Cost-Effective Load Monitoring Methods for Fatigue Life Estimation of Offshore Platform

The lifetime of offshore structures are ruled by accumulated fatigue damage so structural load monitoring is of special importance for re-assessment of offshore platforms. However, direct measuring of the actual loading is usually not feasible due to sensor limitations. An alternative approach to direct load measuring is load estimation from the limited number of measurements of dynamic responses of the structure. This paper presents two, conceptually different, model based, methods for load estimation in time domain: modal expansion method and Kalman filter based method. The Kalman filter based method uses the reduced FEM and provides estimations of limited number of signals, where the modal expansion method expands the mode shape vectors to estimate the displacements and stresses at all unmeasured locations. This paper is a part of ongoing development of methods for linear and nonlinear system identification, FEM updating, wave load calibration and lifetime prediction of offshore structures.