PCA based health indicator for remaining useful life prediction of wind turbine gearbox

Fault prognosis of wind turbine gearbox has received considerable attention as it predicts the remaining useful life which further allows the scheduling of maintenance strategies. However, the studies related towards the RUL prediction of wind turbine gearbox are limited, because of the complexity of gearbox, acute changes in the operating conditions and non-linear nature of the acquired vibration signals. In this study, a health indicator is constructed in order to predict the remaining useful life of the wind turbine gearbox. Run to fail experiments are performed on a laboratory scaled wind turbine gearbox of overall gear ratio 1:100. Vibration signals are acquired and decomposed through continuous wavelet transform to obtain the wavelet coefficients. Various statistical features are computed from the wavelet coefficients which return form high-dimensional input feature set. Principal component analysis is performed to reduce the dimensionality and principal components (PCs) are computed from the input feature set. PC1 is considered as the health indicator and subjected to further smoothening by linear rectification technique. Exponential degradation model is fit to the considered health indicator and the model is able to predict the RUL of the gearbox with an error percentage of 2.73 %

Low-field spin dynamics of Cr₇Ni and Cr₇Ni-Cu-Cr₇Ni molecular rings as detected by μsR

Muon spin rotation measurements were used to investigate the spin dynamics of heterometallic Cr 7 Ni and Cr 7 Ni-Cu-Cr 7 Ni molecular clusters. In Cr 7 Ni the magnetic ions are arranged in a quasiplanar ring and interact via an antiferromagnetic exchange coupling constant J, while Cr 7 Ni-Cu-Cr7Ni is composed of two Cr7Ni linked by a bridging moiety containing one Cu ion, that induces an inter-ring ferromagnetic interaction J ≪ J. The longitudinal muon relaxation rate λ collected at low magnetic fields μ0H 5 K, while the shoulder presented by Cr 7 Ni can be reproduced by a BPP function that incorporates a single electronic characteristic time theoretically predicted to dominate for T < 5 K. The flattening of λ(T ) in Cr 7 Ni-Cu-Cr 7 Ni occurring at very low temperature can be tentatively attributed to field-dependent quantum effects and/or to an inelastic term in the spectral density of the electronic spin fluctuations