| 1. |
- Huang, Xiaoyan, et al.
(författare)
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A Robust Deadbeat Predictive Current Control Method for IPMSM
- 2024
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Ingår i: IEEE Transactions on Transportation Electrification. - : Institute of Electrical and Electronics Engineers (IEEE). - 2332-7782. ; , s. 1-1
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Tidskriftsartikel (refereegranskat)abstract
- Deadbeat predictive current control (DPCC) demonstrates excellent dynamic performance. However, in practical applications, its effectiveness is degraded by parameter mismatches and inverter nonlinearities. Among the various improvement methods addressed for these issues, incremental model-based DPCC (I-DPCC) achieves zero static current error with a low computational burden but suffers from instability under parameter variation, especially when applied to interior permanent magnet synchronous motors (IPMSMs). In this paper, a robust I-DPCC (RI-DPCC) combining feedforward control is proposed for IPMSM, with an adjustable stable operation range that can be extended to twice the actual inductance or even larger. To further improve the robustness of dynamic performance, an inductance correction method is introduced to track the variation of inductance during dynamic processes. Thus, the current commands can be well tracked even when significant inductance variation occurs. With sufficient voltage margin, the dynamic processes under mismatched inductance can be shortened to four control periods. Finally, experimental results validate the effectiveness of the proposed method.
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| 2. |
- Li, Tongkuai, et al.
(författare)
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Kelvin-Helmholtz Waves and Magnetic Reconnection at the Earth's Magnetopause Under Southward Interplanetary Magnetic Field
- 2023
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Ingår i: Geophysical Research Letters. - : American Geophysical Union (AGU). - 0094-8276 .- 1944-8007. ; 50:20
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Tidskriftsartikel (refereegranskat)abstract
- We present Magnetospheric Multiscale (MMS) observations of a K-H wave event under southward IMF conditions, accompanied by ongoing magnetic reconnection. The nonlinear K-H waves are characterized by quasi-periodic fluctuations, the presence of low-density and high-speed ions, and variations in the boundary normal vectors at both the leading and trailing edges. Our observations reveal clear evidence of on-going magnetic reconnection through the identification of Alfvenic ion jets and the escape of energetic magnetospheric electrons. Among the 36 magnetopause current-sheet crossings in this event, 19 exhibit unambiguous signatures of reconnection at both the leading (7) and trailing (12) edges. Notably, the estimated current-sheet thicknesses at both edges are comparable to the ion-inertial scale, confirming the compression effect resulting from the large-scale evolution of the K-H waves. The reconnection jets potentially contribute to the suppression of K-H growth through boundary-layer broadening and the development of complex flow and magnetic field patterns.
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| 3. |
- Patel, Vivek, 1983-, et al.
(författare)
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Enhancing grain refinement and corrosion behavior in AZ31B magnesium alloy via stationary shoulder friction stir processing
- 2022
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Ingår i: Journal of Materials Research and Technology. - : Elsevier. - 2238-7854. ; 17, s. 3150-3156
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Tidskriftsartikel (refereegranskat)abstract
- Stationary shoulder friction stir processing (SSFSP) in thick AZ31B magnesium alloy was performed to refine the microstructure followed by evaluating corrosion behavior. The use of stationary shoulder exhibited low heat input and small temperature gradient across the thickness of stir zone (SZ). Moreover, smooth surface morphology with little flash was obtained. The probe-dominated SZ developed fine equiaxed uniform grain structure across the thickness of SZ, which in turn increased the corrosion resistance of SSFSPed alloy as compared to BM. SSFSPed alloy surface confirm uniform corrosion behavior with mud cracking and intergranual corrosion patterns instead of pitting corrosion in BM. This improvement in corrosion was attributed to homogenization of magnesium alloy microstructure by using low-heat-input stationary shoulder tool.
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| 4. |
- Alm, Love, et al.
(författare)
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MMS Observations of Multiscale Hall Physics in the Magnetotail
- 2019
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Ingår i: Geophysical Research Letters. - : AMER GEOPHYSICAL UNION. - 0094-8276 .- 1944-8007.
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Tidskriftsartikel (refereegranskat)abstract
- We present Magnetospheric Multiscale mission (MMS) observations of Hall physics in the magnetotail, which compared to dayside Hall physics is a relatively unexplored topic. The plasma consists of electrons, moderately cold ions (T similar to 1.5 keV) and hot ions (T similar to 20 keV). MMS can differentiate between the cold ion demagnetization region and hot ion demagnetization regions, which suggests that MMS was observing multiscale Hall physics. The observed Hall electric field is compared with a generalized Ohm's law, accounting for multiple ion populations. The cold ion population, despite its relatively high initial temperature, has a significant impact on the Hall electric field. These results show that multiscale Hall physics is relevant over a much larger temperature range than previously observed and is relevant for the whole magnetosphere as well as for other astrophysical plasma.
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| 5. |
- André, Mats, et al.
(författare)
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Magnetic reconnection and modification of the Hall physics due to cold ions at the magnetopause
- 2016
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Ingår i: Geophysical Research Letters. - : Blackwell Publishing. - 0094-8276 .- 1944-8007. ; 43:13, s. 6705-6712
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Tidskriftsartikel (refereegranskat)abstract
- Observations by the four Magnetospheric Multiscale spacecraft are used to investigate the Hall physics of a magnetopause magnetic reconnection separatrix layer. Inside this layer of currents and strong normal electric fields, cold (eV) ions of ionospheric origin can remain frozen-in together with the electrons. The cold ions reduce the Hall current. Using a generalized Ohm's law, the electric field is balanced by the sum of the terms corresponding to the Hall current, the vxB drifting cold ions, and the divergence of the electron pressure tensor. A mixture of hot and cold ions is common at the subsolar magnetopause. A mixture of length scales caused by a mixture of ion temperatures has significant effects on the Hall physics of magnetic reconnection.
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| 6. |
- Baghdadchi, Amir, 1994-, et al.
(författare)
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Ductilization and grain refinement of AA7075-T651 alloy via stationary shoulder friction stir processing
- 2023
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Ingår i: Journal of Materials Research and Technology. - 2238-7854 .- 2214-0697. ; 27, s. 5360-5367
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Tidskriftsartikel (refereegranskat)abstract
- This study investigates the microstructural evolution, mechanical properties, and fracture behavior of AA7075-T651 aluminium alloy subjected to stationary shoulder friction stir processing (SSFSP). SSFSP samples were produced at three different rotational speeds in a range of 600–1000 rpm. The results reveal that SSFSP leads to a uniform grain refinement within the Stir Zone (SZ), reducing the grain size to approximately 2–3 μm from the initial 15 μm in the base material (BM) irrespective of the probe rotational speeds. After SSFSP, the elongation increased by over 50 % at the cost of 10 % reduction in the ultimate tensile strength for all samples. It was worth to note that variations in tool rotational speed exhibited minimal influence on the microstructure and mechanical properties, offering wide range of probe rotational speeds. This could be attributed to the use of non-rotating shoulder with prob dominated microstructure in the SZ. Fractographic analysis confirmed the ductile nature of fractures, revealing development of fine dimples due to grain refinement. This work underscores the effectiveness of SSFSP in achieving significant grain refinement followed by drastic increase in ductility, which offers valuable insights for using stationary shoulder at wider range of rotational speed.
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| 7. |
- Das, Subhash, et al.
(författare)
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Experimental investigation on welding of 2.25 Cr-1.0 Mo steel with regulated metal deposition and GMAW technique incorporating metal-cored wires
- 2021
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Ingår i: Journal of Materials Research and Technology. - : Elsevier Editora Ltda. - 2238-7854. ; 15, s. 1007-1016
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Tidskriftsartikel (refereegranskat)abstract
- The regulated Metal Deposition (RMD) process is a variant of the gas metal arc welding process (GMAW), which was developed to effectively control the metal transfer in the short-circuiting mode. The process is fundamentally a modified short-circuit GMAW process wherein a uniform droplet deposition, making it easier for the welder to control the puddle and hence achieve an enhanced quality of welded joints. In the present study, the RMD technique has been established for the low alloy steel grade 2.25 Cr - 1.0 Mo particularly for depositing the root pass on a 10 mm thick joint. In addition to this, the RMD technique is attempted with metal-cored wires to enhance the deposition rates and hence productivity. The joint fill-up is further attempted with the GMAW technique using metal-cored wires and analysed. The weldments were subjected to post-weld heat treatment followed by mechanical and metallurgical characterization. Mechanical characterization such as tensile properties, impact properties, bend test as well as all weld tensile properties of the weld joint was evaluated and found to be acceptable. The ductile to brittle transition temperature (DBTT) testing was carried out by breaking series of impact specimen till negative temperatures. The DBTT temperature for the weld joint was found well below -30°C which indicated the strength and soundness of the welded joint. Optical microscopy and scanning electron microscopy was carried out for and favourable results were achieved in microanalysis. The study proposes the use of metal-cored wires for potential applications in the welding of high thickness joints for enhancing the overall productivity.
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| 8. |
- Dokgo, Kyunghwan, et al.
(författare)
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High-Frequency Waves Driven by Agyrotropic Electrons Near the Electron Diffusion Region
- 2020
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Ingår i: Geophysical Research Letters. - : AMER GEOPHYSICAL UNION. - 0094-8276 .- 1944-8007. ; 47:5
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Tidskriftsartikel (refereegranskat)abstract
- National Aeronautics and Space Administration's Magnetosphere Multiscale mission reveals that agyrotropic electrons and intense waves are prevalently present in the electron diffusion region. Prompted by two distinct Magnetosphere Multiscale observations, this letter investigates by theoretical means and the properties of agyrotropic electron beam-plasma instability and explains the origin of different structures in the wave spectra. The difference is owing to the fact that in one instance, a continuous beam mode is excited, while in the other, discrete Bernstein modes are excited, and the excitation of one mode versus the other depends on physical input parameters, which are consistent with observations. Analyses of dispersion relations show that the growing mode becomes discrete when the maximum growth rate is lower than the electron cyclotron frequency. Making use of particle-in-cell simulations, we found that the broadening angle Delta in the gyroangle space is also an important factor controlling the growth rate. Ramifications of the present finding are also discussed. Plain Language Summary Magnetospheric Multiscale mission has observed magnetic reconnection process, which converts magnetic energy to kinetic energy of charged particles. Extremely rapid time scale data reveal that electron scale high-frequency waves exist near the electron diffusion region of magnetic reconnection. Recently, two different types of waves observed; one is discrete electron-Bernstein waves, and the other is continuous beam modes. In this study, we formulated a unified theory for both types of waves. Comparing Magnetosphere Multiscale observations, the theory, and particle-in-cell simulations, this study shows that the same cause (agyrotropic electrons) can make two different wave structures depending on plasma parameters. The condition that the maximum growth rate of instabilities equals the electron cyclotron frequency can be considered as a threshold of the transition from discrete electron Bernstein waves to continuous beam modes.
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| 9. |
- Dokgo, Kyunghwan, et al.
(författare)
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The Effects of Upper-Hybrid Waves on Energy Dissipation in the Electron Diffusion Region
- 2020
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Ingår i: Geophysical Research Letters. - : AMER GEOPHYSICAL UNION. - 0094-8276 .- 1944-8007. ; 47:19
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Tidskriftsartikel (refereegranskat)abstract
- Using a two-dimensional particle-in-cell simulation, we investigate the effects and roles of upper-hybrid waves (UHW) near the electron diffusion region (EDR). The energy dissipation via the wave-particle interaction in our simulation agrees withJ center dot E(')measured by magnetospheric multiscale (MMS) spacecraft. It means that UHW contributes to the local energy dissipation. As a result of wave-particle interactions, plasma parameters which determine the larger-scale energy dissipation in the EDR are changed. They-directional current decreases while the pressure tensorP(yz)increases/decreases when the agyrotropic beam density is low/high, where(x, y, z)-coordinates correspond the(L, M, N)-boundary coordinates. Because the reconnection electric field comes from- partial differential P-yz/ partial differential z, our result implies that UHW plays an additional role in affecting larger-scale energy dissipation in the EDR by changing plasma parameters. We provide a simple diagram that shows how the UHW activities change the profiles of plasma parameters near the EDR comparing cases with and without UHW.
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| 10. |
- Harwani, Deepika, et al.
(författare)
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Developing superplasticity in magnesium alloys with the help of friction stir processing and its variants : A review
- 2021
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Ingår i: Journal of Materials Research and Technology. - : Elsevier. - 2238-7854. ; 12, s. 2055-2075
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Tidskriftsartikel (refereegranskat)abstract
- Friction stir processing (FSP), an adaption of the solid-state joining process friction stir welding (FSW), is now a widely recognized severe plastic deformation (SPD) technique. It induces microstructural refinement in the metallic materials which enhances their formability and other mechanical properties. Dynamic recrystallization occurs during the stirring phase which leads to reduction in the grain size and texture modification. Breaking up of the intermetallics and precipitates with their homogeneous distribution in the matrix is also accompanied. This further improves the material's ability to attain maximum ductility during plastic deformation at higher temperatures, resulting in very large uniform elongations (>200%) termed as ‘superplasticity’. Optimization of FSP parameters activates superplastic behaviour in different magnesium alloys at low temperatures and high strain rates. It has become the focal point of the recent researches owing to its huge potential in the light-weight structural applications. In addition to the essential aspects of superplasticity, this article highlights the major explorations in the area of superplasticity of magnesium alloys using FSP method and it's recently developed variants.
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