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 
       [0001]    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 
       [0002]    1. Field of the Invention 
         [0003]    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? 
         [0004]    2. Description of Related Art 
         [0005]    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 
       [0006]    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. 
         [0007]    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 
         [0008]      FIG. 1  illustrates a three-barge articulated system designed for potable-water production in accordance with the invention; 
           [0009]      FIG. 2  illustrates a U-tube hydraulic system designed to increase the pitching angle of the center barge in accordance with the invention; 
           [0010]      FIG. 3  illustrates a tuning system for the forward  10  and after 18 barges using the U-tube in accordance with the invention; 
           [0011]      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 
           [0012]      FIG. 5  illustrates an articulated barge system composed of Flexifloat barges in accordance with another embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0013]    The Articulate Barge Wave-Energy Conversion System 
         [0014]    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   
         [0015]    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. 
         [0016]    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. 
         [0017]    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. 
         [0018]    Motion Enhancement 
         [0019]    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 . 
         [0020]    A. Center-Barge U-Tube 
         [0021]      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 . 
         [0022]    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. 
         [0023]    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. 
         [0024]    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. 
         [0025]    B. Forward-Barge and After-Barge U-Tubes 
         [0026]      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 . 
         [0027]    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. 
         [0028]    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. 
         [0029]    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. 
         [0030]      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. 
         [0031]    C. Off-the-Shelf Design 
         [0032]      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. 
         [0033]    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: 
         [0034]    a. S-70 End Rake, 10 feet in length, displacing 5.25 tons, coupled to a 
         [0035]    b. S-70 Quadrafloat, 40 feet in length, displacing 17.80 tons 
         [0036]    c. S-70 DuoFloat, 20 feet in length, displacing 9.45 tons 
         [0037]    d. S-70 Quadrafloat, 40 feet in length, displacing 17.80 tons, coupled to a 
         [0038]    e. S-70 DuoFloat, 29 feet in length, displacing 9.45 tons 
         [0039]    The pumps are preferably salt-water pumps of special design. These are located 4 feet above the hinges. 
         [0040]    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.