Mechanical sensitivity analysis of strain gauge configurations in the main shaft of wind turbines

Abstract

Wind turbines are reaching their remaining useful life, thus it is important to guarantee the well status of its components. A common way to check the status is to measure the loads on the Low Speed Shaft with strain gauges, but not always are bonded perfectly. In this work a sensitivity analysis of strain gauge configurations is carried out, where the influence of geometric and material parameters, and misplacement and misalignment parameters is analyzed. An analytical model for a single gauge was developed, obtaining a relation between the exerted loads and the strain measured by the strain gauge. By means of Taylor approximations the estimated loads were approached in order to have into account the influence of the uncertainty of parameters. Results shown that the sensitivities with respect to the geometric and material parameters did not depend on the secondary loads while in the sensitivities with respect to the gauge bonding parameters the cross-talk effect was present. In order to obtain realistic numerical results, a horizontal-axis NREL 5-MW wind turbine was simulated in OpenFAST with two wind-speed scenarios. The uncertainty of the estimated loads by the strain gauge configurations was calculated.