Condition monitoring and fault diagnosis for wind turbine gearbox is significant to save operation and maintenance costs. However, strong interferences from high-speed parallel gears and background noises make fault detection of wind turbine planetary gearbox challenging. This paper addresses the fault diagnosis for wind turbine planetary ring gear, which is intractable for traditional spectral analysis techniques, since the fault characteristic frequency of planetary ring gear can be resulted from the revolving planet gears inducing modulations even in healthy conditions. The main contribution is to establish an adaptive empirical wavelet transform framework for fault-related mode extraction, which incorporates a novel meshing frequency modulation phenomenon to enhance the planetary gear related vibration components in wind turbine gearbox. Moreover, an adaptive Fourier spectrum segmentation scheme using iterative backward-forward search algorithm is developed to achieve adaptive empirical wavelet transform for fault-related mode extraction. Finally, fault features are identified from envelope spectrums of the extracted modes. The simulation and experimental results show the effectiveness of the proposed framework for fault diagnosis of wind turbine planetary ring gear. Comparative studies prove its superiority to reveal evident fault features and avoid the ambiguity from the planet carrier rotational frequency over ensemble empirical mode decomposition and spectral kurtosis.
In our solar system, planetary rings are found around all the giant planets, showing spectacular variety. Jupiter's thin ring system is composed mostly of dust. Saturn's rings are the largest and best studied, and the target of the NASA/ESA Cassini space mission that will begin orbiting Saturn in 2004. Its ring system consists of the broad A and B rings (separated by the Cassini Division) and the optically thinner C and D rings. Outside the main rings are the narrow 'braided' F ring and rings E and G. Uranus has ten narrow, sometimes eccentric rings and a family of dust bands. Neptune has three distinct rings (Galle, LeVervier, and Adams); the outermost Adams ring is patchy, with the thicker segments termed 'arcs.' All the ring systems have moons interspersed, which sculpt, collect, and release ring material. Moons are the likely parents of the present rings, ground down by meteorites and destroyed randomly to produce the relatively short-lived ring systems. Thus, we observe the natural stochastic results of birth and death processes when we examine the rings closely. Ring systems are relatively nearby and provide a natural laboratory for phenomena in flattened disks, including the nebula around our Sun that gave rise to the planets. Cassini will observe Saturn's rings and the numerous physical phenomena occurring within them close-up from 2004 to 2008, refining and possibly redefining our view of ring physics.
The -body ring problem is a classical problem that describes the motion of particle attracted by the gravitational field of primary bodies. These bodies are distributed in a planar ring configuration, that is, a central primary and primaries of equal mass located at the vertices of a regular polygon that is rotating on its own plane about the center with a constant angular velocity. If is large enough, this system models the motion of a small particle close to a planetary ring. The study of the escape of a particle from the potential well of this system requires the use of very accurate numerical integration methods, as we are interested in the integration of the problem over very long spans of time, and large values of . In this paper, we analyze the integration of the equations of motion of this problem by recurrent power series, and compare the resulting numerical solutions against some other methods.
Identifying the differences between the spectra or envelope spectra of a faulty signal and a healthy baseline signal is an efficient planetary gearbox local fault detection strategy. However, causes other than local faults can also generate the characteristic frequency of a ring gear fault; this may further affect the detection of a local fault. To address this issue, a new filtering algorithm based on the meshing resonance phenomenon is proposed. In detail, the raw signal is first decomposed into different frequency bands and levels. Then, a new meshing index and an MRgram are constructed to determine which bands belong to the meshing resonance frequency band. Furthermore, an optimal filter band is selected from this MRgram. Finally, the ring gear fault can be detected according to the envelope spectrum of the band-pass filtering result.
The Cassini spacecraft found a new and unique ring that shares the trajectory of Janus and Epimetheus, co-orbital satellites of Saturn. Performing image analysis, we found this to be a continuous ring. Its width is between 30% and 50% larger than previously announced. We also verified that the ring behaves like a firefly. It can only be seen from time to time, when Cassini, the ring, and the Sun are arranged in a particular geometric configuration, in very high phase angles. Otherwise, it remains "in the dark," invisible to Cassini's cameras. Through numerical simulations, we found a very short lifetime for the ring particles, less than a couple of decades. Consequently, the ring needs to be constantly replenished. Using a model of particle production due to micrometeorites impacts on the surfaces of Janus and Epimetheus, we reproduce the ring, explaining its existence and the "firefly" behavior.
Abell 70 (PN G038.1−25.4, hereafter A 70) is a planetary nebula known for its diamond ring appearance due to a superposition with a background galaxy. The previously unstudied central star is found to be a binary consisting of a G8IV-V secondary at optical wavelengths and a hot white dwarf at ultraviolet wavelengths. The secondary shows Ba ii and Sr ii features enhanced for its spectral type that, combined with the chromospheric Hα emission and possible 20-30 km s−1 radial velocity amplitude, firmly classifies the binary as a Barium star. The proposed origin of Barium stars is intimately linked to planetary nebulae (PNe) whereby wind accretion pollutes the companion with dredged-up material rich in carbon and s-process elements when the primary is experiencing thermal pulses on the asymptotic giant branch (AGB). A 70 provides further evidence for this scenario together with the other very few examples of Barium central stars. The nebula is found to have Type I chemical abundances with helium and nitrogen enrichment, which when combined with future abundance studies of the central star, will establish A 70 as a unique laboratory for studying s-process AGB nucleosynthesis. We also discuss guidelines to discover more binary central stars with cool secondaries in large orbits that are needed to balance our knowledge of binarity in PNe against the currently better studied post-common-envelope binary central stars.
We develop an axisymmetric diffusion model to describe radial density profiles in the vicinity of tiny moons embedded in planetary rings. Our diffusion model accounts for the gravitational scattering of the ring particles by an embedded moon and for the viscous diffusion of the ring matter back into the gap. With test particle simulations, we show that the scattering of the ring particles passing the moon is larger for small impact parameters than estimated by Goldreich & Tremaine and Namouni. This is significant for modeling the Keeler gap. We apply our model to the gaps of the moons Pan and Daphnis embedded in the outer A ring of Saturn with the aim to estimate the shear viscosity of the ring in the vicinity of the Encke and Keeler gap. In addition, we analyze whether tiny icy moons whose dimensions lie below Cassini's resolution capabilities would be able to explain the gap structure of the C ring and the Cassini division.