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The present discussion concerns some doubtful results included in the above paper.

This position paper reviews current research topics in the study of athletic activities, which biomechanists would consider to be important or contentious issues, and focuses on critically evaluating what needs to be done in future research. It concludes that there remain many unresolved issues in the mechanics of athletic activities, many of which overlap with other disciplines. These issues relate to injury mechanisms, the control and co-ordination of movement, and ways of providing biomechanical feedback to enhance performance in athletic activities. Research to address these important issues will increasingly become more question than discipline orientated, must focus more on mechanisms than description, and will involve teams of researchers interacting on interdisciplinary problems.

Experiments are conducted to study the hydrodynamic behavior of three-phase pulp slurry systems at consistencies ranging from 0.1 to 1.0% (weight percent pulp). The pulp phase is a low-density fibrous material which swells to several times its original volume in water. The overall hydrodynamic behavior, including the regime transitions, of a multi-bubble, three-phase pulp slurry is studied by measuring the overall gas holdup and by using a light transmittance probe to determine the bubble characteristics. The results demonstrate that the hydrodynamic behavior of a three-phase pulp slurry varies from the behavior of a gas-liquid system. The deviation in the behavior becomes more pronounced as the pulp consistency increases. The bubble characteristics of bubbles injected through a single bubble injector are studied in a small rectangular column through the use of flow visualization and a particle image velocimetry technique. The measured change in the behavior of single bubbles injected into the pulp slurry through a single injector, is the basis for a proposed mechanism for the increased bubble coalescence in a multi-bubble system.

A serious error has been found in the above paper.

Depending on unique operation characteristics for voltage applied on valve side winding of the converter transformers, it is extraordinarily significant to study the partial discharge (PD) behavior with oil-paper insulation under combined AC–DC voltage. Therefore, this paper investigated PD inception characteristics by pulse current methods with needle-plate electrode system under combined AC–DC voltage. Furthermore, 3D electric field distributions versus combined AC–DC voltage in different ratios were calculated by Finite Element Analysis (FEA). An experimental conclusion was drew that AC partial discharge inception voltage (PDIV) in pure oil would decrease linearly with the DC component increasing but the inception voltage with oil-paper insulation appeared to be independent of DC voltage and dependent of AC voltage. And 3D electric field distribution deduced from simulation provided a supplementary proof on the experimental results. Moreover, high speed photography was used to capture emitted light produced by discharge, estimate streamer velocity (1.8 km/s) and record streamer initiation and propagation process in oil gap. Previous studies have shown that the prebreakdown phenomena involving the generation and propagation of vapor channels through the oil could be divided into a three-stage process.

Cooling tower emissions are harmful for several reasons such as air polluting, wetting, icing and solid particle deposition, but mainly due to human health hazards (i.e. Legionella). There are several methods for measuring drift drops. This paper is focussed on the sensitive paper technique, which is suitable in low drift scenarios and real conditions. The lack of an automatic classification method motivated the development of a digital image process algorithm for the Sensitive Paper method. This paper presents a detailed description of this method, in which, drop-like elements are identified by means of the Canny edge detector combined with some morphological operations. Afterwards, the application of a J48 decision tree is proposed as one of the most relevant contributions. This classification method allows us to discern between stains whose origin is a drop and stains whose origin is not a drop. The method is applied to a real case and results are presented in terms of drift and PM10 emissions. This involves the calculation of the main features of the droplet distribution at the cooling tower exit surface in terms of drop size distribution data, cumulative mass distribution curve and characteristic drop diameters. The Log-normal and the Rosin–Rammler distribution functions have been fitted to the experimental data collected in the tests and it can been concluded that the first one is the most suitable for experimental data among the functions tested (whereas the second one is less suitable). Realistic PM10 calculations include the measurement of drift emissions and Total Dissolved Solids as well as the size and number of drops. Results are compared to the method proposed by the U.S. Environmental Protection Agency assessing its overestimation. Drift emissions have found to be 0.0517% of the recirculating water, which is over the Spanish standards limit (0.05%).

In a previous work, a moisture diffusion coefficient for non-impregnated transformer insulation paper was proposed, which is useful for analysing the moisture dynamics in electrical power transformer insulation during its construction stage. This diffusion coefficient was determined using a set of experimental drying curves obtained in a thermogravimetric analyzer and an optimization process that employs genetic algorithms. The expression for the moisture diffusion coefficient proposed in that previous work is dependent on the temperature, insulation thickness and average moisture concentration. The use of average moisture concentration is not common in diffusion models. In this paper, a new expression for the moisture diffusion coefficient is proposed in which the dependence on average moisture has been substituted by a dependence on the local concentration. This new expression was obtained that is more suitable for diffusion models. To obtain that expression, the same experimental data used in the previous study have been used, but the genetic algorithm’s optimization process was modified. In this paper, a description of the applied procedure is detailed, and the new proposed expression is presented. Finally, a comparison between both equations, the one dependent on average moisture and the one dependent on the local moisture, is performed using a drying diffusion model implemented in a finite element commercial software package.

Images and droplet size measurements show that paper spray operates in two distinct spray modes. Mode 1 occurs in solvent-rich systems in which multiple Taylor conejets are created producing droplets of a range of sizes. Mode 2 occurs at low solvent flow rates and the higher currents (∼1 uA) suggest a contribution from corona discharge. The latter experiment produces monodispersed droplet sizes. A distinguishing feature of paper spray in both modes is a fixed droplet velocity independent of droplet size.

ispartof: COMPOSITE STRUCTURES vol:226 status: published

In our paper titled “CFD analysis on the influence of helical carving in a vortex flow solar reactor”, we have presented a 3D CFD analysis of a turbulent and reactive flow for directly irradiated solar thermochemical reactor to characterize the influence of flow behavior on the heat transfer and solar cracking process. The heat transfer by radiation from carbon particles is considered by providing global absorption and scattering coefficients in the computational domain obtained from Mie code. The flow field is based on RNG k-3 model derived using renormalization group theory. We have validated our numerical procedure by comparing the outlet temperature and cavity temperaturemeasurements of Hirsch and Steinfeld (Solar hydrogen production by thermal decomposition of natural gas using a vortex-flow reactor. Int J Hydrogen Energy 2004; 29:47-55) for Run 1 Configuration 1. As it is seen in our paper, our numerical simulations predict the mixture (gas-particle) flowoutlet and cavitywall temperatures as 1240K and 1751.3K,which deviates from the experimentally

A new two-dimensional network model is proposed as a micromechanics model to simulate paper’s failure process due to sequentially breakages of fibers and/or bonds. Paper is approximated as a network composed of fibers any two of which link to each other by their intersecting point, namely so-called bond. Fibers distribute along three particular directions, leading to network’s macro-level isotropy. In the framework of finite element method, nodes correspond to fiber-to-fiber bonds, while elements are fiber segments between every two neighboring nodes and described by Timoshenko beam theory. Element breaks when its equivalent internal tensile stress reaches the tensile strength of fiber. Strength of nodes, i.e. fiber-to-fiber bonds is assumed to be dependant on shearing interaction between fibers, considering the dominant interaction is shearing in a plane problem. Numerical examples show the model’s capacity of reflecting basic failure characteristic in paper. Influences of fiber length and the ratio of fiber strength to bond strength are analyzed in detail.

Effects of suction pressure and permeability on the steam heating characteristics of the wet paper are studied. Experimental results show that suction pressure enhances the energy absorption in the wet paper and effects of suction pressure strongly appear in the high-permeability paper, and also absorbed energy rate is decreased with increasing in heating time. From the numerical simulation results it is found that increase in moisture content and decrease of pressure gradient reduce the absorbed energy rate. Dimensionless numbers are derived from the basic equations to summarize the experimental and numerical simulation results.

A mechanical model of the elastic, viscous and creep behavior of a cellulose-based Electro-Active Paper (EAPap), including C1, C2, and C6 along three material axes is developed and verified. The model consists of a spring-dashpot system that predicts the response under cyclic loading as a function of temperature. The modeling system providing the most consistent results consists of a spring and dashpot in parallel with each other, both in series with another dashpot. While the spring and dashpot in parallel represents both elastic and viscous response delay, the series dashpot accounts for the higher creep rates associated with elevated temperatures. The three parameters of this model are determined by fitting experimental data to the mathematical solution under cyclic loading conditions through a nonlinear least-squares method. There are a number of complex nonlinear load displacement mechanisms involved in the initial load cycle, thus to minimize modeling errors, most of the simulation modeling was developed to predict the mature portion of the load deflection curve through failure. The results presented in these studies strongly suggest that this three-parameter accurately describes the response of the three electroactive papers studied. The material creeps at elevated temperature, but there is insignificant creep at room temperature. The elastic behavior varies inversely with temperature and with the bias angle tested; however, the overall viscous behavior of the three types of EAPap tested is relatively complex.

The contents of the paper raise several doubts for two reasons. Firstly, the assumptions regarding the shear stress and the velocity profile are wrong for they violate Cauchy’s stress principle. Secondly, the use of Laplace transform to solve the start-up flow problem is incorrect.

Our intention in this write-up is to give a reply for the specious comment of Asterios Pantokratoras on the paper “On Cattaneo-Christov heat flux model for Carreau fluid flow over a slendering sheet, Hashim and Masood Khan, Results in Physics, 7 (2017) 310–319 (Hashim and Masood Khan, 2017)”. The authors talked about each of those comments in detail. In brief, the authors do not comply with those specious comments made by Asterios Pantokratoras (2017).

The present comment concerns some doubtful results included in the above paper.

The most representative papers of M. V. Keldysh (10.02.1911-24.06.1978) in the field of mechanics and applied mathematics concerned with aircraft construction, shipbuilding and explosion theory are reviewed. Formulations of problems with their substantiation, the methods of solving them, which he used, and the main results obtained are given.

Out-of-plane deformations of paper, such as fluting, significantly deteriorate the quality of a printed product. There are several explanations of fluting presented in the literature but there is no unanimously accepted theory regarding fluting formation and retention which is consistent with all field observations. This paper first reviews the existing theories and proposes a mechanism that might give an answer to most of the questions regarding fluting. The fluting formation has been considered as a post-buckling phenomenon which has been analysed with the help of the finite element method. Fluting retention has been modelled by introducing an ink layer over the paper surface with the ink stiffness estimated from experimental results. The impact of fast drying on fluting has been assessed numerically and experimentally. The result of the study suggests that fluting occurs due to small-scale hygro-strain variations, which in turn are caused by the moisture variations created during fast convection (through-air) drying. The result also showed that ink stiffening alone cannot explain the fluting amplitudes observed in practice, but that high drying temperatures promote inelastic (irreversible) deformations in paper and this may itself preserve fluting.

In this paper, a finite element procedure is used to study the dynamic behaviour of a paper web in a free span between two rollers, including effects of transport velocity and surrounding air. The paper web is modelled as a three-dimensional orthotropic structure. The influence of air is accounted for by utilizing fluid-solid interaction analyses based on acoustic theory. The contribution of transport velocity is included through gyroscopic matrices and forces. The structural response on harmonic excitations has been studied using linear and non-linear models. Results show that air significantly reduces eigenfrequencies of the web. So called ''edge-flutter'' is nothing but the result of skew tension profile. Excessive web vibration can be eliminated by adjusting the web tension.

This paper presents a blocked force measurement of electro-active paper (EAPap) with a simple configuration and high accuracy. Blocked force is a force at the tip of a bending actuator when the tip is fixed. A micro-balance with a fixture is used to measure the blocked force of EAPap bending actuator. The measurement is conducted with dc electric fields. A theoretical blocked force is calculated by using the cantilever beam model, and the measured blocked force is compared with the calculated result. Comparing the measured blocked force with the calculated result shows a good agreement. This force measurement method is simple and accurate, and can be applied for measuring blocked forces of EAP actuators.

Paper drying is an exergy costly operation, so also a few percent saving may be of importance. The entropy production for the paper drying process was therefore optimised for a conventional multi-cylinder drying machine, the PM2 newsprint machine at Norske Skog ASA in Skogn, Norway. The machine has 51 cylinders grouped in three drying groups; the cylinders are either heated from the inside by steam, unheated or operated under vacuum conditions. The same inlet drying air is supplied in all upper air-pockets of the machine. Our drying model for the paper temperature profile was first compared with measured data from the machine. The total entropy production of the drying process was next calculated, and then minimised subject to a fixed outlet paper moisture content. Inlet humidity and cylinder group conditions were varied. Optimum conditions were obtained for a range of inlet air humidities, and for different cylinder groupings. We found that it was very favourable to increase the inlet air humidity. Other changes had a negligible effect on the total entropy production. The results further pointed to the need for a revision of the current paper drying model, as the second-law of thermodynamics was violated at high air humidities with this model.

In this paper, the disciplines of experimental research and computational science are conjoined with an objective geared towards an improved understanding of permeability in porous coatings. Three packing structures were considered, each one comprising a distribution with particles of similar shape. Models were built to mimic the experimental structures and then used for computational fluid dynamics (CFD) simulations as well as statistical analyses. Calculations of permeability are reported to within one order of magnitude of the experimental equivalents. A correlation is found to exist between statistical pore space disorder and the variation of permeability within the same packing microstructure.

Heat and mass transfer processes in a cross flow liquid desiccant dehumidifier, in which wet durable honeycomb paper constitutes the packing material, is investigated in this paper. The device is expected to be used in hot and humid areas to control the indoor humidity environment. A mathematical model, able to determine the heat and mass transfer between the air and the falling film of liquid desiccant, is developed, and the analysis on Nusselt and Sherwood numbers at the liquid–air interface is performed considering the solution of 40% H2O/CaCl2. Also obtained is the theoretical Nusselt number under assumed conditions and the relevant analysis, as well as the comparison between the two results.

Extensive computer simulations have been carried out to model imbibition of a coating fluid into a paper. The microstructure of the paper's pore space is represented by a network of interconnected channels or pore throats that are formed between the paper's fibers. The geometrical characteristics of the channels, such as their effective radius and length, as well as their connectivity, are selected from the experimental data presented in Part II of this series. The imbibition process that we simulate is the result of forcing the coating fluid into the pore space by applying a time-dependent flow-driven pressure distribution to the external surface of the paper, or is driven only by capillary forces. The dynamic pressure distribution is representative of a high-speed coating process. The simulations indicate that the connectivity of the pore throats, the anisotropic structure of the paper's pore space, and the dynamic pressure distribution all have a strong influence on imbibition of a coating fluid into a paper's pore space and, hence, on the quality of the coating.

We develop a constitutive model of paper’s in-plane biaxial tensile response accounting for the elastic–plastic hardening behavior, and its orthotropic character. The latter aspect is motivated by machine-made papers, which, in contrast to isotropic laboratory handsheets, are strongly oriented. We focus on modeling paper’s response under monotonic loading, this restriction allowing us to treat the elastic-plastic response as a physically nonlinear elastic one. A strain energy function of a hyperbolic tangent form is developed so as to fit the entire range of biaxial and uniaxial experiments on a commercial grade paper. This function may then be introduced as the free energy function into a model based on thermomechanics with internal variables. # 2003 Published by Elsevier Ltd.

Stochastic two-dimensional elastic–plastic network models are used to represent the inelastic deformation behavior of well-bonded paper. Linear kinematic hardening is employed with an initial non-zero back stress to represent anisotropic fiber yield. Network models are used to simulate simple monotonic tension and simple cyclic tension of paper materials. The performance of the models is compared to experimental results and found to perform reasonably well. The results suggest that interfiber bonding must be explicitly accounted for to adequately describe the material. Some discrepancy between the model and experimental cyclic tension results is believed to be due to time-dependent strain recovery in the material which is not represented in the network models. Experimental results are also presented which show that simple tension failure in these materials occurs along a line of localized deformation in a majority of the samples. This line is generally observed to form immediately prior to failure and is oriented at a well-defined angle with respect to the loading direction.

A substantial portion of the CO and other gaseous smoke constituents generated in the combustion and pyrolysis zones could diffuse out of a cigarette rod through the paper wrapper. In this work, a 2-D model is developed from the basic principles that can predict the fraction of the gas diffusion out of a cigarette rod. The model incorporates the radial diffusion and axial convection of the gaseous species in a porous media. A closed form solution is obtained that eliminates the need for the numerical solution of the partial differential equations. The model was validated by comparing the predictions with the available experimental data. A parametric study was performed to investigate the effects of the above parameters. The results show that the CO diffusion increases as the length of the cigarette, paper permeability, or the external velocity of air increases. The reverse is true when the cigarette diameter, the paper thickness, and or the gas delivery is increased. The model confirms that gases with larger diffusion coefficient diffuse out at a higher rate.

A cross-flow direct evaporative cooler, in which the wet durable honeycomb paper constitutes as the packing material, is investigated. The system is expected to act as both humidifier and evaporative cooler to create a comfortable indoor environment in arid regions. A mathematical model, including the governing equations of liquid film and gas phases as well as the interface conditions, has been developed. The interface temperature of falling film has been predicted and discussed in detail. Analysis results indicate that there exists an optimum length of the air channel, which results in the lowest temperature, and the system performance can be further improved by optimizing the operation parameters, such as the mass flow rates of feed water and process air, as well as the different dimensions of the honeycomb paper.

The assumption that pressures of water and gas in concrete at high temperature are equal one to another and its theoretical consequences are discussed. The results of hygro-thermal simulations performed by Tenchev and Purnell are analysed and compared to the Authors’ results based on the assumption about local thermodynamic equilibrium. � 2006 Elsevier Ltd. All rights reserved.

Flow of water in Whatman #17 chromatography paper and the interpretation of the capillary suction time method for determining filterability of suspensions is examined. Filter paper water flow is described by well-established theory of water flow in porous media. This theory is based on material balance for the water and Darcy’s law. Assuming that the matric potential or suction (arising from the interaction of water with the solid surfaces and their geometry) and the hydraulic conductivity of both the filter paper and the suspension are well-defined functions of the water content, one-dimensional capillary suction time is analysed from considerations of material balance and continuity of water potential on the paper/suspension interface. Experiments agree with theory and illustrate that flow in the paper is unsaturated, with the advance of a wetting front in paper a function of the interaction of the sorptivity-matric potential functions of both the paper and the suspension. Extension of the approach to radial flow in the filter paper is too complicated to permit simple interpretation of wetting front advance. The capillary suction time method must remain a useful empirical tool for practicing engineers. Its weaknesses should be recognised, however, and constant pressure filtration tests, for example, which provide both sorptivity-, and equilibrium water content– pressure relations simply and accurately must ultimately be preferable.

Controlled centrifugal instabilities (called Dean vortices) resulting from flow in helical tubes have been used to reduce concentration polarization and membrane fouling during nanofiltration. These vortices enhance back-migration of solute through convective flow away from the membrane–solution interface and allow for increased membrane permeation rates. Based on the theory of Dean vortex flow, a new prototype vortex generating tubular nanofiltration element was designed. Two sets of nanofiltration modules were constructed; a linear module and a new module containing hollow fibers wrapped around rods of small diameter in helical geometry. Optimization of the design is discussed with respect to the diameter and thickness of the hollow fibers. Axial pressure drop and energy consumption measurements for the helical module agreed very well with available correlations for various experimental conditions. Water permeabilities for the helical modules were similar to those of the conventional linear modules. No significant effect of pH was observed on the water permeability.

The friction between paper surfaces has been studied in a strip-on-drum geometry, under quasistatic and slow sliding conditions. The method provides a better simulation of some practical applications than other more widely used tests. The mechanics of the test have been analysed for two cases: with constant coefficient of friction; and with the friction force related to normal pressure by a power law. The behaviour of four different types of paper was examined. In all cases, the coefficient of friction of the sample fell with repeated sliding; this was associated with progressive damage to the paper surface, and has implications for the design of standard friction test methods for paper. The coefficient of friction (COF) also depended significantly on the contact pressure, in a way that can be correlated with the relative compressibilities of the different paper structures. The pressure dependence of friction, at low pressures, was accurately modelled by a power-law relationship.

The papers presented in the sessions on fluidization and transport phenomena cover a wide range of subjects pertaining to fluid—particle systems. Examples of these subjects include bubble coalescence mechanisms, entrainment, pressure effects and chaos in bubbling and turbulent fluidized beds, wave phenomena and cluster structure in circulating fluidized beds, and spectral and fractal characteristics in gas—liquid—solid fluidized beds. In this summary paper, an overview based on these papers is given and salient results are highlighted.

Buckling behaviour of circular filter papers, as isotropic plates with high aspect ratio, negligible weight-stiffness ratio and little ability to undergo inplane strains prior to delamination, has been studied. The study covers the results of deforming circular papers under three equally spaced radial loads and the effect of holes punched within the samples to help formation of single curvature modes without points of discontinuous slope. The results of a few experiments on eccentricity of the holes are also presented.