ESTIMATION OF STILL-WATER BENDING MOMENT OF SHIP HULL GIRDER USING BEAM FINITE ELEMENT MODEL AND ENSEMBLE KALMAN FILTER

Longitudinal bending strength is the most fundamental strength of ship hull girders, and longitudinal bending moment acting on hull girders should be accurately monitored to ensure structural safety during ship operations. The longitudinal bending moment classified into still-water bending moment and wave-induced bending moment. This study proposes a data assimilation method to estimate the still water bending moment, and especially focuses on inverse estimation of cargo load. In the proposed method, hull-girder response in still water is simulated by a beam finite element model supported by distributed restoring springs. Nonlinearity of restoring force due to change of hull shape under waterline is considered in the simulation. To assimilate simulation by beam FEM with observed strains, ensemble Kalman filter is implemented in the beam FEM. To validate the proposed data assimilation method, a still-water tank test using a backbone-type hydro-elastically scaled model is conducted. The proposed method is applied to the measured data, and the ballast load is inversely estimated from the bending strains. The estimation accuracy of the ballast load is improved as repeating prediction by beam FEM and filtering by ensemble Kalman filter, and estimated ballast load has good agreement with actual.