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Buoyancy engine

The meaning of «buoyancy engine»

A buoyancy engine is a device that alters the buoyancy of a vehicle or object in order to either move it vertically, as in the case of underwater profiling floats and stealth buoys, or provide forward motion (therefore providing variable-buoyancy propulsion) such as with underwater gliders and some autonomous aircraft.[1][2]

For underwater applications, buoyancy engines typically involve a hydraulic pump that either inflates and deflates an external bladder filled with hydraulic fluid, or extends and retracts a rigid plunger. The change in the vehicle's total volume alters its buoyancy, making it float upwards or sink as required.[1] Alternative systems employing gas obtained from water electrolysis, rather than hydraulic fluid, have also been proposed.[2]

The buoyancy engine is a fairly new piece of technology currently in research by many institutions and organizations that utilize underwater surveillance and mapping technologies.  A buoyancy engine works by inflating and deflating an oil bladder. In doing so, this changes the density of the craft the engine is installed on.[3] As a result, an autonomous underwater vehicle such as an underwater glider can adjust its buoyancy without external input.  This allows the glider to remain in operation, untethered to a surface vessel, for a longer duration of time. This increases efficiency and makes the underwater glider a more viable tool for mapping the ocean floor.

An underwater glider works similarly to how a normal glider works.  It utilizes the flow of water over a set of wings to generate lift.[4]  The shape of the wings are a specially designed shape called an airfoil. Underwater gliders use this same principle and design to glide underwater. The way weight is distributed within the underwater glider helps with this by putting the center of gravity at or just in front of the leading edge of the wings.  This promotes an efficient and smooth glide slope. The buoyancy engine allows an underwater glider to continue this gliding process for extended periods of time. Without a buoyancy engine, an underwater glider would either have to be towed by a surface vessel or only be used once and deploy a package that would float to the surface where it can be retrieved.  However, if it is towed by a surface vessel, then it is no longer classified as a glider. With the addition of a buoyancy engine, the underwater glider becomes a viable tool as it can stay in operation longer and can be reused.[3]

An underwater glider, like a normal glider, loses altitude as it moves forward.[4]  In the case of an underwater glider, its depth increases. Eventually, any glider will touch the ground.  With a normal glider, this is not much of an issue since normal gliders are expected to land and are reusable when they do so.  This is not true for an underwater glider. If an underwater glider were to land on the ocean floor, it is essentially lost forever.  Since a buoyancy engine allows a glider to change its density, the glider can glide in two directions. It can glide down like a normal glider, or it can glide up if it makes itself less dense than the water around it.  In this way, as long as the buoyancy engine remains active, an underwater glider can continue to operate.

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