•A 2-DOF model is established for edgewise vibration of a rotating blade with a TMD.•Two slightly different optimal frequency-tuning formulas have been derived using two different optimality ...criteria.•The obtained optimal TMD damping ratio is dependent on the rotor rotational speed.•Equal dynamic amplification does not guarantee equal modal damping ratio due to the rotational effect.•For realistic rotor rotational speeds, the two optimal frequency-tuning formulas lead to almost identical TMD parameters.
This paper presents the explicit formulas for optimal tuning of the tuned mass damper (TMD) for damping edgewise vibrations in rotating wind turbine blades. A 2-DOF model is first established for the rotating blade-TMD system, which acts as the basis for analytically deriving the optimal frequency-tuning and the optimal damping-tuning formulas. Two optimality criteria are considered, one based on equal dynamic amplification at two neutral frequencies and the other one based on equal modal damping ratio of the free vibration modes. As a result, two slightly different optimal frequency-tuning formulas are obtained. The formula for optimal TMD damping ratio is obtained by means of dynamic amplification analysis, and the optimal damping ratio turns out to be dependent on the rotor rotational speed. Comparison of the two optimal frequency-tuning formulas are performed in terms of the dynamic amplification curves and the root loci, using the NREL 5 MW wind turbine as the numerical example. For realistic rotor rotational speeds, the two optimal frequency-tuning formulas lead to almost identical TMD parameters.
Polymers reinforced with virgin carbon fibers (VCF) are being used to make spar caps of wind turbine (WT) blades and polymers with glass fibers (GF) to make skins of the blade components. Here, we ...assess the life cycle environmental performance of the hybrid blades with spar caps based on VCF and the shells and shear webs based on RCF (recycled CF) composites (RCF-hybrid). The production of the WT blades and associated reinforced polymers is assumed to occur in Sweden, with their uses and end-of-life management in the European region. The functional unit is equivalent to three blades in an offshore WT with the market incumbent blades solely based on the GF composite or the hybrid option. The RCF-hybrid blades offer 12–89% better environmental performance in nine out of 10 impact categories and 6–26% better in six out of 10 impact categories. The RCF-hybrid blades exhibit optimum environmental performance when the VCF manufacturing facilities are equipped with pollution abatement systems including regenerative thermal oxidizers to reduce ammonia and hydrogen cyanide emissions; spar caps are made using VCF epoxy composites through pultrusion and resin infusion molding, and the blade scrap is mechanically recycled at the end of life. The energy and carbon payback times for the RCF-hybrid blades were found to be 5–13% lower than those of the market incumbents.
Different aspects on the tool wear behavior of profiled vitrified microcrystalline alumina wheels during creep feed grinding of Ni alloy blade root were investigated. Experimental results indicate ...that the wheel peak regions had the higher wear values than the wheel valley regions by around 21.7%, 42.8%, 34.5%, in terms of the profile heights, circle radii and angles respectively. Furthermore, the wear flats, workpiece material adhesion, and the fractures of grains and bond bridges occurred in the wheel peak regions; while in the wheel valley regions, heavy wheel clogging, fractures of grains, and workpiece material adhesion were produced. Based on the experimental results, an analytical model with the average error of 17.3% to predict the wheel profile wear was finally developed.
•Profiled alumina wheel wear in creep feed grinding of Ni alloy blade root was examined.•The wheel peak region had the higher profile wear than the wheel valley region.•Workpiece speed and sliding length of individual grain greatly affected grinding ratio.•Wear flat and fracture occurred for wheel peak region while clogging for valley region.•Analytical model with the error of 17.3% was developed to predict wheel profile wear.
Thermal barrier coatings (TBCs) – as porous ceramic materials – have varying lifetimes because of their unstable mechanical properties and harsh working conditions. In this paper, a probabilistic ...approach to quantify the risk of interface spallation in TBCs by thermally grown oxide (TGO) growth and thermal mismatch, along with a lifetime prediction method based on the critical failure probability is proposed. First, a failure criterion for TBCs is set to determine a boundary between the failure and safe region. Second, parameters relating to failure, along with the stochastic characteristics of these parameters, are analysed thoroughly. Third, the failure probability is calculated. Finally, the lifetime of TBCs on turbine blades in a hot gas stream is predicted. Under furnace isothermal cycling, the predictive failure probabilities of TBCs are 0.1% (300 cycles), 1.5% (600 cycles), and 7.49% (1000 cycles). The experiment results for turbine blades are 1.03% (300 cycles), 1.73% (600 cycles), and 5.12% (1000 cycles). Under a hot gas stream, the maximum failure probabilities of TBCs after 200, 300, 500, and 1000 h are 40%, 45% 50%, and 70%, respectively. The lifetimes of TBCs are 273, 332, 406, and 523 h if the critical area ratio of the metal substrate exposed to the hot gas is 5%, 10%, 15%, and 20%, respectively.
•A probabilistic approach to quantify the risk of interface spallation in TBCs is proposed.•A lifetime prediction method based on the critical failure probability is developed.•A thermally grown oxide growth model is established.
The identification of particular types of damage in wind turbine blades using acoustic emission (AE) techniques is a significant emerging field. In this work, a 45.7-m turbine blade was subjected to ...flap-wise fatigue loading for 21 days, during which AE was measured by internally mounted piezoelectric sensors. This paper focuses on using unsupervised pattern recognition methods to characterize different AE activities corresponding to different fracture mechanisms. A sequential feature selection method based on a k-means clustering algorithm is used to achieve a fine classification accuracy. The visualization of clusters in peak frequency-frequency centroid features is used to correlate the clustering results with failure modes. The positions of these clusters in time domain features, average frequency-MARSE, and average frequency-peak amplitude are also presented in this paper (where MARSE represents the Measured Area under Rectified Signal Envelope). The results show that these parameters are representative for the classification of the failure modes.
Resin uptake plays a critical role in the stiffness‐to‐weight ratio of wind turbine blades in which sandwich composites are used extensively. This work examines the flexural properties of nominally ...half‐inch thick sandwich composites made with polyvinyl chloride (PVC) foam cores (H60 and H80; PSC and GPC) at several resin uptakes. We found that the specific flexural strength and modulus for the H80 GPC sandwich composites increase from 82.04 to 90.70 kN · m/kg and 6.03 to 7.13 MN · m/kg, respectively, with 11.0% resin uptake reduction, which stands out among the four core sandwich composites. Considering reaching a high stiffness‐to‐weight ratio while preventing resin starvation, 32% to 38% and 40% to 45% resin uptakes are adequate ranges for the H80 PSC and GPC sandwich composites, respectively. The H60 GPC sandwich composites have lower debonding toughness than H60 PSC due to stress concentration in the smooth side skin‐core interphase region. The ailure mode of the sandwich composites depends on the core stiffness and surface texture. The H60 GPC sandwich composites exhibit core shearing and bottom skin‐core debonding failure, while the H80 GPC and PSC sandwich composites show top skin cracking and core crushing failure. The findings indicate that an appropriate range of resin uptake exists for each type of core sandwich composite, and that within the range, a low‐resin uptake leads to lighter blades and thus lower cyclic gravitational loads, beneficial for long blades.
Abstract In order to improve the efficiency of high pressure cylinder of 50∼350MW steam turbine and reduce the manufacturing cost, a steam turbine blade profiles are designed. The numerical ...simulation and test study of the new blade profile are carried out, and the performance of the new blade profile with variable inlet angle and mach number is discussed, and the performance of the new blade profile is improved when applied to stage environment. The results show that the performance of variable inlet angle and variable mach number of the new blade profile is better than that of the original profile. The aerodynamic efficiency of the new blade profile is obviously better than that of the original profile. The blade loss of the new design profile is lower than the original profile, and the aerodynamic efficiency of the new design profile is obviously better than the original profile. The stage test results show that the efficiency of the new design profile increases by about 0.5% compared with that of the original profile.
Wind turbine blades are constantly submitted to different types of particles such as dirt, ice, etc., as well as all the different environmental parameters that affect the behaviour and efficiency of ...the energy generation system. These parameters can cause faults to the wind turbine blades, modifying their behaviour due, for example, to the turbulence. A new method is presented in this paper based on cross-correlations to determine the presence of delamination in the blades. The experiments were conducted in two real wind turbine blades to analyse the fault and non-fault blades using ultrasonic guided waves. Finally, the energy analysis of the signal based on wavelet transforms allowed to determine energies abrupt changes in the correlation of the signals and to locate the faults.
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