Search results
1 – 10 of 13Siya Jiang and Song Fu
The purpose of the paper is to propose some modifications to the SIMPLE (semi-implicit method for pressure-linked equations) algorithm. These modifications can ensure the…
Abstract
Purpose
The purpose of the paper is to propose some modifications to the SIMPLE (semi-implicit method for pressure-linked equations) algorithm. These modifications can ensure the numerical robustness and optimize computational efficiency. They remarkably promote the ability of the SIMPLE algorithm for incompressible DNS (direct numerical simulation) of multiscale problems, such as transitional flows and turbulent flows, by improving the properties of dispersion and dissipation.
Design/methodology/approach
The MDCD (minimized dispersion and controllable dissipation) scheme and MMIM (modified momentum interpolation method) are introduced. Six typical test cases are used to validate the modified algorithm, including the linear convective flow, lid-driven cavity flow, laminar boundary layer, Taylor vortex and DHIT (decaying homogenous isotropic turbulence). Particularly, a highly unsteady DNS of separated-flow transition in turbomachinery is precisely predicted by the modified algorithm.
Findings
The numerical examples show the distinct superiority of the modified algorithm in both internal flows and external flows. The advantages of the MDCD scheme and MMIM make the SIMPLE algorithm a promising method for DNS.
Originality/value
Some effective modifications to the SIMPLE algorithm are addressed. It is the first attempt to introduce the MDCD approach into the SIMPLE-type algorithms. The new algorithm is especially suitable for the incompressible DNS of convection-dominated flows.
Details
Keywords
George Bouzianas, Nikolaos V. Kantartzis and Theodoros D. Tsiboukis
The purpose of this paper is to conduct the accurate analysis and systematic characterisation of realistic generalised bi‐isotropic and lossy chiral metamaterial 3D applications…
Abstract
Purpose
The purpose of this paper is to conduct the accurate analysis and systematic characterisation of realistic generalised bi‐isotropic and lossy chiral metamaterial 3D applications at microwave frequencies.
Design/methodology/approach
An accuracy‐adjustable time‐domain methodology is developed. The technique uses a convex combination of optimal stencils along with an advanced wavefield decomposition to precisely model the highly dispersive, double negative nature of chirality and constitutive parameters. Furthermore, open‐region radiation or scattering problems are terminated through a pertinently modified perfectly matched layer (PML) of variable depth.
Findings
The paper reveals that the proposed algorithm is versatile in the generation of adaptive stencils that attain a very natural way of manipulating continuity conditions at material interfaces. Thus, when periodic structures with split‐ring resonators are to be modelled, the resulting schemes attain optimal precision and minimised dispersion errors. Numerical validation proves these merits via diverse demanding structures of curved shape and multiple layers.
Originality/value
The new technique introduces a family of piecewise polynomials and spatial discretization criteria which lead to additional degrees of freedom for the discrete vectors of the application. In this manner, grid dual is intrinsically embedded in the physical profile of the problem, without resorting to the simplified conventions of other approaches. Moreover, singularity points or demanding geometric discontinuities are properly manipulated, even via coarse lattice resolutions. Thus, the overall accuracy is significantly improved and the computational requirements remain in very logical and affordable levels.
Details
Keywords
V.M Wheeler and K K Tamma
The purpose of this paper is to provide an overview and some recent advances in the models, analysis and simulation of thermal transport of phonons as related to the field of…
Abstract
Purpose
The purpose of this paper is to provide an overview and some recent advances in the models, analysis and simulation of thermal transport of phonons as related to the field of microscale/macroscale heat conduction in solids. The efforts focus upon a fairly comprehensive overview of the subject matter from a unified standpoint highlighting the various approximations inherent in the thermal models. Subsequently, the numerical formulations and illustrations using the current state-of-the-art are provided.
Design/methodology/approach
This paper is dedicated to the approximate solution to the relaxation time phonon Boltzmann equation (BE). While original contributions are pointed out and addressed appropriately, the efforts and contributions will be focussed on a relatively complete overview highlighting the field from one unified standpoint and clearly stating all assumptions that go into the approximations inherent to existing models. The contents will be divided as follows: In the first section the authors will give an overview of semi-classical phonon transport physics. Then the authors will discuss the equation of phonon radiative transport (EPRT) and its approximations—the ballistic-diffusive approximation (BDA) and the new heat equation (NHE). Next the authors derive and discuss the C-F model. A numerical discretization method valid for all models is then presented followed by results to numerical simulations and discussion.
Findings
From a unified treatment based on the introduction of an energy distribution function, the authors have derived the EPRT and its two well-known approximations: BDA and NHE. For completeness and to provide a vehicle for a general numerical discretization approach, the authors have also included analysis of the C-F model and the parabolic and hyperbolic descriptions of heat transfer along with it. The approximation of angular dependence of phonons in radiation-like descriptions of transport has been given special attention. The assumption of isotropy was found to be of paramount importance in the formulation of position space models for phononic thermal transport. For the thin film problem considered here, the NHE along with the proper boundary condition appears to be the best choice to approximate the phonon BE. Not only does it provide predictions that are in excellent agreement with EPRT, it does not require the discretization of phase space making it far more computationally efficient.
Originality/value
The authors hope this work will help dispel the idea that since Fourier’s law describes diffusion (under limiting assumptions) and it has shown to be ineffective in describing heat transfer for very thin films, that diffusion cannot describe heat transfer in thin films and one should look to a radiative description instead. If one considers diffusion in the sense of random motion, as invisaged by the original builders of the subject (Smoluchowski, Einstein, Ornstein et al.), instead of a temperature gradient, the idea that diffusion can govern thermal transport at this scale is not surprising. Indeed, the NHE is essentially a diffusion equation that describes the motion of particles up to the point of true randomness (isotropy) as well as thereafter.
Details
Keywords
Juan Daniel Trejos, Luis Arturo Reyes, Carlos Garza, Patricia Zambrano and Omar Lopez-Botello
An experimental and numerical study of thermal profiles of 316 L stainless steel during selective laser melting (SLM) was developed. This study aims to present a novel approach to…
Abstract
Purpose
An experimental and numerical study of thermal profiles of 316 L stainless steel during selective laser melting (SLM) was developed. This study aims to present a novel approach to determine the significance and contribution of thermal numerical modeling enhancement factors of SLM.
Design/methodology/approach
Surface and volumetric heat models were proposed to compare the laser interaction with the powder bed and substrate, considering the powder size, absorptance and propagation of the laser energy through the effective depth of the metal layer. The approach consists in evaluating the contribution of the thermal conductivity anisotropic enhancement factors to establish the factors that minimized the error of the predicted results vs the experimental data.
Findings
The level of confidence of the carried-out analysis is of 97.8% for the width of the melt pool and of 99.8% for the depth of the melt pool. The enhancement factors of the y and z spatial coordinates influence the most in the predicted melt pool geometry.
Research limitations/implications
Nevertheless, the methodology presented in this study is not limited to 316 L stainless steel and can be applied to any metallic material used for SLM processes.
Practical implications
This study is focused on 316 L stainless steel, which is commonly used in SLM and is considered a durable material for high-temperature, high-corrosion and high-stress situations.
Social implications
The additive manufacturing (AM) technology is a relatively new technology becoming global. The AM technology may have health benefits when compared to the conventional industrial processes, as the workers avoid extended periods of exposure present in conventional manufacturing.
Originality/value
This study presents a novel approach to determine the significance and contribution of thermal numerical modeling enhancement factors of SLM. It was found that the volumetric heat model and anisotropic enhancement thermal approaches used in the present research, had a good agreement with experimental results.
Details
Keywords
“The properties of conventional coolants are limited by the natural characteristics of their hydrocarbon bases which can only be varied slightly by complex formulation, whereas a…
Abstract
“The properties of conventional coolants are limited by the natural characteristics of their hydrocarbon bases which can only be varied slightly by complex formulation, whereas a single synthetic coolant can be formulated to cover a wide range of machining operations”.
Preeti Singh, Sven Saengerlaub, Ali Abas Wani and Horst‐Christian Langowski
The purpose of this paper is to review the new trends in plastic additives, with special focus on developments in food packaging materials.
Abstract
Purpose
The purpose of this paper is to review the new trends in plastic additives, with special focus on developments in food packaging materials.
Design/methodology/approach
Phenomenological research has brought awareness and increased insight into the role of various plastic additives on the packaging of foods. The approach is based on the current trends and the industrial protocols for the additives used in plastic polymer processing for the development of food packaging materials.
Findings
Packaging of foodstuffs is a dynamic process which continually responds to the changes in supply and demand which are the result of adaptations to the varying demands of the consumer, changes in retail practices, technological innovations, new materials and developments in legislation, especially, with respect to environmental concerns. A wide range of additives is available for enhancing the performance and appearance of food packaging, as well as improving the processing of the compound. Polymer additives are important areas of innovation for packaging materials.
Originality/value
The paper reviews and summarizes the recent developments in the functionality of different additives, along with their advantages and disadvantages, currently being used to enhance the properties of food packaging materials that can positively influence the environment within the packaging for the increased demand for raw or processed foods.
Details
Keywords
Ramiro Mantecón, Celia Rufo-Martín, Rodrigo Castellanos and José Diaz-Alvarez
Fused deposition modeling (FDM) is booming as a manufacturing technique in several industrial fields because of its ease of use, the simple-to-meet requirements for its machinery…
Abstract
Purpose
Fused deposition modeling (FDM) is booming as a manufacturing technique in several industrial fields because of its ease of use, the simple-to-meet requirements for its machinery and the possibility to manufacture individual specimens cost-effectively. However, there are still large variations in the mechanical properties of the prints dependent on the process parameters, and there are many discrepancies in the literature as to which are the optimal parameters.
Design/methodology/approach
In this paper, thermal evolution of the printed specimens is set as the main focus and some phenomena that affect this evolution are explored to differentiate their effects on the mechanical properties in FDM. Interlayer waiting times, the thermal effects of the position of the extruder relative to the specimens and the printing layout are assessed. Thermal measurements are acquired during deposition and tensile tests are performed on the specimens, correlating the mechanical behavior with the thermal evolution during printing.
Findings
Additional waiting times do not present significant differences in the prints. Thermal stabilization of the material is observed to be faster than whole layer deposition. The layout is seen to affect the thermal gradients in the printed specimens and increase the fragility. Strain at breakage variations up to 64% are found depending on the layout.
Originality/value
This study opens new research and technological discussions on the optimal settings for the manufacturing of high-performance mechanical components with FDM through the study of the thermal gradients generated in the printed specimens.
Details
Keywords
Xuanya Shi, Francis Boadu and Yifei Du
Both the scope of postentry growth and the scale of postentry growth are essential for Chinese multinational enterprises' aggressive internationalization. Yet, prior literature…
Abstract
Purpose
Both the scope of postentry growth and the scale of postentry growth are essential for Chinese multinational enterprises' aggressive internationalization. Yet, prior literature has not considered the synergistic approach of postentry growth that seeks the scope of growth and the scale of growth simultaneously. Building upon the embeddedness perspective and the learning view, we address how structural embeddedness directly affects firms' postentry growth in the form of scope and scale and indirectly affects postentry growth via both the scope of growth and the scale of growth. Particularly, we investigate the decreasing mediating effect of the growth's scale on the growth's scope when embeddedness strengthens.
Design/methodology/approach
With a survey data set of 206 Chinese multinational firms from manufacturing and service industries, we conduct structural equation modeling (SEM), partial least squares path modeling (PLS-PM), instantaneous indirect effect assessment and hierarchical linear regression model to test our hypotheses.
Findings
First, Chinese multinational enterprises’ (CMNEs) structural embeddedness is positively related to their scope of postentry growth, while has a U-shaped relationship with their scale of postentry growth. Second, CMNEs' scope of postentry growth mediates the relationship between structural embeddedness and the scale of postentry growth, the mediation effect counts for 33.5% of the over effect. Finally, the indirect effect of structural embeddedness on the scope of postentry growth through the scale of postentry growth is nonlinear. As the structural embeddedness strengthens, the positive indirect effect gradually weakens.
Originality/value
We believe this study further connects core international business research on postentry growth to the fast-growing literature on emerging markets multinational enterprises' internationalization. In addition, we undertake an initial effort in addressing an important gap in the literature: how structural embeddedness matters to firms' postentry growth. Moreover, this study finds important evidence to support the direct and indirect effect of structural embeddedness on postentry growth.
Details
Keywords
Iván La Fé-Perdomo, Jorge Andres Ramos-Grez, Gerardo Beruvides and Rafael Alberto Mujica
The purpose of this paper is to outline some key aspects such as material systems used, phenomenological and statistical process modeling, techniques applied to monitor the…
Abstract
Purpose
The purpose of this paper is to outline some key aspects such as material systems used, phenomenological and statistical process modeling, techniques applied to monitor the process and optimization approaches reported. All these need to be taken into account for the ongoing development of the SLM technique, particularly in health care applications. The outcomes from this review allow not only to summarize the main features of the process but also to collect a considerable amount of investigation effort so far achieved by the researcher community.
Design/methodology/approach
This paper reviews four significant areas of the selective laser melting (SLM) process of metallic systems within the scope of medical devices as follows: established and novel materials used, process modeling, process tracking and quality evaluation, and finally, the attempts for optimizing some process features such as surface roughness, porosity and mechanical properties. All the consulted literature has been highly detailed and discussed to understand the current and existing research gaps.
Findings
With this review, there is a prevailing need for further investigation on copper alloys, particularly when conformal cooling, antibacterial and antiviral properties are sought after. Moreover, artificial intelligence techniques for modeling and optimizing the SLM process parameters are still at a poor application level in this field. Furthermore, plenty of research work needs to be done to improve the existent online monitoring techniques.
Research limitations/implications
This review is limited only to the materials, models, monitoring methods, and optimization approaches reported on the SLM process for metallic systems, particularly those found in the health care arena.
Practical implications
SLM is a widely used metal additive manufacturing process due to the possibility of elaborating complex and customized tridimensional parts or components. It is corroborated that SLM produces minimal amounts of waste and enables optimal designs that allow considerable environmental advantages and promotes sustainability.
Social implications
The key perspectives about the applications of novel materials in the field of medicine are proposed.
Originality/value
The investigations about SLM contain an increasing amount of knowledge, motivated by the growing interest of the scientific community in this relatively young manufacturing process. This study can be seen as a compilation of relevant researches and findings in the field of the metal printing process.
Details
Keywords
The purpose of this paper is to study the regions of parameter space of engineering design in which performance is sensitive to design parameters. Some of these parameters (for…
Abstract
Purpose
The purpose of this paper is to study the regions of parameter space of engineering design in which performance is sensitive to design parameters. Some of these parameters (for example, the dimensions and compositions of components) constitute the design, but others are intrinsic properties of materials or Nature. The paper is concerned with narrow regions of parameter space, “cliffs”, in which performance (some measure of the final state of a system, such as ignition or nonignition of a flammable gas, or failure or nonfailure of a ductile material subject to tension) is a sensitive function of the parameters. In these regions, performance is also sensitive to uncertainties in the parameters. This is particularly important for intrinsically indeterminate systems, those whose performance is not predictable from measured initial conditions and is not reproducible.
Design/methodology/approach
We develop models of ignition of a flammable mixture and of failure in plastic flow under tension. We identify and quantify cliffs in performance as functions of the design parameters. These cliffs are characterized by large partial derivatives of performance parameters with respect to the design parameters and with respect to the uncertainties in the model. We calculate and quantify the consequences of small random variations in the parameters of indeterminate systems.
Findings
We find two qualitatively different classes of performance cliffs. In one class, performance is a sensitive function of the parameters in a narrow range that separates wider ranges in which it is insensitive. In the other class, the final state is not defined for parameter values outside some range, and performance is a sensitive function of the parameters as they approach their limiting values. We find that sensitivity of performance to control (design) parameters implies that it is also sensitive to other parameters, some of which may not be known, and to uncertainties of the initial state that are not under the control of the designer. Near or on a cliff performance is degraded. It is also less predictable and less reproducible.
Practical implications
Frequently, design optimization or cost minimization leads to choices of engineering design parameters near cliffs. The sensitivity of performance to uncertainty that we find in those regimes implies that caution and extensive empirical experience are required to assure reliable functioning. Because cliffs are defined as behavior on the threshold of failure, this is a reflection of the trade-off between optimization and margin of safety, and implies the importance of ensuring that margins and uncertainties are quantified. The implications extend far beyond the model systems we consider to engineering systems in general.
Originality/value
Many of these considerations have been part of the informal culture of engineering design, but they were not formalized until the methodology of “Quantification of Margins and Uncertainty” was developed in recent years. Although this methodology has been widely used and discussed, it has only been published in a small number of reports (cited here), and never in a journal article or book. This paper may be its first formal publication, and also its first quantitative application to and illustration with explicit model problems.
Details