A two-step approach to damage localization at supporting structures of offshore wind turbines

This article introduces a new adaptive two-step optimization algorithm for finite element model updating with special emphasis on damage localization at supporting structures of offshore wind turbines. The algorithm comprises an enhanced version of the global optimization algorithm simulated annealing, the simulated quenching method that approximates an initial guess of damage localization. Subsequently, sequential quadratic programming is used to compute the final solution adaptively. For the correlation of numerical model and measurement data, both a measure based on eigenfrequencies and mode shapes and a measure employing time series are implemented and compared with respect to their performance for damage localization. Phase balance of the time signals is achieved using cross-correlation. The localization problem is stated as a minimization problem in which the measures are used in time and modal domain as the objective function subject to constraints. Furthermore, the objective function value of the adjusted model is used to distinguish correct from wrong solutions. The functionality is proven using a numerical model of a monopile structure with simulated damage and a lab-scaled model of a tripile structure with real damage.