bluuebunny/crossref_metadata_2025_split huggingface dataset:
Direct numerical simulation of free convection over a heated plate
Authors: Mellado Juan Pedro 
Published: November 2012

AbstractDirect numerical simulations of free convection over a smooth, heated plate are used to investigate unbounded, unsteady turbulent convection. Four different boundary conditions are considered: free-slip or no-slip walls, and constant buoyancy or constant buoyancy flux. It is first shown that, after the initial transient, the vertical structure agrees with observations in the atmospheric boundary layer and predictions from classical similarity theory. A quasi-steady inner layer and a self-preserving outer layer are clearly distinguished, with an overlap region between them of constant turbulent buoyancy flux. The extension of the overlap region reached in our simulations is more than 100 wall units$ \mathop{ ({\kappa }^{3} / {B}_{s} )}\nolimits ^{1/ 4} $, where${B}_{s} $is the surface buoyancy flux and$\kappa $the corresponding molecular diffusivity (the Prandtl number is one). The buoyancy fluctuation inside the overlap region already exhibits the$\ensuremath{-} 1/ 3$power-law scaling with height for the four types of boundary conditions, as expected in the local, free-convection regime. However, the mean buoyancy gradient and the vertical velocity fluctuation are still evolving toward the corresponding power laws predicted by the similarity theory. The second major result is that the relation between the Nusselt and Rayleigh numbers agrees with that reported in Rayleigh–Bénard convection when the heated plate is interpreted as half a convection cell. The range of Rayleigh numbers covered in the simulations is then$5\ensuremath{\times} 1{0}^{7} \text{{\ndash}} 1{0}^{9} $. Further analogies between the two problems indicate that knowledge can be transferred between steady Rayleigh–Bénard and unsteady convection. Last, we find that the inner scaling based on$\{ {B}_{s} , \hspace{0.167em} \kappa \} $reduces the effect of the boundary conditions to, mainly, the diffusive wall layer, the first 10 wall units. There, near the plate, free-slip conditions allow stronger mixing than no-slip ones, which results in 30 % less buoyancy difference between the surface and the overlap region and 30–40 % thinner diffusive sublayers. However, this local effect also entails one global, substantial effect: with an imposed buoyancy, free-slip systems develop a surface flux 60 % higher than that obtained with no-slip walls, which implies more intense turbulent fluctuations across the whole boundary layer and a faster growth.
A flow in the depth of infinite annular cylindrical cavity
Authors: Shtern Vladimir 
Published: November 2012

AbstractThe paper describes an asymptotic flow of a viscous fluid in an infinite annular cylindrical cavity as the distance from the flow source tends to infinity. If the driving flow near the source is axisymmetric then the asymptotic pattern is cellular; otherwise it is typically not. Boundary conditions are derived to match the asymptotic axisymmetric flow with that near the source. For a narrow cavity, the asymptotic solutions for the axisymmetric and three-dimensional flows are obtained analytically. For any gap, the flow is described by a numerical solution of an eigenvalue problem. The least decaying mode corresponds to azimuthal wavenumber $m= 1$.
Hydrodynamic interactions among multiple circular cylinders in an inviscid flow
Authors: Sun R. , Ng C. O. 
Published: November 2012

AbstractHydrodynamic interactions among multiple circular cylinders translating in an otherwise undisturbed inviscid fluid are theoretically investigated. A constructive method for solving a Neumann boundary-value problem in a domain outside$N$circles (one kind of Hilbert boundary-value problem in the complex plane) is presented in the study to derive the velocity potential of the liquid. The method employs successive offset functions combined with a ‘generalized cyclic permutation’ in turn to satisfy the impenetrable boundary condition on each circle. The complex potential is therefore expressed as$N$isolated singularities in power series form and used to get instantaneous added masses of$N$submerged circular cylinders. Then, based on the Hamilton variational principle, a dynamical equation of motion in vector form is derived to predict nonlinear translations of the submerged bodies under fully hydrodynamic interactions. Also, the equivalence of the energy-based Lagrangian framework and a momentum-type one in the two-dimensional body–liquid system is proved. It implies that the pressure integration around a submerged body is holographic, which provides information about velocities and accelerations of all bodies. The numerical solutions indicate some typical dynamical behaviours of more than two circular cylinders which reveal that interesting nonlinear phenomena would appear in such a system with simple physical assumptions.
Exact solutions for wave propagation over a patch of large bottom corrugations
Authors: Yu Jie , Zheng Guangfu 
Published: November 2012

AbstractApplying the Floquet theory for linear motions (Howard & Yu, J. Fluid Mech., vol. 593, 2007, pp. 209–234) to the problem of wave propagation over a patch of periodic bottom corrugations in an otherwise flat seabed, we show that exact solutions to this scattering problem can be constructed without any constraint on the bottom amplitude and/or slope. These solutions are able to describe both the slowly and fast varying aspects of the flow, in contrast to the analyses based on the general ideas of slowly varying waves. We use as an example the well-studied Bragg scattering by a patch of bottom corrugations to present some quantitative results and comparisons with experimental data.
Flow of power-law fluids in fixed beds of cylinders or spheres
Authors: Singh John P. , Padhy Sourav , Shaqfeh Eric S. G. , Koch Donald L. 
Published: November 2012

AbstractAn ensemble average of the equations of motion for a Newtonian fluid over particle configurations in a dilute fixed bed of spheres or cylinders yields Brinkman’s equations of motion, where the disturbance velocity produced by a test particle is influenced by the Newtonian fluid stress and a body force representing the linear drag on the surrounding particles. We consider a similar analysis for a power-law fluid where the stress $\boldsymbol{\tau} $ is related to the rate of strain $ \mathbisf{e} $ by $\boldsymbol{\tau} = 2m \mathop{ \vert \mathbisf{e} \vert }\nolimits ^{n\ensuremath{-} 1} \mathbisf{e} $, where $m$ and $n$ are constants. In this case, the ensemble-averaged momentum equation includes a body force resulting from the nonlinear drag exerted on the surrounding particles, a power-law stress associated with the disturbance velocity of the test particle, and a stress term that is linear with respect to the test particle’s disturbance velocity. The latter term results from the interaction of the test particle’s velocity disturbance with the random straining motions produced by the neighbouring particles and is important only in shear-thickening fluids where the velocity disturbances of the particles are long-ranged. The solutions to these equations using scaling analyses for dilute beds and numerical simulations using the finite element method are presented. We show that the drag force acting on a particle in a fixed bed can be written as a function of a particle-concentration-dependent length scale at which the fluid velocity disturbance produced by a particle is modified by hydrodynamic interactions with its neighbours. This is also true of the drag on a particle in a periodic array where the length scale is the lattice spacing. The effects of particle interactions on the drag in dilute arrays (periodic or random) of cylinders and spheres in shear-thickening fluids is dramatic, where it arrests the algebraic growth of the disturbance velocity with radial position when $n\geq 1$ for cylinders and $n\geq 2$ for spheres. For concentrated random arrays of particles, we adopt an effective medium theory in which the drag force per unit volume in the medium surrounding a test particle is assumed to be proportional to the local volume fraction of the neighbouring particles, which is derived from the hard-particle packing. The predictions of the averaged equations of motion are validated by comparison with simulations of randomly distributed hydrodynamically interacting cylinders.
Anti-Plane Interaction between a Crack and an Elliptically Cylindrical Layered Media
Authors: Chao C.K. , Wikarta A. 
Published: November 2012

AbstractAnti-plane interaction of an elliptically cylindrical layered media with an arbitrarily oriented crack embedded in an infinite matrix, intermediate layer, or inner inclusion under a remote uniform shear load is considered in this paper. Based on the technique of conformal mapping and the method of analytical continuation in conjunction with the alternating technique, the solution for a screw dislocation in the inclusions and the matrix is first derived in a series form. The integral equations with logarithmic singular kernels for a line crack can easily be obtained by using the screw dislocation solutions as the Green's function together with the principle superposition. The stress intensity factors, which can properly reflect the interaction between a crack and an elliptically cylindrical layered media, are then obtained numerically in terms of the values of the dislocation density functions of the integral equations. The effects of material property combinations and geometric parameters on the normalized mode-III stress intensity factors are discussed in detail and shown in graphic form.
Compression Behavior of Annular Elastic Layers Bonded Between Rigid Plates
Authors: Tsai H.-C. 
Published: November 2012

ABSTRACTAn annular elastic layer bonded between rigid plates and subjected to a compressive force normal to the layer is analyzed through a theoretical approach. On the basis of two kinematic assumptions, the governing equation for the mean pressure is established from the equilibrium equation, which is then solved by satisfying the stress boundary conditions. Through the obtained pressure expression, the compression stiffness of the bonded annular layer is derived in closed form and is very close to the finite element solution. The derived formula has no limitation on the Poisson's ratio and is more concise than the previous research. Through the asymptotic approach, the compression stiffness for the incompressible elastic layers is derived and is more accurate than the previous research obtained by directly neglecting the bulk compressibility. The stiffness reduction caused by the central hole is more prominent when the Poisson's ratio is close to 0.5.
Numerical Study of the Influence of Combustion Models and Kinetic Schemes When Predicting the Diffusion Flames
Authors: Khelil A. , Nechad S. , Naji H. , Loukarfi L. , Braikia M. , Beriache M. 
Published: November 2012

ABSTRACTThis article aims to study numerically three-dimensional (3D) reactive turbulent flow in a combustion chamber of a gas turbine by solving a steady Reynolds-Averaged Navier-Stokes (RANS) )and energy equations. The Reynolds stress model (RSM) is coupled with the probability density function (PDF), laminar flamelet and Chemistry models to describe the turbulent flow and turbulence–chemistry interaction. Numerical computations are conducted to exhibit thermal and concentration behaviour under a quite number of factors, which influence the combustion process. Their influence are examined and compared favourably with available experimental results. Concentration of some radicals as O and OH are obtained assuming the partial-equilibrium assumption and using a PDF in terms of temperature. The 3D simulations demonstrate that the use of RSM, PDF and flamelet model allow simulating velocity and thermochemical fields.
Holographic-Interferometric and Thermoanemometric Study of a Thermoacoustic Prime Mover
Authors: Trávníček Z. , Wang A.-B. , Lédl V. , Vít T. , Chen Y.-C. , Maršík F. 
Published: November 2012

AbstractA thermoacoustic standing-wave prime mover with a quarter-wave resonator has been investigated experimentally. The working fluid is air at the barometric pressure. The holographic interferometry and hot-wire anemometry have been used. A special optical setup, based on a Michelson interferometer, has been developed and used. The setup exhibits a double sensitivity, in comparison with a common Mach-Zehnder holographic interferometer. The results have confirmed a proper function of the prime mover, and advantages of the present optical setup.
Enhancement of Heat Transfer of Mixing Convection in a Vertical Channel by a Moving Block
Authors: Fu W.-S. , Huang J.-C. , Wang Y.-Y. , Huang Y. 
Published: November 2012

AbstractEnhancement of a heat transfer rate of mixed convection flow in a three-dimensional vertical channel with insertion of a moving slender block is investigated numerically. A slender block is installed along the direction of the channel flow, and the movement of the slender block is in periodic motion and transverse to the channel flow. The interaction between the moving block and the channel flow destroys and suppresses the velocity and thermal boundary layers on the heat surface periodically. Various ratios of the Richardson numbers (Gr/Re2) are simulated. The results show that under a higher velocity of the channel flow and a lower magnitude of Gr/Re2, the enhancement of heat transfer rate is better. Oppositely, under a lower velocity of the channel flow and a higher magnitude of Gr/Re2, the effect of natural convection driven by the buoyancy force is stronger and it is unfavorable to the heat transfer. A counter effect of the heat transfer rate is observed. These phenomena which are seldom analyzed before by numerical simulation are carried out in this study.
Thermal Buckling Analysis of Circular FGP with Actuator/Actuator Piezoelectric Layers Based on Neutral Plane Method
Authors: Najafizadeh M. M. , Malmorad M. , Sharifi A. , Joodaky A. 
Published: November 2012

AbstractIn this research, thermal buckling analysis of circular functionally graded plates with Actuator/Actuator piezoelectric layers (FGPs) is studied based on neutral plane, classical and first order shear deformation plate theories. Mechanical properties of the plate are considered as those of Reddy Model. Plate is assumed to be under thermal loading. Nonlinear temperature rises through the thickness and boundary conditions are considered clamped. Equilibrium and stability equations have been derived using calculus of variations and application of Euler equations. Finally, critical buckling temperature changes are studied based on the mentioned theories for a sample plate. An appropriate agreement is seen among the present results and the results of other researches.
Flow Field in a Skimming Flow Over a Vertical Drop Without End-Sill
Authors: Lin Chang , Hsieh S.-C. , Lin W.-J. , Chou S.-H. , Raikar R. V. 
Published: November 2012

ABSTRACTThe flow structure in the shear layer and in the recirculation zone of a skimming flow downstream of a vertical drop without end-sill measured using high speed particle image velocimetry (HSPIV) and flow visualization method is presented. The interface between the sliding jet and the recirculation zone (zone below sliding jet) was enhanced through non-ventilation condition between the drop structure and the jet. The flow field measured through HSPIV was used to represent the characteristics of mean streamwise velocity in the shear layer and mean horizontal velocity in the recirculation zone. With the growth of shear layer as the jet slides down over the recirculation zone, the momentum exchange from the sliding jet into the recirculation zone via the shear layer increases along with energy loss. Hence, it was observed that the amount of energy dissipated in the skimming flow at the drop structure without ventilation is greater than that with ventilation by an average value of 50% forYc/H≥ 0.2 (whereYc= critical depth andH= drop height). However, the flow structure in the recirculation zone is found to be analogous to that of turbulent plane wall jet. The nonlinear regression analysis is used to fit the regressed velocity profiles to the measured HSPIV mean velocity distributions. Further, the appropriate characteristic velocity and length scales are selected to attain the unique similarity profiles both in the shear layer and in the recirculation zone of the skimming flow. The selection of the characteristic scales is also discussed. The similarity profiles are well comparable with those of napped flow without end-sill and with ventilation as well as of skimming flow with end-sill and without ventilation. It is interesting to observe that, the proposed similarity profiles for the shear layer also map the data of backward-facing step flow and cavity shear flow. In addition, the turbulence characteristics in the shear layer, including turbulence intensities, turbulent kinetic energy, viscous and Reynolds shear stresses, and turbulence energy-budget balance, are illustrated in detail. From the variation of turbulence production it is observed that near the drop structure the energy exchange is from the chaotic recirculation zone to the sliding-jet flow, while in the later part it is reversed. Furthermore, the analysis of turbulence energy-budget balance indicates very significant role of turbulence production, pressure diffusion and turbulence diffusion as compared with turbulence advection that has very minor role in turbulence energy-budget balance for the central part of the shear layer.
Experimental Study of Flow Separation over NACA633018 Wing with Synthetic Jet Control at Low Reynolds Numbers
Authors: Lin C.-Y. , Hsiao F.-B. 
Published: November 2012

AbstractThis paper experimentally studies flow separation and aerodynamic performance of a NACA633018 wing using a series of piezoelectric-driven disks, which are located at 12% chord length from the leading edge to generate a spanwise-distributed synthetic jets to excite the passing flow. The experiment is conducted in an open-type wind tunnel with Reynolds numbers (Re) of 8 × 104 and 1.2 × 105, respectively, based on the wing chord. The oscillations of the synthetic jet actuators (SJAs) disturb the neighboring passage flow on the upper surface of the wing before the laminar separation takes place. The disturbances of energy influence the downstream development of boundary layers to eliminate or reduce the separation bubble on the upper surface of the wing. Significant lift increase and drag decrease are found at the tested Reynolds number of 8 × 104 due to the actuators excitation. Furthermore, the effect of drag also reduces dominant with increasing Reynolds number, but the increase on lift is reduced with the Reynolds number increased.
Evaluation of Multi-Order Derivatives by Local Radial Basis Function Differential Quadrature Method
Authors: Shen L. H. , Tseng K. H. , Young D. L. 
Published: November 2012

AbstractIt is difficult to obtain the derivative values from most mesh dependent numerical procedures in general. This study proposes an efficient computational tool to accurately evaluate the multi-order derivatives by the radial basis functions and local differential quadrature (LRBF-DQ) algorithm. Most of the traditional derivative calculations can be only adopted to evaluate the differential values with the regular meshes. Moreover, the traditional numerical schemes are very restricted by the order of the shape functions. The present technique can be applied to both the structured and unstructured meshes as well as meshless numerical algorithms – such as RBFs and LDQ method. In addition, the proposed model can be also used to estimate multi-order or mixed partial derivative values because its test function using RBFs is a multi-order differentiable function. All of the evaluation of derivative results will be compared with the exact solutions and other numerical techniques. Consequently, this study provides an effective algorithm of post process to accurately calculate the multi-order derivative values for any numerical schemes.
Dynamic Responses of Two Beams Connected by a Spring-Mass Device
Authors: Lin H.- P. , Yang D. 
Published: November 2012

AbstractThis paper deals with the transverse free vibrations of a system in which two beams are coupled with a spring-mass device. The dynamics of this system are coupled through the motion of the mass. The entire system is modeled as two two-span beams and each span of the continuous beams is assumed to obey the Euler-Bernoulli beam theory. Considering the compatibility requirements across each spring con-nection position, the eigensolutions (natural frequencies and mode shapes) of this system can be obtained for different boundary conditions. Some numerical results and experimental validations are presented to demonstrate the method proposed in this article.
Sensitivity Analysis on Triaxiality Factor and Lode Angle in Ductile Fracture
Authors: Ghajar R. , Mirone G. , Keshavarz A. 
Published: November 2012

AbstractAccuracy of numerical analysis is always important but it is much more important in failure analysis of ductile materials. In ductile materials, the process of removing the effects of necking to obtain stress-strain curve usually need reverse identification methods which are based on iterative finite element analysis. Moreover, triaxiality factor and Lode angle (two parameters that control failure of ductile materials) are obtained from finite element analysis.In this article based on some experiments, the effect of triaxiality factor and Lode angle on the failure strain of X100 pipeline steel is studied. In order to gain a better understanding of the response of triaxiality and Lode angle to deviations of stress, a sensitivity analysis is done on these two parameters before the start of finite elements (FE) analysis. This sensitivity analysis shows that the two parameters are really sensitive to stress deviations in some areas. Three geometries are selected and their FE analysis shows that it is necessary to reduce the element size lower than what is reported in literature in order to get convergence in triaxiality factor and Lode angle in critical areas.
The Role of Viticulture and Enology in the Development of Economic Thought: How Wine Contributed to Modern Economic Theory
Authors: Chaikind Stephen 
Published: November 2012

AbstractThis paper introduces the role wine has played as a central factor in the history of economic thought. The focus is on an examination of documented sources that connect wine and its viticulture and enology with the evolution of economic concepts. Works by Adam Smith, David Ricardo, Karl Marx, John Stuart Mill, Léon Walras, Alfred Marshall, and others are examined, as well as wine economic ideas postulated by Greek and Roman thinkers. (JEL Classification: A1, B1, B3, N00)