Probabilistic structural reliability analysis of a horizontal axis tidal turbine blade by considering the moisture effec
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ORIGINAL PAPER
Probabilistic structural reliability analysis of a horizontal axis tidal turbine blade by considering the moisture effects on the blade material Rajaram Attukur Nandagopal1 · Srikanth Narasimalu2 · Gin Boay Chai3 Received: 21 July 2020 / Accepted: 15 September 2020 © Sociedade Brasileira de Engenharia Naval 2020
Abstract The use of composite materials in marine structures like the horizontal axis tidal turbine blade introduces inherent uncertainties in the material properties of the blade. Further, the blade material ages because of the absorption of seawater into the material. Hence, whilst performing the static structural analysis of the blade, the probabilistic nature of the material properties, as well as its degradation due to ageing, must be considered. In this study, the probabilistic structural response of a 0.5 m blade was estimated by considering the experimentally determined statistical distributions of the dry and aged material properties. The polynomial chaos expansion (PCE) method was used to build a surrogate model to mimic the static analysis of the blade, which was used in conjunction with the Monte Carlo simulation to estimate the distributions of the structural response of the blade and the probability of failure of the dry and aged blade. Stochastic convergence was used to check the accuracy of the surrogate model built via the PCE method. The study revealed a statistically significant increase in the probability of failure of the blade due to the ageing induced degradation of the blade material. Further, the need for a probabilistic structural analysis was also established. Keywords Uncertainty · Tidal turbine blade · Marine effects · Reliability · Polynomial chaos expansion
1 Introduction Hydrokinetic turbines like the horizontal axis tidal turbine (HATT) converts the kinetic energy of the tidal flow into electrical energy [32]. The torque generated due to the flow across the rotor is responsible for the power generated by the turbine. The flow across the rotor also applies a thrust force on the rotor that results in the flapwise bending of the turbine * Rajaram Attukur Nandagopal [email protected] Srikanth Narasimalu [email protected] Gin Boay Chai [email protected] 1
Interdisciplinary Graduate School, ERI@N, Nanyang Technological University, Singapore, Singapore
2
Energy Research Institute @ Nanyang Technological University (ERI@N), Singapore, Singapore
3
School of Mechanical and Aerospace Engineering, Nanyang Technological University, Singapore, Singapore
blades, which is the significant hydrodynamic load acting on the blade [3]. In order to withstand the high thrust load acting on the rotor, the HATT blade is predominantly fabricated with a high specific strength composite material [24]. The design of such a composite tidal turbine blade must be performed to ensure sufficient reliability over its lifetime. The reliability of a composite tidal blade can be estimated through either a deterministic approach [17, 21, 25, 28] or a probabilistic a
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