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16 H. AKYILDIZ ve E. TÜRKMEN

complexity. The complexity of engineering systems is permanently growing due to the growing
system size and degree of automation, and accordingly increasing are the chances for faults and
at the same time, aggravating the consequences of system failures for engineer and environment.
Therefore, increased attention has to be paid to reliability, safety and fault tolerance in the design
and operation of technical systems in industrial automation. But obviously, compared to the hish
standard of perfection that nature has developed with the ‘self-healing’ and ‘self-repairing’
mechanisms in complex biological organisms, the fault management in engineering systems is far
behind their technological capabilities and is still in its infancy.
In technical automatic control systems, defects may happen in sensors, actuators, the components
of the product itself, or within the hardware or software of the control equipment. Component
faults can develop into a failure of the whole system. This effect can easily be amplified by the
closed loop. The closed loop may also hide an incipent fault from being observed until a situation
is reached in which a failing of the whole system is unavoidable. Even making the closed loop
robust or reliable by robust or reliable control, respectively, can not solve the problem in full. It
may ensure to retain stability of the closed loop and continue its mission with desired or tolerable
degreaded performance in the presence of faults, but when the faulty part continues to miss-
function, it may cause damage to engineer and environment due to the impact of the faults. So,
robust and reliable control using available hard or software redundancy may be efficient ways to
maintain the functionality of the control process, but it can not guaranty environmental
compatibility or safety of the whole system.
A realistic fault management has to provide dependability which includes both reliability and
safety. Dependability is a fundamental requirement in industrial automation, and a cost-effective
way to provide dependability is fault tolerant control (FTC). The key issue of FTC is that local
faults are prevented from developing into a system failure that can end the mission of the system,
and/or cause safety hazards by the faulty devices or the whole system for engineers and
environment. Because of its increasing importance in industrial automation, FTC has become an
emerging topic in control theory.

Figure 1. Basic scheme of a fault tolerant control system
3. General Introduction about ASVs
ASVs can range in complexity but must include four main elements: a body (hull), a propulsion
system, a navigation system, and a data collection and transmission system. There is no standard

GiDB|DERGi Sayı 5, 2016