Patent Publication Number: US-2023146152-A1

Title: Systems, devices, and methods for underwater vehicles

Description:
PRIORITY CLAIM 
     This application claims the benefit of U.S. Provisional Patent Application No. 63/277,892 entitled “DEVICES, SYSTEMS, AND METHODS FOR AUTONOMOUS UNDERWATER VEHICLES” and filed Nov. 10, 2021, the entire contents of which are incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The present disclosure relates to methods, techniques, and systems for underwater vehicles, in particular buoyancy driven vehicles such as vertical profiling floats. 
     SUMMARY 
     Some embodiments provide a vertical profiling float, comprising: a first and second cylindrical pressure housing each having a convex end and a concave end, wherein the concave ends of the pressure housings are coupled to one another such that the concave ends face one another and thereby form a chamber between the concave ends, wherein the chamber is fluidly coupled to the environment, such that water can pass between the chamber and the environment; and a displacement bladder positioned within the chamber, such that the bladder is equidistant from the convex ends of the first and second pressure housings, wherein, when the float is placed in a body of water, the first pressure housing is above the second housing, and wherein the convex ends of the first and second pressure housings are respectively at the top and bottom of the float. The concave ends of the first and second housing are spaced apart and coupled via a plurality of rigid members, leaving gaps between the rigid members that allow for the passage of water between the environment and the chamber. 
     In some embodiments, the concave end of each of the pressure housings forms a concavity that is hemispherical in shape, and wherein the chamber is substantially spherical in shape. The concave end of each of the pressure housings may be flared, such that the diameter of each pressure housing is greater at its concave end than in its mid-section. In some embodiments, the concave ends of each of the pressure housings form a concavity that is cylindrical in shape, and wherein the chamber is cylindrical in shape. 
     In some embodiments, the first pressure housing contains: a fluid reservoir; and a pump fluidly coupled to the fluid reservoir and the displacement bladder, wherein the pump is configured to move fluid from the reservoir to the displacement bladder, thereby expanding the displacement bladder and displacing water from the chamber. The second pressure housing may contain a battery that powers the pump. 
     In other embodiments, the first pressure housing contains a volume-controlled return system configured to deflate the displacement bladder by routing fluid from the bladder to the reservoir. The return system may include a fluid inlet coupled to the displacement bladder; a valve chamber coupled to the fluid inlet; and a porous restrictor disk between the valve inlet and the valve chamber, wherein the disk slows fluid transfer between the fluid inlet and a valve chamber. The valve chamber may include: a spring; and a ball that is biased by the spring to close the valve chamber. The return system may further include an electromechanically driven plunger operable to force the ball into the valve chamber, thereby opening the chamber and allowing fluid passage out of the chamber. 
     In some embodiments, the return system includes: a fluid inlet coupled to the displacement bladder; a valve chamber coupled to the fluid inlet; and a flow restrictor valve that regulates fluid flow into the valve chamber. The return system may further include: a shutoff valve; and a servo motor that is operable to open and close the shutoff valve, such that opening the shutoff valve allows fluid passage through the flow restrictor valve. The shutoff valve may be one of a plug valve, a quarter turn valve, a trunnion valve, and a needle valve. 
     Some embodiments may include a pump that is a fixed-displacement hydraulic pump with clutch transmission configured to deliver a same volume of hydraulic fluid independent of shaft speed or resulting pressure. The pump may include a plurality of motors that each have different windings and power inputs and outputs. The vertical profiling float may be configured to operate a first motor of the plurality of motors in a predetermined first depth range (e.g., between the surface and 10, 50, or 100 meters of depth); and operate a second motor of the plurality of motors in a predetermined second depth range (e.g., deeper than 10, 50, or 100 meters), wherein the first and second depth ranges are different. The pump may further include: a driveshaft; and an angular swashplate coupled directly to the driveshaft, wherein the swashplate is configured to drive pump plungers. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    shows a mid-plane buoyancy-driven vehicle according to one embodiment. 
         FIG.  2    is a cutaway sectional view of the vehicle. 
         FIGS.  3 A- 3 C  are cutaway views of the vehicle. 
         FIGS.  4  and  5    are perspective views of the vehicle. 
         FIGS.  6  and  7    compare the centers of gravity and buoyancy in an example mid-plane float vehicle to those in a prior art float. 
         FIGS.  8 A- 9 B  compare the hydrodynamic flows around an example mid-plane float vehicle and a prior art float. 
         FIGS.  10 - 12    show views of a volume-controlled return system according to a first embodiment. 
         FIGS.  13 - 15 B  show views of a volume-controlled return system according to a second embodiment. 
         FIG.  16    is an elevation view of a fixed-displacement pump according to a first embodiment. 
         FIG.  17    is a perspective view of a fixed-displacement pump according to a first embodiment. 
         FIGS.  18 A- 18 C  show views of a fixed-displacement pump according to a second embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     The present disclosure relates to methods, techniques, and systems for underwater vehicles, in particular buoyancy driven vehicles such as vertical profiling floats. As described in detail below and with reference to the drawings, some embodiments may provide a float vehicle that is constructed from two independent substantially cylindrical pressure housings that each have a concave end. The housings are coupled to one another at their concave ends, such that the concavities face one another and form a chamber. The chamber is open to the environment and houses an external displacement bladder, such that the bladder is located at or about the midplane of the vehicle. In some embodiments, the vehicle may also include a fluid return system that is operable to precisely control the return of fluid from the displacement bladder to an internal reservoir. The vehicle in some embodiments may also include a fixed-displacement pump configured to pump fluid from the internal reservoir to the displacement bladder. 
     Buoyancy-Driven Vehicle with Mid-Plane Displacement 
     Buoyancy-driven vehicles, such as vertical profiling floats use a change in displacement to achieve thrust (buoyant force equal to the volume of the displaced liquid, Archimedes&#39; Principle) in either the positive or negative direction, travelling up and down through the water column or other body of liquid. This change in displacement is typically done with oil transfer from an internal bladder or reservoir to an external one, or driving a piston from inside a pressure housing to the exterior. In addition, the stability of the vehicle is determined by the distance between the center of gravity (CG), also referred to as the center of mass, and the center of buoyancy (CB). The greater this distance the greater the stability. For ease of construction and engineering, the variable displacement (e.g., external bladder) on existing vehicles has always been located on the bottom endcap of pressure housings. 
       FIG.  1    shows a buoyancy-driven vehicle  100  according to one embodiment. The vehicle  100  has a top (or forward) end  101 , a bottom (or aft) end  102 , and a mid-plane  126 . The vehicle  100  includes a communications antenna is located at the top end  101 . The vehicle also includes a sensor ring  122  coupled at or near the mid-plane  126 . The vehicle  100  comprises a top pressure housing  103  and bottom pressure housing  104 . 
     The housings  103  and  104  are independent pressure housings that are generally cylindrical in shape. Each housing has a convex end cap at one end and is flared at the other, distal end. Each pressure housing thus has a diameter at its flared end that is greater than at its mid-section. As shown, housing  103  and  104  respectively have a convex end cap shown at the top end  101  and bottom end  102  of the vehicle  100 . Each housing is concave at its flared end. The housings are symmetrical and are coupled at their flared ends at the mid-plane  126 . As will be discussed further below, the housings  103  and  104  are coupled in such a way that the concavities at their flared ends form a chamber that is open to the environment, such that water may pass between the chamber and the environment (e.g., body of water, ocean, lake). 
       FIG.  2    is a cutaway sectional view of the vehicle according to one embodiment.  FIG.  2    shows some of the internal components of the vehicle  100 . As shown in  FIG.  2   , the top housing  103  of the vehicle includes a fluid reservoir  110 , a pump  112 , a return system  114 . The bottom housing  104  includes a battery  118 . One end of each of the housings is concave, in this example forming a substantially hemi-spherical shape. The housings are coupled such that their concave ends are facing one another, thereby forming a substantially spherical chamber  105  between the housings. One or more gaps  124  at the mid-plane allow for fluid passage into and out of the chamber  105 . These gaps  124  are located between bolts or other rigid members (e.g., tie plates, welds) that are used to couple the top and bottom housings. The housings are constructed from carbon fiber material, although other materials such as aluminum may be used. 
     A bladder  116  is located within the chamber  105  of the vehicle  100 . The bladder  116  is thus “external” to the vehicle, in the sense that it is not located within either of the pressure housings  103  and  104 . The bladder  116  is fluidly connected to the fluid reservoir  110 , via the pump  110  and return system  114 . The pump  110  moves fluid from the reservoir  110  to the bladder. When the bladder is filled, water that was formerly within the chamber  105  is displaced and the volume of the vehicle  100  is increased while retaining the same mass, thereby reducing its density and increasing its buoyancy. With greater buoyancy, the vehicle will travel in a positive direction, or upward through the water column. Conversely, fluid can be moved from the bladder  116  to the reservoir  110  via the return system  114  and/or pump  112 . This causes the volume of the vehicle to be reduced, resulting in a higher density and lower buoyancy. 
       FIGS.  3 A- 3 C  are cutaway views of the vehicle according to one embodiment. In  FIGS.  3 A and  3 B , the bladder is empty and retracted into the concave end  120  of the top housing  103 . In  FIG.  3 C , the bladder  116  is full and shown substantially filling the chamber  105 . Note that while the illustrated embodiment uses a pressure housing with a flared end, other embodiments may not be flared at their concave end. Instead the pressure housing could be a straight cylinder all the way to its concave end. Note also that the illustrated embodiment is constructed from two independent pressure housings coupled together. In other embodiments, the vehicle may be constructed from a single substantially cylindrical housing having a pressure chamber at each end and an open chamber at its midplane. 
       FIGS.  4  and  5    are perspective views of the vehicle.  FIG.  4    is an external perspective view of the vehicle  100 , showing the sensor ring  122  located at the mid-plane.  FIG.  5    is a cutaway view that shows the chamber  105  between the top housing  103  and bottom housing  104 . The illustrated embodiment uses a substantially spherical chamber  105 . Other embodiments may have chambers or voids of other shapes, such as a cylindrical or rectangular prism shape. For example, if each housing has a cup-shaped concavity at its end, then a cylindrical chamber would be formed when the two housings are attached to one another. 
       FIGS.  6  and  7    compare the centers of gravity and buoyancy in an example mid-plane float to those in a prior art float.  FIG.  6    shows a float  100  according to one embodiment labeled with the centers of gravity (CG) and buoyancy (CB).  FIG.  7    shows an example prior art float  150 . In prior art floats, the external bladder is located at the bottom end of the float, within an open cup-shaped member  152 . The prior art float  150  is also labeled with its centers of gravity (CG) and buoyancy (CB). The separation between CG and CB in the float  100  is typically 8 or more inches as compared to 3 or fewer inches in the prior art float  150 . The greater separation between the CG and CB of the float  100  (as compared to prior art float  150 ) significantly increases the stability of the vehicle while the displacement bladder is full, which is typically at the water surface where wave action and instability is greatest. Naomi Ehrich Leonard “Stability of a Bottom-heavy Underwater Vehicle” Automatica, Vol. 33, No. 3. pp. 331-346, 1997). The highest density of the vehicle is the battery pack (therefore having the greatest impact on the location of the center of gravity). The aft endcap is now free to move any distance away from the variable displacement. 
       FIGS.  8  and  9    compare the hydrodynamic flows around an example mid-plane float and a prior art float. With a mid-plane float, both pressure hull endcaps can be optimized for laminar flow around the vehicle, which decreases drag and increases efficiency.  FIGS.  8 A and  8 B  show the flow pattern around a mid-plane float according to one embodiment, as the float respectively moves up and down the water column.  FIGS.  9 A and  9 B  show the flow pattern around a prior art float, as the prior art float respectively moves up and down the water column. As can be seen, the flows around the mid-plane float are much cleaner than those around the prior art float. In addition to greater efficiency of movement, the clean flow also allows for scientific sensors to sample in both the up and down directions, where water flow is the same. Other advantages include, using the lower pressure cap for sensor placement, a drop weight or physical sample collection. The symmetry of the two pressure housings will also lower machining costs. 
     Volume-Controlled Return System for Precision Buoyancy Control 
     Underwater vehicles such as the float  100  encounter many obstacles to proper operation including change in water densities, debris and marine growth. To remain at a desired depth or water density the vehicle needs the ability to change its displaced volume, for a constant neutral buoyant force. Some embodiments provide a cost-effective fluid return system that provides for extremely fine-grained (milliliter, mL) adjustments and measurements. 
     The precision buoyancy control system utilizes a hydraulic fluid (considered to be incompressible) to inflate or deflate an external bladder to change the overall displacement of the vehicle. To inflate the bladder, resulting in a positive buoyant force, a hydraulic displacement pump is used. To deflate the bladder (resulting in a negative buoyant force) in a controlled manner a variation of Bernoulli&#39;s principle, the Continuity Equation is applied. 
     
       
         
           
             
               
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     Routing the returning hydraulic fluid through a small fixed orifice, then into a larger chamber allows the pressure to drop. Any number of these pathways can be put in series to achieve a suitable final hydraulic pressure. 
       FIGS.  10 - 15    show views of volume-controlled return systems according to example embodiments. The described return systems may be used as the return system  114  in the vehicle  100  described above. 
       FIGS.  10 - 12    show a first example return system  200 .  FIG.  10    is a perspective cutaway view of the system  200 .  FIG.  11    is a cutaway elevation view of the system  200 . In the system  200 , pressurized fluid (e.g., from the external bladder) enters a fluid return cavity between the fluid return system  200  and the external bladder. The fluid passes through a fluid inlet  212  and first encounters a porous or sintered restrictor disk  214  (a “snubber disk”), which can be made of various materials and of various porosities. The disk&#39;s purpose is to stabilize the incoming flow velocity and act as a restrictor plate or “road block”. Next is a ball  208  that is biased upwards by a spring  210 . The ball  208  seals a pressure cavity above the ball. An electro-mechanical actuator  220  ( FIG.  12   ) is configured to depress a plunger  202 , which acts upon the ball thereby allowing fluid to pass into the fluid outlet  206 . Bernoulli&#39;s equation gives the resulting pressure drop as the fluid enters the larger cavity of the valve. Because manufacturing the disk is not uniform, the volumetric flow rate data is collected empirically. Once the correct volumetric flow rate has been established the time of opening the ball is used as the variable to control the amount of desired volume transfer. 
       FIGS.  13 - 15    show a second example return system  250 .  FIG.  13    is an external elevation view.  FIG.  14 A  is a perspective cutaway view.  FIG.  14 B  is a cutaway elevation view. The system  250  includes a fluid inlet  252 , a pressure housing  254 , a fluid outlet  256 , and a servo or stepper motor  258 . As shown in  FIG.  14   , inside of the pressure housing  254  is a plug valve  262  controlled by the servo  258 , in addition to a miniature pressure compensated flow restrictor valve  260 , such as a High Pressure Flosert Flow Metering Valve produced by the Lee Company (https://www.theleeco.com/product/250-high-pressure-flosert/). 
     In  FIG.  14 A , the plug valve is in the open position, allowing fluid transfer through the valve  260 . In  FIG.  14 B , the plug valve is in the closed position, stopping any fluid transfer. Other embodiments may use a quarter turn valve, trunnion valve, or needle valve in place of the plug valve  262 . 
       FIG.  15 A  shows a detail of the plug valve  262  in open and closed positions.  FIG.  15 B  shows a comparison of a multi-orifice restrictor  270  and a porous restrictor  272 . The restrictor  270  may be found in the flow restrictor valve  260  in the return system  250 . The restrictor  272  may be used in the return system  200 , for example as implemented by use of the porous disk  214 . 
     Fixed-Displacement Hydraulic Pump with Clutch Transmission 
     Buoyancy driven vehicles use a change in volumetric displacement to achieve thrust in either the positive or negative direction. They are also deployed with a fixed amount of available energy (batteries), making efficiency the key to long duration deployments. 
       FIGS.  16 - 18    show fixed-displacement pumps according to example embodiments. The described pumps may be used as the pump  112  in the vehicle  100  described above. 
       FIGS.  16  and  17    respectively show elevation and perspective views of a first example pump  300 . The pump  300  includes two motors  302   a  and  302   b , a drive belt  304 , an integrated clutch and pulley  306 . The clutch/pulley  306  is coupled to a drive shaft  308 , which is coupled to an angular swash plate that drives pump plungers  312 . The plungers  312  each deliver the same volume of hydraulic fluid per stroke regardless of shaft speed or resulting pressure. Rotation of the shaft  308  in either direction produces the same result. Adding a sprag clutch, which is a free moving bearing in one direction and locked and allowing torque to be applied in the other direction, gives the ability to place more efficient motors online. Alternatively, a roller bearing clutch could be used. A motor with a gearbox or windings designed to operate at high torque for a high-pressure scenario (&gt;6000 psi) would not be as efficient as one geared and winded for much lower pressures (&lt;1000 psi). Using the described techniques, both motors can be attached to the same driveshaft as shown. Each motor is then used during the proper pressure environment, thereby increasing energy efficiency. The coupling between the main drive shaft and additional motors can be done by any mechanical means (i.e., belt, gears, chain). 
       FIGS.  18 A- 18 C  show a second example pump  350 . In this example, the motors  302  are attached to the drive shaft  308  via gears  352  and a directional clutch bearing  360  rather than a belt. Also shown here is a fluid inlet  356  and a high-pressure fluid outlet  354 . 
     While embodiments of the invention have been illustrated and described, as noted above, many changes can be made without departing from the spirit and scope of the invention. Accordingly, the scope of the invention is not limited by the above disclosure.