The Studies On Model Updating For Offshore Platforms

Offshore jacket platforms are the common structural forms in the current ocean petroleum engineering. Some damage may exist in the long-term serving platform of which the baseline (undamaged) structure measurement is unavailable; it is a very challenging and crucial task to accurately estimate the damage and update the analytical model in order to provide a basis for the safety evaluation of offshore platforms in long-term service.Discrepances always exist between the analytical model and experimental measurement of structures in the practical engineering. To obtain the accurate structural dynamic response ,it is necessary to use the measurement information to update the dynamic model. The updated dynamic model can predict the real dynamic response more accurately, also,combined with the practical measurement results it can be used for the damage detection and leaving-life evaluation for structures.For model updating of jacket-type offshore platforms, a method that updates mode shapes first and updates modal frequencies subsequently for FE model is presented. The updating process is achieved as follows: firstly, the elements that have stiffness discrepancies between real model and initial FE model are identified by using a damage detection method, then updating of the mode shapes for FE model is performed by iterative operations; secondly, regarding the foundation as three-dimensional elastic supports and designing them by an optimization method, updating of the modal frequencies for FE model is implemented. The model updating method is proved to be feasible by employing a model test of offshore platform based on hammer excitation.