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RISK ASSESSMENT OF UNDERWATER GLIDERS USING 21
UNCERTAINTY ANALYSIS AND FAULT TOLERANT CONTROL

3.2 Uncertainty Analysis on Underwater Gliders

3.2.1 Faults in Underwater Gliders

Potential faults in underwater gliders can be grouped under these titles:

Power System Faults: Battery problems is the most important parameter in the gliders because
any malfunctioning cause stopping of all systems. Because of that all battery systems are being
monitored autonomously all the time for short circuit, voltage changes and voltages on
components.
Leak Detection System Faults: Underwater gliders’ working depths can reach up to 5000 meters.
That means these vehicles needs proper sealing and water tide systems. Leak detection system
faults can be end with loss of the vehicle. While operation continue this system protect the vehicle
from drowning with surfacing if there is a leak.

Diving System Faults: There are two type of diving mechanism that control the glider. Most
important one is the bladder system that can change the reserve buoyancy of the vehicle with
changing the fluid inside the capsule that located aft side of the vehicle. Water inside the capsule
is replaced with the lighter fluid like oil which is kept inside reservoir cause increase in buoyancy.
Second type is the ballast system that can take and discharge the water with pumps. Leakage in
the capsule block the diving system and make impossible to change buoyancy which result in
drowning of the vehicle. Malfunctioning in buoyancy pumps prevent the changing center of
gravity that affect the control of the glider.

Environmental Detection System Faults: Underwater gliders can be equipped with various type
of sensors that can collect physical, chemical and biological data. However, every underwater
glider equips CTD (Conductivity Temperature and Depth) that can collect changing salinity and
temperature with depth. Malfunctioning in these sensor will abort the mission because of the
inability of the collection of required data.

Collision Avoidance System Faults: Collision of the underwater gliders can be classified in two
groups that are collusion with sea floor and collusion with the floating objects. Trapping in fish
nets also can be considered as the probability of the collusion of underwater glider systems.
Underwater gliders use sonar modem, sonar transponders and altimeter to prevent the collusion.
Any malfunction of these systems can be end with the collusion.

Computer System Faults: Underwater gliders mainly have 3 different computer systems. First
one is for storing the collected data. Faults in this computer makes the mission useless. Second
one is for navigation and planning. Last on is for monitoring the systems and coordination.
Malfunctioning in these computers jeopardize the mission and can lead to system failure.

Propulsion and Stability System Faults: There no propeller on the underwater gliders however
propulsion is fulfilled with the help of wings and fixed fins. Failure or rupture on these parts affect
the gliders moving mechanism. Thus, glider cannot move in horizontal plane and correction of
the diving angle will be impossible. Pitch and roll motion correctors failure lead to unstable diving
and wrong navigation. These faults lead the failure of the mission.

Sayı 8, 2017 GiDB|DERGi