Dynamics of Naval Craft - System Identtficatton 
Cc, Pero. a2 t) . 4446(. 445) . 4446(. 445) 
C, 1, 912(1. 97) 1. 912(1. 97) 2. 114(2. 18) 
Cc. . 5097(. 53) . 5097(. 53) . 5579(. 58) 
C, 2. 668(2. 67) 2. 053(2. 06) 1, 886(1. 87) 
C. . 4427(. 45) . 4427(. 45) . 5126(. 51) 
Cy 0 (0(.2)) 10,0. (10, 3) 0 (0(.2)) 
Ch (0G. 1)) 0 (0(. 2)) 0 (0(. 1)) 
The parameters Cg and C,, represent coefficients of nonlinear 
lift. Nonlinear lift appeared to play an insignificant role in almost 
all the trajectories, making it impossible to obtain firm estimates of 
these parameters. It was only possible to estimate the order of ma- 
gnitude of these parameters. This has been indicated in the table by 
use of an order symbol (as an example, the entry 0(.2) is to be in- 
terpreted to mean that the value of the parameter is no greater than 
+,2).In the case of Cg for configuration B, the nonlinear lift term 
had been artifically increased so that it played a more significant role 
in the trajectory, and was therefore detectable. The comparison with 
the true values in Table 2 shows a remarkable agreement between the 
values estimated by system identification and their respective true 
values, 
More detailed information concerning the results obtained 
for the case of a surface ship and a hydrofoil craft by means of this 
particular system identification method is givenin [4] and [5] . 
In addition to consideration of these particular naval craft, results of 
application of this technique to the case of a V/STOL aircraft using 
experimental trajectory data from a dynamic free-flight test facility 
(for vertical plane motion) and also a full scale airplane using flight 
test data (three lateral modes of motion), are also presented in [5] 
For those cases the agreement with other techniques of data analysis, 
or by virtue of matching measured trajectories, also provide verti- 
fication of the present technique and its ability to successfully iden- 
tify many unknown parameters in large dynamical systems from 
measurements of time histories of state variables (a total of eleven 
stability derivative parameters were determined for the full scale 
aircraft case). 
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