Real-Time Heave Motion Estimation using Adaptive Filtering Techniques

Abstract Active heave compensation (AHC) systems require an accurate estimate of the vertical vessel motion in order to decouple the offshore crane's lift operation from the motion of the vessel. In this work, the heave motion is estimated based on measurements from an inertial measurement unit (IMU) using an adaptive heave filter whose parameters are adapted online. A standard double integrating heave filter introduces large phase errors resulting in large estimation errors for real-time applications. This work presents three modifications of a standard heave filter in order to reduce those phase errors. The error composition of each proposed filter is analyzed. The results are used to derive error functions which are minimized in order to obtain the optimal filter parameters. Furthermore, sea state characteristics, such as the mean heave height and the dominant heave frequency are determined online and utilized for parameter adaptation. The real-time estimation accuracy improves significantly when applying the phase correction algorithms to the filters. This is evaluated using measurement results from the Liebherr AHC test bench.