Kaplan, Sargent and Goodman 
These applications have included vehicle trajectories 
obtained from computer-generated data, as wellas 
full scale data. The utility of the techniques is de- 
monstrated by the results obtained for these appli- 
cations, together with a discussion of limitations in 
different towing tanks throughout the world for this 
purpose, ranging from multi-component balances for 
staticforceand moment measurementyotating arms, 
horizontal and vertical planar motion oscillator me- 
chanisms, etc. (see [1] - [2]). Considering the com- 
putational and data reduction equipment required as 
ancillary elements of the measurement devices, as 
well as the time and expense required to obtain the 
required parameter values by these means, other 
methods that may reduce the effort required for de- 
termination of hydrodynamic coefficients then become 
attractive(especially tolaboratories or organizations 
that do not have such involved instrumentation), 
A particular approach to determine the values of va- 
rious parameters in a mathematical representation 
of the dynamics ofan arbitrary system (whether it is 
a vehicle, a chemical process, control system, etc.) 
has been developed recently as part of modern con- 
trol theory. This procedure is known as ''system 
identification'’, which in the present case is a means 
of determining the numerical values of the coefficients 
that enter into a set of mathematical equations that 
are assumed to represent the dynamic motions of a 
particular vehicle or system (in addition the proce- 
dure can also determine the suitability of a particu- 
lar mathematical model form as well as the sensiti- 
vity of different modes of motion to particular coef- 
ficients, as will be demonstrated herein). These va- 
lues are considered to be the appropriate values re- 
presenting the system dynamics when they are ob- 
tained with the same values from a number of differ- 
ent trajectories of the vehicle motion, thereby insur- 
ing their uniqueness, The extent of realism inherent 
in the coefficient values is related to the capability 
of the mathematical equation model to represent the 
vehicle motions, since the results of captive model 
tests in wind tunnels, water tunnels, towing tanks, 
etc. are aimed at measuring such coefficients ex- 
perimentally, where the coefficient structure is based 
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