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Article

Soheil Oveissi, Davood Toghraie, S. Ali Eftekhari and Ali J. Chamkha

This study aims to study the transverse vibration and instabilities of the fluid-conveying single-walled carbon nanotubes (CNTs). To this purpose, the Euler–Bernoulli beam…

Abstract

Purpose

This study aims to study the transverse vibration and instabilities of the fluid-conveying single-walled carbon nanotubes (CNTs). To this purpose, the Euler–Bernoulli beam model is used. Also, the surface effects, small-size effects of the both fluid and structure and two different elastic mediums viscoelastic and Pasternak elastic are investigated.

Design/methodology/approach

To consider the nano-scale for the CNT, the strain-inertia gradient theory is used and to solve the governing equation of motion for the system, the Galerkin’s method is used. The effect of the flow velocity, aspect ratio, characteristic lengths of the mentioned theory, effects of Knudsen number and effects of the Winkler, the Pasternak elastic and the viscoelastic medium on the frequencies and stabilities of the system are studied. The effects of the above parameters on the vibrational behavior are investigated both separately and simultaneously.

Findings

The results show that the critical flow velocity value is increased as the aspect ratio, characteristic lengths, Winkler modulus, shear and damping factors increase. Also, the critical flow velocity is increased by considering the surface effects. In addition, the consequence of increase in the nano-flow-size effects (Knudsen number) is decreasing the critical flow velocity. Moreover, it can be observed that the effect of the shear factor on increasing the critical flow velocity is different from the rest of parameters.

Originality/value

Use of Timoshenko and modified couple stress theories and taking into account Von-Karman expressions for investigating the nonlinear vibrations of triple-walled CNTs buried within Pasternak foundation.

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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Article

Yuanpeng Cheng, Yu Bai, Zili Li and JianGuo Liu

The purpose of this paper was to investigate the corrosion behavior of X65 steel in the CO2/oil/water environment using mass loss method, potentiodynamic polarization…

Abstract

Purpose

The purpose of this paper was to investigate the corrosion behavior of X65 steel in the CO2/oil/water environment using mass loss method, potentiodynamic polarization technique and characterization of the corroded surface techniques.

Design/methodology/approach

The weight loss analysis, electrochemical study and surface investigation were carried out on X65 steel that had been immersed in the CO2/oil/water corrosive medium to understand the corrosion behavior of gathering pipeline steel. The weight loss tests were carried out in a 3L autoclave, and effects of flow velocity, CO2 partial pressure and water cut on the CO2 corrosion rate of X65 steel were studied. Electrochemical studies were carried out in a three-electrode electrochemical cell with the test temperature of 60°C and CO2 partial pressure of 1 atm by recording open circuit potential/time and potentiodynamic polarization characteristics. The surface and cross-sectional morphologies of corrosion product scales were characterized using scanning electron microscopy. The phases of corrosion product scales were investigated using X-ray diffraction.

Findings

The results showed that corrosion rates of X65 steel both increased at first and then decreased with the increase of flow velocity and CO2 partial pressure, and there were critical velocity and critical pressure in the simulated corrosive environment, below the critical value, the corrosion products formed on the steel surface were loose, porous and unstable, higher than the critical value, the corrosion product ?lms were dense, strong adhesion, and had a certain protective effect. Meanwhile, when the flow velocity exceeded the critical value, oil film could be adsorbed on the steel surface more evenly, corrosion reaction active points were reduced and the steel matrix was protected from being corroded and crude oil played a role of inhibitor, thus it influenced the corrosion rate. Above the critical CO2 partial pressure, the solubility of CO2 in crude oil increased, the viscosity of crude oil decreased and its fluidity became better, so that the probability of oil film adsorption increased, these factors led to the corrosion inhibition of X65 steel reinforced. The corrosion characteristics of gathering pipeline steel in the corrosive environment containing CO2 would change due to the presence of crude oil.

Originality/value

The results can be helpful in selecting the suitable corrosion inhibitors and targeted anti-corrosion measures for CO2/oil/water corrosive environment.

Details

Anti-Corrosion Methods and Materials, vol. 66 no. 2
Type: Research Article
ISSN: 0003-5599

Keywords

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Article

Mouafo Teifouet Armand Robinson and Sarp Adali

Cantilever plates subject to axial flow can lose stability by flutter and properties such as viscoelasticity and laminar friction affect dynamic stability. The purpose of…

Abstract

Purpose

Cantilever plates subject to axial flow can lose stability by flutter and properties such as viscoelasticity and laminar friction affect dynamic stability. The purpose of the present study is to investigate the dynamic stability of viscoelastic cantilever plates subject to axial flow by using the differential quadrature method.

Design/methodology/approach

Equation of motion of the viscoelastic plate is derived by implementing Kelvin-Voigt model of viscoelasticity and applying inverse Laplace transformation. The differential quadrature method is employed to discretize the equation of motion and the boundary conditions leading to a generalized eigenvalue problem. The solution is verified using the existing results in the literature and numerical results are given for critical flow velocities

Findings

It is observed that higher aspect ratios lead to imaginary part of third frequency becoming negative and causing single-mode flutter instability. It was found that flutter instability does not occur at low aspect ratios. Moreover the friction coefficient is found to affect the magnitude of critical flow velocity, however, its effect on the stability behaviour is minor.

Originality/value

The effects of various problem parameters on the dynamic stability of a viscoelastic plate subject to axial flow were established. It was shown that laminar friction coefficient of the flowing fluid increases the critical fluid velocity and higher aspect ratios lead to single-mode flutter instability. The effect of increasing damping of viscoelastic material on the flutter instability was quantified and it was found that increasing viscoelasticity can lead to divergence instability.

Details

Engineering Computations, vol. 34 no. 4
Type: Research Article
ISSN: 0264-4401

Keywords

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Article

Bijan Mohamadi, S. Ali Eftekhari and Davood Toghraie

The purpose of this paper is to investigate nonlinear vibrations of triple-walled carbon nanotubes buried within Pasternak foundation carrying viscous fluids.

Abstract

Purpose

The purpose of this paper is to investigate nonlinear vibrations of triple-walled carbon nanotubes buried within Pasternak foundation carrying viscous fluids.

Design/methodology/approach

Considering the geometry of nanotubes, the governing equations were initially derived using Timoshenko and modified couple stress theories and by taking into account Von-Karman expressions. Then, by determining boundary conditions, type of fluid motion, Knudsen number and, ultimately, fluid viscosity, the principal equation was solved using differential quadrature method, and linear and nonlinear nanotube frequencies were calculated.

Findings

The results indicated that natural frequency is decreased as the fluid velocity and aspect ratio increase. Moreover, as the aspect ratio is increased, the results converge for simple and fixed support boundary conditions, and the ratio of nonlinear to linear frequencies approaches. Natural frequency of vibrations and critical velocity increase as Pasternak coefficient and characteristic length increase. As indicated by the results, by assuming a non-uniform velocity for the fluid and a slip boundary condition at Kn = 0.05, reductions of 10.714 and 28.714% were observed in the critical velocity, respectively. Moreover, the ratio of nonlinear to linear base frequencies decreases as the Winkler and Pasternak coefficients, maximum deflection of the first wall and characteristic length are increased in couple stress theory.

Originality/value

This paper is a numerical investigation of nonlinear vibration analysis for triple-walled carbon nanotubes conveying viscous fluid.

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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Article

Frank C. Mock

IN our recent intensive efforts to carry aeroplane performance to higher speeds and altitudes, we have encountered many complex problems in apparently simple development…

Abstract

IN our recent intensive efforts to carry aeroplane performance to higher speeds and altitudes, we have encountered many complex problems in apparently simple development of previously satisfactory practice. Ignition, cooling, and fuel vapour control are only a few instances. Similarly, the design of an aircraft carburettor airscoop would appear to offer only elementary questions of design. How to locate the opening where it will receive full air‐speed ram, and how to fair it in with the cowling structure, would seem to lie well within current knowledge; actually there are indications that many present designs could be improved. Likewise, many of our ideas as to the effect of airscoops upon carburation have been derived from the past when carburettors were non‐automatic, requiring continuous re‐adjustment by the pilot as soon as the aeroplane left the ground for changes of air pressure, temperature, and ram, and any accompanying disturbances in the scoop duct system could usually, though not always, be taken care of by the same manual adjustment.

Details

Aircraft Engineering and Aerospace Technology, vol. 15 no. 5
Type: Research Article
ISSN: 0002-2667

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Article

Khosro Morovati and Afshin Eghbalzadeh

While many stepped spillways geometry design guidelines were developed for flat steps, designing pooled steps might be an appropriate alternative to spillways working more…

Abstract

Purpose

While many stepped spillways geometry design guidelines were developed for flat steps, designing pooled steps might be an appropriate alternative to spillways working more efficiency. This paper aims to deal with the inception point of air-entrainment and void fraction in the different height of the pools. Following that, pressure distribution was evaluated in aerated and non-aerated regions under the effect of different heights of the pools and slopes through the use of the FLOW-3D software. Comparison of obtained numerical results with experimental ones was in good agreement for all discharges used in this study. Pools height had the insignificant effect on the inception point location. The value of void fraction was more affected in lower discharges in comparison with higher ones. Negative pressure was not seen over the crest of spillway (non-aerated region), and the maximum pressure values were obtained for pools with 15 cm height along the crest in each discharge. In all slopes, negative pressure was not formed near the step bed in the pooled and flat stepped spillways. However, negative pressure was formed in more area near the vertical face in the flat stepped spillway compared with the pooled stepped spillway which increases the probability of cavitation phenomenon in the flat stepped chute.

Design/methodology/approach

A pooled stepped spillway was used in order to evaluate pressure, void fraction, and inception point. Also, different height of the pools was used. Numerical simulation of this study was fulfilled through Flow-3D software. The obtained results indicated that pools can affect two-phase flow characteristics including pressure, void fraction and inception point.

Findings

Over the crest, negative pressure was not seen. Pressure values were different for all used heights and the maximum ones obtained for 15 cm height. Also, pooled stepped played a more effective role in reducing the negative pressure points compared with flat cases. Inception point location was more affected in nappe and transition flow regimes in comparison with skimming flow regime particularly for 9 and 15 cm heights.

Originality/value

The research results of Felder et al. (2012a) from the University of Queensland were used to numerically simulate the flow over the pooled stepped spillway.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 28 no. 4
Type: Research Article
ISSN: 0961-5539

Keywords

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Article

Wei Qu, Huailiang Zhang, Wei Li, Ling Peng and Wenqian Sun

To improve the transmission efficiency and reduce the damage to pipes in the hydraulic systems of tunnel boring machine subjected to random vibration, this paper aims to…

Abstract

Purpose

To improve the transmission efficiency and reduce the damage to pipes in the hydraulic systems of tunnel boring machine subjected to random vibration, this paper aims to propose a novel dynamic characteristic analysis method that considers random vibration.

Design/methodology/approach

A fluid-structure interaction motion equation of the pipe is established by using Hamilton’s principle. The finite element method and discrete analysis method of random vibration are used to construct a model of the dynamic behavior of the pipe.

Findings

The influences of fluid parameters and external excitation parameters on the dynamic characteristics of pipes are analyzed. The experimental results are found to be in good agreement with the simulation results, which demonstrates that the proposed analytical method can provide a theoretical reference for the design and selection of hydraulic pipes subjected to random vibration.

Originality/value

The proposed method can be regarded as a future calculation method for pipes subjected to random vibration, and the transmission efficiency of the pipe can be improved.

Details

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

Keywords

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Article

G. Butler

The influence of water movement on corrosion is of interest in most of the problems concerned with aqueous attack on metals ranging from ships' hulls to metal pipes. Even…

Abstract

The influence of water movement on corrosion is of interest in most of the problems concerned with aqueous attack on metals ranging from ships' hulls to metal pipes. Even in cases where no relative motion is imposed, convection currents arise due to temperature variations in the solution. The rate of many reactions between solids and solutions is controlled by the transport of reactants to the surface and of products from it. The main concentration change takes place in a very thin layer next to the solid surface, the boundary diffusion layer. Here transport takes place slowly by diffusion while in the bulk of the solution the concentration is kept the same at all points by convection currents. This article discusses the influence of the boundary layer on corrosion rate of ferrous materials in water.

Details

Anti-Corrosion Methods and Materials, vol. 8 no. 1
Type: Research Article
ISSN: 0003-5599

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Article

Slawomir Golak and Mirosław Kordos

The attractiveness of functionally graded composites lies in the possibility of a gradual spatial change of their properties such as hardness, strength and wear…

Abstract

Purpose

The attractiveness of functionally graded composites lies in the possibility of a gradual spatial change of their properties such as hardness, strength and wear resistance. The purpose of this paper is to discuss the use of electromagnetic buoyancy to separate the reinforcement particles during the casting process of such a composite.

Design/methodology/approach

The basic problem encountered in the process of casting composites is to obtain electromagnetic buoyancy and simultaneously to avoid a flow of the liquid metal which destroys the desired composite structure. In this paper the authors present the methodology of numerical optimization of inductor geometry in order to homogenize the electromagnetic force field distribution.

Findings

The optimization method based on searching the solution subspace created by applying knowledge of the modelled process physics proved better than the universal local optimization methods. These results were probably caused by the complex shape of the criterion function hypersurface characterized by the presence of local minima.

Practical implications

Due to their characteristics, functionally graded composites are of great interest to the automotive, aerospace and defense industries. In the case of metal matrix composites casting techniques (as the presented one) are the most effective methods of producing functionally graded materials.

Originality/value

The paper presents the optimization of a new process of casting functionally graded composites in a low-frequency alternating electromagnetic field. The process involves problems that did not occur previously in the area of electromagnetic processing of materials. The paper proposes the use of special design of inductors to homogenize the electromagnetic force field.

Details

COMPEL: The International Journal for Computation and Mathematics in Electrical and Electronic Engineering, vol. 35 no. 1
Type: Research Article
ISSN: 0332-1649

Keywords

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Article

Xiantao Zhang and Wei Liu

In the coupling of aircraft pipeline structures, current research works mainly focus on fluid-solid coupling effects or a single part of structure vibration like a…

Abstract

Purpose

In the coupling of aircraft pipeline structures, current research works mainly focus on fluid-solid coupling effects or a single part of structure vibration like a pipeline. Because of the clamp, the pipe vibration caused by fluid pulsation was transmitted to the body, and the body vibration was also transmitted to the pipe structure. Thus, the relationship between the airframe and the pipeline system cannot be separated, and the influence of airframe needs to be considered when coupling structure under vibration. The paper aims to discuss these issues.

Design/methodology/approach

This paper aims to investigate the influence of pipeline layouts on airframe-clamps-pipeline (ACP) structure’s dynamic response by experiment and simulation method. First, ACP structures are established including three parts. The natural frequencies and mode shapes are obtained by hammering experiment. The mode results are in agreement with numerical simulation. By using electromagnetic vibration shaker, extinction is applied on ACP structure, and then the dynamic responses of structure can be obtained by test equipments. The influence principle of pipeline layouts is obtained by dynamic response analysis. The present study provides a method for pipeline layout design in aerospace engineering.

Findings

Under the ACP’s first-order resonance frequency excitation, the maximum stress increases when the Z-shaped pipeline bending position changes from 1/2 to 1/5. The opposite way occurs under the only pipeline resonance frequency excitation. The stress amplitudes near both sides (inner and outer) of the clamp on the plate surface change with the excitation frequency. Under the ACP’s first-order resonance frequency excitation, the outer side stress is larger than the inner side stress, but under the only pipeline resonance frequency excitation, the inner side stress is larger than the outer side stress.

Originality/value

The study of the effect of pipeline layout parameters on ACP structure provides a method for pipeline layout design in aerospace engineering.

Details

Multidiscipline Modeling in Materials and Structures, vol. 16 no. 2
Type: Research Article
ISSN: 1573-6105

Keywords

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