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Article
Publication date: 27 September 2011

Oleg Rybin, Konstantin Yemelyanov, Amjad Pitafi and Tahira Nawaz

The purpose of this paper is to study the microwave behaviour of effective magnetic permeability for two‐component ferrite like metamaterial medium in the direction of a…

Abstract

Purpose

The purpose of this paper is to study the microwave behaviour of effective magnetic permeability for two‐component ferrite like metamaterial medium in the direction of a biasing magnetic field. The metamaterial medium is presented as an infinite host dielectric material (air) with periodically embedded ferric cylindrical and spherical inclusions saturated with an external dc magnetic field. The study is based on the effective medium theory developed for polycrystalline metaferrites. The simulations show that the presented metamaterial can exhibit the ultra‐low refractive index (ULI) phenomenon and the phenomenon of negative magnetic permeability for the case of microwave propagation in the direction of bias.

Design/methodology/approach

The obtained results are based on the wave long approximation of permeability tensor of the presented metamaterial media obtained earlier by the first author. Using the standard approach, the authors apply the above expressions for the microwave propagation in direction of biasing dc magnetic field considering different polarization of the incident microwave.

Findings

The considered artificial material media can become either material with a ULI or with negative values in the GHz frequencies.

Originality/value

The paper is concerned with part of the theory of a new generation of artificial ferrites.

Details

Multidiscipline Modeling in Materials and Structures, vol. 7 no. 3
Type: Research Article
ISSN: 1573-6105

Keywords

Article
Publication date: 11 August 2021

Brent W. Ritchie and Yawei Jiang

This paper aims to summarize the current state of research on risk, crisis and disaster management in the generic field, and in tourism and hospitality. It identifies key…

1670

Abstract

Purpose

This paper aims to summarize the current state of research on risk, crisis and disaster management in the generic field, and in tourism and hospitality. It identifies key themes and compares the main topics studied in both the tourism and hospitality management and marketing literature.

Design/methodology/approach

A narrative (thematic) review and synthesis was completed based on articles published in the top 20 tourism and hospitality management journals from 2011 to March 2021. A review was conducted of the generic literature from 2016 to 2020.

Findings

From 210 papers reviewed, only 47 are in the hospitality field. The authors found that 80% of papers were empirical with slightly more quantitative papers produced. The majority of the papers focused on crises. Three key themes were found from the review and future research proposed to address gaps based on these findings and a review of 26 papers from the generic risk, crisis and disaster management field.

Practical implications

Research is required into planning and preparedness, not just response and recovery to crises and disasters. Future research should consider hospitality rather than tourism, particularly focusing attention outside of the accommodation sector. Hospitality studies also need to go beyond the micro-organizational level to include more meso- and macro-level studies.

Originality/value

The review provides a number of future research directions for tourism and hospitality research in the field. The paper provides a comprehensive multi-dimensional framework to synthesize studies and identifies research gaps. It also provides recommendations on methodologies required to progress these research directions. Research in this field is likely to grow because of the impact of COVID-19.

Details

International Journal of Contemporary Hospitality Management, vol. 33 no. 10
Type: Research Article
ISSN: 0959-6119

Keywords

Article
Publication date: 30 August 2019

Lingyun Kong, Mehdi Ostadhassan, Ran Lin and Chunxiao Li

Evaluating mechanical properties of simply made samples by 3D printing technology at nanoscale provides a clear path to better understand larger-scale responses of complex…

Abstract

Purpose

Evaluating mechanical properties of simply made samples by 3D printing technology at nanoscale provides a clear path to better understand larger-scale responses of complex natural rocks. Therefore, to realize the similarity between synthetically manufactured materials and natural geomaterials, this study focused on nanoscale mechanical characterization of a 3D printed object with only two constituent components (gypsum powder and infiltrant).

Design/methodology/approach

The study method includes nanoindentation technique combined with numerical simulation via discrete element method (DEM).

Findings

Four typical load-displacement curves were identified from nanoindentation of total test points indicating a typical elastic-plastic behavior of the 3D printed gypsum rock sample. Mechanical parameters such as Young’s modulus and hardness were calculated by energy-based methods and a positive correlation was observed. The infiltrant was found to considerably be responsible for the majority of the sample nano-mechanical behavior rather than the gypsum particles, thus expected to control macroscale properties. This was decided from deconvolution and clustering of elastic modulus data. Particle flow modeling in DEM was used to simulate the nanoindentation process in a porous media yielding rock-alike mechanical behavior.

Originality/value

The results show a matching load-displacement response between experimental and simulation results, which verified the credibility of simulation modeling for mechanical behavior of 3D printed gypsum rock at nanoscale. Finally, differential effective medium theory was used to upscale the nanoindentation results to the macroscale mechanical properties, which provided an insight into the geomechanical modeling at multiscale.

Details

Rapid Prototyping Journal, vol. 25 no. 7
Type: Research Article
ISSN: 1355-2546

Keywords

Article
Publication date: 9 August 2011

Oleg Rybin, Konstantin Yemelyanov and Tahira Nawaz

The purpose of this paper is to obtain the long‐wave approximations for the effective electromagnetic response of two‐dimensional sandwich composite structure, as infinite…

Abstract

Purpose

The purpose of this paper is to obtain the long‐wave approximations for the effective electromagnetic response of two‐dimensional sandwich composite structure, as infinite chain of infinitely long metal cylinders symmetrically immersed in an infinite metamaterial slab are obtained. The slab is an infinite magneto‐dielectric matrix with periodically imbedded infinitely long metal cylinders whose diameter is smaller than those of the chain cylinders. The case of ferrite‐like metallic saturated inclusions is considered in the study.

Design/methodology/approach

The result is presented as a generalized expression of the electromagnetic response of the infinite periodic chain of infinitely long metallic cylinders immersed into the flat magneto‐dielectric host medium. Those expressions were obtained utilizing S‐ and T‐matrices approaches.

Findings

A good coincidence between the results of analytical modeling and numerical simulations was found.

Research limitations/implications

Low values of the metal volume fraction; microwave frequency range.

Practical implications

An improving of directivity of patch antennas; a minimization of patch antennas.

Originality/value

The analytical characterization of new artificial substrate‐like structure to be utilized for designing patch antennas of a new generation.

Details

Multidiscipline Modeling in Materials and Structures, vol. 7 no. 2
Type: Research Article
ISSN: 1573-6105

Keywords

Article
Publication date: 12 July 2011

Christian Meiners and Arne F. Jacob

This paper aims at providing information on scattering in layers composed of periodic and non‐periodic arrangements of small metal helices. Metal helices exhibit a…

Abstract

Purpose

This paper aims at providing information on scattering in layers composed of periodic and non‐periodic arrangements of small metal helices. Metal helices exhibit a pronounced resonance and are thus very effective scatterers.

Design/methodology/approach

Scattering is expressed in terms of multipole moments. Non‐periodic layers are investigated using the combination of periodic boundary conditions for sample configurations and averaging many of these configurations. The results and the methodology are compared to the well‐known Clausius‐Mossotti (CM) mixing rule and the assumptions and concepts therein. This is done to deepen the understanding of the scattering behavior.

Findings

The investigations show that only few multipole contributions are necessary to model the interaction correctly.

Originality/value

A systematic comparison of a full‐wave scattering theory and the fast CM mixing theory is conducted, providing some physical insight. From this, conclusions on the validity of the mixing approach are drawn.

Details

COMPEL - The international journal for computation and mathematics in electrical and electronic engineering, vol. 30 no. 4
Type: Research Article
ISSN: 0332-1649

Keywords

Abstract

Details

The Future Of Global Organizing
Type: Book
ISBN: 978-1-78560-422-5

Article
Publication date: 17 May 2021

Akash K. Gupta, Rahul Yadav, Malay K. Das and Pradipta K. Panigrahi

This paper aims to present the implementation of a multi-layer radiation propagation model in simulations of multi-phase flow and heat transfer, for a dissociating methane…

Abstract

Purpose

This paper aims to present the implementation of a multi-layer radiation propagation model in simulations of multi-phase flow and heat transfer, for a dissociating methane hydrate reservoir subjected to microwave heating.

Design/methodology/approach

To model the induced heterogeneity due to dissociation of hydrates in the reservoir, a multiple homogeneous layer approach, used in food processes modelling, is suggested. The multi-layer model is incorporated in an in-house, multi-phase, multi-component hydrate dissociation simulator based on the finite volume method. The modified simulator is validated with standard experimental results in the literature and subsequently applied to a hydrate reservoir to study the effect of water content and sand dielectric nature on radiation propagation and hydrate dissociation.

Findings

The comparison of the multi-layer model with experimental results show a maximum difference in temperature estimation to be less than 2.5 K. For reservoir scale simulations, three homogeneous layers are observed to be sufficient to model the induced heterogeneity. There is a significant contribution of dielectric properties of sediments and water content of the reservoir in microwave radiation attenuation and overall hydrate dissociation. A high saturation reservoir may not always provide high gas recovery by dissociation of hydrates in the case of microwave heating.

Originality/value

The multi-layer approach to model microwave radiation propagation is introduced and tested for the first time in dissociating hydrate reservoirs. The multi-layer model provides better control over reservoir heterogeneity and interface conditions compared to existing homogeneous models.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 32 no. 2
Type: Research Article
ISSN: 0961-5539

Keywords

Article
Publication date: 4 March 2014

Ayush Jain, Imbesat Hassan Rizvi, Subrata Kumar Ghosh and P.S. Mukherjee

Nanofluids exhibit enhanced heat transfer characteristics and are expected to be the future heat transfer fluids particularly the lubricants and transmission fluids used…

Abstract

Purpose

Nanofluids exhibit enhanced heat transfer characteristics and are expected to be the future heat transfer fluids particularly the lubricants and transmission fluids used in heavy machinery. For studying the heat transfer behaviour of the nanofluids, precise values of their thermal conductivity are required. For predicting the correct value of thermal conductivity of a nanofluid, mathematical models are necessary. In this paper, the effective thermal conductivity of various nanofluids has been reported by using both experimental and mathematical modelling. The paper aims to discuss these issues.

Design/methodology/approach

Hamilton and Crosser equation was used for predicting the thermal conductivities of nanofluids, and the obtained values were compared with the experimental findings. Nanofluid studied in this paper are Al2O3 in base fluid water, Al2O3 in base fluid ethylene glycol, CuO in base fluid water, CuO in base fluid ethylene glycol, TiO2 in base fluid ethylene glycol. In addition, studies have been made on nanofluids with CuO and Al2O3 in base fluid SAE 30 particularly for heavy machinery applications.

Findings

The study shows that increase in thermal conductivity of the nanofluid with particle concentration is in good agreement with that predicted by Hamilton and Crosser at typical lower concentrations.

Research limitations/implications

It has been observed that deviation between experimental and theoretical results increases as the volume concentration of nanoparticles increases. Therefore, the mathematical model cannot be used for predicting thermal conductivity at high concentration values.

Originality/value

Studies on nanoparticles with a standard mineral oil as base fluid have not been considered extensively as per the previous literatures available.

Details

Industrial Lubrication and Tribology, vol. 66 no. 2
Type: Research Article
ISSN: 0036-8792

Keywords

Article
Publication date: 6 November 2017

Eric Monier-Vinard, Brice Rogie, Valentin Bissuel, Najib Laraqi, Olivier Daniel and Marie-Cécile Kotelon

Latest Computational Fluid Dynamics (CFDs) tools allow modeling more finely the conjugate thermo-fluidic behavior of a single electronic component mounted on a Printed…

Abstract

Purpose

Latest Computational Fluid Dynamics (CFDs) tools allow modeling more finely the conjugate thermo-fluidic behavior of a single electronic component mounted on a Printed Wiring Board (PWB). A realistic three-dimensional representation of a large set of electric copper traces of its composite structure is henceforth achievable. The purpose of this study is to confront the predictions of the fully detailed numerical model of an electronic board to a set of experiment results to assess their relevance.

Design/methodology/approach

The present study focuses on the case of a Ball Grid Array (BGA) package of 208 solder balls that connect the component electronic chip to the Printed Wiring Board. Its complete geometrical definition has to be coupled with a realistic board layers layout and a fine description of their numerous copper traces to appropriately predict the way the heat is spread throughout that multi-layer composite structure. The numerical model computations were conducted on four CFD software then compare to experiment results. The component thermal metrics for single-chip packages are based on the standard promoted by the Joint Electron Device Engineering Council (JEDEC), named JESD-51. The agreement of the numerical predictions and measurements has been done for free and forced convection.

Findings

The present work shows that the numerical model error is lower than 2 per cent for various convective boundary conditions. Moreover, the establishment of realistic numerical models of electronic components permits to properly apprehend multi-physics design issues, such as joule heating effect in copper traces. Moreover, the practical modeling assumptions, such as effective thermal conductivity calculation, used since decades, for characterizing the thermal performances of an electronic component were tested and appeared to be tricky. A new approach based on an effective thermal conductivity matrix is investigated to reduce computation time. The obtained numerical results highlight a good agreement with experimental data.

Research limitations/implications

The study highlights that the board three-dimensional modeling is mandatory to properly match the set of experiment results. The conventional approach based on a single homogenous layer using effective thermal conductivity calculation has to be banned.

Practical implications

The thermal design of complex electronic components is henceforth under increasing control. For instance, the impact of gold wire-bonds can now be investigated. The three-dimensional geometry of sophisticated packages, such as in BGA family, can be imported with all its internal details as well as those of its associated test board to build a realistic numerical model. The establishment of behavioral models such as DELPHI Compact Thermal Models can be performed on a consistent three-dimensional representation with the aim to minimize computation time.

Originality/value

The study highlights that multi-layer copper trace plane discretization could be used to strongly reduce computation time while conserving a high accuracy level.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 27 no. 11
Type: Research Article
ISSN: 0961-5539

Keywords

Article
Publication date: 27 May 2014

P.K. Kameswaran, Z.G. Makukula, P. Sibanda, S.S. Motsa and P.V.S.N. Murthy

The purpose of this paper is to study heat and mass transfer in copper-water and silver-water nanofluid flow over stretching sheet placed in saturated porous medium with…

Abstract

Purpose

The purpose of this paper is to study heat and mass transfer in copper-water and silver-water nanofluid flow over stretching sheet placed in saturated porous medium with internal heat generation or absorption. The authors further introduce a new algorithm for solving heat transfer problems in fluid mechanics. The model used for the nanofluid incorporates the nanoparticle volume fraction parameter and a consideration of the chemical reaction effects among other features.

Design/methodology/approach

The partial differential equations for heat and mass transfer in copper-water and silver-water nanofluid flow over stretching sheet were transformed into a system of nonlinear ordinary differential equations. Exact solutions for the boundary layer equations were obtained in terms of a confluent hypergeometric series. A novel spectral relaxation method (SRM) is used to obtain numerical approximations of the governing differential equations. The exact solutions are used to test the convergence and accuracy of the SRM.

Findings

Results were obtained for the fluid properties as well as the skin friction, and the heat and mass transfer rates. The results are compared with limiting cases from previous studies and they show that the proposed technique is an efficient numerical algorithm with assured convergence that serves as an alternative to numerical methods for solving nonlinear boundary value problems.

Originality/value

A new algorithm is used for the first time in this paper. In addition, new exact solutions for the energy and mass transport equations have been obtained in terms of a confluent hypergeometric series.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 24 no. 5
Type: Research Article
ISSN: 0961-5539

Keywords

1 – 10 of over 77000