Development and Sea Trials of a Shuttle Type AUV "ALBAC"
Concept of the ALBAC
A prototype of shuttle type autonomous underwater vehicle which is named ALBAC (Photo 1), was designed by the authors and constructed in 1992.Distinctive features of the vehicle are summarized as follows:
FIG. 1 Dimensions of the ALBAC
- The ALBAC does not have a propeller thruster but moves aside by gliding. Thus, the vehicle carries only a small battery of 100 W.
To get large lift force a pair of wings is fitted at the middle of the body as illustrated in Fig. 1(Not yet included).
- The ALBAC controls its trajectory changing pitch angle and roll angle by displacing the center of gravity.Two actuators in a hull move a weight longitudinally and laterally. Thus the major mechanism for control is not fitted outside the hull and the actuator system is not expose to the sea water. The total hardware system, therefore, becomes highly reliable.
- Diving depth is limited to 300 meters so that the mass is only 45 kg.
- The vehicle does not have a communication link to the operator, so that the ALBAC can be called a fully stand alone vehicle. 5) It is easy to design a vehicle which can dive deeper according to the same concept.
********FIG. 2 Mission Scenario of the ALBAC***********
Deployment of the ALBAC consists of three stages as illustrated in Fig. 2.
- Decent stage : The ALBAC descends to the destination depth and measures scientific data of water column along a gliding trajectory.
- Drop of a weight : When the vehicle comes to the destination depth, it drops a decent weight and becomes positive buoyant for ascent. In case of emergency, for instance the vehicle dives over the design depth of 300 meters or the ranging sensor finds an obstacle, the vehicle also drops a weight.
- Ascent stage : The ALBAC glides upward in the same manner as the decent stage and the oceanographic measurement can be continuously carried out through this stage.
At present the ALBAC is able to carry out the following mission scenarios depending on the software system which controls the gliding angle and the turning radius.
- Fixed destination : The ALBAC glides to the target point on the bottom and turns back to the other destination on the surface.
- Constant heading : The ALBAC keeps an azimuth on the way and from the destination depth.
- Corkscrew dive : Since the gliding angle can be changed from 15 to 30 degrees, the ALBAC glides spirally to descend and ascend vertically. Depth rate can be changed by controlling turning radius.
Last modified: Tue June 6 1995