Local structural dynamics identification in offshore wind turbines based on experimental data

摘要

Standard approaches to determine stress in structural components typically use geometrically detailed FEM models including the effect of external loads. Loads are provided by aero-hydro-servo-elastic models, which are geometrically simplified to account for global modes and most relevant non-linarites. However, a common approach for component FEM models assumes a linear and quasi-static w.r.t. global system dynamics. Therefore, actual non-neglectible effects such as local dynamics or local non-linearities are not considered during the structural design process. The present study aims to establish a methodology to study whether those effects are present or not in real prototypes. Each new Wind Turbine design is validated by means of a real prototype. There, main parameters affecting it's performance are monitored; strain gages are installed in main sections to characterize reaction loads; and numerically detected critical positions are also instrumented in order to characterize their stress. Here, we propose a methodology in which dynamic stochastic models are used in order to model experimental time-series data of the structural system. For this purpose models such as ARMAX and BJ are used. The local modal parameters (natural frequencies, damping ratios and mode shapes) are identified and structural frequency response function (FRF) is reproduced. The methodology has been first validated successfully by a synthetic model under different noise levels than has been applied to experimental data from a 6MW Wind Turbine Prototype under different meteorological conditions. Similar modal parameters are identified.