Abstract:
A compensator added to the hydraulic circuit of an ocean profiler. The compensator stores energy by compression of gas during descent and expansion of the gas during ascent, thereby reducing the work required of the active buoyancy mechanism. The pressure from the external liquid medium in which the vehicle is submerged provides the energy, a portion of which is stored within the compensator.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to oceanographic instrumentation, and more particularly to a device which cycles vertically and repeatedly between the surface and a desired depth in the ocean, i.e., profiling. Specifically, the present invention provides a means of reducing the energy expended during these profiles. 
     During observations of the ocean environment, it is desirable to use a vehicle able to drift freely (no physical connection to surface or bottom) and to both profile vertically and remain in equilibrium at predetermined depth. 
     During a descent-ascent profile, i.e., vertical ascent and descent, the properties of the surrounding water at all depths can be observed. At the ocean surface, stored data and vehicle position are reported to a shore station or ship, generally using communications via satellite. The trajectory of observed surface positions provides a measurement of ocean circulation. 
     It is desirable that the oceanographic vehicle and its observational payload be small and inexpensive. The vehicle should be capable of hundreds of profiles to a typical depth of 2000 meters (m) over a period of several years. 
     Commonly used profiler designs use an aluminum hull with an active buoyancy mechanism having a pump or displacer powered by an on-board energy supply. Examples of typical profiler devices may be seen in U.S. Pat. No. 5,283,767 (McCoy); U.S. Pat. No. 4,202,036 (Bowditch et al.); U.S. Pat. No. 4,202,034 (Bowditch et al.); and U.S. Pat. No. 4,191,049 (Bowditch et al.). 
     Most hulls designed to operate to 2000 m depth increase in buoyancy as their depth is increased. This characteristic facilitates finding a stable buoyancy at a fixed depth for deep drifting. When ascending, the active buoyancy mechanism must provide displacement to overcome decreasing vehicle buoyancy as it ascends. The minimal work required is the area shown to the right of the curve depicted in FIG. 2, i.e., [pressure×volume=work]. 
     SUMMARY OF THE INVENTION 
     The present invention discloses an innovation which reduces the energy required to make vertical profiles, thus reducing the size and weight of the on-board battery and machinery, and increasing the performance envelope of the profiler. The present invention incorporates an entirely passive device which reduces the energy required to make vertical profiles. Specifically, the present invention adds a compensator to the hydraulic circuit of the profiler. The compensator stores energy by compression of gas during descent and releases the energy during ascent, thereby reducing the work required of the active buoyancy mechanism. The pressure from the external liquid medium in which the vehicle is submerged provides the energy, a portion of which is stored within the compensator. 
     These together with other objects of the invention, along with various features of novelty which characterize the invention, are pointed out with particularity in the claims annexed hereto and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and the specific objects attained by its uses, reference should be made to the accompanying drawings and descriptive matter in which there is illustrated a preferred embodiment of the invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 illustrates a cross-section of an ocean profiler design currently in regular use today; 
     FIG. 2 illustrates graphically the change of buoyancy with pressure of a typical profiler hull operating in a typical temperate oceanic water column, wherein the buoyancy displacement volume is measured in milliliters and pressure in bars; 
     FIG. 3 illustrates the ocean profiler of FIG. 1 with the addition of the invention compensator; 
     FIG. 4 illustrates graphically the effect on the buoyancy of FIG. 2 by the addition of the compensator in FIG. 3; 
     FIG. 5 illustrates the ocean profiler of FIG. 3 with the addition of a compression spring within the compensator; and 
     FIG. 6 illustrates graphically the effect on the buoyancy of FIG. 4 by the addition of the compensator modification in FIG.  5 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to the drawings in detail wherein like elements are indicated by like numerals, there is shown in FIG. 1 a cross-section of a typical ocean profiler  10 . This ocean profiler  10  is suitable for operation to a pressure of 200 bars (approximately 2,000 meters depth in the ocean) and typically 250 vertical profiles. The ocean profiler  10  has a pressure hull  11  having a bottom  12  from which a cylindrical side wall  13  extends vertically upward terminating in a top  14 , said pressure hull  11  being generally cylindrical in shape, said top  14  and bottom  12  defining a pressure hull longitudinal axis. The top  14 , bottom  12  and side wall  13  define a pressure hull interior  15 . The pressure hull  11  is typically made from an aluminum alloy or other material having similar properties. The pressure hull top  14  has an elongated radio antenna  16  extending vertically upward from said pressure hull top  14 , said antenna  16  having a longitudinal axis parallel with the longitudinal axis of the pressure hull  11 . The purpose of the radio antenna  16  is to transmit ocean profiler data, such as salinity, temperature, pressure and geographical position, to a shore station. The pressure hull bottom  12  has an aperture  17  formed therein opening out into an external flexible bladder  18  attached to the pressure hull bottom  12 . 
     The pressure hull interior  15  is comprised of an upper portion  19  and a lower portion  20 . The upper portion  19  contains batteries, electronic equipment and controllers. The lower portion  20  contains the pumping system  21 . The batteries, electronic equipment, controllers, and buoyancy control equipment are distributed within the pressure hull interior  15  so that the profiler  10  has a center of gravity below the profiler center of buoyancy, thereby causing the profiler  10  to maintain a vertical orientation within water. 
     To change the buoyancy of the profiler  10 , its volume, i.e., displacement, must be changed. As displacement increases, the profiler&#39;s buoyancy B increases. See FIG.  2 . The function of the pumping system  21  is to move oil to and from the external bladder  18 , thereby increasing and decreasing profiler displacement. To do this the pumping system  21  is comprised of a motor  22  connected to a leadscrew  23  which is attached to the top  25  of an upper piston  24  in an upper cylinder  27 . The motor  22  is powered by batteries (not shown) in the pressure hull interior upper portion  19 . The upper cylinder  27  serves to guide the pistons  24  and  30 . The upper piston  24  has a bottom  26  which is attached to a lower piston  30  in a lower cylinder  31 . The lower cylinder  31  contains oil  32 . The lower cylinder  31  has a bottom  33  with an aperture  34  formed therein, said aperture  34  being fluidly connected to said external bladder  18 . As the leadscrew  23  is caused to turn by the motor  22 , the leadscrew  23  in turn drives the upper piston  24  downward forcing the lower piston  30  downward thereby displacing oil  32  out of the lower cylinder  31  into the external bladder  18 . This results in an increase in profiler displacement volume and therefore an increase in profiler buoyancy. The reverse process withdraws oil  32  from the bladder  18  into the lower cylinder  31  thereby decreasing profiler displacement volume and decreasing profiler buoyancy. 
     FIG. 2 shows the typical ocean profiler  10  in equilibrium 200 bar at  1 . This means that the profiler  10  is negatively buoyant anywhere above 200 bar; is positively buoyant below 200 bar; and, therefore, is in equilibrium at 200 bars. For the profiler  10  to ascend from point  1  to point  2 , i.e., profile, the profiler displacement volume must be increased. The work required to do this is indicated by the crosshatched area  3  on the graph. That is, the minimum pressure volume product that must be provided by the pumping system  21  is equal to the crosshatched area  3 . 
     The purpose of the present invention is to reduce the work expended to profile. The present invention does this by storing energy during descent and recovering the stored energy during ascent. The improvement in profiler energy, i.e., storage of energy and reduction of energy expenditure, is the subject of this invention. 
     Referring again to the drawings in detail wherein like elements are indicated by like numerals, there is shown in FIG. 3 the ocean profiler  10  of FIG. 1 with the addition of the invention compensator  40  resulting in an energy-improved profiler  10 ′. The compensator  40  is comprised of a compensator cylinder  41  having a top  42  and bottom  43 , said compensator cylinder  41  being positioned in the pressure hull interior  15  parallel to the lower cylinder  31 . The compensator cylinder  41  has a floating piston  44  separating gas  45  under pressure from oil  46 , said gas  45  being contained in a compensator cylinder upper portion  47  defined by the floating piston  44  and the compensator cylinder top  42 , said oil  46  being contained in a compensator cylinder lower portion  48  defined by the floating piston  44  and the compensator cylinder bottom  43 . The compensator cylinder bottom  43  has an aperture  49  formed therein. The aperture  49  is connected by means of a tube  50  to the external bladder  18 . During profiler descent the increasing ocean pressure, acting on the bladder  18  forces oil  46  into the compensator cylinder lower portion  48  forcing the floating piston  44  upward against the gas  45  in the compensator cylinder upper portion  47  thereby compressing the gas  45 . During profiler ascent the gas  45  expands forcing the floating piston  44  downward forcing oil  46  out into the bladder  18  thereby increasing profiler displacement volume and increasing buoyancy. In this way, during descent energy is stored by compressing the gas in the compensator cylinder. Its energy is then available to assist in the subsequent ascent. Applicant has found that nitrogen is an excellent gas for this application. However, other suitable gases, e.g., Argon, may also be used. Although oil  32 ,  46  was used to illustrate the invention, other fluids, including seawater, could also be used. 
     FIG. 4 illustrates graphically the effect on the buoyancy of FIG. 2 by the addition of the compensator in FIG.  3 . The energy-improved profiler  10 ′ is shown in equilibrium 200 bar at  1 . For the profiler  10 ′ to ascend from point  1  to point  2 , i.e., profile, the profiler displacement volume must be increased. The pressure volume product, i.e., work, that must be provided by the pumping system  21  is equal to the crosshatched area  3 . The dotted line B is the buoyancy curve of a typical profiler  10 . The curve B′ is the buoyancy curve of a profiler modified by the present invention, i.e., profiler  10 ′. The curve from 200 bar to approximately 30 bar is much steeper and has substantially reduced the work  3  needed for ascent. During ascent the compensator  40  is releasing energy previously stored during descent. This is pressure energy absorbed from the surrounding liquid medium during descent. At approximately 30 bar the floating piston  44  has moved downward as far as possible and is resting against the compensator cylinder bottom  43 . The compensator  40  has released all of its energy. The curve B′ then follows a slope exactly like the slope of curve B. The reverse is true as well. There is not sufficient pressure energy from the ocean to act on the compensator floating piston  44  until approximately 30 bar , i.e., approximately 300 meters depth. 
     Referring to FIG. 5 another embodiment of the invention is shown. As may be seen from the graph in FIG. 4, the compensator has little effect between the surface and approximately 300 meters of depth. Non-linearities that result from gas expansion/contraction plus the floating piston  44  stopping at the end of the stroke can be moderated by adding a compression spring  51  to the compensator cylinder lower portion  48  extending from said compensator cylinder bottom  43  to said floating piston  44 . This results in the floating piston  44 , at the low pressure end piston stroke, being in equilibrium with the pressure of the oil  46  (external ocean hydrostatic pressure), the gas  45  and the spring compression. In addition to the gas  45  storing energy, the spring  50  is also storing some supplemental energy which is releasable during the last 300 feet of ascent, i.e., above 30 bar. FIG. 6 illustrates the effect of this in curve B″ where the pressure volume area  3  has been further reduced. 
     Operation between the surface and equilibrium at one depth has been described, however the profiler can equilibrate at many intermediate depths. The invention application includes devices in continuous motion, e.g., profilers and underwater gliders. 
     The invention has been described as a way to reduce work in an oceanic profiler. The benefits accrue from improving profiler performance by decreasing the amount of energy required for a descent/ascent cycle. The work savings may be used for increasing the number of profiling cycles, reducing the size of the profiler, reducing pump size, reducing battery size or other energy sources stored aboard, reducing the cost of the profiler, etc. 
     It is understood that the above-described embodiments are merely illustrative of the application. The pump system  21  described above was selected as an example of what is used in selected profilers. Other pump systems, such as a single stroke piston pump, a swash plate pump, a gear pump, thermal pump, or other suitable pumping systems could also be used. Although a floating piston  44  was disclosed in the above invention description, an elastomer diaphragm or metal bellows could also be used. 
     In other embodiments of the invention the compensator  40  could be mounted outside of the pressure hull  11  and could also have its own bladder. Although the disclosure above described a single compensator, two or more compensators are practical. In a multiple compensator arrangement, adjustments in gas volume and pressure can adjust changes in buoyancy with depth to further reduce the pump work required. Not only is the work reduced, also the volume change required is reduced. This allows the pump to be smaller and lighter. 
     Other embodiments may be readily devised by those skilled in the art which will embody the principles of the invention and fall within the spirit and scope thereof.