High torque density and low torque ripple are crucial for traction applications, which allow electrified powertrains to perform properly during start-up, acceleration, and cruising. High-quality ...anisotropic magnetic materials such as cold-rolled grain-oriented electrical steels can be used for achieving higher efficiency, torque density, and compactness in synchronous reluctance motors equipped with transverse laminated rotors. However, the rotor cylindrical geometry makes utilization of these materials with pole numbers higher than two more difficult. From a reduced torque ripple viewpoint, particular attention to the rotor slot pitch angle design can lead to improvements. This paper presents an innovative rotor lamination design and assembly using cold-rolled grain-oriented electrical steel to achieve higher torque density along with an algorithm for rotor slot pitch angle design for reduced torque ripple. The design methods and prototyping process are discussed, finite-element analyses and experimental examinations are carried out, and the results are compared to verify and validate the proposed methods.
Recent works 22,23,3,33 have shed light on the topological behavior of geodesic planes in the convex core of a geometrically finite hyperbolic 3-manifold M of infinite volume. In this paper, we focus ...on the remaining case of geodesic planes outside the convex core of M, giving a complete classification of their closures in M.
In particular, we show that the behavior is different depending on whether exotic roofs exist or not. Here an exotic roof is a geodesic plane contained in an end E of M, which limits on the convex core boundary ∂E, but cannot be separated from the core by a support plane of ∂E.
A necessary condition for the existence of exotic roofs is the existence of exotic rays for the bending lamination. Here an exotic ray is a geodesic ray that has a finite intersection number with a measured lamination L but is not asymptotic to any leaf nor eventually disjoint from L. We establish that exotic rays exist if and only if L is not a multicurve. The proof is constructive, and the ideas involved are important in the construction of exotic roofs.
We also show that the existence of geodesic rays satisfying a stronger condition than being exotic, phrased only in terms of the hyperbolic surface ∂E and the bending lamination, is sufficient for the existence of exotic roofs. As a result, we show that geometrically finite ends with exotic roofs exist in every genus. Moreover, in genus 1, when the end is homotopic to a punctured torus, a generic one (in the sense of Baire category) contains uncountably many exotic roofs.
Shales with a laminated structure typically exhibit inherent anisotropy and strong brittleness, resulting in complex failure patterns and fracture evolution during hydraulic fracturing. To ...investigate the fracturing mechanism and layer effect of Longmaxi shale from southwest China, a novel testing setup with a high-efficiency sealing method was developed for laboratory hydraulic fracturing, based on which a series of fracturing tests was conducted on shale samples under different confining pressures. The anisotropic mechanical behaviour due to the shale lamination effect was considered by drilling samples at seven different inclinations with reference to the bedding plane. The results showed apparent brittle failure characteristics and anisotropic phenomena both in strength and failure patterns. Three main failure patterns can be identified as split, split-bending and slip along the bedding plane. The corresponding fracture roughness was further analyzed by laser scanning, which shows that the slip mode with shale layer activation can provide a relatively smooth channel. Of particular interest is that anomalously high breakdown pressure, which fluctuates in the samples at different layer orientations and cannot be explained by conventional models, was also observed in our fracturing tests. Inspired by the nonlocal treatment of line stress criterion, an average tensile stress-based model by introducing an equivalent characteristic length was then proposed for interpreting such unusual breakdown pressures, and the inherent mechanism behind hydraulic fracturing was discussed. Comparison analysis showed that the proposed criterion not only predicts the testing data quite well, but can also be degenerated to conventional models in specific cases. The knowledge achieved in this study may provide practical implications for perforation design and breakdown pressure evaluation in field hydraulic fracturing operations.
Pyroclastic currents are catastrophic flows of gas and particles triggered by explosive volcanic eruptions. For much of their dynamics, they behave as particulate density currents and share ...similarities with turbidity currents. Pyroclastic currents occasionally deposit dune bedforms with peculiar lamination patterns, from what is thought to represent the dilute low concentration and fluid‐turbulence supported end member of the pyroclastic currents. This article presents a high resolution dataset of sediment plates (lacquer peels) with several closely spaced lateral profiles representing sections through single pyroclastic bedforms from the August 2006 eruption of Tungurahua (Ecuador). Most of the sedimentary features contain backset bedding and preferential stoss‐face deposition. From the ripple scale (a few centimetres) to the largest dune bedform scale (several metres in length), similar patterns of erosive‐based backset beds are evidenced. Recurrent trains of sub‐vertical truncations on the stoss side of structures reshape and steepen the bedforms. In contrast, sporadic coarse‐grained lenses and lensoidal layers flatten bedforms by filling troughs. The coarsest (clasts up to 10 cm), least sorted and massive structures still exhibit lineation patterns that follow the general backset bedding trend. The stratal architecture exhibits strong lateral variations within tens of centimetres, with very local truncations both in flow‐perpendicular and flow‐parallel directions. This study infers that the sedimentary patterns of bedforms result from four formation mechanisms: (i) differential draping; (ii) slope‐influenced saltation; (iii) truncative bursts; and (iv) granular‐based events. Whereas most of the literature makes a straightforward link between backset bedding and Froude‐supercritical flows, this interpretation is reconsidered here. Indeed, features that would be diagnostic of subcritical dunes, antidunes and ‘chute and pools’ can be found on the same horizon and in a single bedform, only laterally separated by short distances (tens of centimetres). These data stress the influence of the pulsating and highly turbulent nature of the currents and the possible role of coherent flow structures such as Görtler vortices. Backset bedding is interpreted here as a consequence of a very high sedimentation environment of weak and waning currents that interact with the pre‐existing morphology. Quantification of near‐bed flow velocities is made via comparison with wind tunnel experiments. It is estimated that shear velocities of ca 0·30 m.s−1 (equivalent to pure wind velocity of 6 to 8 m.s−1 at 10 cm above the bed) could emplace the constructive bedsets, whereas the truncative phases would result from bursts with impacting wind velocities of at least 30 to 40 m.s−1.
The adoption of high-performance soft magnetic material can be considered a possible way to respect the challenging design specifications for aerospace and automotive electrical machines. This paper ...presents an accurate noninvasive investigation of magnetic and energetic properties of cobalt-iron stator cores. In particular, the focus lies on the annealing processes aimed to maximize the magnetic saturation and the mechanical strength. Three cobalt-iron stator core samples coming from different annealing processes have been analyzed, both from the BH characteristics and losses viewpoints. Stator slot effects on the magnetic measurements have been investigated by finite-element method. A fringing effect correction factor to be applied on the measured BH curves is as well reported. In order to complete the experimental campaign analysis, micrographic analysis of the material structure is presented, as well as the iron losses separation coefficients.
The calcite shells, or tests, of foraminifera provide a window into Earth history because they are archived in most marine sediments and contain useful geochemical proxies for paleoceanography. ...Previous observations of diurnal heterogeneity in proxies like Mg/Ca demonstrate a complex relationship between environmental conditions and test composition. The causes for this diurnal banding and the potential impact for proxy interpretation in systems other than Mg/Ca have yet to be determined. Recently, Mg and Na in shells of the planktic foraminifer species Orbulina universa have been observed to be high at the location of the primary organic sheet (POS), i.e. the organic template upon which the calcite test is formed. Here we use time-of-flight secondary ion mass spectrometry (ToF-SIMS), a chemical and isotope mapping technique with a spatial resolution of 300 nm, to show that Na banding is a consistent feature in the tests of 45 individual cultured O. universa. This banding occurs in two distinct forms: (1) sharp Na bands associated with organic sheets that are embedded in the calcite test after chamber formation; and (2) regular, thicker, but lower-amplitude Na bands that are found throughout the test. We use the pattern of the first type of banding to indicate the extent and sequence of calcite growth during chamber formation. Specifically, we show that new chamber formation involves growth over the previous chamber in Orbulina bilobata, a morphotype of O. universa that develops a second partial spherical chamber attached to the primary sphere. This is consistent with a bilamellar model of foraminiferal growth. However, a SIMS mapping survey of the morphologically more complex Globigerina bulloides and Neogloboquadrina dutertrei suggests that the pattern of growth during chamber formation and the prevalence of different types of Na bands may be species-specific. The wide, repeating Na bands that occur throughout the test of O. universa generally occur in an inverse pattern with respect to Mg banding for the first few days of the foraminifer's life, but this pattern changes as the organism ages. We use the magnitude, timing, and coherency between Na and Mg bands to put constraints on various proposed mechanisms for banding, including antiport Mg2+-2Na+ exchange and kinetic growth rate effects.
In this article, we propose an analytical method to compute the eddy-current loss in nonlinear thick steel laminations (3-12 mm) by considering the return path of the eddy currents. Initially, a 2-D ...finite-element (FE) model is applied to segregate losses measured from toroidal material samples into hysteresis and eddy-current loss components to use them as reference. Afterward, a 2-D analytical time-domain model is proposed for the eddy currents based on the solution of the 2-D field problem. The time-domain model is then used to derive a simple frequency-domain eddy-current loss formulation for the sinusoidal flux density case with the inclusion of a skin-effect correction factor, which accounts for the nonlinearity of the material. Highly accurate results are obtained from the proposed model compared to FE reference results with a mean relative error of 5.1% in the nonlinear region.
In this study, the temperature influence on iron loss of non-oriented steel laminations is investigated. The iron loss variation under different flux densities, frequencies and temperatures is ...systematically measured and analysed by testing two typical non-oriented steel laminations, V300-35 A and V470-50 A. The iron loss variation with temperature is almost linear in the typical operating temperature range of electrical machines. Furthermore, the varying rate of iron loss with temperature varies with flux density and frequency. A coefficient which can fully consider the temperature influence is introduced to the existing iron loss model to improve the iron loss prediction accuracy. The predicted and measured results show that the temperature influence on the iron loss can be effectively considered by utilising the improved model, i.e. the prediction accuracy of the improved iron loss model remains constant, even when the temperature varies significantly. A potential simplification of this improved model is also discussed in this study.
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