Extreme load estimation of the wind turbine tower during power production

Abstract

Wind turbines have to be designed against extreme load during power production with the recurrence period of 50 years. This extreme load is usually calculated through statistical extrapolation. However, large uncertainties exist in the estimation of the extreme load. This study aims to reduce these uncertainties in the statistical extrapolation by using systematic simulations. First, a new criterion is proposed for the data sets to be used for the statistical extrapolation and the resulting uncertainty satisfies the requirement in the standard for prediction of wind load. Then, a new extrapolation factor for load extrapolation is proposed and the predicted maximum tower bending moments at all the heights show favorable agreement with measurement. Finally, empirical formulae are proposed to estimate the expected value of the maximum tower bending moment and the predicted values show good agreement with the numerical simulations.

Reduction in the Fluctuating Load on Wind Turbines by Using a Combined Nacelle Acceleration Feedback and Lidar-Based Feedforward Control

“…The specifications of the turbine are summarized in Table 1. The wind turbine is a horizontal axis, three-bladed, upwind, variable speed and variable pitch control turbine with a rotor diameter of 92 m and a hub height of 80 m. An aeroelastic model of this wind turbine, including the mass and other dynamic properties, is described in [35]. Aeroelastic simulations are carried out by using the dynamic simulation software FAST v8 [36].…”

“…The time step of the simulation and the communication intervals of the controller are both set to 0.002 s. A turbulent wind field is generated by using Turbsim software [37]. Turbulence intensity is defined as a function of the mean wind speed based on the 50 percentile of the normal turbulence model (NTM) defined in IEC61400-1 [38], and the value of I re f is set to 7% based on the measurement [35], as shown in Figure 2. The sampling rate of the cup anemometer is 0.25 Hz.…”

“…Thus, ∆Ω = q(s)∆u + P(s)∆θ f f (35) The purpose of the lidar-based feedforward control is to change the pitch angle ∆θ f f to cancel the fluctuation in rotor speed caused by the fluctuation in wind speed.…”