Engineering Smart Technologies

MSUB II - Underwater Morphing for Buoyancy Control

Midé Technology Corporation is developing a novel means of buoyancy control for submersibles using shape memory alloys (SMA); under a Navy Small Business Innovation Research (SBIR) Phase I contract (Contract #N00014-05-M-0132) with Thomas Curtin as the technical monitor

Problem Description

The efficiency of underwater autonomous vehicles, such as sea gliders, can be increased greatly by means of actively controlling the buoyancy of the vehicle. By altering the center of mass, the vertical, pitch and roll motions can be optimized for specific regimes or missions. Both engine and trim (large and small) devices will be necessary to effectively control submersibles buoyancy. This technology is not only limited to autonomous underwater vehicles. It could also prove beneficial to large or small manned craft as well.

Midé's Solution

After our initial approach to use a "plate" SMA dimple to locally morph the submersible body proved difficult, Midé then successfully developed a flexured dimple (See Figure 2), where material from the dimple was removed in concentric circular patterns. Due to the inherent hoop-stress constraints the "plate" dimple failed to reliably morph between the two potential energy states without locking up. Various other concepts were also examined including using SMA as an actuator to displace a dimple shaped body. These concepts worked but were not considered feasible for the problem of under water buoyancy control.

Several prototypes of the flexured dimple were fabricated and tested successfully. The SMA was machined and memorized using Midé's own facilities. Tests were completed on the prototype to show that it was capable of morphing from one potential energy state to another (See Figure 3).

This flexured SMA dimple was embedded with an electrical heater in rubber to form a simple buoyancy control device (Figure 4). Efforts are continuing to optimize this system for force and displacement while ensuring that the system is capable of morphing between potential energy states.

The current flexured dimple displaces 4.56 in3 and can produce a buoyancy force of 2.25 lbs. The widths of the grooves in the flexure were cut wide due to the router process. A dimple with thin grooves cut by a water jet machine or laser will have a substantially increased force capability. Increasing the SMA's thickness will also increase the force. The current flexured dimple is 0.010 inches thick.

The flexured dimple device (dimple and heater encapsulated in rubber) was installed in a small test body. With the dimple in the unmorphed state, the body sank to the bottom of the tank and with the dimple activated, the body rose to the surface, demonstrating that the dimple is able to actively control the buoyancy of the test article (See Figure 5).

Although efforts are continuing to optimize the flexured dimple design, Midé has successfully demonstrated that morphing SMA dimples can actively control the buoyancy of under water vehicles. The "solid-state" buoyancy control device innovation is simple, it has essentially no moving parts, and based on results to date, it will be able to operate up to depths of 15 m (50 ft), it has an energy density of 150 J/kg and a buoyancy force/mass of 18 N/kg (1.8 lbf/lbm).

Opportunity

This technology may satisfy the needs of other Navy/DoD programs. Orgainizations that are interested in this technology are invited to contact Dr. van Schoor (tienie@midé.com) to discuss their requirements and to indicate support that will help motivate Phase II funding by the Navy.

Video Demonstration

Please select your preferred method for viewing the above demonstration videos

For more information:

Please contact Chris Ludlow (Products), or call: 781-306-0609 x227

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