Dynamics of Naval Craft - System Identtficatton 
Parameter Estimated Value 
1 
posits . 085 
C, 
A 
oe . 965 
2 
B 
= 1, 42 
z 
With the parameter values established by this procedure, 
the resulting trajectories of the craft are presented in comparison™ ,. 
with the measured full scale data (from Experiment 4) in Figure 13. 
The time histories of CG heave h, pitch angle @, and pitch rate 6 
are compared in Figure 13, and it can be seen that there is generally 
good agreement using the estimated coefficients obtained from this 
system identification procedure. Some of the small differences can 
be explained, since the heave motion is obtained by combining various 
measured signals, including that from the height sensor which will 
contain ''noise'' due to local ambient waves as well as waves generat- 
ed by the craft motions themselves. The lack of more precise agree- 
ment in the final values of the pitch angle is due to the inability of 
the present mathematical model (a simplified quasi-linear model, 
with reduced degrees of freedom, and neglecting drag and thrust in- 
fluences, etc. ) to provide a very accurate measure of trim condition 
near or at equilibrium. The deviations in pitch rate are actually 
quite small in magnitude as can be seen from the scale in Figure 13, 
so that the ''tracking'' by the predicted 6 trajectory is better repre- 
sented by the ability to change sign and generally follow the measur- 
ed data, which is done sufficiently well. 
Examination of Figure 12 shows that the representation 
of the parameter values associated with the depth variation caper x 
sion is exhibited in terms of 7 thot al , etc. The values of 2 iy and 
G> for these functions seem to ie oak zero, so that the resulting 
rte of F and F behave in an almost linear variation with ‘Sm R 
while these F, and F, functions approach an almost constant value 
as °F R any for the representation used in the case of the compu- 
ter generated data model. This is shown by the curves in Figures 
14 and 15. A means of judging the effect of this difference is to com- 
pare the values of the products K,F, and KrF. obtained from the 
full scale tests with the values used in the computer simulation ma- 
thematical model, since these terms represent the lift effectiveness d 
1665 
