Submarine periscope-depth depth-keeping using an H-infinity controller together with sea-noise-reduction notch filters

Abstract

The paper shows the usefulness of H-infinity techniques in designing a depth-control autopilot for a submarine at periscope depth. It also shows that a significant reduction in nugatory hydroplane activity can be effected if tracking notch filters are included in the autopilot inputs to discriminate against wave frequencies. The results of simulations of a submarine at periscope depth in sea-state 5 in bow and stern seas are given. The simulation uses a full six-degrees-of-freedom nonlinear mathematical model of the submarine. Depth control is maintained using an H-infinity controller designed using a linear mathematical model of the submarine. The inputs to the controller are depth and pitch and the outputs are bow and stern hydroplane angles. Both input signals contain noise at wave frequencies which cause nugatory motions of the hydroplanes. Previous work, (Daniel and Richards, 1983), with LQG (Linear, Quadratic, Gaussian) controller designs showed that notch filters, designed to track the predominant wave frequency, could be used to reduce the hydroplane activity at periscope depth. This technique has now been applied successfully to an H-infinity controller.