Abstract:
An improved device for discharging water that is capable of efficiently generating an effective wave-like motion within a body of water. Wave generation devices based on water filled elongated tubular chambers having a substantially closed rear end and a substantially open front end and using compressed air to discharge water, such as the wave cannon, may experience operational inefficiencies from variations in quantities of compressed air. Reducing the quantity of compressed gas may result in ineffective waves and damage to the elongated tube as internal low pressure conditions collapse. A source of make-up fluid configured to mitigate internal low pressure conditions can enable effective wave generation with reduced quantities of compressed air.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application claims priority from U.S. Provisional Application Ser. No. 60/878,784, filed Jan. 6, 2007, which is hereby incorporated by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to a wave generating system. More particularly, the present invention is a wave cannon having improved efficiency and durability. 
       BACKGROUND OF THE INVENTION 
       [0003]    The wave cannon is a device described in U.S. Pat. No. 5,833,393 to Carnahan et al. (&#39;393 patent), which is hereby incorporated by reference. The wave cannon generally relies on submerged, elongated chambers (e.g., tubes), which can be effectively or substantially open at one end and substantially closed at the other end. 
         [0004]    The wave cannon can create waves by releasing bursts of pressurized air that force water out of the chamber and into a body of water. The expelled water is generally a discrete volume defined by the chamber. As the water is forced out of the chamber, it can be used to form a wave. In general, the air follows the expelled water and escapes out the opened end of the water chamber and into the body of water. Water from the body of water begins to refill the chamber prior to escape of all of the air. Grading of the chamber can improve the escape of air and the refilling of the chamber. Although the &#39;393 patent was primarily directed to wave generation, alternate applications, such as pumping, are feasible and may be desirable in certain configurations, with modification to the basic wave generating system. 
         [0005]    In practice, it has been found that the &#39;393 patent wave cannon chamber requires the release of sufficient quantity of pressurized air to expel fully the water in the chamber. That is, a release of air sufficient to create a two phase discharge flow, with a large air bubble forcing out a slug of water, has been shown to be effective in generating wave motion in a body of water. However, the volume of pressurized air needed to achieve such effective operation in many embodiments has proven to be somewhat expensive. 
         [0006]    However, increasing the volume and/or pressure of the air released has been found in some cases to stratify the air and water in the chamber, so that the air can escape along a portion or annulus of the chamber without discharging all of the water from the chamber. Such a partial discharge of water creates smaller, inferior waves. Of course, a release of excess compressed air that produces inferior waves is inefficient. 
         [0007]    Reducing the volume and/or pressure of air released has also been discovered to be potentially problematic. If the air released is inadequate to discharge fully the water from the chamber, then depending on the pressure during discharge and that of the surrounding body of water, several problems can arise. First, the inadequate discharge of water from the chamber can cause inferior or low quality waves. Second, the discharge of water has been observed to be reverse, in some cases halting the flow outward and rapidly reversing flow direction so as to return back to the chamber with a significant impact. When the once expelled water returns into the chamber, it creates a suction into the muzzle of the chamber, potentially posing a safety hazard to those in the wave pool. 
         [0008]    Accordingly, it would be useful to have a wave cannon that is capable of effectively expelling a volume of water using a lower, economical quantity of pressurized air, without creating a flow reversal, potential safety issue, or an impact against the chamber. 
       BRIEF SUMMARY OF THE INVENTION 
       [0009]    The present invention is a wave cannon that includes a system for improving efficiency by reducing or mitigating the effect of the low pressure within the chamber created by expelling water from the chamber. 
         [0010]    An aspect of the present invention is that of a device for discharging water that is capable of discharging water and generating a wave-like motion within a body of water. As noted above, this device comprises an elongated tubular chamber having a substantially closed rear end and a substantially open front end, an anchor securing the chamber below a surface of the body of water and for maintaining the tubular chamber in a desired orientation with respect to the body of water, such that the body of water is in fluid communication with the tubular chamber via the open front end, a supply of compressed air fluidly interconnected with the rear end of the tubular chamber, an air control valve in fluid communication with the supply of compressed air for operatively controlling the flow of compressed air into the tubular chamber, and a supply of make-up fluid in fluid communication with the rear end of the tubular chamber. Upon actuation of the air control valve, which releases the compressed air into the rear end of the tubular chamber to forcibly expel water within the chamber out of the open front end into the body of water, if the chamber reaches a predetermined low pressure after the release of air into the rear end of the chamber, then the supply of make-up fluid introduces fluid into the rear end of the chamber to relieve the low pressure. 
         [0011]    The supply of compressed air comprises a compressed air tank fluidly connected with an air compressor. The wave generating device as recited in claim  1 , wherein the compressed air tank has a volume at least equal to the volume of the tubular chamber. Optionally, the supply of compressed air may be fluidly interconnected with the tubular chamber so as to release compressed air substantially in the direction of the open end. 
         [0012]    The predetermined low pressure condition may be any pressure relatively lower than that of the body of water at the open end of the chamber. The supply of make-up fluid may introduce fluid into the chamber based on low pressure within the chamber, with the mass of make-up fluid being zero for a predetermined low pressure equal to that in the body of water at the open end of the chamber and increasing as the relatively low pressure increases with respect to the open end of the chamber. 
         [0013]    In an alternative embodiment, the make-up fluid may be gas, such as air, a liquid, such as water, or a mixture of gasses or liquids. The present invention may include a fluid control valve within the make-up supply for controlling the introduction of make-up fluid into the chamber. This valve may be a check or unidirectional valve. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0014]      FIG. 1  is a schematic overview of an embodiment of the present invention. 
           [0015]      FIG. 2  is a top view of a wave pool embodiment of the present invention. 
           [0016]      FIG. 3  is a schematic side view of an embodiment of the present invention 
           [0017]      FIG. 4  is a schematic overview of an embodiment of the present invention. 
           [0018]      FIG. 5  is an axial cutaway view of a chamber of the present invention. 
           [0019]      FIG. 6  is an alternate embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0020]    The present invention is a wave generating system. In particular, the present invention comprises a wave cannon that includes an additional system for improving efficiency and durability by reducing or mitigating the effect of the formation of low pressure within the discharge chamber, which can be created by the expulsion of water from the chamber. 
         [0021]    The &#39;393 patent generally disclosed that the volume of the pressurized air available should be equal to or greater than the combined volume of air that the elongated water chambers could contain. Col. 2, II. 52-54. In general, the release of compressed air that would discharge or expel all of the water from the chamber would generate an effective wave. However, the &#39;393 patent did not disclose operational issues arising from the release of either too much or too little air into the chamber. 
         [0022]    In general, the release of pressurized air creates a high pressure bubble within the rear or substantially closed end of the elongated chamber; as the bubble expands, it expels the water within the chamber out the substantially open or front end. A side effect of expansion is that the pressure of the gas or air bubble declines during expansion. In the production of effective waves, water is intended to be expelled completely from the chamber. Some portion of the air would escape as large bubbles out the open end of the chamber into the body of water, while other portions of the air might be dispersed into the body of water in a turbulent mix or froth, eventually reducing the pressure within the tube as water returned to refill the chamber. Thus, it had been contemplated that a water slug driven by a large volume gas bubble formed by the released air would produce the most effective discharge of water. 
         [0023]    As discussed above, compressed air can be costly. However, the release of low quantities of pressurized air into the chamber can create adverse effects beyond that of inferior waves. The release of smaller quantities of pressurized air into the chamber can form a bubble that begins the expulsion of water, but the bubble can then decay to a low pressure condition within the chamber prior to the full expulsion of water. This low pressure can cause water within the chamber and previously expelled water to reverse direction and re-enter the chamber as the bubble collapses and air is dispersed. The low pressure bubble can collapse violently as higher pressure water strikes the rear or substantially closed end of the chamber. In some embodiments, a vacuum exceeding 10 bar has been observed. Of course, the resulting impact could damage the chamber, requiring both substantial anchoring of the chamber and the use of “heavy” materials for fabrication of the chamber. See &#39;393 patent, Col. 3, II. 13-18. Further, it has been discovered that the reverse in direction of expelled water creates suction into the chamber from the body of water, which can be unsafe for individuals swimming or surfing in the vicinity. 
         [0024]    An aspect of the present invention is a system for mitigating this low pressure condition within the discharge chamber, while also enabling the discharge of sufficient water from the chamber to generate effective wave motion within the body of water. Preferably, this mitigation may be accomplished by the introduction of fluid into the elongated chamber to reduce such a low pressure condition and to prevent, or reduce the effects of, a reverse flow of expelled water. Of course the fluid may be any of a wide variety of liquids and/or gasses, depending upon the application. Preferably the fluid is water and/or air when available, for simplicity of design. Preferably also, the location for the make up source introduction of fluid is at the substantially closed end of the discharge chamber, also for simplicity of design. 
         [0025]      FIG. 1  is an embodiment of the present invention directed to wave generation, wherein wave cannon  10  is configured with respect to body of water  21 , such as wave pool. Make-up  26  is an additional system directed to mitigating low pressure conditions within chamber  7 . Line  26 L, such as a pipe, conduit, or hose, of make-up  26  provides a mechanism for water from make-up source  26 S of fluid (i.e., in this case body of water  21 ) to be introduced into the chamber  7  when the pressure within chamber  7  drops below a desired setting. For example, make-up  26  could connect to body of water  21  at a particular depth, so that the actuation pressure for introduction of make-up fluid might simply be the water pressure for the depth at the point of connection. Thus, the predetermined low pressure may be any pressure in chamber  7  relatively lower than that of the body of water at the connection. Accordingly, in such cases the mass of fluid introduced by make-up  26  would be zero for a pressure in chamber  7  equal to that in the body of water  21  at the connection and would increase as the relatively low pressure in chamber  7  increases with respect to that at the body of water  21 . 
         [0026]    This embodiment is thus a wave generating device having an elongated chamber  7  oriented such that body of water  21  may fill the chamber  7  via a substantially open front end  7 A, a supply of compressed air  2  (i.e., supported by air compressor  1 ) fluidly interconnected with chamber  7 , an air control valve  5  in fluid communication with the supply of compressed air  2  for controlling the flow of compressed air into chamber  7 , a make-up  26  fluidly connected to chamber  7 , wherein the air control valve  5  can release the compressed air  2  into chamber  7  to expel water within the chamber  7  out of the front end  7 A and further wherein the make-up  26  can introduce water into the chamber  7  to replace at least some of the water expelled out of the front end  7 A. Preferably, but not necessarily, such make-up  26  occurs at substantially closed end  7 B. 
         [0027]    When pressurized air is released into the chamber  7 , pressure within chamber  7  initially increases. Water within chamber  7  is expelled from chamber  7  and into body of water  21  along open front end  7 A. If a low pressure is formed within the chamber  7  during this process (e.g., at substantially closed end  7 B), then water from the make-up  26  would be introduced into the chamber  7  to mitigate or relieve the low pressure condition. A check valve  24 , or other actuating control valve  25  (not shown) is preferably inserted in make-up  26  in order to control the release of fluid into chamber  7 . Because make-up  26  is directed to flow into chamber  7 , such a valve may be useful for controlling the release to a desired low pressure level and to prevent back flow from chamber  7  into make-up  26 . In an alternative embodiment, such a valve could be fluidly connected to atmosphere such that atmospheric air could be released into chamber  7  for mitigation of a low pressure condition. 
         [0028]      FIG. 2  shows an embodiment in which body of water  21  is configured as a wave pool. Waves are generated from chamber  7  in the direction of reef  33 . Optionally, make-up  26  may draw water from river returns  30  (e.g., lazy river or action river return) within body of water  21 , for introduction into chamber  7  to mitigate low pressure conditions. River returns  30  may be formed by integrated islands  34  and reef  33  within wave pool types of body of water  21 . For orientation, integrated islands  34  are shown with bridges  17  for access. Directional arrows  37  show current flow; this configuration of body of water  21  and make-up  26  will increase the flow along river returns  30 . Surfers may ride river returns  30  to travel from the location in body of water  21  where waves break on reef  33  to the point of wave generation near chamber  7 . Personnel access points  35  may be provided at the point where make-up  26  draws from river return  30 . 
         [0029]    Of course, the present invention is not intended to be limited to wave pool applications. In some embodiments, the wave cannon  10  may be adapted for use as a pump or an engine for propulsion of a water based vehicle. For example,  FIG. 3  is a partial schematic of a pump application showing chamber  7 . Make-up  26  may collect fluid from a catch basin, drainage system, or other desired make-up source (not shown). Pressurized air may be released along path  6  in fluid connection with chamber  7  in the direction of arrow  6   d ; compressed air  2  expels or discharges water out the substantially open front end  7 A of chamber  7 . Also not shown in this figure are the pressurized air source, the air actuating valve, and the configuration of elongated chamber  7  with respect to body of water  21 . Open front end  7 A may be submerged or not; if the open front end  7 A is not submerged, then the configuration of the elongated chamber  7  may require some structural accommodation, depending on the application (e.g., optional use of a check valve  24  at open front end  7 A if the wave cannon  10  is used as a pump). 
         [0030]    Operation of make-up  26  is similar to that of other embodiments. Upon initial release of pressurized air into the chamber  7 , a high pressure condition is created and check valve  24  is forced closed. If a low pressure condition in chamber  7  follows release of the pressurized air, then the check valve  24  will open, permitting the fluid contents of make-up  26  to be released into chamber  7  to mitigate or relieve the low pressure condition. For pumping, make-up  26  may be used for refilling chamber  7 . If desired as an option, chamber  7  could also be refilled by water entering via the open front end  7 A of chamber  7 , although that would counter the intended use as a pump. Because the pressure differences will have been reduced, refilling will be by smooth fluid flow. 
         [0031]    Thus, the embodiment of  FIG. 3  may operate as a pump having an elongated chamber  7  oriented such that the make-up  26  fluidly connect to chamber  7  may be used to fill chamber  7 , a supply of compressed air  2  (not shown) fluidly interconnected with the chamber  7 , an air control valve  25  (not shown) in fluid communication with the supply of compressed air  2  (not shown) for controlling the flow of compressed air  2  into the chamber  7 . An air control valve  25  (not shown) can release the compressed air  2  into the chamber  7  to expel water within the chamber  7  out of substantially open front end  7 A and make-up  26  can introduce make up  26  fluid into the chamber  7  to replace at least some of the water expelled out substantially open front end  7 A. Optionally, a water control valve  25  in fluid communication with make-up  26  may be used to control the flow of make up  26  water into chamber  7 . 
         [0032]    It is contemplated that embodiments of the present invention may improve wave cannons used as volume pumps, as shown schematically in  FIG. 4 . Closed end  7 B of chamber  7  may mount check valve  24 . Check valve  24  may vary in size, even to the point of having a diameter equivalent to chamber  7 . Thus, check valve  24  may admit or introduce a release of fluid from make-up  26  into the chamber  7  in the event of a low pressure. Preferably, but not necessarily for such embodiment, the pressurized air source release structure, nozzle  6   e  within chamber  7 , could be configured centrally or axially, in-line with the flow within the elongated chamber  7 . If the substantially open front end  7 A of chamber  7  is submerged in a body of water  21 , it may further be configured with a discharge check valve  24  permitting discharge only. This configuration of wave cannon  10  could be used as a large volume pump for transferring water from make-up  26  to body of water  21 , as shown in  FIG. 4 . In such a case, make up source  26 S could be a catch basin or drainage collection point, while body of water  21  would be a discharge body. 
         [0033]      FIG. 5  is a cross section view of chamber  7  with pressurized air line path  6  running to axially mounted nozzle  6   e  (not shown). Struts  8  may be used to mount nozzle  6   e  (not shown) within the axial orientation. 
         [0034]    This arrangement could be modified for use as an in-line flow engine to drive a waterborne vessel, such that the make-up  26  and substantially closed end  7 B would face forward and the substantially open end  7 A would discharge aft. Thus, in general, the present invention contemplates a variety of configurations that embody the principles disclosed herein. 
         [0035]      FIG. 6  is an example of an alternative embodiment of the present invention wherein make-up  26  draws air from atmosphere into chamber  7  to mitigate a low pressure condition in chamber  7 . Make up control valve  25  may operate upon reaching a predetermined desired low pressure condition within chamber  7 . 
         [0036]    Thus, in summary, an aspect of the present invention is that the volume of compressed or pressurized air released into the chamber  7  may be reduced, depending on the nature of the application, without causing a violent bubble collapse due to a low pressure condition in the chamber  7 . The present invention reduces the consumption of compressed or pressurized air (or other gas), which also reduces the operating cost. A further aspect of the present invention is that the mitigation of a low pressure condition within the chamber  7  reduces the tendency of the low pressure to place a drag on the water expelled from the chamber  7 . Accordingly, the present invention enables a reduction of the compressed air used along with little or no decrease in the ability to expel water, and little or no decrease in the quality or effectiveness of waves generated. Further, the invention enables a reduction in the heaviness of materials of construction. 
         [0037]    For example, with one embodiment of the present invention, a wave cannon discharge chamber having a cross sectional area of about 4 sq. feet and a length of about 24 feet produced an effective wave using a release of air about 30-40% the volume as previously required. In fact, this wave cannon was able to generate a 7 foot wave, which had previously only been demonstrated by a release of air sufficient to clear a chamber having a cross sectional area of 9.6 sq. feet and a length of 80 feet. 
         [0038]    The above examples should be considered to be exemplary embodiments, and are in no way limiting of the present invention. Thus, while the description above refers to particular embodiments, it will be understood that many modifications may be made without departing from the spirit thereof.