GB2037899A - Ocean Wave Energy Device - Google Patents

Abstract

A buoy type energy extraction device is provided in which the natural frequency of vertical oscillation of the buoy is mechanically altered to at least partially conform to the wave frequency occurring during a period of operation, whereby the maximum amount of energy available from each successive wave front is extracted. The device includes a buoy 18, a vertically oscillating rod 17 supporting said buoy, a horizontally oriented motion output means 22, 24 driven by said vertical rod, and a braking means 30, 31 for arresting movement of the buoy at its uppermost limit of travel during any given oscillation, said braking means holding the buoy until the buoy may be dropped under gravity into a following wave trough. <IMAGE>

Description

SPECIFICATION Ocean Wave Energy Device This invention relates generally to the field of ocean wave energy devices, and more particularly to an improved form adapted to extract maximum energy from each vertical oscillation.

It is known in the art to extract energy by causing an ocean wave to raise and lower a float or buoy in a vertical plane and thereby produce a working force. Workers skilled in this art readily acknowledge that only a small fraction of the total energy contained in a given ocean wave can be captured by any given float or buoy system, unless the natural oscillation frequency of the buoy is in resonance with the then existing ocean wave frequency (wave period). If the frequency of the buoy system is close to, or can be matched, to the wave period, the energy which can be captured is greatly increased. In reality, this state of resonance is very difficult to achieve because ocean wave periods commonly vary from as little as four seconds to as much as twenty second intervals.Floats and buoys, however, have only one natural frequency which is based upon the mass and geometric shape thereof. Therefore, a buoy has only one frequency which will be in resonance with a wave period and all other ocean wave periods will be outside this natural frequency and result in an inefficient energy conversion system.

Another problem of attempting to match natural buoy frequency with ocean wave period frequency lies in the fact that in order to construct a buoy with a natural frequency in the range of ocean wave periods, the buoy construction becomes both very large in terms of mass and awkward in terms of shape.

Summary of the Invention It is therefore among the principal objects of the present invention to provide a means of altering the natural frequency of floats and buoys so that the retrieval of energy from the ocean waves is substantially increased Another object of the invention lies in the provision of means for introducing an artifical resonant condition in a float or buoy with respect to the frequency of existing ocean waves.

Yet another object of the invention lies in the provision of means whereby the natural frequency of given floats or buoys may be constantly altered, so as to follow the change of ocean wave frequencies during operation.

A further object of the invention lies in the provision of means for creating a condition in which potential energy is allowed to accumulate to a maximum in a buoy or float, to be subsequently released in sequence with ocean wave frequency, thus providing a means for capturing energy quantities in excess of those quantities theoretically calculated to exist with natural resonance between buoys and sea waves.

Still another object of the invention lies in the provision of means for altering the natural frequency of floats and buoys so that they can be put out of resonance with respect to the frequency of existing ocean waves, thus providing a safeguard to control the damaging effects of uncontrolled resonance between floats and buoys, and the ocean waves.

Briefly stated, the invention contemplates the provision of braking means, the operation of which is controlled by the determination of existing wave frequency, and which arrests movement of the buoy at its uppermost limit of travel, to hold the buoy motionless until the wave crest has past, and subsequently release the buoy so that it may fall under gravity into the following trough to be elevated by the buoyancy of the water below the surface, in addition to the lifting force provided by the next wave crest.

Brief Description of the Drawing In the drawing, to which reference will be made in the specification, similar reference characters have been employed to designate corresponding parts throughout the several views.

Figure 1 is a schematic view in perspective of an embodiment of the invention.

Figure 2 is an enlarged schematic view in perspective corresponding to the upper left hand portion of Figure 1.

Detailed Description of the Disclosed Embodiment In accordance with the invention, the device, generally indicated by reference character 10, comprises broadly: an elevated platform or rig 11 supported from an ocean bed by a plurality of pillars 12, and including a lower platform 13 and an upper platform 14. Aligned openings 15 in the platforms 1 3 and 14 mount bearings (not shown) for guiding a vertical shaft 1 6 for movement along a vertical axis. The lower end 1 7 of the shaft supports a float or buoy 1 8 of considerable mass.

Mounted on the upper surface 20 of the lower platform 13 are one or more bearings 21 supporting a horizontal shaft 22 for rotation. One end 23 of the shaft mounts a power output means 24 of well known type. The means 24 may be a direct current generator having rectification means (not shown) for providing an output of current irrespective of the direction of rotation of the shaft 22.

The shaft 22 is driven through the cooperation of a pinion 25 with a rack 26 on the shaft 1 6. As the details of this particular form of motion transmission in ocean wave energy devices is well known in the art, it need not be further considered herein.

Also mounted on the horizontal shaft 22 is a brake disc 30 controlled by an electricaily operated caliper 31. The calipers are energized by the operation of a revolutions per minute sensor 32 in such manner that a signal is transmitted upon a detection of zero revolutions per minute.

The calipers are released by operation of a wave frequency detector 34 of known type which indicates the presence of a wave trough between successive wave crests, at which time the release of the calipers 31 permits the shaft 1 6 and 1 8 to descend under the action of gravity to enter the trough, and project below the surface until development buoyancy commences an upward movement.

Thus, during each oscillation, the buoy will be raised to the maximum degree possible, depending upon the buoyancy already developed, and enhanced by the height of the wave crest. As the crest is reached, and the force of gravity overcomes the upward inertia, the revolutions per minute sensor will detect the high point, and actuate the brake to hold the buoy at this point.

The brake, once engaged, will halt further motion of the system for a finite period of time. This time can be selected and will have a direct relationship to the ocean wave period of frequency to be matched. After the selected period of time has transpired, the brake will disengage allowing the buoy and buoy shaft to fall and plough back into the water. During the time interval that the disc brake was engaged, the crest of the ocean wave passed beneath the buoy and continued on its path. The approaching trough of the ocean wave causes the water to recede beneath the buoy and allow the buoy to lose its buoyant force and develop potential energy.

The buoy will reenter the water on its downstroke in sequence with the lowest point of the trough of the wave, thus allowing the buoy to be accelerated by gravity through a maximum vertical distance, thus converting its potential energy to kinetic energy.

After the buoy reenters the water, it begins to decelerate, and eventually comes to rest at the low point of its downward vertical movement. The revolutions per minute detector again detects zero revolutions, and sends a signal to the disc brake, whereby, the system is again held in the low position for a predetermined interval of time.

During this time interval, the trough of the wave passes and the water begins to rise as the next wave crest approaches. Since the buoy is held in low position, the rising water increases the buoyant force on the buoy to a maximum displacement which will occur near the crest of the approaching wave. At this point in time, the disc brake is released, allowing the maximum buoyant force of the buoy to accelerate the buoy and shaft in vertically upward direction.

The time interval that the system is halted in the low position is designed to allow the buoy to develop its own buoyant force to a maximum (potential energy) and is also designed to allow the buoy to reach the top of its stroke on the upstroke in sequence with the crest of the next approaching wave, thus allowing the buoy to be accelerated by the buoyant force through a maximum vertical distance, and converting its potential energy to kinetic energy.

It may be noted that where the structure commences operation from rest, during the first cycle, the upward motion of the buoy is only due to the lifting effect of the wave crest. On the second cycle, the upward motion of the buoy is accelerated due to a buoyant force on the buoy developed by restraining the buoy in the low position and then releasing it, so that it will reach the top of its stroke in conjunction with the wave crest of the second cycle. As the buoy is accelerated during the second cycle in an upward direction, it will travel higher than in the first cycle, and thus develop more potential energy.

Consequently, when the buoy is released from the high point on the second cycle, the buoy will plunge deeper into the trough of the following wave before coming to a halt. This increase in total displacement will continue until a point of equilibrium is reached, taking into account the fact that energy is being removed during each cycle. It has been noted during tests that using this artificially created resonance, upward buoy displacements which are even greater than the wave height are possible, even when significant quantities of energy are being extracted.

As a result, it is possible to obtain vertical displacements of the buoy which are greater than that which would occur if it were possible to tune the buoy to follow the resonance of the wave cycle.

It has also been noted that even if the buoy cycle is slightly out of phase with the wave cycle, buoys will still exhibit increased vertical displacements as long as the buoy frequency cycle is close to that of the wave frequency cycle.

It follows that when the device is not in operation, as when there is no power take off, the disc brake may be used to either lock the buoy in an upward position, or to alter the frequency to halt resonance. In this regard, the time interval of the disc brake engagement can be controlled either manually or automatically by a monitoring system.

Instead of using a wave detector for matching buoy frequency, it is also possible to utilize a monitoring system to constantly hunt for the proper timing interval for the disc brake engagement by monitoring the power take off energy and adjusting the timing interval (in increments) until the maximum energy from the power take off is realized. For example, if proper disc brake engagement interval is two seconds for a given wave frequency system, the monitoring system is arranged to increase the time interval of the disc brake engagement until it reaches the two second interval, during which time the power take off would be increasing energy output with each increase in time interval. When the increase in time interval passes two seconds, the power take off output would decrease, and the monitoring system, sensing the decrease in energy, would start decreasing the time interval in search of the maximum output interval. This method has the added advantage of being able to compensate for the damping effect of any powder take off on the total system response.

It should be noted that it is not absolutely necessary for the disc brake to hold the main shaft motionless during its engagement interval to accomplish the above described controlled resonance between the buoy and the wave. If the brake retards the rotation of the main shaft for a period of time on each stroke during the natural buoy response to the sea wave in a similar fashion, the mechanical energy which can be extracted from the system is still increased, although to a lesser degree.

Claims (4)

Claims The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. In an ocean wave energy device, of a type including a buoy, which reciprocates in a substantially vertical direction in response to successive waves passing therebeneath, said buoy being supported upon a substantially vertically oriented shaft; and a power take off means including a shaft driven by movement of said vertical shaft, the improvement comprising: means for imposing an artificial resonance to said buoy where said resonance may be conformed to an instantaneous wave frequency, said last mentioned means including brake means for halting movement of said buoy at at least one of the uppermost and lowermost limits of vertical displacement of said buoy, means sensing said limits and actuating said braking means; and means sensing said instantaneous wave frequency and releasing said brakeing means in accordance therewith.

2. The improvements set forth in Claim 1, further characterized in said braking means including a brake disc on said rotating shaft, and caliper means selectively engaging said disc; said means for sensing said uppermost and lowermost limits of vertical displacement being in the form of a zero revolutions per minute detector.

3. The method of extracting maximum energy from an ocean wave energy device including a vertically reciprocating buoy and power take off means driven by the reciprocation of said buoy, including the steps of: detecting the instantaneous wave frequency; braking the buoy at at least one of the limits of its path of travel; and releasing the buoy after a period of time sufficient to bring the frequency of said buoy into substantial conformance with the instantaneous wave frequency.

4. The method set forth in Claim 3, further characterized in periodically locking said buoy at both the upper and lower limits of its path of travel.