JPH0819894B2 - Wave energy converter - Google Patents

Description

The present invention relates to a wave energy conversion device, and more particularly to a wave energy conversion device using an eccentric rotating body that rotates in one direction inside a floating body.

[Conventional technology]

Regarding wave energy converters, one that has conventionally been proposed and partially put into practical use is one that utilizes changes in the water surface that accompanies waves to cause a flow of seawater or air, thereby extracting energy hydrodynamically. . A wave energy conversion device that utilizes an eccentric rotating body that rotates in one direction in a floating body has also been proposed. (Japanese Patent Laid-Open No. 57-68566, Japanese Utility Model No. 53
[43146) [Problems to be solved by the invention] An energy conversion device that utilizes changes in the water surface due to vibrations has a short life due to corrosion of moving parts exposed to water and adhesion of aquatic organisms. There is a problem that the hydraulic efficiency is low because the mechanical energy is extracted from the flow that has not been performed. In the case of using an eccentric rotating body that rotates in one direction in a floating body, it is an essential condition that the rotation speed of the eccentric rotating body and the frequency of the waves match while maintaining a phase difference within a predetermined range. , The stability of the rotational state of an eccentric rotating body that rotates around a horizontal axis when the floating body and the wave are in resonance has not been clarified, and the natural frequency of the floating body is close to the wave frequency. No energy conversion device was proposed. The present invention has been made to solve the above-described problems, and the natural frequency of a floating body containing an eccentric rotor is kept close to the frequency of waves under a certain condition, and the operation period is long. An object is to provide a highly efficient wave energy conversion device.

[Means for solving problems]

In order to utilize the vertical movement of the floating body, which occupies the major part of the mechanical energy given to the floating body by waves, an eccentric rotating body supported by a horizontal axis is provided in the floating body, and the wave cycle or energy distribution curve with the highest frequency of occurrence is provided. Wave design circular frequency (W _d = 2π / calculated from the design wave period (T _d ) selected from one of the wave periods having the upper maximum value
The ratio (W _d / W _n ) of T _d ) to the natural circular frequency Wn defined by the floating line cross-sectional area of the floating body and the floating body mass is set to be in the range of 0.6 to 1.1.

[Action]

Numerical calculations were performed on the model shown in FIG. 1 to clarify the motion of the floating body and the eccentric rotating body in the present invention, and experiments were conducted on the apparatus shown in FIG.

In FIG. 1, a floating body M has a mass M including a mass m of an eccentric rotating body, and is supported by a spring K having a spring constant K and a damper C having a damping coefficient C. Also, the spring K is displaced An eccentric rotating body supported by a diaphragm operating at (where t is time) is approximated as a mass m rotating at a radius r of rotation. The displacement X ^* from the equilibrium position of the floating body and the rotation angle φ of the eccentric rotating body are used as general coordinates, and the vertical force acting on the floating body and the moment acting on the rotation axis of the eccentric rotating body are used as the general forces for the Lagrangian motion. The equation is expressed as:

Where T _r is the torque transmitted to the output of the eccentric rotor. Where T _G ▼: load torque of the generator connected to the eccentric rotating body T _b : mechanical braking torque ▲ C ^* _b : mechanical loss coefficient of the rotating system and J is the moment of inertia of the rotating system and g is It is the acceleration of gravity.

Equation (1) is a non-linear vibration equation, and a mathematically exact solution cannot be obtained, but the phase difference between the eccentric rotor and the vibration plate is θ, that is, φ = wt + θ, and θ changes over the one week period of wt. Approximate calculation was performed by averaging over a small period for. In this way, the various phases and amplitudes in the steady state were calculated. The result is shown in FIG. The horizontal axis of the graph is the frequency ratio η = W / W _n where W _n is the natural circular frequency of the floating body Is. In the figure, A ₀ : amplitude of floating body / H θ ₀ : phase of eccentric rotating body ξ ₀ : phase of floating body θ ₁ : phase difference of eccentric rotating body (= θ ₀ −ξ ₀ ).

Further, calculation is made as to whether or not the phase will be in a stable state when the phase deviates from a steady value, and the range of instability is shown by a broken line in the curve of FIG.

An experiment was performed by the apparatus shown in FIG. 2 to confirm the validity of the above calculation results, and the obtained values are plotted on the graph of FIG.

In FIG. 2, one end of the floating body M is swingably supported, and the other end is Is supported via a spring K having a spring constant K by a diaphragm vibrating with the displacement of The mass of the floating body M is M, and a damper C having a damping coefficient C is provided between the floating body M and the fixed wall. The eccentric rotor m, which is rotatably supported on the floating body M by a horizontal axis, has a mass m and a radius r of rotation. The load value of the generator in which the rotation of the eccentric rotating body is transmitted through the gearbox can be changed by a switch.

Symbols in FIG. 3 are ○: ξ ₀ , ●: θ ₁ , Δ:
θ ₀ , ▲: A ₀ .

The parameters used in the above calculations and experiments are shown in Table 1.

However, Cc in the equivalent damping ratio indicates the critical damping coefficient. First
Calculations and experiments were also performed on parameters different from those shown in the table. As a result, the lower limit of η in the unstable region (≈1.1) did not change, and the upper limit only changed.
The calculated instability region and the instability region shown by the experiment agree relatively well, and the rotation of the eccentric rotor was disturbed or stopped in this region.

Furthermore, the ratio of the conversion energy to the available energy of the wave (efficiency Ψ%), the rotary shaft output P _net , the rotary shaft torque T _r
Calculations and experiments were performed for (max) and the results are shown in FIG.

The following facts are clarified from FIGS. 3 and 4.
That is, it is desirable that the frequency ratio η is 0.6 or more in order to enhance the energy conversion efficiency, and that η <1.1 is desirable in order to obtain a stable output.

The period of waves generated on the sea surface is distributed over a relatively wide range, but when observed over a long period of time, its energy distribution and frequency of appearance distribution are on a fixed curve. Figure 5 shows the results observed by the wave power test ship "Kaimei". According to the graph of FIG. 5, the cycle of the wave showing the highest appearance frequency is smaller than the cycle of the wave showing the maximum value on the energy distribution curve. (The reverse relation holds for the circular frequency W). From the above facts, in order to maximize the converted wave energy, the wave circular frequency having the maximum value on the energy distribution curve is set to the design circular frequency W _d. As W _d / W _n is 0.6 to 1.1
It can be seen that it is desirable to determine the natural circular frequency W _n of the floating body so that it falls within the range. In addition, in order to maximize the period during which wave energy can be used for a certain period of time and to enable efficient operation, the wave circular frequency with the highest frequency of occurrence is the design circular frequency W _d , and W _d / W _n is It is advantageous to determine the natural circular frequency W _n of the floating body so that it falls within the range of 0.6 to 1.1.

〔Example〕

An embodiment of the present invention will be described below with reference to FIGS. 6 to 10.

In the first embodiment shown in FIGS. 6 and 7, an eccentric rotating body 2 is rotatably supported by a horizontal shaft 6 inside a floating body 1 floating above the sea surface 5. The horizontal shaft 6 is connected to the generator 4 via the gearbox 3. The generator 4 is connected to the outside of the floating body 1 by a cable 7, and has a function as a generator and an electric motor and a function as a flywheel for an eccentric rotating body. The phase difference between the vertical movement of the floating body and the vertical movement of the sea surface is measured by a water level gauge (not shown), and the rotation angle of the eccentric rotor 2 from the reference position is measured by an angle meter (not shown). The horizontal cross-sectional area of the floating body 2 at the waterline is constant in the vertical direction, so the equivalent spring constant K is also constant. Assuming that the mass of the floating body is M, the natural circular motion W _n of the floating body is Is required. Design of waves Ratio of circular frequencies W _d and W _n W _d / W _n
Is in the range of 0.6 to 1.1, but the intermediate value is 0.85
It is desirable to set the degree to be effective because the energy can be effectively converted with respect to waves having a wide range of periods. When the present apparatus is started up, the generator 1 is first operated as an electric motor to accelerate the eccentric rotor until the phase difference between the eccentric rotor and the floating body is stabilized within a predetermined range. After that, the connection is switched so that the generator 1 acts as a generator, and the wave energy is used as electric power. The size of the eccentric rotor that receives the wave energy is proportional to sin α, where α is the rotation delay angle of the eccentric rotor with respect to the vibration of the floating body. Therefore, as the delay angle increases, the rotational speed of the eccentric rotor increases, and the eccentric rotor rotates in synchronization with the waves when the ratio of the circular frequency W of the waves to the natural circular frequency W _n is 1.1 or less. However, since the output that can be taken out from the generator is limited, the generator load is adjusted while detecting the delay angle α. If the load of the generator is limited to the lower limit with sufficient margin, the device can be operated over a wide range without performing the above control.

Sections of the floating bodies of the second, third and fourth embodiments of the present invention are shown in FIGS. 8 to 10. In these examples, the same constituent elements as those in the first example are provided inside the floating body.
In the second embodiment natural circular frequency W _n When so upwardly and cross-sectional area of the lower is larger floating body Fuhaba increases the water line increases. When the circular frequency W of the wave is large, the floating body and the wave are in resonance with each other, and the amplitude of the floating body is large, so that W _n is large. In that case, W / W _n is maintained at 1.1 or less, and the device can operate.

In the third embodiment shown in FIG. 9, since the horizontal cross-sectional area is small above and below the waterline, the natural circular frequency is small when the swing of the floating body is large. Generally, when the wave cycle is long, the amplitude becomes large, and in that case W _n becomes small and W / W _n approaches 1, so this device has high energy conversion efficiency when the wave cycle is long. Like In the fourth embodiment shown in FIG. 10, W _n can be changed by pumping or discharging water in the ballast tank 8. When water is injected into the ballast tank, the floating body weight M increases and the water line rises, so the equivalent spring constant K decreases. Becomes smaller. On the contrary, when draining water from the ballast tank, W _n becomes large. Since the natural circular frequency of the floating body can be adjusted according to the wave cycle thus generated, efficient energy conversion is possible over a wide range of the wave cycle.

〔The invention's effect〕

In the wave energy conversion device according to the present invention, since the movable part is housed inside the floating body, corrosion by seawater does not occur, maintenance is easy, and the life of the device is long. Further, the energy is extracted as a smooth rotational movement in one direction, so the mechanical efficiency is high. Furthermore, since the vertical movement of the floating body is used to keep the vibration of the floating body and the vertical movement of the waves close to resonance, the amount of energy transferred from the waves to the floating body is large, and the device is generally high over a wide cycle range of the waves. It can be operated with energy conversion efficiency.

[Brief description of drawings]

FIG. 1 is a drawing showing a mechanical model of an apparatus according to the present invention, FIG. 2 is a drawing showing the same experimental apparatus, and FIGS. 3 and 4 are graphs showing calculation results and experimental results by the above mechanical model and experimental apparatus. FIG. 5 is a graph showing the energy distribution and appearance frequency of waves, FIG. 6 is a transverse sectional view in the first embodiment of the present invention, FIG. 7 is a longitudinal sectional view thereof, and FIGS. It is sectional drawing which shows the 2nd thru | or 4th Example of invention. 1 ... Floating body, 2 ... Eccentric rotating body, 3 ... Gearbox, 4 ... Generator,
5 ... sea surface, 6 ... axis, 7 ... cable, 8 ... ballast tank.

Claims (5)

[Claims] 1. A wave energy converter that converts wave energy received by a floating body into rotational energy of an eccentric rotating body that is rotatably supported by a horizontal axis inside the floating body. Wave design circular frequency (W _d = 2π / T _d ) calculated from the design wave period (T _d ) selected from one of the wave periods having the maximum value on the distribution curve and the cross-sectional area of the floating body on the waterline A wave energy conversion device characterized in that the ratio (W _d / W _n ) of the natural circular frequency Wn, which is determined by the mass of the floating body, is in the range of 0.6 to 1.1. 2. The wave energy converter according to claim 1, wherein the floating body has a position higher than the stationary water line and sinking below the water surface during operation, and a position lower than the stationary water line of the floating body and exposed above the water surface during operation. Wave energy conversion device, characterized in that the horizontal cross-sectional area at is substantially larger than the horizontal cross-sectional area of the water line at rest. 3. The wave energy conversion device according to claim 1, wherein the floating body is above the stationary water line and sinks below the water surface during operation, and the floating body is below the stationary water line and exposed above the water surface during operation. The horizontal energy conversion device according to claim 1, wherein the horizontal cross-sectional area is substantially smaller than the horizontal cross-sectional area of the static water line. 4. The wave energy converter according to claim 1, wherein the mass of the floating body can be substantially increased or decreased by injecting or draining water into a ballast tank provided in the floating body. Wave energy converter. 5. The wave energy converter according to claim 4, wherein the horizontal cross-sectional area of the part which moves up and down the water surface during operation is made smaller at the upper side and larger at the lower side.