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Article
Publication date: 5 December 2019

Frank Gardea, Daniel P. Cole, Bryan Glaz and Jaret C. Riddick

This study aims to discuss the effect of carbon nanotubes (CNTs) on the mechanical properties of acrylonitrile–butadiene–styrene (ABS) composites fabricated by additive…

Abstract

Purpose

This study aims to discuss the effect of carbon nanotubes (CNTs) on the mechanical properties of acrylonitrile–butadiene–styrene (ABS) composites fabricated by additive manufacturing (AM). Insight into the energy-dissipation mechanisms introduced and/or enhanced by the addition of CNTs is presented in this study.

Design/methodology/approach

ABS/CNT filaments were fabricated with different concentrations of CNTs. Using a fused deposition modeling approach, unidirectional specimens were printed using a MakerBot Replicator 2X (MakerBot Industries, Brooklyn, NY, USA). Specimens were tested under static and dynamic conditions, with the loading coinciding with the printing direction, to determine elastic modulus, strength and viscoelastic properties.

Findings

A CNT reinforcing effect is evident in a 37 per cent increase in elastic modulus. Likewise, the strength of the composite increases by up to 30 per cent with an increase in weight fraction of CNTs. At low dynamic strain amplitudes (0.05 per cent), a correlation between dissipated strain energy of the butadiene phase and strength of the composite is found such that less dissipation, from constraint of the butadiene particles by the CNTs, leads to higher strength of the composite. At higher dynamic strains, the presence of a high concentration of CNT leads to increased energy dissipation, with a maximum measured value of 24 per cent higher loss factor compared to baseline specimens. Because the trend of the composite behavior is similar (with a higher absolute value) to that of neat ABS, this study’s results indicate that well-established polymer/CNT dissipation mechanisms (such as stick-slip) are not significant, but that the CNTs amplify the dissipation of the ABS matrix by formation of crazes through stress concentrations.

Originality/value

This study provides knowledge of the dissipation behavior in additively manufactured ABS/CNT composites and provides insight into the expansion to new printable materials for dynamics applications.

Details

Rapid Prototyping Journal, vol. 26 no. 3
Type: Research Article
ISSN: 1355-2546

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Article
Publication date: 1 October 1995

E. Dick and J. Steelant

A comparison of the accuracy of the central discretization scheme withartificial dissipation and the upwind flux‐difference TVD scheme has beenmade for the compressible…

Abstract

A comparison of the accuracy of the central discretization scheme with artificial dissipation and the upwind flux‐difference TVD scheme has been made for the compressible Navier‐Stokes equations for high Reynolds number flows. First, a comparison is made on two one‐dimensional model problems. Then the schemes are compared on flat plate boundary layer flow. It is shown that a central scheme basically has poor accuracy due to the isotropic nature of the artificial dissipation. An upwind scheme decomposes the flow into different components and adapts the dissipation to the velocity of the components. The associated ansitropic dissipation results in a good accuracy. It is further discussed how a central discretization scheme with artificial dissipation can be improved at the expense of the same complexity of an upwind scheme.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 5 no. 10
Type: Research Article
ISSN: 0961-5539

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Article
Publication date: 1 June 1993

A. KANIEL, M. MOND and G. BEN‐DOR

Isotropic artificial dissipation is added to the Navier‐Stokes equations along with a correction term which cancels the artificial dissipation term in the limit when the…

Abstract

Isotropic artificial dissipation is added to the Navier‐Stokes equations along with a correction term which cancels the artificial dissipation term in the limit when the mesh size is zero. For a finite mesh size, the correction term replaces the artificial viscosity terms with hyperviscosity terms, i.e., with an artificial dissipation which depends on the fourth derivatives of the velocity. Hyperviscosity more effectively suppresses the higher wave number modes and has a smaller effect on the inertial modes of the flow field than does artificial viscosity. This scheme is implemented using the finite element method and therefore the required amount of dissipation is determined by analysing the discretization on a finite element. The scheme is used to simulate the flow in a driven cavity and over a backward facing step and the results are compared to existing results for these cases.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 3 no. 6
Type: Research Article
ISSN: 0961-5539

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Article
Publication date: 3 September 2018

Siddhartha Biswas and Soumen Shaw

The purpose of this paper is to analyze the thermal shock response on the deformation of circular hollow cylinder in a thermodynamically consistent manner.

Abstract

Purpose

The purpose of this paper is to analyze the thermal shock response on the deformation of circular hollow cylinder in a thermodynamically consistent manner.

Design/methodology/approach

The investigation is carried out under the light of generalized thermoelasticity theory with energy dissipation. In order to obtain the analytical expressions of the components of stress and strain fields, appropriate integral transform technique is adopted and the salient features are emphasized.

Findings

It has been observed that the existence of energy dissipation can minimize the development of the stress components into the cylindrical wall. Since more amount of heat is propagate into the medium in a short period of time consequently, the medium deformed in a high rate in presence of energy dissipation. Two special phenomena are also revealed in the particular cases.

Originality/value

The numerical simulated results are demonstrated through a numerous diagrams and some important observations are explained. This work may be helpful for those researchers who are devoted on several types of heat or fluid flow into the pipeline made with anisotropic solids.

Details

Multidiscipline Modeling in Materials and Structures, vol. 14 no. 3
Type: Research Article
ISSN: 1573-6105

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Article
Publication date: 30 June 2020

Kaili Yao, Dongyang Chu, Ting Li, Zhanli Liu, Bao-Hua Guo, Jun Xu and Zhuo Zhuang

The purpose of this paper is to calculate the Hugoniot relations of polyurea; also to investigate the atomic-scale energy change, the related chain conformation evolution…

Abstract

Purpose

The purpose of this paper is to calculate the Hugoniot relations of polyurea; also to investigate the atomic-scale energy change, the related chain conformation evolution and the hydrogen bond dissociation of polyurea under high-speed shock.

Design/methodology/approach

The atomic-scale simulations are achieved by molecular dynamics (MD). Both non-equilibrium MD and multi-scale shock technique are used to simulate the high-speed shock. The energy dissipation is theoretically derived by the thermodynamic and the Hugoniot relations. The distributions of bond length, angle and dihedral angle are used to characterize the chain conformation evolution. The hydrogen bonds are determined by a geometrical criterion.

Findings

The Hugoniot relations calculated are in good agreement with the experimental data. It is found that under the same impact pressure, polyurea with lower hard segment content has higher energy dissipation during the shock-release process. The primary energy dissipation way is the heat dissipation caused by the increase of kinetic energy. Unlike tensile simulation, the molecular potential increment is mainly divided into the increments of the bond energy, angle energy and dihedral angle energy under shock loading and is mostly stored in the soft segments. The hydrogen bond potential increment only accounts for about 1% of the internal energy increment under high-speed shock.

Originality/value

The simulation results are meaningful for understanding and evaluating the energy dissipation mechanism of polyurea under shock loading, and could provide a reference for material design.

Details

Engineering Computations, vol. ahead-of-print no. ahead-of-print
Type: Research Article
ISSN: 0264-4401

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Article
Publication date: 30 January 2020

Hamidreza Ghanbari Khorram and Alireza Kokabi

Several ultra-low power and gigahertz current-starved voltage-controlled oscillator (CSVCO) circuits have been proposed and compared here. The presented structures are…

Abstract

Purpose

Several ultra-low power and gigahertz current-starved voltage-controlled oscillator (CSVCO) circuits have been proposed and compared here. The presented structures are based on the three-stage hybrid circuit of the carbon nanotube field-effect transistors (CNTFETs) and low-power MOSFETs. The topologies exploit modified and compensated Schmitt trigger comparator parts to demonstrate better consumption power and frequency characteristics. The basic idea in the presented topologies is to compensate the Schmitt trigger comparator part of the basic CSVCO for achieving faster carrier mobility of the holes, reducing transistor leakage current and eliminating dummy transistors.

Design/methodology/approach

This study aims to propose and compare three different comparator-based VCOs that have been implemented using the CNTFETs. The considered circuits are shown to be capable of delivering the maximum 35 tuning frequency in the order of 1 GHz to 5 GHz. A major power thirsty part of the high-frequency ring VCOs is the Schmitt trigger stage. Here, several fast and low-power Schmitt trigger topologies are exploited to mitigate the dissipation power and enhance the oscillation frequency.

Findings

As a result of proposed modifications, more than one order of magnitude mitigation in the VCO power consumption with respect to the previously presented three-stage CSVCO is reported here. Thus, a VCO dissipation power of 3.5 µW at the frequency of 1.1 GHz and the tuning range of 26 per cent is observed for the well-established 32 nm technology and the supply voltage of 1 V. Such a low dissipation power is obtained around the operating frequency of the battery-powered cellular phones. In addition, using the p-carrier mobility compensation and enhancing the rise time of the Schmitt trigger part of the CSVCO, a maximum of 2.38 times higher oscillation frequency and 72 per cent wider tuning range with respect to Rahane and Kureshi (2017) are observed. Simultaneously, this topology exhibits an average of 20 per cent reduction in the power consumption.

Originality/value

Several new VCO topologies are presented here, and it is shown that they can significantly enhance the power dissipation of the GHz CSVCOs.

Details

Circuit World, vol. 46 no. 3
Type: Research Article
ISSN: 0305-6120

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Article
Publication date: 1 April 2005

Rajeevan Chandel, S. Sarkar and R.P. Agarwal

Delay and power dissipation are the two major design constraints in very large scale integration (VLSI) circuits. These arise due to millions of active devices and…

Abstract

Purpose

Delay and power dissipation are the two major design constraints in very large scale integration (VLSI) circuits. These arise due to millions of active devices and interconnections connecting this gigantic number of devices on the chip. Important technique of repeater insertion in long interconnections to reduce delay in VLSI circuits has been reported during the last two decades. This paper deals with delay, power dissipation and the role of voltage‐scaling in repeaters loaded long interconnects in VLSI circuits for low power environment.

Design/methodology/approach

Trade off between delay and power dissipation in repeaters inserted long interconnects has been reviewed here with a bibliographic survey. SPICE simulations have been used to validate the findings.

Findings

Optimum number of uniform sized CMOS repeaters inserted in long interconnects, lead to delay minimization. Voltage‐scaling is highly effective in reduction of power dissipation in repeaters loaded long interconnects. The new finding given here is that optimum number of repeaters required for delay minimization decreases with voltage‐scaling. This leads to area and further power saving.

Research limitations

The bibliographic survey needs to be revised in future, taking the various other aspects of VLSI interconnects viz. noise, cross talk extra into account.

Originality/value

The paper is of high significance in VLSI design and low‐power high‐speed applications. It is also valuable for new researchers in this emerging field.

Details

Microelectronics International, vol. 22 no. 1
Type: Research Article
ISSN: 1356-5362

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Article
Publication date: 15 May 2009

Joaquín Zueco

The unsteady natural convection flow of a viscous dissipative fluid along a semi‐infinite vertical plate subjected to periodic surface temperature oscillation is investigated.

Abstract

Purpose

The unsteady natural convection flow of a viscous dissipative fluid along a semi‐infinite vertical plate subjected to periodic surface temperature oscillation is investigated.

Design/methodology/approach

An electrical‐network model based on the Network Simulation Method is developed to solve the governing equations. The accuracy and effectiveness of the method are demonstrated.

Findings

The increasing of the viscous dissipation and the decreasing in the Prandtl number lead to a decrease in Nusselt number and an increase in the local skin‐friction. Also, it is found that the oscillations of the Nusselt number and of the local skin‐friction depend on the frequency and amplitude of the oscillating surface temperature. For Pr = 1,000 and ε = 0.005 (realistic case) the effect of the viscous dissipation is appreciable at large distances from the leading edge.

Research limitations/implications

The inclusion of viscous dissipation in the energy equation, except of the theoretical interest, has applications in very special cases, for example, gases at very low temperature and also for high Prandtl number liquids.

Originality/value

The influence of the non‐uniformity of wall temperature on the heat transfer by natural convection along of the plate together with the viscous dissipation of the fluid are analysed by means of a new numerical technique based on the electrical analogy.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 19 no. 3/4
Type: Research Article
ISSN: 0961-5539

Keywords

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Article
Publication date: 31 July 2007

Min Tang, J.F. Mao and L.L. Jiang

This paper aims to obtain the optimal wire sizing of buffered global interconnects and to investigate the impact of weight factor on the optimized system performance for…

Abstract

Purpose

This paper aims to obtain the optimal wire sizing of buffered global interconnects and to investigate the impact of weight factor on the optimized system performance for various technology nodes.

Design/methodology/approach

The width and spacing of interconnects are optimized under two scenarios, and corresponding optimum line width is determined by minimizing the value of power‐delay product which is defined as a figure of merit (FOM). Based on the results, the impact of weight factor on the optimized system performance, such as delay and power dissipation per unit length, is analyzed for various technology nodes.

Findings

The analytical expressions of the optimum width are derived under two scenarios. Better FOMs can be achieved for the S=W scenario, but the wireability of the chip degrades considerably. The optimized delay increases with the increasing of weight factor, while the optimized power dissipation decreases with it. For a given weight factor, smaller latency and less power dissipation can be achieved for the S=W case.

Originality/value

The analytical expressions of the optimum width of interconnects are given, and a comprehensive study of the impact of weight factor on the optimized results under two scenarios is presented.

Details

Microelectronics International, vol. 24 no. 3
Type: Research Article
ISSN: 1356-5362

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Article
Publication date: 20 May 2019

Tomasz Janusz Teleszewski

The purpose of this paper is to apply the boundary element method (BEM) to Stokes flow between eccentric rotating cylinders, considering the case when viscous dissipation

Abstract

Purpose

The purpose of this paper is to apply the boundary element method (BEM) to Stokes flow between eccentric rotating cylinders, considering the case when viscous dissipation plays a significant role and determining the Nusselt number as a function of cylinder geometry parameters.

Design/methodology/approach

The problem is described by the equation of motion of Stokes flow and an energy equation with a viscous dissipation term. First, the velocity field and the viscous dissipation term were determined from the momentum equation. The determined dissipation of energy and the constant temperature on the cylinder walls are the conditions for the energy equation, from which the temperature distribution and the heat flux at the boundary of the cylinders are determined. Numerical calculations were performed using the author’s own computer program based on BEM. Verification of the model was carried out by comparing the temperature determined by the BEM with the known theoretical solution for the temperature distribution between two rotating concentric cylinders.

Findings

As the ratio of the inner cylinder diameter to the outer cylinder diameter (r1/r2) increases, the Nusselt number increases. The angle of inclination of the function of the Nusselt number versus r1/r2 increases as the distance between the centers of the inner and outer cylinders increases.

Originality/value

The computational results may be used for the design of slide bearings and viscometers for viscosity testing of liquids with high viscosity where viscous dissipation is important. In the work, new integral kernels were determined for BEM needed to determine the viscous dissipation component.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 30 no. 4
Type: Research Article
ISSN: 0961-5539

Keywords

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