The research project on sea-state estimation deals with estimation of wave height, direction and frequency from the vehicle's response. Different types of sensors can be used such as IMUs and RTK GNSS. Both zero speed applications (DP ships and marine structures), and ships in transit are studied. The latter requires that the encounter frequency is estimated on-line.
Fig 1. Model ship in the towing tank.
Fig 2. Wave spectrum.
Belleter, D. J., D. A. Breu, T. I. Fossen and H. Nijmeijer (2013). A Globally K-Exponential Nonlinear Observer for Wave Encounter Frequency.
9th IFAC Conference on Control Applications in Marine Systems (CAMS), 209-214. Open Access doi.org/10.3182/20130918-4-JP-3022.00016
Belleter, D. J., R. Galeazzi and T. I. Fossen (2015). Experimenal Verification of a Globally Exponentially Stable Nonlinear Wave Encounter Frequency Estimator. Ocean Engineering 97(15), 48–56. Preprintdoi.org/10.1016/j.oceaneng.2014.12.030
Dallolio, A., J. A. Alfredsen, T. I. Fossen and T. A. Johansen (2021). Experimental Validation of a Nonlinear Wave Encounter Frequency Estimator Onboard a Wave-Propelled USV. IFAC Conference on Control Applications in Marine Systems, Robotics, and Vehicles, 188-194. Open Access doi.org/10.1016/j.ifacol.2021.10.092
Dirdal, J. A., R. Skjetne, J. Rohac and T. I. Fossen (2023). A Phase-Time-Path-Difference Approach for Online Wave Direction and Wave Number Estimation from Measured Ship Motions in Zero and Forward Speed using a Single Inertial Measurement Unit. Ocean Engineering 288, 1-25. Open Access doi.org/10.1016/j.oceaneng.2023.116131
Dirdal, J., R. Skjetne, J. Rohac and T. I. Fossen (2022). Online Wave Direction and Wave Number Estimation from Surface Vessel Motions using Distributed Inertial Measurement Arrays and Phase-Time-Path-Differences. Ocean Engineering 249. Open Access doi.org/10.1016/j.oceaneng.2022.110760