Modal parameter estimation for jacket-type platforms using noisy free-vibration data: Sea test study

Accurate estimate of the modal parameters of an offshore structure is crucial to many practical engineering issues, such as finite element (FE) model updating/validation, damage detection, etc. Using noisy acceleration signals collected from a step-relaxation test of a jacket-type offshore platform, we estimate its modal frequencies and damping ratios by an extended Prony's method, which includes a noise removal procedure to yield filtered signals before implementing the classical Prony's method on the filtered signals. To validate the applicability of the proposed approach, numerical simulations were firstly performed. Investigating corrupted relaxation response signals simulated from a FE model of the test platform, we conclude that the proposed approach is very accurate on estimating the modal parameters. A significant improvement can be achieved when the filtered, rather than the originally measured, signals are used. Using sea test data measured from accelerometers mounted at three different locations of the test platform, we find that the modal parameters estimated from the filtered signals of the three locations separately are in excellent agreement.

► An extend Prony's method, which includes a noise removal procedure to obtain filtered signals, was employed to identify multiple modal frequencies and damping ratios of a jacket-type platform from corrupted free-vibration data.
► Evaluated based on synthesized data, the proposed approach was very accurate on estimating the modal parameters.
► While using sea test data, the modal parameters estimated from three accelerometers mounted at different locations of the test platform were in excellent agreement.