85 research outputs found
Thermal Modeling of Permanent Magnet Synchronous Motors for Electric Vehicle Application
Permanent magnet synchronous motor (PMSM) is a better choice as a traction motor since it has high power density and high torque capability within compact structure. However, accommodating such high power within compact space is a great challenge, as it is responsible for significant rise of heat in PMSM. As a result, there is considerable increase in operating temperature which in turn negatively affects the electromagnetic performance of the motor. Further, if the temperature rise exceeds the permissible limit, it can cause demagnetization of magnets, damage of insulation, bearing faults, etc. which in turn affect the overall lifecycle of the motor. Therefore, thermal issues need to be dealt with carefully during the design phase of PMSM. Hence, the main focus of this thesis is to develop efficient ways for thermal modeling to address thermal issues properly. Firstly, a universal lumped parameter thermal network (LPTN) is proposed which can be used for all types of PMSMs regardless of any winding configuration and any position of magnets in the rotor. Further, a computationally efficient finite element analysis (FEA) thermal model is proposed with a novel hybrid technique utilizing LPTN strategy for addressing the air gap convection in an efficient way. Both proposed LPTN and FEA thermal models are simplified ways to predict motor temperature with a comparatively less calculation process. Finally, the proposed thermal models have been experimentally validated for the newly designed interior and surface mounted PMSM prototypes. Again, a procedure for effective cooling design process of PMSM has been suggested by developing an algorithm for cooling design optimization of the motor. Further, a computational fluid dynamics (CFD) model with a proposed two-way electro-thermal co-analysis strategy has been developed to predict both thermal and electromagnetic performance of PMSM more accurately considering the active cooling system. The developed step algorithm and CFD modeling approach will pave the way for future work on cooling design optimization of the newly designed interior and surface mounted PMSM prototypes
Proof of Renyi QNEC for free fermions
Quantum null energy condition (QNEC) is usually stated as a bound on the
expectation value of null components of the stress energy tensor at a point in
terms of second null shape variations of the entanglement entropy at the same
point. It can be recast as the statement that the sign of the second null shape
variation of the relative entropy of any state with respect to the vacuum is
positive. Using instead a Renyi generalization of relative entropy, called
sandwiched Renyi divergence (SRD), leads to what is termed the Renyi QNEC: the
second null shape variation of SRD of any state with respect to the vacuum is
positive. In this work, we prove the Renyi QNEC for free and
superrenormalizable fermionic quantum field theories in spacetime dimensions
greater than 2 using null quantization, for the case where the Renyi parameter
. We end with comments on multiple possible generalizations.Comment: 25 page
Oscillating Shells and Oscillating Balls in AdS
It has recently been reported that certain thin timelike shells undergo
oscillatory motion in AdS. In this paper, we compute two-point function of a
probe field in the geodesic approximation in such an oscillating shell
background. We confirm that the two-point function exhibits an oscillatory
behaviour following the motion of the shell. We show that similar oscillatory
dynamics is possible when the perfect fluid on the shell has a polytropic
equation of state. Moreover, we show that certain ball like configurations in
AdS also exhibit oscillatory motion and comment on how such a solution can be
smoothly matched to an appropriate exterior solution. We also demonstrate that
the weak energy condition is satisfied for these oscillatory configurations.Comment: 23 pages, 5 figures; v2: refs added; v3: JHEP versio
Topological Triviality of Flat Hamiltonians
Landau levels play a key role in theoretical models of the quantum Hall
effect. Each Landau level is degenerate, flat and topologically non-trivial.
Motivated by Landau levels, we study tight-binding Hamiltonians whose energy
levels are all flat. We demonstrate that in two dimensions, for such
Hamiltonians, the flat bands must be topologically trivial. To that end, we
show that the projector onto each flat band is necessarily strictly local. Our
conclusions do not need the assumption of lattice translational invariance.Comment: 7 pages, 2 figure
Scattering Expansion for Localization in One Dimension: from Disordered Wires to Quantum Walks
We present a perturbative approach to a broad class of disordered systems in
one spatial dimension. Considering a long chain of identically disordered
scatterers, we expand in the reflection strength of any individual scatterer.
This expansion accesses the full range of phase disorder from weak to strong.
We apply this expansion to several examples, including the Anderson model, a
general class of periodic-on-average-random potentials, and a two-component
discrete-time quantum walk, showing analytically in the latter case that the
localization length can depend non-monotonically on the strength of phase
disorder (whereas expanding in weak disorder yields monotonic decrease).
Returning to the general case, we extend the perturbative derivation of
single-parameter scaling to another order and obtain to all orders a particular
non-separable form for the joint probability distribution of the
log-transmission and reflection phase. Furthermore, we show that for weak local
reflection strength, a version of the scaling theory of localization holds: the
joint distribution is determined by just three parameters.Comment: 23+15 pages, 10 figures. Longer version of arXiv:2210.0799
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