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Article

Peng Du, Haibao Hu, Feng Ren and Dong Song

The maintenance of the air–water interface is crucial for the drag reduction on hydrophobic surfaces. But the air bubbles become unstable and even washed away under high…

Abstract

Purpose

The maintenance of the air–water interface is crucial for the drag reduction on hydrophobic surfaces. But the air bubbles become unstable and even washed away under high speed flow, causing the failure of surface hydrophobicity. Thereby, this paper aims to understand the relations between bubble behaviors and surface properties, flow conditions and to discover new methods to maintain the air–water interface.

Design/methodology/approach

Bubble properties on hydrophobic surfaces were characterized using single-component multiphase lattice Boltzmann simulation. Three equations of state (EOSs), including the Peng–Robinson, Carnahan–Starling and modified Kaplun–Meshalkin EOSs, were incorporated to achieve high density ratios.

Findings

Both the static and dynamic properties of bubbles on hydrophobic surfaces were investigated and analyzed under different flow conditions, solid–liquid interactions and surface topology.

Originality/value

By revealing the properties of bubbles on hydrophobic surfaces, the effects of flow conditions and surface properties were characterized. The maintenance method of air–water interface can be proposed according to the bubble properties in the study.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 27 no. 6
Type: Research Article
ISSN: 0961-5539

Keywords

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Article

De-Cheng Feng, Cheng-Dong Yang and Xiao-Dan Ren

This paper aims to present a multi-scale stochastic damage model (SDM) for concrete and apply it to the stochastic response analysis of reinforced concrete shear wall structures.

Abstract

Purpose

This paper aims to present a multi-scale stochastic damage model (SDM) for concrete and apply it to the stochastic response analysis of reinforced concrete shear wall structures.

Design/methodology/approach

The proposed SDM is constructed at two scales, i.e. the macro-scale and the micro-scale. The general framework of the SDM is established on the basis of the continuum damage mechanics (CDM) at the macro-scale, whereas the detailed damage evolution is determined through a parallel fiber buddle model at the micro-scale. The parallel buddle model is made up of micro-elements with stochastic fracture strains, and a one-dimensional random field is assumed for the fracture strain distribution. To represent the random field, a random functional method is adopted to quantify the stochastic damage evolution process with only two variables; thus, the numerical efficiency is greatly enhanced. Meanwhile, the probability density evolution method (PDEM) is introduced for the structural stochastic response analysis.

Findings

By combing the SDM and PDEM, the probabilistic analysis of a shear wall structure is performed. The mean value, standard deviation and the probability density function of the shear wall responses, e.g., shear capacity, accumulated energy consumption and damage evolution, are obtained.

Originality/value

It is noted that the proposed method can reflect the influences of randomness from material level to structural level, and is efficient for stochastic response determination of shear wall structures.

Details

Engineering Computations, vol. 35 no. 6
Type: Research Article
ISSN: 0264-4401

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Article

Arash Tavakoli, M. Pourseifi and Sara Rezaei

The purpose of this paper is to provide a theoretical analysis of the fracture behavior of multiple axisymmetric interface cracks between a homogeneous isotropic layer and…

Abstract

Purpose

The purpose of this paper is to provide a theoretical analysis of the fracture behavior of multiple axisymmetric interface cracks between a homogeneous isotropic layer and its functionally graded material (FGM) coating under torsional loading.

Design/methodology/approach

In this paper, the authors employ the distributed dislocation technique to the stress analysis, an FGM coating-substrate system under torsional loading with multiple axisymmetric cracks consist of annular and penny-shaped cracks. First, with the aid of the Hankel transform, the stress fields in the homogeneous layer and its FGM coating are obtained. The problem is then reduced to a set of singular integral equations with a Cauchy-type singularity. Unknown dislocation density is achieved by numerical solution of these integral equations which are employed to calculate the SIFs.

Findings

From the numerical results, the following key points were observed: first, for two types of the axisymmetric interface cracks, the SIFs decrease with growing in the values of the non-homogeneity. Second, the SIFs increase with increases in interface crack length. Third, the magnitude of the SIFs decreases with increases in the FGM coating thickness. Fourth, the interaction between cracks is an important factor affecting the SIFs of crack tips.

Originality/value

New analytical dislocation solution in an FGM coating-substrate system is developed.

Details

Multidiscipline Modeling in Materials and Structures, vol. 15 no. 6
Type: Research Article
ISSN: 1573-6105

Keywords

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Article

Ana L. Fernández and Liberto de Pablo

Nanocrystalline cobalt spinels were synthesized under hydrothermal conditions, starting from metal chlorides. The color properties in these systems mainly depend upon the…

Abstract

Nanocrystalline cobalt spinels were synthesized under hydrothermal conditions, starting from metal chlorides. The color properties in these systems mainly depend upon the preparative method and cation distributions, which have been determined by X‐ray powder diffraction using Rietveld refinements and visible near infrared absorption spectra. We observe the influence of tetrahedral and octahedral preference of cations such as Co2+, Cr3+, Mn3+ upon the formation and the color development of cobalt spinel pigments. All the samples prepared revealed the formation of single spinel with particle size at about 0.8‐2.1 μm; CoAl2O4 reveals king's blue, CoMn2O4 dark blue and CoCr2O4 bluish green. Cobalt blues developed giving deep absorption characteristic of tetrahedral Co2+ ions at about 550‐680 nm; therefore, color changed from king's blue to bluish green in CoCr2O4, showing the absorption band of octahedral Cr3+ ions owing to the large excess octahedral crystal field stabilization energy.

Details

Pigment & Resin Technology, vol. 31 no. 6
Type: Research Article
ISSN: 0369-9420

Keywords

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Article

Chuang Wang, Ziwen Xing, Xi Pan and Zhilong He

The well-operating condition of journal bearing is the assurance to keep superior performance of water-lubricated twin-screw compressor. To design the journal bearing more…

Abstract

Purpose

The well-operating condition of journal bearing is the assurance to keep superior performance of water-lubricated twin-screw compressor. To design the journal bearing more reasonably for this type of compressor, this paper aims to study the effects of rotating speed and design parameters on bearing characteristics, considering surface roughness and bending deformation of the shaft at the same time.

Design/methodology/approach

The average Reynolds equation considering the effect of surface roughness is adopted and solved by finite difference method and successive over-relaxation method to calculate pressure distribution with real bearing shapes and boundary conditions. The bending deformation of the shaft is calculated using simply supported beam model of variable cross-section.

Findings

The dynamic lubrication characteristics of four water-lubricated journal bearings in twin-screw air compressor are calculated and analyzed. In addition, the static characteristics of journal bearing including friction coefficient, film thickness ratio distribution and water film pressure distribution are calculated numerically with different rotating speed and design parameters. Moreover, some design principles of water-lubricated bearing for twin-screw compressor are put forward.

Originality/value

The lubrication characteristics of the water-lubricated journal bearing in twin-screw air compressor are calculated considering surface roughness and bending deformation of the shaft at the same time. The paper’s results may provide design guidelines for journal bearing in this kind of twin-screw compressor.

Details

Industrial Lubrication and Tribology, vol. 70 no. 8
Type: Research Article
ISSN: 0036-8792

Keywords

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Article

Zhenjie Wang, Zhuquan Wang and Xinhui Su

The authors point out that the existing research confuses the operational liabilities formed based on the “transaction” relationship with the financial liabilities formed…

Abstract

Purpose

The authors point out that the existing research confuses the operational liabilities formed based on the “transaction” relationship with the financial liabilities formed based on the “investment” relationship, which not only exaggerates the value of leverage but also underestimates the level of protection that companies provide for creditors alone. That is, the confusion of concepts not only triggers the problem of leverage misestimate but also triggers the short-term financial risk misestimate. The performance of “nominal leverage” and “nominal short-term solvency” based on total assets calculation cannot reflect the real leverage level and the real short-term financial risk of enterprises.

Design/methodology/approach

To distinguish the concepts of “assets” and “capital” and rationalize the relationship between “transactions” and “investments”, authors systematically design the “real leverage” indicators and “real short-term solvency” indicators, and measure the degree of misestimate of leverage and short-term financial risk indicators by traditional research. On this basis, this paper describes and analyses the trends of leveraged misestimate and short-term financial risk misestimate of listed companies in China and analyses which companies have more serious leverage misestimate. And it helps readers to form an objective understanding of the leveraged misestimate and short-term financial risk misestimate of listed companies in China.

Findings

Firstly, the overall high level of leverage of listed companies in China in the traditional sense is largely because of the misestimate of indicators. And this kind of misestimate is more serious among firms that have advantages in trading, such as state-owned enterprises and firms with higher market shares. Secondly, for most firms with normal solvency, traditional research systematically overestimated the negative impact of “nominal leverage” on financial risk indicators (represented by short-term solvency). The overestimation is significant in firms with serious leverage misestimate. Thirdly, indicators’ misestimate of the traditional research makes the banks cannot make effective credit decisions according to the firm's “real leverage” and “real short-term solvency”.

Originality/value

Firstly, clarify the differences between the concepts of “assets” and “capital”, and clarify the level of “real leverage” of listed companies in China, which is conducive to the process of “de-leveraging”. Secondly, revise the problem of misestimate of related indicators, so that financial institutions can clearly identify the true profitability and real risk level of the entity domain, and thus improve the effectiveness of credit decisions.

Details

Nankai Business Review International, vol. 11 no. 4
Type: Research Article
ISSN: 2040-8749

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Article

Xueye Chen, Jienan Shen and Zengliang Hu

The purpose of this study is to provide a micromixer for achieving effective mixing of two liquids. The mixing of two liquids is difficult to achieve in microfluidic chips…

Abstract

Purpose

The purpose of this study is to provide a micromixer for achieving effective mixing of two liquids. The mixing of two liquids is difficult to achieve in microfluidic chips because they cannot form turbulence at small dimensions and velocities.

Design/methodology/approach

In this paper, four kinds of passive micromixers based on splitting–recombination and chaotic convection are compared. First, a better E-shape mixing unit based on the previous F-shape mixing unit has been designed. Then, the E-shape mixing units are further combined to form three micromixers (i.e. E-mixer, SESM and FESM).

Findings

Finally, the mixing experimental results show that the mixing indexes of E-mixer, SESM and FESM are more than those of F-mixer when the Reynolds number range is from 0.5 to 100. And at Re = 15, the lowest mixing index of E-mixer is 71%, which is the highest of the four micromixers.

Originality/value

At Re = 80, the highest mixing index of F-mixer and E-mixer is 92 and 94 per cent, respectively, and then it begins to decrease. But the mixing index of SESM and FESM remains close to 100 per cent.

Details

Sensor Review, vol. 38 no. 3
Type: Research Article
ISSN: 0260-2288

Keywords

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Article

Cong Bang Pham, Kah Fai Leong, Tze Chiun Lim and Kerm Sin Chian

The purpose of this paper is to develop a new bio‐plotter using a rapid freeze prototyping (RFP) technique and to investigate its potential applications in fabricating…

Abstract

Purpose

The purpose of this paper is to develop a new bio‐plotter using a rapid freeze prototyping (RFP) technique and to investigate its potential applications in fabricating tissue scaffolds.

Design/methodology/approach

The development of cryogenic bio‐plotters including design steps of hardware as well as software is addressed. Effects of structural parameters and process parameters on the properties of tissue scaffolds are demonstrated through simulation and experimental results.

Findings

The paper finds that the RFP method is suitable to fabricate macro‐ and micro‐porous scaffolds, especially for temperature‐sensitive polymers. In addition, through simulation and experiment results, it also shows that macro‐ and micro‐porous properties could be manipulated by structural parameters and process parameters, respectively.

Research limitations/implications

This paper shows that the chamber temperature is an important process parameter that can provide the means to control the micro‐porous structure of the scaffold. However, if the temperature is set too high, the fiber is frozen so rapidly that it cannot be fused with other fibers of the previous layer. On the other hand, if the temperature is too low, the fiber is not solidified fast enough. So, the chamber temperature, together with extruding pressure and nozzle velocity, must be optimized, which will be further investigated in future work.

Originality/value

The RFP technique is successfully proposed to construct 3D tissue scaffolds. In addition, a new cryogenic bio‐plotter is designed and developed, in which general algorithms of rapid prototyping method are presented and implemented, facilitating the fabrication of tissue scaffolds with various cross‐hatching patterns in a RFP process.

Details

Rapid Prototyping Journal, vol. 14 no. 4
Type: Research Article
ISSN: 1355-2546

Keywords

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Article

Qin Zhu, Renan Jia and Xiaohua Lin

In the context of China, the purpose of this paper is to empirically answer three related questions: Could circular agriculture (CA) attain economic, ecological and social…

Abstract

Purpose

In the context of China, the purpose of this paper is to empirically answer three related questions: Could circular agriculture (CA) attain economic, ecological and social benefits simultaneously? What is key to a successful CA business in emerging economies? And who plays the vital role in building and sustaining a circular business?

Design/methodology/approach

The paper is based on a field study and looks at a farm in China. It uses a triangulation methodology to collect information. Besides longitudinal filed work at the farm, the researchers have also interviewed multiple stakeholders and conducted field research at the local markets.

Findings

With concrete performance data, the study proves that a circular approach can help achieve ecological, economic and social goals together. It shows that economic viability is essential to succeeding in circular operation, sufficient production pathways are required to make such operation sustainable, and entrepreneurship is key to build and grow a circular business.

Research limitations/implications

The findings point to the crucial role of entrepreneurship in promoting the circular model in emerging economies. These findings, however, may not be readily generalizable, given the limitations of the case study approach.

Practical implications

The study highlights a few areas in which government assistance can make a difference, including financial incentives, information provision, technical support and most importantly the creation of a positive environment for entrepreneurial development.

Originality/value

While prior research emphasizes the role of government in promoting circular economy in developing and emerging markets, the study proves that entrepreneurship is key to turning government initiatives into economically viable and sustainable circular operation.

Details

Management Decision, vol. 57 no. 4
Type: Research Article
ISSN: 0025-1747

Keywords

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Article

Yanbing Ni, Biao Zhang, Wenxia Guo and Cuiyan Shao

The purpose of this paper is to develop a means of the kinematic calibration of a parallel manipulator with full-circle rotation.

Abstract

Purpose

The purpose of this paper is to develop a means of the kinematic calibration of a parallel manipulator with full-circle rotation.

Design/methodology/approach

An error-mapping model based on the space vector chain is formulated and parameter identification is proposed based on double ball-bar (DBB) measurements. The measurement trajectory is determined by the motion characteristics of this mechanism and whether the error sources can be identified. Error compensation is proposed by modifying the inputs, and a two-step kinematic calibration method is implemented.

Findings

The simulation and experiment results show that this kinematic calibration method is effective. The DBB length errors and the position errors in the end-effector of the parallel manipulator with full-circle rotation are greatly reduced after error compensation.

Originality/value

By establishing the mapping relationship between measured error data and geometric error sources, the error parameters of this mechanism are identified; thus, the pose errors are unnecessary to be measured directly. The effectiveness of the kinematic calibration method is verified by computer simulation and experiment. This proposed calibration method can help the novel parallel manipulator with full-circle rotation and other similar parallel mechanisms to improve their accuracy.

Details

Industrial Robot: An International Journal, vol. 43 no. 3
Type: Research Article
ISSN: 0143-991X

Keywords

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