215 resultados para Radial diffuser
Resumo:
Blocks of 3Y-TZP were indented with conical diamond indenters. indentation caused tetragonal to monoclinic phase transformation in a subsurface. Of the cracks generated in the subsurface, radial and lateral cracks can be accounted for by a continuum model of the indented subsurface, built using a combination of the Boussinesq and blister stress fields. Additional ring, median and cone cracks were also observed. It is hypothesized that the latter are motivated by the reduction in blister strength or residual energy brought about by the material damage caused by the phase transformation. This damage reduces the load bearing capacity of the material progressively with increasing normal load.
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In the present study, a lug joint fitted with an interference fit (oversized) pin is considered with radial through cracks situated at diametrically opposite points perpendicular to the loading direction. A finite element contact stress algorithm is developed with linear elastic assumptions to deal with varying partial contact/separation at the pin-plate interface using a marching solution. Stress Intensity Factor (SIF) at the crack tips is evaluated using the Modified Crack Closure Integral (MCCI) method. The effect of change in crack length and edge distance on the load-contact relation, SIFs and stress distributions are studied. A rigorous plane stress elasticity solution of the pin-plate interface at the crack mouth confirmed the existence of the stress concentration leading to a local peak in the radial stress at the crack mouth and provided a method of estimating it quantitatively. Copyright (C) 1996 Elsevier Science Ltd.
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An exact three-dimensional elasticity solution has been obtained for an infinitely long, thick transversely isotropic circular cylindrical shell panel, simply supported along the longitudinal edges and subjected to a radial patch load. Using a set of three displacement functions, the boundary value problem is reduced to Bessel's differential equation. Numerical results are presented for different thickness to mean radius ratios and semicentral angles of the shell panel. Classical and first-order shear deformation orthotropic shell theories have been examined in comparison with the present elasticity solution.
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In this work, dynamic crack growth along a ductile-brittle interface under anti-plane strain conditions is studied. The ductile solid is taken to obey the J(2) flow theory of plasticity with linear isotropic strain hardening, while the substrate is assumed to exhibit linear elastic behavior. Firstly, the asymptotic near-tip stress and velocity fields are derived. These fields are assumed to be variable-separable with a power singularity in the radial coordinate centered at the crack tip. The effects of crack speed, strain hardening of the ductile phase and mismatch in elastic moduli of the two phases on the singularity exponent and the angular functions are studied. Secondly, full-field finite element analyses of the problem under small-scale yielding conditions are performed. The validity of the asymptotic fields and their range of dominance are determined by comparing them with the results of the full-field finite element analyses. Finally, theoretical predictions are made of the variations of the dynamic fracture toughness with crack velocity. The influence of the bi-material parameters on the above variation is investigated.
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We report a study of the kinematics of the cometary globules in the Gum Nebula using the J = 1 yields 0 transition line of (CO-12)O. A morphological center for the system with which 60 percent of the globules are associated is identified. It is shown that the observed radial velocities of the heads of the globules are consistent with an expansion of the system. Systematic velocity gradients are present along some of the tails. The estimated expansion age and the tail stretching age are both about a few million years, suggesting a common origin for the expansion and the formation of the tails. The presence of young stars of similar ages in some of the globules points to star formation triggered by the same cause. Possible scenarios are briefly discussed.
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The contributions of full-wake dynamics in trim analysis are demonstrated for finding the control inputs and periodic responses simultaneously, as well as in Floquet eigenanalysis for finding the damping levels. The equations of flap bending, lag bending, and torsion are coupled with a three-dimensional, finite state wake, and low-frequency (<1/rev) to high frequency (>1/rev) multiblade modes are considered. Full blade-wake dynamics is used in trim analysis and Floquet eigenanalysis. A uniform cantilever blade in trimmed flight is investigated over a range of thrust levels, advance ratios, number of blades, and blade torsional frequencies. The investigation includes the convergence characteristics of control inputs, periodic responses, and damping levels with respect to the number of spatial azimuthal harmonics and radial shape functions in the wake representation. It also includes correlation with the measured lag damping of a three-bladed untrimmed rotor. The parametric study shows the dominant influence of wake dynamics on control inputs, periodic responses, and damping levels, and wake theory generally improves the correlation.
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The present work is a numerical study of heat transfer characteristics from the bottom tip of a cylinder spinning about a vertical axis in an infinitely saturated porous medium. The problem is axisymmetric. The non-dimensionalized governing equations are solved using the SIMPLER algorithm on a staggered grid. The influence of rotational Reynolds numbers and Darcy numbers on the heat transfer for a Grashof number of 104 and Prandtl number of 7.0 is studied. It is found that for very high Darcy numbers, over a wide range of rotational Reynolds numbers, the heat transfer takes place mainly due to conduction. The convective heat transfer takes place for lower Darcy numbers and for higher rotational Reynolds numbers. Moreover, there is a rapid increase in the overall Nusselt number below a certain Darcy number with increase in the rotational Reynolds numbers. The effect of the Darcy number and the rotational Reynolds number on the heat transfer and fluid flow in the porous medium is depicted in the form of streamline and isotherm plots. The variation of the overall Nusselt number with respect to the Darcy number for various rotational Reynolds numbers is plotted. The variation of the local Nusselt number with respect to the radial coordinate at the heated tip of the vertical cylinder is plotted for various Darcy and rotational Reynolds numbers.
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A molecular dynamics calculation of argon in NaCaA zeolite at 393 K and 1 atom per cage is reported. Equilibrium properties such as guest-host interaction energy, guest-guest dimerization and bonding energy, various guest-host and guest-guest radial distribution functions and dynamical properties such as the mean-square displacement, power spectra and diffusion coefficient have been obtained.
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The modification of the axisymmetric viscous flow due to relative rotation of the disk or fluid by a translation of the boundary is studied. The fluid is taken to be compressible, and the relative rotation and translation velocity of the disk or fluid are time-dependent. The nonlinear partial differential equations governing the motion are solved numerically using an implicit finite difference scheme and Newton's linearisation technique. Numerical solutions are obtained at various non-dimensional times and disk temperatures. The non-symmetric part of the flow (secondary flow) describing the translation effect generates a velocity field at each plane parallel to the disk. The cartesian components of velocity due to secondary flow exhibit oscillations when the motion is due to rotation of the fluid on a translating disk. Increase in translation velocity produces an increment in the radial skin friction but reduces the tangential skin friction.
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We show that meridional circulation can have a profound influence on dynamo models for the solar cycle. Motivated by the observed tilt angles of sunspot groups we assume that the generation of the poloidal field takes place near the surface, while a shear layer of radial differential rotation produces the toroidal field at the bottom of the convection zone. Both layers are coupled by a circulation with a poleward directed flow in the upper part and an equatorward flow in the deep layers of the convection zone. The circulation forces the toroidal field belts (which are responsible for the surface activity) to move equatorward. This leads to butterfly diagrams in qualitative agreement with the observations, even if the dynamo wave would propagate poleward in the absence of circulation. This result opens the possibility to construct models for the solar cycle which are based on observational data (tilt angles, differential rotation, and meridional circulation).
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This paper investigates the loss of high mass ions due to their initial thermal energy in ion trap mass analyzers. It provides an analytical expression for estimating the percentage loss of ions of a given mass at a particular temperature, in a trap operating under a predetermined set of conditions. The expression we developed can be used to study the loss of ions due to its initial thermal energy in traps which have nonlinear fields as well as those which have linear fields. The expression for the percentage of ions lost is shown to be a function of the temperature of the ensemble of ions, ion mass and ion escape velocity. An analytical expression for the escape velocity has also been derived in terms of the trapping field, drive frequency and ion mass. Because the trapping field is determined by trap design parameters and operating conditions, it has been possible to study the influence of these parameters on ion loss. The parameters investigated include ion temperature, magnitude of the initial potential applied to the ring electrode (which determines the low mass cut-off), trap size, dimensions of apertures in the endcap electrodes and RF drive frequency. Our studies demonstrate that ion loss due to initial thermal energy increases with increase in mass and that, in the traps investigated, ion escape occurs in the radial direction. Reduction in the loss of high mass ions is favoured by lower ion temperatures, increasing low mass cut-off, increasing trap size, and higher RF drive frequencies. However, dimensions of the apertures in the endcap electrodes do not influence ion loss in the range of aperture sizes considered. (C) 2010 Elsevier B.V. All rights reserved.
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A mechanism is presented here for the amplification of large-scale nonaxisymmetric magnetic fields as a manifestation of the dynamo effect. We generalize a result on restrictions of dynamo actions due to laminar flow originally derived by Zeldovich, Ruzmaikin, and Sokolov [Magnetic Fields in Astrophysics (Gordon and Breach, New York, 1983)]. We show how a screwlike motion having phi and z components of velocity can help to grow a magnetic field. This model postulates a large-scale flow having phi and z components with radial dependences (helical flow). Shear in the radial field, because of a near-flux-freezing condition, causes amplification of the phi component of the magnetic field. The radial and axial components grow due to the presence of turbulent diffusion. The shear in the large scale flow induces an indefinite growth of magnetic field without the a effect; nevertheless, turbulent diffusion forms an important part in the overall mechanism.
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A mathematical model describing the dynamics of mammalian cell growth in hollow fibre bioreactor operated in closed shell mode is developed. Mammalian cells are assumed to grow as an expanding biofilm in the extra-capillary space surrounding the fibre. Diffusion is assumed to be the dominant process in the radial direction while axial convection dominates in the lumen of the bioreactor. The transient simulation results show that steep gradients in the cell number are possible under the condition of substrate limitation. The precise conditions which result in nonuniform growth of cells along the length of the bioreactor are delineated. The effect of various operating conditions, such as substrate feed rate, length of the bioreactor and diffusivity of substrate in different regions of the bioreactor, on the bioreactor performance are evaluated in terms of time required to attain the steady-state. The rime of growth is introduced as a measure of effectiveness factor for the bioreactor and is found to be dependent on two parameters, a modified Peclet number and a Thiele modulus. Diffusion, reaction and/or convection control regimes are identified based on these two parameters. The model is further extended to include dual substrate growth limitations, and the relative growth limiting characteristics of two substrates are evaluated. (C) 1997 Elsevier Science Ltd.
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A vertical jet of water impinging on a horizontal surface produces a radial film flow followed by a circular hydraulic jump. We report a phenomenon where fairly large (1 mi) drops of liquid levitate just upstream of the jump on a thin air layer between the drop and the film flow. We explain the phenomenon using lubrication theory. Bearing action both in the air film and the water film seems to be necessary to support large drops. Horizontal support is given to the drop by the hydraulic jump. A variety of drop shapes is observed depending on the volume of the drop and liquid properties. We show that interaction of the forces due to gravity, surface tension, viscosity and inertia produces these various shapes.
Resumo:
Flows with velocity profiles very different from the parabolic velocity profile can occur in the entrance region of a tube as well as in tubes with converging/diverging cross-sections. In this paper, asymptotic and numerical studies are undertaken to analyse the temporal stability of such 'non-parabolic' flows in a flexible tube in the limit of high Reynolds numbers. Two specific cases are considered: (i) developing flow in a flexible tube; (ii) flow in a slightly converging flexible tube. Though the mean velocity profile contains both axial and radial components, the flow is assumed to be locally parallel in the stability analysis. The fluid is Newtonian and incompressible, while the flexible wall is modelled as a viscoelastic solid. A high Reynolds number asymptotic analysis shows that the non-parabolic velocity profiles can become unstable in the inviscid limit. This inviscid instability is qualitatively different from that observed in previous studies on the stability of parabolic flow in a flexible tube, and from the instability of developing flow in a rigid tube. The results of the asymptotic analysis are extended numerically to the moderate Reynolds number regime. The numerical results reveal that the developing flow could be unstable at much lower Reynolds numbers than the parabolic flow, and hence this instability can be important in destabilizing the fluid flow through flexible tubes at moderate and high Reynolds number. For flow in a slightly converging tube, even small deviations from the parabolic profile are found to be sufficient for the present instability mechanism to be operative. The dominant non-parallel effects are incorporated using an asymptotic analysis, and this indicates that non-parallel effects do not significantly affect the neutral stability curves. The viscosity of the wall medium is found to have a stabilizing effect on this instability.