Abstract:
A free floating wave energy converter includes at least one flexible pipe, adapted to float at a surface of a body of water, having an inlet end for receiving alternating slugs of water and air when the pipe is moored facing at an angle to a wave direction in the body of water and having an outlet end in fluid communication with a power takeoff and other devices, a plurality of supports attached to the pipe at spaced apart locations, each of the supports extending traverse to a longitudinal axis of the pipe and outwardly in opposite directions and at least two inflatable tubes attached to the supports on opposite sides of the pipe extending longitudinally substantially parallel to the longitudinal axis of the pipe, wherein the pipe is raised and lowered relative to the surface of the water by respectively inflating and deflating the tubes with a gas.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to the field of ocean wave energy converters (WECs). More particularly the present invention is an apparatus that can be fitted to a new WEC or retrofitted to an existing WEC which provides improved variable buoyancy and enhanced capture width to the flexible pipe or plurality thereof for use with wave energy converters for extracting wave energy, thereby improving efficiency and energy conversion capacity of such WECs. 
       BACKGROUND OF THE INVENTION 
       [0002]    Certain freely floating wave energy types of wave energy converters have been disclosed by the present applicant&#39;s previous patent applications and granted patents, namely the “Free Floating A Wave Energy Converter” under Indian Patent Number 239882, “Free Floating Wave Energy Converter” (FFWEC)/(US Patent # US20080229745), etc., “An Improved Free Floating Wave Energy Converter” (IFFWEC)/[Indian Application 2511/CHE/3458], WO 2013014682 A2), PCT/1N2012/000510, EP20120753590, CA2844023A1, CN103814211A, US20140157767], and as well the US application titled, “Free Floating Wave Energy Converter With Control Devices”. 
         [0003]    The above quoted inventions essentially consist of Inlet and flexible pipe, floating on a body of water, i.e. ocean surface and adapting to wave form. The mouth of the flexible pipe is in fluid communication with an inlet and its outlet in further fluid communication with power takeoff and other devices. The inlet doses air-water slugs into the flexible pipe, which get pushed forward by transverse waves, progressively building up pressure in it—which could be used to drive conventional Hydro-generators or pump water for any other purpose. 
         [0004]    The present invention discloses certain improvements for enhancing and controlling buoyancy of WECs employing flexible pipes to extract wave energy. 
         [0005]    In the prior art, an Indian Application No. 2511/CHE/2011, describes the use of inflatable tubes  1300 ,  1302 , wherein FIG. 13B shows an embodiment having certain means and methods for preventing the flexible pipe from sagging or sinking in a body of water. 
         [0006]    The arrangement was also meant to let a segment of the flexible pipe  204  to go below a wave trough, up to a controlled depth, thereby increasing the amplitude or the effective wave height of the flexible pipe  204 , as compared with the wave height of the body of water. Consequently, the wave energy absorption capacity of the flexible pipe  204  would increase, proportional with the effective wave height. To expose the flexible pipe to a larger wave front, the flexible pipe could be oriented at an angle to the oncoming waves. 
         [0007]    Reference is also made to FIG. 1 of the India Patent Application 2511/CHE/2011 and the corresponding explanation therein, in which the pressure head created by the flexible pipe  204  is shown as the sum total of the effective wave heights, less frictional and other losses. 
         [0008]    However, it would be apparent to one skilled in the art that, to create a pressure head in actual conditions, several other factors would also be involved, such as the force required for pushing the water slugs forward, at certain velocity, friction and rate of discharge against a pressure head. In addition to these forces there will also be certain frictional losses, when the flexible pipe goes below water surface, due to water friction on the exterior surface of the flexible pipe. 
         [0009]    As such, the effective width or capture width of the air segment of flexible pipe  204  and inflatable tube  1300   1302  might not be sufficient to prevent the arrangement from sagging or sinking below wave crests, particularly when the pressure differential (effective wave height) is increased. 
         [0010]    Furthermore, details of attaching the inflatable tubes  1300   1302  to the flexible pipe  204  and the added advantages that would accrue from the arrangement were not discussed in the previous invention application. 
         [0011]    The present invention discloses details of an embodiment having certain improvements, additional features and advantages. 
       SUMMARY OF THE INVENTION 
       [0012]    The objectives of the invention are, to enhance energy extraction capacity of freely floating wave energy converters employing flexible pipe for extracting wave energy, by increasing the capture width, effective wave height or pressure differential of water segments and restrain sagging of the flexible pipe. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]    The above and other advantages of the present invention would become readily apparent from the following detailed description of preferred embodiments when considered in the light of the accompanying drawings in which: 
           [0014]      FIG. 1 ( a )  depicts flexible pipe with air and water slugs, with no pressure head and  1  ( b ) depicts a pressure head, causing “Phase Shift” and loss in wave height. 
           [0015]      FIGS. 2 ( a ) ,  2  ( b ) and  2  ( c ) depict side, front and plan views of the preferred embodiment, respectively. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0016]    The description and appended drawing describe and illustrate various exemplary embodiments of the invention to make and use the invention, and are not intended to limit the scope of the invention in any manner. In respect of the methods disclosed, the steps presented are exemplary in nature, and thus, the order of the steps is not necessary or critical. Certain design principles to achieve the desired results are discussed in the succeeding paragraphs. 
         [0017]      FIG. 1( a )  depicts waves “Wd” moving from the left to the right hand side of the page. A flexible pipe  204  floating in phase with waves  1100 . An inlet doses slugs of air  1012  and water  1011  are into the mouth of the flexible pipe  204  or plurality thereof, (not shown in the figure), wherein no energy is being extracted, shown as an empty overhead tank  1120 , with no water in it or “zero” pressure head (PH 0 ) and frictional loss has not been considered. 
         [0018]    In this case, the flexible pipe  204  follows the waves  1100 , while the Center of Buoyancy “B” and Center of Gravity “G” and the air and water slug  1102 / 1101  remain at the center of the respective crests and troughs. The buoyant force (F b ) and the weight (W), act through Center of Buoyancy (B) and C of G (G) of each wave. However, the trough portions of the flexible pipe go slightly below the wave troughs, due to the weight of water in them. The amplitude a p  of the flexible pipe  204  and the wave height “H” are nearly the same. 
         [0019]      FIG. 1 ( b ) , on the other hand, shows a flexible pipe floating on water surface and an inlet doses slugs of air  1011  and water  1012  are fed into the mouth of the flexible pipe  204  (not shown in the figure) The flexible pipe is extracting wave energy and thereby creating a pressure head “PH x ”, represented by an overhead tank  1120  having some water in it. 
         [0020]    Slugs of air and water from the flexible pipe  204  are pumped, under pressure through outlet of the flexible pipe, into the tank  1120 , creating pressure head PH x . Pumping water, against a pressure head PH x , at a certain rate and mass flow, together with fluid friction, creates a backpressure H p(x)  which acts through G of each trough pushing the flexible pipe  204  back against wave motion. The forces could be resolved into horizontal H p(x)  and vertically downwards H p(y)  components. In addition to this, the weight of a water slug “W” also acts downwards in the vertical plane. 
         [0021]    Furthermore, the portion of the flexible pipe  204 , which goes under water, creates drag/friction “f w ” from the body of water outside, as the waves move forward, following along the flexible pipe  204 . 
         [0022]    The total horizontal and vertical components at G can be resolved as a resultant “R”. 
         [0023]    Besides these, a buoyant force “F b ” acts vertically upwards, through the Center of Buoyancy “B”. A horizontal component F y  opposes forward motion of the flexible pipe  204 , while the vertical component provides lifting force F x . 
         [0024]    To balance the aforementioned forces, water slugs  1011  get pushed backwards and tend to ride up the crests of the advancing waves, while the air segments  1012  shift behind and goes below the wave crests. The Center of Gravity “G” and buoyancy “B” too lag. 
         [0025]    This causes the flexible pipe to  204  to exert horizontal H p(x) +F w  and vertical H p(y)  pressures on the surface of advancing waves  1100  in the direction a resultant vector “R”, causing a phase shift “φ s ” and reduction in the amplitude a px , of the flexible pipe  204 , as compared with the wave height H, by certain wave height loss H L . Consequently, the Pressure Differential “P d ” of the water slugs also reduces and the water slugs start sinking/sagging. Advancing waves could overrun the crests of flexible pipe, causing it to sag or sink. 
         [0026]    Therefore, the more the pressure head, the more the phase shift, the lesser the Pressure Differential and the lesser the extractable wave energy. 
         [0027]    This would also let water slugs flow down from one trough segment to another, causing the flexible pipe to sag, despite the additional buoyancy provided by the inflatable tube  1300  embodiments disclosed in the previous invention. 
         [0028]    An embodiment  1330  of the present invention offers solutions for overcoming the aforementioned shortcomings. 
         [0029]      FIGS. 2( a ), 2( b ) and 2( c )  show flexible pipe  204 , or plurality thereof, suitably moored, oriented facing at an angle to the waves, floating on a body of water, i.e. ocean surface, and adapting to the wave form. 
         [0030]    Wherein, the mouth of the flexible pipe  204  is in fluid communication with an inlet and its outlet being in further fluid communication with power takeoff and other devices, which are not shown in the present figures. 
         [0031]    Wherein, the inlet doses air-water slugs  1012 - 1011  into the flexible pipe, which get pushed forward by transverse waves, progressively building up pressure in it, which could be used to drive conventional Hydro-generators or pump water for any other purpose. 
         [0032]    Wherein, on an exterior of the flexible pipe  204  or plurality thereof, a plurality of horizontal supports  1315  are attached all along the length of the flexible pipe  204 . 
         [0033]    Wherein, the horizontal supports  1315  extend equally outwards on either side and are spaced evenly all along the length of a flexible pipe  204 . 
         [0034]    Wherein, the horizontal supports  1315  are of suitable span. 
         [0035]    Wherein, the horizontal supports  1315  are evenly and suitably spaced. 
         [0036]    The horizontal supports  1315  could be beams, ribs, and the like, preferably made of non-corrosive and light weight materials, such as composites, having enough tensile strength to withstand continuous load fluctuations, such as latticed constructions, of the desired lengths and profile. 
         [0037]    Wherein, onto the horizontal supports  1315  at least two inflatable tubes  1300  attached along the length of flexible pipe  204  or plurality thereof. 
         [0038]    Wherein, the inflatable tubes  1300  are generally arranged substantially parallel to the flexible pipe  204 . 
         [0039]    Wherein, inflatable tubes  1300  could be attached on an upper, lower or both sides of the horizontal supports  1315 . 
         [0040]    Wherein, inflatable tubes  1300  are preferably made of polymeric material or elastic rubber and the like is selectively inflated and deflated for varying its buoyancy. 
         [0041]    Wherein, inflatable tubes  1300  are selectively inflated and deflated for varying their buoyancy. 
         [0042]    Wherein, inflatable tubes  1300  can be of smaller lengths and suitably interconnected in fluid communication with each other in series. 
         [0043]    Wherein, the openings at the fore and aft ends of the inflatable tubes  1300  are in fluid communication with the pressure source, through pneumatic hoses  1317 , such a blower pump or the pressure chamber  208 , compressor, with pressure regulators, controls, micro-processor, etc., which are not shown in the present figures. 
         [0044]    By increasing the number and/or diameter of the inflatable tubes  1300  and span of the horizontal supports  1315 , the buoyancy and the capture width of the flexible pipe could be proportionately increased. 
         [0045]    When the inflatable tubes  1300  are fully pressurized, the buoyancy along its entire length would be high enough to keep flexible pipe  204  always floating above water, even if it is filled completely with water. 
         [0046]    When the inflatable tubes  1300  are depleted, and the flexible pipe or plurality thereof are mostly filled with water, there would be no buoyancy enhancement. Consequently, the flexible pipe and the attached device  1330  could be made to submerge, particularly during storms. By pumping air back into the inflatable tubes  1300 , the device could be resurfaced and resume normal operations. 
         [0047]    As the pressure in the inflatable tube  1300  is reduced to an extent, the trough segments  1300 B would start sinking due to the combined weight of water slugs, flexible pipe and the attached device  1330 . Consequently air from the trough segments  1300 B would be squeezed out and get pushed into the crest segments of the inflatable tubes  1300 A, further increasing the buoyancy thereat. 
         [0048]    It can be seen that, the crest of the inflatable tube can be made to remain always above wave crests, while its trough segment below troughs. 
         [0049]    By regulating the volume of air in the inflatable tube  1300 , the amplitude a p  of the inflatable tubes and flexible pipe  204  or plurality thereof arrangement  1330 , as well as the pressure differential p d  can be varied to a substantial extent, as compared with the corresponding wave height H of a wave. 
         [0050]    Further, as a trough segment  1300 B of an inflatable tube sinks, the water pressure acting on its exterior surface rises with depth, thereby progressively constricting/sealing the passage within  1300 B, which would impede/prevent air from flowing freely between its crests segments. 
         [0051]    Consequently, the crest segments of the inflatable tubes  1300 A would always remain above the crests of the waves, i.e. a phase lock would be formed, thereby preventing the flexible pipe from going below the wave crests; which would otherwise lead to sagging. 
         [0052]    The air inside the inflatable/deflatable tubes  1300 A/ 1300 B gets pushed forward along with the waves, as they progress from front to rear end of the tubes and is looped through the pneumatic hoses  1317 , as discussed above. 
         [0053]    Since there will be variation in wave parameters, wave heights and lengths will vary, warranting exchange of air and water slugs between segments. When this happens, difference of air pressure between the effected segments of inflatable pipe  1300  would exceed the sealing limits of the squeezed portions of the inflatable tube  1300 B, thereby permitting air to get transferred between segments. 
         [0054]    Thus, the objectives of the present invention could be achieved by adopting the means and methods disclosed in the preceding paragraphs. 
         [0055]    Various other permutations and combinations of the same principle of operation and arrangements are also possible, but not mentioned herein. 
         [0056]    Numerous characteristics and advantages of the invention covered by this document will be set forth in the foregoing description. It will be understood, however, that this disclosure is, in many respects, only illustrative. 
         [0057]    Changes may be made in details, particularly in matters of shape, size, and arrangement of parts without exceeding the scope of the invention. 
         [0058]    In accordance with the provisions of the patent statutes, the present invention has been described in what is considered to represent its preferred embodiment. However, it should be noted that the invention can be practiced otherwise than as specifically illustrated and described without departing from its spirit or scope.