Considering the structural characteristics and both internal and external excitations of offshore wind turbines, a rigid-flexible coupled multi-body dynamic model for large-scale turbines is established. A comprehensive performance evaluation method is proposed, integrating the interpretive structural modeling(ISM) technique with the analytic network process(ANP). A multi-dimensional performance evaluation framework is built, including five primary indicators and eleven secondary indicators. The ISM method is employed to analyze the interrelationships among evaluation indicators and to develop a multi-level hierarchical structure for comprehensive assessment. The ANP is then used to construct judgment matrices, supermatrices, and limit supermatrices, through which the weights of evaluation indicators are determined. Based on these results, the comprehensive performance of offshore wind turbines is quantitatively evaluated, and a comparative analysis of two turbine models is conducted. The results show that the most influential factors affecting overall performance include blade length, time-varying reliability of bearings, gear contact fatigue reliability, and unit megawatt weight. Additionally, the 5 MW wind turbine demonstrates superior comprehensive performance compared with the 6.2 MW model.

The dual-rotor wind turbine is an innovative horizontal axis design that harnesses the wake of the front turbine for additional power generation, leading to a higher wind energy utilization coefficient. However, the longer axial span required to minimize the flow field interference between the front and rear turbines complicates the drivetrain’s modal characteristics, raising the risk of resonance due to multi-point elastic support in the flexible frame. This study incorporates frame flexibility and elastic support into a rigid-flexible coupling dynamic model of the drivetrain using multibody dynamics. The analysis of the drivetrain’s coupling vibration modes reveals that the first two torsional vibration natural frequencies are 5.63 Hz and 6.01 Hz, corresponding to the rear and front turbine drivetrains, respectively. The drivetrain exhibits three vibration modes: local vibration in either the front or rear turbine, coupled vibration in either turbine drivetrain, and coupled vibration between both turbines. The study concludes that frame flexibility redistributes modal energy across components, affecting the drivetrain’s natural characteristics.

In the entire life cycle of a wind turbine, the probability distribution of long-term wind speeds introduces randomness to the dynamic load on the wind turbine gearbox transmission system appear random, thereby affecting the accuracy of fatigue damage prediction. In this paper, a fatigue damage prediction method is proposed for the wind turbine gearbox transmission system with considering the characteristics of the long-term wind speed probability distribution. The approach involves assessing the short-term fatigue damage of gears in the transmission system of wind turbine gearbox based on an OpenFAST-SIMPACK combined simulation model built for high power offshore wind turbines. Subsequently, surrogate model technology is used to reconstruct the mapping relationship between “average wind speed, turbulence intensity, and short-term fatigue damage” enabling the prediction of long-term fatigue damage for the gears. The research results show that the low-speed sun gear in the wind turbine gearbox transmission system is prone to contact fatigue failure. Below the rated wind speed, the short-term fatigue damage of the low-speed sun gear correlates positively with the average wind speed, thereby increasing the uncertainty of long-term fatigue damage and elevating the risk of fatigue failure.