Abstract:
A wave power converter employing a flow-controlled duct for capturing and converting useful wave surge energy to electric power over a relatively broad range of surf or river flow conditions. The power converter includes an inclined ramp with several openings for receiving wave or river water and retaining surge water in hydraulic isolation, permitting water to flow into a flow-controlled conduit and a generator for producing electrical power from water flow in the conduit. The power converter apparatus is suitable for low-cost manufacture, offers simple robust operation suitable for underdeveloped regions of the world, may be fabricated from commonly-available components, requires few moving parts and no valuable (lootable) components other than a generator, and is self-flushing for low maintenance operation.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is filed under 37 C.F.R. §1.53(b) as a Continuation-In-Part of U.S. patent application Ser. No. 11/845,778 filed on Aug. 27, 2007 by the same inventor and now issued as U.S. Pat. No. 7,479,708 B1 on Jan. 20, 2009. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates generally to a flow power converter and more particularly to a flow power converter employing a flow-controlled duct to capture both vertical and horizontal components of surge energy from overtopping waves and river flows. 
     2. Description of the Related Art 
     Wave power as a means of generating electricity has been the focus of low-key study in the US and Europe for over thirty years, but with little public support. Wave energy flux arises primarily from wind friction at the sea surface and is entirely distinct from the diurnal flux of tidal energy arising from the lunar cycle and from the steady flow of the major ocean currents arising primarily from the several solar heating and cooling cycles. Wave power generation is not a widely employed technology. The world&#39;s first commercial wave energy conversion farm, the Agucçadora Wave Park in Portugal, was established in 2006. Public interest in this carbon-free power source is now growing because of recent public concern over the accumulating effects of atmospheric carbon loading on world climate. 
     Ocean waves are generated from a portion of the wind energy coupled to the ocean surface over large areas and the available wave energy in a local region is greater than the solar and wind energies available in the same area. Wave energy available from U.S. coasts alone exceeds the entire U.S. production of coal-fired electrical power, constitutes a perpetual, renewable energy source, and is perhaps the only carbon-free energy source suitable for replacing carbon-based power production on a very large scale without concomitant environmental effects. 
     The prior art is replete with wave power conversion proposals. Wave power conversion devices may be generally categorized by the choice of energy capture method used to capture the wave energy. They may also be categorized by choice of location and by choice of power extractor. Types of energy capture methods well-known in the art include point absorber or buoy; surfacing and following or attenuator; terminator with perpendicular alignment to wave propagation; oscillating water column; and overtopping. Location types well-known in the art include shoreline, near-shore and offshore. Well-known types of power extraction systems include: hydraulic ram, elastomeric hose pump, pump-to-shore, hydroelectric turbine, air turbine, and linear electrical generator. 
     For example, in U.S. Pat. No. 4,622,471, Schroeder proposes a terminator system using a plurality of units with unidirectional intake gates disposed horizontally at one elevation to operate independently to capture wave surges upstream from an input penstock. They are adapted to intercept waves and convert their kinetic energy to drive a turbine. Each gate unit includes a horizontally-hinged movable gate adapted to permit the incoming waves to slide over the upper surfaces of the gates and into the penstock. The penstock back pressure operates to push each gate upward to direct the remaining forward moving wave energy to a higher elevation, thereby increasing the water head in the penstock. Schroeder controls the penstock head by applying the same penstock back pressure to every gate unit, which are accordingly hydraulically coupled to one another (not in hydraulic isolation). Schroeder neither considers nor suggests adapting his wave power converter to an overtopping method that retains the captured water at different head pressures in a plurality of substantially isolated chambers each coupled to a penstock, some by way of a check valve. 
     As another example, in U.S. Pat. No. 7,040,089, Andersen proposes an overtopping wave power station device of the kind where the waves flow up a ramp provided with fixed openings arranged so that little of the water flowing up the ramp flows down through the openings and water flowing down the ramp flows down through the openings and into storage reservoirs positioned below the ramp and extending horizontally at various elevations. Andersen couples each storage reservoirs to an associated penstock and turbine intake. All turbine outlets are coupled together, thereby equalizing the head pressures. Andersen relies on ramp intake closing devices to reduce water and head losses at the ramp openings to the lower storage reservoirs and neither considers nor suggests adapting his overtopping wave power converter to retain the captured water at different head pressures in a plurality of substantially isolated chambers each coupled to a penstock, some by way of a check valve. 
     In U.S. Pat. No. 4,216,655, Ghesquiere discloses a wave-operated power plant configured to optimally exploit the horizontal force component from the incoming waves. 
     Normally, the relation between output and investment grows advantageously with the size of the plant. In many cases, it pays to build large plants. However, a large rotating machine, such as a turbine equipped with a generator, costs more than a number of smaller machines with a corresponding total capacity. Complex systems such as hydraulic control systems, are not well suited to incremental implementation (do not scale up well), and have high costs and risks associated with large installations. 
     Traditionally, low head water turbines have been of an open type, as exemplified for example by conventional water wheels, and have had extremely low efficiency. Conventional power generation turbines such as Francis turbines and Peleton turbines traditionally require high heads of water to generate the water pressure and velocity required to move the turbine blades. Such arrangements require large high dams, additional flumes and the like, requiring massive capital expenditures. A more efficient class of turbines, such as the Root Turbine, for example, can be economically constructed to operate at the higher efficiencies suitable for low head electric power generation applications requiring closed turbine systems to maintain siphon. 
     Another well-known challenge is to provide a wave power converter able to tolerate the sometimes volatile conditions of the sea surface. Some practitioners suggest selecting installation sites where the average waves are similar in scope to the extreme waves. Also, the wave power converter must withstand a major storm while also operating with acceptable efficiency during average wave conditions. 
     These unresolved problems and deficiencies are clearly felt in the art and are solved by this invention in the manner described below. 
     SUMMARY OF THE INVENTION 
     This invention solves the above described problems by introducing for the first time a flow power converter having means for the capture of vertical and horizontal wave surge energy components from a broad range of wave and river flow conditions and a flow-controlled conduit to facilitate a stable supply of hydraulic head pressure for conversion to electrical power. 
     It is a purpose of the apparatus of this invention to provide flow power converter apparatus employing surge energy capture for converting useful wave surge energy over a relatively broad range of surf conditions, including relatively calm surf conditions and abnormally higher surf conditions. It is an advantage of the apparatus of this invention that some energy may be captured from low surf and more energy may be captured from higher surf without the need for adjusting the apparatus. It is a feature of the apparatus of this invention that the storage chamber and flow-controlled duct are disposed to capture and convert a significant amount of the horizontal surge kinetic energy component into potential energy in the form of elevated hydraulic head. 
     It is another purpose of this invention to provide a flow surge power converter suitable for low-cost manufacture and simple robust operation in underdeveloped regions of the world. It is an advantage of the apparatus of this invention that it is suitable for fabrication from low-cost commonly-available components. It is another advantage of the apparatus of this invention that it has few moving parts, has no valuable (lootable) components other than a generator, is self-flushing and requires little maintenance. 
     In one aspect, the invention is a wave surge power converter including a plurality of openings each disposed on an incline at an elevation to receive wave surge water when a wave surges up the incline; a storage chamber coupled to one or more of the ramp openings for capturing wave surge water received thereby and retaining the captured water; one or more check valves each disposed within one of the ramp openings to permit water flow into the storage chamber responsive to a hydraulic pressure difference across the check valve; a discharge duct defining a cross-sectional flow area (A) and having a length (L) disposed to hydraulically couple the storage chamber to an exit; and a generator for producing electrical power from a flow of captured water in the discharge duct arising from a hydraulic pressure difference between the storage chamber and the discharge duct exit. 
     In another aspect, the invention is a river flow power converter including a plurality of openings each disposed on an incline at an elevation to receive river flow water as the water flows over the incline; a storage chamber coupled to one or more of the ramp openings for capturing river flow water received thereby and retaining the captured water; a discharge duct defining a cross-sectional flow area (A) and having a length (L) disposed to hydraulically couple the storage chamber to an exit that is disposed so that the local hydraulic pressure at the discharge duct exit is reduced by the flow of river water over the discharge duct exit; and a generator for producing electrical power from a flow of captured water in the discharge duct arising from a hydraulic pressure difference between the storage chamber and the discharge duct exit. 
     The foregoing, together with other objects, features and advantages of this invention, can be better appreciated with reference to the following specification, claims and the accompanying drawing. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a more complete understanding of this invention, reference is now made to the following detailed description of the embodiments as illustrated in the accompanying drawing, in which like reference designations represent like features throughout the several views and wherein: 
         FIG. 1  is a diagram illustrating a perspective view of a first embodiment of the wave surge power converter apparatus of this invention; 
         FIG. 2  is a diagram illustrating a side cross-sectional view of the apparatus of  FIG. 1 ; 
         FIG. 3  is a diagram illustrating an exploded perspective view of a first check valve embodiment suitable for use with the apparatus of  FIG. 1 ; 
         FIG. 4 , including detail  FIG. 4A , is a diagram illustrating a front view of the apparatus of  FIG. 1 ; 
         FIG. 5  is a diagram illustrating a rear view of the apparatus of  FIG. 1  with the tail-wall removed to expose the interior of the rear chamber; 
         FIG. 6A  is a diagram illustrating a side cross-sectional view of an alternative embodiment of the wave surge power converter apparatus of this invention showing exemplary check valve dispositions during normal flow conditions; 
         FIG. 6B  is a diagram illustrating a side cross-sectional view of the wave surge power converter apparatus of  FIG. 6A  showing exemplary check valve dispositions during abnormal back-flow conditions; and 
         FIGS. 7A-B  are schematic diagrams illustrating a top view of an illustrative transmission embodiment suitable for use with the apparatus of  FIGS. 6A-B  under the two exemplary flow conditions illustrated in  FIGS. 6A-B . 
         FIG. 8 , including detail  FIG. 8A , is a diagram illustrating a perspective view of a preferred “wedge” embodiment of a wave surge power converter apparatus of this invention in operation during a wave surge peak; 
         FIG. 9  is a diagram illustrating a perspective view of the embodiment of  FIG. 8  in operation during a wave surge trough; 
         FIG. 10A  is a schematic diagram illustrating a partial top view of the embodiment of  FIG. 8  revealing a plurality of ramp openings; 
         FIG. 10B  is a schematic diagram illustrating a partial bottom view of the ramp surface of  FIG. 10A  revealing a plurality of check valve flaps; 
         FIG. 10C  is a cross-sectional view of the ramp surface of  FIG. 10A  at A-A revealing the ramp openings and check valve flaps in cross-section; 
         FIG. 11 , including detail  FIG. 11A , is a diagram illustrating a perspective view of a preferred “wedge” embodiment of a river flow power converter apparatus of this invention for capturing and converting river flow energy; 
         FIG. 12  is a schematic diagram illustrating the principle of operation of a preferred controlled-flow duct embodiment of this invention; and 
         FIG. 13  is a schematic diagram illustrating the principle of operation of another preferred controlled-flow duct embodiment of this invention showing detailed references to the elements of Bernoulli&#39;s equation. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       FIG. 1  illustrates a first wave surge power converter embodiment  10  of this invention, showing the inclined ramp  12 . During operation, converter  10  is preferably disposed at an ocean surface  14  having episodic wave surges generally oriented in the direction indicated by the arrow  16  such that a typical wave surges vertically generally along the vertical surge component  18  and horizontally generally along the horizontal surge component  20 . Ramp  12  is shown with a slope of about 33% (17-18 degrees) and is preferably oriented generally along surge direction  16  such that the wave surge water moves up ramp  12 , progressing along a series of openings  22 A-D therein. Each of openings  22 A-D that is thereby exposed to the wave surge then receives surge water into the associated one of the plurality of independent chambers  24 A-D. Each of the first independent chambers  24 A-C is substantially isolated hydraulically from its neighbors by means of a single check valve (described below in connection with  FIGS. 2 ,  3  and  6 A-B) disposed in the associated one of the plurality of drain assemblies  26 A-C. No check valve is required in drain assembly  26 D for the final chamber  24 D because the hydraulic head in chamber  24 D is made equal to the hydraulic head in conduit  28  for reasons described in more detail below. As may be readily appreciated from this description, any surge water captured within each chamber  24 A-D flows down by gravity through the associated drain assembly  26 A-D into a plenary conduit  28  and out into the ambient ocean  30  through the draft tube  32 . This flow of captured water from each of one or more chamber(s)  24 A-D through the associated drain assembly  26 A-D into conduit  28  and out draft tube  32  arises from the hydraulic pressure difference between at least one chamber(s)  24 A-D and ambient ocean  30  and may be employed to turn a low-head turbine (not visible, see  FIGS. 2 ,  5  and  6 A-B) within conduit  28  that is coupled by means of, for example, a shaft  34  to a generator  36  for generating electrical power. The substantial hydraulic isolation of chambers  24 A-D is an important feature of converter  10  for reasons that are described in more detail below. Another important feature of converter  10  is the grill  38  or “trash rack” formed from a plurality of slats, exemplified by the slat  40  ( FIG. 4A ), disposed over openings  22 A-D to prevent most floating debris from entering chambers  24 A-D by facilitating the sloughing of debris back into the surf during the relaxation of the wave surges. For clarity, grill  38  is only partially illustrated in  FIG. 1  and actually extends across the entire width of converter  10  to completely cover all of openings  22 A-D. 
       FIG. 2  is a diagram illustrating a side view of converter  10  disposed in an exemplary operating position under a pier  42  by means of, for example, the two structural supports  44 A-B. The disposition of the closed low-head turbine  46  may also be seen in draft tube  32  and the disposition of each of the plurality of check valves  48 A-C may be seen in the associated drain assemblies  26 A-C. For example, check valve  48 A operates to prevent water flow from conduit  28  to chamber  24 A in the following manner.  FIG. 3  illustrates an exploded perspective view of an illustrative embodiment of check valve  48 A, which exemplifies any of the plurality of check valves  48 A-C. During operation check valve  48 A is oriented with respect to gravity as shown by the gravity arrow  50 . A float ball  52 A is retained within a drain pipe  54 A between a lower sieve plate  56 A and an upper valve seat  58 A so that, when hydraulic pressure at the bottom of chamber  24 A exceeds the hydraulic pressure in conduit  28  ( FIGS. 1-2 ), water flow urges float ball  52 A away from valve seat  58 A, thereby permitting water to flow downward through drain pipe  54 A and through sieve plate  56 A into conduit  28  ( FIGS. 1-2 ). Should the hydraulic pressure in conduit  28  equal or exceed the hydraulic pressure at the bottom of chamber  24 A, then check valve  48 A closes to prevent any water flow in the upward direction because float ball  52 A urges against valve seat  58 A, thereby closing off all flow in drain pipe  54 A. These elements of check valve  48 A are suitable for simple and inexpensive manufacture for robust performance. For example, valve seat  58 A and drain pipe  54 A may be embodied as simple sections of PVC pipe, float ball  52 A may be embodied as a simple rubber sphere (e.g., a ball), and sieve plate  56 A may be embodied as a simple plastic drain sieve, for example. 
     Returning to  FIG. 2 , the hydraulic chamber independence feature of converter  10  is now described. From  FIG. 2 , it may be readily appreciated that the hydraulic head within conduit  28  generally approaches but cannot exceed the highest of the independent chamber hydraulic heads  57 A-D within chambers  24 A-D. Hydraulic heads  57 A-D illustrated in  FIG. 2  exemplify a snapshot of the relationship among chambers  24 A-D typically resulting from the cumulative capture of water from various wave surges overtopping ramp  12  and encountering openings  22 A-D ( FIG. 1 ) and an unchecked flow of water from chamber  24 D down and out through drain assembly  26 D to conduit  28 . Accordingly, check valve  48 A is illustrated as operating to check water flow through drain assembly  26 A from chamber  24 A into conduit  28  because hydraulic head  57 A (the water level) in chamber  24 A is illustrated to be less than hydraulic head  57 C (the highest chamber water level) within conduit  28 . Similarly, check valve  48 B is illustrated as operating to restrict water flow through drain assembly  26 B from chamber  24 B into conduit  28  because the water level (hydraulic head) in chamber  24 B is illustrated to be less than the hydraulic head within conduit  28  but greater than the hydraulic head  57 A in chamber  24 A. Finally, check valve  48 C is illustrated as fully open to permit unchecked water flow through drain assembly  26 A from chamber  24 A into conduit  28  because hydraulic head  57 C (the water level) in chamber  24 C is illustrated to be the highest chamber water level, which is equal to the hydraulic head in conduit  28  unless incoming wave surges fill chamber  24 D. No check valve is required in drain assembly  26 D for the final chamber  24 D because the hydraulic head in chamber  24 D is always equal to or less than the hydraulic head in conduit  28  and final chamber  24 D operates as a surge chamber for the remaining chambers  24 A- 24 C to moderate hydraulic head fluctuations and temporarily store water not immediately flowing through conduit  28  to turbine  46 . The relatively large volume of chamber  24 D contributes to the maintenance of a steady useable flow and generation of power therefrom. 
     From the above, it may be readily appreciated that the primary flow through conduit  28  results from the chamber having the highest hydraulic head (water level). As the highest-head chamber drains and approaches the head of neighboring independent chambers, these begin to flow into conduit  28 , thereby maintaining the water flow through turbine  46  necessary for effective power generation. As illustrated in  FIG. 2 , unchecked chamber  24 D is prevented from flowing only by the back-pressure from conduit  28  from the higher hydraulic head  57 C in chamber  24 C. As hydraulic head  57 C falls, hydraulic head  57 B begins to flow, followed by hydraulic head  57 D, and finally by hydraulic head  57 A. This staged capture and flow procedure exemplifies the operation of converter  10 . Because chambers  24 A-D are disposed in substantial alignment with horizontal surge component  20  ( FIG. 1 ) and openings  22 A-D are disposed at different elevation along vertical wave surge component  18 , each chamber  24 A-D will capture water from certain wave surges and not from others; but the staged capture and flow operation ensures a steady useable generation of power therefrom. Because turbine power output increases exponentially with the hydraulic head and flow rate, converter  10  is suitable for operation at low hydraulic pressure differences and high flow rates. This is advantageous because the mass and velocity of incoming wave surges tends to limit available hydraulic head but flow volume is limited only by the scale of converter  10 , which may be scaled up in either horizontal dimension to any useful size and number of isolated chambers. 
       FIG. 4  illustrates a front view of converter  10 , showing the entire embodiment of grill  38  and detail  FIG. 4A  illustrates a cross-sectional view of a useful embodiment of slat  40 , showing the upper surface  60  to be larger than the lower surface  62 . This trapezoidal cross-section facilitates trash rejection without significant reduction of water capture when slats of this cross-section are arrayed to form grill  38 . Moreover, the narrow separations urge the incoming wave surge water further up ramp  12  before capture, thereby converting a significant amount of the horizontal surge kinetic energy component  20  into potential energy in the form of elevated hydraulic head. This improved conversion of horizontal kinetic energy into stored potential energy is an important feature of the converter  10 . Although ramp  12  is illustrated as having a single linear slope from end to end, an alternative ramp embodiment (not shown) having a concave or convex curved surface whose elevation varies non-linearly from end to end may be useful for optimizing kinetic to potential energy conversion in various alternative ocean conditions. 
     During operation, as described above, converter  10  continuously captures and converts the surge kinetic energy component into stored hydraulic head. This stored potential energy is then converted to electrical energy by releasing the stored water through closed low-head turbine  46 . The combined storage volume of independent chambers  24 A-D is balanced with the flow rate exiting from draft tube  32  to facilitate continuous stable rotation of closed low-head turbine  46  and the coupled electrical generator  36 , thereby providing a steady supply of electrical power from episodic wave surges. 
     The theoretical relationship between the surge kinetic energy KE in joules and the resulting stored potential energy PE in joules (assuming lossless conversion) is expressed by the following:
 
 KE=m·v   2 /2 =m·g·h=PE   [Eqn. 1]
 
     where:
         m=Mass of incoming surge water (kg),   v=Surge water velocity (m/s),   g=Gravitational constant (m/s 2 ), and   h=Available hydraulic head (m).       

     Eqn. 1 demonstrates that hydraulic head h varies directly with the square of surge water velocity v, making the faster wave surge a more useful source of energy. During operation of converter  10 , surge kinetic energy is converted to potential energy because surge water rushes up grill  38  before draining down into one or more independent chambers  24 A-D. Water held in each chamber is isolated hydraulically from the other chambers by check valves  48 A-C, which together facilitate a generally evacuated (entrainment air-free) and continuous supply of seawater to turbine  46 . Independent chambers  24 A-D operate to maintain a full flow in conduit  28  by providing a staged reserve supply during wave surge “dry spells.” Turbine  46  rotates responsive to the flow of water from conduit  28  through draft tube  32  and into ambient ocean  30 . Draft tube  32  extends downward to preserve a siphon (suction) head when ocean surface  14  drops below the base of turbine  46 , which contributes to the aggregated hydraulic head powering turbine  46  and thus to the resulting output power from generator  36 . The exit of draft tube  32  must remain submerged to maintain siphon head. 
     Available converter output power is expressed by the following:
 
 P=Q·h·n/C   [Eqn. 2]
 
     where:
         P=Power delivered by the turbine (W)   Q=Mass flow rate through the turbine (kg/s)   h=Available hydraulic head.(m)   n=Turbine efficiency (%), and   C=Unit conversion factor.       

     Eqn. 2 demonstrates that turbine output power P varies directly with hydraulic head h and mass flow rate Q. Accordingly, converter  10  operates at high mass flow rates to produce useful power from low hydraulic heads. The available hydraulic head h is limited by the mass and velocity of the incoming wave surges and mass flow rate Q is limited by the scale of conduit  28  and chambers  24 A-D; that is, by the scale of the structure of converter  10 . 
       FIG. 5  illustrates a rear view of converter  10 , with the tail-wall removed to show the interior of final chamber  24 D and other elements of converter  10  described above in connection with  FIGS. 1-4 . Note that draft tube  32  has a submerged exit, which should be disposed to ensure that the siphon lock between draft tube  32  and ambient ocean  30  is not lost during normal wave action. 
       FIG. 6A  illustrates a side view of an alternative wave surge power converter apparatus embodiment  100  showing the plurality of drain assemblies  126 A-D and exemplary dispositions of the check valves  148 A-C during normal flow conditions, which occur when ocean surface  14  remains below the highest of the independent chamber hydraulic heads  157 A-D while remaining above the exit of the draft tube  132  to maintain siphon head through the turbine  146 . Converter  100  includes a shaft  134  for coupling turbine  146  to a generator  136  but also provides an additional reversible transmission  166  to facilitate uninterrupted power conversion during backflow conditions that are now described. 
     Backflow conditions may arise whenever the ocean surface  114  rises and remains above one or more of independent chamber hydraulic heads  157 A-D so that water is urged up through the draft tube  132 , backing up through turbine  146 , and into the conduit  128 . Backflow operation should not be necessary for most ocean conditions, but converter embodiment  100  is now described as a useful solution to operations in ocean surf states leading to occasional backflow conditions. 
       FIG. 6B  is a diagram illustrating a side view wave surge power converter  100  showing illustrative dispositions of check valves  148 A-C during abnormal backflow conditions that may arise when ocean surface  114  is elevated above the highest one of independent chamber hydraulic heads  157 A-D. During operation, significant backflow up draft tube  132  and turbine  146  causes turbine  146  to reverse direction and rise up, thereby lifting shaft  134  to effect a gear shift in transmission  166 , thereby preventing a polarity reversal in generator  136 . 
       FIGS. 7A-B  are two top view illustrations of transmission  166  suitable for use with converter  100  the two flow conditions illustrated in  FIGS. 6A-B .  FIG. 7A  illustrates the gearing arrangement for normal down-flow operation ( FIG. 6A ) wherein shaft  134  turns clockwise, an idler gear  170  turns counterclockwise, and the generator shaft  172  turns clockwise. A ratchet-type mechanism (not shown) may be provided to limit generator shaft  172  to clockwise rotation, for example.  FIG. 7B  illustrates the gearing arrangement for backflow or up-flow operation ( FIG. 6B ) wherein shaft  134  turns counter-clockwise, a first idler gear  170 A turns clockwise, a second idler gear  170 B turns counter-clockwise, and generator shaft  172  turns clockwise. The backflow also lifts the turbine gear on shaft  134  to facilitate its engagement with idler gear  170 A, which is located above idler gear  170  to form, for example, the two-level transmission  166  illustrated in  FIGS. 6A-B . When turbine gear at shaft  134  rises, it disengages from the normal flow gears in  FIG. 7A  and engages the backflow gears in  FIG. 7B . Using two idler gear levels permits generator gear at shaft  172  to rotate counter-clockwise under all flow conditions. 
     As may be readily appreciated from the above description, this wave surge power converter embodiment offers several advantages. For example, other than the turbine and generator elements all converter elements may be embodied to include only concrete, PVC, rubber and neoprene. Such inexpensive and corrosion-resistant materials are well-adapted for this marine application and even better suited to fresh water applications having significant wave surges, such as the shorelines of the Great Lakes. 
     The preferred vertical orientation of the walls separating each of the horizontal array of independent chambers  24 A-D facilitates the capture of the smaller available increments of potential energy, such as a single foot of hydraulic head. A vertical array of horizontal chambers disadvantageously requires larger hydraulic head differentials and cannot capture the smaller potential energy increments available in many surf conditions. For example, the horizontal chambers disclosed in the above-cited Anderson reference (U.S. Pat. No. 7,040,089) cannot capture significant energy from wave surges of less than two feet. Moreover, instead of the multiple load-bearing floors required for a vertical array of horizontal chambers, a single load-bearing chamber floor is sufficient for this converter embodiment. Similarly, instead of the disadvantageously large amount of air entrainment experienced with a vertical array of horizontal chambers as draining water powers a turbine, this converter embodiment entrains a minimal amount of air in water passing through drain assemblies  26 A-D, plenary conduit  28 , turbine  46  and out draft tube  32  to the ambient ocean  30 . 
     During operation of this converter embodiment, hydraulic head is not lost to backflow as it is in a horizontal chamber array, for example, when a new wave fills a lower horizontal chamber while it is also receiving drainage from an upper chamber. This feature of a vertical array of horizontal chambers causes overtopping of the lower chamber; thereby losing captured potential energy to the surrounding ocean. 
     During operation of this converter embodiment, large volumes of water are reserved in independent chambers and remain available to buffer the continuous flow of water to the conduit and the turbine necessary for stable power output; even during a prolonged intermission (dry spell) between wave surges. 
       FIGS. 8-9  illustrate a preferred “wedge” wave surge power converter embodiment  200  of this invention adapted for use in sea shore and littoral environments and employing principles similar to those described above, showing the inclined ramp  202 . During operation, converter  200  is preferably disposed at an ocean surface  204  having episodic wave surges generally oriented in the direction indicated by the arrow  206  such that a typical wave surge  216 A moves generally along the vertical surge component  208  and generally along the horizontal surge component  210 . Ramp  202  is shown with an exemplary fixed slope of about 33% (17-18 degrees) and is preferably oriented generally along surge direction  206  such that the wave surge water moves up ramp  202 , progressing along a series of rows of openings exemplified by the opening  212 A and the row  214 A, which together are disposed to function as a grill. Each row of openings is fitted with a check valve embodied as, for example, a float valve flap exemplified by the float valve flap  217 A in row  214 A (see  FIGS. 10A-C  for detail) that operates to permit wave surge water entry into the storage chamber  218  while blocking the exit of water from storage chamber  218 . Each of openings exemplified by opening  212 A that are exposed to the wave surge  216 A ( FIG. 8 ) then receives surge water into the storage chamber  218 . But each of float valve flaps that are exposed to captured water in storage chamber  218 , exemplified by float valve flap  217 B ( FIG. 9 ), is floated up to cover the corresponding openings and block the escape of captured water during wave relaxation  216 B. The spacing between the rows and the openings within each row serves to block entry of floating debris into storage chamber  218  and to facilitate sloughing of trapped debris back into the surf during wave relaxation  216 B ( FIG. 9 ). 
     As may be readily appreciated from this description, the captured surge water  220  within storage chamber  218  flows down by gravity through the discharge duct assembly  222  ( FIG. 8 ) and out the exit  224  into the ambient ocean  204 . This flow of captured water  220  from storage chamber  218  through discharge duct assembly  222  and out exit  224  arises from the hydraulic pressure difference  225  ( FIG. 9 ) between storage chamber  218  and ambient ocean  204  and may be employed to turn a low-head turbine  226  that is disposed within discharge duct assembly  222  and is coupled by means of, for example, a shaft  228  to, for example, a flywheel  230  that is further coupled by, for example, a geared transmission assembly  232  to a generator  234  for generating electrical power for transmission over a transmission line  236  to a remote power grid (not shown). The various generating elements may be housed in a generator house  238  disposed on a base support  240  above the rear wall  242  of converter  200 , for example. Converter  200  may be disposed on a number of pylons exemplified by the pylon  244 . 
     Discharge duct assembly  222  includes a discharge duct  246  ( FIG. 8A ), which has a cross-sectional flow area (A) and a length (L). For example, as shown in  FIG. 8A , discharge duct  246  has a cross-sectional flow area (A) that varies (reduces) monotonically from (A 1 ) to (A 2 ) over the duct length (L). The particular variation of the cross-sectional flow area (A) over the length (L) of discharge duct  246  is an important feature of converter  200  for reasons that are described in more detail below in connection with  FIGS. 12-13 . Another important feature of converter  200  is the inclined ramp  202 , which operates to capture and convert incoming horizontal kinetic energy (velocity head) to potential energy (hydraulic head or depth of captured water  220 ) stored within the structure. Because of this important feature of converter  200 , the interior head of captured water  220  exceeds the exterior head of ambient ocean surface  204  and it is primarily this hydraulic pressure difference  225  that drives the low-head turbine  226  (see the discussion of  FIGS. 12-13  below). Another important feature of converter  200  is the spacing between rows and the openings within each row of openings in inclined ramp  202 , which are disposed to prevent most floating debris from entering storage chamber  218  by facilitating the sloughing of debris back into the surf during the relaxation of the wave surges. 
     Converter embodiment  200  offers several advantages. The lack of interior walls in storage chamber  218  increases its storage capacity, minimizes interior wall maintenance (e.g., scraping barnacles) and permits the use of a larger diameter for low-head turbine  226 . The float valve embodiment exemplified by float valve flap  217 B ( FIG. 9 ) minimizes valve friction head loss, thereby increasing the hydraulic head  225 , which increases the output power proportionately with the hydraulic head raised to the three-halves power; [generator power] is proportional to [turbine head]. 3/2  Because the interior head  220  of the captured surge water is uniform throughout storage chamber  218 , low-head turbine  226  may be disposed anywhere in the base  241  without loss of output power. In fact, base  241  provides room to dispose several low-flow turbines (not shown) operating under the same head, thereby optimizing output power, which is proportional to the total turbine area. 
       FIG. 10A  is a schematic diagram illustrating a partial top view of inclined ramp  202  that shows the rows of openings exemplified by the opening  212 A and the row  214  described above.  FIG. 10B  provides the bottom view of the ramp surface of  FIG. 10A  to reveal a plurality of check valve flaps  217 A-B.  FIG. 10C  is a cross-sectional view (A-A) of the ramp surface of  FIGS. 10A-B  that reveals the detail of check valve flaps  217 A-B in their open disposition. Each check valve  217  includes a float flap  248  that is retained by a float valve mounting bracket  250  by means of, for example, a retaining brick  252 , all of which extend along the respective row of openings. Float flap  248 A is sufficiently buoyant to cover all openings in row  214 A when it is urged up against the underside  254  of inclined ramp  202  by the water trapped within storage chamber  218  ( FIGS. 8-9 ) and sufficiently flexible to permit unobstructed flow of surge water into storage chamber  218  from the top side  256  of inclined ramp  202 . The preferred interior slope (not shown) of base  241  toward discharge duct  246  depends on local conditions influencing sediment and debris loading. Heavy loading requires a base (not shown) with the interior floor sloped towards the discharge duct, and light loading does not. 
       FIG. 11  illustrate a preferred “wedge” river flow power converter embodiment  300  of this invention adapted for use in riverine environments and employing principles similar to those described above, showing the inclined ramp  302 . During operation, converter  300  is preferably disposed at an upstream river surface  303  characterized by a rapid continuous horizontal flow component  310  such that some part of the horizontal flow component  310  is redirected vertically as a vertical surge component  308  to provide a net flow energy directed generally along the direction indicated by the arrow  306 . Ramp  302  is shown with an exemplary fixed slope of about 33% (17-18 degrees) and is preferably oriented generally along flow surge direction  306  such that the flow surge water moves up ramp  302 , progressing along a series of rows of openings exemplified by the opening  312 A in the row  314 A, which together are disposed to function as a grill. Each of openings exemplified by opening  312 A that are exposed to the flow surge  306  then receives flow water into the storage chamber  318 . These rows of openings do not require check valves because upstream flow and its associated pressure on the captured flow water  320  are generally constant and unlikely to permit the return of captured flow water  320  to the up-stream river surface  304 . Converter  300  is adapted for operation in a fast-moving river or creek. For operation in a slow moving river, some additional provision (not shown) is preferred for spanning the waterway in a manner that creates an upstream-to-downstream head differential sufficient to emulate a more rapidly moving stream. Water moving past inclined ramp  302  at 8 mph (3.6 m/s) should provide a net hydraulic pressure difference  325  of about two feet (equivalent to hydrostatic pressure of about 6 kN/m 2 ), which should be sufficient to overcome converter drive train friction losses to provide constant power output. The exterior upstream river surface water pressure at  303  generally balances the interior water pressure  320  at inclined ramp  302  because the exterior river velocity head pressure at each of the openings (exemplified by opening  312 A) operates as a check valve by retaining the captured flow water  320  within the storage chamber  318  at a height greater than the downstream ambient river surface  304 , thereby providing a hydraulic pressure difference  325  suitable for conversion to electrical power. The spacing between the rows and the openings within each row serves to block entry of floating debris into storage chamber  318  and to facilitate sloughing of trapped debris back into the river. 
     As may be readily appreciated from this description, the captured flow water  320  within storage chamber  318  flows down by gravity through the discharge duct assembly  322  and out the exit  324  into the downstream ambient river  304 . This flow of captured water  320  from storage chamber  318  through discharge duct assembly  322  and out exit  324  arises from the hydraulic pressure difference  325  between storage chamber  318  and downstream ambient river  304  and may be employed to turn a low-head turbine  326  that is disposed within discharge duct assembly  322  and is coupled by means of, for example, a shaft  328  to, for example, a flywheel  330  that is further coupled by, for example, a geared transmission assembly  332  to a generator  334  for generating electrical power for transmission over a transmission line  336  to a remote power grid (not shown). The various generating elements may be housed in a generator house  338  disposed on a base support  340  above the rear wall  342  of converter  300 , for example. Converter  300  may be disposed on a number of pylons exemplified by the pylon  344 . 
     Discharge duct assembly  322  includes a discharge duct  346  ( FIG. 11A ), which has a cross-sectional flow area (A) and a length (L). For example, as shown in  FIG. 11A , discharge duct  346  has a cross-sectional flow area (A) that varies from (A 1 ) to (A 2 ) over the duct length (L), first narrowing to a minimum (A 3 ) in the vicinity of turbine  338  and then flaring to (A 2 ) and forming a turbine shroud  348  extending below turbine  338 . The particular variation of the cross-sectional flow area A over the length L of discharge duct  346  is an important feature of converter  300  for reasons that are described in more detail below in connection with  FIGS. 12-13 . Another important feature of converter  300  is the inclined ramp  302 , which operates to capture and convert incoming horizontal kinetic energy (velocity head) to potential energy (hydraulic head or depth of captured water  320 ) stored within the structure. Because of this important feature of converter  300 , the interior head of captured water  320  exceeds the exterior head of river surface  304  and it is primarily this hydraulic pressure difference  325  that drives the low-head turbine  326  (see the discussion of  FIGS. 12-13  below). Another important feature of converter  300  is the spacing between rows and the openings within each row of openings in inclined ramp  302 , which are disposed to prevent most floating debris from entering storage chamber  318  by facilitating the sloughing of debris back into the river. 
     Converter embodiment  300  offers several advantages. The lack of interior walls in storage chamber  318  increases its storage capacity, minimizes interior wall maintenance and permits the use of a larger diameter for low-head turbine  326 . Because the interior head  320  of the captured surge water is uniform throughout storage chamber  318 , low-head turbine  326  may be disposed anywhere in the base  341  without loss of output power. In fact, base  341  provides room to dispose several low-flow turbines (not shown) operating under the same head, thereby optimizing output power, which is proportional to the total turbine area. The preferred interior slope (not shown) of base  341  toward discharge duct  346  depends on local conditions influencing sediment and debris loading. Heavy loading requires a base (not shown) with the interior floor sloped towards the discharge duct, and light loading does not. 
     Power output from low-head turbine  326  increases proportionately with the net difference between interior pressure head (level) of captured flow water  320  and the pressure head localized at exit  324  beneath turbine  326 . If turbine shroud  348  is extended below the base  341  and the local river flow velocity is fast and parallel to the base, the resulting venturi effect reduces local fluid pressure and thereby increases the effective hydraulic pressure difference  325  and the resulting net converter output power for the reasons now described. 
     Bernoulli&#39;s Principle says that increased local fluid velocity produces decreased local fluid pressure, as is well-known in the hydraulic arts. Bernoulli&#39;s incompressible flow equation can be written as follows: 
     
       
         
           
             
               
                 
                   
                     ( 
                     
                       
                         
                           P 
                           1 
                         
                         γ 
                       
                       + 
                       
                         z 
                         1 
                       
                       + 
                       
                         
                           v 
                           1 
                           2 
                         
                         
                           2 
                           ⁢ 
                           g 
                         
                       
                     
                     ) 
                   
                   = 
                   
                     ( 
                     
                       
                         
                           P 
                           2 
                         
                         γ 
                       
                       + 
                       
                         z 
                         2 
                       
                       + 
                       
                         
                           v 
                           2 
                           2 
                         
                         
                           2 
                           ⁢ 
                           g 
                         
                       
                     
                     ) 
                   
                 
               
               
                 
                   [ 
                   
                     Eqn 
                     . 
                     
                         
                     
                     ⁢ 
                     3 
                   
                   ] 
                 
               
             
           
         
       
     
     where:
         P=local fluid pressure in N/m 2  (kg/m/s 2 );   γ=ρg in kg/m 2 /s 2 ;   ρ=fluid mass density in kg/m 3 ;   g=9.80665 m/s 2 ;   v=local fluid velocity in m/s;   P/γ is the pressure head in meters;   z is the elevation head in meters; and   v 2 /2 g is the velocity head in meters.       

     Head is energy per unit weight and, because energy has units of Newton-meters, head has length units. Pressure head is the energy per unit weight stored in the fluid pressure. Elevation head is the potential energy per unit weight stored in the fluid elevation. Velocity head is the kinetic energy per unit weight stored in the fluid speed and direction. Eqn. 3 is valid only when the fluid is incompressible so that even though pressure varies, the density is constant and there are no local viscous forces, such as occur in the boundary layer. 
     Eqn. 3 suggests that the exit water velocity head increases as the exit flow velocity increases while passing through the narrowing exit throat, which is offset by a pressure head reduction to balance Bernoulli&#39;s equation. The increased velocity head provides an increase in turbine output power (which is related to fluid velocity) over that available from the same pressure and elevation head with no venturi effect. This effect is enhanced in situations where the external water is moving rapidly across the conduit exit such as may be expected in the river embodiment of  FIG. 11 . Slightly enlarging the internal diameter of discharge conduit  346  from A 3  to A 2  decreases counterproductive upwelling pressure head on the turbine in a manner analogous to the draft tube  32  of  FIG. 5 . 
       FIG. 12  is a schematic diagram illustrating the principle of operation of a preferred controlled-flow duct embodiment  400  of this invention, showing the shaped discharge duct  446  and the base  441  disposed in the flowing water  450 . Shaped discharge duct  446  increases the horizontal and lateral water velocity (velocity head) beneath the turbine  426  in the venturi eddy  454 . As velocity head increases, Eqn. 3 demands a corresponding reduction in that exterior local pressure head beneath turbine  426  in the venturi eddy  454 . As upwelling pressure decreases in eddy  454 , the internal net pressure head ( 225  in  FIGS. 9 and 325  in  FIG. 11 ) increases proportionately, forcing more captured water through discharge duct  446  and out the exit  424 . This increased power turns turbine  426  and is transferred through the shaft  428  to the generator house (not shown). Output power is greater than that available from the captured flow water pressure head alone, which is an important advantage of controlled-flow duct embodiment  400  because power output (P) from a turbine diameter (D) increases exponentially with the internal net pressure head (H) at turbine  426  according to the equation P=CD 2 H 1.5  where C is a fixed conversion factor. The venturi effect at eddy  454  may also be created by simply extending a discharge duct  346  ( FIG. 11 ) below base  341  to form a turbine shroud  348  ( FIG. 11A ). Responsive to the velocity of water flow  450 , a low pressure zone forms immediately downstream of the shroud lip (not shown). The cross-sectional area (A) does not have to vary over any of the discharge conduit length (L) to enjoy this benefit but sloping the base interior towards the discharge outlet promotes the suspension, transport, and expulsion of sediment and debris out of the structure and is preferred. Turbine shroud  348  ( FIG. 11 ) is preferably disposed sharply below base  341  to enhance the resulting pressure drop and power benefit. 
       FIG. 13  is a schematic diagram of the wedge converter  500  of this invention illustrating the energy distribution.  FIG. 13  shows the water flow  504  up the ramp  502  and the ambient flow  550  below the base  541  and the discharge duct assembly  522 . The venturi (low pressure) effect occurs at the eddy  554  that forms below the turbine shroud  548  responsive to the velocity of water flow  550 . The sea floor or river bottom  555  is represented by a horizontal line, with the datum  556  below that for referencing elevation head. The symbols used in  FIG. 13  are defined herein as follows: 
     EL D =downstream energy line; 
     H fD =downstream friction head; 
     V D   2 /2 g=downstream velocity head; 
     Y D =downstream depth; 
     Z D =downstream elevation head; 
     H=net internal head; 
     EL R =ramp energy line; 
     H fR =ramp friction head; 
     V R   2 /2 g=ramp velocity head; 
     Y R =ramp depth; 
     Z R =ramp elevation head; 
     HGL R =ramp hydraulic grade line; 
     H fB =base friction head; 
     V B   2 /2 g=base velocity head; 
     P B /γ=base pressure head; 
     Z B =base elevation head; 
     EL B =base energy line; 
     HGL B =base hydraulic grade line; 
     EL U =upstream energy line; 
     V u   2 /2 g=upstream velocity head; 
     Y U =upstream depth; and 
     Z=upstream elevation head. 
     Clearly, other embodiments and modifications of this invention may occur readily to those of ordinary skill in the art in view of these teachings. Therefore, this invention is to be limited only by the following claims, which include all such embodiments and modifications when viewed in conjunction with the above specification and accompanying drawing.