Estimation of Blade Forces in Wind Turbines Using Strain Measurements Collected on Blades Bridget Moynihan, Babak Moaveni, Sauro Liberatore, and Eric Hines Abstract This paper introduces a method for computing the forces and bending moments on operating wind turbine blades based on strain and SCADA data in the absence of comprehensive design specifications. Operational data from 4 months of a Clipper Liberty C96 2.5 MW turbine instrumented with interferometric strain sensors placed at the blade roots as well as supervisory Control and Data Acquisition (SCADA) data such as wind speed, rotor hub speed, and blade pitch angle allow for accurate calculation of blade forces and moments. In order to perform such calculations, certain structural properties of the turbine blades must be established in the absence of detailed, proprietary information. This is done by inferring certain properties from National Renewable Energy Laboratory (NREL) reference wind turbine specifications. In these specifications, NREL also provides descriptions of resulting forces and other parameters to be used in the design of wind turbines. The authors independently computed these forces and moments as a function of wind speed and compared them to NREL’s results in the paper, demonstrating that this method can be used to successfully estimate the internal forces and bending moments acting on the blades. Keywords Wind turbine · Condition monitoring · Strain sensors · Wind energy · Structural health monitoring 1 Introduction In 2019 alone, 39% of new additions to the U.S. electricity supply came from wind power, and total U.S. wind power capacity has now surpassed 100 GW, which is four times the existing operating capacity from 10 years ago [1]. As the wind industry has grown, so have the wind turbines (WT) themselves. As OWTs grow in size, the reliability of such massive structures is a key consideration to ensure the availability of low-cost renewable energy. One of the largest components of wind’s levelized cost of energy (LCOE) is that of operation and maintenance (O&M), which can constitute 10–20% of the LCOE in WT and reach up to 35% at the end of life [2]. O&M not only increases total costs, but it creates downtime which can reach up to 3% of WT and OWT total lifetimes [3]. Structural health monitoring (SHM) as a form of condition monitoring (CM) is an important tool for ensuring the integrity of WT infrastructure [4], as it allows for maintenance before failure occurs, reducing O&M costs [5]. Application of SHM methods on strain measurement is well studied but obtaining further information on the condition of WT from strain measurements can make CM systems more cost efficient. In traditional CM systems, strain sensors are typically placed on the gearbox, generators, and drivetrain [6] more commonly than on other major components such as the blades or tower. Some WT are instrumented with strain sensors on additional components such as the blades. Fiber optic strain gauges placed on blades can be used for CM of blades, though it is one of the most expensive approaches compared to other methods [7]. This type of CM is utilized by WT operators to measure blade-root bending moments [7]. Analyzing the root reaction forces and bending moments on the blades in addition to blade-root bending moments would be useful for understanding the effects of certain loading conditions [8], but to utilize strain measurements for making these calculations, WT design details must be known. B. Moynihan ( ) · B. Moaveni · E. Hines Tufts University, Medford, MA, USA e-mail: bridget.moynihan@tufts.edu; babak.moaveni@tufts.edu; eric.hines@tufts.edu S. Liberatore MIDE Technology Corporation, Woburn, MA, USA e-mail: sliberatore@mide.com © The Society for Experimental Mechanics, Inc. 2022 K. Grimmelsman (ed.), Dynamics of Civil Structures, Volume 2, Conference Proceedings of the Society for Experimental Mechanics Series, https://doi.org/10.1007/978-3-030-77143-0_4 43
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