(Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 1994-09)
Willy, Christopher J.
This paper presents a method for estimating the spectra of water wave disturbances on
five of the six axes of a stationary, slender body underwater vehicle in an inertia dominated wave
force regime, both in head seas and in beam seas. Inertia dominated wave forces are typical of
those encountered by a 21 inch diameter, torpedo shaped underwater vehicle operating in coastal
waters and sea state 2. Strip theory is used to develop transfer function phase and magnitude
between surface water waves and the slender body pitch, heave, and surge forces and moment for
the vehicle in head seas, and for pitch, heave, yaw, and sway forces and moments in beam seas.
Experiments are conducted which verify this method of transfer function calculation, and
demonstrate the effects of vehicle forward motion in the head seas case. Using known sea spectra
and linear time invariant systems theory allows for estimation of the water wave disturbance
spectra for these forces and moments.
Application of sliding control techniques are then developed for the underwater vehicle
longitudinal plane equations of motion. Computer simulations are used to demonstrate the
dependence of underwater vehicle depth control upon the pitch control, and adaptive pitch control
is shown to provide good performance in the presence of substantial parametric uncertainty.
Pitch disturbance rejection properties of variations of the sliding controller are investigated. Both
single frequency and stochastic disturbances are used, and the stochastic disturbance is developed
using the results of the earlier investigation.
