Thermal residual stresses have a major impact on the bond line fatigue of wind turbine blades, which can initiate tunneling cracks in the adhesive layer of the bond lines early in the operational life of the blade. This work investigates the simulation accuracy for predicting thermal residual stresses within a thick bond line. The trailing-edge bond line strip of a 34 m blade was modeled with classical laminated plate theory (CLT) on the one hand and with finite element (FE) plate models of different fidelities on the other. For the model benchmark, the thermal residual stresses were on the basis of a thermal simulation. These develop during the cooling after a typical curing cycle of a wind turbine blade manufacturing process. It was found that the analytical model on the basis of CLT was in good agreement with the plate models of higher fidelity. Additionally, a full 3D FE blade model was used to calculate the shape distortion and the thermal residual stresses. It was found that the analytical model, which did not take into account effects stemming from the whole blade structure, underestimated the full 3D FE model.
In this work the improved version of an engineering model which accounts for rotational augmentation effects by means of computational fluid dynamics (CFD) calibration is explored and discussed. Based on an analysis of the NREL Phase VI wind turbine, the novel modeling is presented, which uses as base line the formulation proposed by Chaviaropoulos and Hansen. The model is calibrated based on CFD simulations using OpenFOAM. The corresponding correction of the two dimensional polars is straightforward implemented within MoWiT, an in-house software for load calculation. The novel formulation results in improved lift and drag coefficients prediction in all considered cases, reducing the deviation with respect to the rotating CFD cases down to few percent. The optimal configuration including the correction for tip effects of Shen shows better agreements at the very tip of the blade. Furthermore the range of applicability for large wind turbine rotor blades based on a virtual 10MW rotor model is discussed.
For the first time, effects of polymer hardness on the abrasive wear resistance of organic coatings, designed for the corrosion protection of offshore wind power structures, are investigated at varying normal forces. The tests are performed with a specially designed Taber abrasion machine. The results reveal statistically significant effects of the polymer material Vickers hardness on the coating resistance against abrasive wear. With respect to the generic polymer type, the following ranking of the abrasive wear resistance is estimated: epoxy > polysiloxane > polyurethane. Thus, the most frequently applied top coat material (polyurethane) exhibits the lowest abrasive wear resistance and may not be capable to protect the underlaying epoxy-based intermediate coats. Polysiloxane would provide a longer protection against abrasive wear. The dominant material removal modes in all polymers are microcutting and microfracturing, whereby the former mode is dominant at lower normal forces, and the latter mode is dominant at higher normal forces. The power exponent of the classical power relationship VA infinity HP n depends on the mixture of the associated removal modes. The authors introduce a new transition parameter in order to rank the associated individual material removal processes. Based on an empirical-mathematical model, a two-parameter Weibull distribution function is derived, which links the transition parameter to the applied normal force. A two-dimensional graph (nomogram) is designed, where the different material removal modes are situated as functions of normal force and transition parameter.