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To improve the stability of the ship by reducing the vertical acceleration, intelligent
controllers based on fuzzy logic are proposed due to the complex and strongly non-
linear dynamics of these marine systems. In this chapter, the control is focused on
the pitch acceleration as the other vertical component, the heave signal, does not
contribute so significantly to the motion (Giron-Sierra et al. 2002 ).
Some stabilizer fins have been added to the fast ferry, two flaps at stern and a T-foil
at bow, working underwater (see Sect. 10.2 ). These surfaces originate lift forces
that can be applied to counteract the vertical motion. Two different fuzzy control
approaches have been designed and implemented, Mamdani and Sugeno types. Both
of them have been applied to control the flaps and the T-foil, independently.
10.3.1 Fuzzy-PID Mamdani Type Control
Based on the study of the behavior of a craft, Mamdani-type fuzzy systems have been
developed to control the vertical motion of the ferry. The knowledge that has been
used to design the controllers come from the experimental data of this ship sailing
in regular waves, the description of the vertical dynamics of the craft, and the model
of the actuators (flaps and T-foils) added to the craft.
The fuzzy systems control the movement of the fins, two flaps and a T-foil, so
that to reduce the total pitch moment of the ship. The fuzzy controllers work on
the actuators by controling their opening angles (amplitude), and the phase and
frequency of the oscillation. By varying them, it is possible to decrease the impact
of the pitch acceleration on the total moment of the craft. Therefore, two different
sets of rules have been designed for different purposes: (i) to control the amplitude
of the opening angle of the control surfaces, and (ii) to reduce the phase between the
actuator oscillation and the pitch moment.
The amplitude fuzzy controller has, as inputs:
ω 0 = 1.19 to 0.41 (rad/s), defined by 5 labels, SSNi.
The sea state number,
μ =−
Speed, Ucos
40 to 40 (knots), 8 labels: VH (Very High), H (High), M
(Medium), L (Low), when heading sea, and the same for following seas (VHF,
HF, MF, LF).
The fuzzy rules give the corrections of the pitch moment that the actuators can
provide, depending on the working angle of the fins,
ϕ max . Four labels have been
used for this fuzzy output: None (without correction), Small, Medium, and Large,
not uniformly distributed (Fig. 10.4 , left). The rules of the amplitude controller are:
If SSN is 3 and Ucos μ is VHF, HF, VH then Moment_correction is
None otherwise is Large
If SSN is 4 and Ucos μ is VHF, HF, L, M, H, VH then
Moment_correction is Large otherwise is None
If SSN is 5 and Ucos μ is VHF, MDP, M, H, VH then Moment_correction
is Large otherwise is None
If SSN is 6 and Ucos μ is VHF, M, H, VH then Moment_correction is
Large
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