The Experts below are selected from a list of 168 Experts worldwide ranked by ideXlab platform
Tianyang Wang - One of the best experts on this subject based on the ideXlab platform.
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meshing frequency modulation assisted empirical wavelet transform for fault diagnosis of wind turbine Planetary Ring gear
Renewable Energy, 2019Co-Authors: Yun Kong, Tianyang WangAbstract:Abstract 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.
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fault diagnosis for wind turbine Planetary Ring gear via a meshing resonance based filteRing algorithm
Isa Transactions, 2017Co-Authors: Tianyang WangAbstract: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.
Ove Havnes - One of the best experts on this subject based on the ideXlab platform.
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The Charging of Planetary Rings
Space Science Reviews, 2008Co-Authors: A. L. Graps, Geraint H. Jones, A. Juhasz, Mihaly Horanyi, Ove HavnesAbstract:This chapter will review what is known about the charging of Planetary Rings, in particular the sum of the individual currents from the time-varying charge dQ/dt, of the Planetary Ring particle. For the smallest Ring particles, in addition to checking the plasma conditions for the charging currents, one must consider if collective effects in the Ring environment are relevant. Two Planetary Ring environments that have held a strong interest for Ring scientists in the last two decades are Saturn’s spokes in the B Ring and the environment of Saturn’s E Ring. Two sections of this chapter will describe these Planetary Ring charging environments in detail. Finally, we describe two charging effects that demonstrate areas of future studies while providing fresh examples of the intriguing effects from Planetary Ring charging processes.
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Low frequency dust wave modes in Planetary Rings
Planetary and Space Science, 2000Co-Authors: F Li, Ove HavnesAbstract:Abstract The effects of gravity are taken into consideration for low frequency wave modes in a Planetary Ring. The electrons and ions are considered to be magnetized and corotate with the planet, while the dust grains are unmagnetized. Under the action of gravity the dust particles oscillate normal to the Ring plane and move around the planet on Keplerian orbits. Two wave modes of low frequency in such dusty plasma, propagating along the Ring in the azimuthal direction, have been analyzed based on the susceptibilities derived from the kinetic theory. The first is a gravity-drift wave which is found as an instability in Planetary Rings. The instability exists in a limited space region around the synchronous orbit. Grains of small sizes are most likely to produce the instability, and the unstable wavelength increases with the distance from the synchronous orbit. This instability could be of some importance for the evolution of spokes in Saturn’s Rings. The second is a dust-magnetosonic wave in the gravity-influenced dust plasma of the Ring. This mode has different dispersion and polarization character than a magnetosonic wave in an electron–ion plasma. A two-steam instability in the Ring which can generate a dust-magnetosonic wave has also been analyzed.
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probing the properties of Planetary Ring dust by the observation of mach cones
Journal of Geophysical Research, 1995Co-Authors: Ove Havnes, Frank Melandso, T Aslaksen, T W Hartquist, F Li, G E Morfill, Tore NitterAbstract:Compressive dust acoustic waves can be excited in dusty plasmas. Big boulders in Planetary Rings move at the Keplerian velocity, while smaller dust particles move at a slightly different velocity due to the action of the Lorentz force. If the difference in velocity Δυ is larger than the dust acoustic wave velocity, αd, a wake will be formed with an opening angle of 2θ where sin θ = |αd/Δυ|. The discovery of wakes and the measurement of their opening angles by the space experiment Cassini to Saturn will yield added information on the dusty plasma conditions in regions through which Cassini will not pass. We find that in some regions the waves that are excited by the boulders may be weak because a large fraction of the interacting dust is absorbed rather than deflected by the boulder. For a given dust size the most favourable conditions for the observations of wakes exist in two fairly narrow regions, one inside and one outside the corotation radius. The favorable regions are closest to the corotation radius for the smallest dust particles and progressively further away for larger dust particles.
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Dynamics of dust in a plasma sheath and injection of dust into the plasma sheath above Moon and asteroidal surfaces
Earth Moon and Planets, 1992Co-Authors: Tore Nitter, Ove HavnesAbstract:We have examined single dust particle dynamics in a plasma sheath near the surface of solid bodies in space, consideRing conditions which resemble those of Planetary system bodies, when photoelectric effect can be neglected. The forces on the dust particles are assumed to be from the electric field in the sheath and from gravitation only. As the dust particles will charge negatively in the sheath, these forces will act in opposite directions and may balance. The charge delay of a moving dust particle is responsible for many of the interesting dynamical properties, and we show that for a stationary plasma, dust motion is unstable to about one Debye length out from the surface of the solid body. This part of the sheath will therefore be devoid of dust particles as they will either fall down, escape completely from the solid body or collect and make damped oscillations at stable positions in the outer part of the sheath. With increasing plasma bulk speed towards the surface, the inner unstable part of the sheath will decrease in thickness. The sources for the dust in the sheath are assumed to be mainly ejecta from meteorites and micrometeorites, but may also, for the smallest solid bodies, be from electrostatic levitation of very small dust particles. We have for different sizes of solid bodies calculated the sizes of ejecta that can be ‘floated’ in the sheath. For the solar wind plasma, the suspended dust particles range from less than 1 Μm for the Moon to about 80 Μm for an asteroid with radius 1 km. These particles create a ‘dust atmosphere’. The results in this paper hold when the dust particle density is so low that the charges on the dust particles do not contribute significantly to the total space charge; a higher density will lead to a modification of the sheath. Our calculations show that ejecta below a certain size will be accelerated in the sheath and totally escape from the body even if they have near zero initial vertical velocity, while ejecta above this size will need a much larger velocity to escape. This is especially significant for the small solid bodies (radius of order km and less) which will therefore act as important sources of micronsized dust. This could be of significance for the dust production and the size distribution of dust in Planetary Ring systems.
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on dust charges and plasma potentials in a dusty plasma with dust size distribution
Journal of Geophysical Research, 1990Co-Authors: Ove Havnes, Torsten K Aanesen, Frank MelandsoAbstract:The authors have reconsidered the question of charges on dust particles and local potential of a collection of dust embedded in a plasma. Distribution of dust sizes and photoelectric effects are included. They show that the existence of small undetected dust can have a considerable effect on the charges in, for example, a Planetary Ring. They give simple rational function approximations to facilitate the calculations of dust charges and cloud potentials. The results are given for different ions and ratios between photoelectron and plasma electron fluxes.
Hiroshi Daisaka - One of the best experts on this subject based on the ideXlab platform.
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N -body Simulations of Planetary Rings
Symposium - International Astronomical Union, 2016Co-Authors: Hiroshi DaisakaAbstract:We present the formation and evolution of a structure in particles obtained from a local N -body simulation of a dense Planetary Ring like Saturn's Ring. Our simulations show in a particle system the spontaneous formation of a spatial structure like wakes, clumps, and a structure which could be induced by the viscous overstability. Such a formation depends on parameters characterizing a Ring system: the wake is likely to form in Saturn's Ring and the existence of the wake is consistent with observations. The viscous overstability would be a good candidate for the explanation of subRing structures in the Ring.
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viscosity in a dense Planetary Ring with self gravitating particles
Icarus, 2001Co-Authors: Hiroshi Daisaka, Hidekazu TanakaAbstract:We have investigated the viscosity (the angular momentum flux) in dense, self-gravitating particle disks such as Saturn's main Ring, by performing local N-body simulations. Viscosity could play important roles in evolution and structure formation of Planetary Rings. The Ring's viscosity has been investigated with both theoretical and numerical approaches (e.g., Goldreich and Tremaine, 1978, Icarus34, 227–239; Wisdom and Tremaine, 1988, Astron. J.95, 925–940). However, these studies mainly considered systems including physical collisions of particles but not mutual gravitational interactions. Local N-body simulations by Salo (1995, Icarus117, 287–312) and Daisaka and Ida (1999, Earth, Planet Space51, 1195–1213) showed that a wake-like structure and clumps of particles are formed by the self-gravitational instability and that in such situations coherent motion of particles is dominant rather than random motion, which leads to an increase in radial velocity dispersion of particles. The wake structure and associated coherent motion are considered to affect the Ring viscosity significantly. Our simulation in this paper shows that the viscosity is strongly enhanced by the wakes. When the wake structure strongly develops, the coherent motion considerably enhances the translational viscosity, which was usually referred to as a local component in previous studies, and the effective viscosity is dominated by both gravitational torque due to the wake structure and the enhanced translational viscosity. We also find that in the presence of the wakes, the viscosity ν is given as ν⋍CG2Σ2/Ω30, where G, Σ, and Ω0 are the gravitational constant, the surface mass density of a Ring, and the angular velocity, respectively. The non-dimensional correction factor C depends on the distance from the central planet. For example, C⋍6–20 for Saturn's B-Ring. The effects of the enhanced viscosity on the structure and evolution of Saturn's main Ring are also discussed.
Tore Nitter - One of the best experts on this subject based on the ideXlab platform.
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probing the properties of Planetary Ring dust by the observation of mach cones
Journal of Geophysical Research, 1995Co-Authors: Ove Havnes, Frank Melandso, T Aslaksen, T W Hartquist, F Li, G E Morfill, Tore NitterAbstract:Compressive dust acoustic waves can be excited in dusty plasmas. Big boulders in Planetary Rings move at the Keplerian velocity, while smaller dust particles move at a slightly different velocity due to the action of the Lorentz force. If the difference in velocity Δυ is larger than the dust acoustic wave velocity, αd, a wake will be formed with an opening angle of 2θ where sin θ = |αd/Δυ|. The discovery of wakes and the measurement of their opening angles by the space experiment Cassini to Saturn will yield added information on the dusty plasma conditions in regions through which Cassini will not pass. We find that in some regions the waves that are excited by the boulders may be weak because a large fraction of the interacting dust is absorbed rather than deflected by the boulder. For a given dust size the most favourable conditions for the observations of wakes exist in two fairly narrow regions, one inside and one outside the corotation radius. The favorable regions are closest to the corotation radius for the smallest dust particles and progressively further away for larger dust particles.
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Dynamics of dust in a plasma sheath and injection of dust into the plasma sheath above Moon and asteroidal surfaces
Earth Moon and Planets, 1992Co-Authors: Tore Nitter, Ove HavnesAbstract:We have examined single dust particle dynamics in a plasma sheath near the surface of solid bodies in space, consideRing conditions which resemble those of Planetary system bodies, when photoelectric effect can be neglected. The forces on the dust particles are assumed to be from the electric field in the sheath and from gravitation only. As the dust particles will charge negatively in the sheath, these forces will act in opposite directions and may balance. The charge delay of a moving dust particle is responsible for many of the interesting dynamical properties, and we show that for a stationary plasma, dust motion is unstable to about one Debye length out from the surface of the solid body. This part of the sheath will therefore be devoid of dust particles as they will either fall down, escape completely from the solid body or collect and make damped oscillations at stable positions in the outer part of the sheath. With increasing plasma bulk speed towards the surface, the inner unstable part of the sheath will decrease in thickness. The sources for the dust in the sheath are assumed to be mainly ejecta from meteorites and micrometeorites, but may also, for the smallest solid bodies, be from electrostatic levitation of very small dust particles. We have for different sizes of solid bodies calculated the sizes of ejecta that can be ‘floated’ in the sheath. For the solar wind plasma, the suspended dust particles range from less than 1 Μm for the Moon to about 80 Μm for an asteroid with radius 1 km. These particles create a ‘dust atmosphere’. The results in this paper hold when the dust particle density is so low that the charges on the dust particles do not contribute significantly to the total space charge; a higher density will lead to a modification of the sheath. Our calculations show that ejecta below a certain size will be accelerated in the sheath and totally escape from the body even if they have near zero initial vertical velocity, while ejecta above this size will need a much larger velocity to escape. This is especially significant for the small solid bodies (radius of order km and less) which will therefore act as important sources of micronsized dust. This could be of significance for the dust production and the size distribution of dust in Planetary Ring systems.
Yun Kong - One of the best experts on this subject based on the ideXlab platform.
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meshing frequency modulation assisted empirical wavelet transform for fault diagnosis of wind turbine Planetary Ring gear
Renewable Energy, 2019Co-Authors: Yun Kong, Tianyang WangAbstract:Abstract 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.