Dynamites of Naval Craft - System Identtftcatton 
the motions was appropriate to a sea state that was generated by a 
summation of separate regular sinusoidal waves, 
The method of analysis used in the identification procedure 
is based upon assuming that the pressure is a known measured 
quantity, which is the actual real case, and it is also assumed that 
continuous time histories of z, 2z, 6 and @ are available. On that 
basis it is then possible to analyze the equations for heave and pitch 
separately, so that only 4 coefficients are required in each case, 
i.e. the derivative Z,, Z,, 25, Zg can be obtained from a model 
based on Equation (40), while values of Mg, Mg, M;, and M, 
are obtained from a model using Equation (41), Computations were 
carried out for the pitch motion case primarily, since the heave 
motion is mainly due to the effects of pressure and both hydrostatic 
and hydrodynamic force terms have only a small influence for that 
particular motion, 
For the heave motion case the hydrostatic terms are the 
only contributions from the sidewalls, while there is a hydrodynamic 
term in addition that contributes to Mg, as well asa small desta- 
bilizing effect due to the bubble pressure. It is expected that the 
hydrostatic term is the predominant effect for Mg in this case. 
However, there is also some influence of the seals, on the moment 
derivatives, and that may be difficult to estimate accurately since 
the seals are not ''statically'' maintained in the water but partake of 
their own motion, and hence are a complicated element in this entire 
representation. The values found from the identification procedures 
are essentially the hydrodynamic stability derivatives divided by the 
particular inertia term in the equation, i.e. the mass m for the 
stability derivatives in the heave motion and the moment of inertia 
Iy for the pitch stability derivatives. 
Computations were made for the heave equations initially, 
with pressure as an input that is precisely known and using the values 
of 2, z,6 and @ as obtained from the simulated trajectory out- 
puts. Values of the coefficients in the heave equation were found, 
and an examination made of the results. In a number of simulations 
it was found that the signs of certain terms changed, and in addition 
values of some coefficients were found to have signs that were dif- 
ferent than would be ordinarily expected. When such "unrealistic"! 
values are produced in a number of different identification studies, 
this is an indication that the parameter may not have a significant 
influence on the resulting motions of the craft. The terms that did 
not appear to have a particular influence on the heave motion were 
the derivatives Zg and Zg , and special studies were made to 
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