US20090084296A1

US20090084296A1 - Wave-Powered Energy Conversion System

Info

Publication number: US20090084296A1
Application number: US12/095,200
Authority: US
Inventors: Michael E. McCormick
Original assignee: Ocean Energy Systems LLC
Current assignee: OCEAN ENERGY SYSTEMS Inc; Ocean Energy Systems LLC
Priority date: 2005-11-30
Filing date: 2006-11-30
Publication date: 2009-04-02
Also published as: EP1960661A1; WO2007065121A1

Abstract

A wave-powered device having enhanced motion. The device including first, second, and third barges, with the second barge having a first reservoir and a second reservoir. The first and second reservoirs being coupled by a first passageway to permit a first fluid to selectively and passively move between the first and second reservoirs in a predetermined manner to increase the pitching moment of the second barge while the second barge pitches while floating over waves. A first coupling mechanism is coupled between the first and second barges to enable the first and second barges to move relative to one another, and a second coupling mechanism is coupled between the second and third barges to enable the second and third barges to move relative to one another.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of provisional U.S. Patent Application Ser. No. 60/740,674, entitled “Wave-Powered Energy Conversion System,” filed Nov. 30, 2005, which is hereby incorporated by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention
The utilization of ocean wave energy has been the goal of many for more than a century. There are primarily two products of wave energy conversion, those being electricity and potable water. Because electricity production is more “exciting” to humankind, most of the efforts in wave energy conversion have been focused on electricity. For those of us more interested in the benefit to humankind, potable water is more desirable. To realize this fact, the reader should answer the following two questions: (a) How long can I survive without electricity? (b) How long can I survive without water?
2. Description of Related Art
Of all of the wave energy techniques, the most apropos for water production, in the opinion of this writer, is the articulated barge system. There are two versions of this technique. The first is the Hagen-Cockerell raft and second is the McCabe Wave Pump. These are disclosed in U.S. Pat. Nos. RE 31,111 to Hagen; 4,210,821 to Cockerell; and 5,132,550 to McCabe, each of which is incorporated by reference thereto. The former is simply a system of freely-floating hinged rafts having pumps located over the hinges. The latter is a three-barge system having a horizontal damping plate suspended below the center barge. It has been found that the McCabe concept is more efficient than the Hagen-Cockerell raft system, which is a wave-following system. Because of its low efficiency, the Hagen-Cockerell raft system was never developed; while, the McCabe Wave Pump is now in the development stage.

BRIEF SUMMARY OF THE INVENTION

Described herein is a passive technique for improving the efficiency of a wave-following, articulated raft wave-energy system. The motion-enhanced system is promising for the production of potable water for coastal communities and island communities.
One aspect of the application relates to a wave-powered device, including a first barge; a second barge having a first reservoir and a second reservoir, the first and second reservoirs being coupled by a first passageway to permit a first fluid to selectively and passively move between the first and second reservoirs in a predetermined manner to increase the pitching moment of the second barge while the second barge pitches while floating over waves; a third barge; a first coupling mechanism coupled between the first and second barges to enable the first and second barges to move relative to one another; and a second coupling mechanism coupled between the second and third barges to enable the second and third barges to move relative to one another.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a three-barge articulated system designed for potable-water production in accordance with the invention;

FIG. 2 illustrates a U-tube hydraulic system designed to increase the pitching angle of the center barge in accordance with the invention;

FIG. 3 illustrates a tuning system for the forward 10 and after 18 barges using the U-tube in accordance with the invention;

FIG. 4 illustrates a displacement configuration of the wave-following articulated barge system in a design wave, where L/λ≅0.5, in accordance with one embodiment of the invention; and

FIG. 5 illustrates an articulated barge system composed of Flexifloat barges in accordance with another embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

The Articulate Barge Wave-Energy Conversion System
A computer-generated picture of an articulated barge system is shown in FIG. 1. In that figure, we see that the system preferably may be comprised of three barges of differing lengths. The forward barge 10 is the barge facing into the waves. The wave action causes the barge to rise and fall in a rotational fashion about the hinges 12 coupling this barge to the center barge 14. It has been found that this barge is capable of capturing approximately 60% of the incident wave energy. The relative rotational motions of the forward 10 and center 14
Barges excite the pumps 16 located over the hinges. These pumps 16 are preferably hydraulic pumps designed to draw in salt water, pre-filter the water and pump the water at high pressure to a reverse-osmosis (RO) desalination plant. Depending on the application and product water (potable water) requirements of the system, the RO can be on shore or on the deck of the after barge 18 of the system.
The center barge 14 preferably has a length that is less than half of the forward barge 10 length, by design. This ensures that the relative angular displacements of each barge will be relatively large.
The after barge 18 is preferably the longest of the three for two reasons. First, since it receives about 40% of the incident wave power, it needs to be longer to capture that power. Second, a longer after barge 18 provides a certain amount of directional stability to the system. That is, it helps the system face into the direction of the incident waves.
Motion Enhancement
There are two types of motion enhancement of the system sketched in FIG. 1 provided by passive hydraulic systems. By the term “passive”, it is meant that the system needs no adjustment during deployment. The motion enhancements involve the tuning of the forward 10 and after 18 barges to a selected wave period, and the motion increasing hydraulic moment of the center barge 14.
A. Center-Barge U-Tube
FIG. 2 illustrates a U-Tube hydraulic system designed to increase the pitching angle of the center barge. The hydraulic valve 40 controls the losses in the pipes 24 connecting the forward 30 and after 32 reservoirs. The check valves 42 at the top of each reservoir 30, 32 is designed to prevent water entering the breathing (air) pipe 44. The pneumatic valve 46 at the top can be used to add resistance to the transport of the water between the reservoirs 30, 32.
In FIG. 2 a, we see the internal U-Tube hydraulic system 20 designed to increase the angular displacement of the center barge 14. Referring to FIG. 2 b, this is done by shifting the center of mass of the water 22 in the hydraulic system towards either the bow-down side or the stern-down side. In FIG. 2 b, we see the bow-down orientation of the center barge 14. In FIG. 2 b, the counterclockwise displacement of the center barge 14 causes the water 22 to shift in the U-Tube 24 towards the left-hand side (bow side 26). This would occur during the passing of a trough of a wave. When a crest passes, the forward barge 10 rises, lifting the front 26 of the center barge 14, and the water 22 shifts to the left. This increase in water mass on one side of the center barge 14 and the subsequent decrease in water mass on the other side of the tube 24 cause an unstable moment resulting in an increase of the angular displacement.
It is known that U-tubes 24 have natural periods of oscillation. That period, without any damping in the system, is T=2π√ (l/2 g), where l is the linear distance from the center of the air-water interface in the center of one reservoir to the same point in the other reservoir. This frequency should be avoided. To do this, both hydraulic and pneumatic valves are used to increase the flow resistance. This changes the period and causes the transfer of water between the reservoirs to be orderly.
The volume of fresh water within the hydraulic system is determined from both performance predictions in a design sea, and the ballast requirements of the system. For performance, the reservoirs should be separated by a relatively large transfer pipe 24 in order to produce a high pitching moment. The weight of the water 22 acts as ballast, and will help determine the operating draft of the system.
B. Forward-Barge and After-Barge U-Tubes
FIG. 3 illustrates a tuning system for the forward 10 and after 18 barges using the U-Tube. The bi-directional air pump is needed to change the water level when deployed. The float check valves 42 prevent water from entering the air line 44.
For optimal performance, there are two considerations: First, the forward 10 and after 18 barges should be in resonance with the incident waves. Pitching about the hinges 12 attaching the barge-pairs (forward-and-center and center-and-after) is the production motion of system. The natural pitching period of each barge 10, 14, 18 depends on the ballast and the location of the center of gravity. The U-Tube technique can be used to tune the pitching motions of the barges 10, 14, 18 to the design wave period. Referring to FIG. 3, the U-Tube tuning system is sketched for the forward barge 10. En this case, the water 22 is initially transferred from one reservoir 30 to the other 32. As shown, the water 22 transfer would move the center of gravity of the barge 10 forward of its as designed position. This would increase the natural pitching period of the barge 10 from the as-designed value.
The second optimization concerns the relationship between the total length (L) of the system in FIG. 1 and the wavelength, λ. It has been found that the two optimal length ratios are L/λ=0.5 and 1.0. For a 7-second design wave (the average wave period off the central Atlantic coast of the U.S.), the wavelength is approximately 250 feet, 50 less than a football field.
We may choose the smaller of the length ratios: so, for the 7-second wave, the ideal length is 125 feet. For this length, the displaced system as the crest of a design wave passes would resemble that in FIG. 4. The increased pitching angles due to the inclusion of the U-tubes in the barges would result in increased pitching amplitudes of all of the barges. This would improve the performance of the system by increasing the strokes of the pumps above the hinges.
FIG. 4 illustrates a displacement configuration of the wave-following articulated barge system in a design wave, where L/λ≅0.5. Using the motion-enhancing U-Tubes in all of the barges, the pitching angle amplitudes would be increased, increasing the relative angles between the barge-pairs. This would, in turn, increase the strokes on the pumps above the hinges.
C. Off-the-Shelf Design
FIG. 5 illustrates an articulated barge system composed of Flexifloat barges 110, 114, 118. The system shown is preferably, approximately 138 feet in length. For the 7-second sea, the length ratio is L/λ≅0.55, which is nearly optimal. This length coupled with the U-Tube enhancement systems would result in optimal performance.
For L/λ=0.5, a system can be constructed using the Flexifloat 110, 114, 118 barges or some other commercially available barges. Using the Series S-70 Flexifloat 110, 114, 118 barges to illustrate the system is shown in FIG. 5. The system shown in FIG. 5 is approximately 138 feet in length, which is about 55% of the design wavelength corresponding to a 7-second wave. The system in FIG. 5, from bow to stern, consists of the following:
a. S-70 End Rake, 10 feet in length, displacing 5.25 tons, coupled to a
b. S-70 Quadrafloat, 40 feet in length, displacing 17.80 tons
c. S-70 DuoFloat, 20 feet in length, displacing 9.45 tons
d. S-70 Quadrafloat, 40 feet in length, displacing 17.80 tons, coupled to a
e. S-70 DuoFloat, 29 feet in length, displacing 9.45 tons
The pumps are preferably salt-water pumps of special design. These are located 4 feet above the hinges.
While the invention has been described with reference to the certain illustrated embodiments, the words which have been used herein are words of description, rather than words or limitation. Changes may be made, within the purview of the appended claims, without departing from the scope and spirit of the invention in its aspects. Although the invention has been described herein with reference to particular structures, acts, and materials, the invention is not to be limited to the particulars disclosed, but rather extends to all equivalent structures, acts, and materials, such as are within the scope of the appended claims.

Claims

1. A wave-powered devices comprising:

a first barge;

a second barge having a first reservoir and a second reservoir, said first and second reservoirs being coupled by a first passageway to permit a first fluid to selectively and passively move between said first and second reservoirs in a predetermined manner to increase the pitching moment of said second barge while said second barge pitches while floating over waves;

a third barge;

a first coupling mechanism coupled between said first and second barges to enable the first and second barges to move relative to one another; and

a second coupling mechanism coupled between said second and third barges to enable the second and third barges to move relative to one another.

2. A device according to claim 1, wherein

said second barge includes a second passageway between said first and second reservoirs for a second fluid to enter said first and second reservoirs.

3. A device according to claim 2, wherein

said first fluid is water and said second fluid is a gas.

4. A device according to claim 1, wherein

each of said first and second coupling mechanisms includes a hinge.