THE APPLICATION OF SYSTEM IDENTIFICATION 
TO DYNAMICS OF NAVAL CRAFT 
Paul Kaplan, Theodore P. Sargent 
and Theodore R. Goodman 
Oceantes, Ine 
Platnvtew, New York 
ABSTRACT 
An important problem associated with establishing a 
mathematical model that adequately represents the 
motions of a naval vessel is the question of the pro- 
per form of the equations, as well as the values of 
the various parameters entering the equation system. 
A technique for determining the ability of a particul- 
ar mathematical form to represent the motions of 
such a vehicle, together with the determination ofthe 
numerical values of various parameters(such as sta- 
bility derivatives, etc.) is carried out by application 
of the technique known as system identification. The 
method of system identification is used in this con- 
text for the means to determine the unknown para- 
meters in a dynamical system representation from 
measurements of the time histories of the vehicle 
trajectories. Different techniques are used for ap- 
plication to problems that are of transient ncture, 
following a sudden disturbance or control deflection 
in a smooth seaway, and for those problems associ- 
ated with the motions ofa vehicle in a disturbed sea- 
way where the motionis continuously forced ina ran- 
dom manner. In addition the influence of noise in its 
generalized effect asa source of measurement error 
is also considered in this work. These techniques 
have been successfully applied to the determination 
of the stability derivatives (and nonlinear function 
coefficients) of a conventional surface ship, a hydro- 
foil craft, and an SES (surface effect ship) craft. 
1629 
