Estimating design reliability of composite rotor blades under ultimate loading

Abstract

A probabilistic stress analysis tool predicting reliability of composite wind turbine rotor blades was developed and validated by comparing with results from a three‐dimensional shell finite element model of a blade. Stress analysis was based on thin wall multicellular Euler–Bernoulli beam theory using as input section stress resultants directly from aeroelastic simulations; a finite strip method was implemented for elastic stability calculations. Reliability analysis was performed at the ply level of the multidirectional laminates implementing various methods such as the response surface method, β‐index and crude Monte Carlo simulation. Physical and statistical uncertainties of the basic variables was taken into account while several model uncertainties related to the material properties were further introduced and quantified in the light of appropriate test results. To prove the efficiency of the code as a design tool, the effect of various probabilistic assumptions concerning the material properties was directly investigated on the estimated reliability β‐index values for two rotor blade design cases typical of stall‐regulated and pitch‐regulated wind turbines. Copyright © 2014 John Wiley & Sons, Ltd.

Probabilistic design of wind turbine blades

“…Thus, only part of the DoE was completed using the commercial code, indicating the limitations of commercial reliability fi nite element tools for direct use as a structural design tool for wind turbine blades. The work of Bacharoudis and Philippidis (2010) was recently extended, in Bacharoudis and Philippidis (2012), to the investigation of the elastic stability of the blade as the limit state function, with similar conclusions being reached.…”

“…Probabilistic assessment of the blade using three-dimensional fi nite element models was considered in Bacharoudis and Philippidis (2010), where results were presented using a full 3-D fi nite element shell model produced by the commercial code ANSYS. Reliability of an actual blade under extreme loading was investigated and, for the purposes of the probabilistic analysis, a procedure to convert the bending moment distribution, obtained from the aeroelastic beam model, to an equivalent system of concentrated forces acting on the 3-D shell fi nite element blade model, was developed.…”

“…To this end, a suitable equivalent system is required, which it has been shown can be achieved by modifying the methodology used for the evaluation of the blade strength on the basis of load component distribution during blade testing (IEC/TS 61400-23:2001) (see e.g. Bacharoudis and Philippidis, 2010). An image of the distributed load in the fl ap and lead lag directions for the blade fi nite element model is shown in Fig.…”

“…eu), within work packages WP3 (see e.g. Lekou and Philippidis, 2009;Bacharoudis and Philippidis, 2010;Bacharoudis et al ., 2011), or within the framework of the Danish national projects at Aalborg University (see e.g. Toft and Soerensen, 2011;Toft et al ., 2011aToft et al ., , 2011b.…”

Effect of uncertainty sources on the reliability level of wind turbine rotor blades

“…This information is of high importance if comparisons are to be made between candidate materials or the effect of a parameter, whether environmental or other, on the material properties is to be sought. Moreover, to identify the role of measurement uncertainty on the reliability level of the blade, the probability of failure under static and variable amplitude loading is estimated based on probabilistic analysis tools developed for application on wind turbine blades in . The application is performed on the 90‐m INNWIND.EU reference MW wind turbine blade .…”