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Article
Publication date: 1 June 1996

Victor P. Janule

Water‐based inks and coatings require alcohols and surfactants to lower their surface tensions to acceptable levels, but have inherent problems of surface wetting…

Abstract

Water‐based inks and coatings require alcohols and surfactants to lower their surface tensions to acceptable levels, but have inherent problems of surface wetting, foaming, flow and levelling common to water‐based systems. They are formulated quite differently from solvent‐based systems, which wet readily and transfer well on to most ink train materials. Surfactants used in water‐based systems tend to be highly surface‐active and can vary significantly with concentration and speed of diffusion depending on the surfactant type and molecular weight and structure compared with inherently low surface tension alcohols. A coating process is dynamic and, because active surfactants are utilized, surface tension will vary as application and press speed vary. It is the resulting variation in the speed of diffusion of the surfactant molecules that directly impacts on the quality of spreading and adhesion. Ink and coatings formulators must have knowledge of the principles of dynamic surface tension, and have instruments that can measure surface tension characteristics. Instruments must be simple to use, accurate, and as automatic as possible, to allow formulators to spend a minimum amount of time gathering necessary data.

Details

Pigment & Resin Technology, vol. 25 no. 6
Type: Research Article
ISSN: 0369-9420

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Book part
Publication date: 6 January 2016

Michel van der Wel, Sait R. Ozturk and Dick van Dijk

The implied volatility surface is the collection of volatilities implied by option contracts for different strike prices and time-to-maturity. We study factor models to…

Abstract

The implied volatility surface is the collection of volatilities implied by option contracts for different strike prices and time-to-maturity. We study factor models to capture the dynamics of this three-dimensional implied volatility surface. Three model types are considered to examine desirable features for representing the surface and its dynamics: a general dynamic factor model, restricted factor models designed to capture the key features of the surface along the moneyness and maturity dimensions, and in-between spline-based methods. Key findings are that: (i) the restricted and spline-based models are both rejected against the general dynamic factor model, (ii) the factors driving the surface are highly persistent, and (iii) for the restricted models option Δ is preferred over the more often used strike relative to spot price as measure for moneyness.

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Article
Publication date: 1 September 2005

M.J. Chern, A.G.L. Borthwick and R. Eatock Taylor

The research is directed at development of an efficient and accurate technique for modelling incompressible free surface flows in which viscous effects may not be…

Abstract

Purpose

The research is directed at development of an efficient and accurate technique for modelling incompressible free surface flows in which viscous effects may not be neglected. The paper describes the methodology, and gives illustrative results for simple geometries.

Design/methodology/approach

The pseudospectral matrix element method of discretisation is selected as the basis for the CFD technique adopted, because of its high spectral accuracy. It is implemented as a means of solving the Navier‐Stokes equations coupled with the modified compressibility method.

Findings

The viscous solver has been validated for the benchmark cases of uniform flow past a cylinder at a Reynolds number of 40, and 2D cavity flows. Results for sloshing of a viscous fluid in a tank have been successfully compared with those from a linearised analytical solution. Application of the method is illustrated by the results for the interaction of an impulsive wave with a surface piercing circular cylinder in a cylindrical tank.

Research limitations/implications

The paper demonstrates the viability of the approach adopted. The limitation of small amplitude waves should be tackled in future work.

Practical implications

The results will have particular significance in the context of validating computations from more complex schemes applicable to arbitrary geometries.

Originality/value

The new methodology and results are of interest to the community of those developing numerical models of flow past marine structures.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 15 no. 6
Type: Research Article
ISSN: 0961-5539

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Article
Publication date: 1 January 2004

Matthias Hase and Bernhard Weigand

A numerical study of heat transfer enhancement due to the deformation of droplets at high Reynolds numbers is described. The two phase‐flow has been computed with a 3D DNS…

Abstract

A numerical study of heat transfer enhancement due to the deformation of droplets at high Reynolds numbers is described. The two phase‐flow has been computed with a 3D DNS program using the volume‐of‐fluid method. The droplets are deformed because of the surrounding gas stream especially due to a sudden rise of flow velocity from zero to Ui. As the governing non‐dimensional parameter the Weber number of the droplets has been varied between 1.3 and 10.8 by assuming different surface tensions at Reynolds numbers between 360 and 853. The dynamical behavior of the droplets as a function of the Weber and the Ohnsorge number are in good agreement with experimental results from the literature. At the highest Reynolds number Re=853, a significant dependency of Nu on We has been found. The comparison of a Nusselt number computed with the real surface area with a Nusselt number computed with the spherical surface area shows that the heat transfer increases not only due to the droplet motion but also due to the larger surface area of the deformed droplet.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 14 no. 1
Type: Research Article
ISSN: 0961-5539

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Article
Publication date: 8 May 2018

Linlin Li and Jiajun Yang

The purpose of this paper is to study the effects of surface roughness on the lubrication performances of the linear rolling guide, which provides theoretical guidance for…

Abstract

Purpose

The purpose of this paper is to study the effects of surface roughness on the lubrication performances of the linear rolling guide, which provides theoretical guidance for its lubrication design.

Design/methodology/approach

The two-variable Weierstrass–Mandelbrot function is used to represent the random and multi-scale characteristics of the rough surface topography. The elastohydrodynamic lubrication (EHL) model of contact between the steel ball and raceway is built. The full numerical solutions of the pressure and film thickness are obtained by using the multi-grid technique.

Findings

The presence of surface roughness can cause the random fluctuations of the pressure and film thickness, and the fluctuations can become more dramatic for the rougher surfaces. It is also found that the film characteristics can be influenced significantly by the working conditions, such as the load, velocity and ambient viscosity of lubricants.

Originality/value

Characterization of surface topographies regarding EHL problems in the past studies cannot reflect random and multi-scale characteristics. In this paper, the fractal-based method is introduced to analysis of the point-contact micro-EHL. It reveals the mechanism and law of contact lubrication influenced by the fractal surface roughness and enriches the lubrication principle and method of the linear rolling guide.

Details

Industrial Lubrication and Tribology, vol. 70 no. 4
Type: Research Article
ISSN: 0036-8792

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Article
Publication date: 15 December 2020

H. Abd El-Wahab, A.M. Nasser, H.M. Abd ElBary, M. Abd Elrahman and M. Hassanein

This paper aims to study the effect of the new modified dispersing agent, milling time of the properties and particle size distribution (PSD) of inkjet ink formulation for…

Abstract

Purpose

This paper aims to study the effect of the new modified dispersing agent, milling time of the properties and particle size distribution (PSD) of inkjet ink formulation for polyester fabric printing.

Design/methodology/approach

The study’s methods include preparation of different formulations of textile inkjet inks based on different types of dispersing agents, then applying and evaluating the prepared formulations on the polyester fabric. The properties of the prepared ink formulations were analyzed by measuring viscosity, surface tension and particle size. The current work is including the study of the effect of using different doses of different dispersing agents and the milling time on their characteristics. Also, the study was extended to evaluate the printed polyester by using the prepared inks according to light fastness, washing fastness, alkali perspiration fastness and crock fastness.

Findings

The results showed that the used dispersing agents and the different milling time enhanced the viscosity and dynamic surface tension in the accepted range, but it was largely cleared in the PSD which tends to perform the inks on the printhead and prevent clogging of nozzles. Light fastness, washing fastness, alkali perspiration fastness and crock fastness gave good results in agreement with this type of inkjet inks for textile printing.

Research limitations/implications

In this work, good results were obtained with this type of dispersing agent for inkjet ink formulations, but for other dispersing agents, other tests could be performed. The inkjet ink could also be formulated with other additives to prevent clogging of nozzles on the printhead.

Practical implications

These ink formulations could be used for printing on polyester fabric by the inkjet printing.

Originality/value

Recently, there was a considerable interest in the study of the effect of PSD on the inkjet inks to prevent clogging of nozzles on the printhead and to improve the print quality on the textile fiber.

Details

Pigment & Resin Technology, vol. 50 no. 4
Type: Research Article
ISSN: 0369-9420

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Article
Publication date: 20 December 2018

Soheil Bazazzadeh, Arman Shojaei, Mirco Zaccariotto and Ugo Galvanetto

The purpose of this paper is to apply the Peridynamic differential operator (PDDO) to incompressible inviscid fluid flow with moving boundaries. Based on the potential…

Abstract

Purpose

The purpose of this paper is to apply the Peridynamic differential operator (PDDO) to incompressible inviscid fluid flow with moving boundaries. Based on the potential flow theory, a Lagrangian formulation is used to cope with non-linear free-surface waves of sloshing water in 2D and 3D rectangular and square tanks.

Design/methodology/approach

In fact, PDDO recasts the local differentiation operator through a nonlocal integration scheme. This makes the method capable of determining the derivatives of a field variable, more precisely than direct differentiation, when jump discontinuities or gradient singularities come into the picture. The issue of gradient singularity can be found in tanks containing vertical/horizontal baffles.

Findings

The application of PDDO helps to obtain the velocity field with a high accuracy at each time step that leads to a suitable geometry updating for the procedure. Domain/boundary nodes are updated by using a second-order finite difference time algorithm. The method is applied to the solution of different examples including tanks with baffles. The accuracy of the method is scrutinized by comparing the numerical results with analytical, numerical and experimental results available in the literature.

Originality/value

Based on the investigations, PDDO can be considered a reliable and suitable approach to cope with sloshing problems in tanks. The paper paves the way to apply the method for a wider range of problems such as compressible fluid flow.

Details

Engineering Computations, vol. 36 no. 1
Type: Research Article
ISSN: 0264-4401

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Article
Publication date: 2 May 2017

Mahmood Khalid and Khalid A. Juhany

The purpose of this paper is to obtain close form expressions for the dynamic stability of conical wave riders with flat surfaces which could be equipped with lifting…

Abstract

Purpose

The purpose of this paper is to obtain close form expressions for the dynamic stability of conical wave riders with flat surfaces which could be equipped with lifting surfaces on its plain flat surface. Numerical simulation would require very large meshes to resolve flows at subscale level and the experimental evaluations would be equally difficult, requiring expensive measurement facilities with challenging procedures to secure such vehicles in confined test sections to obtain satisfactory wind on and wind off oscillations.

Design/methodology/approach

The design method uses appropriate pressure fields using small disturbance theory, which, in turn, is perturbed using the unsteady shock expansion theory to recover suitable expressions for the dynamic stability behaviour.

Findings

It was observed that the dynamic stability of the standard half-cone-type wave riders with flat upper surfaces deteriorates with the axis position measured from the pointed apex reaching a minimum at around x/co = 0.666. The half-cone wave rider with flat upper surfaces is dynamically less stable than a pure cone.

Research limitations/implications

The method is typically less accurate when the similarity parameter Mθ ≤ 1 = 1 or if the angle of attack is not small.

Practical implications

With renewed interest in hypersonic, future hypersonically would be designed as fast lifting bodies whose shapes would be close to the configurations of hypersonic wave riders, especially if they are designed to operate at upper atmosphere altitudes.

Originality/value

The analytic approach outlined in this paper for the evaluation of dynamic and static stability derivatives is original, drawing from the strengths of the small disturbance theory and shock expansion techniques. The method is particularly important, as there are no reported theoretical, numerical or experimental results in the literature.

Details

Aircraft Engineering and Aerospace Technology, vol. 89 no. 3
Type: Research Article
ISSN: 1748-8842

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Article
Publication date: 1 January 1995

Victor P. Janule

Formulators must control coating transfer and adhesion by developing formulations that perform well under widely varying application speeds and operating conditions. There…

Abstract

Formulators must control coating transfer and adhesion by developing formulations that perform well under widely varying application speeds and operating conditions. There are factors that can be controlled, and others that cannot be controlled. It is especially useful, and often essential, for the formulator to have an understanding of the principles and relationships of surface and interfacial tension, and surface energy or “wetting tension”. A review of these important principals and relationships, with a brief introduction to formulation variables sets the stage for introduction of an instrument that can easily measure the surface tension of coatings and the wetting tension of the surfaces or “substrates” to be coated.

Details

Pigment & Resin Technology, vol. 24 no. 1
Type: Research Article
ISSN: 0369-9420

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Article
Publication date: 1 February 1995

Nick Foster and Dimitri Metaxas

A software package is developed for the modelling and animation of viscous incompressible fluids. The full time‐dependent Navier‐Stokes equations are used to simulate 2D…

Abstract

A software package is developed for the modelling and animation of viscous incompressible fluids. The full time‐dependent Navier‐Stokes equations are used to simulate 2D and 3D incompressible fluid phenomena which include shallow and deep fluid flow, transient dynamic flow, vorticity and splashing in simulated physical environments. The package also allows the inclusion of variously shaped and spaced static or moving obstacles that are fully submerged or penetrate the fluid surface. Stable numerical analysis techniques based on finite‐differences are used for the solution of the Navier‐Stokes equations. To model free‐surface fluids, a technique based on the Marker‐and‐Cell method is presented. Based on the fluid’s pressure and velocities obtained from the solution of the Navier‐Stokes equations this technique allows modelling of the fluid’s free surface either by solving a surface equation of by tracking the motion of marker particles. The latter technique is suitable for visualization of splashing and vorticity. Furthermore, an editing tool is developed for easy definition of a physical‐world which includes obstacles, boundaries and fluid properties such as viscosity, initial velocity and pressure. Using the editor, complex fluid simulations can be performed without prior knowledge of the underlying fluid dynamics equations. Finally, depending on the application fluid rendering techniques are developed using standard Silicon Graphics workstation hardware routines.

Details

Engineering Computations, vol. 12 no. 2
Type: Research Article
ISSN: 0264-4401

Keywords

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