Dynamtes of Naval Craft - System Identtficatton 
Among these are using measurements of additional state variables, 
applying a gain on the 6c vector (to inhibit any over-correction), 
and to vary the length of the record in steps (from a short record to 
longer records, using the converged outputs of each step as the ini- 
tial guess for the next longer record length until the entire record is 
processed), 
Another problem is that of the proper values of the parameters, 
even if they produce trajectories that match the measured values 
quite well. Sometimes a parameter that has only a small influence on 
the particular motion data being analyzed is sought by the system 
identification technique. In that case very little information related 
to that parameter is contained in the data, and the value determined 
by this procedure is spurious (and could also sometimes ''contamin- 
ate'' other parameter values), Various means of increasing confidence 
have been developed as a result of experience. Among these are using 
as many state variable measurements as possible, as well as moni- 
toring the change in the estimates of the converged c* values as the 
record length is increased. Since lengthening the record introduces 
more information, the c* values should begin to settle at some value 
(i.e. to stabilize), after which no further record lengthening is ne- 
cessary. Another means of establishing confidence in the results is 
to vary the weighting factors. When a change in the weighting factors 
produces no apparent effect on the results, confidence in these results 
is increased, 
APPLICATIONS OF THE ITERATION TECHNIQUE 
The iteration technique described above was applied toa 
number of dynamic systems for which transient motion response data 
was available. The naval craft of interest that were treated by this 
method are a surface ship and a hydrofoil craft. Forthe case of the 
surface ship, the nonlinear three degree of freedom system of equa- 
tions describing the steering and maneuvering of that ship are 
a = f(u) + civ + Cyt m Eau 6.4 
rv@ 2 
ym C uv + Cpur + Cy en Cou 5 (13) 
2 
oo Gets Get sat Cun = +C,)u 6 
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