Browsing by Author "Wang, S."
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Item Active Cancellation of Vibration in Switched Reluctance Motor Using Mechanical Impulse Response Method(Institute of Electrical and Electronics Engineers Inc., 2019-05-13) Kimpara, M. L. M.; Wang, S.; Caicedo-Narvaez, Carlos Andres; Chen, Tianyu; Pinto, J.; Borges da Silva, L. E.; Moallem, M.; Fahīmī, Bābak; 0000-0001-8398-126X (Fahīmī, B); 0000-0002-1605-6944 (Cacedo-Narvaez, C); 0000-0001-7704-0770 (Chen, T); 56099860 (Fahīmī, B); Caicedo-Narvaez, Carlos Andres; Chen, Tianyu; Fahīmī, BābakVibration and acoustic noise are considered as major factors preventing the widespread use of switched reluctance motor (SRM) drives in industrial and commercial applications. In this paper, a new active vibration cancellation (AVC) strategy for radial vibration is proposed based on the optimal current switching instants. The mechanical impulse response method has been used to estimate the radial vibration of the stator and an optimization routine was developed to define the optimal instants for phase current switching in such a way that the resulting vibration would cancel the vibration caused by prior switching. Experimental verification was conducted on an 8/6 SRM and the results show significant reduction in the stator radial vibration which in turn contributes to reduction of acoustic noise.Item Generation of Lower Harmonic Magnetosonic Waves through Nonlinear Wave-Wave Interactions(Blackwell Publishing Ltd) Gao, X.; Sun, J.; Lu, Q.; Chen, Lunjin; Wang, S.; Chen, LunjinAlthough magnetosonic waves in the Earth's magnetosphere have been well understood by the linear theory, low harmonic magnetosonic waves, which often lack of free energy, can be unusually present. By employing a 1-D particle-in-cell simulation model, we have investigated the generation of those unusual lower harmonic magnetosonic waves in a plasma containing a proton ring distribution. In our simulation, the higher harmonic magnetosonic waves (from~9Ω_h to ~12Ω_h) are firstly excited due to the unstable proton ring, which can be well explained by the linear theory. Several lower harmonic magnetosonic waves (below 5Ω_h), which well separates away from the higher harmonics, soon appear in the system. Those lower harmonics, which do not have any positive linear growth rates, can be generated by a nonlinear mechanism. The bicoherence analysis demonstrates that there is a strong phase coupling among the unusual lower harmonic magnetosonic waves and the magnetosonic waves generated due to the proton ring, supporting the idea that the lower harmonic waves could be driven by the wave-wave couplings of the generated magnetosonic waves. This wave-wave coupling generation mechanism is further confirmed by another two simulations, where two or three pump magnetosonic waves are initially injected. The lower-frequency waves, that is, the fundamental wave and its second harmonic, are also successfully reproduced due to the nonlinear coupling of pump magnetosonic waves. Our simulations not only propose a potential generation mechanism of unusual lower harmonic magnetosonic waves in the Earth's magnetosphere, but also give some new insights on the evolution of magnetosonic spectra.Item A Parametric Study for the Generation of Ion Bernstein Modes from a Discrete Spectrum to a Continuous One in the Inner Magnetosphere. II. Particle-In-Cell Simulations(American Institute of Physics Inc, 2016-02-10) Sun, J.; Gao, X.; Lu, Q.; Chen, Lunjin (; Tao, X.; Wang, S.; 0000-0003-2489-3571 (Chen, L); Chen, LunjinIn this paper, we perform one-dimensional particle-in-cell simulations to investigate the properties of perpendicular magnetosonic waves in a plasma system consisting of three components: cool electrons, cool protons, and tenuous ring distribution protons, where the waves are excited by the tenuous proton ring distribution. Consistent with the linear theory, the spectra of excited magnetosonic waves can change from discrete to continuous due to the overlapping of adjacent unstable wave modes. The increase of the proton to electron mass ratio, the ratio of the light speed to the Alfven speed, or the concentration of protons with a ring distribution tends to result in a continuous spectrum of magnetosonic waves, while the increase of the ring velocity of the tenuous proton ring distribution leads to a broader one, but with a discrete structure. Moreover, the energization of both cool electrons and protons and the scattering of ring distribution protons due to the excited magnetosonic waves are also observed in our simulations, which cannot be predicted by the linear theory. Besides, a thermalized proton ring distribution may lead to the further excitation of several lower discrete harmonics with their frequencies about several proton gyrofrequencies.Item Two-Dimensional gcPIC Simulation of Rising-Tone Chorus Waves in a Dipole Magnetic Field(Blackwell Publishing Ltd, 2019-06-18) Lu, Q.; Ke, Y.; Wang, X.; Liu, K.; Gao, X.; Chen, Lunjin; Wang, S.; 0000-0003-2489-3571 (Chen, L); Chen, LunjinRising-tone chorus waves have already been successfully produced in a mirror magnetic field with the use of one- and two-dimensional particle-in-cell (PIC) simulations. However, in reality, the background magnetic field in the inner Earth's magnetosphere is a dipole magnetic field, unlike symmetric mirror fields. In this paper, with the two-dimensional (2-D) general curvilinear PIC (gcPIC) code, we investigate the generation of rising-tone chorus waves in the dipole magnetic field configuration. The plasma consists of three components: immobile ions, cold background, and hot electrons. In order to save computational resource, the topology of the magnetic field is roughly equal to that at L = 0.6 R_{E}, although the plasma parameters corresponding to those at L = 6 R_{E} (R_{E} is the Earth's radius) are used. Whistler mode waves are first excited around the magnetic equator by the hot electrons with a temperature anisotropy. The excited whistler mode waves propagate almost parallel and antiparallel to the background magnetic field in their source region, which is limited at ∣λ ∣ ≤ 3° (where λ is the magnetic latitude). When the waves leave from the source region and propagate toward high latitudes, both their amplitude and wave normal angle become larger. However, the group velocity of the waves is directed toward high latitudes almost along the magnetic field. During such a process, the waves have a frequency chirping, as shown by a rising tone in the frequency-time spectrogram. To our best knowledge, it is for the first time that rising-tone chorus are generated in a dipole magnetic field with a PIC simulation. ©2019. American Geophysical Union. All Rights Reserved.Item Two-Dimensional Particle-In-Cell Simulation of Magnetosonic Wave Excitation in a Dipole Magnetic Field(Blackwell Publishing Ltd) Chen, Lunjin; Sun, Jicheng; Lu, Q.; Wang, X.; Gao, X.; Wang, D.; Wang, S.; 0000-0002-5059-5394 (Sun, J); Chen, Lunjin; Sun, JichengThe excitation of magnetosonic waves in the meridian plane of a rescaled dipole magnetic field is investigated, for the first time, using a general curvilinear particle-in-cell simulation. Our simulation demonstrates that the magnetosonic waves are excited near the equatorial plane by tenuous ring distribution protons. The waves propagate nearly perpendicularly to the background magnetic field along both radially inward and outward directions. Different speeds of inward and outward propagation result in the asymmetrical distribution about the source region. The waves are accompanied by energization of both cool protons and electrons near the wave source region. The cool protons are heated perpendicularly, while the cool electrons can be heated in the parallel direction and also experience enhanced perpendicular drift at the presence of intense wave power. The implications of simulation results to the observations of magnetosonic waves and related particle heating in the inner magnetosphere are also discussed. ©2018 American Geophysical Union. All Rights Reserved.