (m) Damping coefficient of energy conversion mechanism (N·m / s) Center of mass 3 13937.54 1.1 10000 (0,0,-0.2)

[0059] Furthermore, based on Ansys / Aqwa hydrodynamic simulation software, the power generation of a traditional point-absorbing wave energy conversion device and a multi-frequency resonant point-absorbing wave energy conversion device under different sea states was compared (the traditional point-absorbing device is based on the structure of this invention, except that the variable stiffness mechanism is removed, while the rest remains the same). The tested sea states were all regular waves with a wave height of 1m and frequencies of 0.46, 0.48, 0.50, and 0.52Hz. The power generation was calculated as follows: In the formula, C is the damping coefficient of the energy conversion mechanism, and v is the buoy velocity. The simulation time t is 100s. The simulation results are shown in Table 2. The results show that the net power generation of the point absorption wave energy conversion device after adjustment by the variable stiffness mechanism is significantly higher than that of the traditional point absorption type, and the power generation performance is more prominent at higher frequency sea states. This indicates that the multi-frequency resonance point absorption wave energy conversion device proposed in this invention can adjust the natural frequency of the buoy's motion by applying a suitable excitation current to make it resonate with the waves, ultimately achieving the goal of increasing power generation.

[0060] Table 2 Comparison of power generation between variable stiffness point absorption type and traditional point absorption type:

[0061]

[0062] The specific embodiments of the present invention have been described in detail above with reference to the accompanying drawings. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention.

Claims

1. A multi-frequency resonant point absorption wave energy conversion device, characterized in that, It includes a fixed base, a wave energy absorption mechanism, an energy conversion mechanism, a variable stiffness mechanism, and a power generation mechanism; the fixed base houses the energy conversion mechanism, the variable stiffness mechanism, and the power generation mechanism, and the variable stiffness mechanism and the power generation mechanism are connected to the energy conversion mechanism; one end of the wave energy absorption mechanism passes through the fixed base, and the end of the wave energy absorption mechanism passing through the fixed base is connected to the energy conversion mechanism.

2. The multi-frequency resonance point absorption wave energy conversion device according to claim 1, characterized in that, The energy conversion mechanism includes two first drive shafts, and the power generation mechanism includes one second drive shaft; the axes of the two first drive shafts and the one second drive shaft are parallel, and the three axes extend along the axial direction to form a "triangular prism" space; the transmission gear installed on the first drive shaft meshes with the generator gear installed on the second drive shaft.

3. The multi-frequency resonance point absorption wave energy conversion device according to claim 2, characterized in that, The energy conversion mechanism includes a positive threaded screw, a negative threaded screw, a thrust plate, a positive and negative threaded screw fixing seat, a positive and negative threaded screw nut, a positive and negative threaded screw support seat, a first coupling, a first transmission gear, a second transmission gear, a first overrunning clutch, and a second overrunning clutch. It also includes a screw drive shaft serving as a first drive shaft. The positive and negative threaded screws, arranged in parallel, pass through both ends of the thrust plate. One end of each screw is fixed to one end of the fixed base, and the other end passes through the positive and negative threaded screw support seat fixed to the fixed base and connects to one end of the first coupling. The other end of the first coupling connects to one end of the screw drive shaft, and the other end of the screw drive shaft connects to the other end of the fixed base. A first transmission gear is mounted on the screw drive shaft connected to the negative threaded screw via a first overrunning clutch, and a second transmission gear is mounted on the screw drive shaft connected to the positive threaded screw via a second overrunning clutch. The center of the thrust plate, away from the screw drive shaft, is connected to the wave energy absorption mechanism.

4. The multi-frequency resonance point absorption wave energy conversion device according to claim 3, characterized in that, Both the first overrunning clutch and the second overrunning clutch employ an inner ring that locks in direction A and unlocks in direction B; where direction A and direction B represent two opposite directions.

5. The multi-frequency resonant point absorption wave energy conversion device according to claim 1, characterized in that, The wave energy absorption mechanism consists of a float and a drive shaft. One end of the drive shaft is connected to the float, and the other end of the drive shaft is connected to the energy conversion mechanism via a fixed base.

6. The multi-frequency resonance point absorption wave energy conversion device according to claim 1, characterized in that, The variable stiffness mechanism includes a magnetorheological damper, a damper mounting base, a spring, and a spring mounting plate. One end of the spring is fixedly installed at the center of the thrust plate in the energy conversion mechanism on the side away from the wave energy absorption mechanism. The other end of the spring is fixed to the spring mounting plate. The spring mounting plate is connected to the piston shaft end of the magnetorheological damper. The magnetorheological damper is connected to the damper mounting base fixed in the fixed base.

7. The multi-frequency resonant point absorption wave energy conversion device according to claim 2, characterized in that, The power generation mechanism includes a generator gear, a generator, a second coupling, and a gear shaft serving as a second transmission shaft; the generator gear is fixed on the gear shaft, and one end of the gear shaft is mounted on a fixed base via a first bearing seat, while the other end of the gear shaft transmits power to the generator via the second coupling.

8. A control method for a multi-frequency resonant point absorption wave energy conversion device, characterized in that, include: A mathematical model of a multi-frequency resonant point absorption wave energy conversion device was established. This paper addresses a multi-frequency resonant point-absorbing wave energy conversion device, revealing that the variable stiffness mechanism in this device can achieve an equivalent stiffness K by adjusting the magnitude of the excitation current. n Adjustment; the output spring force F in the mathematical model of the point absorption wave energy conversion device. ks (t) is replaced with the equivalent stiffness K. n The relevant expressions are used to obtain a mathematical model of a point-absorbing wave energy conversion device based on variable stiffness. Based on the mathematical model of the point-absorbing wave energy conversion device based on variable stiffness, the relationship between the natural frequency of the float and the equivalent stiffness is defined, realizing that the natural frequency of the float is affected by the equivalent stiffness K. n adjust.

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