Frequency detuning control by doppler shift

Abstract

In this work, a control strategy for ship parametric roll resonance is developed by changing the frequency of the parametric excitation. This is achieved by varying the ship's forward speed. This changes the perceived frequency of the waves, known as the encounter frequency (and thus the frequency of parametric excitation), via Doppler shift. A novel control philosophy based on a 1-DOF roll model, capable of describing the roll motion when the encounter frequency is non-constant, is proposed. The stability properties of the closed-loop system are mathematically proven and the effectiveness of the control system is demonstrated by simulating the closed-loop system using both a 6-DOF ship model and a simplified 1-DOF model describing the roll motion. The simulations are in agreement with the theoretical analysis.