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22 M.O. ŞERİFOĞLU, T. HIZARCI and H. AKYILDIZ

Communication System Faults: Underwater gliders communicate with the control center
throughout satellite. Connection occur at surface and glider transmit the collected data and take
the upcoming mission requirements. If communication cut off glider can be lost and start to drift
uncontrollably.

Navigation System Faults: Location data collected with the GPS antenna which can be located
on one of the wings or aft section of the underwater glider. Antenna locates on the surface in order
to get data in a stable condition. If the antenna locates on one of the wing gliders need to roll at
the surface with moving its battery side to side. Other type need to put its aft section out of the
water with the help of buoyancy mechanism. Any malfunction on these systems resulted in loss
of the glider.

3.2.2 Uncertainty and Reliability of Underwater Gliders

Underwater gliders are autonomous and unmanned systems therefore reliability is the most
important parameter to prevent the loss. Minimal cut sets and cut sets will be used to determine
the effect of subsystems to the entire system failure, to find the focus points on the subsystems
and which system create the most unreliability on the entire system. Cut sets are the unique
combinations of component failures that can cause system failure. Minimal cut sets can be used
to understand the structural vulnerability of a system. The longer a minimal cut set is, the less
vulnerable the system is to that combination of events. Also, numerous cut sets indicate higher
vulnerability. Cut sets can also be used to discover single point failures (one independent element
of a system which causes an immediate hazard to occur and/or causes the whole system to fail).
To find the minimal cut sets, formula (1) that below is used and the chart is created. P(MCs) and
MCsI values are found with the stress and reliability tests that applied to glider. These tests
showed effect of the subsystem failure to the entire failure of the system and critical subsystems
for the system unreliability. Tests also revealed that the failure rate of the subsystems and the
occurrence probabilities.

= ()⁄() (1)

6.018 6.957 6.805P(MCs) MCsI6.832 6.957 7.616 7.214

0.564 0.762 0.881 0.862 0.865 0.881 0.964 0.913 0.622
4.453 4.914

Figure 1. Minimal cut-sets (MCs) and minimal cut-sets importance (MCsI) of the systems

GiDB|DERGi Sayı 8, 2017