Mooring line tension observed through a maximum entropy spectrum
SVEIN IVAR SAGATUN1, FINN GUNNAR NIELSEN1, ERLING HANDAL2, and NILS VELAND2
1 Norsk Hydro Exploration and production ASA, Research Center, Department of Marine Science, N5020 Bergen, Norway
2 Det norske Veritas, Oslo, Norway
Abstract: A method for measuring mooring line tension is proposed based on observation of the natural frequencies of the mooring line segment between the winch and the fairlead. The anchor line tension is observed through the string equation where an analytical expression for the line's eigenfrequencies is obtained. The tension is observed on line by utilizing a nonparametric system identification approach in which the peaks of a maximum entropy spectrum of the transverse acceleration measures of the vibrating string are automatically identified. The method is verified against full-scale data from the Troll B floating concrete oil production platform operating in the North Sea.
