The application of signal processing techniques for real-time monitoring of the dynamic stability of a ship via its motion responses

Significant changes of stability at sea can lead to dangerous situations and eventually stability failure. Despite its importance, the current intact stability criteria do not evaluate the motion responses of a vessel. More recently, the International Maritime Organization has identified phenomena in seaways responsible for stability failures. These phenomena can cause large roll angles and/or accelerations that can endanger ships due to critical stability situations in waves. The measurement of waves while a ship is underway is a major challenge, but ship motion is a good reflection of the wave characteristics and can be captured. Signal processing techniques are used in the detection and estimation of the influential parameters of a wave through the analysis of motion responses. Some variables of the system can be detected by spectral analysis of heave and pitch responses. These variables are the peak wave frequencies and associated magnitudes which can cause a high roll motion when similar to the roll natural frequency. The instantaneous frequency present in the signal is revealed through spectral analysis of short-time Fourier transforms in less than a minute. The instantaneous frequency is a parameter of practical importance which can be used in decision-making processes to avoid high roll motions.