NO145353B - CONSTRUCTION FOR CHANGE OF CHANGE ENERGY TO OTHER ENERGY - Google Patents

Description

CONSTRUCTION FOR THE CONVERSION OF WAVE ENERGY INTO OTHER ENERGY

This invention relates to a construction which has

purpose of transforming energy in waves on the sea into other energy,

e.g. useful energy. The structure is wholly or partly placed in the sea, and has one or more moving parts which are made of rigid or elastic material, and which, under the influence of the waves on the sea, are able to carry out oscillations. The moving part(s) is connected to one or more damping resistances which are capable of emitting usable energy and/or dissipating energy.

The construction is especially intended to be used for production

Energy. Alternatively, the primary purpose of the construction may be to dampen the waves.

Various constructions for extraction are already known

of wave energy. In the past, the energy in the waves has been used to obtain small amounts of energy for special purposes, e.g. for bilge pumps or for energy supply for warning buoys at sea. In recent times, specific proposals have also been made for procedures for energy extraction on a large scale. (See journal articles in Nature, 249, pp 720-724 (1974) and in IEEE Ocean, _1, 240-243 (1974).)

These submissions apply to large mechanical swing systems with tubular construction parts made of concrete or other solid construction materials. The waves interact with the swing system through these tubular parts. The pipe parts drive pumps which in turn drive a turbine which is connected to an electric generator.

Another known proposal concerns a hydraulic resonator.

(See US Patent No. 2,886,951). In a tube or in a chamber, a liquid mass that is in direct interaction with the sea is seen to be stirred by the waves. The fluctuating liquid mass can be used to generate energy, e.g. by the fact that the liquid, when it is in its highest position, is drained into a pool that lies above sea level and by the fact that the liquid from there is led through a turbine back to the sea.

The natural frequency of a mechanical swing system is (1 /2tt ) |/S/m, where S is the stiffness or spring constant of the system and m the total effective mass. In proposed wave absorbers, S has its origin in buoyancy forces or other gravitational effects, □a total effective mass includes the hydrodynamic co-oscillating fluid mass and possibly the transformed tuning mass which is discussed later.

It is well known that the swing amplitude of a swing system

is greatest when the natural frequency of the oscillating system is equal to the frequency of the excitation. It is known to use this effect when it comes to energy extraction from the ocean waves by means of resonantly tuned liquid masses (hydraulic resonator, see US patent no. 2,886,951). It is also previously known to influence the extraction of wave energy for mechanical constructions by means of internal mobile masses which are indirectly set into oscillations by the waves. (See US Patent No. 3,696,251 and French Patent No. 1,602,911).

However, known mechanical systems have an eigenfrequency that lies significantly above the typical frequency range for ocean waves. Previously known mechanical constructions also do not have advice to regulate the natural frequency so that the natural frequency of the system can change as the characteristic frequency of the waves (the frequency at which the power spectrum of the waves has its maximum) changes.

Resonance-tuned hydraulic swing systems with the purpose of producing useful energy have certain disadvantages. Firstly, there is, according to the method, a large loss of energy due to fluid friction. Secondly, the swing system must have one. large spatial extent. Thirdly, it would be a problem to tune the frequency of such an oscillation system within an entire octave, which is desirable in order to achieve optimal absorption of current ocean waves in most sea areas.

The problem of constructing a tuned mechanical swing system can be illustrated by the construction shown in fig.1 of the attached drawings. This system consists of a tank that performs vertical oscillations in the sea as a result of the influence of the waves. Energy production can e.g. happen by means of a propeller 3 on the free end of a long shaft 2 which from the other end drives an electric generator inside the tank. The natural period of the oscillation system is approximately T = 2ir V l/g, where g

is the acceleration due to gravity, and 1 is the distance between the sea surface and the bottom of the tank when the tank is in its 1 zero-equilibrium position.

Typical values for the period of ocean waves are usually in the range 7-14 s, and it is desirable that T can be freely chosen in this range. This means that 1 must be able to be regulated within the range of 12-50 m. Now such a large construction is unfortunate for several reasons. Firstly, the excitation forces that the waves exert on the tank are greatly reduced when the bottom of the tank is far below the sea surface. This comes from the fact that the pressure fluctuations that the wave establishes decrease (exponentially for sinusoidal waves) with the distance from the sea surface. This means that the tank should be shallow. A deep tank also has a lot of dead volume, so the swing amplitude of the tank will be much less than the height 1. The frictional forces are also greater the larger the construction.

The main objective of this invention is to use a resonance-tuned mechanical swing system designed for efficient transformation of wave energy into other energy. It is also

an aim to achieve this by exploiting the large excitation forces near the sea surface. Furthermore, there is a purpose to avoid an unnecessarily large construction. Furthermore, it is an aim to achieve a relatively simple method to change the natural frequency of the system so that it can follow the changes in the characteristic frequency of the waves. And finally, there is an aim to aim for an efficient transformation of mechanical vibration energy in the system into useful energy or other energy.

A secondary main objective of the invention is to increase the energy absorption in irregular waves beyond what can be optimally extracted with a resonance-tuned swing system. This happens by controlling the swing tube with a motor or another drive mechanism so that the absorption becomes more efficient.

The main objective of the invention can be fulfilled by a construction which is a swing system where the natural frequency has such a value that the energy absorbed by the construction,

becomes a maximum. In the case of stationary sinusoidal or near-sinusoidal waves, this means that the natural frequency must be equal or close to the frequency of the wave. In the case of wind-generated or other irregular waves, this means that the eigenfrequency has a value that is equal to a typical annual mean value for the frequency of the waves, or that the eigenfrequency is regulated to

be equal or close to the frequency corresponding to the maximum in the relevant power spectrum of the waves. This latter frequency is hereafter called the characteristic frequency of the waves.

This main objective is fulfilled by the present invention

in such a way that the interaction part (i.e. the part of the structure which is exposed to the wave forces, and which comes in oscillations) is connected to one or more flywheels with adjustable moments of inertia (hereafter called the tuning mass) which are placed inside the structure, in the sea, on the seabed or on land,

and which are not to a significant extent directly affected by the wave forces, but which oscillate in step with the interaction part so that the effective mass of the total oscillating system becomes large enough for the natural frequency of the system to be equal or approximately equal to the characteristic frequency of the waves. The tuning mass (flywheel) that rotates i

time with the oscillations so that he rotates one way when the interaction part moves in one direction and rotates the opposite way when he moves in the opposite direction.

Ideally, the tuning mass should oscillate much faster than the interaction part. Thereby, it can be achieved that the necessary tuning mass is relatively small so that the construction does not become unnecessarily large. A small mass also has the advantage that it can be more easily varied in size and/or shape than a large mass. Thereby one achieves that the natural frequency of the system can be varied more easily. Furthermore, it is technologically easier with a mass that oscillates quickly than with one that oscillates slowly, to transform the kinetic energy in the mass into other energy! e.g. useful energy.

The system can produce useful energy by e.g. the tuning mass, directly or indirectly, drives an electric generator. The electric generator will then dampen the movement of the reciprocating part. The damping can be characterized by means of a damping resistance R, defined by the power that the alternating current part delivers to the generator (i.e. approximately the useful power),

in time average is £Ru<2> where u is the speed amplitude of the alternating current protection oo r

the part by harmonic oscillation. The interaction part is also dampened by the fact that he generates outgoing waves. The effect that goes into generating the outgoing waves is equal in time

*^ruo' c'er ^r is c'en - called the radiation resistance, which is a characteristic (frequency-dependent) quantity for each construction. It turns out that the useful effect jRu o has its maximum when R = R r, i.e. the load power is equal to the radiated power. This applies to harmonic waves. It is therefore important that the damping resistance R is sufficiently large for the construction to act as an effective absorber of wave energy. If the oscillating system oscillates with its maximum amplitude and/or if the waves are not purely harmonic (e.g. wind-generated), we 1 the optimal value of the load resistance R will be somewhat greater than R , so that the radiated ;r ;effect is then somewhat less than the load effect. The operation of a resonantly tuned system, which has been discussed above, can be explained as follows: The incoming waves set the system in motion. As a consequence of the movement, the system will generate an outgoing wave (which is an annular wave if the swing system is point-shaped or circular-symmetric). This outgoing wave is superimposed on the incoming wave in such a way that the resulting wave that passes the system has reduced amplitude and thus reduced energy. The system must therefore have absorbed energy from the wave. It is clear that the outgoing wave's ability to cancel out the incoming wave is greater the more the ring wave is similar in time variation to the incoming wave. But a linear swing system with time-independent system parameters (mass, damping resistance and spring constant) can only reproduce the time variation of the incoming wave in one case; namely when the incoming wave is purely sinusoidal. Ocean waves are not sinusoidal. This means that the outgoing wave will only approximately resemble the incoming wave, and the deviation is the larger the deviation of the incoming wave from sinusoidal form. form ocean waves, but that the system becomes somewhat less effective in normal wind-generated waves. In the latter case, the wave energy absorption system - in accordance with the aforesaid side order or main objective - can be improved in the following way. Let the tuning mass (flywheel) be affected by a force from a controlled or regulated motor/generator or another adjustable control mechanism in addition to the mass force, the spring force (e.g. buoyancy force), the damping force and the force from the waves so that the tuning mass, and thus the interaction part , can perform a more arbitrary swing movement. Alternatively, the flow to the interaction section can be controlled by replacing the tuning mass, in whole or in part, with a controlled or regulated, combined motor and generator that affects the interaction section. The movement of the interaction part must be controlled so that it generates outgoing waves with approximately the same time variation as the incoming waves, but with opposite phase. It is clear that such a controlled swing system functions as a very effective wave absorber in all kinds of waves, since the system is able to generate, and therefore to wipe out, waves with arbitrary time variation. The net energy absorption is achieved by the generator delivering more energy than the engine consumes. The difference corresponds to the useful energy. As an alternative to direct control using a combined engine and generator, the control can be done hydraulically by a combination of a turbine and a pump. The energy transfer from the incoming wave to the swing system can, quite generally, be positive for part (at least half) of the swing period and negative the rest of the time. When the oscillating speed of the interaction part is in phase with the elevation fluctuation of the incoming wave, the said energy transfer is positive all the time. This condition on the pipe to the interaction part must be fulfilled or nearly fulfilled if the swing system is to function as an optimal absorber of wave energy. A further design of the invention is that the structure has two or more moving parts (the interaction part) which are placed in different positions in the sea, but which can still be connected to each other. One can then take advantage of the fact that the fluctuation to the sea surface in the various positions is in a different phase and use this effect to increase the energy absorption of the system. E.g. there can be two moving parts which are at a distance of half a wavelength from each other, and which oscillate in counter-rhythm with each other. ;Energy-absorbing oscillation system that works in accordance with the optimization principle as explained above, has an oscillation amplitude that is monally greater than the amplitude of the incoming wave. But in practice, the swing of a given swing system cannot exceed a certain maximum limit. The system must therefore be arranged so that, when the incoming wave has an amplitude above a certain limit, it can be dampened more strongly than corresponds to the above-mentioned optimization principle, so that the fluctuation of the swing system is limited to the maximum limit. Further details regarding the invention will be apparent from the following explanations of examples of constructions illustrated in the attached drawings, and from the requirements. In the attached drawings, Figure 1, as shown above, is an illustration of a system for explanation. Figures 2 to 7 illustrate examples of how constructions according to the invention can be carried out in practice. In all these figures, identical reference numbers are used for structural parts that correspond to each other. ;In Figure 2, as well as in Figure 1, a floating tank is shown which is in a halfway submerged jam weight position in the sea. In Figure 2, the tank 1 is held in the half-submerged jambweight position by means of the tensile force in a wire, a belt, a chain or the like 2 which goes around rollers (pulleys, pulleys, drums or the like) on the shafts 3 and 4, ;mounted in a house 5 attached to the bottom of the sea, and which is stretched using the buoyancy force of the float 6 so that the wire 2 is exposed to tension all the time while the system is swinging. A flywheel 7 and possibly an electric generator or a pump (not shown in the figure) are connected to the axle 3. The tank 1 and the float 6 can be made of solid construction materials such as concrete or steel or they can be gas-filled balloons in strong nets. ;, (YSks^YSrknadscjelRn,), ;When the tank v<*>performs forced vertical oscillations under the influence of the waves, the shaft 3 and thus the flywheel 7 and the generator are forced to perform alternating rotation. The flywheel thus becomes part of the total swing system. By making the mass of the flywheel and/or the turnover ratio between the translation pipe to the tank 1 and the rotation of the flywheel 7 suitably large, one can aim for the swing system to have a natural frequency that is close to the characteristic frequency of the waves. The peripheral speed of the flywheel should ideally be much greater than the speed of tank 1. Then the mass (gravitational mass) of the flywheel will be relatively small. The useful energy can possibly be taken out of the system by e.g. to place an electric generator on the periphery of the flywheel. Such a generator becomes cheaper when the peripheral speed is high.

When the characteristic frequency of the waves changes

itself, the natural frequency of the swing system must also be changed.

This can e.g. do by changing the voting mass. Flywheels are particularly suitable for this purpose as the moment of inertia can be easily regulated. Alternatively, the tuning mass can be regulated by changing the turnover ratio between the linear movement of the tank 1 and the rotation of the flywheel 7 by means of a gear.

Axle 3 can optionally be equipped with a regulated one

or controlled control mechanism that can give the flywheel 7 and thus the tank 1 (the interaction part) an oscillating movement of arbitrary time variation, so that the oscillating system can function as an optimal energy absorber even in waves that do not vary sinusoidally with time. The force from the steering mechanism affects the swing motion in addition to the other forces that affect the system, namely the mass force, the spring force, the damping force and the force from the waves. Alternatively, the flywheel can be completely replaced with a controlled or regulated combined motor and generator which can be electric, mechanical or hydraulic (such as

turbine and pump) and which controls the pipe stroke so that the reciprocating part moves essentially in step with the incoming wave, i.e.

that the speed of the interaction part is in phase, or approximately in phase, with the elevation fluctuation of the incoming wave.

Fig. 3 shows a variant of the system shown in Fig. 2.

Here the rough 11-swing wheel 1 combination 3-7 is duplicated and placed inside the tank, while the duplicated rollers (pulleys) 4 are mounted in a foundation 5 on the seabed. Wire 2 is also duplicated. Both wires are fixed with one end in the seabed and the other end

in the float 6 which sizzles because the wire is always under tension.

Fig. 4 shows a construction where the flywheels 7 are forced to rotate by means of the racks 8 which engage in the gears .3. The racks are held in a fixed position by means of the float platform 9 which is moored by means of wires 10 which descend

for anchoring on the seabed.

Fig. 5 shows a construction that differs from the one in

fig. 4 with the floating platform 9 being replaced by a frame structure 11 which stands on the bottom of the sea.

In the example shown in fig. 2 - 5, another wire or toothed rack is used to connect the interaction part to the rest of the swing system. But power transmission can also happen in other ways, e.g. by hydraulic power transmission.

Fig. 6 shows a submerged construction according to the invention. The containers 12 and 13 are filled with gas and are connected to each other via a pipe 14. The tank 12 has a movable or flexible wall 15 (the interaction part) which is placed below the water surface. The tank 13 is designed with rigid walls and can optionally be placed completely above or completely below the water surface or on the seabed. The wave forces cause the wall 15 to swing

so that the volume of the tank 12 changes. Thus, gas will flow back and forth between 12 and 13. A turbine 16 is placed in the pipe 14. The system can be regulated for optimal energy absorption by the turbine being designed as a combined pump and motor with a flywheel as explained earlier.

Another way is to fill part of the tube with liquid,

so that you get a fluctuating column of liquid which then fully or partially constitutes the tuning mass of the system. The natural frequency of the system can be varied by changing the length of the liquid column.

Fig. 7 shows a further design of the construction in Fig. 6

in that both containers 12 and 13 have flexible walls 15. The containers are placed at a distance from each other of approx. half a wavelength. Thus, the waves, which come in along the longitudinal direction of the system, will produce pressure in opposite phase in the two containers. This will lead to greater flow of liquid or gas through the turbine 16 in the tube 14.

Claims (2)

REQUIREMENTS: 1. Construction which aims to transform energy in waves at sea into other energy, and which has at least one moving part, hereafter called the interaction part, of solid material (where said part can be a float 1 or a piston) or of elastic material (where the said part can be an elastic membrane 15), where the interaction part is an integral part of a dampened swing system, which contains at least one damping mechanism designed to release usable energy and/or dissipate energy, and where the said interaction part interacts with the waves and are thereby exposed to oscillating forces from the waves, so that the reciprocating part and thus the aforementioned swing system come into oscillation, characterized in that the reciprocating part (1) is coupled to at least one flywheel (7), which has an adjustable moment of inertia, and which is placed inside in the structure, in the sea, on the seabed or on land, and which oscillates in step with the interaction part (1), and which is designed to increase the eff effective mass of the total oscillating system, so that the natural frequency of the system, which is known in and of itself, becomes or can be regulated to become equal or nearly equal to the characteristic frequency of the waves. 2. Construction whose purpose is to transform energy in waves on the sea into other energy, and which has at least one moving part, hereinafter called the interaction part, of solid material (where said part can be a float 1 or a piston) or of elastic material (where the said part can be an elastic membrane 15), where the interaction part is an integral part of a damped swing system, which contains at least one damping mechanism designed to release usable energy and/or dissipate energy, and where the said interaction part interacts with the waves and thereby becomes exposed to oscillating forces from the waves, so that the interaction part and thus the aforementioned swing system will oscillate, characterized by the construction being equipped with a control mechanism, e.g. combined motor and generator, designed to establish an adjustable force on the reciprocating part (1) in addition to forces that otherwise act on it, - where the aforementioned adjustable force has the purpose of giving the reciprocating part (1) a controlled or regulated swing movement, so that the interaction part (1) has a speed that fluctuates in step with the oscillating force that the incoming wave exerts on the interaction part. Construction according to claims 1 and 2, characterized in that the system is equipped with a flywheel as mentioned in claim 1 and equipped with a steering mechanism as mentioned in claim 2. Construction as mentioned in claim 1, 2 or 3, characterized in that the interaction part consists of two tubular parts (15) which are connected together and which are placed at a distance from each other equal to or approximately equal to half the characteristic wavelength of the waves.