The basic design concept of the AUV ISiMI is hinged on the implementation of a small vehicle that can be easily launched, recovered and operated without special handling equipment. This concept of a small AUV is intended to provide researchers with fast experimental feedback on new algorithms and instruments necessary to develop AUV technologies. Several AUVs were reviewed to lead the concept of ISiMI. Sea Squirt AUV, which is 1m long and weighs 35 kg, was built in 1988 under the MIT Sea Grant to gather oceanographic data from the Charles River and serve as a test-bed for software and instrumentation, with component costs of $40,000. Then the MIT Sea Grant built Odyssey I and II for oceanographic research, with component costs of $50,000 and $75,000, respectively (Bellingham et al., 1993). Hydroid's REMUS (Allen et al., 1997; Stokey et al., 2001) and GAVIA AUV, developed by WHOI and Hafmynd, respectively, are small commercially available AUVs with diameters less than 25 cm.
MOERI-KORDI has a big square basin, OEB, for simulation of real sea conditions. OEB is 68.8m long, 37.2m wide and 4.5m deep. Wave, current and wind generators are installed in the basin. The purpose of ISiMI is to serve as a test-bed AUV for the development of AUV technologies with fast experimental feedback in an OEB environment. The size of ISiMI is constrained by the OEB environment, so ISiMI is able to run free in OEB. Its downsizing is at the highest level of the design process. Because the dimensions of the AUV conflict with the space and payload for instruments, however, the hull size and weight of ISiMI were determined in the spiral design process, which is a feedback design from the basic design to the detailed design.
In general, the hull shape of AUVs has mainly two types. The first is the cruising type, which looks like a torpedo, and which surveys from hundreds of meters to hundreds of kilometers. Its streamlined shape is adopted for AUVs to minimize the drag forces acting on the hull while the AUV is cruising. They use axial thrusters and control planes to control their motion. The other type of hull shape is the hovering type, which inspects a specific area from several meters to hundreds of meters. Several thrusters are installed to keep their precise positions and attitudes in hovering motion. Since ISiMI is a test-bed for underwater survey and docking technologies, the torpedo-type hull shape was adopted. Moreover, a pressure hull structure was chosen rather than an open frame structure for spatial efficiency.
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