Reliability Analysis of Fatigue Failure of Cast Components for Wind Turbines

Abstract

Abstract:Fatigue failure is one of the main failure modes for wind turbine drivetrain components made of cast iron. The wind turbine drivetrain consists of a variety of heavily loaded components, like the main shaft, the main bearings, the gearbox and the generator. The failure of each component will lead to substantial economic losses such as cost of lost energy production and cost of repairs. During the design lifetime, the drivetrain components are exposed to variable loads from winds and waves and other sources of loads that are uncertain and have to be modeled as stochastic variables. The types of loads are different for offshore and onshore wind turbines. Moreover, uncertainties about the fatigue strength play an important role in modeling and assessment of the reliability of the components. In this paper, a generic stochastic model for fatigue failure of cast iron components based on fatigue test data and a limit state equation for fatigue failure based on the SN-curve approach and Miner's rule is presented. The statistical analysis of the fatigue data is performed using the Maximum Likelihood Method which also gives an estimate of the statistical uncertainties. Finally, illustrative examples are presented with reliability analyses depending on various stochastic models and partial safety factors.

Fatigue Reliability Analysis of Wind Turbine Cast Components

“…Finally, the stochastic model established on the basis of the above statistical analysis in combination with the reliability model for the fatigue failure of wind turbine cast components can be applied for the calibration of partial safety factors to a specified target reliability level, e.g., 5 × 10 −4 per year as recommended in [7]. In Section 4, the reliability assessment and methodology to evaluate the probability of failure is briefly explained, see [2] for more details.…”

“…The data should be collected and used to compute the value of the test statistics (F) in Equation (2). Each data value is categorized according to the different groups to be compared statistically to each other.…”

“…Structural reliability methods, such as first order reliability method and second order reliability method, can be used to evaluate the probability of failure/reliability [2].…”

“…Furthermore, the measure of uncertainty is not directly related to the uncertainty of the SN curve. The uncertainty of SN curves used in the next section has been evaluated by the maximum likelihood method (MLM) [2].…”

“…Offshore wind turbines have been installed many places, especially in the North Sea, and many new, larger wind farms are planned. Due to the harsh environmental conditions for offshore wind turbines, and the access difficulties for maintenance and repairs, it is very important to minimize failures of wind turbine components including fatigue failures of casted components [2] in the wind turbine drivetrain.…”