OPTIMUM STABILIZATION OF A NEAR-SURFACE SUBMARINE IN A RANDOM OCEAN.

The vehicle-environment interactions are modelled using strip theory and a spectral seaway representation. Expressions are derived for the generalized forces in Lebesque and Rieman integrals as functions of the vehicle motion and the stochastic time variation due to waves. A careful linearization and Taylor expansion yield linear equations of motion with two new features suction and parametric excitation. The former makes the vehicle motion inherently unstable without controller. The latter has been traditionally overlooked. Our derivations specialized to the beam sea case coincide with a previously obtained result provided that a new transcendental identity holds. The control problem of maintaining a horizontal straight path ought ideally be solved in an input adaptive fashion. A Wiener-optimal controller is derived but implies a difficult a priori input global identification as well as only an approximate synthesis. An all-out digital simulation of a submarine in a seaway at various speeds and headings shows that neglecting parametric excitation can cause large errors in predicting motion amplitudes and that the proposed full thrust controller compares quite successfully with a conventionally designed controller. Author