In this work, a formulation is developed within the phase field method for modeling interactions between interfacial damage and bulk brittle cracking in complex microstructures. The method is ...dedicated to voxel-based models of highly complex microstructures, as obtained from X-ray microtomography images. A smoothed displacement jump approximation is introduced by means of level-set functions to overcome the issue of pixelized interfaces in voxel-based models. A simple technique is proposed to construct the level-set function in that case. Compared to recent work aiming at modeling cohesive cracks within the phase field method, our framework differs in several points: the formulation is such that interfaces are not initially damaged; no additional variables are required to describe the discontinuities at the interface and fatigue cracks can be modeled. The technique allows interaction between bulk and interface cracks, e.g. nucleation from interfaces and propagation within the matrix, and for arbitrary geometries and interactions between cracks. Several benchmarks are presented to validate the model. The technique is illustrated through numerical examples involving complex microcracking in X-ray CT image-based models of concrete microstructures.
In this paper, switched flux permanent magnet (SFPM) machines are analyzed from the perspective of the air-gap field harmonics. It is found that the modulation of the salient rotor to PM and armature ...reaction fields in SFPM machines is similar to that of the iron pieces to those fields in the magnetic gear and magnetically geared machine. The magnetic gearing effect is analyzed in SFPM machines with different stator/rotor pole combinations, winding configurations, and stator lamination segment types by a simple magnetomotive force-permeance model, and validated by finite-element (FE) analysis. Different from fractional-slot surface-mounted PM machines in which the working air-gap field harmonic generates 95% of the average electromagnetic torque, 95% of the average electromagnetic torque in SFPM machines having ps stator pole pairs and n r rotor poles are contributed by several dominating field harmonics, i.e., rotating ones with |kn r ± (2i - 1)p s | pole pair (k = 1, i = 1, 2, 3) and static ones with (2i - 1)ps pole pair (i = 1, 2, 3). The FE predicted average static torques in SFPM machines are validated by measurements on prototype machines.
In this paper, the torque production of fractional-slot concentrated-winding (FSCW) permanent-magnet synchronous machines (PMSMs) is analyzed from the perspective of the air-gap field harmonics ...modulation accounting for slotting effect. It is found that the average torque of FSCW PMSM is produced by both the principle of conventional PMSM and the magnetic gearing effect. A finite-element analysis (FEA) based equivalent current sheet model and harmonic restoration method is first used in FSCW PM machines with different slot-pole number combinations to quantify the respective contribution of the conventional PMSM and the magnetic gearing effect to the average torque. The influence of slot opening on the magnetic gearing effect, cogging torque, and torque ripple is analyzed. The results show that the magnetic gearing effect makes a nonignorable contribution to the average torque when a large slot opening stator is used. The expression of the gear ratio in FSCW PMSMs is derived. The influence of gear ratio on the contribution of the magnetic gearing effect to the total torque is investigated by FEA. The FEA-predicted torques are validated by experiments on the prototypes.
Due to the fixed and limited sampling period in the real-time system, three-phase permanent-magnet synchronous machine (PMSM) drives using switching-table-based direct torque control (ST-DTC) usually ...suffer from steady-state error and ripple of torque. For the case of the dual three-phase system that has been widely investigated recently, the harmonic currents inevitably occur, which can be regarded as the third issue. This harmonic currents lead to the increase of losses and the decrease of system efficiency. Previous literature has addressed the aforementioned issues but only deals with either the torque ripple issues or harmonic currents. Therefore, this paper first introduces two types of synthetic vectors, which can reduce the harmonic currents effectively, as well as the most suitable switching sequences. Then, a modified five-level torque regulator has been proposed to improve the torque performance. With the proposed method, not only the harmonic currents have been suppressed, but also the steady-state error and ripple of torque can be considerably reduced, whereas the merits of classical ST-DTC, such as simple structure and excellent dynamic performance, are preserved. The experimental results validate the effectiveness of the proposed strategy.
In this paper, stator/rotor pole combinations, winding configurations, and electromagnetic performance of novel variable flux reluctance machines (VFRMs), which employ a doubly salient structure ...similar to switched reluctance machines (SRMs) but with stator-located dc field windings, are investigated. VFRMs with 12 stator poles are taken as examples to illustrate the method for determining the winding connections and winding factors. The back-electromotive force (EMF), self- and mutual inductances, cogging torque, static torque, torque ripple, and unbalanced magnetic force (UMF) are investigated by finite-element analyses. It is found that many stator/rotor pole combinations, i.e., 12/8 (which may be derived from the conventional three-phase SRM), 12/10, 12/11, 12/13, and 12/14, are feasible for the 12-stator-pole VFRMs. Among these pole number combinations, the 10- and 14-rotor-pole VFRMs can eliminate the inherent UMF in 6/5 and 6/7 VFRMs and exhibit more sinusoidal back-EMF waveforms and have higher torque density than an 8-rotor-pole VFRM, whereas the 11- and 13-rotor-pole VFRMs exhibit similar torque density as the 10- and 14-rotor-pole VFRMs, but with negligible cogging torque and torque ripple, albeit with UMF. Five prototype VFRMs with 12 stator poles and different rotor poles have been designed, manufactured, and tested to verify the analyses.
This paper reviews the relative merits of induction, switched reluctance, and permanent-magnet (PM) brushless machines and drives for application in electric, hybrid, and fuel cell vehicles, with ...particular emphasis on PM brushless machines. The basic operational characteristics and design requirements, viz. a high torque/power density, high efficiency over a wide operating range, and a high maximum speed capability, as well as the latest developments, are described. Permanent-magnet brushless dc and ac machines and drives are compared in terms of their constant torque and constant power capabilities, and various PM machine topologies and their performance are reviewed. Finally, methods for enhancing the PM excitation torque and reluctance torque components and, thereby, improving the torque and power capability, are described
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•Application of the phase field (PP) to microcracking in concrete microstructures.•Crack initiation and propagation in complex voxel-based models of microstructures.•An enhanced ...algorithm within PP is proposed to increase the load increments.
In this work, crack initiation and propagation in 2D and 3D highly heterogeneous materials models, such as those obtained by micro-CT imagery of cementitious materials, is investigated for the first time by means of the phase field method. A shifted strain split operator algorithm is proposed to handle unilateral contact within cracks in a very efficient manner. The various advantages of the phase field method for voxel-based models are discussed. More specifically, we show that the resolution related to the initial image and thus to meshes for discretizing the same microstructure does not significantly affect the simulated crack path.
The TET (ten-eleven translocation) family of α-ketoglutarate (α-KG)-dependent dioxygenases catalyzes the sequential oxidation of 5-methylcytosine (5mC) to 5-hydroxymethylcytosine (5hmC), ...5-formylcytosine and 5-carboxylcytosine, leading to eventual DNA demethylation. The TET2 gene is a bona fide tumor suppressor frequently mutated in leukemia, and TET enzyme activity is inhibited in IDH1/2-mutated tumors by the oncometabolite 2-hydroxyglutarate, an antagonist of α-KG, linking 5mC oxidation to cancer development. We report here that the levels of 5hmC are dramatically reduced in human breast, liver, lung, pancreatic and prostate cancers when compared with the matched surrounding normal tissues. Associated with the 5hmC decrease is the substantial reduction of the expression of all three TET genes, revealing a possible mechanism for the reduced 5hmC in cancer cells. The decrease of 5hmC was also observed during tumor development in different genetically engineered mouse models. Together, our results identify 5hmC as a biomarker whose decrease is broadly and tightly associated with tumor development.
This paper proposes a method for online estimating the rotor flux linkage and voltage-source inverter (VSI) nonlinearity of permanent magnet synchronous machine (PMSM) drives. Thermocouples are ...employed for measuring the temperature variation of the stator winding in order to obtain the actual value of stator winding resistance. An Adaline estimator is used for online estimation of distorted voltage Vdead due to VSI nonlinearity. Both are subsequently used for the estimation of the rotor flux linkage. The proposed method is experimentally validated on a PMSM drive system and shows good performance in tracking the variation of the rotor flux linkage and compensating the VSI nonlinearity.
High-energy cosmic-ray electrons and positrons (CREs), which lose energy quickly during their propagation, provide a probe of Galactic high-energy processes and may enable the observation of ...phenomena such as dark-matter particle annihilation or decay. The CRE spectrum has been measured directly up to approximately 2 teraelectronvolts in previous balloon- or space-borne experiments, and indirectly up to approximately 5 teraelectronvolts using ground-based Cherenkov γ-ray telescope arrays. Evidence for a spectral break in the teraelectronvolt energy range has been provided by indirect measurements, although the results were qualified by sizeable systematic uncertainties. Here we report a direct measurement of CREs in the energy range 25 gigaelectronvolts to 4.6 teraelectronvolts by the Dark Matter Particle Explorer (DAMPE) with unprecedentedly high energy resolution and low background. The largest part of the spectrum can be well fitted by a 'smoothly broken power-law' model rather than a single power-law model. The direct detection of a spectral break at about 0.9 teraelectronvolts confirms the evidence found by previous indirect measurements, clarifies the behaviour of the CRE spectrum at energies above 1 teraelectronvolt and sheds light on the physical origin of the sub-teraelectronvolt CREs.
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