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arXiv 2024年

作者： Abukhwejah, Abdullah Jagad, Pankaj Samtaney, Ravi Schmid, Peter Mechanical Engineering Physical Science and Engineering Division King Abdullah University of Science and Technology Thuwal Saudi Arabia

The simulation of fluid flow problems, specifically incompressible flows governed by the Navier-Stokes equations (NSE), holds fundamental significance in a range of scientific and engineering applications. Traditional numerical methods employed for solving these equations on three-dimensional (3D) meshes are commonly known for their moderate conservation properties, high computational intensity and substantial resource demands. Relying on its ability to capture the intrinsic geometric and topological properties of simplicial meshes, discrete exterior calculus (DEC) provides a discrete analog to differential forms and enables the discretization of partial differential equations (PDEs) on meshes. We present a hybrid discretization approach for the 3D incompressible Navier-Stokes equations based on DEC and Fourier transform (FT). An existing conservative primitive variable DEC discretization of incompressible Navier–Stokes equations over surface simplicial meshes developed by Jagad et al. [1] is considered in the planar dimension while the Fourier expansion is applied in the third dimension. The test cases of three-dimensional lid-driven cavity and viscous Taylor-Green three-dimensional vortex (TGV) flows show that the simulation results using this hybrid approach are comparable to literature. Copyright © 2024, The Authors. All rights reserved.

关键词： Navier Stokes equations

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Annealing embrittlement of Fe78Si9B13 (METGLAS-2605S2)

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Hyperfine Interactions 2014年第1-3期226卷 7-14页

作者： Cadogan, J.M. Campbell, S.J. Jing, J. Foley, C.P. Kater, P. Mai, Y.W. School of Physical Environmental and Mathematical Sciences UNSW Canberra at the Australian Defence Force Academy ACT BC 2610 Australia CSIRO Division of Materials Science and Engineering Bradfield Road West Lindfield NSW 2070 Australia Centre for Advanced Materials Technology School of Aerospace Mechanical and Mechatronic Engineering J07 The University of Sydney Sydney NSW 2006 Australia

The ductile to brittle transition that occurs in amorphous Fe78Si9B13 (METGLAS-2605S2) has been investigated using mechanical measurements over the temperature range 250-370 °C. The fracture toughness values, K Ic, have been determined for a range of annealing times (5-30 min) and cooling rates of 15-45 °C/min. A pronounced ductile to brittle transition is observed around 310(10) °C although no obvious structural changes are evident as indicated by x-ray diffraction. Comparison of transmission and back-scattered conversion electron 57Fe Mössbauer spectra for the bulk as-received ribbon in the ductile state (KIc=52~MPa √m) and the ribbon annealed to the brittle state (KIc~10 MPa √m) indicates magnetic texture effects in both the bulk and on the surface of these amorphous ribbons, related to the magnetostriction resulting from the quenched-in stress during the ribbon production process, and the ensuing stress-relief upon annealing. © 2013 Springer science+Business Media Dordrecht.

关键词： Fracture toughness

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A hybrid discrete exterior calculus and finite difference method for Boussinesq convection in spherical shells

arXiv

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arXiv 2022年

作者： Mantravadi, Bhargav Jagad, Pankaj Samtaney, Ravi Mechanical Engineering Division of Physical Science and Engineering King Abdullah University of Science and Technology Thuwal Saudi Arabia

We present a new hybrid discrete exterior calculus (DEC) and finite difference (FD) method to simulate fully three-dimensional Boussinesq convection in spherical shells subject to internal heating and basal heating, relevant in the planetary and stellar phenomenon. We employ DEC to compute the surface spherical flows, taking advantage of its unique features of structure preservation (e.g., conservation of secondary quantities like kinetic energy) and coordinate system independence, while we discretize the radial direction using FD method. The grid employed for this novel method is free of problems like the coordinate singularity, grid non-convergence near the poles, and the overlap regions. We have developed a parallel in-house code using the PETSc framework to verify the hybrid DEC-FD formulation and demonstrate convergence. We have performed a series of numerical tests which include quantification of the critical Rayleigh numbers for spherical shells characterized by aspect ratios ranging from 0.2 to 0.8, simulation of robust convective patterns in addition to stationary giant spiral roll covering all the spherical surface in moderately thin shells near the weakly nonlinear regime, and the quantification of Nusselt and Reynolds numbers for basally heated spherical shells. The method exhibits slightly better than second order error convergence with the mesh size. Copyright © 2022, The Authors. All rights reserved.

关键词： Finite difference method

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Specific heat capacity of gallium nitride

Specific heat capacity of gallium nitride

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作者： Lee, Sanghyun Kwon, Su Yong Ham, Hye Jeong Division of Physical Metrology Korea Research Institute of Standards and Science Daejeon 305-340 Korea Republic of Department of Mechanical Engineering Kyungpook National University Daegu 702-701 Korea Republic of

The specific heat capacity of gallium nitride (GaN) was measured for polycrystalline powder and single crystal samples. We present the temperature dependence of the specific heat capacity for single crystal and powdered GaN from 100 to 1300 K. The difference between the polycrystalline powder and single crystal arises from thermal evaporation in the high-temperature region, and this depends on the degree of heat transfer at 100-200 K. The temperature dependence of the specific heat capacity in the form cp = 7.1380 × 10-17 T6 - 2.9836 × 10-13 T 5 + 4.2185 × 10-10 T4 - 1.5068 ×10-7 T3 - 1.6713 ×10-4 T 2 + 0.1774 T - 1.3545 (J mol-1 K-1) was derived from a least squares fitting routine. © 2011 The Japan Society of Applied Physics.

关键词： Gallium nitride

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Flux-limited diffusion coefficients in reactor physics applications

Flux-limited diffusion coefficients in reactor physics appli...

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Joint International Topical Meeting on Mathematics and Computations and Supercomputing in Nuclear Applications, M and C + SNA 2007

作者： Pounders, Justin Rahnema, Farzad Szilard, Ronaldo Nuclear and Radiological Engineering/Medical Physics Program George W. Woodruff School of Mechanical Engineering Georgia Institute of Technology Atlanta GA 30332-0405 Idaho National Laboratory Nuclear Programs Nuclear Science and Engineering Division Idaho Falls ID 83415

ISBN: (纸本)0894480596

Flux-limited diffusion theory has been successfully applied to problems in radiative transfer and radiation hydrodynamics, but its relevance to reactor physics has not yet been explored. The current investigation compares the performance of a flux-limited diffusion coefficient against the traditionally defined transport cross section. A one-dimensional BWR benchmark problem is examined at both the assembly and full-core level with varying degrees of heterogeneity.

关键词： Boiling water reactors

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On the Capacity of Rician Fading Channels With Full Channel State Information at Low SNR

On the Capacity of Rician Fading Channels With Full Channel ...

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IEEE International Conference on Communications

作者： Zouheir Rezki Mohamed-Slim Alouini Electrical Engineering Program Physical Science and Engineering (PSE) Division King Abdullah University of Science and Technology (KAUST)

ISBN: (纸本)9781457720529

The capacity of flat Rayleigh fading channels with full channel state information (CSI) at the transmitter and at the receiver at asymptotically low SNR has been recently shown to scale essentially as SNR log(1/SNR). In this paper, we investigate the Rician fading channel capacity with full CSI, and show that the capacity of this channel scales essentially as 1/1+K SNR log(1/SNR), where K is the Rician factor. This characterization includes perfect CSI at both the transmitter and the receiver or noisy CSI at the transmitter and perfect CSI at the receiver. We also show that one-bit CSI at the transmitter is enough to achieve this asymptotic capacity using an On-Off power control scheme. Our framework may be seen as a generalization of previous works as it captures the Rayleigh fading channel as a special case by letting K goes to zero.

关键词： Ergodic capacity Rician fading channel Imperfect channel estimation On-off signaling Channel state information low SNR Raleigh fading channels Transmitters Rician fading channels Receivers Rician fading Transmitter Channel capacity transmitter receivers signal to noise ratios Supernova remnants

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Altered micromechanical function precedes overt surface roughening in early cartilage degeneration

Altered micromechanical function precedes overt surface roug...

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ASME 2011 Summer Bioengineering Conference, SBC 2011

作者： Bevill, Scott L. Thambyah, Ashvin Broom, Neil D. Dept. of Physical and Environmental Sciences Mechanical Engineering Program Mesa State College Grand Junction CO United States Department of Materials Science University of Auckland Auckland NZ New Zealand

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Tailoring dielectric properties and crystallinity in poly(vinylidene fluoride-co-hexafluoropropylene) nanocomposites via iron (III) chloride hexahydrate incorporation

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Scientific reports 2025年第1期15卷 17810页

作者： Jureeporn Yuennan Nantakan Muensit Nikruesong Tohluebaji Wichain Chailad Liu Yang Nathapong Sukhawipat Ghulam Abbas Ashraf Phongpichit Channuie Surface Technology Research Unit (STRU) Faculty of Science and Technology Nakhon Si Thammarat Rajabhat University Nakhon Si Thammarat 80280 Thailand. Division of Physical Science (Physics) Faculty of Science Prince of Songkla University Songkhla 90112 Thailand. Faculty of Science and Technology Princess of Naradhiwas University Narathiwat 96000 Thailand. Department of Materials and Metallurgical Engineering Faculty of Engineering Rajamangala University of Technology Thanyaburi Pathum Thani 12110 Thailand. Department of Mechanical and Aerospace Engineering University of Strathclyde Glasgow UK. Department of Mechanical Engineering Technology College of Industrial Technology King Mongkut's University of Technology North Bangkok Bangkok 10800 Thailand. Materials Research Center at Khazar University 1096 Baku Azerbaijan. Shanghai MKS Material Technology Co. Ltd Anting Jiading Shanghai 200240 China. School of Science Walailak University Thasala Nakhon Si Thammarat 80160 Thailand. channuie@***.

This study investigates the impact of iron (III) chloride hexahydrate (FeCl·6HO) incorporation on the structural, thermal, and dielectric properties of poly(vinylidene fluoride-co-hexafluoropropylene) [P(VDF-HFP)] nanocomposites, which were prepared using a solution casting method with varying filler concentrations (1-4 wt%). Scanning electron microscopy revealed a systematic increase in porosity-from 0.72% in pure P(VDF-HFP) to 27.5% at 4 wt% FeCl·6HO-along with increased pore size and surface heterogeneity. Atomic force microscopy confirmed enhanced surface roughness correlating with increased filler content. Fourier-transform infrared spectroscopy demonstrated a significant α-to-β phase transformation, indicating the formation of the polar β-phase with increasing FeCl·6HO content. X-ray diffraction analysis corroborated these findings, revealing a notable increase in crystallinity and β-phase content, with 4 wt% FeCl·6HO achieving the highest β-phase fraction (88.99%). Thermogravimetric analysis confirmed thermal stability up to approximately 500 °C, with a gradual shift in degradation onset attributed to FeCl·6HO interactions. Dielectric measurements at 10 Hz showed a remarkable enhancement in dielectric constant-from 5.62 in pure P(VDF-HFP) to 19.16 at 4 wt% FeCl·6HO-while maintaining a low dielectric loss (< 0.30). These improvements are attributed to the synergistic effects of FeCl·6HO on porosity, phase transformation, crystallinity, thermal stability, and dielectric properties. The superior performance of these nanocomposites makes them promising candidates for flexible electronics, energy storage systems, and advanced sensors.

关键词： Dielectric properties FeCl3·6H2O doping Hydrogen bonding interactions P(VDF-HFP) composites Thermal stability

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Large-eddy simulation of flow over a circular cylinder in the sub-critical regime 10

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10th International Symposium on Turbulence and Shear Flow Phenomena, TSFP 2017

作者： Cheng, W. Pullin, D.I. Samtaney, R. Mechanical Engineering Physical Sciences and Engineering Division King Abdullah University of Science and Technology Thuwal Saudi Arabia Graduate Aerospace Laboratories California Institute of Technology 1200 E. California Blvd. PasadenaCA91125 United States

ISBN: (纸本)9780000000002

We present wall-resolved, large-eddy simulation (LES) of flow over a circular cylinder up to ReD = 105, based on the cylinder diameter D, in the subcritical regime. The numerical method is a fully centered-finite-difference scheme on a standard curvilinear O-grid. The stretched-vortex sub-grid scale model is used in the whole domain, including regions of large-scale separated flow. Both secondand fourth-order accurate schemes are used separately, and results, specifically the skin-friction coefficient along the cylinder surface and its variation with ReD, are compared with literature data.

关键词： Circular cylinders

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Large-eddy simulations of a separation/reattachment bubble in a turbulent-boundary-layer subjected to a prescribed upper-boundary, vertical-velocity profile 9

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9th International Symposium on Turbulence and Shear Flow Phenomena, TSFP 2015

作者： Cheng, Wan Pullin, D.I. Samtaney, Ravi Graduate Aerospace Laboratories California Institute of Technology 1200 E. California Blvd. PasadenaCA91125 United States Mechanical Engineering Physical Sciences and Engineering Division King Abdullah University of Science and Technology Thuwal Saudi Arabia

ISBN: (纸本)9780000000002

We describe large-eddy simulations of turbulent boundary-layer flow over a flat plate at high Reynolds number in the presence of an unsteady, three-dimensional flow separation/reattachment bubble. The stretched-vortex subgrid-scale model is used in the main flow domain combined with a wall-model that is a two-dimensional extension of that developed by Chung & Pullin (2009). Flow separation and re-attachment of the incoming boundary layer is induced by prescribing wall-normal velocity distribution on the upper boundary of the flow domain that produces an adverse-favorable stream-wise pressure distribution at the wall. The LES predicts the distribution of mean shear stress along the wall including the interior of the separation bubble. Several properties of the separation/reattachment flow are discussed.

关键词： Flow separation

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