Reconstructing Stress Resultants in Wind Turbine Towers Based on Strain Measurements

Marko Kinne,Ronald Schneider,Sebastian Thöns

doi:10.1007/978-3-030-77256-7_18

Marko Kinne, Ronald Schneider + Show 1 more

Open Access

https://doi.org/10.1007/978-3-030-77256-7_18

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Abstract

AbstractSupport structures of offshore wind turbines are subject to cyclic stresses generated by different time-variant random loadings such as wind, waves, and currents in combination with the excitation by the rotor. In the design phase, the cyclic demand on wind turbine support structure is calculated and forecasted with semi or fully probabilistic engineering models. In some cases, additional cyclic stresses may be induced by construction deviations, unbalanced rotor masses and structural dynamic phenomena such as, for example, the Sommerfeld effect. Both, the significant uncertainties in the design and a validation of absence of unforeseen adverse dynamic phenomena necessitate the employment of measurement systems on the support structures. The quality of the measurements of the cyclic demand on the support structures depends on (a) the precision of the measurement system consisting of sensors, amplifier and data normalization and (b) algorithms for analyzing and converting data to structural health information. This paper presents the probabilistic modelling and analysis of uncertainties in strain measurements performed for the purposes of reconstructing stress resultants in wind turbine towers. It is shown how the uncertainties in the strain measurements affect the uncertainty in the individual components of the reconstructed forces and moments. The analysis identifies the components of the vector of stress resultants that can be reconstructed with sufficient precision.

Highlights

The main components of a fixed offshore wind turbine are the rotor including the blades, the nacelle housing the generator, the tower, and the support structure [1]
Strain gauge rosettes can be applied at different elevations of the turbine tower to monitor its actual strain and stress state
The reconstruction of stress resultants from the strain measurements is subject to uncertainty

Summary

Introduction

The main components of a fixed offshore wind turbine are the rotor including the blades, the nacelle housing the generator, the tower, and the support structure [1]. If the rosettes are positioned appropriately around the circumference of a turbine tower, the actual timedependent stress resultants (forces and moments) in this cross-section can be monitored These load effects can, for example, be applied to updated predictions of the system’s fatigue performance and improve decisions on inspection and maintenance actions as well as support decisions on a lifetime extension. In this contribution, an approach to reconstruct stress resultants in a turbine tower cross-section from measured strains is presented. Their impact on the reconstructed stress resultants is investigated in a numerical example

Prior Probabilistic Model of the Measurement Uncertainty

Bayesian Updating of the Measurement Uncertainty

Inverse Mechanical Model (Relating a Strain State to Stress Resultants)

Probabilistic Inverse Mechanical Model

Numerical Example

Summary and Concluding Remarks