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is caused by the vertical acceleration, both heave and pitch motion. The vertical
acceleration originates the seasickness, a most important concern, which can be
measured by theMSI (Motion Sickness Incidence) (O'Hanlon andMcCawley 1974 ).
In order to control this system and so to improve the quality of the traveling by
reducing the vertical acceleration, control-orientedmodels are needed to then develop
and evaluate the controllers. Because of the fact that the environment is continuously
changing, the uncertainty that comes from the sea waves, and the complexity and
strongly non-linear nature of the system itself, neuro-fuzzy techniques have been
considered.
10.2 Neuro-Fuzzy Models of the Ship
The description of the high speed craft behavior is complex, its dynamics changes
with the ship speed and the sea state in a strong non-linear way. Besides, some of its
parameters are coupled and/or time variant. It presents oscillatory movements and
huge inertias.
In this chapter two neuro-fuzzy models are proposed. Amodel based on simulated
data obtained with ideal waves, that provides the amplitude and phase of the vertical
motion (both heave and pitch), and also the pitch moment of the ship. The second
model predicts the value of those signals based on the values of the height of the
waves at previous moments.
These models are Sugeno-type Fuzzy Inference Systems (FIS) which are gener-
ated by applying subtractive clustering. The computational procedure used is called
ANFIS (Jang 1993 ; Brown and Harris 1994 ). The acronym ANFIS derives its name
from “Adaptive Neuro-Fuzzy Inference System”. Using a given input/output data
set, this procedure constructs a fuzzy inference system whose membership function
parameters are tuned using either backpropagation algorithm alone, or in combina-
tion with a least squares type of method. This allows the fuzzy systems to learn from
the data.
The experimental and simulated data have been collected and provided by
CEHIPAR (CEHIPAR 2013 ), a specialized towing tank, working with a small replica
of the ship. The knowledge about the dynamics of the system mainly comes from:
Physics equations of marine systems (Lloyd 1989 ; Fossen 1994 ) and hypothesis
on the waves motion;
Simulations (Precal: numeric program based on a CAD description for regular
waves);
Experiments in a towing tank carried out with a small replica.
Most of the models that have been obtained for this ferry consist of a set of different
linear models for specific operation points (wavelength, speed, etc.) under certain
conditions (Aranda et al. 2000 ;Cruzetal. 1998 ; Andres et al. 2000 ; Fossen 1994 ).
The models described in this chapter are more general and can be applied in a wider
range of sailing conditions.
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