Measurement of Rolling Period by IMU and Estimation of Metacentric Height

Abstract

Ensuring sufficient stability is crucial for the safe operation of a ship, while stability can decrease during a voyage. One method for real-time estimation of stability magnitude is through the rolling period. Being aware of the natural period is beneficial in preventing synchronous and parametric rolling, phenomena linked to significant cargo damage. In this study, we installed Inertial Measurement Unit (IMU) on a full-scale ship and collected motion data. In addition to an industrial-grade Micro-Electro-Mechanical Systems (MEMS)-IMU, we also utilized a smartphone in which a consumer-grade MEMS-IMU is embedded. The IMU consists of gyro and acceleration sensors, and we compared the performance of these two sensors. We applied time-frequency analysis to the motion data to compute the rolling frequency/period. We assessed the accuracy of the estimated GM from the rolling period against the one obtained from condition calculations. Our findings indicate that the gyro sensor is better suited for measuring the rolling period. Although it observed that a ship does not always roll at the same period; by considering the most frequently occurring period as the natural period, GM can be estimated with an error of less than 10%.