HyFatigue

The overall life prediction procedure of the wind turbine blades based on the MMF is depicted in Figure 1. The time varying loads are first calculated from the aerodynamic simulation tool such as the FAST or BLADED. The structural analysis is then performed using programs such as FEM tools, FOCUS or 3D-beam, providing the macro stress distribution. The fatigue prediction module based on the MMF is called HyFatigue. The HyBlade and HyFatige will be integrated with FOCUS and FEM tools (see Figure 2). The inputs and outputs will be compatible between the tools, including ultimate and spectrum loads. Various failure criteria such as PUCK FC and maximum failure strains are to be incorporated.

Figure 1. Fatigue life prediction procedure for wind turbine blades based on multi-scale approach.

Figure 2. Proposed link of HyFatigue with commercial softwares and our own programs

A fatigue prediction method should allow consideration of three factors: the multi-directionality, mean values of loads and damage accumulation. One of simplest method is to use Goodman diagram and Miner’s rule, which are explained in the IEC standard. However, this simple approach does not fully take into account the laminate sequences, leading to very conservative design. To achieve a more competitive design, we consider the detailed micro stress distribution of laminates with arbitrary ply angles. Then, it allows us reduce weight with confidence. As one of examples from the HyBlade and HyFatigue, Figure 3 shows the effects of mean values of the applied load on the fatigue life, calculated from the Hyblade together with HyFatigue.

Figure 3. Contour of fatigue damage indices of the wind turbine blades, calculated using the HyFatigue module.