Viscous Flow Model Research Articles

Response to “Comments on ‘A theoretical model of the pressure distributions arising from asymmetric intraglottal flows applied to a two-mass model of the vocal folds’” [J. Acoust. Soc. Am. 130, 389–403 (2011)

Hirschberg [J. Acoust. Soc. Am. 134, 9-12 (2013)] presents a commentary and criticisms of the viscous flow model presented by Erath et al. [J. Acoust. Soc. Am. 130, 389-403 (2011)] that solves for the asymmetric pressure loading on the vocal fold walls. This pressure loading arises from asymmetric flow attachment to one vocal fold wall when the glottal channel forms a divergent configuration. Hirschberg proposes an alternative model for the asymmetric loading based upon inviscid flow curvature at the glottal inlet. In this manuscript further evidence is provided in support of the model of Erath et al. and the underlying assumptions, and demonstrates that the primary criticisms presented by Hirschberg are unwarranted. The model presented by Hirschberg is compared with the model from the original paper by Erath et al., and it is shown that each model describes different and complementary aspects of divergent glottal flows.

Conditions for thermal stabilization of the superconductor’s critical state

Conditions for thermal stabilization of the electrodynamic states of a superconductor are studied. The macroscopic states are simulated in the nonisothermal approximation by numerically solving a set of the Fourier and Maxwell equations with the magnetic flux penetration boundary unknown. Stability criteria for the critical state described by the viscous flow model are formulated. The results are compared with those fol� lowing from the isothermal theory. It is shown that errors inherent in the isothermal approximation are sig� nificant for a thermally insulated superconductor. Therefore, the wellknow n adiabatic criterion of stability formulated in the isothermal approximation limits the domain of stable states, since a correct determination of conditions for the superconducting-normal state transition must take into account the thermal history of the stable superconducting state formation. On the whole, the error of loss calculation in the isothermal approximation increases when the heat transfer coefficient decreases or an external magnetic field sweep and the size of the superconductor's cross section increases. On the other hand, nonisothermal stability condi� tions expand the variety of allowable states, since they include conditions that links the currently developed theory of thermomagnetic instability, the theory of losses, and the theory of a superconductor's thermal sta�

Model of incompressible viscous fluid flow driven by pressure difference in a given channel

Air motion problems in ventilation systems of buildings, underground facilities (mines, the underground), etc. can be simulated by means of the motion of an incompressible homogeneous viscous fluid. The aim of this work is to develop a method of solving stationary traffic in the channel of an incompressible homogeneous viscous fluid with the given pressure at the inlet and outlet of the channel and to study the stability of the solutions.

The instability of continental passive margins and its effect on continental topography and heat flow

AbstractThe long geological history of passive margin evolution is complex yet typified by an initial ramp‐like tilting of the subaerial surface toward the continent‐ocean boundary, followed by episodic uplift and subsidence at a smaller wavelength. We argue that this behavior is due to changes in margin structure brought about by buoyancy‐driven lithospheric flow. Continental lithosphere is melt‐depleted, buoyant, and thick. It will resist convective breakdown into the asthenosphere below, but will be prone to lateral flow due to horizontal density contrasts. Changes in lithosphere thickness at the transition between continent and ocean will nucleate convection cells. Using a numerical model of viscous upper mantle flow, we show that stability or instability of the continental lithosphere at a passive margin is a function of the lithospheric rheology and composition. Increased compositional buoyancy leads to oceanward lateral flow of the continental lithosphere whereas decreased buoyancy has the opposite effect, causing landward lateral flow of the continental lithosphere. In model simulations, a continental lithosphere thought typical of Phanerozoic continental platforms experiences first a margin‐wide ramp‐like tilting, followed by topographic fluctuations due to an evolving array of convection cells in the mantle. The timing and magnitude of predicted changes in topography are similar to those observed at the eastern North American margin, suggesting that the tilting and episodic uplift and subsidence at continental passive margins are a natural consequence of the evolution of continental lithosphere after breakup and during mature seafloor spreading.

An accurate SPH modeling of viscous flows around bodies at low and moderate Reynolds numbers

A weakly compressible SPH scheme has been used to describe the evolution of viscous flows around blunt bodies at Reynolds numbers ranging from 10 to 2400. The simulation of such a wide range, rarely addressed to in the SPH literature, has been possible thanks to the use of a proper ghost-fluid technique and to an accurate enforcement of the boundary conditions along the solid boundaries. In this context, a new numerical technique based on previous works by Takeda et al. (1994) [48], Marrone et al. (2011) [28] and De Leffe et al. (2011) [16] has been proposed, along with a new method for the evaluation of the global loads on bodies. Particular care has been taken to study the influence of the weakly-compressibility assumption and of different ghost-fluid techniques on the numerical results. An in-depth validation of the model has been performed by comparing the numerical outcome with experimental data from the literature and other numerical references. The influence of the domain size has been discussed in order to avoid wall side effects and, at the same time, to limit the computational costs. The convergence of the numerical solutions has been checked on both global and local quantities by choosing appropriate Reynolds-cell number.

Model of Flow in the Side Chambers of an Industrial Centrifugal Pump for Delivering Viscous Oil

A series of experiments has been conducted to identify the effects of both fluid viscosity and wear-rings gap on the performance of a low specific speed industrial centrifugal pump of type 65Y60 for transporting viscous oils by the author group. Unfortunately, the experimental results remained unexplained on a fluid dynamics base. To remedy this problem, a highly viscous oil flow model and computational method in the side chambers in that pump were proposed based on the existing theoretical and experimental results. The flow coupling between the chambers and the gaps of the wear-rings and/or the balance holes was realized. The model was validated by making use of the existing experiment data in the chamber between a rotating disk and the walls of a stationary cylindrical container. Then the flow model was applied into the two side chambers in that pump when the wear-rings clearances and liquid viscosity were changed. The results demonstrated that the flow model is sensitive to wear-rings gap, liquid viscosity, the roughness of the wet walls of the chambers, and leakage flow rate. For this pump, an enlarged clearance can improve the mechanical efficiency, but the increment in the efficiency is unable to compensate for the considerable drop in the volumetric efficiency, causing the gross efficiency not be improved, especially at a high viscosity.

Solutions for MHD viscous flow due to a shrinking sheet by Hankel‐Padé method

PurposeIn this paper, an analysis is performed to find the solution of a nonlinear ordinary differential equation that appears in a model for MHD viscous flow caused by a shrinking sheet.Design/methodology/approachThe cases of two dimensional and axisymmetric shrinking have been discussed. When the sheet is shrinking in the x‐direction, the analytical solutions are obtained by the Hankel‐Padé method. Comparison to exact solutions reveals reliability and high accuracy of the procedure, even in the case of multiple solutions. The case of sheet shrinking in the y‐direction is also considered, with success.FindingsWhen the sheet shrinks in the x‐direction, the analytical solutions are obtained by Hankel‐Padé method. Also, when the sheet shrinks in the y‐direction, the obtained results with Hankel‐Padé method are presented.Practical implicationsComparison to exact solutions reveals reliability and high accuracy of the procedure and convincingly could be used to obtain multiple solutions for certain parameter domains of this case of the governing nonlinear problem.Originality/valueThe numerical solutions are given for both two‐dimensional and axisymmetric shrinking sheets by using Hankel‐Padé method. It is clear that the Hankel‐Padé method is, by far, more simple, straightforward and gives reasonable results for large Hartman numbers and suction parameters.

Almost periodic homogenization of a generalized Ladyzhenskaya model for incompressible viscous flow

We study the existence and almost periodic homogenization of some model of generalized Navier–Stokes equations. We establish an existence result for nonstationary Ladyzhenskaya equations with a given nonconstant density and an external force depending nonlinearly on the velocity. In the case of a nonconstant density of the fluid, we study the asymptotic behavior of the velocity field by combining some compactness arguments with the sigma-convergence method. Bibliography: 37 titles.

Laser Joining of Continuous Glass Fiber Composite Preforms

A laser fusion joining method is investigated for the purpose of through thickness strengthening of glass fiber reinforced laminate composites. Laser fusion joining is evaluated as a potential process to replace mechanical reinforcements used in conventional laminate composite fabrication. A two step laser process is developed to form fusion bonds between fibers within a single bundle and between adjacent fiber bundles. Coupled heat transfer and viscous flow modeling is carried out to investigate the temperature and dynamics of the joining process under three experimentally observed conditions. Linear elastic finite element analysis is used to investigate the effect of joint morphology on stress concentrations and strength. Joint strength is found to be a function of the fiber contact angle and packing density at the joint interface. Tensile tests show that laser joined fiber bundle strength is on the same order of magnitude as the raw fiber bundles. The challenges to laser processing of three dimensional fiber reinforcements in laminate composite fabrication are discussed.

サブナノ細孔の気体透過モデルとNormalized Knudsen-based Permeance (NKP) による細孔径評価

Viscous flow, Knudsen diffusion, and surface diffusion models are commonly accepted in diffusion inside porous materials and permeation through porous membranes, including polymeric and inorganic materials. However, the permeation equation through subnano?porous membranes is still under discussion. In this contribution, permeation models of gaseous molecules through porous membranes, including gas translation model (GT model) and uniform potential model, are summarized, and then the modified GT model that was recently proposed, was introduced. In addition, Normalized Knudsen?based Permeance (NKP), which was theoretically derived based on the modified GT model, was introduced to the evaluation of pore sizes of porous membranes with sub?nanometer in size.

Magnetohydrodynamic transient flow through a porous medium bounded by a hot vertical plate in the presence of radiation: a theoretical analysis

The transient magnetohydrodynamic free convective flow of a viscous, incompressible, electrically conducting, gray, absorbing–emitting, but non-scattering, optically thick fluid medium which occupies a semi-infinite porous region adjacent to an infinite hot vertical plate moving with a constant velocity is analyzed. A uniform magnetic field is assumed to be applied transversely to the flow. The Darcian viscous flow model for the porous medium is used. The momentum and thermal boundary-layer equations under physically realistic boundary conditions are solved through the use of the Laplace transform technique. The influence of the characteristic parameters of the problem on the velocity, temperature, and shear stress is investigated.

Selective focused-ion-beam sculpting of TiO2nanotubes and mechanism understanding

Anodic TiO(2) nanotubes with different structures, doping agents, and decorations have been studied in order to improve energy conversion and storage efficiencies such as in dye sensitized solar cells, solar fuels, and electrochemical supercapacitors. However, the top surface modification of TiO(2) nanotubes has never been addressed. In this study, anodic TiO(2) nanotubes have been selectively closed by high energy focused ion beams and re-opened by low energy focused ion beams. Under a 30 kV Ga(+) beam, TiO(2) nanotubes are closed with a 65 nm shield layer covering the top entrance when the ion dose is larger than 1.2 × 10(17) ions per cm(2); under a 5 kV Ga(+) beam, the shield layer is removed and the closed tubes are re-opened. An ion-induced viscous flow model has been proposed to explain the influence of Ga(+) ion beam flux, substrate temperature, initial tube diameter, ion beam dwell time, and the incidence angle of the ion beam.

Viscous flow during spark plasma sintering of Ti-based metallic glassy powders

Viscous flow has rarely been observed in solid-state sintering of metal, while operates the dominant mass transport mechanisms in vitreous materials. In the present study, Ti-based bulk metallic glasses (BMGs) with nearly 100% relative density were fabricated by spark plasma sintering of a gas-atomized Ti48Ni32Cu8Si8Sn4 glassy alloy powder. Two main shrinkage stages of densification occurred at a constant heating rate. Based on the analysis of experimental data and microstructure observations of samples sintered at various temperatures, sintering mechanisms are proposed for the sintering of Ti-based metallic glassy powders in light of the viscous flow model.

Unsteady MHD double-diffusive convection boundary-layer flow past a radiate hot vertical surface in porous media in the presence of chemical reaction and heat sink

This paper presents an analytical study of the unsteady MHD free convective heat and mass transfer flow of a viscous, incompressible, gray, absorbing-emitting but non-scattering, optically-thick and electrically conducting fluid occupying a semi-infinite porous regime adjacent to an infinite moving hot vertical plate with constant velocity. We employ a Darcian viscous flow model for the porous medium the Rosseland diffusion approximation is used to describe the radiative heat flux in the energy equation. The homogeneous chemical reaction of first order is accounted in mass diffusion equation. The governing equations are solved in closed form by Laplace-transform technique. A parametric study of all involved parameters is conducted and representative set of numerical results for the velocity, temperature, concentration, shear stress function \(\frac{\partial u}{\partial y} \vert_{y=0}\), temperature gradient \(\frac{\partial \theta }{ \partial y}\vert_{y=0}\), and concentration gradient \(\frac{ \partial \phi }{\partial y}\vert_{y=0}\) is illustrated graphically and physical aspects of the problem are discussed.

Numerical computation and analysis of high-speed autonomous underwater vehicle (AUV) moving in head sea based on dynamic mesh

Autonomous underwater vehicles (AUVs) navigating on the sea surface are usually required to complete the communication tasks in complex sea conditions. The movement forms and flow field characteristics of a multi-moving state AUV navigating in head sea at high speed were studied. The mathematical model on longitudinal motion of the high-speed AUV in head sea was established with considering the hydrodynamic lift based on strip theory, which was solved to get the heave and pitch of the AUV by Gaussian elimination method. Based on this, computational fluid dynamics (CFD) method was used to establish the mathematical model of the unsteady viscous flow around the AUV with considering free surface effort by using the Reynolds-averaged Navier-Stokes (RANS) equations, shear-stress transport (SST) k-w model and volume of fluid (VOF) model. The three-dimensional numerical wave in the computational field was realized through defining the unsteady inlet boundary condition. The motion forms of the AUV navigating in head sea at high speed were carried out by the program source code of user-defined function (UDF) based on dynamic mesh. The hydrodynamic parameters of the AUV such as drag, lift, pitch torque, velocity, pressure, and wave profile were got, which reflect well the real ambient flow field of the AUV navigating in head sea at high speed. The computational wave profile agrees well with the experimental phenomenon of a wave-piercing surface vehicle. The force law of the AUV under the impacts of waves was analyzed qualitatively and quantitatively, which provides an effective theoretical guidance and technical support for the dynamics research and shape design of the AUV in real complex environment.

Lateral fold growth and fold linkage

We use a three-dimensional finite element model for viscous flow to investigate the lateral linkage mode of two initially isolated fold segments. Depending on the separation distance between the fold hinge lines, four different fold linkage scenarios are observed. Linear linkage yields a sub-cylindrical fold with a saddle at the location where the two initial folds linked. Oblique linkage produces a fold resembling a type II refold structure. Oblique–no linkage results in two curved folds with fold axes plunging in opposite directions. Linear–no linkage yields a fold train of two separate subcylindrical folds with fold axes plunging in opposite directions. Representative numerical models for detachment and matrix folding for both power-law and linear viscous rheologies exhibit the same four fold linkage modes. The transition from linkage to no linkage occurs when the fold separation between the initially isolated folds is slightly larger than one-half of the low-amplitude fold wavelength. We demonstrate a natural example of lateral fold linkage from the Kurdistan region of Iraq, and point out the economic interest of saddle points linking the initially isolated fold segments.

A fractal model of melt viscosity of a polypropylene-carbon nanotube nanocomposite

The change in the melt viscosity of polypropylene-carbon nanotube nanocomposites upon variation in the nanofiller content has been studied. It has been shown that the continuous models developed to describe the polymer composites melt viscosity cannot describe this parameter in the case of nanocomposites. A correct description of the rheological properties of such composites can be made in terms of a fractal model of viscous flow.

Numerical Study of Free Convection Flow past a Vertical Cone with Variable Heat and Mass Flux

ABSTRACT A numerical study of buoyancy-driven unsteady natural convection boundary layer flow past a vertical cone embedded in a non-Darcian isotropic porous regime with transverse magnetic field applied normal to the surface is considered. The heat and mass flux at the surface of the cone is modeled as a power-law according to () m q x x w  and * () n q x x w  respectively, where x denotes the coordinate along the slant face of the cone. Both Darcian drag and Forchheimer quadratic porous impedance are incorporated into the two-dimensional viscous flow model. The transient boundary layer equations are then non-dimensionalized and solved by the Crank-Nicolson implicit difference method. The velocity, temperature and concentration fields have been studied for the effect of Grashof number, Darcy number, Forchheimer number, Prandtl number, surface heat flux power-law exponent (m), surface mass flux power-law exponent (n), Schmidt number, buoyancy ratio parameter and semi-vertical angle of the cone. Present results for selected variables for the purely fluid regime are compared with the published work nonand are found to be in excellent agreement. The local skin friction, Nusselt number and Sherwood number are also analyzed graphically. The study finds important applications in geophysical heat transfer, industrial manufacturing processes and hybrid solar energy systems.

Modeling and simulation of polymer melts flow in the extrusion process of plastic profile with metal insert

The extrusion technology of plastic profile with metal insert is recently an advanced plastic processing method whose products keeps rising today for their excellent performance. However, the related fundamental research on polymer forming mechanism in the extrusion process of plastic profile with metal insert is lagging behind. With the development of computational fluid dynamics (CFD) theory, numerical method becomes an effective way to investigate such complex material forming problems as in the polymer extrusion process. In the present study, the mathematical model for three-dimensional non-isothermal viscous flow of the polymer melts obeying a Carreau model is developed based on the CFD theory. The Williams–Landel–Ferry equation is employed to involve the temperature dependence of material parameters. A decoupled numerical algorithm based on the penalty finite element method is conducted to predict the rheological behaviors of polymer melts within the complex flow channel. The streamline upwind/Petrov–Galerkin scheme is employed to improve the computational stability for the calculation of temperature field. Based on the theoretical model, the essential flow characteristics of polymer melts in the extrusion process of plastic profile with metal insert is investigated. The distributions of principal field variables like flow velocity, melt temperature, flow stress and pressure drop are predicted. The effects of die structure parameters including the intake angle and the distribution section length upon the melts flow patterns are further discussed. The variations of melt rheological properties versus different processing conditions like the volume flow rate and the metal insert moving velocity are also investigated. Some advice on practical processing operations of the extrusion process of plastic profile with metal insert is accordingly put forward based on the numerical results.

Geometric singular perturbation approach to the existence and instability of stationary waves for viscous traffic flow models

The purpose of this work is to study the existence and stability of stationary waves for viscous traffic flow models. From the viewpoint of dynamical systems, the steady-state problem of the systems can be formulated as a singularly perturbed problem. Using the geometric singular perturbation method, we establish the existence of stationary waves for both the inviscid and viscous systems. The inviscid stationary waves contain smooth waves and discontinuous transonic waves. Both waves admit viscous profiles for the viscous systems. Then we consider the linearized eigenvalue problem of the systems along smooth stationary waves. Applying the technique of center manifold reduction, we show that any one of the supersonic smooth stationary waves is spectrally unstable.