9,742 research outputs found
A comparative study of methods for modelling the structural stiffness of generator components
Direct-drive generators are low speed electrical machines requiring robust and large supporting structures designed to resist the significant loads present during assembly and operation. Generator structures have to be stiff, especially in the radial direction for radial-flux machines. This paper presents three different structural modelling approaches: finite element, analytical and hybrid (a combination of the results obtained from dimensional studies and finite element analyses). These are used along with models of electromagnetic active material, to parametrically calculate the minimum structural stiffness and mass of the components forming the machine
Structural analysis and characterization of radial flux PM generators for direct-drive wind turbines
Wind turbine direct-drive generator structures are analysed in order to optimise and reduce mass. A method for modelling key stiffness parameters including a magnetic air-gap stiffness is outlined. Different approaches are used to parametrically calculate structural stiffness and mass. Finite element and analytical techniques are used to model mode 0 and mode 1 deflections and these can be used along with parametric models of electromagnetically active material
Longitudinal spin Seebeck coefficient: heat flux vs. temperature difference method
The determination of the longitudinal spin Seebeck effect (LSSE) coefficient
is currently plagued by a large uncertainty due to the poor reproducibility of
the experimental conditions used in its measurement. In this work we present a
detailed analysis of two different methods used for the determination of the
LSSE coefficient. We have performed LSSE experiments in different laboratories,
by using different setups and employing both the temperature difference method
and the heat flux method. We found that the lack of reproducibility can be
mainly attributed to the thermal contact resistance between the sample and the
thermal baths which generate the temperature gradient. Due to the variation of
the thermal resistance, we found that the scaling of the LSSE voltage to the
heat flux through the sample rather than to the temperature difference across
the sample greatly reduces the uncertainty. The characteristics of a single
YIG/Pt LSSE device obtained with two different setups was Vm/W and Vm/W with the heat flux method
and V/K and V/K
with the temperature difference method. This shows that systematic errors can
be considerably reduced with the heat flux method.Comment: PDFLaTeX, 10 pages, 6 figure
A lightweight approach for airborne wind turbine drivetrains
Buoyant airborne wind turbines are devices capable of harnessing stronger winds at higher altitudes and with their automated and rapidly deployable system they are suited to niche applications such as emergency power generation. Although much of the wind turbine technology for these systems is common with their ‘grounded’ cousins, an additional design limitation is the requirement for the wind turbine equipment to be lightweight. This paper concentrates on the drivetrain of the wind turbine and the different potential ways of reducing its mass. A buoyant airborne wind turbine with different types of drivetrains, going from gearless to geared systems with distinct gear ratios, has been analysed. Special attention was paid to the mass of the supporting structure of the permanent magnet electrical generator and this was minimized by utilising low density materials, such as composites, in its design. The model showed that a significant reduction in the mass of the drivetrain can be achieved in the gearless case by using materials with a higher ratio of Young’s Modulus to density for the electrical machine supporting structure. For the geared systems, mass decrease was less significant as the gearbox mass had also to be considered. Keywords: Airborne, lightweight, generator structure, composite material
Facilitating the additive manufacture of high-performance polymers through polymer blending: A review
Fused Filament Fabrication (FFF, a.k.a. fused deposition modeling, FDM) is presently the most widespread material extrusion (MEX) additive manufacturing technique owing to its flexibility and robustness. Nonetheless, it remains underutilized in load-bearing applications, as often seen in aerospace, automotive and biomedical industries. This is largely due to the processing challenges associated with high performance polymers (HPPs) like poly-ether-ether-ketone (PEEK) or polyetherimide (PEI). Compared with commercial-grade plastics such as polylactic acid (PLA), parts produced with HPPs have outstanding mechanical properties and thermal stability. However, HPPs have bulkier chemical structures and stronger intermolecular forces than common FFF feedstock materials, and this results in much higher printing temperatures and greater melt viscosities. The demanding processing requirements of HPPs have thus impaired their adoption within FFF. Polymer blending, which consists in properly mixing HPPs with other thermoplastics, makes it possible to alleviate these printing issues, while also providing additional advantages such as improved tensile strength and reduced friction. Further to this, manipulating the crystallisation processes of HPPs mitigates distortion or warping upon printing. This review explores some emerging trends in the field of HPP blends and how they address the challenges of excessive melt viscosity, polymer crystallization, moisture uptake, and part shrinkage in 3D printing. Also, the various structural/mechanical/chemical enhancements that are afforded to FFF parts through HPP blending are critically analysed based on recent examples from the literature. Such insights will not only aid researchers in this field, but also facilitate the development of novel, 3D printable HPP blends
Electrical capability of 3D printed unpoled polyvinylidene fluoride (PVDF)/thermoplastic polyurethane (TPU) sensors combined with carbon black and barium titanate
The development of three-dimensional (3D) printed sensors attracts high interest from the smart electronic industry owing to the significant geometric freedom allowed by the printing process and the potential for bespoke composite feedstocks being imbued with specific material properties. In particular, feedstock for material extrusion (MEX) additive manufacturing by fused filament fabrication can be provided with piezoelectricity and electrical conductivity. However, piezoelectricity often requires electrical poling for activation. In this study, a candidate material containing thermoplastic polyurethane (TPU) and carbon black (CB) with conductive and flexible properties is incorporated with piezoelectric elements like polyvinylidene fluoride (PVDF) and barium titanate (BaTiO3) to assess its suitability for sensor applications without electrical poling. Texturing the surface of BaTiO3 particles and adding tetraphenylphosphonium chloride (TPPC) to the composite are evaluated as non-poling treatments to improve the sensor response. It was found that TPU and PVDF produced segregated domain structures within the printed sensors that aligned along the printing direction. Due to the effect of this preferential orientation combined with the presence of raster-raster interfaces, printed sensors exhibited significant electrical anisotropy registering greater electrical waveforms when the electrodes aligned parallel to the raster direction. An improvement of current baseline from 0.4 μA to 12 μA in the parallel direction was observed in sensors functionalised with both treatments. Similarly, when the waveform responses were measured under a standardised impact force, current amplitudes in both orientations registered a twofold increase for any impact force when both treatments were applied to the feedstock material. The results achieved within this study elucidate how composite formulations can enhance the sensor response prior to conducting electrical poling
Solid-state phase transformations in thermally treated Ti-6Al-4V alloy fabricated via laser powder bed fusion
Laser Powder Bed Fusion (LPBF) technology was used to produce samples based on the Ti-6Al-4V alloy for biomedical applications. Solid-state phase transformations induced by thermal treatments were studied by neutron diffraction (ND), X-ray diffraction (XRD), scanning transmission electron microscopy (STEM) and energy-dispersive spectroscopy (EDS). Although, ND analysis is rather uncommon in such studies, this technique allowed evidencing the presence of retained \u3b2 in \u3b1' martensite of the as-produced (#AP) sample. The retained \u3b2 was not detectable byXRDanalysis, nor by STEM observations. Martensite contains a high number of defects, mainly dislocations, that anneal during the thermal treatment. Element diffusion and partitioning are the main mechanisms in the \u3b1 \u2194 \u3b2 transformation that causes lattice expansion during heating and determines the final shape and size of phases. The retained \u3b2 phase plays a key role in the \u3b1' \u2192 \u3b2 transformation kinetics
Hamiltonian dynamics and geometry of phase transitions in classical XY models
The Hamiltonian dynamics associated to classical, planar, Heisenberg XY
models is investigated for two- and three-dimensional lattices. Besides the
conventional signatures of phase transitions, here obtained through time
averages of thermodynamical observables in place of ensemble averages,
qualitatively new information is derived from the temperature dependence of
Lyapunov exponents. A Riemannian geometrization of newtonian dynamics suggests
to consider other observables of geometric meaning tightly related with the
largest Lyapunov exponent. The numerical computation of these observables -
unusual in the study of phase transitions - sheds a new light on the
microscopic dynamical counterpart of thermodynamics also pointing to the
existence of some major change in the geometry of the mechanical manifolds at
the thermodynamical transition. Through the microcanonical definition of the
entropy, a relationship between thermodynamics and the extrinsic geometry of
the constant energy surfaces of phase space can be naturally
established. In this framework, an approximate formula is worked out,
determining a highly non-trivial relationship between temperature and topology
of the . Whence it can be understood that the appearance of a phase
transition must be tightly related to a suitable major topology change of the
. This contributes to the understanding of the origin of phase
transitions in the microcanonical ensemble.Comment: in press on Physical Review E, 43 pages, LaTeX (uses revtex), 22
PostScript figure
Can electro-magnetic field, anisotropic source and varying be sufficient to produce wormhole spacetime ?
It is well known that solutions of general relativity which allow for
traversable wormholes require the existence of exotic matter (matter that
violates weak or null energy conditions [WEC or NEC]). In this article, we
provide a class of exact solution for Einstein-Maxwell field equations
describing wormholes assuming the erstwhile cosmological term to be
space variable, viz., .
The source considered here not only a matter entirely but a sum of matters
i.e. anisotropic matter distribution, electromagnetic field and cosmological
constant whose effective parts obey all energy conditions out side the wormhole
throat. Here violation of energy conditions can be compensated by varying
cosmological constant. The important feature of this article is that one can
get wormhole structure, at least theoretically, comprising with physically
acceptable matters.Comment: Some changes have been mad
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