Underwater Vehicle Bouyancy System

Abstract

A multiple stage buoyancy changing system, or variable buoyancy device, for an underwater vehicle. The multiple stage buoyancy changing system comprises: a pressure hull containing a flexibly-sized internal fluid reservoir; a flexibly-sized external fluid reservoir attached to the pressure hull and connected to the internal reservoir; a system of devices and channels configured to move fluid between the internal fluid reservoir and the external fluid reservoir to change a displaced volume of the vehicle. Each stage of the variable buoyancy device can be optimized for maximum energy efficiency while changing the vehicle's displaced volume within an ambient pressure range. A control system for the variable buoyancy device engages different stages depending on ambient external pressure such that maximum energy efficiency is achieved over a large range of pressures/depths.

That which is claimed is: 
     
         1 . A multi-stage buoyancy changing system for an autonomous underwater vehicle, the system comprising:
 an internal reservoir configured to hold a fluid;   an external bladder connected to the internal reservoir via one or more channels and configured to exchange fluid with the internal reservoir via the one or more channels;   a first device configured to move fluid through a first channel from the internal reservoir to the external bladder at an optimized efficiency for an ambient pressure of a first segment of a dive profile to increase an apparent displacement and a buoyancy of the autonomous underwater vehicle;   a second device configured to move fluid through a second channel from the internal reservoir to the external bladder at an optimized efficiency for an ambient pressure of a second segment of the dive profile to increase an apparent displacement and a buoyancy of the autonomous underwater vehicle, wherein the first channel and the second channel are arranged in parallel rather than in series; and   a third channel configured to allow fluid to move from the external bladder to the internal reservoir, the third channel including a solenoid valve that can be selectively opened to allow water to pass from the external bladder to the internal reservoir,   wherein the first segment of the dive profile includes a different ambient pressure range than the second segment of the dive profile, and   wherein a check valve is located in each of the first channel and the second channel and is configured to prevent fluid from moving from the external reservoir to the internal reservoir through either of the first channel and the second channel.   
     
     
         2 . The system of  claim 1 , further comprising a mass distribution mechanism configured to shift a center of gravity of the autonomous underwater vehicle to allow a portion of the autonomous underwater vehicle to surface when a buoyancy of the underwater vehicle is positive. 
     
     
         3 . The system of  claim 2 , wherein the autonomous underwater vehicle remains surfaced by maintaining positive buoyancy and a shifted center of mass, so that a tail end of the autonomous underwater vehicle is held above a surface of the water while information is transmitted and received. 
     
     
         4 . The system of  claim 2 , wherein the autonomous underwater vehicle is configured to shift its center of mass to travel horizontally in a neutrally buoyant state. 
     
     
         5 . The system of  claim 1 , wherein the autonomous underwater vehicle comprises an expandable internal reservoir that is capable of withstanding ambient pressures of surrounding water up to a predetermined depth. 
     
     
         6 . The system of  claim 5 , wherein the autonomous underwater vehicle displaces a volume of water and is configured to expand or contract the internal reservoir to increase or decrease, respectfully, the displaced volume of water to control a buoyancy and a center of gravity of the autonomous underwater vehicle. 
     
     
         7 . The system of  claim 1 , wherein the autonomous underwater vehicle comprises a nose and a tail, the tail comprising a portion configured to rise above a surface of the water that includes one or more of an antenna for radio communication and a GPS locator configured to communicate data that the autonomous underwater vehicle has collected while submerged and obtain a geographical location of the autonomous underwater vehicle. 
     
     
         8 . The system of  claim 1 , further comprising one or more sensors that collect data while the underwater vehicle is submerged. 
     
     
         9 . The system of  claim 1 , wherein the autonomous underwater vehicle has a front and a rear, and is configured to shift its center of buoyancy and center of mass toward the front or the rear while decreasing and increasing its buoyancy, respectfully. 
     
     
         10 . A method for employing a multi-stage buoyancy changing system for an autonomous underwater vehicle having an internal reservoir connected to an external bladder via one or more channels, the method comprising:
 in a first segment of a dive profile, increasing an apparent displacement and buoyancy of the autonomous underwater vehicle by moving water from the internal reservoir to the external bladder using a first device configured to move fluid through a channel from the internal reservoir to the external bladder at an optimized efficiency for an ambient pressure of the first segment of the dive profile; and   in a second segment of the dive profile, increasing an apparent displacement and buoyancy of the autonomous underwater vehicle by moving water from the internal reservoir to the external bladder using a second device configured to move fluid through a channel from the internal reservoir to the external bladder at an optimized efficiency for an ambient pressure of the second segment of the dive profile,   wherein the first segment of the dive profile includes a different ambient pressure range than the second segment of the dive profile,   wherein the first device moves fluid from the internal reservoir to the external bladder through a first channel and the second device moves fluid from the internal reservoir to the external bladder through a second channel that is different than the first channel and is arranged in parallel with the first channel, and   wherein a check valve is located in each of the first channel and the second channel and is configured to ensure that fluid does not move from the external reservoir to the internal reservoir through the first channel and the second channel.   
     
     
         11 . The method of  claim 10 , further comprising shifting a center of mass of the autonomous underwater vehicle so that a nose portion of the underwater vehicle is raised before increasing the apparent displacement and a buoyancy of the autonomous underwater vehicle. 
     
     
         12 . A multi-stage buoyancy changing system for an autonomous'underwater vehicle, the system comprising:
 an internal reservoir configured to hold a fluid; an external bladder connected to the internal reservoir via one or more channels and configured to exchange fluid with the internal reservoir via the one or more channels;   a pump motor in combination with a continuous variable transmission that can adapt to a torque-speed curve to obtain an optimal pressure/pumping rate needed for a current ambient pressure of the autonomous underwater vehicle, the pump motor and continuous variable transmission being configured to move fluid through a first channel from the internal reservoir to the external bladder at an optimized efficiency for an ambient pressure of more than one segment of a dive profile to increase an apparent displacement and a buoyancy of the autonomous underwater vehicle; and   a third channel configured to allow fluid to move from the external reservoir to the internal reservoir, the third channel comprising a solenoid valve that can be selectively opened to allow water to pass from the external bladder to the internal reservoir.