Fragility analysis of the IEA-15MW wind turbine blades using the surrogate modelling approach

Abstract

With the concerns related to global warming and the political scenario threatening energy security, all the nations are moving toward renewable energy sources. Wind energy has seen tremendous scale and power generation growth over the last couple of decades. Especially the offshore wind turbines are driving the growth where large-scale multi-megawatt wind turbines can be installed with ease without disrupting the urban built environment. The offshore wind turbines also offer access to higher wind speeds and relatively less turbulence, further improving power production. To cater to the increasing demand and lower the energy cost, engineers are pushing the boundaries to design large-scale wind turbines with higher hub heights and longer blades to achieve higher power production. However, with the increase in scale, wind turbines are becoming more and more flexible. The wind turbines are subjected to a very harsh dynamic load environment, which, coupled with the low stiffness, makes the wind turbines dynamically sensitive.

The new generation wind turbines face challenges such as higher loads, higher vibration levels and more fatigue damage. In this study, the authors aim to perform the fragility analysis of the IEA-15MW reference wind turbine blades, which represent the largest stand-alone wind turbine at the moment. This wind turbine has a hub height of 150m and a blade length of 117m. These blades are very flexible in nature and can experience tip deflection of the order of 23m for the worst-case load combination. Although a detailed aerodynamic performance of these blades has been presented, the structural performance and failure limits are not well established. Also, the fact that these blades are subjected to a highly uncertain and turbulent loading environment calls for a rigorous analysis for their safe operations. This study developed a detailed finite element of the IEA-15MW reference wind turbine blades to address this problem. The structural failure limits for these blades are established by performing the push-over analysis. A blade's response is influenced by various factors, including wind speed, inflow direction, turbulence intensity, pitching angle, etc. The input-output relationship is established using a surrogate model since capturing the impact of these parameters is challenging through an analytical expression. Using the surrogate model and the failure limits, the fragility curves for the blade are developed for the stochastic load environment, and failure probability at different loading conditions is evaluated.