Thermoelastic wave propagation in a rotating elastic medium without energy dissipation
Directory of Open Access Journals (Sweden)
S. K. Roychoudhuri
2005-02-01
Full Text Available A study is made of the propagation of time-harmonic plane thermoelastic waves of assigned frequency in an infinite rotating medium using Green-Naghdi model (1993 of linear thermoelasticity without energy dissipation. A more general dispersion equation is derived to examine the effect of rotation on the phase velocity of the modified coupled thermal dilatational shear waves. It is observed that in thermoelasticity theory of type II (Green-Naghdi model, the modified coupled dilatational thermal waves propagate unattenuated in contrast to the classical thermoelasticity theory, where the thermoelastic waves undergo attenuation (Parkus, Chadwick, and Sneddon. The solutions of the more general dispersion equation are obtained for small thermoelastic coupling by perturbation technique. Cases of high and low frequencies are also analyzed. The rotation of the medium affects both quasielastic dilatational and shear wave speeds to the first order in ÃÂ‰ for low frequency, while the quasithermal wave speed is affected by rotation up to the second power in ÃÂ‰. However, for large frequency, rotation influences both the quasidilatational and shear wave speeds to first order in ÃÂ‰ and the quasithermal wave speed to the second order in 1/ÃÂ‰.
Vibration of imperfect rotating disk
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Půst L.
2011-12-01
Full Text Available This study is concerned with the theoretical and numerical calculations of the flexural vibrations of a bladed disk. The main focus of this study is to elaborate the basic background for diagnostic and identification methods for ascertaining the main properties of the real structure or an experimental model of turbine disks. The reduction of undesirable vibrations of blades is proposed by using damping heads, which on the experimental model of turbine disk are applied only on a limited number of blades. This partial setting of damping heads introduces imperfection in mass, stiffness and damping distribution on the periphery and leads to more complicated dynamic properties than those of a perfect disk. Calculation of FEM model and analytic—numerical solution of disk behaviour in the limited (two modes frequency range shows the splitting of resonance with an increasing speed of disk rotation. The spectrum of resonance is twice denser than that of a perfect disk.
Simultaneity on the Rotating Disk
Koks, Don
2017-04-01
The disk that rotates in an inertial frame in special relativity has long been analysed by assuming a Lorentz contraction of its peripheral elements in that frame, which has produced widely varying views in the literature. We show that this assumption is unnecessary for a disk that corresponds to the simplest form of rotation in special relativity. After constructing such a disk and showing that observers at rest on it do not constitute a true rotating frame, we choose a "master" observer and calculate a set of disk coordinates and spacetime metric pertinent to that observer. We use this formalism to resolve the "circular twin paradox", then calculate the speed of light sent around the periphery as measured by the master observer, to show that this speed is a function of sent-direction and disk angle traversed. This result is consistent with the Sagnac Effect, but constitutes a finer analysis of that effect, which is normally expressed using an average speed for a full trip of the periphery. We also use the formalism to give a resolution of "Selleri's paradox".
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Singh R.
2016-02-01
Full Text Available In this study an eigen value approach has been employed to examine the mechanical force applied along with a transverse magnetic field in a two dimensional generalized magneto micropolar thermoelastic infinite space. Results have been obtained by treating rotational velocity to be invariant. Integral transforms have been applied to solve the system of partial differential equations. Components of displacement, normal stress, tangential couple stress, temperature distribution, electric field and magnetic field have been obtained in the transformed domain. Finally numerical inversion technique has been used to invert the result in the physical domain. Graphical analysis has been done to described the study.
Magnetoelastic plane waves in rotating media in thermoelasticity of type II (G-N model
Directory of Open Access Journals (Sweden)
S. K. Roychoudhuri
2004-01-01
Full Text Available A study is made of the propagation of time-harmonic plane waves in an infinite, conducting, thermoelastic solid permeated by a uniform primary external magnetic field when the entire medium is rotating with a uniform angular velocity. The thermoelasticity theory of type II (G-N model (1993 is used to study the propagation of waves. A more general dispersion equation is derived to determine the effects of rotation, thermal parameters, characteristic of the medium, and the external magnetic field. If the primary magnetic field has a transverse component, it is observed that the longitudinal and transverse motions are linked together. For low frequency (χ≪1, χ being the ratio of the wave frequency to some standard frequency ω∗, the rotation and the thermal field have no effect on the phase velocity to the first order of χ and then this corresponds to only one slow wave influenced by the electromagnetic field only. But to the second order of χ, the phase velocity, attenuation coefficient, and the specific energy loss are affected by rotation and depend on the thermal parameters cT, cT being the nondimensional thermal wave speed of G-N theory, and the thermoelastic coupling εT, the electromagnetic parameters εH, and the transverse magnetic field RH. Also for large frequency, rotation and thermal field have no effect on the phase velocity, which is independent of primary magnetic field to the first order of (1/χ (χ≫1, and the specific energy loss is a constant, independent of any field parameter. However, to the second order of (1/χ, rotation does exert influence on both the phase velocity and the attenuation factor, and the specific energy loss is affected by rotation and depends on the thermal parameters cT and εT, electromagnetic parameter εH, and the transverse magnetic field RH, whereas the specific energy loss is independent of any field parameters to the first order of (1/χ.
Instability of counter-rotating stellar disks
Hohlfeld, R. G.; Lovelace, R. V. E.
2015-09-01
We use an N-body simulation, constructed using GADGET-2, to investigate an accretion flow onto an astrophysical disk that is in the opposite sense to the disk's rotation. In order to separate dynamics intrinsic to the counter-rotating flow from the impact of the flow onto the disk, we consider an initial condition in which the counter-rotating flow is in an annular region immediately exterior the main portion of the astrophysical disk. Such counter-rotating flows are seen in systems such as NGC 4826 (known as the "Evil Eye Galaxy"). Interaction between the rotating and counter-rotating components is due to two-stream instability in the boundary region. A multi-armed spiral density wave is excited in the astrophysical disk and a density distribution with high azimuthal mode number is excited in the counter-rotating flow. Density fluctuations in the counter-rotating flow aggregate into larger clumps and some of the material in the counter-rotating flow is scattered to large radii. Accretion flow processes such as this are increasingly seen to be of importance in the evolution of multi-component galactic disks.
Effect of rotation in magneto-micropolar thermoelastic medium due to mechanical and thermal sources
Energy Technology Data Exchange (ETDEWEB)
Kumar, Rajneesh [Department of Mathematics, Kurukshetra University, Kurukshetra 136 119 (India)], E-mail: rajneesh_kuk@rediffmail.com; Rupender [Department of Mathematics, Kurukshetra University, Kurukshetra 136 119 (India)], E-mail: rupee_kuk@rediffmail.com
2009-08-30
In this work, a two dimensional problem in electromagnetic micropolar generalized thermoelastic medium, in the presence of a transverse magnetic field subjected to mechanical force or thermal source (concentrated or uniformly distributed), is investigated. The entire elastic medium is rotating with a uniform angular velocity. Laplace and Fourier transform techniques are used to solve the problem and the Descartes' method along with irreducible case of Cardan's method is used to obtain the roots of eight degree equation. The transformed components of normal strain, normal stress, tangential couple stress, temperature distribution, induced electric field and magnetic field are obtained. The integral transforms have been inverted by using a numerical technique. Magnetic effects and effect of rotation have been depicted graphically on the resulting quantities. Particular cases of interest are also deduced from the present investigation.
Exact Relativistic Magnetized Haloes around Rotating Disks
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Antonio C. Gutiérrez-Piñeres
2015-01-01
Full Text Available The study of the dynamics of magnetic fields in galaxies is one of important problems in formation and evolution of galaxies. In this paper, we present the exact relativistic treatment of a rotating disk surrounded by a magnetized material halo. The features of the halo and disk are described by the distributional energy-momentum tensor of a general fluid in canonical form. All the relevant quantities and the metric and electromagnetic potentials are exactly determined by an arbitrary harmonic function only. For instance, the generalized Kuzmin-disk potential is used. The particular class of solutions obtained is asymptotically flat and satisfies all the energy conditions. Moreover, the motion of a charged particle on the halo is described. As far as we know, this is the first relativistic model describing analytically the magnetized halo of a rotating disk.
INTELLIGENT INTEGRATION CONTROL OF ROTATING DISK VIBRATION
Institute of Scientific and Technical Information of China (English)
无
2001-01-01
The rotating disk is a basic machine part that is u sed widely in industry. The motion equation is transformed into the dynamic equa tion in real modal space. The personating intelligent integration is introduced to improve the existing control method. These modes that affect the transverse v ibration mainly are included to simulate the vibration of rotating disk, and two methods are applied separately on condition that the sensor and the ac tuator are collocated and non-collocated. The results obtained by all-sided si mulations show that the new method can obtain better control effect, especially when the sensor and the actuator are non-collocated.
MODELING OF THERMOELASTIC WAVES IN ROTATING CYLINDRICAL PANEL BY USING MATRIX FROBENIUS METHOD
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HARJIT SINGH
2015-07-01
Full Text Available In this paper, free vibrations are investigated in a homogeneous transversely isotropic, rotating cylindrical panel, in context of the linear theory of thermoelasticity. Three displacement potential functions have been introduced in the equations of motion and heat conduction in order to decouple purely shear and longitudinal motions. The purely transverse wave is not affected by thermal field. By using the method of separation of variables, the system of governing partial differential equations is reduced to four second order coupled ordinary differential equations in radial coordinate. The Matrix Frobenius method of extended power series is employed to obtain the solution in radial direction. The secular equations are obtained by using traction free and thermally insulated boundary conditions. In order to illustrate the analytic results, the numerical solution of various relations and equations has been carried out to compute the lowest frequency, phase velocity, frequency shift and damping factor of vibrations in a rotating cylindrical panel of zinc material with MATLAB software programming. The computer simulated results have been presented graphically.
Directory of Open Access Journals (Sweden)
A. M. Abd-Alla
2013-01-01
Full Text Available Estimation is done to investigate the gravitational and rotational parameters effects on surface waves in fibre-reinforced thermoelastic media. The theory of generalized surface waves has been firstly developed and then it has been employed to investigate particular cases of waves, namely, Stoneley waves, Rayleigh waves, and Love waves. The analytical expressions for surface waves velocity and attenuation coefficient are obtained in the physical domain by using the harmonic vibrations and four thermoelastic theories. The wave velocity equations have been obtained in different cases. The numerical results are given for equation of coupled thermoelastic theory (C-T, Lord-Shulman theory (L-S, Green-Lindsay theory (G-L, and the linearized (G-N theory of type II. Comparison was made with the results obtained in the presence and absence of gravity, rotation, and parameters for fibre-reinforced of the material media. The results obtained are displayed by graphs to clear the phenomena physical meaning. The results indicate that the effect of gravity, rotation, relaxation times, and parameters of fibre-reinforced of the material medium is very pronounced.
Streaming potential near a rotating porous disk.
Prieve, Dennis C; Sides, Paul J
2014-09-23
Theory and experimental results for the streaming potential measured in the vicinity of a rotating porous disk-shaped sample are described. Rotation of the sample on its axis draws liquid into its face and casts it from the periphery. Advection within the sample engenders streaming current and streaming potential that are proportional to the zeta potential and the disk's major dimensions. When Darcy's law applies, the streaming potential is proportional to the square of the rotation at low rate but becomes invariant with rotation at high rate. The streaming potential is invariant with the sample's permeability at low rate and is proportional to the inverse square of the permeability at high rate. These predictions were tested by determining the zeta potential and permeability of the loop side of Velcro, a sample otherwise difficult to characterize; reasonable values of -56 mV for zeta and 8.7 × 10(-9) m(2) for the permeability were obtained. This approach offers the ability to determine both the zeta potential and the permeability of materials having open structures. Compressing them into a porous plug is unnecessary. As part of the development of the theory, a convenient formula for a flow-weighted volume-averaged space-charge density of the porous medium, -εζ/k, was obtained, where ε is the permittivity, ζ is the zeta potential, and k is the Darcy permeability. The formula is correct when Smoluchowski's equation and Darcy's law are both valid.
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Arefi Mohammad
2015-12-01
Full Text Available Thermo-mechanical analysis of the functionally graded orthotropic rotating hollow structures, subjected to thermo-mechanical loadings is studied in this paper. The relations were derived for both plane strain and plane stress conditions as a cylinder and disk, respectively. Non homogeneity was considered arbitrary through thickness direction for all mechanical and thermal properties. The responses of the system including temperature distribution, radial displacement and radial and circumferential stresses were derived in the general state. As case study, power law gradation was assumed for functionally graded cylinder and the mentioned results were evaluated in terms of parameters of the system such as non-homogeneous index and angular velocity.
Directory of Open Access Journals (Sweden)
Maity N.
2017-06-01
Full Text Available The article is concernedwith the possibility of plane wave propagation in a rotating elastic medium under the action of magnetic and thermal fields. The material is assumed to be fibre-reinforced with increased stiffness, strength and load bearing capacity. Green and Nagdhi’s concepts of generalized thermoelastic models II and III have been followed in the governing equations expressed in tensor notation. The effects of various parameters of the applied fields on the plane wave velocity have been shown graphically.
Stability of accretion disk around rotating black holes
Mukhopadhyay, B
2004-01-01
I discuss the stability of accretion disks when the black hole is considered to be rotating. I show, how the fluid properties get changed for different choices of angular momentum of black holes. I treat the problem in pseudo-Newtonian approach with a suitable potential from Kerr geometry. When the angular momentum of a black hole is considered to be significant, the valid disk parameter region affects and a disk may become unstable. Also the possibility of shock in an accretion disk around rotating black holes is checked. When the black hole is chosen to be rotating, the sonic locations of the accretion disk get shifted or disappear, making the disk unstable by means of loosing entropy. To bring the disk in a stable situation, the angular momentum of the accreting matter has to be reduced/enhanced (for co/counter-rotating disk) by means of some physical process.
Instability patterns between counter-rotating disks
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F. Moisy
2003-01-01
Full Text Available The instability patterns in the flow between counter-rotating disks (radius to height ratio R/h from 3.8 to 20.9 are investigated experimentally by means of visualization and Particle Image Velocimetry. We restrict ourselves to the situation where the boundary layers remain stable, focusing on the shear layer instability that occurs only in the counter-rotating regime. The associated pattern is a combination of a circular chain of vortices, as observed by Lopez et al. (2002 at low aspect ratio, surrounded by a set of spiral arms, first described by Gauthier et al. (2002 in the case of high aspect ratio. Stability curve and critical modes are measured for the whole range of aspect ratios. From the measurement of a local Reynolds number based on the shear layer thickness, evidence is given that a free shear layer instability, with only weak curvature effect, is responsible for the observed patterns. Accordingly, the number of vortices is shown to scale as the shear layer radius, which results from the competition between the centrifugal effects of each disk.
Institute of Scientific and Technical Information of China (English)
Kh. Lotfy
2012-01-01
In the present paper,we introduce the coupled theory (CD),Lord Schulman (LS) theory,and Green-Lindsay (GL) theory to study the influences of a magnetic field and rotation on a two-dimensional problem of fibre-reinforced thermoelasticity.The material is a homogeneous isotropic elastic half-space.The method applied here is to use normal mode analysis to solve a thermal shock problem.Some particular cases are also discussed in the context of the problem.Deformation of a body depends on the nature of the force applied as well as the type of boundary conditions.Numerical results for the temperature,displacement,and thermal stress components are given and illustrated graphically in the absence and the presence of the magnetic field and rotation.
Flow Structure and Heat Transfer Between Two Disks Rotating Independently
Institute of Scientific and Technical Information of China (English)
Chyi-Yeou Soong
2003-01-01
In the present paper, fluid flow and convective heat transfer between two co-axial disks rotating independently are dealt with mainly based on the author's recent research on that topic. Three rotational modes, i.e. co-rotation, rotor-stator, and counter-rotation, are considered. Theory of rotating non-isothermal fluids with the presence of disk rotation and thermal effects is addressed. Rotational buoyancy effects on the flow structure development are highlighted. Results of flow visualization and heat transfer measurements are discussed to explore the thermal flow mechanisms involved in the two-disk flows at various rotational and geometric conditions. Potential issues open to the future investigation are also proposed.
Galactic Rotation Described with Bulge+Disk Gravitational Models
Gallo, C F
2008-01-01
Observations reveal that mature spiral galaxies consist of stars, gases and plasma approximately distributed in a thin disk of circular shape, usually with a central bulge. The rotation velocities quickly increase from the galactic center and then achieve a constant velocity from the core to the periphery. The basic dynamic behavior of a mature spiral galaxy, such as the Milky Way, is well described by simple models balancing Newtonian gravitational forces against the centrifugal forces associated with a rotating thin axisymmetric disk. In this research, we investigate the effects of adding central bulges to thin disk gravitational models. Even with the addition of substantial central bulges, all the critical essential features of our thin disk gravitational models are preserved. (1) Balancing Newtonian gravitational and centrifugal forces at every point within the disk yields computed radial mass distributions that describe the measured rotation velocity profiles of mature spiral galaxies successfully. (2) T...
Rotation of melting ice disks due to melt fluid flow.
Dorbolo, S; Adami, N; Dubois, C; Caps, H; Vandewalle, N; Darbois-Texier, B
2016-03-01
We report experiments concerning the melting of ice disks (85 mm in diameter and 14 mm in height) at the surface of a thermalized water bath. During the melting, the ice disks undergo translational and rotational motions. In particular, the disks rotate. The rotation speed has been found to increase with the bath temperature. We investigated the flow under the bottom face of the ice disks by a particle image velocimetry technique. We find that the flow goes downwards and also rotates horizontally, so that a vertical vortex is generated under the ice disk. The proposed mechanism is the following. In the vicinity of the bottom face of the disk, the water eventually reaches the temperature of 4 °C for which the water density is maximum. The 4 °C water sinks and generates a downwards plume. The observed vertical vorticity results from the flow in the plume. Finally, by viscous entrainment, the horizontal rotation of the flow induces the solid rotation of the ice block. This mechanism seems generic: any vertical flow that generates a vortex will induce the rotation of a floating object.
Convective heat and mass transfer in rotating disk systems
Shevchuk, Igor V
2009-01-01
The book describes results of investigations of a series of convective heat and mass transfer problems in rotating-disk systems. Methodology used included integral methods, self-similar and approximate analytical solutions, as well as CFD.
Counter-Rotation in Disk Galaxies
Corsini, E M
2014-01-01
Counter-rotating galaxies host two components rotating in opposite directions with respect to each other. The kinematic and morphological properties of lenticulars and spirals hosting counter-rotating components are reviewed. Statistics of the counter-rotating galaxies and analysis of their stellar populations provide constraints on the formation scenarios which include both environmental and internal processes.
Transient mass transfer at the rotating disk electrode.
Nanis, L.; Klein, I.
1972-01-01
Transient mass transfer at the rotating disk has been investigated theoretically and experimentally for cathodic reduction of ferricyanide in the redox system ferricyanide-ferrocyanide with potassium hydroxide supporting electrolyte. It has been shown that overpotential-time predictions for the rotating disk are fitted very well for decay (current interruption) but poorly for build-up following switching on of constant current. As an explanation for this behavior, attention is directed to the inadequacy of the assumption that a radially independent concentration profile exists at the disk surface just at the start of galvanostatic current passage.
Local Axisymmetric Instability Criterion in the Thin, Rotating, Multicomponent Disk
Rafikov, R R
2000-01-01
Purely gravitational perturbations are considered in a thin rotating disk composed of several gas and stellar components. The dispersion relation for the axisymmetric density waves propagating through the disk is found and the criterion for the local axisymmetric stability of the whole system is formulated. In the appropriate limit of two-component gas we confirm the findings of Jog & Solomon (1984) and extend consideration to the case when one component is collisionless. Gravitational stability of the Galactic disk in the Solar neighborhood based on the multicomponent instability condition is explored using recent measurements of the stellar composition and kinematics in the local Galactic disk obtained by Hipparcos satellite.
Containment of high-speed rotating disk fragments
Institute of Scientific and Technical Information of China (English)
Hai-jun XUAN; Lu-lu LIU; Yi-ming FENG; Qing HE; Juan-juan LI
2012-01-01
Disk burst accidents sometimes happen in aeroengines.To avoid tragic consequences,aeroengine casings must have sufficient containment capability.Experiments and simulations need to be conducted to study the impact,distortion,and perforation caused by disk burst and which may give important clues to potential failure mechanisms.This paper presents some containment tests of high-speed rotating disk fragments,in which the original disks were burst into three equal fragments within a predetermined rotating speed range.The failure modes of the containment casing varied significantly with the thickness of the containment casing.Shearing,tearing,tensile fracture,and large plastic stretching deformation occurred in a thin-walled containment casing,while a thick-walled casing could contain disk fragments and withstand large plastic deformation.Numerical simulations were carried out to study the impact process and failure modes further.Good agreement was found between the results of the simulations and the tests.
Analytic Creep Durability of Rotating Uniform Disks
Directory of Open Access Journals (Sweden)
Yuriy Nyashin
1998-01-01
Full Text Available Turbine disks of aircraft engines in operation are subjected to alternating thermocyclic deformation under high temperatures. Operation gives rise to sufficiently high stresses and subsequent creep damaging effects.
Povstenko, Yuriy
2015-01-01
This book is devoted to fractional thermoelasticity, i.e. thermoelasticity based on the heat conduction equation with differential operators of fractional order. Readers will discover how time-fractional differential operators describe memory effects and space-fractional differential operators deal with the long-range interaction. Fractional calculus, generalized Fourier law, axisymmetric and central symmetric problems and many relevant equations are featured in the book. The latest developments in the field are included and the reader is brought up to date with current research. The book contains a large number of figures, to show the characteristic features of temperature and stress distributions and to represent the whole spectrum of order of fractional operators. This work presents a picture of the state-of-the-art of fractional thermoelasticity and is suitable for specialists in applied mathematics, physics, geophysics, elasticity, thermoelasticity and engineering sciences. Corresponding sections of ...
Xin, Libiao; Yang, Shengyou; Ma, Baoyu; Dui, Guansuo
2015-11-01
A thermoelastic solution for the functionally graded rotating thick-walled tube subjected to axisymmetric mechanical and thermal loads is given in terms of volume fractions of constituents. We assume that the tube consists of two linear elastic constituents and the volume fraction of one phase is a power function varied in the radial direction. By using the assumption of a uniform strain field within the representative volume element, the theoretical solutions of the displacement and the stresses are presented. Based on the relation of the volume average stresses of constituents and the macroscopic stresses of the composite material in micromechanics, the present method can avoid the assumption of the distribution regularities of unknown overall material parameters appeared in existing papers, such as Young's modulus, thermal expansion coefficient, thermal conductivity, and density. The effects of the angular velocity, the volume fraction, the ratio of two thermal expansion coefficients, the ratio of two thermal conductivities, and the ratio of two densities on the displacement and stresses are systematically studied, which should help structural engineers and material scientists optimally design thick-walled tube comprised inhomogeneous materials.
General thermo-elastic solution of radially heterogeneous, spherically isotropic rotating sphere
Energy Technology Data Exchange (ETDEWEB)
Bayat, Yahya; EkhteraeiToussi, THamid [Ferdowsi University of Mashhad, Mashhad (Iran, Islamic Republic of)
2015-06-15
A thick walled rotating spherical object made of transversely isotropic functionally graded materials (FGMs) with general types of thermo-mechanical boundary conditions is studied. The thermo-mechanical governing equations consisting of decoupled thermal and mechanical equations are represented. The centrifugal body forces of the rotation are considered in the modeling phase. The unsymmetrical thermo-mechanical boundary conditions and rotational body forces are expressed in terms of the Legendre series. The series method is also implemented in the solution of the resulting equations. The solutions are checked with the known literature and FEM based solutions of ABAQUS software. The effects of anisotropy and heterogeneity are studied through the case studies and the results are represented in different figures. The newly developed series form solution is applicable to the rotating FGM spherical transversely isotropic vessels having nonsymmetrical thermo-mechanical boundary condition.
Electrovacuum Static Counter-Rotating Relativistic Dust Disks
González, G A
2002-01-01
A detailed study of the Counter-Rotating Model (CRM) for generic electrostatic (magnetostatic) axially symmetric thin disks without radial pressure is presented. We find a general constraint over the counter-rotating tangential velocities needed to cast the surface energy-momentum tensor of the disk as the superposition of two counter-rotating charged dust fluids. We then show that this constraint is satisfied if we take the two counter-rotating streams as circulating along electrogeodesics with equal and opposite tangential velocities. We also find explicit expressions for the energy densities, electrostatic (magnetostatic) charge densities and velocities of the counter-rotating fluids. Three specific examples are considered where we obtain some CRM well behaved based in simple solutions to the Einstein-Maxwell equations. The considered solutions are Reissner-Nordstrom in the electrostatic case, its magnetostatic counterpart and two solutions obtained from Taub-NUT and Kerr solutions.
The universal rotation curve of dwarf disk galaxies
Karukes, Ekaterina V
2016-01-01
We use the concept of the spiral rotation curves universality (see Parsic et al. 1996) to investigate the luminous and dark matter properties of the dwarf disk galaxies in the local volume (size $\\sim11$ Mpc). Our sample includes 36 objects with rotation curves carefully selected from the literature. We find that, despite the large variations of our sample in luminosities ($\\sim$ 2 of dex), the rotation curves in specifically normalized units, look all alike and lead to the lower-mass version of the universal rotation curve of spiral galaxies found in Parsic et al. 1996. We mass model $V(R/R_{opt})/V_{opt}$, the double normalized universal rotation curve of dwarf disk galaxies: the results show that these systems are totally dominated by dark matter whose density shows a core size between 2 and 3 stellar disk scale lengths. Similar to galaxies of different Hubble types and luminosities, the core radius $r_0$ and the central density $\\rho_0$ of the dark matter halo of these objects are related by $ \\rho_0 r_0 ...
Rotating plasma disks in dense Z-pinch experiments
Energy Technology Data Exchange (ETDEWEB)
Bennett, M. J., E-mail: m.bennett11@imperial.ac.uk, E-mail: s.lebedev@imperial.ac.uk; Lebedev, S. V., E-mail: m.bennett11@imperial.ac.uk, E-mail: s.lebedev@imperial.ac.uk; Suttle, L.; Burdiak, G.; Suzuki-Vidal, F.; Hare, J.; Swadling, G.; Patankar, S.; Bocchi, M.; Chittenden, J. P.; Smith, R. [Blackett Laboratory, Imperial College London (United Kingdom); Hall, G. N. [Blackett Laboratory, Imperial College London, UK and Lawrence Livermore National Laboratory (United States); Frank, A.; Blackman, E. [Department of Physics and Astronomy, University of Rochester (United States); Drake, R. P. [Department of Atmospheric, Oceanic and Space Science, University of Michigan (United States); Ciardi, A. [Universite Pierre et Marie Curie, Observatiore de Paris (France)
2014-12-15
We present data from the first z-pinch experiments aiming to simulate aspects of accretion disk physics in the laboratory. Using off axis ablation flows from a wire array z-pinch we demonstrate the formation of a hollow disk structure that rotates at 60 kms{sup −1} for 150 ns. By analysing the Thomson scattered spectrum we make estimates for the ion and electron temperatures as T{sub i} ∼ 60 eV and ZT{sub e} ∼ 150 to 200 eV.
Microscale flow and heat transfer between rotating disks
Energy Technology Data Exchange (ETDEWEB)
Jiji, Latif M., E-mail: jiji@ccny.cuny.ed [Department of Mechanical Engineering, City College of the City University of New York, New York, NY 10031 (United States); Ganatos, Peter, E-mail: ganatos@ccny.cuny.ed [Department of Mechanical Engineering, City College of the City University of New York, New York, NY 10031 (United States)
2010-08-15
In this paper we consider steady laminar flow and heat transfer generated by two infinite parallel disks separated by a gas-filled micro-gap {delta}. One disk rotates with angular velocity {Omega} and the second with angular velocity s{Omega}. The analysis takes into consideration velocity slip, temperature jump, rarefaction and dissipation. A solution based on similarity transformation is obtained and used to examine the effects of the governing parameters on the velocity field, temperature distribution, disks' torque and power, and Nusselt number. The solution requires numerical integration of the resulting coupled ordinary non-linear differential equations. An exact analytical solution is obtained for the limiting case of small Reynolds numbers.
Numerical simulation on heat transfer inside rotating porous disk subjected to local heat flux
Institute of Scientific and Technical Information of China (English)
ZHU; XingDan; ZHANG; JingZhou; TAN; XiaoMing
2013-01-01
Numerical simulation was carried out to study the centrifugally-driven flow and heat transfer inside rotating metallic porous disk subjected to local heat flux. The effects of rotational speed, solid thermal conductivity and porosity on heat transfer were analyzed. The thermal transport coefficient, defined as the ratio of local heat flux to maximum temperature difference on the disk, was introduced to evaluate the thermal transport capacity in rotating porous disk. For convenience, the conjugation between convective heat transfer inside the rotating porous disk and convective heat transfer over the rotating disk surface was decoupled in the present study. Firstly, the convective heat transfer over the free rotating disk surface was investigated indi-vidually to determine the heat transfer coefficient over the disk surface to the ambient air. Then the convective heat transfer over a rotating disk surface was treated as the thermal boundary condition for the computation of convective heat transfer in-side rotating porous disk. Under the present research conditions, the results show that the centrifugally-driven flow is enhanced significantly with the increase of rotational speed. Consequently, the maximum temperature on the disk surface is decreased and the temperature distribution tends to be uniform. The thermal transport capacity in rotating porous disk is also enhanced with the increase of solid thermal conductivity or the decrease of solid porosity. In the rotating porous disk, the solid phase heat transfer is clearly the dominant mode of heat transport and the fluid phase makes an incremental contribution to the total heat transfer.
Said, Samia M.; Othman, Mohamed I. A.
2016-09-01
In the present paper, the three-phase-lag model and Green-Naghdi theory without energy dissipation are used to study the effect of a mechanical force and a rotation on the wave propagation in a two-temperature fiber-reinforced thermoelastic problem for a medium with an internal heat source that is moving with a constant speed. The methodology applied here is the use of the normal mode analysis to solve the problem of a thermal shock problem to obtain the exact expressions of the displacement components, force stresses, thermal temperature, and conductivity temperature. Numerical results for the considered variables are given and illustrated graphically in the absence and presence of a rotation as well as a mechanical force. A comparison is made with the results in the context of the two theories in the absence and presence of a moving internal heat source.
Segmentally structured disk triboelectric nanogenerator for harvesting rotational mechanical energy.
Lin, Long; Wang, Sihong; Xie, Yannan; Jing, Qingshen; Niu, Simiao; Hu, Youfan; Wang, Zhong Lin
2013-06-12
We introduce an innovative design of a disk triboelectric nanogenerator (TENG) with segmental structures for harvesting rotational mechanical energy. Based on a cyclic in-plane charge separation between the segments that have distinct triboelectric polarities, the disk TENG generates electricity with unique characteristics, which have been studied by conjunction of experimental results with finite element calculations. The role played by the segmentation number is studied for maximizing output. A distinct relationship between the rotation speed and the electrical output has been thoroughly investigated, which not only shows power enhancement at high speed but also illuminates its potential application as a self-powered angular speed sensor. Owing to the nonintermittent and ultrafast rotation-induced charge transfer, the disk TENG has been demonstrated as an efficient power source for instantaneously or even continuously driving electronic devices and/or charging an energy storage unit. This work presents a novel working mode of TENGs and opens up many potential applications of nanogenerators for harvesting even large-scale energy.
Magneto-rotational instability in the protolunar disk
Carballido, Augusto; Taylor, G Jeffrey
2015-01-01
(Abridged) We perform the first study of magnetohydrodynamic processes in the protolunar disk (PLD). With the use of published data on the chemical composition of the PLD, along with existing analytical models of the disk structure, we show that the high temperatures that were prevalent in the disk would have led to ionization of Na, K, SiO, Zn and, to a lesser extent, O$_2$. We assume that the disk has a vapor structure. The resulting ionization fractions, together with a relatively weak magnetic field, would have been sufficient to trigger the magneto-rotational instability, or MRI. We calculate the intensity of the resulting magnetohydrodynamic turbulence, as parameterized by the dimensionless ratio $\\alpha$ of turbulent stresses to gas pressure, and obtain maximum values $\\alpha\\sim 10^{-2}$ along most of the vertical extent of the disk, and at different orbital radii. Under these conditions, turbulent mixing within the PLD due to the MRI was likely capable of transporting isotopic and chemical species ef...
Thermo-Rotational Instability in Plasma Disks Around Compact Objects
Coppi, Bruno
2008-01-01
Differentially rotating plasma disks, around compact objects, that are imbedded in a ``seed'' magnetic field are shown to develop vertically localized ballooning modes that are driven by the combined radial gradient of the rotation frequency and vertical gradients of the plasma density and temperature. When the electron mean free path is shorter than the disk height and the relevant thermal conductivity can be neglected, the vertical particle flows produced by of these modes have the effect to drive the density and temperature profiles toward the ``adiabatic condition'' where $\\eta_{T}\\equiv(dlnT/dz)/(dlnn/dz)=2/3$. Here $T$ is the plasma temperature and $n$ the particle density. The faster growth rates correspond to steeper temperature profiles $(\\eta_{T}>2/3)$ such as those produced by an internal (e.g., viscous) heating process. In the end, ballooning modes excited for various values of $\\eta_{T}$ can lead to the evolution of the disk into a different current carrying configuration such as a sequence of pl...
Rotationally-supported disks around Class I sources in Taurus: disk formation constraints
Harsono, Daniel; van Dishoeck, Ewine F; Hogerheijde, Michiel R; Bruderer, Simon; Persson, Magnus V; Mottram, Joseph C
2013-01-01
(Abridged) Disks are observed around pre-main sequence stars, but how and when they form is still heavily debated. While disks around young stellar objects have been identified through thermal dust emission, spatially and spectrally resolved molecular line observations are needed to determine their nature. We present subarcsecond observations of dust and gas toward four Class I low-mass young stellar objects in Taurus. The 13CO and C18O J=2-1 transitions at 220 GHz were observed with the Plateau de Bure Interferometer at a spatial resolution of ~0.8'' and analyzed using uv-space position velocity diagrams to determine the nature of their observed velocity radient. Rotationally supported disks (RSDs) are detected around 3 of the 4 Class I sources studied. The derived masses identify them as Stage I objects; i.e., their stellar mass is higher than their envelope and disk masses. The outer radii of the Keplerian disks toward our sample of Class I sources are 100 AU around these sources are dominated by infallin...
Convective heat transfer to Sisko fluid over a rotating disk
Munir, Asif
2016-01-01
This article deals with study of the steady flow and heat transfer characteristics of Sisko fluid over a rotating infinite disk. The flow and heat transfer aspects are thoroughly investigated encompassing highly shear thinning/thickening Sisko fluids. The modeled boundary layer equations are reduced to a system of nonlinear ordinary differential equations using the appropriate transformation. The resulting equations are then solved numerically by shooting method in the domain . The numerical data for the velocity and temperature fields are graphically sketched and effects of the relevant parameters are discussed in detail. In addition, the velocity gradients at the disk surface and the local Nusselt number for different values of the pertaining parameters are given in tabulated form. Further, the flow and temperature fields of power-law and Newtonian fluids are also compared with those Sisko fluid. Moreover, a comparison with previously published work, as a special case of the problem, has been provided and t...
General relativistic spectra of accretion disks around rotating neutron stars
Bhattacharya, S; Thampan, A V
2000-01-01
General relativistic spectra from accretion disks around rotating neutron stars in the appropriate space-time geometry for several different equation of state, spin rates and mass of the compact object have been computed. The analysis involves the computation of the relativistically corrected radial temperature profiles and the effect of Doppler and gravitational red-shifts on the spectra. Light bending effects have been omitted for simplicity. The relativistic spectrum is compared with the Newtonian one and it is shown that the difference between the two is primarily due to the different radial temperature profile for the relativistic and Newtonian disk solutions. To facilitate direct comparison with observations, a simple empirical function has been presented which describes the numerically computed relativistic spectra well. This empirical function (which has three parameters including normalization) also describes the Newtonian spectrum adequately. Thus the function can in principle be used to distinguish...
Unsteady Flow Produced by Oscillations of Eccentric Rotating Disks
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H. Volkan Ersoy
2012-01-01
Full Text Available While the disks are initially rotating eccentrically, the unsteady flow caused by their oscillations in their own planes and in the opposite directions is studied. The analytical solutions to the problem are obtained for both small and large times, and thus the velocity field is determined for every value of time. The variations of all the parameters on the flow are scrutinized by means of the graphical representations. In particular, the effect of the ratio of the frequency of oscillation to the angular velocity of the disks is analyzed. The dependence of the oscillations in both - and -directions on the flow is examined. The influence of the Reynolds number is also investigated.
Disk-driven rotating bipolar outflow in Orion Source I
Hirota, Tomoya; Machida, Masahiro N.; Matsushita, Yuko; Motogi, Kazuhito; Matsumoto, Naoko; Kim, Mi Kyoung; Burns, Ross A.; Honma, Mareki
2017-07-01
One of the outstanding problems in star formation theory concerns the transfer of angular momentum so that mass can accrete onto a newly born young stellar object (YSO). From a theoretical standpoint, outflows and jets are predicted to play an essential role in the transfer of angular momentum 1,2,3,4 and their rotations have been reported for both low- 5 and high-mass 6,7 YSOs. However, little quantitative discussion on outflow launching mechanisms has been presented for high-mass YSOs due to a lack of observational data. Here we present a clear signature of rotation in the bipolar outflow driven by Orion Source I, a high-mass YSO candidate, using the Atacama Large Millimeter/Submillimeter Array (ALMA). A rotational transition of silicon monoxide (Si18O) reveals a velocity gradient perpendicular to the outflow axis, which is consistent with that of the circumstellar disk traced by a high excitation water line. The launching radii and outward velocity of the outflow are estimated to be >10 au and 10 km s-1, respectively. These parameters rule out the possibility that the observed outflow is produced by the entrainment of a high-velocity jet 8 , and that contributions from the stellar wind 9 or X-wind 10 , which have smaller launching radii, are significant in the case of Source I. Thus these results provide convincing evidence of a rotating outflow directly driven by the magneto-centrifugal disk wind launched by a high-mass YSO candidate 6,11 .
Experimental study of absolute instability over a rotating disk
Othman Bekhit, Hesham Abdel Ghafar
2005-07-01
A series of experiments were performed to study the absolute instability of Type I traveling cross-flow modes in the boundary layer on a smooth disk rotating at constant speed. The basic flow agreed with analytic theory, and the growth of natural disturbances matched linear theory predictions. Controlled temporal disturbances were introduced by a short-duration air pulse from a hypodermic tube located above the disk and outside the boundary layer. The air pulse was positioned just outboard of the critical radius for Type I cross-flow modes. A hot-wire sensor primarily sensitive to the azirnuthal velocity component, was positioned at different spatial locations on the disk to document the growth of disturbances produced by the air pulses. Ensemble averages conditioned on the air pulses revealed wave packets that evolved in time and space. Two amplitudes of air pulses were used. The lower amplitude produced wave packets with linear amplitude characteristics that agreed with linear-theory wall-normal eigenfunction distributions and spatial growth rates. The higher amplitude pulse produced wave packets that had nonlinear amplitude characteristics. The space-time evolution of the leading and trailing edges of the wave packets were followed well past the critical radius for the absolute instability based on Lingwood (1995). With the linear amplitudes, the absolute instability was dominated by the convective modes, agreeing with the linear DNS simulations of Davies and Carpenter (2003). With the nonlinear amplitudes, larger temporal growth of the wave packets existed which supports the finite amplitude analysis of Pier (2003), and more closely resembles the wave packet evolution in the experimental study of Lingwood (1996). This suggests that the disturbance levels in the experiment that was intended to demonstrate the linear analysis, were likely fuite.
The Magneto-Rotational Decay Instability in Keplerian Disks
Shtemler, Yuri; Mond, Michael
2013-01-01
The saturation of the magnetorotational (MRI) instability in thin Keplerian disks through three wave resonant interactions is introduced and discussed. That mechanism is a natural generalization of the fundamental decay instability discovered five decades ago for infinite, homogeneous and immovable plasmas. The decay instability relies on the energy transfer from the MRI to stable slow Alfv'en-Coriolis (AC) as well as magnetosonic (MS) waves. A second order forced Duffing amplitude equation for the initially unstable MRI as well as two first order equations for the other two waves are derived. The solutions of those equations exhibit bounded bursty nonlinear oscillations for the MRI as well as unbounded growth for the linearly stable slow AC and MS perturbations, thus giving rise to the magneto-rotational decay instability (MRDI).
THE CONNECTION BETWEEN EKMAN AND STEWARTSON LAYERS FOR A ROTATING-DISK
When a disk of finite radius and the surrounding medium rotate coaxially with slightly different angular velocities, a so-called Stewartson layer exists at the edge of the disk. The properties of this layer outside the boundary layer of the disk have been given in a previous publication. In the
Axisymmetric rotational stagnation-point flow impinging on a rotating disk
Weidman, Patrick
2015-12-01
Agrawal's (Q J Mech Appl Math, 10:42-44, 1957) stagnation-point flow problem is extended to flow impingement normal to a uniformly rotating disk. This is the analog of the extension of Homann's (Z Angew Math Mech (ZAMM), 16:153-164, 1936) stagnation flow when impinging on a rotating disk as reported by Hannah (Rep Mem Aerosp Res Coun Lond 2772, 1947). While both oncoming stagnation flows are axisymmetric, in the far field Homann's stagnation flow is irrotational while Agrawal's is rotational. A similarity reduction of the Navier-Stokes equations yields a pair of coupled ordinary differential equations governed by a dimensionless rotation rate σ. Integrations were carried out up to σ = 30 beyond which the equations become stiff and solution independence of integration length cannot be ensured. Results for the radial and azimuthal shear stresses are presented along with the strength of the flow induced into the boundary layer and the thickness of the azimuthal flow boundary layer. Analytic results found at σ = 0 are shown to be in excellent agreement with the numerical calculations. Sample velocity profiles for the radial and azimuthal flows are presented.
Louvet, F; Cabrit, S; Hales, A; Pinte, C; Menard, F; Bacciotti, F; Coffey, D; Mardones, D; Bronfman, L; Gueth, F
2016-01-01
Differences in Doppler shifts across the base of four close classical T-Tauri star jets have been detected with the HST in optical and NUV emission lines, and interpreted as rotation signatures under the assumption of steady state flow. To support this interpretation, it is necessary that the underlying disks rotate in the same sense. Agreement between disk rotation and jet rotation determined from optical lines has been verified in two cases and rejected in one. We propose here to perform this test on the fourth system, Th 28. We present ALMA high angular resolution Band 7 continuum, 12CO(2-1) and 13CO(2-1) observations of the circumstellar disk around the T-Tauri star Th 28. The sub-arcsecond angular resolution (0.46"x0.37") and high-sensitivity reached enable us to detect in CO and continuum clear signatures of a disk in Keplerian rotation around Th28. The 12CO emission allows us to derive estimates of disk position angle and inclination. The large velocity separation of the peaks in 12CO combined with the...
Near-Infrared Structure of Fast and Slow Rotating Disk Galaxies
Schechtman-Rook, Andrew
2014-01-01
We investigate the stellar disk structure of six nearby edge-on spiral galaxies using high-resolution JHKs-band images and 3D radiative transfer models. To explore how mass and environment shape spiral disks, we selected galaxies with rotational velocities between 69 150 km/sec) galaxies, only NGC 4013 has the super-thin+thin+thick nested disk structure seen in NGC 891 and the Milky Way, albeit with decreased oblateness, while NGC 1055, a disturbed massive spiral galaxy, contains disks with hz $\\lesssim$ 200 pc. NGC 4565, another fast-rotator, contains a prominent ring at a radius ~5 kpc but no super-thin disk. Despite these differences, all fast-rotating galaxies in our sample have inner truncations in at least one of their disks. These truncations lead to Freeman Type II profiles when projected face-on. Slow-rotating galaxies are less complex, lacking inner disk truncations and requiring fewer disk components to reproduce their light distributions. Super-thin disk components in undisturbed disks contribute...
Natural frequencies of rotating disk-like structures submerged viewed from the stationary frame
Presas, Alexandre; Valentin, David; Egusquiza, Eduard; Valero, Carme; Seidel, Ulrich; Weber, Wilhelm
2016-11-01
To understand the effect of rotation in the dynamic response of pump-turbine runners, simplified models such as disk-like structures can be used. In previous researches the natural frequencies and mode shapes of rotating disk-like structures submerged and confined have been analysed from the rotating frame. Nevertheless to measure these parameters experimentally from the rotating point of view can be a difficult task, since sensors have to withstand with large forces and dynamic loads. In this paper the dynamic response of rotating disk-like structures is analysed from the stationary frame. For this purpose an experimental test rig has been used. It consists on a disk confined that rotates inside a tank. The disk is excited with a PZT attached on it and the response is measured from both rotating frame (with miniature accelerometers) and from the stationary frame (with a Laser Doppler Vibrometer). In this way the natural frequencies and mode shapes of the rotating structure can be determined from the stationary reference frame. The transmission from the rotating to the stationary frame is compared for the case that the rotating structure rotates in a low density medium (air) and in a high density medium (water).
Rotation of a metal gear disk in an ultrasonic levitator
Rendon, Pablo L.; Boullosa, Ricardo R.; Salazar, Laura
2016-11-01
The phenomenon known as acoustic radiation pressure is well-known to be associated with the time-averaged momentum flux of an acoustic wave, and precisely because it is a time-averaged effect, it is relatively easy to observe experimentally. An ultrasonic levitator makes use of this effect to levitate small particles. Although it is a less-well studied effect, the transfer of angular momentum using acoustic waves in air or liquids has nonetheless been the subject of some recent studies. This transfer depends on the scattering and absorbing properties of the object and is achieved, typically, through the generation of acoustic vortex beams. In the present study, we examine the manner in which the acoustic standing wave located between two disks of an ultrasonic levitator in air may transfer angular momentum to objects with different shapes. In this case, a non-spherical object is subjected to, in addition to the radiation force, a torque which induces rotation. Analytical solutions for the acoustic force and torque are available, but limited to a few simple cases. In general, a finite element model must be used to obtain solutions. Thus, we develop and validate a finite element simulation in order to calculate directly the torque and radiation force.
Louvet, F.; Dougados, C.; Cabrit, S.; Hales, A.; Pinte, C.; Ménard, F.; Bacciotti, F.; Coffey, D.; Mardones, D.; Bronfman, L.; Gueth, F.
2016-12-01
Aims: Recently, differences in Doppler shifts across the base of four close classical T Tauri star jets have been detected with the HST in optical and near-ultraviolet (NUV) emission lines, and these Doppler shifts were interpreted as rotation signatures under the assumption of steady state flow. To support this interpretation, it is necessary that the underlying disks rotate in the same sense. Agreement between disk rotation and jet rotation determined from optical lines has been verified in two cases and rejected in one case. Meanwhile, the near-ultraviolet lines, which may trace faster and more collimated inner spines of the jet than optical lines, either agree or show no clear indication. We propose to perform this test on the fourth system, Th 28. Methods: We present ALMA high angular resolution Band 7 continuum, 12CO(3-2) and 13CO(2-1) observations of the circumstellar disk around the T Tauri star Th 28. Results: The sub-arcsecond angular resolution (0.46''× 0.37'') and high sensitivity reached enable us to detect, in CO and continuum, clear signatures of a disk in Keplerian rotation around Th 28. The 12CO emission is clearly resolved, allowing us to derive estimates of disk position angle and inclination. The large velocity separation of the peaks in 12CO, combined with the resolved extent of the emission, indicate a central stellar mass in the range 1-2 M⊙. The rotation sense of the disk is well detected in both 13CO and 12CO emission lines, and this direction is opposite to that implied by the transverse Doppler shifts measured in the optical lines of the jet. Conclusions: The Th 28 system is now the second system, among the four investigated so far, where counter-rotation between the disk and the optical jet is detected. These findings imply either that optical transverse velocity gradients detected with HST do not trace jet rotation or that modeling the flow with the steady assumption is not valid. In both cases jet rotation studies that rely solely
Spontaneous rotation of an ice disk while melting on a solid plate
Dorbolo, S.; Vandewalle, N.; Darbois Texier, B.
2016-12-01
Ice disks were released at the surface of a thermalised aluminium plate. The fusion of the ice creates a lubrication film between the ice disk and the plate. The situation is similar to the Leidenfrost effect reported for a liquid droplet evaporating at the surface of a plate which temperature is above the boiling temperature of the liquid. An analogy is depicted between the Leidenfrost phenomenon and the rapid fusion of a solid at the contact of a hot plate. Similarly to Leidenfrost droplet, we observe that, while the ice disks were melting, the disks were very mobile: translation and rotation. A hole was drilled in the plate and allowed the canalising of the melted liquid. Under these conditions, we discover that the rotation of the ice disk is systematic and persistent. Moreover, the rotation speed increases with the temperature of the plate and with the load put on the ice disk. A model is proposed to explain the spontaneous rotation of the ice disk. We claim that the rotation is due to the viscous drag of the liquid that flows around the ice disk.
Numerical simulation of turbulent flow between shrouded contra-rotating disks
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Shu-Xian Chen
2016-06-01
Full Text Available The turbulent flow between shrouded contra-rotating disks was numerically studied with a two-layer turbulence model and a modified Launder–Sharma low-Reynolds number k-ε model. The dissipation rate decrease caused by solid body rotation was considered in the second model. The comparisons of the effectiveness between these two turbulence models for capturing the critical radius of flow structure transition and reproducing the flow velocity measurements data were presented. For the flow between shrouded disks rotating at the same speed but in opposite senses, that is, the angular velocity ratio of the two disks equals to −1, the Stewartson-type flow structure is found in the cavity. For the flow with one disk rotating more slowly than the other, Stewartson-type flow coexists with Batchelor-type flow, that is, Batchelor-type flow occurs radially outward of the stagnation point where two opposing boundary layer flows meet, and Stewartson-type flow occurs radially inward. The stagnation points near the slower disk move radially outward as the angular velocity ratio decreases toward −1. Theory of rotating fluids with the presence of centrifugal and Coriolis forces stemming from the disk rotation is employed to manifest the flow structure transition mechanisms as the rotation ratio of the disks is varied. The source of the earlier transition to turbulent flow in counter-rotating disk cavity compared with rotor-stator disk cavity is also explained through the research of instability of the flowing free shear layer formed by the counter secondary circulations. With the aid of the numerical results obtained from the two turbulence models, it is found that a more turbulent flow in the core can destroy the Batchelor-type flow and creates a larger Stewartson-type flow region.
3D Relativistic MHD Simulation of a Tilted Accretion Disk Around a Rapidly Rotating Black Hole
Fragile, P Chris; Blaes, Omer M; Salmonson, Jay D
2016-01-01
We posit that accreting compact objects, including stellar mass black holes and neutron stars as well as supermassive black holes, may undergo extended periods of accretion during which the angular momentum of the disk at large scales is misaligned with that of the compact object. In such a scenario, Lense-Thirring precession caused by the rotating compact object can dramatically affect the disk. In this presentation we describe results from a three-dimensional relativistic magnetohydrodynamic simulation of an MRI turbulent disk accreting onto a tilted rapidly rotating black hole. For this case, the disk does not achieve the commonly described Bardeen-Petterson configuration; rather, it remains nearly planar, undergoing a slow global precession. Accretion from the disk onto the hole occurs predominantly through two opposing plunging streams that start from high latitudes with respect to both the black-hole and disk midplanes. This is a consequence of the non-sphericity of the gravitational spacetime of the bl...
On unsteady two-phase fluid flow due to eccentric rotation of a disk
Directory of Open Access Journals (Sweden)
A. K. Ghosh
2003-01-01
in a double-disk configuration, a result which is the reverse to that of solid-body rotation. Finally, the results are presented graphically to determine the quantitative response of the particle on the flow.
THE STEWARTSON LAYER OF A ROTATING-DISK OF FINITE RADIUS
1992-01-01
It is shown that if a disk of finite radius and the surrounding medium rotate coaxially with slightly different angular velocities, an axial layer in the form of a cylindrical shell exists at the edge of the disk. This shell of thickness O(E1/3) has length O(E-1) in axial direction, where E is the E
An Approximate Solution for Flow between Two Disks Rotating about Distinct Axes at Different Speeds
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H. Volkan Ersoy
2007-01-01
Full Text Available The flow of a linearly viscous fluid between two disks rotating about two distinct vertical axes is studied. An approximate analytical solution is obtained by taking into account the case of rotation with a small angular velocity difference. It is shown how the velocity components depend on the position, the Reynolds number, the eccentricity, the ratio of angular speeds of the disks, and the parameters satisfying the conditions u=0 and ν=0 in midplane.
ROTATIONAL LINE EMISSION FROM WATER IN PROTOPLANETARY DISKS
Meijerink, R.; Poelman, D. R.; Spaans, M.; Tielens, A. G. G. M.; Glassgold, A. E.
2008-01-01
Circumstellar disks provide the material reservoir for the growth of young stars and for planet formation. We combine a high-level radiative transfer program with a thermal-chemical model of a typical T Tauri star disk to investigate the diagnostic potential of the far-infrared lines of water for pr
Optical Tip Clearance Measurements as a Tool for Rotating Disk Characterization
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Iker García
2017-01-01
Full Text Available An experimental investigation on the vibrational behavior of a rotating disk by means of three optical fiber sensors is presented. The disk, which is a scale model of the real disk of an aircraft engine, was assembled in a wind tunnel in order to simulate real operation conditions. The pressure difference between the upstream and downstream sides of the disk causes an airflow that might force the disk to vibrate. To characterize this vibration, a set of parameters was determined by measuring the tip clearance of the disk: the amplitude, the frequency and the number of nodal diameters in the disk. All this information allowed the design of an upgraded prototype of the disk, whose performance was also characterized by the same method. An optical system was employed for the measurements, in combination with a strain gauge mounted on the disk surface, which served to confirm the results obtained. The data of the strain gauge coincided closely with those provided by the optical fiber sensors, thus demonstrating the suitability of this innovative technique to evaluate the vibrational behavior of rotating disks.
Optical Tip Clearance Measurements as a Tool for Rotating Disk Characterization.
García, Iker; Zubia, Joseba; Beloki, Josu; Arrue, Jon; Durana, Gaizka; Aldabaldetreku, Gotzon
2017-01-15
An experimental investigation on the vibrational behavior of a rotating disk by means of three optical fiber sensors is presented. The disk, which is a scale model of the real disk of an aircraft engine, was assembled in a wind tunnel in order to simulate real operation conditions. The pressure difference between the upstream and downstream sides of the disk causes an airflow that might force the disk to vibrate. To characterize this vibration, a set of parameters was determined by measuring the tip clearance of the disk: the amplitude, the frequency and the number of nodal diameters in the disk. All this information allowed the design of an upgraded prototype of the disk, whose performance was also characterized by the same method. An optical system was employed for the measurements, in combination with a strain gauge mounted on the disk surface, which served to confirm the results obtained. The data of the strain gauge coincided closely with those provided by the optical fiber sensors, thus demonstrating the suitability of this innovative technique to evaluate the vibrational behavior of rotating disks.
Optical Tip Clearance Measurements as a Tool for Rotating Disk Characterization
García, Iker; Zubia, Joseba; Beloki, Josu; Arrue, Jon; Durana, Gaizka; Aldabaldetreku, Gotzon
2017-01-01
An experimental investigation on the vibrational behavior of a rotating disk by means of three optical fiber sensors is presented. The disk, which is a scale model of the real disk of an aircraft engine, was assembled in a wind tunnel in order to simulate real operation conditions. The pressure difference between the upstream and downstream sides of the disk causes an airflow that might force the disk to vibrate. To characterize this vibration, a set of parameters was determined by measuring the tip clearance of the disk: the amplitude, the frequency and the number of nodal diameters in the disk. All this information allowed the design of an upgraded prototype of the disk, whose performance was also characterized by the same method. An optical system was employed for the measurements, in combination with a strain gauge mounted on the disk surface, which served to confirm the results obtained. The data of the strain gauge coincided closely with those provided by the optical fiber sensors, thus demonstrating the suitability of this innovative technique to evaluate the vibrational behavior of rotating disks. PMID:28098845
Response to rotating forcing of the von-Karman disk boundary layer
Energy Technology Data Exchange (ETDEWEB)
Vasudevan, Mukund; Siddiqui, M Ehtisham; Pier, Benoit; Scott, Julian; Azouzi, Alexandre; Michelet, Roger; Nicot, Christian, E-mail: benoit.pier@ec-lyon.fr [Laboratoire de mecanique des fluides et d' acoustique (CNRS-Universite de Lyon) Ecole centrale de Lyon, 36 avenue Guy-de-Collongue, 69134 Ecully (France)
2011-12-22
In the present experimental investigation of the three-dimensional boundary layer due to a disk rotating in otherwise still air, the aim is to study the response to a radially localized perturbation applied with a prescribed relative frequency with respect to the disk. The response to localized rotating forcing is measured with a hot-wire probe. The rotation rate of the forcing element is controlled independently of the disk rotation rate, and the dynamics of the spatial response is studied as a function of the ratio between the two rotation rates. The theoretically expected disturbance trajectories are derived from an instability analysis based on the exact local dispersion relations computed from the complete linearized Navier-Stokes equations. Theoretical predictions and experimental measurements are shown to be in good agreement.
Institute of Scientific and Technical Information of China (English)
无
2010-01-01
The instability of forced flow in a rotating cylindrical pool with a differentially rotating disk on the free surface is investigated through a series of unsteady three-dimensional numerical simulations.The results show that the basic flow state of this system is axisymmetric and steady,but has rich structures at the meridian plane.However,when the rotation Reynolds number exceeds a critical value,the flow will undergo a transition to three-dimensional oscillatory flow,characterized by the velocity fluctuation waves traveling in the azimuthal direction.The main characteristics of the flow patterns are presented,including the propagating direction,velocity,amplitude and wave number,which depend on the rotation rates and directions of the disk and the cylindrical pool,and the critical conditions for the onset of oscillatory flow are also determined.For the case of disk-only rotation,the centrifugal instability is responsible for the flow transition,and when the disk isoand counter-rotates with the cylindrical pool,the mechanisms for the transition are elliptic and of circular shear instabilities,respectively.
The variable rotation period of the inner region of Saturn's plasma disk.
Gurnett, D A; Persoon, A M; Kurth, W S; Groene, J B; Averkamp, T F; Dougherty, M K; Southwood, D J
2007-04-20
We show that the plasma and magnetic fields in the inner region of Saturn's plasma disk rotate in synchronism with the time-variable modulation period of Saturn's kilometric radio emission. This relation suggests that the radio modulation has its origins in the inner region of the plasma disk, most likely from a centrifugally driven convective instability and an associated plasma outflow that slowly slips in phase relative to Saturn's internal rotation. The slippage rate is determined by the electrodynamic coupling of the plasma disk to Saturn and by the drag force exerted by its interaction with the Enceladus neutral gas torus.
Hession, E F; Donald, G D
1993-01-01
An acute case of low back pain in a high school athlete is described. Onset of nonradicular back pain was related to "squat-type" weightlifting in preparation for high school football. Magnetic resonance images demonstrated central posterior disk herniations with thecal sac effacement of the lower three disk levels. Clinical and electrophysiological evaluation revealed no neurological deficits. Flexion distraction and rotational manipulation with adjunctive paraspinal muscle stimulation resulted in early improvement and apparent long-term resolution of this patient's symptoms. The effectiveness of flexion distraction and rotational manipulation in reducing subjective symptoms are compared utilizing visual analog pain scales. Literature review of the conservative treatment of lumbar disk herniations is discussed.
Rotational evolution of magnetars in the presence of a fallback disk
Tong, H; Liu, X W; Xu, R X
2016-01-01
Magnetars may have strong surface dipole field. Observationally, two magnetars may have passive fallback disks. In the presence of a fallback disk, the rotational evolution of magnetars may be changed. In the self-similar fallback disk model, it is found that: (1) When the disk mass is significantly smaller than $10^{-6} \\,\\rm M_{\\odot}$, the magnetar is unaffected by the fallback disk and it will be a normal magnetar. (2) When the disk mass is large, but the magnetar's surface dipole field is $10^{14} \\,\\rm G$, the magnetar will also be a normal magnetar. A magnetar plus a passive fallback disk system is expected. This may correspond to the observations of magnetars 4U 0142$+$61, and 1E 2259$+$586. (3) When the disk mass is large, and the magnetar's surface dipole field is as high as $4\\times 10^{15} \\,\\rm G$, the magnetar will evolve from the ejector phase to the propeller phase, and then enter into rotational equilibrium. The magnetar will be slowed down quickly in the propeller phase. The final rotational...
Flow between caoxial rotating disks: with and without externally applied magnetic field
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R. K. Bhatnagar
1981-01-01
when such a fluid is confined between two infinite rotating coaxial disks. The governing system of a pair of non-linear ordinary differential equation is solved by treating Reynolds number to small. The three cases discussed are: (I one disks is held at rest while other rotates with a constant angular velocity, (ii one disk rorates faster than the other but in the same sense and (iii the disks rotate in opposite senses and with different angular velocities. The radial, tranverse and axial components of the velocity field are plotted for the above three cases for different values of the Reynolds number. The results obtained for a viscoelastic fluid are compared with those for a Newtonian fluid. The velocity field for case (i is also computed when a magnetic field is applied in a direction perpendicular to the discs and the results are compared with the case when magnetic field is absent. Some interesting features are observed for a viscoelastic fluid.
Beld, van den W.T.E.; Cadena, N.L.; Bomer, J.G.; Weerd, de E.L.; Abelmann, L.; Berg, van den A.; Eijkel, J.C.T.
2015-01-01
We demonstrate a novel, flexible and programmable method to pump liquid through microchannels in lab-on-a-chip systems without the use of an external pump. The pumping principle is based on the rotation of ferromagnetic Janus microspheres around permalloy disks, driven by an external rotating magnet
Krticka, Jiri; Krtickova, Iva
2014-01-01
Evolutionary models of fast-rotating stars show that the stellar rotational velocity may approach the critical speed. Critically rotating stars cannot spin up more, therefore they lose their excess angular momentum through an equatorial outflowing disk. The radial extension of such disks is unknown, partly because we lack information about the radial variations of the viscosity. We study the magnetorotational instability, which is considered to be the origin of anomalous viscosity in outflowing disks. We used analytic calculations to study the stability of outflowing disks submerged in the magnetic field. The magnetorotational instability develops close to the star if the plasma parameter is large enough. At large radii the instability disappears in the region where the disk orbital velocity is roughly equal to the sound speed. The magnetorotational instability is a plausible source of anomalous viscosity in outflowing disks. This is also true in the region where the disk radial velocity approaches the sound ...
A SEARCH FOR CONSISTENT JET AND DISK ROTATION SIGNATURES IN RY TAU
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Coffey, Deirdre [School of Physics, University College Dublin, Belfield, Dublin 4 (Ireland); Dougados, Catherine [UMI LFCA Universidad de Chile (Chile); Cabrit, Sylvie [I.P.A.G. (UMR 5274), BP 53, F-38041 Grenoble Cédex 9 (France); Pety, Jerome [LERMA, Observatoire de Paris, UMR 8112 du CNRS, ENS, UPMC, UCP, 61 Av. de l’Observatoire, F-75014 Paris (France); Bacciotti, Francesca [I.N.A.F., Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, I-50125 Florence (Italy)
2015-05-01
We present a radial velocity study of the RY Tau jet–disk system, designed to determine whether a transfer of angular momentum from disk to jet can be observed. Many recent studies report on the rotation of T Tauri disks and on what may be a signature of T Tauri jet rotation. However, due to observational difficulties, few studies report on both disk and jet within the same system to establish if the senses of rotation match and hence can be interpreted as a transfer of angular momentum. We report a clear signature of Keplerian rotation in the RY Tau disk, based on Plateau de Bure observations. We also report on the transverse radial velocity profile of the RY Tau jet close to the star. We identify two distinct profile shapes: a v-shape, which appears near jet shock positions, and a flat profile, which appears between shocks. We do not detect a rotation signature above 3σ uncertainty in any of our transverse cuts of the jet. Nevertheless, if the jet is currently in steady-state, the errors themselves provide a valuable upper limit on the jet toroidal velocity of 10 km s{sup −1}, implying a launch radius of ≤0.45 AU. However, possible contamination of jet kinematics, via shocks or precession, prevents any firm constraint on the jet launch point, since most of its angular momentum could be stored in magnetic form rather than in rotation of matter.
Transverse nonlinear vibrations of a circular spinning disk with a varying rotating speed
Institute of Scientific and Technical Information of China (English)
无
2010-01-01
We analyze the transverse nonlinear vibrations of a rotating flexible disk subjected to a rotating point force with a periodically varying rotating speed. Based on Hamilton’s principle, the nonlinear governing equations of motion (coupled equations among the radial, tangential and transverse displacements) are derived for the rotating flexible disk. When the in-plane inertia is ignored and a stress function is introduced, the three nonlinearly coupled partial differential equations are reduced to two nonlinearly coupled partial differential equations. According to Galerkin’s approach, a four-degree-of-freedom nonlinear system governing the weakly split resonant modes is derived. The resonant case considered here is 1:1:2:2 internal resonance and a critical speed resonance. The primary parametric resonance for the first-order sin and cos modes and the fundamental parametric resonance for the second-order sin and cos modes are also considered. The method of multiple scales is used to obtain a set of eight-dimensional nonlinear averaged equations. Based on the averaged equations, using numerical simulations, the influence of different parameters on the nonlinear vibrations of the spinning disk is detected. It is concluded that there exist complicated nonlinear behaviors including the periodic, period-n and multi-pulse type chaotic motions for the spinning disk with a varying rotating speed. It is also found that among all parameters, the damping and excitation have great influence on the nonlinear responses of the spinning disk with a varying rotating speed.
Model of Head-Positioning Error Due to Rotational Vibration of Hard Disk Drives
Matsuda, Yasuhiro; Yamaguchi, Takashi; Saegusa, Shozo; Shimizu, Toshihiko; Hamaguchi, Tetsuya
An analytical model of head-positioning error due to rotational vibration of a hard disk drive is proposed. The model takes into account the rotational vibration of the base plate caused by the reaction force of the head-positioning actuator, the relationship between the rotational vibration and head-track offset, and the sensitivity function of track-following feedback control. Error calculated by the model agrees well with measured error. It is thus concluded that this model can predict the data transfer performance of a disk drive in read mode.
Experimental analysis and flow visualization of a thin liquid film on a stationary and rotating disk
Thomas, S.; Faghri, A.; Hankey, W.
1991-01-01
The mean thickness of a thin liquid film of deionized water with a free surface on a stationary and rotating horizontal disk has been measured with a nonobtrusive capacitance technique. The measurements were taken when the rotational speed ranged from 0-300 rpm and the flow rate varied from 7.0-15.0 lpm. A flow visualization study of the thin film was also performed to determine the characteristics of the waves on the free surface. When the disk was stationary, a circular hydraulic jump was present on the disk. Upstream from the jump, the film thickness was determined by the inertial and frictional forces on the fluid, and the radial spreading of the film. The surface tension at the edge of the disk affected the film thickness downstream from the jump. For the rotating disk, the film thickness was dependent upon the inertial and frictional forces near the center of the disk and the centrifugal forces near the edge of the disk.
The competition of convective and absolute instabilities in rotating-disk flow transition
Imayama, Shintaro; Alfredsson, P. Henrik; Lingwood, R. J.
2014-11-01
The main objective of this experimental study is to investigate laminar-turbulent transition mechanisms in the rotating-disk boundary-layer flow. Lingwood (1995) found that the flow becomes locally absolutely unstable above a critical Reynolds number and suggested that absolutely unstable travelling waves triggered nonlinearity leading to transition. However, the growth of convectively unstable stationary vortices is also a possible alternative route if the surface roughness of the disk is sufficiently large. The convectively unstable stationary vortices are attributed to an inviscid crossflow mechanism. Flow-visualization studies and hot-wire measurements of the rotating-disk boundary layer typically capture 28-32 stationary vortices in the transition regime (e.g. Imayama et al. 2014). The hot-wire measurements presented here were performed on a smooth glass disk with a diameter of 474 mm. To excite stationary vortices disk-shaped roughness elements with a diameter of 2 mm and a height of 5 micron were put on the disk at a radial position of 110 mm. In the presentation, the details of the convectively unstable stationary vortices in the rotating-disk boundary layer are shown and compared with travelling waves and similarities/differences in the turbulent transition discussed. This work is supported by the Swedish Research Council (VR) and the Linné FLOW Centre.
Experiments on Heat Transfer in a Thin Liquid Film Flowing Over a Rotating Disk
Sankaran, Subramanian (Technical Monitor); Ozar, B.; Cetegen, B. M.; Faghri, A.
2004-01-01
An experimental study of heat transfer into a thin liquid film on a rotating heated disk is described. Deionized water was introduced at the center of a heated. horizontal disk with a constant film thickness and uniform radial velocity. Radial distribution of the disk surface temperatures was measured using a thermocouple/slip ring arrangement. Experiments were performed for a range of liquid flow rates between 3.01pm and 15.01pm. The angular speed of the disk was varied from 0 rpm to 500 rpm. The local heat transfer coefficient was determined based on the heat flux supplied to the disk and the temperature difference between the measured disk surface temperature and the liquid entrance temperature onto the disk. The local heat transfer coefficient was seen to increase with increasing flow rate as well as increasing angular velocity of the disk. Effect of rotation on heat transfer was largest for the lower liquid flow rates with the effect gradually decreasing with increasing liquid flow rates. Semi-empirical correlations are presented in this study for the local and average Nusselt numbers.
A Search for Consistent Jet and Disk Rotation Signatures in RY Tau
Coffey, Deirdre; Cabrit, Sylvie; Pety, Jerome; Bacciotti, Francesca
2015-01-01
We present a radial velocity study of the RY Tau jet-disk system, designed to determine whether a transfer of angular momentum from disk to jet can be observed. Many recent studies report on the rotation of T Tauri disks, and on what may be a signature of T Tauri jet rotation. However, due to observational difficulties, few studies report on both disk and jet within the same system to establish if the senses of rotation match and hence can be interpreted as a transfer of angular momentum. We report a clear signature of Keplerian rotation in the RY Tau disk, based on Plateau de Bure observations. We also report on the transverse radial velocity profile of the RY Tau jet close to the star. We identify two distinct profile shapes: a v-shape which appears near jet shock positions, and a flat profile which appears between shocks. We do not detect a rotation signature above 3 sigma uncertainty in any of our transverse cuts of the jet. Nevertheless, if the jet is currently in steady-state, the errors themselves prov...
The formation of massive primordial stars in rapidly rotating disks
Latif, M A
2014-01-01
Massive primordial halos exposed to moderate UV backgrounds are the potential birthplaces of very massive stars or even supermassive black holes. In such a halo, an initially isothermal collapse will occur, leading to high accretion rates of $\\sim0.1$~M$_\\odot$~yr$^{-1}$. During the collapse, the gas in the interior will turn into a molecular state, and form an accretion disk due to the conservation of angular momentum. We consider here the structure of such an accretion disk and the role of viscous heating in the presence of high accretion rates for a central star of $10$, $100$ and $10^4$~M$_\\odot$. Our results show that the temperature in the disk increases considerably due to viscous heating, leading to a transition from the molecular to the atomic cooling phase. We found that the atomic cooling regime may extend out to several $100$~AU for a $10^4$~M$_\\odot$ central star and provides substantial support to stabilize the disk. It therefore favors the formation of a massive central object. The comparison o...
The formation of supermassive black holes in rapidly rotating disks
Latif, M. A.; Schleicher, D. R. G.
2015-06-01
Massive primordial halos exposed to moderate UV backgrounds are the potential birthplaces of supermassive black holes. In these halos, an initially isothermal collapse will occur, leading to high accretion rates of ~0.1 M⊙ yr-1. During the collapse, the gas in the interior will turn into a molecular state, and will form accretion disk in order to conserve angular momentum. We consider here the structure of such an accretion disk and the role of viscous heating in the presence of high accretion rates for a central star of 10, 100, and 104 M⊙. Our results show that the temperature in the disk increases considerably due to viscous heating, leading to a transition from the molecular to the atomic cooling phase. We found that the atomic cooling regime may extend out to several 100 AU for a 104 M⊙ central star and that it provides substantial support to stabilize the disk. It therefore favors the formation of a massive central object. The comparison of clump migration and contraction time scales shows that stellar feedback from these clumps may occur during the later stages of the evolution. Overall, viscous heating provides an important pathway to obtain an atomic gas phase within the center of the halo, and helps in the formation of very massive objects. The massive object may collapse to form a massive black hole of about ≥104 M⊙.
The flow of a thin liquid film on a stationary and rotating disk. II - Theoretical prediction
Rahman, M. M.; Faghri, A.; Hankey, W. L.
1990-01-01
The existing theoretical models are improved and a systematic procedure to compute the free surface flow of a thin liquid film is suggested. The solutions for axisymmetric radial flow on a stationary horizontal disk and for the disk rotating around its axis are presented. The theoretical predictions are compared with the experimental data presented in Part I of this report. The analysis shows results for both supercritical and subcritical flows and the flow structure in the vicinity of a hydraulic jump which isolates these two flow types. The detailed flow structure in a hydraulic jump was computed and shown to contain regions of separation including a 'surface roller'. The effects of surface tension are found to be important near the outer edge of the disk where the fluid experiences a free fall. At other locations, the surface tension is negligible. For a rotating disk, the frictional resistance in the angular direction is found to be as important as that in the radial direction.
An approximate solution to the stress and deformation states of functionally graded rotating disks
Sondhi, Lakshman; Sanyal, Shubhashis; Saha, Kashi Nath; Bhowmick, Shubhankar
2016-07-01
The present work employs variational principle to investigate the stress and deformation states and estimate the limit angular speed of functionally graded high-speed rotating annular disks of constant thickness. Assuming a series approximation following Galerkin's principle, the solution of the governing equation is obtained. In the present study, elasticity modulus and density of the disk material are taken as power function of radius with the gradient parameter ranging between 0.0 and 1.0. Results obtained from numerical solutions are validated with benchmark results and are found to be in good agreement. The results are reported in dimensional form and presented graphically. The results provide a substantial insight in understanding the behavior of FGM rotating disks with constant thickness and different gradient parameter. Furthermore, the stress and deformation state of the disk at constant angular speed and limit angular speed is investigated to explain the existence of optimum gradient parameters.
Flow of a Second Order Fluid Between Two Infinite Porous Rotating Disks
Directory of Open Access Journals (Sweden)
H. G. Sharma
1983-07-01
Full Text Available The flow of an incompressible second-order fluid between two infinite porous rotating disks has been studied with the assumption that the rate of injuction of the fluid at one disc is equal to the rate of suction at the other. The velocity components have been expressed in terms of three dimensionless functions, which in turn are obtained in ascending powers of the Reynold number (taken to be small, defined in terms of the angular velocities of the disks.
van den Beld, Wesley T E; Cadena, Natalia L; Bomer, Johan; de Weerd, Eddy L; Abelmann, Leon; van den Berg, Albert; Eijkel, Jan C T
2015-07-07
We demonstrate a novel, flexible and programmable method to pump liquid through microchannels in lab-on-a-chip systems without the use of an external pump. The pumping principle is based on the rotation of ferromagnetic Janus microspheres around permalloy disks, driven by an external rotating magnetic field. By placing the disks close to the edge of the microchannel, a pumping rate of at least 0.3 nL min(-1) was measured using tracking microspheres. Geometric programming of the pumping direction is possible by positioning the magnetic disk close to the side wall. A second degree of freedom in the pumping direction is offered by the rotational direction of the external magnetic field. This method is especially suited for flow-controlled recirculation of chemical and biological species in microchannels - for example, medium recirculation in culture chambers - opening the way towards novel, portable, on-chip applications without the need for external fluidic or electrical connections.
Structural dynamics studies of rotating bladed-disk assemblies coupled with flexible shaft motions
Loewy, R. G.; Khader, N.
1983-01-01
In order to analyze the dynamic behavior of the first stage compressor/fan of the 'E3' turbofan engine, a classical structural dynamics approach is employed to couple the motions of a flexible bladed disk to a rotating flexible shaft. The analysis accounts for flexible disk displacements which are transverse to the plane of rotation, and radial as well as tangential, and also accounts for rigid disk translations along, and rotations about, axes normal to the undeformed shaft axes. In the case of a wide range of E3 engine shaft flexibilities and speeds, some of the one-diametral node frequencies are shown to be affected by shaft degrees of freedom whose stiffness values are in general range of design practice. Coriolis forces are also found to significantly affect natural frequencies where strong coupling between certain modes is present.
Jet magnetically accelerated from disk-corona around a rotating black hole
Gong, Xiaolong
2012-01-01
A jet acceleration model for extracting energy from disk-corona surrounding a rotating black hole is proposed. In the disk-corona scenario, we obtain the ratio of the power dissipated in the corona to the total for such disk-corona system by solving the disk dynamics equations. The analytical expression of the jet power is derived based on the electronic circuit theory of the magnetosphere. It is shown that jet power increases with the increasing black hole (BH) spin, and concentrates in the inner region of the disk-corona. In addition, we use a sample consisting of 37 radio loud quasars to explore their jet production mechanism, and show that our jet formation mechanism can simulate almost all sources with high power jet, that fail to be explained by the Blandford-Znajek (BZ) process.
Using High Speed Rotating Gas to Study Angular Momentum in Accretion Disks
Berrios, William; Greess, Samuel; Merino, Enrique; Ji, Hantao
2013-10-01
Accretion disks are a sheet of gas and dust which surrounds black holes and quasars. The angular momentum in accretion disks is one of the biggest mysteries in astrophysics. A machine was recently built to create accretion disks in a closed chamber. In order to study this, there are several important instruments that are used: a fog machine to see the accretion disks form within the chamber, a high speed camera to observe and record the formation of the accretion disks, and Particle Image Velocimetry (PIV) to analyze velocity profile of the rotating gas and better understand this phenomenon. By collecting relevant data and subsequent computational analysis, results from a previous experiment are reproduced, expanded and the new properties observed with this experiment are characterized. A discussion of any modifications done to the machine, technical challenges and preliminary results will be presented.
Flow between two stretchable rotating disks with Cattaneo-Christov heat flux model
Hayat, Tasawar; Qayyum, Sumaira; Imtiaz, Maria; Alsaedi, Ahmed
An analysis is performed to investigate flow between two stretchable rotating disks. Thermal equation is constructed by Cattaneo-Christov heat flux theory. Porous medium is also taken into account. The nonlinear partial differential equations are first converted to ordinary differential equations and then computed for the convergent series solutions. Discussion about impact of dimensionless parameters on velocities, temperature and skin friction coefficient is given. It is observed that the radial velocity at upper disk enhances for larger values of ratio of corresponding stretching rate to angular velocity. Velocity in y-direction decays with an increase in rotational parameter. Magnitude of temperature profile decays for larger Prandtl number and thermal relaxation parameter.
Directory of Open Access Journals (Sweden)
Liu Bo
2014-01-01
Full Text Available A simplified physical model is built up to study the swirl flow effect induced by a rotating disk on the jet impingement behaviors, which is adopted to simulate the grinding process. To solve the definition problem of the interface between a rotating disk and a stationary plate in the computational simulation, a tiny gap is set between the rotating disk and the stationary plate. The results show that the rotating disk suspended above the surface adds more complexity to the flow field of jet impingement on a stationary plate. The swirling flow around the rotating disk obstructs the impinging jet flow to penetrate into the interfacial contact zone and forces the wall jet across the rotating disk to flow along transverse directions. For the given jet impinging velocity and nozzle orientation, as the disk rotational speed increases, the effect of the rotating disk on the impinging jet flow behaves more significantly. The impinging jet with small inject velocity is difficult to penetrate through the interfacial contact zone to follow by the disk swirl flows. For smaller jet impinging distance or larger oblique angle, the flow recirculation away from the interfacial contact zone becomes stronger.
Energy Technology Data Exchange (ETDEWEB)
Santos-Lima, R.; De Gouveia Dal Pino, E. M. [Instituto de Astronomia, Geofisica e Ciencias Atmosfericas, Universidade de Sao Paulo, R. do Matao, 1226, Sao Paulo, SP 05508-090 (Brazil); Lazarian, A. [Department of Astronomy, University of Wisconsin, Madison, WI 53706 (United States)
2012-03-01
The formation of protostellar disks out of molecular cloud cores is still not fully understood. Under ideal MHD conditions, the removal of angular momentum from the disk progenitor by the typically embedded magnetic field may prevent the formation of a rotationally supported disk during the main protostellar accretion phase of low-mass stars. This has been known as the magnetic braking problem and the most investigated mechanism to alleviate this problem and help remove the excess of magnetic flux during the star formation process, the so-called ambipolar diffusion (AD), has been shown to be not sufficient to weaken the magnetic braking at least at this stage of the disk formation. In this work, motivated by recent progress in the understanding of magnetic reconnection in turbulent environments, we appeal to the diffusion of magnetic field mediated by magnetic reconnection as an alternative mechanism for removing magnetic flux. We investigate numerically this mechanism during the later phases of the protostellar disk formation and show its high efficiency. By means of fully three-dimensional MHD simulations, we show that the diffusivity arising from turbulent magnetic reconnection is able to transport magnetic flux to the outskirts of the disk progenitor at timescales compatible with the collapse, allowing the formation of a rotationally supported disk around the protostar of dimensions {approx}100 AU, with a nearly Keplerian profile in the early accretion phase. Since MHD turbulence is expected to be present in protostellar disks, this is a natural mechanism for removing magnetic flux excess and allowing the formation of these disks. This mechanism dismisses the necessity of postulating a hypothetical increase of the ohmic resistivity as discussed in the literature. Together with our earlier work which showed that magnetic flux removal from molecular cloud cores is very efficient, this work calls for reconsidering the relative role of AD in the processes of star
Flow in a Narrow Gap Along an Enclosed Rotating disk with Through-Flow
黒川, 淳一; 佐久問, 真人
1988-01-01
Flow in a narrow gap along an enclosed rotating disk superimposed with through-flow is studied theoretically and experimentally. When the axial gap is narrow, or a large outward through-flow is imposed, the boundary layers on the rotating and the stationary walls interfere with each other. The present study proposes an analytical model for such interference of gap flow and gives a theoretical analysis which is easily applicable to various boundary conditions. For non-interference of gap flow,...
Powerful, Rotating Disk Winds from Stellar-mass Black Holes
Miller, J M; Kaastra, J; Kallman, T; King, A L; Proga, D; Raymond, J; Reynolds, C S
2015-01-01
We present an analysis of ionized X-ray disk winds observed in the Fe K band of four stellar-mass black holes observed with Chandra, including 4U 1630-47, GRO J1655-40, H 1743-322, and GRS 1915+105. High-resolution photoionization grids were generated in order to model the data. Third-order gratings spectra were used to resolve complex absorption profiles into atomic effects and multiple velocity components. The Fe XXV line is found to be shaped by contributions from the intercombination line (in absorption), and the Fe XXVI line is detected as a spin-orbit doublet. The data require 2-3 absorption zones, depending on the source. The fastest components have velocities approaching or exceeding 0.01c, increasing mass outflow rates and wind kinetic power by orders of magnitude over prior single-zone models. The first-order spectra require re-emission from the wind, broadened by a degree that is loosely consistent with Keplerian orbital velocities at the photoionization radius. This suggests that disk winds are ro...
Warm gas in the rotating disk of the Red Rectangle: accurate models of molecular line emission
Bujarrabal, V
2013-01-01
We aim to study the excitation conditions of the molecular gas in the rotating disk of the Red Rectangle, the only post-Asymptotic-Giant-Branch object in which the existence of an equatorial rotating disk has been demonstrated. For this purpose, we developed a complex numerical code that accurately treats radiative transfer in 2-D, adapted to the study of molecular lines from rotating disks. We present far-infrared Herschel/HIFI observations of the 12CO and 13CO J=6-5, J=10-9, and J=16-15 transitions in the Red Rectangle. We also present our code in detail and discuss the accuracy of its predictions, from comparison with well-tested codes. Theoretical line profiles are compared with the empirical data to deduce the physical conditions in the disk by means of model fitting. We conclude that our code is very efficient and produces reliable results. The comparison of the theoretical predictions with our observations reveals that the temperature of the Red Rectangle disk is typically ~ 100-150 K, about twice as h...
Ligament and Droplet Generation by Oil Film on a Rotating Disk
Directory of Open Access Journals (Sweden)
Hengchao Sun
2015-01-01
Full Text Available The lubrication and heat transfer designs of bearing chamber depend on an understanding of oil/air two-phase flow. As initial and boundary conditions, the characteristics of ligament and droplet generation by oil film on rotating parts have significant influence on the feasibility of oil/air two-phase flow analysis. An integrated model to predict the oil film flow, ligament number, and droplet Sauter mean diameter (SMD of a rotating disk, which is an abstraction of the droplet generation sources in a bearing chamber, is developed based on the oil film force balance analysis and wave theory. The oil film thickness and velocity, ligaments number, and droplet SMD are calculated as functions of the rotating disk radius, rotational speed and oil volume flow rate and oil properties. The theoretical results show that the oil film thickness and SMD are decreased with an increasing rotational speed, while the radial, transverse velocities, and ligament number are increased. The oil film thickness, radial velocity, and SMD are increased with an increasing oil flow rate, but the transverse velocity and ligament number are decreased. A test facility is built for the investigation into the ligament number of a rotating disk, and the measurement of ligament number is carried out by means of a high speed photography.
Thomas, S.; Faghri, A.; Hankey, W.
1990-01-01
The mean thickness of a thin liquid film of deionized water with a free surface on a stationary and rotating horizontal disk has been measured with a nonobtrusive capacitance technique. The measurements were taken when the rotational speed was 0-300 RPM and the flow rate was 7.0-15.0 LPM. A flow visualization study of the thin film was also performed to determine the characteristics of the waves on the free surface. When the disk was stationary, a circular hydraulic jump was present on the disk. Surface waves were found in the supercritical and subcritical regions at all flow rates studied. When the rotational speed of the disk is low, a standing wave at the edge of the disk was present. As the rotational speed increased, the surface waves changed from the wavy-laminar region to a region in which the waves ran nearly radially across the disk on top of a thin substrate of fluid.
Directory of Open Access Journals (Sweden)
Alexandre Presas
2014-07-01
Full Text Available In this paper, PZT actuators are used to study the dynamic behavior of a rotating disk structure due to rotor-stator interaction excitation. The disk is studied with two different surrounding fluids—air and water. The study has been performed analytically and validated experimentally. For the theoretical analysis, the natural frequencies and the associated mode shapes of the rotating disk in air and water are obtained with the Kirchhoff-Love thin plate theory coupled with the interaction with the surrounding fluid. A model for the Rotor Stator Interaction that occurs in many rotating disk-like parts of turbomachinery such as compressors, hydraulic runners or alternators is presented. The dynamic behavior of the rotating disk due to this excitation is deduced. For the experimental analysis a test rig has been developed. It consists of a stainless steel disk (r = 198 mm and h = 8 mm connected to a variable speed motor. Excitation and response are measured from the rotating system. For the rotating excitation four piezoelectric patches have been used. Calibrating the piezoelectric patches in amplitude and phase, different rotating excitation patterns are applied on the rotating disk in air and in water. Results show the feasibility of using PZT to control the response of the disk due to a rotor-stator interaction.
Presas, Alexandre; Egusquiza, Eduard; Valero, Carme; Valentin, David; Seidel, Ulrich
2014-07-07
In this paper, PZT actuators are used to study the dynamic behavior of a rotating disk structure due to rotor-stator interaction excitation. The disk is studied with two different surrounding fluids-air and water. The study has been performed analytically and validated experimentally. For the theoretical analysis, the natural frequencies and the associated mode shapes of the rotating disk in air and water are obtained with the Kirchhoff-Love thin plate theory coupled with the interaction with the surrounding fluid. A model for the Rotor Stator Interaction that occurs in many rotating disk-like parts of turbomachinery such as compressors, hydraulic runners or alternators is presented. The dynamic behavior of the rotating disk due to this excitation is deduced. For the experimental analysis a test rig has been developed. It consists of a stainless steel disk (r = 198 mm and h = 8 mm) connected to a variable speed motor. Excitation and response are measured from the rotating system. For the rotating excitation four piezoelectric patches have been used. Calibrating the piezoelectric patches in amplitude and phase, different rotating excitation patterns are applied on the rotating disk in air and in water. Results show the feasibility of using PZT to control the response of the disk due to a rotor-stator interaction.
Modeling the Newtonian dynamics for rotation curve analysis of thin-disk galaxies
Institute of Scientific and Technical Information of China (English)
James Q. Feng; C. F. Gallo
2011-01-01
We present an efficient,robust computational method for modeling the Newtonian dynamics for rotation curve analysis of thin-disk galaxies.With appropriate mathematical treatments,the apparent numerical difficulties associated with singularities in computing elliptic integrals are completely removed.Using a boundary element discretization procedure,the governing equations are transformed into a linear algebra matrix equation that can be solved by straightforward Gauss elimination in one step without further iterations.The numerical code implemented according to our algorithm can accurately determine the surface mass density distribution in a disk galaxy from a measured rotation curve (or vice versa).For a disk galaxy with a typical fiat rotation curve,our modeling results show that the surface mass density monotonically decreases from the galactic center toward the periphery,according to Newtonian dynamics.In a large portion of the galaxy,the surface mass density follows an approximately exponential law of decay with respect to the galactic radial coordinate.Yet the radial scale length for the surface mass density seems to be generally larger than that of the measured brightness distribution,suggesting an increasing mass-to- light ratio with the radial distance in a disk galaxy.In a nondimensionalized form,our mathematical system contains a dimensionless parameter which we call the “galactic rotation number” that represents the gross ratio of centrifugal force and gravitational force.The value of this galactic rotation number is determined as part of the numerical solution.Through a systematic computational analysis,we have illustrated that the galactic rotation number remains within ±10％ of 1.70 for a wide variety of rotation curves.This implies that the total mass in a disk galaxy is proportional to V(0)2 Rg,with V(0) denoting the characteristic rotation velocity (such as the “fiat” value in a typical rotation curve) and Rg the radius of the galactic
Analysis of laminar flow between stationary and rotating disks with inflow
Rohatgi, U.; Reshotko, E.
1974-01-01
The laminar flow between a rotating and a stationary disk with inflow was analyzed. Solutions to the dimensionless governing equations are sought by expanding each of the velocity components in powers of inverse radius. The equations to leading order are those for the configuration with no inflow. The subsequent orders yield sets of linear ordinary differential equations. Solutions are obtained for the first two of these subsequent orders. The solutions indicate that inflow tends to increase the magnitude of the azimuthal velocity in the flow between the two disks and to decrease the torque on the rotating disk. For Prandtl number one, an energy integral is obtained which relates the temperature distribution to the velocity distribution for all Reynolds numbers and therefore eliminates the needs for separate solution of the energy equation.
Convective heat transfer from rotating disks subjected to streams of air
aus der Wiesche, Stefan
2016-01-01
This Brief describes systematically results of research studies on a series of convective heat transfer phenomena from rotating disks in air crossflow. Phenomena described in this volume were investigated experimentally using an electrically heated disk placed in the test section of a wind tunnel. The authors describe findings in which transitions between different heat transfer regimes can occur in dependency on the involved Reynolds numbers and the angle of incidence, and that these transitions could be related to phenomenological Landau and Landau-de Gennes models. The concise volume closes a substantial gap in the scientific literature with respect to flow and heat transfer in rotating disk systems and provides a comprehensive presentation of new and recent results not previously published in book form.
Review of fluid flow and convective heat transfer within rotating disk cavities with impinging jet
Harmand, Souad; Poncet, Sébastien; Shevchuk, Igor V; 10.1016/j.ijthermalsci.2012.11.009
2013-01-01
Fluid flow and convective heat transfer in rotor-stator configurations, which are of great importance in different engineering applications, are treated in details in this review. The review focuses on convective heat transfer in predominantly outward air flow in the rotor-stator geometries with and without impinging jets and incorporates two main parts, namely, experimental/theoretical methodologies and geometries/results. Experimental methodologies include naphthalene sublimation techniques, steady state (thin layer) and transient (thermochromic liquid crystals) thermal measurements, thermocouples and infra-red cameras, hot-wire anemometry, laser Doppler and particle image velocimetry, laser plane and smoke generator. Theoretical approaches incorporate modern CFD computational tools (DNS, LES, RANS etc). Geometries and results part being mentioned starting from simple to complex elucidates cases of a free rotating disk, a single disk in the crossflow, single jets impinging onto stationary and rotating disk,...
Rotation-disk connection for very low mass and substellar objects in the Orion Nebula Cluster
Rodriguez-Ledesma, Maria V; Eislöffel, Jochen
2010-01-01
Angular momentum loss requires magnetic interaction between the forming star and both the circumstellar disk and the magnetically driven outflows. In order to test these predictions many authors have investigated a rotation-disk connection in pre-main sequence objects with masses larger than about 0.4Msun. For brown dwarfs this connection was not investigated as yet because there are very few samples available. We aim to extend this investigation well down into the substellar regime for our large sample of BDs in the Orion Nebula Cluster, for which we have recently measured rotational periods. In order to investigate a rotation-disk correlation, we derived near-infrared (NIR) excesses for a sample of 732 periodic variables in the Orion Nebula Cluster with masses ranging between 1.5-0.02 Msun and whose IJHK colors are available. Circumstellar NIR excesses were derived from the Delta[I-K] index. We performed our analysis in three mass bins.We found a rotation-disk correlation in the high and intermediate mass r...
DEFF Research Database (Denmark)
Pedersen, Christoffer Mølleskov; Escribano, Maria Escudero; Velazquez-Palenzuela, Amado Andres
2015-01-01
We present up-to-date benchmarking methods for testing electrocatalysts for polymer exchange membrane fuel cells (PEMFC), using the rotating disk electrode (RDE) method. We focus on the oxygen reduction reaction (ORR) and the hydrogen oxidation reaction (HOR) in the presence of CO. We have chosen...
Jet magnetically accelerated from disk-corona around a rotating black hole
Institute of Scientific and Technical Information of China (English)
GONG XiaoLong; LI LiXin
2012-01-01
A jet acceleration model for extracting energy from disk-corona surrounding a rotating black hole (BH) is proposed.In the diskcorona scenario,we obtain the ratio of the power dissipated in the corona to the total for such disk-corona system by solving the disk dynamics equations.The analytical expression of the jet power is derived based on the electronic circuit theory of the magnetosphere.It is shown that jet power increases with the increasing BH spin,and concentrates in the inner region of the disk-corona.In addition,we use a sample consisting of 37 radio loud quasars to explore their jet production mechanism,and show that our jet formation mechanism can simulate almost all sources with high power jet,which fails to be explained by the Blandford-Znajek (BZ) process.
Forced response of rotating bladed disks: Blade Tip-Timing measurements
Battiato, G.; Firrone, C. M.; Berruti, T. M.
2017-02-01
The Blade Tip-Timing is a well-known non-contact measurement technique currently employed for the identification of the dynamic behaviours of rotating bladed disks. Although the measurement system has become a typical industry equipment for bladed disks vibration surveys, the type of sensors, the positioning of the sensors around the bladed disk and the used algorithm for data post-processing are still not standard techniques, and their reliability has to be proved for different operation conditions by the comparison with other well-established measurement techniques used as reference like strain gauges. This paper aims at evaluating the accuracy of a latest generation Tip-Timing system on two dummy blisks characterized by different geometrical, structural and dynamical properties. Both disks are tested into a spin-rig where a fixed number of permanent magnets excite synchronous vibrations with respect to the rotor speed. A new positioning for the Blade Tip-Timing optical sensors is tested in the case of a shrouded bladed disk. Due to the presence of shrouds, the sensors cannot be positioned at the outer radius of the disk pointing radially toward the rotation axis as in the most common applications, since the displacements at the tips are very small and cannot be detected. For this reason a particular placement of optical laser sensors is studied in order to point at the leading and trailing edges' locations where the blades experience the largest vibration amplitudes with the aim of not interfering with the flow path. Besides the typical Blade Tip-Timing application aimed at identifying the dynamical properties of each blade, an original method is here proposed to identify the operative deflection shape of a bladed disk through the experimental determination of the nodal diameters. The method is applicable when a small mistuning pattern perturbs the ideal cyclic symmetry of the bladed disk.
Internal variables in thermoelasticity
Berezovski, Arkadi
2017-01-01
This book describes an effective method for modeling advanced materials like polymers, composite materials and biomaterials, which are, as a rule, inhomogeneous. The thermoelastic theory with internal variables presented here provides a general framework for predicting a material’s reaction to external loading. The basic physical principles provide the primary theoretical information, including the evolution equations of the internal variables. The cornerstones of this framework are the material representation of continuum mechanics, a weak nonlocality, a non-zero extra entropy flux, and a consecutive employment of the dissipation inequality. Examples of thermoelastic phenomena are provided, accompanied by detailed procedures demonstrating how to simulate them.
Magnetohydrodynamics flow over a rapidly rotating axisymmetric wavy disk
Energy Technology Data Exchange (ETDEWEB)
Yoon, Myung Sup [Korea Testing Laboratory, 222-13 Guro3-dong Guro-gu, Seoul 152-718 (Korea, Republic of); Park, Jun Sang [Department of Mechanical Engineering, Halla University, Halla dae 1-gil, HeungUp, Wonju, Kangwon-do 220-712 (Korea, Republic of); Hyun, Jae Min, E-mail: jspark@halla.ac.kr [Department of Mechanical Engineering, Korea Advanced Institute of Science and Technology, 373-1 Kusong-dong, Yusong-gu, Taejon 305-701 (Korea, Republic of)
2011-08-15
A numerical study of Magnetohydrodynamics boundary layer flow over a rapidly rotating wavy disc was performed under which magnetic fields are imposed by a circular electric coil. The shape of the disc is assumed to be axisymmetric and sinusoidal in the radial direction, and semi-infinite space over the disc steadily rotating is occupied by an electrically conducting fluid. The study was conducted for the case where the representative Reynolds number is very large and the magnetic Reynolds number is negligibly small. The effect of Lorentz force on fluid motion was precisely investigated as the main external controlling force. The generalized boundary layer equation, including both magnetic field and heat flux, is derived to examine interactions among the effects of wavy surface shape, magnetic field and heat flux from the disc surface. Two cases of uniform magnetic field, much studied in previous research, and of non-uniform magnetic field, realized by a circular coil, have been scrutinized. Details of velocity profile, skin friction coefficient and heat transfer coefficient are given.
Effects of temperature distribution and level on heat transfer on a rotating free disk
Institute of Scientific and Technical Information of China (English)
ZHAO Xi; XU Guo-qiang; LUO Xiang
2011-01-01
In gas turbine engines, with the existence of the intense forced convection and significant buoyancy effects, temperature distribution and level on turbine or compressor disks affect the heat transfer characteristics strongly. In this paper, numerical simulations were performed to analyze these influences for a free disk, with the laminar and turbulent flow respectively. The influences of temperature distribution on the heat transfer were observed by using incompressible cooling air, and temperature profiles of nth order monomial and polynomial were assumed on the disk. The analysis revealed that the heat transfer for two flow states on the free disk is determined by the exponent n of the monomial profile when specifying the rotating Reynolds number; for an arbitrary polynomial profile, the local Nusselt number can be deduced from results of monomial profiles. To study the effects of temperature level on heat transfer singly, monomial profiles were used and the local Nusselt number of compressible and incompressible cooling air were compared. And both for two flow states, the following conclusions could be drawn: the relative difference of local Nusselt number is mainly controlled by nondimensional local temperature difference, and almost independent of the monomial's coefficient C, exponent n and the rotating Reynolds number. Subsequently, a correction method for heat transfer of the free disk is presented and verified computationally, with which the local Nusselt number, obtained with a uniform and low temperature profile, can be revised by arbitrary distribution and high temperature magnitude.
Sofue, Y; Omodaka, T
2008-01-01
We present a unified rotation curve of the Galaxy re-constructed from the existing data by re-calculating the distances and velocities for a set of galactic constants R_0=8 kpc and V_0=200 km/s. We decompose it into a bulge with de Vaucouleurs-law profile of half-mass scale radius 0.5 kpc and mass 1.8 x 10^{10}M_{sun}, an exponential disk of scale radius 3.5 kpc of 6.5 x 10^{10}M_{sun}, and an isothermal dark halo of terminal velocity 200 km/s. The r^{1/4}-law fit was obtained for the first time for the Milky Way's rotation curve. After fitting by these fundamental structures, two local minima, or the dips, of rotation velocity are prominent at radii 3 and 9 kpc. The 3-kpc dip is consistent with the observed bar. It is alternatively explained by a massive ring with the density maximum at radius 4 kpc. The 9-kpc dip is clearly exhibited as the most peculiar feature in the galactic rotation curve. We explain it by a massive ring of amplitude as large as 0.3 to 0.4 times the disk density with the density peak at...
Slip flow by a variable thickness rotating disk subject to magnetohydrodynamics
Imtiaz, Maria; Hayat, Tasawar; Alsaedi, Ahmed; Asghar, Saleem
Objective of the present study is to determine the characteristics of magnetohydrodynamic flow by a rotating disk having variable thickness. At the fluid-solid interface we consider slip velocity. The governing nonlinear partial differential equations of the problem are converted into a system of nonlinear ordinary differential equations. Obtained series solutions of velocity are convergent. Impact of embedded parameters on fluid flow and skin friction coefficient is graphically presented. It is observed that axial and radial velocities have an opposite impact on the thickness coefficient of disk. Also surface drag force has a direct relationship with Hartman number.
Gyromagnetic factor of rotating disks of electrically charged dust in general relativity
Liu Pynn, Yu-Chun; Macedo, Rodrigo Panosso; Breithaupt, Martin; Palenta, Stefan; Meinel, Reinhard
2016-11-01
We calculated the dimensionless gyromagnetic ratio ("g -factor") of self-gravitating, uniformly rotating disks of dust with a constant specific charge ɛ . These disk solutions to the Einstein-Maxwell equations depend on ɛ and a "relativity parameter" γ (0 <γ ≤1 ) up to a scaling parameter. Accordingly, the g -factor is a function g =g (γ ,ɛ ). The Newtonian limit is characterized by γ ≪1 , whereas γ →1 leads to a black-hole limit. The g -factor, for all ɛ , approaches the values g =1 as γ →0 and g =2 as γ →1 .
Gyromagnetic factor of rotating disks of electrically charged dust in general relativity
Pynn, Yu-Chun; Breithaupt, Martin; Palenta, Stefan; Meinel, Reinhard
2016-01-01
We calculated the dimensionless gyromagnetic ratio ("$g$-factor") of self-gravitating, uniformly rotating disks of dust with a constant specific charge $\\epsilon$. These disk solutions to the Einstein-Maxwell equations depend on $\\epsilon$ and a "relativity parameter" $\\gamma$ ($0<\\gamma\\le 1$) up to a scaling parameter. Accordingly, the $g$-factor is a function $g=g(\\gamma,\\epsilon)$. The Newtonian limit is characterized by $\\gamma \\ll 1$, whereas $\\gamma\\to 1$ leads to a black-hole limit. The $g$-factor, for all $\\epsilon$, approaches the values $g=1$ as $\\gamma\\to 0$ and $g=2$ as $\\gamma\\to 1$.
Chasing Shadows: Rotation of the Azimuthal Asymmetry in the TW Hya Disk
Debes, John H.; Poteet, Charles A.; Jang-Condell, Hannah; Gaspar, Andras; Hines, Dean; Kastner, Joel H.; Pueyo, Laurent; Rapson, Valerie; Roberge, Aki; Schneider, Glenn;
2017-01-01
We have obtained new images of the protoplanetary disk orbiting TW Hya in visible, total intensity light with the Space Telescope Imaging Spectrograph (STIS) on the Hubble Space Telescope (HST), using the newly commissioned BAR5 occulter. These HSTSTIS observations achieved an inner working angle of approximately 0 "2, or11.7 au, probing the system at angular radii coincident with recent images of the disk obtained by ALMA and in polarized intensity near-infrared light. By comparing our new STIS images to those taken with STIS in 2000 and with NICMOS in 1998, 2004, and 2005, we demonstrate that TW Hyas azimuthal surface brightness asymmetry moves coherently in position angle. Between 50 au and 141 au we measure a constant angular velocity in the azimuthal brightness asymmetry of 22.deg7 yr(exp -1) in a counterclockwise direction, equivalent to a period of 15.9yrassuming circular motion. Both the (short) inferred period and lack of radial dependence of the moving shadow pattern are inconsistent with Keplerian rotation at these disk radii. We hypothesize that the asymmetry arises from the fact that the disk interior to 1 au is inclined and precessing owing to a planetary companion, thus partially shadowing the outer disk. Further monitoring of this and other shadows on protoplanetary disks potentially opens anew avenue for indirectly observing the sites of planet formation.
Effect of Shear Stress in Flow on Cultured Cell: Using Rotating Disk at Microscope
Directory of Open Access Journals (Sweden)
Haruka Hino
2016-08-01
Full Text Available An experimental system of the Couette type flow with a rotating disk has been designed to apply wall shear stress quantitatively on the cell culture at the microscopic observation in vitro. The shear stress on the wall is calculated with an estimated Couette type of the velocity profile between the rotating disk and the culture plate. The constant rotational speed (lower than 400 rpm produces the wall shear stress lower than 2 Pa. The rotating disk system is mounted on the stage of an inverted phase contrast microscope to observe the behavior of cells adhered on the plate under the shear flow. Two kinds of cells were used in the test: C2C12 (mouse myoblast cell line, and MC3T3-E1 (mouse osteoblast precursor cell line. The experiments show that C2C12 tends to make orientation diagonal to the stream line, and that MC3T3-E1 tends to make orientation parallel to the stream line. Deformation and exfoliation of cells can be observed under controlled wall shear stress by the experimental system.
Mass Distribution in Rotating Thin-Disk Galaxies According to Newtonian Dynamics
Directory of Open Access Journals (Sweden)
James Q. Feng
2014-04-01
Full Text Available An accurate computational method is presented for determining the mass distribution in a mature spiral galaxy from a given rotation curve by applying Newtonian dynamics for an axisymmetrically rotating thin disk of finite size with or without a central spherical bulge. The governing integral equation for mass distribution is transformed via a boundary-element method into a linear algebra matrix equation that can be solved numerically for rotation curves with a wide range of shapes. To illustrate the effectiveness of this computational method, mass distributions in several mature spiral galaxies are determined from their measured rotation curves. All the surface mass density profiles predicted by our model exhibit approximately a common exponential law of decay, quantitatively consistent with the observed surface brightness distributions. When a central spherical bulge is present, the mass distribution in the galaxy is altered in such a way that the periphery mass density is reduced, while more mass appears toward the galactic center. By extending the computational domain beyond the galactic edge, we can determine the rotation velocity outside the cut-off radius, which appears to continuously decrease and to gradually approach the Keplerian rotation velocity out over twice the cut-off radius. An examination of circular orbit stability suggests that galaxies with flat or rising rotation velocities are more stable than those with declining rotation velocities especially in the region near the galactic edge. Our results demonstrate the fact that Newtonian dynamics can be adequate for describing the observed rotation behavior of mature spiral galaxies.
MHD flow of Burger's fluid over an off-centered rotating disk in a porous medium
Khan, Najeeb Alam; Khan, Sidra; Ullah, Saif
2015-08-01
In this study, off-centered stagnation flow of three dimensional Burger's fluid over an infinite rotating disk in a porous medium with a uniform magnetic field, which is applying normal to the disk, is investigated. A uniform suction/injection is applied through the surface of the porous disk. The structure has been modeled in the form of ordinary differential equations, which are reduced from partial differential equations by using the similarity transformation. Analytical solution is obtained by non-perturbation technique of homotopy analysis method (HAM). The influence of non-dimensional parameters on velocity profile is presented in graphical form and the numerical comparison is made with the viscous fluid as a special case.
Boundary layer development in the flow field between a rotating and a stationary disk
van Eeten, K. M. P.; van der Schaaf, J.; Schouten, J. C.; van Heijst, G. J. F.
2012-03-01
This paper discusses the development of boundary layers in the flow of a Newtonian fluid between two parallel, infinite disks. One of the disks is rotating at a constant angular velocity while the other remains stationary. An analytical series approximation and a numerical solution method are used to describe the velocity profiles of the flow. Both methods rely on the commonly used similarity transformation first proposed by Von Kármán [T. von Kármán, ZAMM 1, 233 (1921)], 10.1002/zamm.19210010401. For Reh Batchelor type of flow was observed for Reh > 300, with two boundary layers near the disks and a non-viscous core in the middle. A remarkable conclusion of the current work is the coincidence of the power series' radius of convergence, a somewhat abstract mathematical notion, with the physically tangible concept of the boundary layer thickness. The coincidence shows a small deviation of only 2% to 4%.
Health Monitoring of a Rotating Disk Using a Combined Analytical-Experimental Approach
Abdul-Aziz, Ali; Woike, Mark R.; Lekki, John D.; Baaklini, George Y.
2009-01-01
Rotating disks undergo rigorous mechanical loading conditions that make them subject to a variety of failure mechanisms leading to structural deformities and cracking. During operation, periodic loading fluctuations and other related factors cause fractures and hidden internal cracks that can only be detected via noninvasive types of health monitoring and/or nondestructive evaluation. These evaluations go further to inspect material discontinuities and other irregularities that have grown to become critical defects that can lead to failure. Hence, the objectives of this work is to conduct a collective analytical and experimental study to present a well-rounded structural assessment of a rotating disk by means of a health monitoring approach and to appraise the capabilities of an in-house rotor spin system. The analyses utilized the finite element method to analyze the disk with and without an induced crack at different loading levels, such as rotational speeds starting at 3000 up to 10 000 rpm. A parallel experiment was conducted to spin the disk at the desired speeds in an attempt to correlate the experimental findings with the analytical results. The testing involved conducting spin experiments which, covered the rotor in both damaged and undamaged (i.e., notched and unnotched) states. Damaged disks had artificially induced through-thickness flaws represented in the web region ranging from 2.54 to 5.08 cm (1 to 2 in.) in length. This study aims to identify defects that are greater than 1.27 cm (0.5 in.), applying available means of structural health monitoring and nondestructive evaluation, and documenting failure mechanisms experienced by the rotor system under typical turbine engine operating conditions.
Directory of Open Access Journals (Sweden)
Tasawar Hayat
Full Text Available This paper investigates the unsteady MHD flow of viscous fluid between two parallel rotating disks. Fluid fills the porous space. Energy equation has been constructed by taking Joule heating, thermal stratification and radiation effects into consideration. We convert system of partial differential equations into system of highly nonlinear ordinary differential equations after employing the suitable transformations. Convergent series solutions are obtained. Behavior of different involved parameters on velocity and temperature profiles is examined graphically. Numerical values of skin friction coefficient and Nusselt number are computed and inspected. It is found that tangential velocity profile is increasing function of rotational parameter. Fluid temperature reduces for increasing values of thermal stratification parameter. At upper disk heat transfer rate enhances for larger values of Eckert and Prandtl numbers.
Hayat, Tasawar; Qayyum, Sumaira; Imtiaz, Maria; Alsaedi, Ahmed
2016-01-01
This paper investigates the unsteady MHD flow of viscous fluid between two parallel rotating disks. Fluid fills the porous space. Energy equation has been constructed by taking Joule heating, thermal stratification and radiation effects into consideration. We convert system of partial differential equations into system of highly nonlinear ordinary differential equations after employing the suitable transformations. Convergent series solutions are obtained. Behavior of different involved parameters on velocity and temperature profiles is examined graphically. Numerical values of skin friction coefficient and Nusselt number are computed and inspected. It is found that tangential velocity profile is increasing function of rotational parameter. Fluid temperature reduces for increasing values of thermal stratification parameter. At upper disk heat transfer rate enhances for larger values of Eckert and Prandtl numbers.
Perturbation of a Schwarzschild Black Hole Due to a Rotating Thin Disk
Čížek, P.; Semerák, O.
2017-09-01
Will, in 1974, treated the perturbation of a Schwarzschild black hole due to a slowly rotating, light, concentric thin ring by solving the perturbation equations in terms of a multipole expansion of the mass-and-rotation perturbation series. In the Schwarzschild background, his approach can be generalized to perturbation by a thin disk (which is more relevant astrophysically), but, due to rather bad convergence properties, the resulting expansions are not suitable for specific (numerical) computations. However, we show that Green’s functions, represented by Will’s result, can be expressed in closed form (without multipole expansion), which is more useful. In particular, they can be integrated out over the source (a thin disk in our case) to yield good converging series both for the gravitational potential and for the dragging angular velocity. The procedure is demonstrated, in the first perturbation order, on the simplest case of a constant-density disk, including the physical interpretation of the results in terms of a one-component perfect fluid or a two-component dust in a circular orbit about the central black hole. Free parameters are chosen in such a way that the resulting black hole has zero angular momentum but non-zero angular velocity, as it is just carried along by the dragging effect of the disk.
Machida, Mami; NAKAMURA, Kenji E.; Kudoh, Takahiro; Akahori, Takuya; Yoshiaki, SOFUE; Matsumoto, Ryoji
2013-01-01
We carried out global three-dimensional magneto-hydrodynamic simulations of dynamo activities in galactic gaseous disks without assuming equatorial symmetry. Numerical results indicate the growth of azimuthal magnetic fields non-symmetric to the equatorial plane. As magneto-rotational instability (MRI) grows, the mean strength of magnetic fields is amplified until the magnetic pressure becomes as large as 10% of the gas pressure. When the local plasma $\\beta$ ($ = p_{\\rm gas}/p_{\\rm mag}$) be...
Directory of Open Access Journals (Sweden)
Cha'o-Kuang Chen
2009-01-01
Full Text Available The main object of this paper is to study the weakly nonlinear hydrodynamic stability of the thin Newtonian fluid flowing on a rotating circular disk. A long-wave perturbation method is used to derive the nonlinear evolution equation for the film flow. The linear behaviors of the spreading wave are investigated by normal mode approach, and its weakly nonlinear behaviors are explored by the method of multiple scales. The Ginzburg-Landau equation is determined to discuss the necessary condition for the existence of such flow pattern. The results indicate that the superctitical instability region increases, and the subcritical stability region decreases with the increase of the rotation number or the radius of circular disk. It is found that the rotation number and the radius of circular disk not only play the significant roles in destabilizing the flow in the linear stability analysis but also shrink the area of supercritical stability region at high Reynolds number in the weakly nonlinear stability analysis.
Simulations of turbulent flow between a rotating and a stationary disk
Energy Technology Data Exchange (ETDEWEB)
Lygren, Magne
2001-07-01
The main focus of this thesis is turbulent flow between a rotating and a stationary disk. The extension of the disks is assumed to be large enough to prevent the outer boundary conditions to influence the flow at the region of interest. This flow is driven by the shear between the disks, but an imbalance between centrifugal and pressure forces in the radial direction induces a radial cross flow. The result is a complex three-dimensional flow where the direction of the mean flow varies with the axial position. Direct numerical simulations (DNS) and large eddy simulations (LES) have been used to investigate the flow. The simulations utilised a special set of quasi-periodic boundary conditions which allowed the use of a computational domain which captured only a section of the flow. Locally, the disk flow is characterised by a rotational Reynolds number and a local gap ratio of 0.02. Turbulence statistics were compared to results from the turbulent plane Couette flow and from an experimental investigation of an enclosed rotor-stator flow. The plane Couette flow is a two-dimensional equivalence to the flow between the disks. Although the turbulence statistics had many similarities in the two cases, there were differences caused by three-dimensionality of the mean-flow in the disk case. In the disk flow the direction of the Reynolds shear stress vector was not aligned with the mean-gradient vector and the ratio of the magnitude of the shear stress vector to the mean turbulent kinetic energy was reduce compared to the Couette flow. The flow between the disks statistically stationary. It is therefore a suitable case for studying effects of mean-flow three-dimentionality on the underlying coherent structures in the boundary layers. Ensemble averages, probability-density functions and a quadrant analysis of conditional averages in the regions near the disks were performed in order to study the coherent quasistreamwise vortices. By comparing with corresponding conditional
A Correlation Between Circumstellar Disks and Rotation in the Upper Scorpius OB Association
Dahm, S E; White, R J
2011-01-01
We present projected rotational velocities for 20 early-type (B8-A9) and 74 late-type (F2-M8) members of the ~5 Myr old Upper Scorpius OB Association derived from high dispersion optical spectra obtained with the High Resolution Echelle Spectrometer (HIRES) on Keck I and the Magellan Inamori Kyocera Echelle (MIKE) on the Magellan Clay telescope. The spectroscopic sample is composed of stars and brown dwarfs with infrared signatures of circumstellar disks, both primordial and debris, and non-excess sources of comparable spectral type. We merge projected rotational velocities, accretion diagnostics, and Spitzer Space Telescope Infrared Array Camera (IRAC) and Multiband Imaging Photometer for Spitzer (MIPS) 24 micron photometry to examine the relationship between rotation and circumstellar disks. The rotational velocities are strongly correlated with spectral type, a proxy for mass, such that the median vsini for B8-A9 type stars is: 195(+/-)70 km/s, F2-K4: 37.8(+/-)7.4 km/s, K5-K9: 13.8(+21.3/-8.2) km/s, M0-M5:...
Loghman, A.; Hammami, M.; Loghman, E.
2017-05-01
The history of stresses and creep strains of a rotating composite cylinder made of an aluminum matrix reinforced by silicon carbide particles is investigated. The effect of uniformly distributed SiC micro- and nanoparticles on the initial thermo-elastic and time-dependent creep deformation is studied. The material creep behavior is described by Sherby's constitutive model where the creep parameters are functions of temperature and the particle sizes vary from 50 nm to 45.9 μm. Loading is composed of a temperature field due to outward steady-state heat conduction and an inertia body force due to cylinder rotation. Based on the equilibrium equation and also stress-strain and strain-displacement relations, a constitutive second-order differential equation for displacements with variable and time-dependent coefficients is obtained. By solving this differential equation together with the Prandtl-Reuss relation and the material creep constitutive model, the history of stresses and creep strains is obtained. It is found that the minimum effective stresses are reached in a material reinforced by uniformly distributed SiC particles with the volume fraction of 20% and particle size of 50 nm. It is also found that the effective and tangential stresses increase with time at the inner surface of the composite cylinder; however, their variation at the outer surface is insignificant.
Chasing Shadows: Rotation of the Azimuthal Asymmetry in the TW Hya Disk
Debes, John H.; Poteet, Charles A.; Jang-Condell, Hannah; Gaspar, Andras; Hines, Dean; Kastner, Joel H.; Pueyo, Laurent; Rapson, Valerie; Roberge, Aki; Schneider, Glenn; Weinberger, Alycia J.
2017-02-01
We have obtained new images of the protoplanetary disk orbiting TW Hya in visible, total intensity light with the Space Telescope Imaging Spectrograph (STIS) on the Hubble Space Telescope (HST), using the newly commissioned BAR5 occulter. These HST/STIS observations achieved an inner working angle of ∼0.″2, or 11.7 au, probing the system at angular radii coincident with recent images of the disk obtained by ALMA and in polarized intensity near-infrared light. By comparing our new STIS images to those taken with STIS in 2000 and with NICMOS in 1998, 2004, and 2005, we demonstrate that TW Hya’s azimuthal surface brightness asymmetry moves coherently in position angle. Between 50 au and 141 au we measure a constant angular velocity in the azimuthal brightness asymmetry of 22.°7 yr‑1 in a counterclockwise direction, equivalent to a period of 15.9 yr assuming circular motion. Both the (short) inferred period and lack of radial dependence of the moving shadow pattern are inconsistent with Keplerian rotation at these disk radii. We hypothesize that the asymmetry arises from the fact that the disk interior to 1 au is inclined and precessing owing to a planetary companion, thus partially shadowing the outer disk. Further monitoring of this and other shadows on protoplanetary disks potentially opens a new avenue for indirectly observing the sites of planet formation. Based on observations made with the NASA/ESA Hubble Space Telescope, obtained from the data archive at the Space Telescope Science Institute. STScI is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555.
Prediction of powder particle size during centrifugal atomisation using a rotating disk
Directory of Open Access Journals (Sweden)
Huiping Li and Xucheng Deng
2007-01-01
Full Text Available The centrifugal atomisation of metallic melts using a rotating disk is an important process for powder production and spray deposition. The theoretical prediction of powder particle size is desirable for the design of atomisers. In this paper, wave theory was applied to analyse the disintegration of metallic melts in the film disintegration regime during centrifugal atomisation using a rotating disk. A mathematical model was proposed to predict the spray parameters. The governing equation for the fastest-growing wave number was developed and solved numerically. The effect of the variation in film thickness during film extension was taken into account. Film length and powder particle size were calculated and compared with available experimental data in the literature, and a good agreement was achieved. The influence of the break-up parameter was studied, and it is shown that the break-up parameter is not sensitive to the predicted powder particle size. Both simulated results and experimental data showed that fine powders can be produced by increasing disk speed.
Liquid flow on a rotating disk prior to centrifugal atomization and spray deposition
Zhao, Y. Y.; Jacobs, M. H.; Dowson, A. L.
1998-12-01
Video observations of the flow patterns that develop on a rotating disk during centrifugal atomization and spray deposition, and subsequent metallographic studies conducted on solid skulls removed from the disk after processing, have indicated a circular discontinuity or hydraulic jump, which is manifested by a rapid increase in the thickness of the liquid metal and by a corresponding decrease in the radial velocity. A mathematical model has been developed that is capable of predicting both the occurrence and location of the jump, and the associated changes in the thickness profile and in the radial and tangential velocities of the liquid metal. Good correlations have been observed between model predictions and the flow patterns observed on the skull after atomization, and the effects of changes in material and operational parameters such as kinematic viscosity, volume flow rate, metallostatic head, and disk rotation speed have been quantified. Liquid metal flow is controlled primarily by the volume flow rate and by the metallostatic head prior to the hydraulic jump and by the centrifugal forces after the jump. The implications of these observations in terms of the atomization process are discussed.
Institute of Scientific and Technical Information of China (English)
孔泳; 穆绍林
2003-01-01
The electrolysis of catechol was studied in the pH values of 1 to 10. The results from the rotating ring-disk electrode (RRDE) experiments show that at low pH values,the electrochemical polymerization of catechol was performed by one step,and at higher pH values,the electrochemical polymerization of catechol was carried out by two steps,i.e.oxidation of catechol and followed by polymerization.The intermediates generated at the disk were detected at the ring electrode in the ring potential region of -0.2 to 0 V(vs.Ag/AgCl).One of reasons for the decrease in the ratio of ir to id with increasing the ring potential is caused by formation of positively charged intermediates at the disk electrode.This ratio increases with increasing the rotation rate of the RRDE,which indicates that the intermediates are not stable.A shielding effect during polymerization of catechol was observed when the ring potential was set at 0.1 V (vs.Ag/AgCl).The electron spin resonance(ESR) of polycatechol show that polycatechol possesses unpaired electrons.The images of polycatechol films synthesized at differentconditions are described.
The effects of flow multiplicity on GaN deposition in a rotating disk CVD reactor
Gkinis, P. A.; Aviziotis, I. G.; Koronaki, E. D.; Gakis, G. P.; Boudouvis, A. G.
2017-01-01
The effect of gas flow multiplicity, i.e. the possibility of two very different flow regimes prevailing at random in a rotating disk metalorganic chemical vapor deposition (MOCVD) reactor, on the deposited GaN film is investigated. A transport model coupled with a system of chemical reactions in the gas phase and on the wafer where the film is formed, is implemented in the parameter regions where multiple flows are possible. In the region of multiplicity where either plug flow, imposed by forced convection, or buoyancy-dominated flow is possible, the results in the latter case indicate high deposition rate and decreased uniformity. In the former case, increasing the pressure and the rotation rate has a favorable effect on the deposition rate without sacrificing uniformity. In the parameter window of multiplicity where either rotation or combined rotation/buoyancy may prevail, the effects of buoyancy lead to higher deposition rate at the center of the wafer and reduced uniformity. The Arrhenius plots in the regions of multiplicity for exactly the same operating conditions reveal that the system operates in a diffusion-limited regime in the plug flow and in the rotation-dominated flow, in the first and second region of multiplicity respectively. In contrast, in the buoyancy-dominated flow and the combined rotation/buoyancy flow (first and second region of multiplicity respectively) the process shifts into the kinetics-limited regime.
Hummel, W.; Vrancken, M.
2000-07-01
We improve the theory of Horne & Marsh on shear broadening in accretion disks of CVs and adapt it to Be star circumstellar disks. Stellar obscuration and shell absorption are taken into account in detail. It is shown that shell absorption is already present in those emission lines where the central depression does not drop below the stellar continuum. The model profiles are fitted to observed symmetric Hα net emission lines with low equivalent width. The derived disk radii range from Rd = 5.3 R_* to Rd = 18 R_* and the surface emissivity varies as ~ R-m with 1.6 (1)/(2) with the optically thick Hα profile of HR 5440 rules out the range of j>(1)/(2). This can be understood by the lack of velocity shear in the outer disk regions. We conclude that Keplerian rotation (j=(1)/(2)) is a valid approximation. Based on observations collected at the German-Spanish Astronomical Center (DSAZ), Calar Alto, operated by the Max-Plank-Institut für Astronomie Heidelberg jointly with the Spanish National Commission for Astronomy. Based on observations collected at the Observatoire de Haute-Provence (OHP), CNRS, France.
Experimental characterization of transition region in rotating-disk boundary layer
Siddiqui, M. E.; Mukund, V.; Scott, J.; Pier, B.
2013-03-01
The three-dimensional boundary layer due to a disk rotating in otherwise still fluid is well known for its sudden transition from a laminar to a turbulent regime, the location of which closely coincides with the onset of local absolute instability. The present experimental investigation focuses on the region around transition and analyses in detail the features that lead from the unperturbed boundary layer to a fully turbulent flow. Mean velocity profiles and high-resolution spectra are obtained by constant-temperature hot-wire anemometry. By carefully analysing these measurements, regions in the flow are identified that correspond to linear, weakly nonlinear, or turbulent dynamics. The frequency that dominates the flow prior to transition is explained in terms of spatial growth rates, derived from the exact linear dispersion relation. In the weakly nonlinear region, up to six clearly identifiable harmonic peaks are found. High-resolution spectra reveal the existence of discrete frequency components that are deemed to correspond to fluctuations stationary with respect to the disk surface. These discrete components are only found in the weakly nonlinear region. By systematically acquiring low- and high-resolution spectra over a range of narrowly spaced radial and axial positions, it is shown that while the transition from laminar to turbulent regimes occurs sharply at some distance from the disk surface, a complex weakly nonlinear region of considerable radial extent continues to prevail close to the disk surface.
An experimental study of the edge effect on transition of the rotating-disk boundary-layer flow
Imayama, Shintaro; Lingwood, R. J.; Alfredsson, P. Henrik
2011-11-01
Lingwood [J. Fluid Mech., 299, 17 (1995)] showed that the flow instability in the rotating-disk boundary layer is not only of convective nature but also that the flow becomes absolutely unstable. Furthermore, in the absence of bypass mechanisms, the absolute instability triggers nonlinearity and transition to turbulence at a fixed Reynolds number (Re). Healey [J. Fluid Mech., 663, 148 (2010)] suggested that the observed spread (albeit small) in transition Re in different experiments is an effect of the Re at the disk edge and provided a nonlinear model to take this effect into account. Here, we further investigate this problem experimentally with hot-wire measurements on a rotating polished glass disk with a diameter of 474 mm and a total imbalance and surface roughness less than 10 μm. To investigate the influence of the disk edge, we vary Re at the disk edge by changing the rotational speed and map the development of the disturbance velocity in the radial direction. Furthermore, the effect of a stationary annular plate around the edge of the rotating disk is also investigated. Our experiments show no effect of the disk edge Re on the stability and transition, however there was a shift of both the growth curve and the transition Re by about 10 units with and without the outer stationary plate, with the lower Re observed with the plate.
Modelling of liquid flow after a hydraulic jump on a rotating disk prior to centrifugal atomization
Zhao, Y. Y.; Dowson, A. L.; Jacobs, M. H.
2000-01-01
This paper describes a simplified numerical model which is used to calculate the height distribution, and the radial and tangential velocities of a liquid on a rotating disk after a hydraulic jump and prior to centrifugal atomization. The results obtained from this numerical model are compared with predictions made using previously derived `hydraulic jump' and `analytical' models. Calculations, in conjunction with experimental measurements relating to the trajectory of liquid flow on the atomizing disk, have shown that the numerical model can not only give a reasonable prediction of the hydraulic jump location, but also yields more accurate information regarding the variations in liquid height, and radial and tangential velocities. The model is ideally suited for engineering applications.
Energy Technology Data Exchange (ETDEWEB)
Barbosa, Marcos Pinotti
1992-07-01
Flow study in the formatted channel for two disks in rotation is discussed including the following main issues: flow description between disks in rotation; computational model; and numerical results. The parametric studies accomplished of the spacing between disks, of the diameter, and of the rotor angular speed allowed the influence analysis of these variables in the flow inside the channel and in the generated pressure difference. The disks rotation, evaluated through Reynolds' rotational number, is the main parameter that influences the pressure difference between channel entrance and exit. It verified although how much larger the rotation larger the pressure difference.
The neutral curve for stationary disturbances in rotating-disk flow
Malik, M. R.
1986-01-01
The neutral curve for stationary vortex disturbances in rotating-disk flow is computed up to a Reynolds number of 10 to the 7th using the sixth-order system of linear stability equations which includes the effects of streamline curvature and Coriolis force. It is found that the neutral curve has two minima: one at R = 285.36 (upper branch) and the other at R = 440.88 (lower branch). At large Reynolds numbers, the upper branch tends to Stuart's asymptotic solution while the lower branch tends to a solution that is associated with the wave angle corresponding to the direction of zero mean wall shear.
Direct spatial resonance in the laminar boundary layer due to a rotating-disk
Indian Academy of Sciences (India)
M Turkyilmazoglu; J S B Gajjar
2000-12-01
Numerical treatment of the linear stability equations is undertaken to investigate the occurrence of direct spatial resonance events in the boundary layer flow due to a rotating-disk. A spectral solution of the eigenvalue problem indicates that algebraic growth of the perturbations shows up, prior to the amplification of exponentially growing instability waves. This phenomenon takes place while the flow is still in the laminar state and it also tends to persist further even if the non-parallelism is taken into account. As a result, there exists the high possibility of this instability mechanism giving rise to nonlinearity and transition, long before the unboundedly growing time-amplified waves.
Off-centered stagnation point flow of a couple stress fluid towards a rotating disk.
Khan, Najeeb Alam; Riaz, Fatima
2014-01-01
An investigation has been made to study the off-centered stagnation flow of a couple stress fluid over a rotating disk. The model developed for the governing problem in the form of partial differential equations has been converted to ordinary differential equations with the use of suitable similarity transformation. The analytical approximation has been made with the most promising analytical approach, homotopy analysis method (HAM). The convergence region of the obtained solution is determined and plotted. The effects of couple stress and nondimensional parameters have been observed on the flows of couple stress fluid. Also comparison has been made with the Newtonian fluid as the special case of considered problem.
Radiation Effects in Flow through Porous Medium over a Rotating Disk with Variable Fluid Properties
Directory of Open Access Journals (Sweden)
Shalini Jain
2016-01-01
Full Text Available The present study investigates the radiation effects in flow through porous medium over a permeable rotating disk with velocity slip and temperature jump. Fluid properties density (ρ, viscosity (μ, and thermal conductivity (κ are taken to be dependent on temperature. Particular case considering these fluid properties’ constant is also discussed. The governing partial differential equations are converted into nonlinear normal differential equation using similarity alterations. Transformed system of equations is solved numerically by using Runge-Kutta method with shooting technique. Effects of various parameters such as porosity parameter K, suction parameter Ws, rotational Reynolds number Re, Knudsen number Kn, Prandtl number Pr, radiation parameter N, and relative temperature difference parameter ε on velocity profiles along radial, tangential, and axial direction and temperature distribution are investigated for both variable fluid properties and constant fluid properties. Results obtained are analyzed and depicted through graphs and table.
Routes to turbulence in the rotating disk boundary-layer of a rotor-stator cavity
Yim, Eunok; Serre, Eric; Martinand, Denis; Chomaz, Jean-Marc
2016-11-01
The rotating disk is an important classical problem, due to the similarities between the 3D boundary layers on a disk and a swept aircraft wing. It is nowadays admitted that a direct transition to turbulence may exist through a steep-fronted nonlinear global mode located at the boundary between the locally connectively and absolutely unstable regions (Pier 2003; Viaud et al. 2008, 2011; Imayama et al. 2014 and others). However, recent studies (Healey 2010; Harris et al. 2012; Imayama et al. 2013) suggest that there may be an alternative route starting at lower critical Reynolds number, based on convective travelling waves but this scenario is still not fully validated and proven. To better characterize such transition, direct numerical simulations are performed in a closed cylindrical rotor-stator cavity (without hub) up to Re = O (105) . All boundaries are no slip and for the stable region around the rotation axis prevents the disturbances coming from the very unstable stator boundary to disturb the rotor boundary layer. Different transition scenarii to turbulence are investigated when the rotor boundary layer is forced at different positions and forcing amplitude. The associated dynamics of coherent structures in various flow regions are also investigated when increasing Re .
A Stefan model for mass transfer in a rotating disk reaction vessel
BOHUN, C. S.
2015-05-04
Copyright © Cambridge University Press 2015. In this paper, we focus on the process of mass transfer in the rotating disk apparatus formulated as a Stefan problem with consideration given to both the hydrodynamics of the process and the specific chemical reactions occurring in the bulk. The wide range in the reaction rates of the underlying chemistry allows for a natural decoupling of the problem into a simplified set of weakly coupled convective-reaction-diffusion equations for the slowly reacting chemical species and a set of algebraic relations for the species that react rapidly. An analysis of the chemical equilibrium conditions identifies an expansion parameter and a reduced model that remains valid for arbitrarily large times. Numerical solutions of the model are compared to an asymptotic analysis revealing three distinct time scales and chemical diffusion boundary layer that lies completely inside the hydrodynamic layer. Formulated as a Stefan problem, the model generalizes the work of Levich (Levich and Spalding (1962) Physicochemical hydrodynamics, vol. 689, Prentice-Hall Englewood Cliffs, NJ) and will help better understand the natural limitations of the rotating disk reaction vessel when consideration is made for the reacting chemical species.
Modal parameters of a rotating multiple-disk-shaft system from simulated frequency response data
Directory of Open Access Journals (Sweden)
Khader N.
2014-12-01
Full Text Available Modal parameters of a rotating multiple disk-shaft system are estimated in Multiple Input/Multiple Output (MIMO scheme. The response at multiple output degrees of freedom (dofs and excitations at multiple input (reference dofs are related through the Frequency Response Function (FRF matrix. The corresponding Impulse Response Function (IRF matrix is obtained by Inverse Fast Fourier Transform (IFFT of the FRF matrix. The resulting FRF matrix is not symmetric due to the gyroscopic effects introduced by rotation. The Eigensystem Realization Algorithm (ERA and its equivalent low order time domain algorithm, based on the Unified Matrix Polynomial Approach (UMPA are employed to estimate the desired modal parameters, i.e., system eigenvalues and the associated right hand and left hand eigenvectors. The right hand vectors are estimated from multiple columns of the FRF matrix with the structure rotating in one direction, and the left hand vectors are estimated from the multiple rows of the FRF matrix, which are calculated as the transpose of the same multiple columns of the FRF matrix, estimated with rotation in the opposite direction. The obtained results are found to be in excellent agreement with results obtained from Theoretical Modal Analysis (TMA.
Fowle, A. A.; Soto, L.; Strong, P. F.; Wang, C. A.
1980-01-01
A low Bond number simulation technique was used to establish the stability limits of cylindrical and conical floating liquid columns under conditions of isorotation, equal counter rotation, rotation of one end only, and parallel axis offset. The conditions for resonance in cylindrical liquid columns perturbed by axial, sinusoidal vibration of one end face are also reported. All tests were carried out under isothermal conditions with water and silicone fluids of various viscosities. A technique for the quantitative measurement of stream velocity within a floating, isothermal, liquid column confined between rotatable disks was developed. In the measurement, small, light scattering particles were used as streamline markers in common arrangement, but the capability of the measurement was extended by use of stereopair photography system to provide quantitative data. Results of velocity measurements made under a few selected conditions, which established the precision and accuracy of the technique, are given. The general qualitative features of the isothermal flow patterns under various conditions of end face rotation resulting from both still photography and motion pictures are presented.
SPARC: Mass Models for 175 Disk Galaxies with Spitzer Photometry and Accurate Rotation Curves
Lelli, Federico; McGaugh, Stacy S.; Schombert, James M.
2016-12-01
We introduce SPARC (Spitzer Photometry and Accurate Rotation Curves): a sample of 175 nearby galaxies with new surface photometry at 3.6 μm and high-quality rotation curves from previous H i/Hα studies. SPARC spans a broad range of morphologies (S0 to Irr), luminosities (∼5 dex), and surface brightnesses (∼4 dex). We derive [3.6] surface photometry and study structural relations of stellar and gas disks. We find that both the stellar mass–H i mass relation and the stellar radius–H i radius relation have significant intrinsic scatter, while the H i mass–radius relation is extremely tight. We build detailed mass models and quantify the ratio of baryonic to observed velocity (V bar/V obs) for different characteristic radii and values of the stellar mass-to-light ratio (ϒ⋆) at [3.6]. Assuming ϒ⋆ ≃ 0.5 M ⊙/L ⊙ (as suggested by stellar population models), we find that (i) the gas fraction linearly correlates with total luminosity (ii) the transition from star-dominated to gas-dominated galaxies roughly corresponds to the transition from spiral galaxies to dwarf irregulars, in line with density wave theory; and (iii) V bar/V obs varies with luminosity and surface brightness: high-mass, high-surface-brightness galaxies are nearly maximal, while low-mass, low-surface-brightness galaxies are submaximal. These basic properties are lost for low values of ϒ⋆ ≃ 0.2 M ⊙/L ⊙ as suggested by the DiskMass survey. The mean maximum-disk limit in bright galaxies is ϒ⋆ ≃ 0.7 M ⊙/L ⊙ at [3.6]. The SPARC data are publicly available and represent an ideal test bed for models of galaxy formation.
An experimental investigation of the three-dimensional boundary layer on a rotating disk
Littell, Howard Steven
The velocity field above a large spinning disk has been studied using pressure probes and hotwire anemometers. The flowfield consists of a three-dimensional boundary layer due to a crossflow caused by centrifugal forces. The disk was 1 m in diameter and was spun at speeds up to 1500 rpm, giving momentum thickness Reynolds numbers in excess of 6000. The mean flow in both the laminar and turbulent regimes compares well with previous studies of 'infinite' smooth rotating disks. All six Reynolds stresses and the ten triple products have been measured using established crosswire anemometry techniques. These results are compared to previous three-dimensional boundary layer measurements and several key differences are noted. The ratio of the shear stress vector magnitude to the turbulent kinetic energy is a common descriptor of boundary layer flow and is used in many modeling efforts because it is usually a constant over most of a two-dimensional boundary layer. Three-dimensionality has been observed to depress this parameter near the wall in many pressure-driven boundary layers. In the disk flow, this parameter was at a maximum near the wall at close to the 2-D value, but dropped off almost linearly away from the wall. Two-point velocity correlations were also measured using a pair of crosswire anemometers to gain insight into the structure of the turbulence. These measurements were obtained at two different heights at momentum thickness Reynolds numbers of 2650 and 5000 to test for possible scaling effects. These measurements showed that the turbulence exhibits asymmetry in the crossflow direction, which cannot occur in two-dimensional boundary layers. A mechanism by which the crossflow may be modifying the turbulence structure is proposed which exhibits several features of the asymmetric two-point correlations.
Shen, Liye; Ma, Jingxing; Song, Pengfei; Lu, Zhihao; Yin, Yao; Liu, Yongdi; Cai, Lankun; Zhang, Lehua
2016-10-01
A rotating disk electrode (RDE) was used to investigate the concentration loss and impedance characteristics of anodic biofilms in microbial fuel cells (MFCs). Amperometric time-current analysis revealed that at the rotation rate of 480 rpm, a maximum current density of 168 µA cm(-2) can be achieved, which was 22.2 % higher than when there was no rotation. Linear sweep voltammetry and electrochemical impedance spectroscopy tests showed that when the anodic potential was set to -300 mV vs. Ag/AgCl reference, the power densities could increase by 59.0 %, reaching 1385 mW m(-2), the anodic resistance could reduce by 19 %, and the anodic capacitance could increase by 36 %. These results concur with a more than 85 % decrease of the diffusion layer thickness. Data indicated that concentration loss, diffusion layer thickness, and the mixing velocity play important roles in anodic resistance reduction and power output of MFCs. These findings could be helpful to the design of future industrial-scale MFCs with mixed bacteria biofilms.
Christodoulou, Dimitris M
2015-01-01
By solving analytically the various types of Lane-Emden equations with rotation, we have discovered two new coupled fundamental properties of rotating, self-gravitating, gaseous disks in equilibrium: Isothermal disks must, on average, exhibit strict power-law density profiles in radius $x$ on their equatorial planes of the form $A x^{k-1}$, where $A$ and $k-1$ are the integration constants; and ``flat'' rotation curves precisely such as those observed in spiral galaxy disks. Polytropic disks must, on average, exhibit strict density profiles of the form $\\left[\\ln(A x^k)\\right]^n$, where $n$ is the polytropic index; and ``flat'' rotation curves described by square roots of upper incomplete gamma functions. By ``on average,'' we mean that, irrespective of the chosen boundary conditions, the actual profiles must oscillate around and remain close to the strict mean profiles of the analytic singular equilibrium solutions. We call such singular solutions the ``intrinsic'' solutions of the differential equations bec...
Clem, Michelle M.; Woike, Mark R.
2013-01-01
The Aeronautical Sciences Project under NASA`s Fundamental Aeronautics Program is extremely interested in the development of novel measurement technologies, such as optical surface measurements in the internal parts of a flow path, for in situ health monitoring of gas turbine engines. In situ health monitoring has the potential to detect flaws, i.e. cracks in key components, such as engine turbine disks, before the flaws lead to catastrophic failure. In the present study, a cross-correlation imaging technique is investigated in a proof-of-concept study as a possible optical technique to measure the radial growth and strain field on an already cracked sub-scale turbine engine disk under loaded conditions in the NASA Glenn Research Center`s High Precision Rotordynamics Laboratory. The optical strain measurement technique under investigation offers potential fault detection using an applied high-contrast random speckle pattern and imaging the pattern under unloaded and loaded conditions with a CCD camera. Spinning the cracked disk at high speeds induces an external load, resulting in a radial growth of the disk of approximately 50.0-im in the flawed region and hence, a localized strain field. When imaging the cracked disk under static conditions, the disk will be undistorted; however, during rotation the cracked region will grow radially, thus causing the applied particle pattern to be .shifted`. The resulting particle displacements between the two images will then be measured using the two-dimensional cross-correlation algorithms implemented in standard Particle Image Velocimetry (PIV) software to track the disk growth, which facilitates calculation of the localized strain field. In order to develop and validate this optical strain measurement technique an initial proof-of-concept experiment is carried out in a controlled environment. Using PIV optimization principles and guidelines, three potential speckle patterns, for future use on the rotating disk, are developed
Numerical simulation of fluid flow and heat transfer in a thin liquid film over a rotating disk
Rahman, M. M.; Faghri, A.
1992-01-01
The results of a numerical simulation of the flow field and associated heat transfer coefficient are presented for the free surface flow of a thin liquid film adjacent to a horizontal rotating disk. The computation has been performed for different flow rates and rotational velocities using a three-dimensional boundary-fitted coordinate system. Since the geometry of the free surface is unknown and dependent on flow rate, rate of rotation, and other parameters, an interative procedure had to be used to ascertain its location. The computed film height agreed well with existing experimental measurements. The flow was dominated by inertia near the entrance and close to the free surface, and dominated by centrifugal force at larger radii and adjacent to the disk. The rotation enhanced the heat transfer coefficient by a significant amount.
Experimental investigation of absolute instability of a rotating-disk boundary layer
Othman, H.; Corke, T. C.
2006-10-01
A series of experiments were performed to study the absolute instability of Type I travelling crossflow modes in the boundary layer on a smooth disk rotating at constant speed. The basic flow agreed with analytic theory, and the growth of natural disturbances matched linear theory predictions. Controlled temporal disturbances were introduced by a short-duration air pulse from a hypodermic tube located above the disk and outside the boundary layer. The air pulse was positioned just outboard of the linear-theory critical radius for Type I crossflow modes. A hot-wire sensor primarily sensitive to the azimuthal velocity component, was positioned at different spatial (r,theta) locations on the disk to document the growth of disturbances produced by the air pulses. Ensemble averages conditioned on the air pulses revealed wave packets that evolved in time and space. Two amplitudes of air pulses were used. The lower amplitude was verified to produced wave packets with linear amplitude characteristics. The space time evolution of the leading and trailing edges of the wave packets were followed past the critical radius for the absolute instability, r_{c_{A}}. With the lower amplitudes, the spreading of the disturbance wave packets did not continue to grow in time as r_{c_{A}} was approached. Rather, the spreading of the trailing edge of the wave packet decelerated and asymptotically approached a constant. This result supports previous linear DNS simulations where it was concluded that the absolute instability does not produce a global mode and that linear disturbance wave packets are dominated by the convective instability. The larger-amplitude disturbances were found to produce larger temporal spreading of the wave packets. This was accompanied by a sharp growth in the wave packet amplitude past r_{c_{A}}. Explanations for this are discussed.
Manzo, Valentina; Navarro, Orielle; Honda, Luis; Sánchez, Karen; Inés Toral, M; Richter, Pablo
2013-03-15
The microextraction of crystal violet (CV) from water samples into polydimethylsiloxane (PDMS) using the rotating disk sorptive extraction (RDSE) technique was performed. The extracting device was a small Teflon disk that had an embedded miniature magnetic stirring bar and a PDMS (560 μL) film attached to one side of the disk using double-sided tape. The extraction involves a preconcentration of CV into the PDMS, where the analyte is then directly quantified using solid phase spectrophotometry at 600 nm. Different chemical and extraction device-related variables were studied to achieve the best sensitivity for the determination. The optimum extraction was performed at pH 14 because under this condition, CV is transformed to the neutral and colorless species carbinol, which can be quantitatively transferred to the PDMS phase. Although the colorless species is the chemical form extracted in the PDMS, an intense violet coloration appeared in the phase because the -OH bond in the carbinol molecule is weakened through the formation of hydrogen bonds with the oxygen atoms of the PDMS, allowing the resonance between the three benzene rings to compensate for the charge deficit on the central carbon atom of the molecule. The accuracy and precision of the method were evaluated in river water samples spiked with 10 and 30 μg L(-1) of CV, yielding a relative standard deviation of 6.2% and 8.4% and a recovery of 98.4% and 99.4%, respectively. The method detection limit was 1.8 μg L(-1) and the limit of quantification was 5.4 μg L(-1), which can be decreased if the sample volume is increased.
Magnetohydrodynamic (MHD) flow of Cu-water nanofluid due to a rotating disk with partial slip
Energy Technology Data Exchange (ETDEWEB)
Hayat, Tasawar [Department of Mathematics, Quaid-I-Azam University 45320, Islamabad 44000 (Pakistan); Nonlinear Analysis and Applied Mathematics Research Group, Department of Mathematics, Faculty of Science, King Abdulaziz University, Jeddah 21589 (Saudi Arabia); Rashid, Madiha; Imtiaz, Maria, E-mail: mi-qau@yahoo.com [Department of Mathematics, Quaid-I-Azam University 45320, Islamabad 44000 (Pakistan); Alsaedi, Ahmed [Nonlinear Analysis and Applied Mathematics Research Group, Department of Mathematics, Faculty of Science, King Abdulaziz University, Jeddah 21589 (Saudi Arabia)
2015-06-15
This paper investigates MHD steady flow of viscous nanofluid due to a rotating disk. Water is treated as a base fluid and copper as nanoparticle. Nanofluid fills the porous medium. Effects of partial slip, viscous dissipation and thermal radiation are also considered. Similarity transformations reduce the nonlinear partial differential equations to ordinary differential equations. Flow and heat transfer characteristics are computed by HAM solutions. Also computations for skin friction coefficient and Nusselt number are presented and examined for pertinent parameters. It is noted that higher velocity slip parameter decreases the radial and azimuthal velocities while temperature decreases for larger values of the thermal slip parameter. Also the rate of heat transfer enhances when the nanoparticle volume fraction increases.
Generation of droplets to serpentine threads on a rotating compact-disk platform
Kar, Shantimoy; Joshi, Sumit; Chaudhary, Kaustav; Maiti, Tapas Kumar; Chakraborty, Suman
2015-12-01
We generate stable monodisperse droplets of nano-liter volumes and long serpentine liquid threads in a single, simple "Y"-shaped microchannel mounted on a rotationally actuated lab-on-a-compact-disk platform. Exploitation of Coriolis force offers versatile modus operandi of the present setup, without involving any design complications. Based on the fundamental understanding and subsequent analysis, we present scaling theories consistent with the experimental observations. We also outline specific applications of this technique, in the biological as well as in the physical domain, including digital polymerase chain reaction (PCR), controlled release of medical components, digital counting of colony forming units, hydrogel engineering, optical sensors and scaffolds for living tissues, to name a few.
Li, H; Finn, J M; Colgate, S A
2001-01-01
We study the evolution of a magnetic arcade that is anchored to an accretion disk and is sheared by the differential rotation of a Keplerian disk. By including an extremely low external plasma pressure at large distances, we obtain a sequence of axisymmetric magnetostatic equilibria and show that there is a fundamental difference between field lines that are affected by the plasma pressure and those are not (i.e., force-free). Force-free fields, while being twisted by the differential rotation of the disk, expand outward at an angle of $\\sim 60^\\circ$ away from the rotation axis, consistent with the previous studies. These force-free field lines, however, are enclosed by the outer field lines which originate from small disk radii and come back to the disk at large radii. These outer fields experience most of the twist, and they are also affected most by the external plasma pressure. At large cylindrical radial distances, magnetic pressure and plasma pressure are comparable so that any further radial expansion...
Experiments on the Flow of a Thin Liquid Film Over a Horizontal Stationary and Rotating Disk Surface
Ozar, B.; Cetegen, B. M.; Faghri, A.
2003-01-01
Experiments on characterization of thin liquid films flowing over stationary and rotating disk surfaces are described. The thin liquid film was created by introducing deionized water from a flow collar at the center of an aluminum disk with a known initial film thickness and uniform radial velocity. Radial film thickness distribution was measured using a non-intrusive laser light interface reflection technique that enabled the measurement of the instantaneous film thickness over a finite segment of the disk. Experiments were performed for a range of flow rates between 3.01pm and 15.01pm, corresponding to Reynolds numbers based on the liquid inlet gap height and velocity between 238 and 1,188. The angular speed of the disk was varied from 0 rpm to 300 rpm. When the disk was stationary, a circular hydraulic jump was present in the liquid film. The liquid-film thickness in the subcritical region (down-stream of the hydraulic jump) was an order of magnitude greater than that in the supercritical region (upstream of the hydraulic jump) which was of the order of 0.3 mm. As the Reynolds number increased, the hydraulic jump migrated toward the edge of the disk. In the case of rotation, the liquid-film thickness exhibited a maximum on the disk surface. The liquid-film inertia and friction influenced the inner region where the film thickness progressively increased. The outer region where the film thickness decreased was primarily affected by the centrifugal forces. A flow visualization study of the thin film was also performed to determine the characteristics of the waves on the free surface. At high rotational speeds, spiral waves were observed on the liquid film. It was also determined that the angle of the waves which form on the liquid surface was a function of the ratio of local radial to tangential velocity.
Directory of Open Access Journals (Sweden)
Mohammad Zamani Nejad
2014-01-01
Full Text Available Using disk form multilayers, a semi-analytical solution has been derived for determination of displacements and stresses in a rotating cylindrical shell with variable thickness under uniform pressure. The thick cylinder is divided into disk form layers form with their thickness corresponding to the thickness of the cylinder. Due to the existence of shear stress in the thick cylindrical shell with variable thickness, the equations governing disk layers are obtained based on first-order shear deformation theory (FSDT. These equations are in the form of a set of general differential equations. Given that the cylinder is divided into n disks, n sets of differential equations are obtained. The solution of this set of equations, applying the boundary conditions and continuity conditions between the layers, yields displacements and stresses. A numerical solution using finite element method (FEM is also presented and good agreement was found.
SPARC: Mass Models for 175 Disk Galaxies with Spitzer Photometry and Accurate Rotation Curves
Lelli, Federico; Schombert, James M
2016-01-01
We introduce SPARC (Spitzer Photometry & Accurate Rotation Curves): a sample of 175 nearby galaxies with new surface photometry at 3.6 um and high-quality rotation curves from previous HI/Halpha studies. SPARC spans a broad range of morphologies (S0 to Irr), luminosities (~5 dex), and surface brightnesses (~4 dex). We derive [3.6] surface photometry and study structural relations of stellar and gas disks. We find that both the stellar mass-HI mass relation and the stellar radius-HI radius relation have significant intrinsic scatter, while the HI mass-radius relation is extremely tight. We build detailed mass models and quantify the ratio of baryonic-to-observed velocity (Vbar/Vobs) for different characteristic radii and values of the stellar mass-to-light ratio (M/L) at [3.6]. Assuming M/L=0.5 Msun/Lsun (as suggested by stellar population models) we find that (i) the gas fraction linearly correlates with total luminosity, (ii) the transition from star-dominated to gas-dominated galaxies roughly correspond...
Zhang, Binbin; Chen, Jun; Jin, Long; Deng, Weili; Zhang, Lei; Zhang, Haitao; Zhu, Minhao; Yang, Weiqing; Wang, Zhong Lin
2016-06-28
Wireless traffic volume detectors play a critical role for measuring the traffic-flow in a real-time for current Intelligent Traffic System. However, as a battery-operated electronic device, regularly replacing battery remains a great challenge, especially in the remote area and wide distribution. Here, we report a self-powered active wireless traffic volume sensor by using a rotating-disk-based hybridized nanogenerator of triboelectric nanogenerator and electromagnetic generator as the sustainable power source. Operated at a rotating rate of 1000 rpm, the device delivered an output power of 17.5 mW, corresponding to a volume power density of 55.7 W/m(3) (Pd = P/V, see Supporting Information for detailed calculation) at a loading resistance of 700 Ω. The hybridized nanogenerator was demonstrated to effectively harvest energy from wind generated by a moving vehicle through the tunnel. And the delivered power is capable of triggering a counter via a wireless transmitter for real-time monitoring the traffic volume in the tunnel. This study further expands the applications of triboelectric nanogenerators for high-performance ambient mechanical energy harvesting and as sustainable power sources for driving wireless traffic volume sensors.
Bulge-forming galaxies with an extended rotating disk at z~2
Tadaki, Ken-ichi; Kodama, Tadayuki; Wuyts, Stijn; Wisnioski, Emily; Schreiber, Natascha M Förster; Burkert, Andreas; Lang, Philipp; Tacconi, Linda J; Lutz, Dieter; Belli, Sirio; Davies, Richard I; Hatsukade, Bunyo; Hayashi, Masao; Herrera-Camus, Rodrigo; Ikarashi, Soh; Inoue, Shigeki; Kohno, Kotaro; Koyama, Yusei; Mendel, J Trevor; Nakanishi, Kouichiro; Shimakawa, Rhythm; Suzuki, Tomoko L; Tamura, Yoichi; Tanaka, Ichi; Übler, Hannah; Wilman, Dave J
2016-01-01
We present 0".2-resolution Atacama Large Millimeter/submillimeter Array observations at 870 um for 25 Halpha-seleced star-forming galaxies (SFGs) around the main-sequence at z=2.2-2.5. We detect significant 870 um continuum emission in 16 (64%) of these SFGs. The high-resolution maps reveal that the dust emission is mostly radiated from a single region close to the galaxy center. Exploiting the visibility data taken over a wide $uv$ distance range, we measure the half-light radii of the rest-frame far-infrared emission for the best sample of 12 SFGs. We find nine galaxies to be associated with extremely compact dust emission with R_{1/2,870um}1e10 Msol/kpc^2 in several hundred Myr, i.e. by z~2. Moreover, ionized gas kinematics reveal that they are rotation-supported with an angular momentum as large as that of typical SFGs at z=1-3. Our results suggest bulges are commonly formed in extended rotating disks by internal processes, not involving major mergers.
Rotating bouncing disks, tossing pizza dough, and the behavior of ultrasonic motors.
Liu, Kuang-Chen; Friend, James; Yeo, Leslie
2009-10-01
Pizza tossing and certain forms of standing-wave ultrasonic motors (SWUMs) share a similar process for converting reciprocating input into continuous rotary motion. We show that the key features of this motion conversion process such as collision, separation and friction coupling are captured by the dynamics of a disk bouncing on a vibrating platform. The model shows that the linear or helical hand motions commonly used by pizza chefs and dough-toss performers for single tosses maximize energy efficiency and the dough's airborne rotational speed; on the other hand, the semielliptical hand motions used for multiple tosses make it easier to maintain dough rotation at the maximum speed. The system's bifurcation diagram and basins of attraction also provide a physical basis for understanding the peculiar behavior of SWUMs and provide a means to design them. The model is able to explain the apparently chaotic oscillations that occur in SWUMs and predict the observed trends in steady-state speed and stall torque as preload is increased.
Rotating bouncing disks, tossing pizza dough, and the behavior of ultrasonic motors
Liu, Kuang-Chen; Friend, James; Yeo, Leslie
2009-10-01
Pizza tossing and certain forms of standing-wave ultrasonic motors (SWUMs) share a similar process for converting reciprocating input into continuous rotary motion. We show that the key features of this motion conversion process such as collision, separation and friction coupling are captured by the dynamics of a disk bouncing on a vibrating platform. The model shows that the linear or helical hand motions commonly used by pizza chefs and dough-toss performers for single tosses maximize energy efficiency and the dough’s airborne rotational speed; on the other hand, the semielliptical hand motions used for multiple tosses make it easier to maintain dough rotation at the maximum speed. The system’s bifurcation diagram and basins of attraction also provide a physical basis for understanding the peculiar behavior of SWUMs and provide a means to design them. The model is able to explain the apparently chaotic oscillations that occur in SWUMs and predict the observed trends in steady-state speed and stall torque as preload is increased.
Spread of Matter over a Neutron-Star Surface During Disk Accretion: Deceleration of Rapid Rotation
Sunyaev, R A
2011-01-01
The problem of disk accretion onto the surface of a neutron star with a weak magnetic field at a luminosity exceeding several percent of Eddington is reduced to the problem of the braking of a hypersonic flow with a velocity that is 0.4-0.5 of the speed of light above the base of the spreading layer -- a dense atmosphere made up of previously fallen matter. We show that turbulent braking in the Prandtl-Karman model with universally accepted coefficients for terrestrial conditions and laboratory experiments and a ladder of interacting gravity waves in a stratified quasi-exponential atmosphere at standard Richardson numbers lead to a spin-up of the massive zone that extends to the ocean made up of a plasma with degenerate electrons. Turbulent braking in the ocean at the boundary with the outer solid crust reduces the rotation velocity to the solid-body rotation velocity of the star. This situation should lead to strong heating of deep atmospheric layers and to the switch-off of the explosive helium burning mech...
Thermoelastic Correction in the Torsion Pendulum Experiment
Institute of Scientific and Technical Information of China (English)
胡忠坤; 王雪黎; 罗俊
2001-01-01
The thermoelastic effect of the suspension fibre in the torsion pendulum experiment with magnetic damping was studied. The disagreement in the oscillation periods was reduced by one order of magnitude through monitoring the ambient temperature and thermoelastic correction. We also found that the period on uncertainty due to noise increases with the amplitude attenuation after thermoelastic correction.
Coupling in poroelasticity and thermoelasticity
Energy Technology Data Exchange (ETDEWEB)
Zimmerman, R.W. [Imperial Coll. of Science, Technology and Medicine, T.H. Huxley School of Environment, Earth Sciences and Engineering, London (United Kingdom)
2000-02-01
A brief derivation is given of the equations of linearised poroelasticity and thermoelasticity. Dimensionless parameters are presented that quantify the strength of the coupling between mechanical and hydraulic (or thermal) effects. The poroelastic coupling parameter is shown to be the product of the Biot coefficient and the Skempton coefficient; the thermoelastic coupling parameter can be interpreted as the ratio of stored elastic strain energy to stored thermal energy. For liquid-saturated rocks, the poroelastic coupling parameter usually lies between 0.1 and 1.0, which means that the mechanical deformation has a strong influence on the pore pressure. The thermoelastic coupling parameter is usually very small, so that, although the temperature field influences the stresses and strains, the stresses and strains do not appreciably influence the temperature field. (Author)
Clem, Michelle M.; Woike, Mark R.; Abdul-Aziz, Ali
2014-04-01
The Aeronautical Sciences Project under NASA's Fundamental Aeronautics Program is interested in the development of novel measurement technologies, such as optical surface measurements for the in situ health monitoring of critical constituents of the internal flow path. In situ health monitoring has the potential to detect flaws, i.e. cracks in key components, such as engine turbine disks, before the flaws lead to catastrophic failure. The present study, aims to further validate and develop an optical strain measurement technique to measure the radial growth and strain field of an already cracked disk, mimicking the geometry of a sub-scale turbine engine disk, under loaded conditions in the NASA Glenn Research Center's High Precision Rotordynamics Laboratory. The technique offers potential fault detection by imaging an applied high-contrast random speckle pattern under unloaded and loaded conditions with a CCD camera. Spinning the cracked disk at high speeds (loaded conditions) induces an external load, resulting in a radial growth of the disk of approximately 50.0-μm in the flawed region and hence, a localized strain field. When imaging the cracked disk under static conditions, the disk will be undistorted; however, during rotation the cracked region will grow radially, thus causing the applied particle pattern to be `shifted'. The resulting particle displacements between the two images is measured using the two-dimensional cross-correlation algorithms implemented in standard Particle Image Velocimetry (PIV) software to track the disk growth, which facilitates calculation of the localized strain field. A random particle distribution is adhered onto the surface of the cracked disk and two bench top experiments are carried out to evaluate the technique's ability to measure the induced particle displacements. The disk is shifted manually using a translation stage equipped with a fine micrometer and a hotplate is used to induce thermal growth of the disk, causing the
Numerical modeling and design of a disk-type rotating permanent magnet induction pump
Energy Technology Data Exchange (ETDEWEB)
Koroteeva, E., E-mail: koroteeva@physics.msu.ru [Institute of Physics of University of Latvia, Salaspils 2169 (Latvia); Lomonosov Moscow State University, Moscow 119991 (Russian Federation); Ščepanskis, M. [Laboratory for Mathematical Modelling of Environmental and Technological Processes, University of Latvia, Rīga 1002 (Latvia); Bucenieks, I.; Platacis, E. [Institute of Physics of University of Latvia, Salaspils 2169 (Latvia)
2016-05-15
Highlights: • The design and performance of a disk-type induction pump are described. • A 3D numerical model based on an iterative coupling between EM and hydrodynamic solvers is developed. • The model is verified by comparing with the experiments in a Pb-Bi loop facility. • The suggestions are given to estimate the pump performance in a Pb-Li loop at high pressures. - Abstract: Electromagnetic induction pumps with rotating permanent magnets appear to be the most promising devices to transport liquid metals in high-temperature applications. Here we present a numerical methodology to simulate the operation of one particular modification of these types of pumps: a disk-type induction pump. The numerical model allows for the calculation and analysis of the flow parameters, including the pressure–flow rate characteristics of the pump. The simulations are based on an iterative fully coupled scheme for electromagnetic and hydrodynamic solvers. The developed model is verified by comparing with experimental data obtained using a Pb-Bi loop test facility, for pressures up to 4 bar and flow rates up to 9 kg/s. The verified model is then expanded to higher pressures, beyond the limits of the experimental loop. Based on the numerical simulations, suggestions are given to extrapolate experimental data to higher (industrially important) pressure ranges. Using the numerical model and analytical estimation, the pump performance for the Pb-Li loop is also examined, and the ability of the designed pump to develop pressure heads over 6 bar and to provide flow rates over 15 kg/s is shown.
Thermoelasticity with Finite Wave Speeds
Ignaczak, Józef
2009-01-01
Generalized dynamic thermoelasticity is a vital area of research in continuum mechanics, free of the classical paradox of infinite propagation speeds of thermal signals in Fourier-type heat conduction. Besides that paradox, the classical dynamic thermoelasticity theory offers either unsatisfactory or poor descriptions of a solid's response at low temperatures or to a fast transient loading (say, due to short laser pulses). Several models have been developed and intensively studiedover the past four decades, yet this book, which aims to provide a point of reference in the field, is the first mo
Problems and solutions in thermoelasticity and magneto-thermoelasticity
Das, B
2017-01-01
This book presents problems and solutions of the mathematical theories of thermoelasticity and magnetothermoelasticity. The classical, coupled and generalized theories are solved using the eigenvalue methodology. Different methods of numerical inversion of the Laplace transform are presented and their direct applications are illustrated. The book is very useful to those interested in continuum mechanics.
The optimization of Blister Disk geometry for mixing performance in co-rotating twin-screw extruder
Matsumoto, Koki; Kayamori, Natsuki; Tanaka, Tatsuya; Arao, Yoshihiko
2015-05-01
Extensional flow has been taken notice as the more efficient solution for improving the dispersion of nanocomposites than shear flow. One of the production processes of nanocomposites is melt extrusion with co-rotating twin-screw extruder (TSE) which is superior in terms of productivity and mixing performance. Then, we focused on "Blister Disk" which had many small holes for generating the extensional flow. However, the influences on the mixing performance by changing the geometry of Blister Disk have not been investigated as far as we know. Therefore, the objective of this study is the optimization of Blister Disk geometry (e.g. hole numbers, hole diameter and disk length) for improving the dispersion of nanocomposites. Primary, the extensional flow state was investigated at the Blister Disk with FEM analysis. Secondly, to validate the simulation results experimentally, the polypropylene reinforced multi-walled carbon nanotube (PP/CNT nanocomposite) was used as the model of nanocomposite, and the dispersion state of CNT was investigated by morphological observation. As the result of these experiments, the better dispersion state of CNT was obtained as total permeation area and shorter hole length of Blister Disk was smaller because extensional and shear stress were increased.
DEFF Research Database (Denmark)
Bayat, M.; Sahari, B. B.; Saleem, M.
2012-01-01
In this paper the elastic solutions of a disk composed of FGM – Functionaly Graded Material, is presented.......In this paper the elastic solutions of a disk composed of FGM – Functionaly Graded Material, is presented....
Noever, David A.; Koczor, Ronald J.; Roberson, Rick
1998-01-01
We have previously reported results using a high precision gravimeter to probe local gravity changes in the neighborhood of large bulk-processed high-temperature superconductors. Podkietnov, et al (Podkietnov, E. and Nieminen, R. (1992) A Possibility of Gravitational Force Shielding by Bulk YBa2 Cu3 O7-x Superconductor, Physica C, C203:441-444.) have indicated that rotating AC fields play an essential role in their observed distortion of combined gravity and barometric pressure readings. We report experiments on large (15 cm diameter) bulk YBCO ceramic superconductors placed in the core of a three-phase, AC motor stator. The applied rotating field produces up to a 12,000 revolutions per minute magnetic field. The field intensity decays rapidly from the maximum at the outer diameter of the superconducting disk (less than 60 Gauss) to the center (less than 10 Gauss). This configuration was applied with and without a permanent DC magnetic field levitating the superconducting disk, with corresponding gravity readings indicating an apparent increase in observed gravity of less than 1 x 10(exp -6)/sq cm, measured above the superconductor. No effect of the rotating magnetic field or thermal environment on the gravimeter readings or on rotating the superconducting disk was noted within the high precision of the observation. Implications for propulsion initiatives and power storage flywheel technologies for high temperature superconductors will be discussed for various spacecraft and satellite applications.
The rapid formation of a large rotating disk galaxy three billion years after the Big Bang.
Genzel, R; Tacconi, L J; Eisenhauer, F; Schreiber, N M Förster; Cimatti, A; Daddi, E; Bouché, N; Davies, R; Lehnert, M D; Lutz, D; Nesvadba, N; Verma, A; Abuter, R; Shapiro, K; Sternberg, A; Renzini, A; Kong, X; Arimoto, N; Mignoli, M
2006-08-17
Observations and theoretical simulations have established a framework for galaxy formation and evolution in the young Universe. Galaxies formed as baryonic gas cooled at the centres of collapsing dark-matter haloes; mergers of haloes and galaxies then led to the hierarchical build-up of galaxy mass. It remains unclear, however, over what timescales galaxies were assembled and when and how bulges and disks--the primary components of present-day galaxies--were formed. It is also puzzling that the most massive galaxies were more abundant and were forming stars more rapidly at early epochs than expected from models. Here we report high-angular-resolution observations of a representative luminous star-forming galaxy when the Universe was only 20% of its current age. A large and massive rotating protodisk is channelling gas towards a growing central stellar bulge hosting an accreting massive black hole. The high surface densities of gas, the high rate of star formation and the moderately young stellar ages suggest rapid assembly, fragmentation and conversion to stars of an initially very gas-rich protodisk, with no obvious evidence for a major merger.
IRAS 16293-2422: Evidence for Infall onto a Counter-Rotating Protostellar Accretion Disk
Remijan, A J; Remijan, Anthony J.
2006-01-01
We report high spatial resolution VLA observations of the low-mass star-forming region IRAS 16293-2422 using four molecular probes: ethyl cyanide (CH$_3$CH$_2$CN), methyl formate (CH$_3$OCHO), formic acid (HCOOH), and the ground vibrational state of silicon monoxide (SiO). Ethyl cyanide emiss ion has a spatial scale of $\\sim20''$ and encompasses binary cores A and B as determined by continuum emission peaks. Surrounded by formic acid emission, methyl formate emission has a spatial scale of $\\sim6''$and is confined to core B. SiO emission shows two velocity components with spatial scales less than 2$''$ that map $\\sim2''$ northeast of the A and B symmetry axis. The redshifted SiO is $\\sim2''$ northwest of blueshifted SiO along a position angle of $\\sim135^o$ which is approximately parallel to the A and B symmetry axis. We interpret the spatial position offset in red and blueshifted SiO emission as due to rotation of a protostellar accretion disk and we derive $\\sim$1.4 M$_{\\odot}$ interior to the SiO emission....
Stauffer, John; Akeson, Rachel; Allen, Lori; Ardila, David; Barrado, David; Bayo, Amelia; Bouvier, Jerome; Calvet, Nuria; Carey, Sean; Carpenter, John; Ciardi, David; Covey, Kevin; Favata, Fabio; Flaherty, Kevin; Forbrich, Jan; Guieu, Sylvain; Gutermuth, Rob; Hartmann, Lee; Hillenbrand, Lynne; Hora, Joe; McCaughrean, Mark; Megeath, Tom; Morales-Calderon, Maria; Muzerolle, James; Plavchan, Peter; Rebull, Luisa; Skrutskie, Mike; Smith, Howard; Song, Inseok; Stapelfeldt, Karl; Sung, Hwankyung; Terebey, Susan; Vrba, Fred; Werner, Mike; Whitney, Barbara; Winston, Elaine; Wood, Kenny
2008-12-01
Spitzer/IRAC in the warm mission is the only facility now existing or planned capable of carrying out an extensive, accurate time series photometric monitoring survey of star-forming regions in the thermal infrared. The demonstrated sensitivity and stability of IRAC allows measurement of the relative fluxes of YSO's down to the substellar mass limit to 1-2% accuracy in star-forming regions out to >500 pc. We propose a time series monitoring exploration science survey of the Orion Nebula Cluster and 11 very young, populous embedded star-forming cores which will provide >D 80 epochs of data for > 1500 YSO's. We will complement these observations with contemporaneous optical and near-IR monitoring data in order to allow comparison of the phase, amplitude and light-curve shape as a function of wavelength. These data will allow us to: (a) provide otherwise unobtainable constraints on the structure of the inner disks in Class I and II YSOs - and hence, perhaps, provide clues to the formation and migration of planets at young ages; (b) measure the short and long-term stability of hot spots on the surfaces of YSO's of all evolutionary stages; and (c) determine rotational periods for the largest sample to date of Class I YSO's and hence obtain the best measure of the initial angular momentum distribution of young stars.
Institute of Scientific and Technical Information of China (English)
M. Turkyilmazoglu
2012-01-01
The present paper is concerned with a class of exact solutions to the steady Navier-Stokes equations for the incompressible Newtonian viscous electrically conducting fluid flow due to a porous disk rotating with a constant angular speed.The three-dimensional hydromagnetic equations of motion are treated analytically to obtained exact solutions with the inclusion of suction and injection.The well-known thinning/thickening flow field effect of the suction/injection is better understood from the constructed closed form velocity equations.Making use of this solution,analytical formulas for the angular velocity components as well as for the permeable wall shear stresses are derived.Interaction of the resolved flow field with the surrounding temperature is further analyzed via the energy equation.The temperature field is shown to accord with the dissipation and the Joule heating.As a result,exact formulas are obtained for the temperature field which take different forms corresponding to the condition of suction or injection imposed on the wall.
Effects of Thermal Radiation on Hydromagnetic Flow due to a Porous Rotating Disk with Hall Effect
Directory of Open Access Journals (Sweden)
S.P Anjali Devi
2012-01-01
Full Text Available Radiation effect on steady laminar hydromagnetic flow of a viscous, Newtonian and electrically conducting fluid past a porous rotating infinite disk is studied taking Hall current into account. The system of axisymmetric nonlinear partial differential equations governing the MHD flow and heat transfer are reduced to nonlinear ordinary differential equations by introducing suitable similarity variables introduced by von Karman and the resulting nonlinear equations are solved numerically using Runge-Kutta based shooting method. A parametric study of all parameters involved was conducted and a representative set of results showing the effect of the magnetic field, the radiation parameter, the uniform suction/injection parameter and Hall parameter are illustrated graphically. The numerical values of the radial and tangential skin-friction coefficient and Nusselt number are calculated and displayed in the tables showing the effects of various parameters. Finally, a good comparison between the present numerical predictions and the previously published data are presented in the absence of magnetic field and radiation.
MHD flow of Burger’s fluid over an off-centered rotating disk in a porous medium
Directory of Open Access Journals (Sweden)
Najeeb Alam Khan
2015-08-01
Full Text Available In this study, off-centered stagnation flow of three dimensional Burger’s fluid over an infinite rotating disk in a porous medium with a uniform magnetic field, which is applying normal to the disk, is investigated. A uniform suction/injection is applied through the surface of the porous disk. The structure has been modeled in the form of ordinary differential equations, which are reduced from partial differential equations by using the similarity transformation. Analytical solution is obtained by non-perturbation technique of homotopy analysis method (HAM. The influence of non-dimensional parameters on velocity profile is presented in graphical form and the numerical comparison is made with the viscous fluid as a special case.
Richter, Pablo; Cañas, Alejandro; Muñoz, Carlos; Leiva, Claudio; Ahumada, Inés
2011-06-10
A novel and very simple microextraction approach for pre-concentration and direct solid phase spectrophotometric measurement has been developed for the determination of chromogenic analytes. The model analyte to assess this approach was the chromophore malachite green (MG). The analyte was extracted from water samples onto a small rotating disk made of Teflon containing a sorbent phase of polydimethylsiloxane (PDMS) on one of its surfaces. We refer to the extraction procedure as rotating disk sorptive extraction (RDSE). After extraction, the sorbent phase with the concentrated analyte was separated from the Teflon disk and used directly for MG determination by solid phase spectrophotometry at 624 nm, without the necessity of a desorption step. Chemical and extraction variables such as concentration of sodium sulfate, pH, disk rotational velocity, extraction time, and temperature were studied in order to establish the best conditions for extraction. Under optimum conditions, the extraction of MG was carried out in 18 min and 90 min, for sample volumes of 100mL or 1000 mL, respectively. The detection limit, based on three times the standard deviation of the blank phase (3σ(b)), was 1.4 μg L⁻¹ and the repeatability, expressed as relative standard deviation (RSD), for 20 μg L⁻¹ MG was 8.1%. This study also applied the method to real samples, obtaining quantitative recovery (mean recovery of 99.3%). The PDMS phases could be reused after desorbing the MG into methanol for 3h. Replacement of the PDMS film onto the disk is very easy and low cost.
Rao, P. V.; Rao, N. S. L.; Rao, B. C. S.
1982-01-01
The cavitation erosion behavior including the initiation, dynamics and mechanism of damage process on perspex and epoxy resin specimens tested in a rotating disk device were discussed with respect to exposure time. The inception of erosion always took place at the location nearest to the center of rotation of the disk. Subsequently, as exposure time increased, erosion initiated at other locations as well. Light optical photographs and scanning electron micrographs clearly indicate that most of the material loss appears to occur form the networks of cracks due to their interaction and pits indicate particle debris. The optical degradation (loss of transmittance) on perspex was observed to be more on the rear side than on the front side.
MHD UNSTEADY FLOWS DUE TO NON-COAXIAL ROTATIONS OF A DISK AND A FLUID AT INFINITY
Institute of Scientific and Technical Information of China (English)
T.HAYAT; S.MUMTAZ; R.ELLAHI
2003-01-01
Exact analytical solution for flows of an electrically conducting fluid over an infinite oscillatory disk in the presence of a uniform transverse magnetic field is constructed.Both the disk and the fluid are in a state of non-coaxial rotation.Such a flow model has a great significance not only due to its own theoretical interest,but also due to applications to geophysics and engineering.The resulting initial value problem has been solved analytically by applying the Laplace transform technique and the explicit expressions for the velocity for steady and unsteady cases have been established.The analysis of the obtained results shows that the flow field is appreciably influenced by the applied magnetic field,the frequency and rotation parameters.
Partial slip effect in flow of magnetite-Fe3O4 nanoparticles between rotating stretchable disks
Hayat, Tasawar; Qayyum, Sumaira; Imtiaz, Maria; Alzahrani, Faris; Alsaedi, Ahmed
2016-09-01
This paper addresses the flow of magnetic nanofluid (ferrofluid) between two parallel rotating stretchable disks with different rotating and stretching velocities. Water based fluid comprising magnetite-Fe3O4 nanoparticles is addressed. Velocity slip and temperature jump at solid-fluid interface are also taken into account. Appropriate transformations reduce the nonlinear partial differential system to ordinary differential system. Convergent series solutions are obtained. Effects of various pertinent parameters on the velocity and temperature profiles are shown and evaluated. Computations for skin friction coefficient and Nusselt number are presented and examined for the influence of involved parameters. It is noted that tangential velocity of fluid decreases for larger velocity slip parameter. Fluid temperature also reduces for increasing value of thermal slip parameter. Surface drag force and heat transfer rate at lower disk are enhanced when magnetic field strength is increased.
MHD UNSTEADY FLOWS DUE TO NON—COAXIAL ROTATIONS OF A DISK AND A FLUID AT INFINITY
Institute of Scientific and Technical Information of China (English)
T.HAYAT
2003-01-01
Exact analytical solution for flows of an electrically conducting fluid over an infiniteoscillatory disk in the presence of a uniform transverse magnetic field is constructed. Both the disk andthe fluid are in a state of non-coaxial rotation. Such a flow model has a great significance not only clueto its own theoretical interest, but also clue to applications to geophysics and engineering. The resultinginitial value problem has been solved analytically by applying the Laplace transform technique and theexplicit expressions for the velocity for steady and unsteady cases have been established. The analysisof the obtained results shows that the flow field is appreciably influenced by the applied magnetic field,the frequency and rotation parameters.
Papaloizou, J C B
2004-01-01
We carry out a general study of the stability of astrophysical flows that appear steady in a uniformly rotating frame. Such a flow might correspond to a stellar pulsation mode or an accretion disk with a free global distortion giving it finite eccentricity. We consider perturbations arbitrarily localized in the neighbourhood of unperturbed fluid streamlines.When conditions do not vary around them, perturbations take the form of oscillatory inertial or gravity modes. However, when conditions do vary so that a circulating fluid element is subject to periodic variations, parametric instability may occur. For nearly circular streamlines, the dense spectra associated with inertial or gravity modes ensure that resonance conditions can always be satisfied when twice the period of circulation round a streamline falls within. We apply our formalism to a differentially rotating disk for which the streamlines are Keplerian ellipses, with free eccentricity up to 0.7, which do not precess in an inertial frame. We show tha...
Mid-IR Observations of T Tauri stars: Probing the Star-Disk Connection in Rotational Evolution
Kundurthy, P; Robberto, M; Beckwith, S V W; Herbst, T; Kundurthy, Praveen; Meyer, Michael R.; Robberto, Massimo; Beckwith, Steven V.W.; Herbst, Tom
2006-01-01
We present mid-IR N-band $(\\lambda_{eff} = 10.2\\micron)$ photometry of a carefully selected sample of T Tauri stars thought to be single from the Taurus-Auriga molecular cloud. Infrared excesses in these stars are generally attributed to circumstellar dust-disks. Combining observations at 2.16$\\micron$ (K$_{s}$-band) and 10.2$\\micron$ (N-band) we probe a region in the circumstellar dust-disk from a few stellar radii through the terrestrial planet zone (0.02-1.0AU). By analyzing the distribution of the $(K_{s}-N)$ color index with respect to previously measured photometric rotation periods we investigate what role circumstellar disks play in the rotational evolution of the central star. The resulting positive correlation between these two variables is consistent with the notion that a star-disk interaction facilitates the regulation of angular momentum during the T Tauri stage. We also demonstrate, how including non-single stars in such an analysis will \\textit{weaken} any correlation in the relation between $...
Energy Technology Data Exchange (ETDEWEB)
Hayat, Tasawar [Department of Mathematics, Quaid-I-Azam University 45320, Islamabad 44000 (Pakistan); Nonlinear Analysis and Applied Mathematics (NAAM) Research Group, Department of Mathematics, Faculty of Science, King Abdulaziz University, Jeddah 21589 (Saudi Arabia); Qayyum, Sumaira [Department of Mathematics, Quaid-I-Azam University 45320, Islamabad 44000 (Pakistan); Imtiaz, Maria, E-mail: mi_qau@yahoo.com [Department of Mathematics, Quaid-I-Azam University 45320, Islamabad 44000 (Pakistan); Alzahrani, Faris; Alsaedi, Ahmed [Nonlinear Analysis and Applied Mathematics (NAAM) Research Group, Department of Mathematics, Faculty of Science, King Abdulaziz University, Jeddah 21589 (Saudi Arabia)
2016-09-01
This paper addresses the flow of magnetic nanofluid (ferrofluid) between two parallel rotating stretchable disks with different rotating and stretching velocities. Water based fluid comprising magnetite-Fe{sub 3}O{sub 4} nanoparticles is addressed. Velocity slip and temperature jump at solid–fluid interface are also taken into account. Appropriate transformations reduce the nonlinear partial differential system to ordinary differential system. Convergent series solutions are obtained. Effects of various pertinent parameters on the velocity and temperature profiles are shown and evaluated. Computations for skin friction coefficient and Nusselt number are presented and examined for the influence of involved parameters. It is noted that tangential velocity of fluid decreases for larger velocity slip parameter. Fluid temperature also reduces for increasing value of thermal slip parameter. Surface drag force and heat transfer rate at lower disk are enhanced when magnetic field strength is increased. - Highlights: • Flow and heat transfer of ferrofluid induced by two stretchable rotating disks with velocity and thermal slips are explored. • Fluid temperature increases for larger solid volume fraction of nanofluid. • Heat transfer rate decreases for increasing values of thermal slip parameter.
Venuti, L.; Bouvier, J.; Cody, A. M.; Stauffer, J. R.; Micela, G.; Rebull, L. M.; Alencar, S. H. P.; Sousa, A. P.; Hillenbrand, L. A.; Flaccomio, E.
2017-02-01
Context. The low spin rates measured for solar-type stars at an age of a few Myr ( 10% of the break-up velocity) indicate that some mechanism of angular momentum regulation must be at play in the early pre-main sequence. This may be associated with magnetospheric accretion and star-disk interaction, as suggested by observations that disk-bearing objects (CTTS) are slower rotators than diskless sources (WTTS) in young star clusters. Aims: We characterize the rotation properties for members of the star-forming region NGC 2264 ( 3 Myr) as a function of mass, and investigate the accretion-rotation connection at an age where about 50% of the stars have already lost their disks. Methods: We examined a sample of 500 cluster members (40% with disks, 60% without disks), distributed in mass between 0.15 and 2 M⊙, whose photometric variations were monitored in the optical for 38 consecutive days with the CoRoT space observatory. Light curves were analyzed for periodicity using three different techniques: the Lomb-Scargle periodogram, the autocorrelation function and the string-length method. Periods were searched in the range between 0.17 days (i.e., 4 h, twice the data sampling adopted) and 19 days (half the total time span). Period detections were confirmed using a variety of statistical tools (false alarm probability, Q-statistics), as well as visual inspection of the direct and phase-folded light curves. Results: About 62% of sources in our sample were found to be periodic; the period detection rate is 70% among WTTS and 58% among CTTS. The vast majority of periodic sources exhibit rotational periods shorter than 13 d. The period distribution obtained for the cluster consists of a smooth distribution centered around P = 5.2 d with two peaks, located respectively at P = 1-2 d and at P = 3-4 d. A separate analysis of the rotation properties for CTTS and WTTS indicates that the P = 1-2 d peak is associated with the latter, while both groups contribute to the P = 3-4 d peak
Prieto, Carlos Allende; Cropper, Mark
2016-01-01
Previous studies have found that the Galactic rotation velocity-metallicity (V-[Fe/H]) relations for the thin and thick disk populations show negative and positive slopes, respectively. The first Gaia Data Release includes the Tycho-Gaia Astrometric Solution (TGAS) information, which we use to analyze the V-[Fe/H] relation for a strictly selected sample with high enough astrometric accuracy. We aim to arrive at an explanation for the slopes of the V-[Fe/H] relationship. We measure the V-[Fe/H] relation for thin and thick disk stars classified on the basis of their [$\\alpha$/Fe] and [Fe/H] abundances. We find dV/d[Fe/H]= -18 +/- 2 km/s/dex for stars in the thin disk and dV/d[Fe/H]= +23 +/- 10 km/s/dex for thick disk stars, so we confirm the different signs for the slopes. The negative value of dV/d[Fe/H] for thick disk stars is consistent with previous studies, but the combination of TGAS and APOGEE data provide higher precision, even though systematic errors could exceed +/-5 km/s/dex . Our average measuremen...
Singh Bhatia, Tanayveer; Mukhopadhyay, Banibrata
2016-10-01
The emergence of turbulence in shear flows is a well-investigated field. Yet, there are some lingering issues that have not been sufficiently resolved. One of them is the apparent contradiction between the results of linear stability analysis showing a flow to be stable and yet experiments and simulations proving it to be otherwise. There is some success, in particular in astrophysical systems, based on magnetorotational instability (MRI), revealing turbulence. However, MRI requires the system to be weakly magnetized. Such instability is neither a feature of general magnetohydrodynamic (MHD) flows nor revealed in purely hydrodynamic flows. Nevertheless, linear perturbations of such flows are non-normal in nature, which argues for a possible origin of nonlinearity therein. The concept behind this is that non-normal perturbations could produce huge transient energy growth (TEG), which may lead to nonlinearity and further turbulence. However, so far, non-normal effects in shear flows have not been explored much in the presence of magnetic fields. In this spirit, here we consider the perturbed viscoresistive MHD shear flows with rotation in general. Basically we recast the magnetized momentum balance and associated equations into the magnetized version of Orr-Sommerfeld and Squire equations and their magnetic analogs. We also assume the flow to be incompressible and in the presence of Coriolis effect solve the equations using a pseudospectral eigenvalue approach. We investigate the possible emergence of instability and large TEG in three different types of flows, namely, the Keplerian flow, the Taylor-Couette (or constant angular momentum) flow, and plane Couette flow. We show that, above a certain value of magnetic field, instability and TEG both stop occurring. We also show that TEG is maximum in the vicinity of regions of instability in the wave number space for a given magnetic field and Reynolds number, leading to nonlinearity and plausible turbulence. Rotating
Radu, Aleksandar; Telting-Diaz, Martin; Bakker, Eric
2003-12-15
The extent of optimization of the lower detection limit of ion-selective electrodes (ISEs) can be assessed with an elegant new method. At the detection limit (i.e., in the absence of primary ions in the sample), one can observe a reproducible change in the membrane potential upon alteration of the aqueous diffusion layer thickness. This stir effect is predicted to depend on the composition of the inner solution, which is known to influence the lower detection limit of the potentiometric sensor dramatically. For an optimized electrode, the stir effect is calculated to be exactly one-half the value of the case when substantial coextraction occurs at the inner membrane side. In contrast, there is no stir effect when substantial ion exchange occurs at the inner membrane side. Consequently, this experimental method can be used to determine how well the inner filling solution has been optimized. A rotating disk electrode was used in this study because it provides adequate control of the aqueous diffusion layer thickness. Various ion-selective membranes with a variety of inner solutions that gave different calculated concentrations of the complex at the inner membrane side were studied to evaluate this principle. They contained the well-examined silver ionophore O,O' '-bis[2-(methylthio)ethyl]-tert-butylcalix[4]arene, the potassium ionophore valinomycin, or the iodide carrier [9]mercuracarborand-3. Stir effects were determined in different background solutions and compared to theoretical expectations. Correlations were good, and the results encourage the use of such stir-effect measurements to optimize ISE compositions for real-world applications. The technique was also found to be useful in estimating the level of primary ion impurities in the sample. For an iodide-selective electrode measured in phosphoric acid, for example, apparent iodide impurity levels were calculated as 5 x 10(-10) M.
Photocatalytic degradation of phenol, chlorinated phenols, and lindane was evaluated in a continuous flow TiOz rotating disk photocatalytic reactor (RDPR). The RDPR operated at a hydraulic residence time of 0.25 day and at a disk angular velocity of 12 rpm. At low molar feed conc...
Donmez, Orhan
The shocked wave created on the accretion disk after different physical phenomena (accretion flows with pressure gradients, star-disk interaction etc.) may be responsible observed Quasi Periodic Oscillations (QPOs) in X-ray binaries. We present the set of characteristics frequencies associated with accretion disk around the rotating and non-rotating black holes for one particle case. These persistent frequencies are results of the rotating pattern in an accretion disk. We compare the frequency's from two different numerical results for fluid flow around the non-rotating black hole with one particle case. The numerical results are taken from Refs. 1 and 2 using fully general relativistic hydrodynamical code with non-selfgravitating disk. While the first numerical result has a relativistic tori around the black hole, the second one includes one-armed spiral shock wave produced from star-disk interaction. Some physical modes presented in the QPOs can be excited in numerical simulation of relativistic tori and spiral waves on the accretion disk. The results of these different dynamical structures on the accretion disk responsible for QPOs are discussed in detail.
Thermoelastic wave propagation in laminated composites plates
Directory of Open Access Journals (Sweden)
Verma K. L.
2012-12-01
Full Text Available The dispersion of thermoelastic waves propagation in an arbitrary direction in laminated composites plates is studied in the framework of generalized thermoelasticity in this article. Three dimensional field equations of thermoelasticity with relaxation times are considered. Characteristic equation is obtained on employing the continuity of displacements, temperature, stresses and thermal gradient at the layers’ interfaces. Some important particular cases such as of free waves on reducing plates to single layer and the surface waves when thickness tends to infinity are also discussed. Uncoupled and coupled thermoelasticity are the particular cases of the obtained results. Numerical results are also obtained and represented graphically.
Directory of Open Access Journals (Sweden)
Liyong Hu
2015-03-01
Full Text Available When a soft polishing tool is compressed on a stiff workpiece of curved surface, the contact area is a piece of the curved surface. In the process of aspheric surface polishing, the machining speed is always provided by the rotational speed of the spindle of a computer numerical control lathe. Yet, the polishing tool is usually made rotating to remove cutting scraps and broken abrasives from the contact area. The rotational speed of the polishing tool would change the distribution state of the relative speed in the whole contact area, and it would definitely change the volume of material removal in the surface of the workpiece. This article studies how the rotational speed of the polishing tool changes the distribution state of the relative speed in the whole contact area and material removal in the volume of the surface of the workpiece. The computing results show that the volume of material removal increases with the increase in both the rotational speed of polishing disk and the rotational speed of lathe spindle, but the polishing quality is totally not in this case.
Directory of Open Access Journals (Sweden)
Hayat Tasawar
2003-01-01
Full Text Available The governing equations for the unsteady flow of a uniformly conducting incompressible fourth-grade fluid due to noncoaxial rotations of a porous disk and the fluid at infinity are constructed. The steady flow of the fourth-grade fluid subjected to a magnetic field with suction/blowing through the disk is studied. The nonlinear ordinary differential equations resulting from the balance of momentum and mass are discretised by a finite-difference method and numerically solved by means of an iteration method in which, by a coordinate transformation, the semi-infinite physical domain is converted to a finite calculation domain. In order to solve the fourth-order nonlinear differential equations, asymptotic boundary conditions at infinity are augmented. The manner in which various material parameters affect the structure of the boundary layer is delineated. It is found that the suction through the disk and the magnetic field tend to thin the boundary layer near the disk for both the Newtonian fluid and the fourth-grade fluid, while the blowing causes a thickening of the boundary layer with the exception of the fourth-grade fluid under strong blowing. With the increase of the higher-order viscosities, the boundary layer has the tendency of thickening.
Batygin, Konstantin
2013-01-01
The presence of giant gaseous planets that reside in close proximity to their host stars may be a consequence of large-scale radial migration through the proto-planetary nebulae. Within the context of this picture, significant orbital obliquities characteristic of a substantial fraction of such planets can be attributed to external torques that perturb the disks out of alignment with the spin axes of their host stars. Therefore, the acquisition of orbital obliquity exhibits sensitive dependence on the physics of disk-star interactions. Here, we analyze the primordial excitation of spin-orbit misalignment of Sun-like stars, in light of disk-star angular momentum transfer. We begin by calculating the stellar pre-main sequence rotational evolution, accounting for spin-up due to gravitational contraction and accretion as well as spin-down due to magnetic star-disk coupling. We devote particular attention to angular momentum transfer by accretion, and show that while generally subdominant to gravitational contract...
García-Reyes, Gonzalo
2008-01-01
A detailed study is presented of the counterrotating model (CRM) for electrovacuum stationary axially symmetric relativistic thin disks of infinite extension without radial stress, in the case when the eigenvalues of the energy-momentum tensor of the disk are real quantities, so that there is not heat flow. We find a general constraint over the counterrotating tangential velocities needed to cast the surface energy-momentum tensor of the disk as the superposition of two counterrotating charged dust fluids. We then show that, in some cases, this constraint can be satisfied if we take the two counterrotating tangential velocities as equal and opposite or by taking the two counterrotating streams as circulating along electro-geodesics. However, we show that, in general, it is not possible to take the two counterrotating fluids as circulating along electro-geodesics nor take the two counterrotating tangential velocities as equal and opposite. A simple family of models of counterrotating charged disks based on the...
Mathematical analysis of thermoelastic characteristics in plasma-sprayed thermal barrier coatings.
Go, Jaegwi; Jungo, Yeon-Gil; Kim, Seokchan; Ali, Md Afsar; Paik, Ungyu
2012-02-01
The thermoelastic characteristics of plasma-sprayed thermal barrier coatings (TBCs) have been analyzed using mathematical modeling. Two types of TBC model, cylinder and circular disk which are commercial plasma-sprayed TBCs, subjecting to symmetric temperature distribution to the radial and longitudinal directions, respectively, were taken into consideration. Based on the thermoelastic theories, a second order ordinary differential equation was derived for the cylinder model and a pair of partial differential equations were set up for the circular disk model. The analytic solution was obtained from the ordinary differential equation, while a finite volume method was developed for numerical solutions to the pair of partial differential equations due to the complexity of governing equations. The thermoelastic characteristics of TBC models, such as temperature distributions, displacements, and stresses, were displayed according to the obtained solutions. The rate of heat conduction in the section of the top coat is relatively slow in comparison with the substrate, and no profound difference appears in the temperature distribution between two TBC models. The highest longitudinal tensile stress is expressed at the bond coat of both models, and the substrate is under the compressive stresses to the circumferential direction. While the cylinder expands to the positive longitudinal direction only, the expansion in the circular disk occurs to both the positive and negative longitudinal directions. Relatively large displacement and stresses exhibit in the cylinder as compared with the circular disk. In the circular disk, the stresses to the radial direction undulate at each section, and the displacement profile displays that the width of the circular disk is slightly narrowed. The results demonstrate that the mechanical and thermal properties of the top and bond coats are the crucial factors to be considered in controlling the thermoelastic characteristics of plasma
Energy Technology Data Exchange (ETDEWEB)
Yin, Chenguang; Zheng, Liancun [Univ. of Science and Technology Beijing (China). School of Mathematics and Physics; Zhang, Chaoli [Univ. of Science and Technology Beijing (China). School of Mathematics and Physics; Univ. of Science and Technology Beijing (China). School of Mechanical Engineering; Zhang, Xinxin [Univ. of Science and Technology Beijing (China). School of Mechanical Engineering
2015-09-01
In this article, we discuss the flow and heat transfer of nanofluids over a rotating porous disk with velocity slip and temperature jump. Three types of nanoparticles - Cu, Al{sub 2}O{sub 3}, and CuO - are considered with water as the base fluid. The nonlinear governing equations are reduced into ordinary differential equations by Von Karman transformations and solved using homotopy analysis method (HAM), which is verified in good agreement with numerical ones. The effects of involved parameters such as porous parameter, velocity slip, temperature jump, as well as the types of nanofluids on velocity and temperature fields are presented graphically and analysed.
Kazanas, Demosthenes; Fukumura, K.
2009-01-01
We present detailed computations of photon orbits emitted by flares at the ISCO of accretion disks around rotating black holes. We show that for sufficiently large spin parameter, i.e. $a > 0.94 M$, following a flare at ISCO, a sufficient number of photons arrive at an observer after multiple orbits around the black hole, to produce an "photon echo" of constant lag, i.e. independent of the relative phase between the black hole and the observer, of $\\Delta T \\simeq 14 M$. This constant time delay, then, leads to the presence of a QPO in the source power spectrum at a frequency $\
Directory of Open Access Journals (Sweden)
Vardanyan S. A.
2007-09-01
Full Text Available In the framework of the asymmetrical momental micropolar theory in the present work the boundary value problem of thermal stresses in a three-dimensional thin plate with independent fields of displacements and rotations is studied on the basis of asymptotic method. Depending on the values of physical dimensionless constants of the material three applied two-dimensional theories of thermoelasticity of micropolar thin plate are constructed (theories with independent rotations, with constrained rotations and with small shift rigidity.
ALMA detection of the rotating molecular disk wind drom the young star HD 163296
Klaassen, P D; Mathews, G S; De Gregorio-Monsalvo, J C Mottram I; van Dishoeck, E F; Takahashi, S; Akiyama, E; Chapillon, E; Espada, D; Hales, A; Hogerheijde, M R; Rawlings, M; Schmalzl, M; Testi, L
2013-01-01
Disk winds have been postulated as a mechanism for angular momentum release in protostellar systems for decades. HD 163296 is a Herbig Ae star surrounded by a disk and has been shown to host a series of HH knots (HH 409) with bow shocks associated with the farthest knots. Here we present ALMA Science Verification data of CO J=2-1 and J=3-2 emission which are spatially coincident with the blue shifted jet of HH knots, and offset from the disk by -18.6 km/s. The emission has a double corkscrew morphology and extends more than 10" from the disk with embedded emission clumps coincident with jet knots. We interpret this double corkscrew as emission from material in a molecular disk wind, and that the compact emission near the jet knots is being heated by the jet which is moving at much higher velocities. We show that the J=3-2 emission is likely heavily filtered by the interferometer, but the J=2-1 emission suffers less due to the larger beam and measurable angular scales. Excitation analysis suggests temperatures...
Cur'e, M
2004-01-01
The theory of radiation driven wind including stellar rotation is re-examined. After a suitable change of variables, a new equation for the mass loss rate is derived analytically. The solution of this equation remains within 1% confidence when compared with numerical solutions. Also, a non-linear equation for the position of the critical (singular) point is obtained. This equation shows the existence of an additional critical point, besides the standard m--CAK critical point. For a stellar rotation velocity larger than aprox. 0.7 - 0.8 V_{breakup}, there exists only one critical point, located away from the star's surface. Numerical solutions crossing through this new critical point, are attained. In these cases, the wind has a very low terminal velocity and therefore a higher density wind. Disk formation in Be stars is discussed in the frame of this new line driven stellar wind solution.
Kahouadji, L.; Witkowski, L. Martin
2014-07-01
The flow driven by a rotating disk at the bottom of an open fixed cylindrical cavity is studied numerically and experimentally. The steady axisymmetric Navier-Stokes equations projected onto a curvilinear coordinate system are solved by a Newton-Raphson algorithm. The free surface shape is computed by an iterative process in order to satisfy a zero normal stress balance at the interface. In previous studies, regarding the free surface deflection, there is a significant disagreement between a first-order approximation [M. Piva and E. Meiburg, "Steady axisymmetric flow in an open cylindrical container with a partially rotating bottom wall," Phys. Fluids 17, 063603 (2005)] and a full numerical simulation [R. Bouffanais and D. Lo Jacono, "Unsteady transitional swirling flow in the presence of a moving free surface," Phys. Fluids 21, 064107 (2009)]. For a small deflection, the first-order approximation matches with our numerical simulation and for a large deflection a good agreement is found with experimental measurements.
Donmez, O
2006-01-01
The shocked wave created on the accretion disk after different physical phenomena (accretion flows with pressure gradients, star-disk interaction etc.) may be responsible observed Quasi Periodic Oscillations (QPOs) in $X-$ray binaries. We present the set of characteristics frequencies associated with accretion disk around the rotating and non-rotating black holes for one particle case. These persistent frequencies are results of the rotating pattern in an accretion disk. We compare the frequency's from two different numerical results for fluid flow around the non-rotating black hole with one particle case. The numerical results are taken from our papers Refs.\\refcite{Donmez2} and \\refcite{Donmez3} using fully general relativistic hydrodynamical code with non-selfgravitating disk. While the first numerical result has a relativistic tori around the black hole, the second one includes one-armed spiral shock wave produced from star-disk interaction. Some physical modes presented in the QPOs can be excited in nume...
Counter-rotating gaseous disks in the 'Evil Eye' galaxy NGC4826
Braun, Robert; Walterbos, Rene A. M.; Kennicutt, Robert C., Jr.
1992-12-01
The discovery of two counterrotating gaseous disks in the otherwise normal early-type spiral NGC4826 is reported. This is the most disklike galaxy in which any kinematic substructure has yet been found. This discovery raises the possibility that even spiral galaxies may have undergone a significant degree of structural evolution due to mergers.
Pickett, B. K.; Durisen, R. H.; Davis, G. A.
1993-05-01
Nonaxisymmetric instabilities driven by self-gravity and rapid rotation may play a critical role during the collapse and accretion phases of star formation. To date, except for studies of tori, most work on global dynamic instabilities of rotating, self-gravitating equilibrium states has focused on only moderately compressible equations of state and on two extreme cases of the specific angular momentum distribution. In the most commonly considered case, uniform initial cloud conditions yield an angular momentum distribution equivalent to that of the Maclaurin spheroids. Rapidly rotating starlike objects with this angular momentum distribution are subject to barlike instabilities. Hydrodynamic simulations have demonstrated that these instabilities generally result in spiral arm ejection of mass and angular momentum, producing a ring of material about a central, tumbling bar (Williams and Tohline 1988 Astrophys. J. 315, 594). Strongly centrally condensed initial cloud conditions yield the other extreme. A star/disk protostellar system forms which is subject to multiple spiral instabilities. Previous work (Yang, Durisen, Cohl, Imamura, and Toman 1991 BAAS 22, 1257) has suggested that these systems display complex behavior, with many tightly wrapped spiral modes present and growing simultaneously. We have recently begun a survey of dynamic instabilities for a wider range of equations of state and of specific angular momentum distributions. The evolution of our equilibrium objects is followed using a second-order 3D hydrodynamics code. We present results for simulations of isentropic, n=3/2 and 5/2 polytropic stars with angular momentum distributions intermediate between the two extremes. In general, only modest shifts away from the Maclaurin spheroid angular momentum distribution lead to behavior resembling that of star/disk systems. This work is supported by NASA Grant NAGW-3399.
A parametric study on the growth of yield front in rotating annular disks
African Journals Online (AJOL)
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The growth of elastic-plastic front under post-elastic conditions in high speed rotating ... In a recent work Alexandrova and Villa Real (2007) reported the influences of ... approximate the radial displacement field are generated numerically ...
Li, Kan; Zhang, Hongbo; Tang, Tiantian; Tang, Yanping; Wang, Yalin; Jia, Jinping
2016-08-01
Polypyrrole (PPy) film is synthesized on Ti substrate through electrochemical polymerization method and is applied as cathode material in a TiO2 NTs-PPy dual rotating disk photo fuel cell (PFC). The optimized PPy electrochemical polymerization is carried out using linear sweep voltammetry from 0 V to 1.2 V (vs. SCE) with scan rate of 0.1 V s-1, 100 circles. Sixty milliliter real textile wastewater with the initial COD and conductivity of 408 ± 6 mgO2 L-1 and 20180 μS cm-1 is treated in this PFC under UV irradiation. About 0.46 V open-circuit voltage (VOC) and 1.8-2.2 mA short-circuit current (JSC) are obtained. Due to the effective electron-hole separation effect, the COD removal rate is as high as 0.0055 min-1. Stable current and COD removal can be obtained at different output voltage. Two influence factors including rotating speed and pH are investigated. Better electricity generation performance and COD removal activity are achieved at high rotating speed and in acidic condition. In comparison with platinized cathode, though VOC is lower, similar JSC is measured. Considering the high cost of Pt, PPy is a promising alternative cathode material in PFC that can also generate electricity efficiently and stably.
Refraction and wave matching in hyperbolic thermoelasticity
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Józef Rafa
2015-03-01
Full Text Available The subject of the publication concerns the propagation of thermoelastic waves with a particular emphasis on the refraction of waves at the boundary of a layer laying (resting on a halfspace. Analogously to the effect of wave matching, which appears in the case of acoustic and electromagnetic waves, the impedance of a thermoelastic wave has been introduced and its influence and the reflection andrefraction on the boundary at media has been investigated. The model of the medium describes a mutual coupling of mechanical and thermalinteractions with a wave type propagation of heat in media taken into account.[b]Keywords[/b]: hyperbolic thermoelasticity, wave impedance of a thermoelastic medium,refraction and wave matching
Separation of contact in a sliding system with frictionally excited thermoelastic instability
Directory of Open Access Journals (Sweden)
Voldřich J.
2007-10-01
Full Text Available The first phase of the thermoelastic instability, which is characterized by a full contact regime, can be modelled using Fourier decomposition and application of an analytical description. However, in case of further increase of instability, a separation of the contact occurs which is more difficult to cover by mathematical means. The contribution deals with numerical simulations of the separation. The problems are topical in connection with the disk brakes design, should we give an example.
Khan, Najeeb Alam
2016-01-01
This study deals with the investigation of MHD flow of Williamson fluid over an infinite rotating disk with the effects of Soret, Dufour, and anisotropic slip. The anisotropic slip and the Soret and Dufour effects are the primary features of this study, which greatly influence the flow, heat and mass transport properties. In simultaneous appearance of heat and mass transfer in a moving fluid, the mass flux generated by temperature gradients is known as the thermal-diffusion or Soret effect and the energy flux created by a composition gradient is called the diffusion-thermo or Dufour effect, however, difference in slip lengths in streamwise and spanwise directions is named as anisotropic slip. The system of nonlinear partial differential equations (PDEs), which governs the flow, heat and mass transfer characteristics, is transformed into ordinary differential equations (ODEs) with the help of von K\\'arm\\'an similarity transformation. A numerical solution of the complicated ODEs is carried out by a MATLAB routi...
A rotating molecular disk toward IRAS 18162-2048, the exciting source of HH 80-81
Fernández-López, M; Curiel, Salvador; Gómez, Yolanda; Ho, Paul T P; Patel, Nimesh
2011-01-01
We present several molecular line emission arcsec and subarcsec observations obtained with the Submillimeter Array (SMA) in the direction of the massive protostar IRAS 18162-2048, the exciting source of HH 80-81. The data clearly indicates the presence of a compact (radius~425-850 AU) SO2 structure, enveloping the more compact (radius~150 AU) 1.4 millimeter dust emission (reported in a previous paper). The emission spatially coincides with the position of the prominent thermal radio jet which terminates at the HH 80-81 and HH 80N Herbig-Haro objects. Furthermore, the molecular emission is elongated in the direction perpendicular to the axis of the thermal radio jet, suggesting a disk-like structure. We derive a total dynamic mass (disk-like structure and protostar) of 11-15 msun. The SO2 spectral line data also allow us to constrain the structure temperature between 120-160 K and the volume density \\geq 2 \\times 10^9 cm3. We also find that such a rotating flattened system could be unstable due to gravitationa...
Numerical Simulation of Rotating Accretion Disk Around the Schwarzschild Black Hole Using GRH Code
Donmez, O
2006-01-01
The 2D time dependent solution of thin accretion disk in a close binary system have been presented on the equatorial plane around the Schwarzschild black hole. To do that, the special part of the General Relativistic Hydrodynamical(GRH) equations are solved using High Resolution Shock Capturing (HRSC) schemes. The spiral shock waves on the accretion disk are modeled using perfect fluid equation of state with adiabatic indices $\\gamma = 1.05, 1.2$ and 5/3. The results show that the spiral shock waves are created for gammas except the case $\\gamma=5/3$. These results consistent with results from Newtonian hydrodynamic code except close to black hole. Newtonian approximation does not give good solution while matter closes to black hole. Our simulations illustrate that the spiral shock waves are created close to black hole and the location of inner radius of spiral shock wave is around $10M$ and it depends on the specific heat rates. We also find that the smaller $\\gamma$ is the more tightly the spiral winds.
Mass transfer studies of Geobacter sulfurreducens biofilms on rotating disk electrodes.
Babauta, Jerome T; Beyenal, Haluk
2014-02-01
Electrochemical impedance spectroscopy has received significant attention recently as a method to measure electrochemical parameters of Geobacter sulfurreducens biofilms. Here, we use electrochemical impedance spectroscopy to demonstrate the effect of mass transfer processes on electron transfer by G. sulfurreducens biofilms grown in situ on an electrode that was subsequently rotated. By rotating the biofilms up to 530 rpm, we could control the microscale gradients formed inside G. sulfurreducens biofilms. A 24% increase above a baseline of 82 µA could be achieved with a rotation rate of 530 rpm. By comparison, we observed a 340% increase using a soluble redox mediator (ferrocyanide) limited by mass transfer. Control of mass transfer processes was also used to quantify the change in biofilm impedance during the transition from turnover to non-turnover. We found that only one element of the biofilm impedance, the interfacial resistance, changed significantly from 900 to 4,200 Ω under turnover and non-turnover conditions, respectively. We ascribed this change to the electron transfer resistance overcome by the biofilm metabolism and estimate this value as 3,300 Ω. Additionally, under non-turnover, the biofilm impedance developed pseudocapacitive behavior indicative of bound redox mediators. Pseudocapacitance of the biofilm was estimated at 740 µF and was unresponsive to rotation of the electrode. The increase in electron transfer resistance and pseudocapacitive behavior under non-turnover could be used as indicators of acetate limitations inside G. sulfurreducens biofilms.
Modeling grain-scale thermoelastic stresses on airless bodies
Molaro, J.; Byrne, S.
2013-12-01
Thermal stress weathering is the mechanical breakdown of rock from expansion and contraction caused by changes in temperature. Damage occurs in the form of microscopic cracks that result from a thermal cycle or thermal shock. This process may play an important role in the evolution of airless landscapes, by contributing to regolith production and crater degradation. Without the presence of an atmosphere, rock surfaces experience very dramatic temperature changes that induce high thermoelastic stresses in the near sub-surface. The thermoelastic behavior of each surface is primarily controlled by its distance to the sun and its solar day length, providing a unique experience on each body. For example, slowly rotating bodies that are close to the sun (such as Mercury) experience a very wide diurnal temperature range. Bodies further from the sun (such as NEAs) have a much smaller range, but rotate quickly and experience rapid temperature 'shocks' during sunrise/set. While many studies suggest stresses induced by these temperature changes may cause rock breakdown, the extent of the damage produced as a result is unknown. In this study, we modeled thermoelastic stresses produced on airless surfaces at the mineral grain scale. Finite Element Analysis of Microstructures (OOF2) is a 2-D finite element modeling program, developed at NIST and designed to help scientists calculate macroscopic properties of real or simulated microstructures. This allows us to model thermal behavior of microstructures with varying grain sizes and thermophysical properties, and to explore the relationship between the spatial and temporal temperature gradients and stress. Using OOF2, we imposed the solar and conductive fluxes calculated by our 1-D thermal model at the surface and at 5mm depth on a microstructure. The microstructure has bulk properties typical of a basalt, and a grain size of ~0.3 mm. We assigned 20% and 80% of the grains a thermal conductivity of 1 and 3 W/mK, respectively. The
Energy Technology Data Exchange (ETDEWEB)
Repetto, P.; Martinez-Garcia, Eric E.; Rosado, M.; Gabbasov, R., E-mail: prsatch6@gmail.com [Instituto de Astronomia, Universidad Nacional Autonoma de Mexico (UNAM), Apdo. Postal 70-264, 04510 Mexico, D.F. (Mexico)
2013-03-01
In this work we extend the study on the mass distribution of the spiral galaxy NGC 5278, performing 1D and 2D (GALFIT) bulge-disk decomposition to determine which components constitute the baryonic mass in this galaxy. Our analysis does not detect any bulge; instead we find a bright source probably related to the central active galactic nucleus and an exponential disk. We fix the stellar disk contribution to the rotation curve (RC) with broadband photometric observations and population synthesis models, to obtain the 2D mass distribution of the stellar disk. In the particular case of NGC 5278, we find that the typical assumption of considering the mass-to-luminosity ratio (M/L) of the disk as constant along the galactocentric radius is not valid. We also extract a baryonic RC from the mass profile to determine the inability of this baryonic RC and also the baryonic RC with more than and less than 30% disk mass (in order to consider the disk mass errors) to fit the entire RC. We perform the RC decomposition of NGC 5278 by considering the baryonic RC and four types of dark matter (DM) halo: Hernquist, Burkert, Navarro, Frenk, and White, and Einasto. Our results determine that the Hernquist DM halo better models our observed RC in the case of disk mass M{sub d} = 5.6 Multiplication-Sign 10{sup 10} M {sub Sun} and also with less than 30% disk mass. In the case of more than 30% disk mass, the cored Einasto (n < 4) DM halo is the best-fitting model.
Bhatia, Tanayveer Singh
2016-01-01
The emergence of turbulence in shear flows is a well-investigated field. Yet, one of major issues is the apparent contradiction between linear stability analysis quoting a flow to be stable and results from experiments and simulations proving it to be otherwise. There is some success, in particular in astrophysical systems, based on Magneto-Rotational Instability (MRI). However, MRI requires the system to be weakly magnetized, which is not a feature of general magnetohydrodynamic (MHD) flows. Nevertheless, linear perturbations of such flows are nonnormal in nature which argues for an origin of nonlinearity therein. The idea is, nonnormal perturbations could produce huge transient energy growth (TEG), which may lead to non-linearity and further turbulence. However, so far, nonnormal effects in shear flows have not been explored much in the presence of magnetic fields. Here, we consider the perturbed visco-resistive incompressible MHD shear flows with rotation in general. Basically we consider the magnetized ve...
Venuti, L; Cody, A M; Stauffer, J R; Micela, G; Rebull, L M; Alencar, S H P; Sousa, A P; Hillenbrand, L A; Flaccomio, E
2016-01-01
The low spin rates measured for solar-type stars at an age of a few Myr (~10% of the break-up velocity) indicate that some mechanism of angular momentum regulation must be at play in the early pre-main sequence. We characterize the rotation properties for members of the region NGC 2264 (~3 Myr), and investigate the accretion-rotation connection at an age where about 50% of the stars have already lost their disks. We examined a sample of 500 cluster members whose photometric variations were monitored in the optical for 38 consecutive days with CoRoT. Light curves were analyzed for periodicity using the Lomb-Scargle periodogram, the autocorrelation function and the string-length method. The period distribution obtained for the cluster consists of a smooth distribution centered around P=5.2 d with two peaks at P=1-2 d and 3-4 d. A separate analysis of CTTS and WTTS indicates that the P=1-2 d peak is associated with the latter, while both groups contribute to the P=3-4 d peak. The comparison between CTTS and WTTS...
Cold gas dynamics in Hydra-A: evidence for a rotating disk
Hamer, S L; Swinbank, A M; Oonk, J B R; Mittal, R; McNamara, B R; Russell, H R; Bremer, M N; Combes, F; Fabian, A C; Nesvadba, N P H; O'Dea, C P; Baum, S A; Salomé, P; Tremblay, G; Donahue, M; Ferland, G J; Sarazin, C L
2013-01-01
We present multi-frequency observations of the radio galaxy Hydra-A (3C218) located in the core of a massive, X-ray luminous galaxy cluster. IFU spectroscopy is used to trace the kinematics of the ionised and warm molecular hydrogen which are consistent with a ~ 5 kpc rotating disc. Broad, double-peaked lines of CO(2-1), [CII]157 $\\mu$m and [OI]63 $\\mu$m are detected. We estimate the mass of the cold gas within the disc to be M$_{gas}$ = 2.3 $\\pm$ 0.3 x 10$^9$ M$_{\\odot}$. These observations demonstrate that the complex line profiles found in the cold atomic and molecular gas are related to the rotating disc or ring of gas. Finally, an HST image of the galaxy shows that this gas disc contains a substantial mass of dust. The large gas mass, SFR and kinematics are consistent with the levels of gas cooling from the ICM. We conclude that the cold gas originates from the continual quiescent accumulation of cooled ICM gas. The rotation is in a plane perpendicular to the projected orientation of the radio jets and I...
Repetto, P; Rosado, M; Gabbasov, R F
2013-01-01
In this work we extend the study on the mass distribution of the spiral galaxy NGC 5278, performing 1D and 2D bulge-disk decomposition to determine which components constitute the baryonic mass in this galaxy. Our analysis does not detect any bulge, instead we find a bright source, probably related with the central AGN, and an exponential disk. We fix the stellar disk contribution to the rotation curve (RC) with broad band photometric observations and population synthesis models, to obtain 2D mass distribution of the stellar disk. In the particular case of NGC 5278, we find that the typical assumption of considering the mass-to-luminosity ratio (M/L) of the disk as constant along the galactocentric radius is not valid. We also extract a baryonic RC from the mass profile, to determine the inability of this baryonic RC and also of the baryonic RC with more and less 30% disk mass (in order to consider the disk mass errors) to fit the entire RC. We perform the RC decomposition of NGC 5278 considering the baryonic...
Bershady, Matthew A.; Martinsson, Thomas P. K.; Verheijen, Marc A. W.; Westfall, Kyle B.; Andersen, David R.; Swaters, Rob A.
2011-01-01
We measure the contribution of galaxy disks to the overall gravitational potential of 30 nearly face-on intermediate-to-late-type spirals from the DiskMass Survey. The central vertical velocity dispersion of the disk stars (sigma(disk)(z,R=0)) is related to the maximum rotation speed (V-max) as sigm
Directory of Open Access Journals (Sweden)
Xi Wu
2008-01-01
Full Text Available A mathematical model of a cracked rotor and an asymmetric rotor with two disks representing a turbine and a generator is utilized to study the vibrations due to imbalance and side load. Nonlinearities typically related with a “breathing” crack are included using a Mayes steering function. Numerical simulations demonstrate how the variations of rotor parameters affect the vibration response and the effect of coupling between torsional and lateral modes. Bode, spectrum, and orbit plots are used to show the differences between the vibration signatures associated with cracked shafts versus asymmetric shafts. Results show how nonlinear lateral-torsional coupling shifts the resonance peaks in the torsional vibration response for cracked shafts and asymmetric rotors. The resonance peaks shift depending on the ratio of the lateral-to-torsional natural frequencies with the peak responses occurring at noninteger values of the lateral natural frequency. When the general nonlinear models used in this study are constrained to reduce to linear torsional vibration, the peak responses occur at commonly reported integer ratios. Full spectrum analyses of the X and Y vibrations reveal distinct vibration characteristics of both cracked and asymmetric rotors including reverse vibration components. Critical speeds and vibration orders predicted using the models presented herein include and extend diagnostic indicators commonly reported.
Directory of Open Access Journals (Sweden)
R. S. Agarwal
1980-04-01
Full Text Available The Newton Raphson technique has been employed to solve the set of non-linear equations governing the problem of flow and heat transfer from an enclosed rotating disc. /The disc called rotor is subjected to uniform injection while the top of the housing called stator, to an equal suction. The results for small Reynold numbers are found in good agreement to that obtained earlier by series solution. The radial and transverse velocity profiles for large Reynolds have been plotted in the regions of no recirculation. The effect of net radial inflow and outflow on temperature in the no-recirculation region has also been studied. The method is significant in this respect that it yields satisfactory results for large Reynolds numbers.
PROJECTED ROTATIONAL VELOCITIES OF 136 EARLY B-TYPE STARS IN THE OUTER GALACTIC DISK
Energy Technology Data Exchange (ETDEWEB)
Garmany, C. D.; Glaspey, J. W. [National Optical Astronomy Observatory, 950 N. Cherry Ave., Tucson, AZ 85719 (United States); Bragança, G. A.; Daflon, S.; Fernandes, M. Borges; Cunha, K. [Observatório Nacional-MCTI, Rua José Cristino, 77. CEP: 20921-400, Rio de Janeiro, RJ (Brazil); Oey, M. S. [University of Michigan, Department of Astronomy, 311 West Hall, 1085 S. University Ave., Ann Arbor, MI: 48109-1107 (United States); Bensby, T., E-mail: garmany@noao.edu [Lund Observatory, Department of Astronomy and Theoretical Physics, Box 43, SE-22100, Lund (Sweden)
2015-08-15
We have determined projected rotational velocities, v sin i, from Magellan/MIKE echelle spectra for a sample of 136 early B-type stars having large Galactocentric distances. The target selection was done independently of their possible membership in clusters, associations or field stars. We subsequently examined the literature and assigned each star as Field, Association, or Cluster. Our v sin i results are consistent with a difference in aggregate v sin i with stellar density. We fit bimodal Maxwellian distributions to the Field, Association, and Cluster subsamples representing sharp-lined and broad-lined components. The first two distributions, in particular, for the Field and Association are consistent with strong bimodality in v sin i. Radial velocities are also presented, which are useful for further studies of binarity in B-type stars, and we also identify a sample of possible new double-lined spectroscopic binaries. In addition, we find 18 candidate Be stars showing emission at Hα.
Strength optimized designs of thermoelastic structures
DEFF Research Database (Denmark)
Pedersen, Pauli; Pedersen, Niels Leergaard
2010-01-01
For thermoelastic structures the same optimal design does not simultaneously lead to minimum compliance and maximum strength. Compliance may be a questionable objective and focus for the present paper is on the important aspect of strength, quantified as minimization of the maximum von Mises stress...... to mathematical programming, which with a large number of both design variables and strength constraints, is found non-practical, we choose simple recursive iterations to obtain uniform energy density and find by examples that the obtained designs are close to fulfilling also strength maximization. In compliance...... minimization it may be advantageous to decrease the total volume, but for strength maximization it is argued that it is advantageous to keep the total permissible volume. With the thermoelastic analysis presented directly in a finite element formulation, simple explicit formulas for equivalent thermoelastic...
Thermoelastic bending of locally heated orthotropic shells
Shevchenko, V. P.; Gol'tsev, A. S.
2007-03-01
The thermoelastic bending of locally heated orthotropic shells is studied using the classical theory of thermoelasticity of thin shallow orthotropic shells and the method of fundamental solutions. Linear distribution of temperature over thickness and the Newton's law of cooling are assumed. Numerical analysis is carried out for orthotropic shells of arbitrary Gaussian curvature made of a strongly anisotropic material. The behavior of thermal forces and moments near the zone of local heating is studied for two areas of thermal effect: along a coordinate axis and along a circle of unit radius. Generalized conclusions are drawn
Energy Technology Data Exchange (ETDEWEB)
Costa, S.L.F.A. da; Nobe, K. [Univ. of California, Los Angeles, CA (United States). Dept. of Chemical Engineering; Agostinho, S.M.L. [Univ. de Sao Paulo (Brazil). Dept. de Quimica Fundamental
1993-12-01
The electrodissolution behavior of Cu and Cu-rich Cu-Zn alloys in 1M HCl containing benzotriazole (BTA) was studied using rotating ring-disk electrodes. Cu(I) was the main product of Cu-Zn alloy dissolution with Cu(II) detected only at higher potentials. Electrodissolution of the Cu component was similar to that of copper with an apparent Tafel slope of 60 mV/dec. Cu component dissolution rates exhibited strong mass-transfer effects in the entire potential range studied. A CuCl film formed on the alloy surfaces in the current peak region. In the limiting current region the rates of Cu(I) dissolution from both alloys and copper were essentially equivalent and indicate CuCl{sup {minus}}{sub 2} as the principal diffusing species. Significant selective electrodissolution of Zn was observed in the apparent Tafel region. The formation of a duplex film was indicated in the presence of BTA with a nonporous Cu(I) BTA inner layer and a porous CuCl outer layer.
Energy Technology Data Exchange (ETDEWEB)
Kocha, Shyam S; Shinozaki, Kazuma; Zack, Jason W; Myers, Deborah J.; Kariuki, Nancy N.; Nowicki, Tammi L.; Stamenkovic, Vojislav; Kang, Yijin; Li, Dongguo; Papageorgopoulos, Dimitrios
2017-07-01
Abstract Thin-film-rotating disk electrodes (TF-RDEs) are the half-cell electrochemical system of choice for rapid screening of oxygen reduction reaction (ORR) activity of novel Pt supported on carbon black supports (Pt/C) electrocatalysts. It has been shown that the magnitude of the measured ORR activity and reproducibility are highly dependent on the system cleanliness, evaluation protocols, and operating conditions as well as ink formulation, composition, film drying, and the resultant film thickness and uniformity. Accurate benchmarks of baseline Pt/C catalysts evaluated using standardized protocols and best practices are necessary to expedite ultra-low-platinum group metal (PGM) catalyst development that is crucial for the imminent commercialization of fuel cell vehicles. We report results of evaluation in three independent laboratories of Pt/C electrocatalysts provided by commercial fuel cell catalyst manufacturers (Johnson Matthey, Umicore, Tanaka Kikinzoku Kogyo—TKK). The studies were conducted using identical evaluation protocols/ink formulation/film fabrication albeit employing unique electrochemical cell designs specific to each laboratory. The ORR activities reported in this work provide a baseline and criteria for selection and scale-up of novel high activity ORR electrocatalysts for implementation in proton exchange membrane fuel cells (PEMFCs).
Directory of Open Access Journals (Sweden)
Dan Qin
2017-01-01
Full Text Available Recycling and reusing of poly (ethylene terephthalate (PET fabrics waste are essential for reducing serious waste of resources and environmental pollution caused by low utilization rate. The liquid-phase polymerization method has advantages of short process flow, low energy consumption, and low production cost. However, unlike prepolymer, the material characteristics of PET fabrics waste (complex composition, high intrinsic viscosity, and large quality fluctuations make its recycling a technique challenge. In this study, the falling film-rotating disk combined reactor is proposed, and the continuous liquid-phase polymerization is modeled by optimizing and correcting existing models for the final stage of PET polymerization to improve the product quality in plant production. Through modeling and simulation, the weight analysis of indexes closely related to the product quality (intrinsic viscosity, carboxyl end group concentration, and diethylene glycol content was investigated to optimize the production process in order to obtain the desired polymer properties and meet specific product material characteristics. The model could be applied to other PET wastes (e.g., bottles and films and extended to investigate different aspects of the recycling process.
Indian Academy of Sciences (India)
H VOLKAN ERSOY
2017-03-01
This paper is concerned with the unsteady flow of a disk performing non-torsional oscillation in its own plane and a Newtonian fluid at infinity while they are initially rotating with the same angular velocity about non-coaxial axes. For a more general study, it is considered that the disk executes non-torsional oscillation along any desired direction in its own plane. An exact solution obtained for the velocity field is compared with aperiodic solution presented in order to find the time when the periodic flow starts. A very good agreement is found between the two solutions in the periodic state. It is an interesting result that the x- and y-components of the force per unit area exerted by the fluid on the disk vary in almost opposite direction when the non-torsional oscillation takes place along the eccentricity direction. Further, the change in the y-component of the translational velocity becomes noticeable in this case.
Bernardez, Letícia Alonso
2009-01-01
Texto completo: acesso restrito. p. 415-424 A rotating disk apparatus was used to investigate the biodegradation of PAHs from non-aqueous phase liquids to solutions of Brij 35. The mass transfer of PAHs in absence of surfactant solution was not large enough to replenish the degraded PAHs. The addition of surfactant resulted in an overall enhancement of biodegradation rates compared to that observed in pure aqueous solution. This is because surfactant partition significant amount of PAHs in...
Gnerucci, A.; Marconi, A.; Capetti, A.; Axon, D. J.; Robinson, A.; Neumayer, N.
2011-01-01
We measure the black hole mass in the nearby active galaxy Centaurus A (NGC 5128) using a new method based on spectroastrometry of a rotating gas disk. The spectroastrometric approach consists in measuring the photocenter position of emission lines for different velocity channels. In a previous paper we focused on the basic methodology and the advantages of the spectroastrometric approach with a detailed set of simulations demonstrating the possibilities for black hole mass measurements going...
Null controllability of a thermoelastic plate
Directory of Open Access Journals (Sweden)
Assia Benabdallah
2002-01-01
Full Text Available Thermoelastic plate model with a control term in the thermal equation is considered. The main result in this paper is that with thermal control, locally distributed within the interior and square integrable in time and space, any finite energy solution can be driven to zero at the control time T.
Effect of Rotation in an Orthotropic Elastic Slab
Directory of Open Access Journals (Sweden)
Santra S.
2017-02-01
Full Text Available The fundamental equations of the two dimensional generalized thermoelasticity (L-S model with one relaxation time parameter in orthotropic elastic slab has been considered under effect of rotation. The normal mode analysis is used to the basic equations of motion and heat conduction equation. Finally, the resulting equations are written in the form of a vector-matrix differential equation which is then solved by the eigenvalue approach. The field variables in the space time domain are obtained numerically. The results corresponding to the cases of conventional thermoelasticity CTE, extended thermoelasticity (ETE and temperature rate dependent thermoelasticity (TRDTE are compared by means of graphs.
Energy Technology Data Exchange (ETDEWEB)
Pronkin, Sergey N., E-mail: sergey.pronkin@unistra.f [Laboratory of Materials, Surfaces and Catalytic Processes, UMR 7515 of CNRS-UdS-ECPM, 25 rue Becquerel, 67087 Strasbourg (France); Bonnefont, Antoine [Institut de Chimie de Strasbourg, UMR 7177, CNRS-Universite de Strasbourg, 4 rue Blaise Pascal, 67000 Strasbourg (France); Ruvinskiy, Pavel S.; Savinova, Elena R. [Laboratory of Materials, Surfaces and Catalytic Processes, UMR 7515 of CNRS-UdS-ECPM, 25 rue Becquerel, 67087 Strasbourg (France)
2010-03-30
This work reports on the kinetics of the hydrogen oxidation reaction (HOR) on model Pd nanoparticles supported on a low surface area carbon substrate. Two Pd/C samples, with the average particle size 2.6 and 4.0 nm were used. The structure of the catalysts was characterized with the ex situ (electron microscopy) and in situ (electrochemical) methods. We utilized the electrochemical impedance spectroscopy (EIS) and the rotating disk electrode (RDE) voltammetry to study the kinetics of the HOR on Pd/C. The relevance of these techniques for elucidating the kinetics and the mechanism of the HOR on Pd/C was explored. The experimental results suggest that the catalytic activity of Pd in the HOR is more than 2 orders of magnitude lower than that of Pt, and does not depend on the particle size in the range from 2.6 to 4.0 nm. Computational modeling of the experimental steady-state (RDE) and non-steady-state (EIS) data shows that the reaction kinetics can be adequately described within Heyrovsky-Volmer mechanism, with the rate constants upsilon{sub 0H} = (8.8 +- 1.5) x 10{sup -10} mol cm{sup -2} s{sup -1} and upsilon{sub 0V} = (1.0 +- 0.3) x 10{sup -8} mol cm{sup -2} s{sup -1}. The model suggests that underpotentially deposited hydrogen H{sub UPD} is unlikely to be the active intermediate H{sub ad} of the HOR. It is concluded that the surface coverage of H{sub ad} deviates from that of H{sub UPD} with increasing overpotential, and the lateral interactions within H{sub ad} adlayer are weak.
Gnerucci, A; Capetti, A; Axon, D J; Robinson, A
2012-01-01
We present new CRIRES spectroscopic observations of BrGamma in the nuclear region of the Circinus galaxy, obtained with the aim of measuring the black hole (BH) mass with the spectroastrometric technique. The Circinus galaxy is an ideal benchmark for the spectroastrometric technique given its proximity and secure BH measurement obtained with the observation of its nuclear H2O maser disk. The kinematical data have been analyzed both with the classical method based on the analysis of the rotation curves and with the new method developed by us and based on spectroastrometry. The classical method indicates that the gas disk rotates in the gravitational potential of an extended stellar mass distribution and a spatially unresolved mass of (1.7 +- 0.2) 10^7 Msun, concentrated within r < 7 pc. The new method is capable of probing gas rotation at scales which are a factor ~3.5 smaller than those probed by the rotation curve analysis. The dynamical mass spatially unresolved with the spectroastrometric method is a fa...
Faghri, Amir; Swanson, Theodore D.
1990-01-01
In the first section, improvements in the theoretical model and computational procedure for the prediction of film height and heat-transfer coefficient of the free surface flow of a radially-spreading thin liquid film adjacent to a flat horizontal surface of finite extent are presented. Flows in the presence and absence of gravity are considered. Theoretical results are compared to available experimental data with good agreement. In the presence of gravity, a hydraulic jump is present, isolating the flow into two regimes: supercritical upstream from the jump and subcritical downstream of it. In this situation, the effects of surface tension are important near the outer edge of the disk where the fluid experiences a free fall. A region of flow separation is present just downstream of the jump. In the absence of gravity, no hydraulic jump or separated flow region is present. The variation of the heat-transfer coefficient for flows in the presence and absence of gravity are also presented. In the second section, the results of a numerical simulation of the flow field and associated heat transfer coefficients are presented for the free surface flow of a thin liquid film adjacent to a horizontal rotating disk. The computation was performed for different flow rates and rotational velocities using a 3-D boundary-fitted coordinate system. Since the geometry of the free surface is unknown and dependent on flow rate, rate of rotation, and other parameters, an iterative procedure had to be used to ascertain its location. The computed film height agreed well with existing experimental measurements. The flow is found to be dominated by inertia near the entrance and close to the free surface and dominated by centrifugal force at larger radii and adjacent to the disk. The rotation enhances the heat transfer coefficient by a significant amount.
Cañas, Alejandro; Richter, Pablo; Escandar, Graciela M
2014-12-10
This work presents a green and very simple approach which enables the accurate and simultaneous determination of benzo[a]pyrene, dibenz[a,h]anthracene, benz[a]anthracene, and chrysene, concerned and potentially carcinogenic heavy-polycyclic aromatic hydrocarbons (PAHs) in interfering samples. The compounds are extracted from water samples onto a device composed of a small rotating Teflon disk, with a nylon membrane attached to one of its surfaces. After extraction, the nylon membrane containing the concentrated analytes is separated from the Teflon disk, and fluorescence excitation-emission matrices are directly measured on the nylon surface, and processed by applying parallel factor analysis (PARAFAC), without the necessity of a desorption step. Under optimum conditions and for a sample volume of 25 mL, the PAHs extraction was carried out in 20 min. Detection limits based on the IUPAC recommended criterion and relative errors of prediction were in the ranges 20-100 ng L(-1) and 5-7%, respectively. Thanks to the combination of the ability of nylon to strongly retain PAHs, the easy rotating disk extraction approach, and the selectivity of second-order calibration, which greatly simplifies sample treatment avoiding the use of toxic solvents, the developed method follows most green analytical chemistry principles.
Bender, R; Bower, G; Green, R; Thomas, J; Danks, A C; Gull, T R; Hutchings, J B; Joseph, C L; Kaiser, M E; Lauer, T R; Nelson, C H; Richstone, D O; Weistrop, D; Woodgate, B; Bender, Ralf; Kormendy, John; Bower, Gary; Green, Richard; Thomas, Jens; Danks, Anthony C.; Gull, Theodore; Lauer, Tod R.; Nelson, Charles H.; Richstone, Douglas; Weistrop, Donna; Woodgate, Bruce
2005-01-01
We present HST spectroscopy of the nucleus of M31 obtained with STIS. Spectra taken around the CaT lines at 8500 see only the red giants in the double bright- ness peaks P1 and P2. In contrast, spectra taken at 3600-5100 A are sensitive to the tiny blue nucleus embedded in P2, the lower surface brightness red nucleus. P2 has a K-type spectrum, but the embedded blue nucleus has an A-type spectrum with strong Balmer absorption lines. Given the small likelihood for stellar collisions, a 200 Myr old starburst appears to be the most plausible origin of the blue nucleus. In stellar population, size, and velocity dispersion, the blue nucleus is so different from P1 and P2 that we call it P3. The line-of-sight velocity distributions of the red stars in P1+P2 strengthen the support for Tremaine s eccentric disk model. The kinematics of P3 is consistent with a circular stellar disk in Keplerian rotation around a super-massive black hole with M_bh = 1.4 x 10^8 M_sun. The P3 and the P1+P2 disks rotate in the same sense a...
Energy Technology Data Exchange (ETDEWEB)
Wang, Li-Fang; Ou, Chin-Ching; Striebel, Kathryn A.; Chen, Jenn-Shing
2003-07-01
The goal of this research was to measure Mn dissolution from a thin porous spinel LiMn{sub 2}O{sub 4} electrode by rotating ring-disk collection experiments. The amount of Mn dissolution from the spinel LiMn{sub 2}O{sub 4} electrode under various conditions was detected by potential step chronoamperometry. The concentration of dissolved Mn was found to increase with increasing cycle numbers and elevated temperature. The dissolved Mn was not dependent on disk rotation speed, which indicated that the Mn dissolution from the disk was under reaction control. The in situ monitoring of Mn dissolution from the spinel was carried out under various conditions. The ring currents exhibited maxima corresponding to the end-of-charge (EOC) and end-of-discharge (EOD), with the largest peak at EOC. The results suggest that the dissolution of Mn from spinel LiMn{sub 2}O{sub 4} occurs during charge/discharge cycling, especially in a charged state (at >4.1 V) and in a discharged state (at <3.1 V). The largest peak at EOC demonstrated that Mn dissolution took place mainly at the top of charge. At elevated temperatures, the ring cathodic currents were larger due to the increase of Mn dissolution rate.
Wave propagation in thermoelastic saturated porous medium
Indian Academy of Sciences (India)
M D Sharma
2008-12-01
Biot ’s theory for wave propagation in saturated porous solid is modiﬁed to study the propagation of thermoelastic waves in poroelastic medium. Propagation of plane harmonic waves is considered in isotropic poroelastic medium. Relations are derived among the wave-induced temperature in the medium and the displacements of ﬂuid and solid particles. Christoffel equations obtained are modiﬁed with the thermal as well as thermoelastic coupling parameters. These equations explain the existence and propagation of four waves in the medium. Three of the waves are attenuating longitudinal waves and one is a non-attenuating transverse wave. Thermal properties of the medium have no effect on the transverse wave. The velocities and attenuation of the longitudinal waves are computed for a numerical model of liquid-saturated sandstone. Their variations with thermal as well as poroelastic parameters are exhibited through numerical examples.
Abdel-Wahed, Mohamed; Akl, Mohamed
2016-09-01
Analysis of the MHD Nanofluid boundary layer flow over a rotating disk with a constant velocity in the presence of hall current and non-linear thermal radiation has been covered in this work. The variation of viscosity and thermal conductivity of the fluid due to temperature and nanoparticles concentration and size is considered. The problem described by a system of P.D.E that converted to a system of ordinary differential equations by the similarity transformation technique, the obtained system solved analytically using Optimal Homotopy Asymptotic Method (OHAM) with association of mathematica program. The velocity profiles and temperature profiles of the boundary layer over the disk are plotted and investigated in details. Moreover, the surface shear stress, rate of heat transfer explained in details.
Indian Academy of Sciences (India)
M Turkyilmazoglu
2009-12-01
In this paper the linear stability properties of the magnetohydro-dynamic ﬂow of an incompressible, viscous and electrically conducting ﬂuid are investigated for the boundary-layer due to an inﬁnite permeable rotating-disk. The ﬂuid is subjected to an external magnetic ﬁeld perpendicular to the disk. The interest lies also in ﬁnding out the effects of uniform suction or injection. In place of the traditional linear stability method, a theoretical approach is adopted here based on the high-Reynolds-number triple-deck theory. It is demonstrated that the nonstationary perturbations evolve in accordance with an eigenrelation analytically obtained.
Melt-Mixing by Novel Pitched-Tip Kneading Disks in a co-rotating Twin-Screw Extruder
Nakayama, Yasuya; Shigeishi, Takashi; Tomiyama, Hideki; Kajiwara, Toshihisa
2010-01-01
Melt-mixing in twin-screw extruders is a key process for development of polymer composites, and quantification of mixing performance of kneading elements based on the physical process in them is a challenging problem. We discuss melt-mixing by novel kneading elements, called "pitched-tip kneading disk (ptKD)". Disk-stagger angle and tip angle are the main geometrical parameters of the ptKDs. We investigated four typical arrangements of the ptKDs, which are forwarding and backwarding disk-staggers combined with forwarding and backwarding tips, respectively. Numerical simulations under a certain feed rate and screw revolution speed were performed and mixing process was investigated by using Lagrangian statistics. It is found that the four types had different mixing characteristics, and their mixing processes were explained by a coupling effect of drag flow by disk staggering and pitched-tip and pressure flow, which is controlled by operational conditions.
Gnerucci, A.; Marconi, A.; Capetti, A.; Axon, D. J.; Robinson, A.; Neumayer, N.
2011-12-01
We measure the black hole mass in the nearby active galaxy Centaurus A (NGC 5128) using a new method based on spectroastrometry of a rotating gas disk. The spectroastrometric approach consists in measuring the photocenter position of emission lines for different velocity channels. In a previous paper we focused on the basic methodology and the advantages of the spectroastrometric approach with a detailed set of simulations demonstrating the possibilities for black hole mass measurements going below the conventional spatial resolution. In this paper we apply the spectroastrometric method to multiple longslit and integral field near infrared spectroscopic observations of Centaurus A. We find that the application of the spectroastrometric method provides results perfectly consistent with the more complex classical method based on rotation curves: the measured BH mass is nearly independent of the observational setup and spatial resolution and the spectroastrometric method allows the gas dynamics to be probed down to spatial scales of ~0.02″, i.e. 1/10 of the spatial resolution and ~1/50 of BH sphere of influence radius. The best estimate for the BH mass based on kinematics of the ionised gas is then log (MBH sin i2/M⊙) ≃ 7.5 ± 0.1 which corresponds to MBH= 9.6-1.8+2.5 × 107 M⊙ for an assumed disk inclination of i = 35°. The complementarity of this method with the classic rotation curve method will allow us to put constraints on the disk inclination which cannot be otherwise derived from spectroastrometry. With the application to Centaurus A, we have shown that spectroastrometry opens up the possibility of probing spatial scales smaller than the spatial resolution, extending the measured MBH range to new domains which are currently not accessible: smaller BHs in the local universe and similar BHs in more distant galaxies.
1991-01-01
The 3390 disks rotated faster than those in the previous model 3380. Faster disk rotation reduced rotational delay (ie. the time required for the correct area of the disk surface to move to the point where data could be read or written). In the 3390's initial models, the average rotational delay was reduced to 7.1 milliseconds from 8.3 milliseconds for the 3380 family.
Directory of Open Access Journals (Sweden)
S. Srinivas
2016-01-01
Full Text Available The present work investigates the effects of thermal-diffusion and diffusion-thermo on MHD flow of viscous fluid between expanding or contracting rotating porous disks with viscous dissipation. The partial differential equations governing the flow problem under consideration have been transformed by a similarity transformation into a system of coupled nonlinear ordinary differential equations. An analytical approach, namely the homotopy analysis method is employed in order to obtain the solutions of the ordinary differential equations. The effects of various emerging parameters on flow variables have been discussed numerically and explained graphically. Comparison of the HAM solutions with the numerical solutions is performed.
Inaba, Masanori; Quinson, Jonathan; Arenz, Matthias
2017-06-01
We investigated the influence of the ink properties of proton exchange membrane fuel cell (PEMFC) catalysts on the oxygen reduction reaction (ORR) activity determined in thin film rotating disk electrode (TF-RDE) measurements. It was found that the adaption of a previously reported ink recipe to home-made catalysts does not lead to satisfying results, although reported work could be reproduced using commercial catalyst samples. It is demonstrated that the pH of the catalyst ink, which has not been addressed in previous TF-RDE studies, is an important parameter that needs to be carefully controlled to determine the intrinsic ORR activity of high surface area catalysts.
Institute of Scientific and Technical Information of China (English)
邓兆祥; 林祥钦; 童中华
2005-01-01
An exponentially expanded space grid technique has been employed in the network simulation of chronoamperometric and voltammetric problems in spherical, cylindrical and rotating-disk electrode systems, leading to an effective simulation strategy for electrochemical problems: exponentially expanded grid network approach (EEGNA). The success of this method is largely due to the improved ability in processing the boundary singularities existing for non-planar diffusions and the enhanced simulation speed and accuracy in contrast to the uniform or quasi-uniform grid network approach.
Gnerucci, A; Capetti, A; Axon, D J; Robinson, A; Neumayer, N
2011-01-01
We measure the black hole mass in the nearby active galaxy Centaurus A (NGC 5128) using a new method based on spectroastrometry of a rotating gas disk. The spectroastrometric approach consists in measuring the photocenter position of emission lines for different velocity channels. In a previous paper we focused on the basic methodology and the advantages of the spectroastrometric approach with a detailed set of simulations demonstrating the possibilities for black hole mass measurements going below the conventional spatial resolution. In this paper we apply the spectroastrometric method to multiple longslit and integral field near infrared spectroscopic observations of Centaurus A. We find that the application of the spectroastrometric method provides results perfectly consistent with the more complex classical method based on rotation curves: the measured BH mass is nearly independent of the observational setup and spatial resolution and the spectroastrometric method allows the gas dynamics to be probed down...
Thermoelastic stress analysis system developed for industrial applications
DEFF Research Database (Denmark)
Haldorsen, Lars Magne
The thesis is divided into three parts. The first part describes an extensive evaluation of the existing thermoelastic theory. The second part describes the development and results af a reliable numerical simulation code of the thermoelastic effect and the associated heat transfer effects. Finally...
Theoretical analysis and simulation of thermoelastic deformation of bimorph microbeams
Institute of Scientific and Technical Information of China (English)
SHANG; YuanFang; YE; XiongYing; FENG; JinYang
2013-01-01
In this paper, a purely mechanical model for the thermoelastic behavior of a bimorph microbeam is presented. The thermoelastic coupling problem of the microbeam is converted to a mechanical problem by simply replacing the thermal stress in the beam with a bulk force and a surface force. Thermoelastic deformation of the bimorph microbeams with constraints frequently used in micro-electro-mechanical systems (MEMS) devices has been derived based on this model and is characterized by FEA simulation. Coincidence of the results from theory and simulation demonstrates the validity of the model. The analysis shows that a bimorph microbeam with a soft constraint and a uniform temperature field has a larger thermoelastic deformation than that with a hard constraint and a linear temperature field. In addition to the adoption of materials with large CTE mismatch,thickness ratio and length ratio of the two layers need to be optimized to get a large thermoelastic deformation.
Energy Technology Data Exchange (ETDEWEB)
Manzo, Valentina; Ulisse, Karla [Department of Inorganic and Analytical Chemistry, Faculty of Chemical and Pharmaceutical Sciences, University of Chile, P.O. Box 653, Santiago (Chile); Rodríguez, Inés [Department of Analytical and Inorganic Chemistry, Faculty of Chemical Sciences, University of Concepción (Chile); Pereira, Eduardo, E-mail: epereira@udec.cl [Department of Analytical and Inorganic Chemistry, Faculty of Chemical Sciences, University of Concepción (Chile); Richter, Pablo, E-mail: prichter@ciq.uchile.cl [Department of Inorganic and Analytical Chemistry, Faculty of Chemical and Pharmaceutical Sciences, University of Chile, P.O. Box 653, Santiago (Chile)
2015-08-19
The microextraction of diclofenac and mefenamic acid from water samples was performed by using rotating disk sorptive extraction (RDSE) with molecularly imprinted polymer (MIP) as the sorptive phase. The MIP was synthesized from the monomer 1-vinylimidazol (VI) together with the cross-linker divinylbenzene (DVB) using diphenylamine as the template molecule. Scanning electron microscopy (SEM) analyses of the MIP revealed clusters of spherical particles having a narrow size distribution, with diameters of approximately 1 μm. The optimized extraction conditions involved a disk rotation velocity of 3000 rpm, an extraction time of 120 min, a sample volume of 50 mL, and a sample pH of 2 as well as 25 mg of MIP immobilized in the disk. Desorption of the extracted analytes was performed with 5 mL of methanol for 10 min. Analysis by gas chromatography-mass spectrometry (GC–MS) was carried out after derivatization of the analytes with N-tert-butyldimethylsilyl-N-methyltrifluoroacetamide (MTBSTFA). Nonmolecularly imprinted polymer (NIP) was also synthesized for comparison. It was observed that under the same conditions, MIP extracted significantly more NSAIDs containing diphenylamine (or part of this molecule) in their structure than NIP. Higher significant differences between MIP and NIP were observed for diclofenac, mefenamic acid and paracetamol, clearly indicating the effect of the template on the extraction. Recoveries of the method were between 100 and 112%, with relative standard deviations of 5–6%. The limits of detection were between 60 and 223 ng L{sup −1}. Water samples from a wastewater treatment plant (WWTP) of Santiago de Chile, were found to contain concentrations of these acidic drugs between 1.6 and 4.3 μg L{sup −1} and between 1.4 and 3.3 μg L{sup −1} in the influent and effluent, respectively. - Highlights: • A MIP immobilized in a rotating disk sucessfully extracts NSAIDs from wastewater. • MIP had remarkably superior binding
Uncoupled thermoelasticity solutions applied on beam dumps
Ouzia, A.; Antonakakis, T.
2016-06-01
In particle accelerators the process of beam absorption is vital. At CERN particle beams are accelerated at energies of the order of TeV. In the event of a system failure or following collisions, the beam needs to be safely absorbed by dedicated protecting blocks. The thermal shock caused by the rapid energy deposition within the absorbing block causes thermal stresses that may rise above critical levels. The present paper provides a convenient expression of such stresses under hypotheses described hereafter. The temperature field caused by the beam energy deposition is assumed to be Gaussian. Such a field models a non-diffusive heat deposition. These effects are described as thermoelastic as long as the stresses remain below the proportional limit and can be analytically modeled by the coupled equations of thermoelasticity. The analytical solution to the uncoupled thermoelastic problem in an infinite domain is presented herein and matched with a finite unit radius sphere. The assumption of zero diffusion as well as the validity of the match with a finite geometry is quantified such that the obtained solutions can be rigorously applied to real problems. Furthermore, truncated series solutions, which are not novel, are used for comparison purposes. All quantities are nondimensional and the problem reduces to a dependence of five dimensionless parameters. The equations of elasticity are presented in the potential formulation where the shear potential is assumed to be nil due to the source being a gradient and the absence of boundaries. Nevertheless equivalent three-dimensional stresses are computed using the compressive potential and optimized using standard analytical optimization methods. An alternative algorithm for finding the critical points of the three-dimensional stress function is presented. Finally, a case study concerning the proton synchrotron booster dump is presented where the aforementioned analytical solutions are used and the preceding assumptions
Sankaran, Subramanian (Technical Monitor); Rice, Jeremy; Faghri, Amir; Cetegen, Baki M.
2005-01-01
A detailed analysis of the liquid film characteristics and the accompanying heat transfer of a free surface controlled liquid impinging jet onto a rotating disk are presented. The computations were run on a two-dimensional axi-symmetric Eulerian mesh while the free surface was calculated with the volume of fluid method. Flow rates between 3 and 15 1pm with rotational speeds between 50 and 200 rpm are analyzed. The effects of inlet temperature on the film thickness and heat transfer are characterized as well as evaporative effects. The conjugate heating effect is modeled, and was found to effect the heat transfer results the most at both the inner and outer edges of the heated surface. The heat transfer was enhanced with both increasing flow rate and increasing rotational speeds. When evaporative effects were modeled, the evaporation was found to increase the heat transfer at the lower flow rates the most because of a fully developed thermal field that was achieved. The evaporative effects did not significantly enhance the heat transfer at the higher flow rates.
Magneto-thermoelastic waves in a perfectly conducting elastic half-space in thermoelasticity III
Directory of Open Access Journals (Sweden)
S. K. Roychoudhuri
2005-01-01
Full Text Available The propagation of magneto-thermoelastic disturbances in an elastic half-space caused by the application of a thermal shock on the stress-free bounding surface in contact with vacuum is investigated. The theory of thermoelasticity III proposed by Green and Naghdi is used to study the interaction between elastic, thermal, and magnetic fields. Small-time approximations of solutions for displacement, temperature, stress, perturbed magnetic fields both in the vacuum and in the half-space are derived. The solutions for displacement, temperature, stress, perturbed magnetic field in the solid consist of a dilatational wave front with attenuation depending on magneto-thermoelastic coupling and also consists of a part diffusive in nature due to the damping term present in the heat transport equation, while the perturbed field in vacuum represents a wave front without attenuation traveling with Alfv'en acoustic wave speed. Displacement and temperatures are continuous at the elastic wave front, while both the stress and the perturbed magnetic field in the half-space suffer finite jumps at this location. Numerical results for a copper-like material are presented.
Steinberg, Spencer; Hodge, Vernon; Schumacher, Brian; Sovocool, Wayne
2017-03-01
Amendment of a carbon paste electrode consisting of graphite and Nujol®, with a variety of organic and inorganic materials, allows direct adsorption of silver nanoparticles (AgNPs) from aqueous solution in either open or close circuit modes. The adsorbed AgNPs are detected by stripping voltammetry. Detection limits of less than 1 ppb Ag are achievable with a rotating disk system. More than one silver peak was apparent in many of the stripping voltammograms. The appearance of multiple peaks could be due to different species of silver formed upon stripping or variation in the state of aggregation or size of nanoparticles. With most of these packing materials, dissolved Ag(+) was also extracted from aqueous solution, but, with a packing material made with Fe(II,III) oxide nanoparticles, only AgNPs were extracted. Therefore, it is the best candidate for determination of metallic AgNPs in aqueous environmental samples without interference from Ag(+).
Yin, Haibo; Chen, Xiaofang; Hou, Rujing; Zhu, Huijuan; Li, Shiqing; Huo, Yuning; Li, Hexing
2015-09-16
Ag/BiOBr film coated on the glass substrate was synthesized by a solvothermal method and a subsequent photoreduction process. Such a Ag/BiOBr film was then adhered to a hollow rotating disk filled with long-afterglow phosphor inside the chamber. The Ag/BiOBr film exhibited high photocatalytic activity for organic pollutant degradation owing to the improved visible-light harvesting and the separation of photoinduced charges. The long-afterglow phosphor could absorb the excessive daylight and emit light around 488 nm, activating the Ag/BiOBr film to realize round-the-clock photocatalysis. Because the Ag nanoparticles could extend the light absorbance of the Ag/BiOBr film to wavelengths of around 500 nm via a surface plasma resonance effect, they played a key role in realizing photocatalysis induced by long-afterglow phosphor.
Cure, M; Cidale, L
2005-01-01
The effects of rapid rotation and bi-stability upon the density contrast between the equatorial and polar directions of a B[e] supergiant are re-investigated. Based upon a new slow solution for different high rotational radiation driven winds (Cur\\'e 2004) and the fact that bi--stability allows a change in the line--force parameters ($\\alpha$, $k$, and $\\delta$), the equatorial densities are about $10^2$--$10^4$ times higher than the polar ones. These values are in qualitative agreement with the observations.
Indian Academy of Sciences (India)
M Turkyilmazoglu
2009-12-01
Direct spatial resonance phenomenon occurring in the viscous incompressible boundary layer ﬂow due to a rotating-disk is investigated in this paper based on the linear stability theory. The possible effects of suction and injection are explored on the direct spatial resonance instability mechanism detected earlier in the case of zero-suction. This instability leads to an algebraic growth of disturbances while the ﬂow is yet in the laminar regime and this in turn, may initiate the non-linearity and transition, competing with the unboundedly growing time-amplified perturbations. In line with the physical intuition, results show that suction delays the onset of resonance instability by increasing the critical Reynolds number, whereas it is enhanced by the presence of injection. The critical parameter for direct spatial resonance instability always precedes the onset value for absolute instability mechanism, after a comparison with the previous work. Therefore, in the case of suction, the onset parameter is close to the transition value as determined from the earlier experimental observations. It is further examined the inviscid nature of both absolute as well as direct spatial resonance instabilities when suction or injection is applied through the disk, and is demonstrated that these instability mechanisms are not in any way an artifact of the parallel ﬂow approximation assumed during the linearization of viscous incompressible stability equations.
Simulation of thermo-Elastics Properties of Thermal Barrier Coatings ...
African Journals Online (AJOL)
Simulation of thermo-Elastics Properties of Thermal Barrier Coatings. ... entailing improved lifetime of the coating, but with a higher thermal conductivity. ... elasticity and its evolution with the temperature as well as thermal expansion, aiming at ...
The Characteristic of Thermoelastic Waves in Transversely Isotropic Finite Cylinders
Directory of Open Access Journals (Sweden)
Bai Hao
2017-01-01
Full Text Available A theoretical as well as a numerical investigation of the propagation of thermoelastic waves and vibration of transversely isotropic cylinders of finite length is discussed. Lord-Shulman theory is adopted here to model the thermoelastic deformation of cylinders. A semi analytical finite element (SAFE method is employed to study dispersion of thermoelastic waves and natural frequencies of vibration of finite cylinders with traction free curved surfaces having both ends insulated and constrained by frictionless rigid walls. Numerical results obtained by the SAFE method for the frequencies of vibration of a sapphire rod are found to be in excellent agreement with published results. Natural frequencies of vibration for first three axisymmetric and asymmetric modes are presented graphically for a silicon nitride thermoelastic cylinder. Also, numerical results showing dispersion of both propagating and evanescent circumferential waves in infinite and finite cylinders are presented also.
APPLICATION OF BOUNDARY INTEGRAL EQUATION METHOD FOR THERMOELASTICITY PROBLEMS
Directory of Open Access Journals (Sweden)
Vorona Yu.V.
2015-12-01
Full Text Available Boundary Integral Equation Method is used for solving analytically the problems of coupled thermoelastic spherical wave propagation. The resulting mathematical expressions coincide with the solutions obtained in a conventional manner.
Thermoelastic properties of minerals at high temperature
Indian Academy of Sciences (India)
Sanjay Upadhyay; Hem Chandra; Meenakashi Joshi; Deepika P Joshi
2011-01-01
The knowledge of elasticity of the minerals is useful for interpreting the structure and composition of the lower mantle and also in seismic studies. The purpose of the present study is to discuss a simple and straightforward method for evaluating thermoelastic properties of minerals at high temperatures. We have extended the Kumar’s formulation by taking into the account the concept of anharmonicity in minerals above the Debye temperature (D). In our present study, we have investigated the thermophysical properties of two minerals (pyrope-rich garnet and MgAl2O4) under high temperatures and calculated the second-order elastic constant () and bulk modulus (T) of the above minerals, in two cases ﬁrst by taking Anderson–Gruneisen parameter (T) as temperature-independent and then by treating T as temperature-dependent parameter. The results obtained when T is temperature-dependent are in close agreement with experimental data.
Penna, Rachele R.; de Sanctis, Ugo; Catalano, Martina; Brusasco, Luca; Grignolo, Federico M.
2017-01-01
AIM To compare the repeatability/reproducibility of measurement by high-resolution Placido disk-based topography with that of a high-resolution rotating Scheimpflug camera and assess the agreement between the two instruments in measuring corneal power in eyes with keratoconus and post-laser in situ keratomileusis (LASIK). METHODS One eye each of 36 keratoconic patients and 20 subjects who had undergone LASIK was included in this prospective observational study. Two independent examiners worked in a random order to take three measurements of each eye with both instruments. Four parameters were measured on the anterior cornea: steep keratometry (Ks), flat keratometry (Kf), mean keratometry (Km), and astigmatism (Ks-Kf). Intra-examiner repeatability and inter-examiner reproducibility were evaluated by calculating the within-subject standard deviation (Sw) the coefficient of repeatability (R), the coefficient of variation (CoV), and the intraclass correlation coefficient (ICC). Agreement between instruments was tested with the Bland-Altman method by calculating the 95% limits of agreement (95% LoA). RESULTS In keratoconic eyes, the intra-examiner and inter-examiner ICC were >0.95. As compared with measurement by high-resolution Placido disk-based topography, the intra-examiner R of the high-resolution rotating Scheimpflug camera was lower for Kf (0.32 vs 0.88), Ks (0.61 vs 0.88), and Km (0.32 vs 0.84) but higher for Ks-Kf (0.70 vs 0.57). Inter-examiner R values were lower for all parameters measured using the high-resolution rotating Scheimpflug camera. The 95% LoA were -1.28 to +0.55 for Kf, -1.36 to +0.99 for Ks, -1.08 to +0.50 for Km, and -1.11 to +1.48 for Ks-Kf. In the post-LASIK eyes, the intra-examiner and inter-examiner ICC were >0.87 for all parameters. The intra-examiner and inter-examiner R were lower for all parameters measured using the high-resolution rotating Scheimpflug camera. The intra-examiner R was 0.17 vs 0.88 for Kf, 0.21 vs 0.88 for Ks, 0.17 vs 0
Faghri, Amir; Swanson, Theodore D.
1989-01-01
The numerical and experimental analysis of a thin liquid film on a rotating and a stationary disk related to the development of an absorber unit for a high capacity spacecraft absorption cooling system, is described. The creation of artificial gravity by the use of a centrifugal field was focused upon in this report. Areas covered include: (1) One-dimensional computation of thin liquid film flows; (2) Experimental measurement of film height and visualization of flow; (3) Two-dimensional computation of the free surface flow of a thin liquid film using a pressure optimization method; (4) Computation of heat transfer in two-dimensional thin film flow; (5) Development of a new computational methodology for the free surface flows using a permeable wall; (6) Analysis of fluid flow and heat transfer in a thin film in the presence and absence of gravity; and (7) Comparison of theoretical prediction and experimental data. The basic phenomena related to fluid flow and heat transfer on rotating systems reported here can also be applied to other areas of space systems.
East, Gaston A; Marinho, Epitácio P
2005-03-01
A simple and reliable method for the determination of mercury in hair on a rotating gold disk electrode using subtractive anodic stripping voltammetry without removal of oxygen is reported. Voltammetric and microwave parameters were optimized to obtain the best analytical results. Parameters such as supporting electrolyte concentration, influence of chloride in the Hg peak, deposition potential, scan rate, accumulation time, rotation rate, square-wave amplitude, and electrode conditioning were studied. Pressurized microwave-assisted digestion of hair, suitable for the accurate voltammetric determination of Hg, was evaluated using six acid mixtures and several time-power programs. Under the optimized conditions, no interference by copper, cadmium, lead, nickel, manganese, iron, or zinc was found at concentrations corresponding to their occurrence in normal hair. A calibration plot between 6,67 and 46,69 microg/L was linear, with r(2) better than 0.999. The detection limit for a deposition time of 60 s at 254 g was calculated as 1.92 nM (3omega). Validation of the method was demonstrated with the use of a certified reference sample of hair. Eight real samples of hair (four unexposed children and four exposed persons) were also analyzed.
Fuente, A.; Gerin, M.; Pety, J.; Commerçon, B.; Agúndez, M.; Cernicharo, J.; Marcelino, N.; Roueff, E.; Lis, D. C.; Wootten, H. A.
2017-10-01
The extremely young Class 0 object B1b-S and the first hydrostatic core (FSHC) candidate, B1b-N, provide a unique opportunity to study the chemical changes produced in the elusive transition from the prestellar core to the protostellar phase. We present 40″ × 70″ images of Barnard 1b in the 13CO 1 → 0, C18O 1 → 0, NH2D 11,1a→ 10,1s, and SO 32→ 21 lines obtained with the NOEMA interferometer. The observed chemical segregation allows us to unveil the physical structure of this young protostellar system down to scales of 500 au. The two protostellar objects are embedded in an elongated condensation, with a velocity gradient of 0.2-0.4 m s-1 au-1 in the east-west direction, reminiscent of an axial collapse. The NH2D data reveal cold and dense pseudo-disks (R 500 - 1000 au) around each protostar. Moreover, we observe evidence of pseudo-disk rotation around B1b-S. We do not see any signature of the bipolar outflows associated with B1b-N and B1b-S, which were previously detected in H2CO and CH3OH, in any of the imaged species. The non-detection of SO constrains the SO/CH3OH abundance ratio in the high-velocity gas. Based on observations carried out with the IRAM Northern Extended Millimeter Array (NOEMA). IRAM is supported by INSU/ CNRS (France), MPG (Germany), and IGN (Spain).The reduced datacube is only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/606/L3
DEFF Research Database (Denmark)
Sørensen, Jens Nørkær; Gelfgat, A. Yu; Naumov, I. V.;
2009-01-01
The three-dimensional axisymmetry-breaking instability of axisymmetric flow between a rotating lid and a stationary cylinder is analyzed both numerically and experimentally for the case of tall cylinders with the height/radius aspect ratio between 3.3 and 5.5. A complete stability diagram...... for each mode. The onset of three-dimensional flow behavior is measured by combining the high spatial resolution of particle image velocimetry and the temporal accuracy of laser Doppler anemometry. The results are compared to the numerical stability analysis. The measured onset of three dimensionality...... is in a good agreement with the numerical results. Disagreements observed in supercritical regimes can be explained by secondary bifurcations that are not accounted for by linear stability analysis of the primary base flow. ©2009 American Institute of Physics...
Gnerucci, A.; Marconi, A.; Capetti, A.; Axon, D. J.; Robinson, A.
2013-01-01
We present new CRIRES spectroscopic observations of the Brγ emission line in the nuclear region of the Circinus galaxy, obtained with the aim of measuring the black hole (BH) mass with the spectroastrometric technique. The Circinus galaxy is an ideal benchmark for the spectroastrometric technique given its proximity and secure BH measurement obtained with the observation of its nuclear H2O maser disk. The kinematical data have been analyzed both with the classical method based on the analysis of the rotation curves and with the new method developed by us that is based on spectroastrometry. The classical method indicates that the gas disk rotates in a gravitational potential resulting from an extended stellar mass distribution and a spatially unresolved dynamical mass of (1.7 ± 0.2) × 107 M⊙, concentrated within r curve analysis, highlighting the potential of spectroastrometry. The dynamical mass, which is spatially unresolved with the spectroastrometric method, is a factor ~2 smaller, 7.9+1.4-1.1 × 106M⊙, indicating that spectroastrometry has been able to spatially resolve the nuclear mass distribution down to 2 pc scales. This unresolved mass is still a factor ~4.5 larger than the BH mass measurement obtained with the H2O maser emission, indicating that even with spectroastrometry, it has not been possible to resolve the sphere of influence of the BH. Based on literature data, this spatially unresolved dynamical mass distribution is likely dominated by warm molecular gas and has been tentatively identified with the circum-nuclear torus that prevents a direct view of the central BH in Circinus. This mass distribution, with a size of ~2 pc, is similar in shape to that of the star cluster of the Milky Way, suggesting that a molecular torus, forming stars at a high rate, might be the earlier evolutionary stage of the nuclear star clusters that are common in late-type spirals. Based on observations made with ESO Telescopes at the Paranal Observatory under
Decay property of Timoshenko system in thermoelasticity
Said-Houari, Belkacem
2011-12-30
We investigate the decay property of a Timoshenko system of thermoelasticity in the whole space for both Fourier and Cattaneo laws of heat conduction. We point out that although the paradox of infinite propagation speed inherent in the Fourier law is removed by changing to the Cattaneo law, the latter always leads to a solution with the decay property of the regularity-loss type. The main tool used to prove our results is the energy method in the Fourier space together with some integral estimates. We derive L 2 decay estimates of solutions and observe that for the Fourier law the decay structure of solutions is of the regularity-loss type if the wave speeds of the first and the second equations in the system are different. For the Cattaneo law, decay property of the regularity-loss type occurs no matter what the wave speeds are. In addition, by restricting the initial data to U 0∈H s(R)∩L 1,γ(R) with a suitably large s and γ ∈ [0,1], we can derive faster decay estimates with the decay rate improvement by a factor of t -γ/2. © 2011 John Wiley & Sons, Ltd.
Krittayavathananon, Atiweena; Srimuk, Pattarachai; Luanwuthi, Santamon; Sawangphruk, Montree
2014-12-16
Although metal nanoparticle/graphene composites have been widely used as the electrode in electrochemical sensors, two effects, consisting of the particle size of the nanoparticles and the hydrodynamic diffusion of analytes to the electrodes, are not yet fully understood. In this work, palladium nanoparticles/reduced graphene oxide (PdNPs/rGO) composites were synthesized using an in situ polyol method. Palladium(II) ions and graphene oxide were reduced together with a reducing agent, ethylene glycol. By varying the concentration of palladium(II) nitrate, PdNPs with different sizes were decorated on the surface of rGO sheets. The as-fabricated PdNPs/rGO rotating disk electrodes (RDEs) were investigated toward hydrazine detection. Overall, a 3.7 ± 1.4 nm diameter PdNPs/rGO RDE exhibits high performance with a rather low limit of detection of about 7 nM at a rotation speed of 6000 rpm and provides a wide linear range of 0.1-1000 μM with R(2) = 0.995 at 2000 rpm. This electrode is highly selective to hydrazine without interference from uric acid, glucose, ammonia, caffeine, methylamine, ethylenediamine, hydroxylamine, n-butylamine, adenosine, cytosine, guanine, thymine, and l-arginine. The PdNPs/rGO RDEs with larger sizes show lower detection performance. Interestingly, the detection performance of the electrodes is sensitive to the hydrodynamic diffusion of hydrazine. The as-fabricated electrode can detect trace hydrazine in wastewater with high stability, demonstrating its practical use as an electrochemical sensor. These findings may lead to an awareness of the effect of the hydrodynamic diffusion of analyte that has been previously ignored, and the 3.7 ± 1.4 nm PdNPs/rGO RDE may be useful toward trace hydrazine detection, especially in wastewater from related chemical industries.
Directory of Open Access Journals (Sweden)
Khan Najeeb Alam
2017-03-01
Full Text Available An investigation is performed for an alyzing the effect of entropy generation on the steady, laminar, axisymmetric flow of an incompressible Powell-Eyring fluid. The flow is considered in the presence of vertically applied magnetic field between radially stretching rotating disks. The Energy and concentration equation is taking into account to investigate the heat dissipation, Soret, Dufour and Joule heating effects. To describe the considered flow non-dimensionalized equations, an exact similarity function is used to reduce a set of the partial differential equation into a system of non-linear coupled ordinary differential equation with the associated boundary conditions. Using homotopy analysis method (HAM, an analytic solution for velocity, temperature and concentration profiles are obtained over the entire range of the imperative parameters. The velocity components, concentration and temperature field are used to determine the entropy generation. Plots illustrate important results on the effect of physical flow parameters. Results obtained by means of HAM are then compared with the results obtained by using optimized homotopy analysis method (OHAM. They are in very good agreement.
Directory of Open Access Journals (Sweden)
Patrizia Bocchetta
2016-01-01
Full Text Available This paper reports on the quantitative assessment of the oxygen reduction reaction (ORR electrocatalytic activity of electrodeposited Mn/polypyrrole (PPy nanocomposites for alkaline aqueous solutions, based on the Rotating Disk Electrode (RDE method and accompanied by structural characterizations relevant to the establishment of structure-function relationships. The characterization of Mn/PPy films is addressed to the following: (i morphology, as assessed by Field-Emission Scanning Electron Microscopy (FE-SEM and Atomic Force Microscope (AFM; (ii local electrical conductivity, as measured by Scanning Probe Microscopy (SPM; and (iii molecular structure, accessed by Raman Spectroscopy; these data provide the background against which the electrocatalytic activity can be rationalised. For comparison, the properties of Mn/PPy are gauged against those of graphite, PPy, and polycrystalline-Pt (poly-Pt. Due to the literature lack of accepted protocols for precise catalytic activity measurement at poly-Pt electrode in alkaline solution using the RDE methodology, we have also worked on the obtainment of an intralaboratory benchmark by evidencing some of the time-consuming parameters which drastically affect the reliability and repeatability of the measurement.
A collimated jet and an infalling-rotating disk in G192.16-3.84 traced by H2O maser emission
Imai, H; Hirota, T; Umemoto, T; Sorai, K; Kondo, T; Imai, Hiroshi; Omodaka, Toshihiro; Hirota, Tomoya; Umemoto, Tomofumi; Sorai, Kazuo; Kondo, Tetsuro
2006-01-01
We report H2O masers associated with the massive-star forming region G192.16-3.84 observed with the new Japan VLBI network at three epochs spanned for two months, which have revealed the three-dimensional kinematical structure of the whole \\h2o maser region in G192.16-3.84, containing two young stellar objects separated by ~1200 AU. The maser spatio-kinematical structure has well persisted since previous observations, in which the masers are expected to be associated with a highly-collimated bipolar jet and an infalling-rotating disk in the northern and southern clusters of H2O maser features, respectively. We estimated a jet expansion speed of ~100 km/s and re-estimated a dynamical age of the whole jet to be 5.6x10^4 yrs. We have investigated the spatial distribution of Doppler velocities during the previous and present observations and relative proper motions of H2O maser features in the southern cluster, and a relative bulk motion between the two maser clusters. They are well explained by a model of an inf...
New Poisson's Type Integral Formula for Thermoelastic Half-Space
Directory of Open Access Journals (Sweden)
Victor Seremet
2009-01-01
Full Text Available A new Green's function and a new Poisson's type integral formula for a boundary value problem (BVP in thermoelasticity for a half-space with mixed boundary conditions are derived. The thermoelastic displacements are generated by a heat source, applied in the inner points of the half-space and by temperature, and prescribed on its boundary. All results are obtained in closed forms that are formulated in a special theorem. A closed form solution for a particular BVP of thermoelasticity for a half-space also is included. The main difficulties to obtain these results are in deriving of functions of influence of a unit concentrated force onto elastic volume dilatation Θ( and, also, in calculating of a volume integral of the product of function Θ( and Green's function in heat conduction. Using the proposed approach, it is possible to extend the obtained results not only for any canonical Cartesian domain, but also for any orthogonal one.
A Study of Appropriate Arrangement of Thermoelastic Actuator
Directory of Open Access Journals (Sweden)
Bohus Ulrych
2008-01-01
Full Text Available The actuators working on the principle of thermoelasticity belong to novel elements of this kind that are characterized by very high forces acting at relatively low shifts of the dilatation element. The paper analyses their operation properties in the dependence of selected geometrical parameters of the device and also the amplitude and frequency of the field current. The task is solved as a coupled electromagnetic-thermoelastic problem. The theoretical considerations are illustrated on an example whose results are discussed.
Solving the Linear 1D Thermoelasticity Equations with Pure Delay
Directory of Open Access Journals (Sweden)
Denys Ya. Khusainov
2015-01-01
Full Text Available We propose a system of partial differential equations with a single constant delay τ>0 describing the behavior of a one-dimensional thermoelastic solid occupying a bounded interval of R1. For an initial-boundary value problem associated with this system, we prove a well-posedness result in a certain topology under appropriate regularity conditions on the data. Further, we show the solution of our delayed model to converge to the solution of the classical equations of thermoelasticity as τ→0. Finally, we deduce an explicit solution representation for the delay problem.
Energy Technology Data Exchange (ETDEWEB)
Moulai-Mostefa, N. [Centre Universitaire Yahia Fares, Ain D' Heb, Medea (Algeria); Brou, A.; Ding, L.H.; Jaffrin, M.Y. [Universite de Technologie de Compiegne, UMR CNRS 6600, Dept. Genie Bilogique, 60 (France)
2005-04-01
Oil separation from oil-water effluents containing secondary emulsions is very difficult by traditional techniques and requires using ultrafiltration through a membrane. Oil-water emulsions were ultra-filtered using a prototype of a rotating disk dynamic filtration system equipped with a 190 cm{sup 2} 50 kDa circular membrane. The turbidity of initial solution at 4%wt oil concentration (21 900 NTU) dropped to 2 NTU in the permeate after 15 min of filtration, representing an oil rejection coefficient of 99.5%. Permeate fluxes increased with disk rotation speed to reach 90 l.h{sup -1}.m{sup -2} at 2000 rpm and 24 deg. C. The addition of 6 mm vanes on the disk increased the permeate flux by 100% at the same speed. Micro emulsions were composed of 4 to 20% of cyclohexane, 0.5 to 16% of 2-butanol and 0.25 to 8% of dodecyl sodium sulphate (SDS) in pure water. Permeate fluxes, which were very high (200 l.h{sup -1}.m{sup -2}) at 2000 rpm with a smooth disk and the most dilute solution, dropped to 15 l.h{sup -1}.m{sup -2} for the most concentrated one. Addition of vanes permitted to increase these fluxes by 100%. (authors)
Nonlocal theory of longitudinal waves in thermoelastic bars
Directory of Open Access Journals (Sweden)
Esin Inan
1991-05-01
Full Text Available The longitudinal waves in thermoelastic bars are investigated in the context of nonlocal theory. Using integral forms of constitutive equations, balance of momenta and energy, field equations are obtained. Then the frequency equation is found in generalized form. To obtain tangible results, an approximate procedure is applied and numerical results are given for short waves.
A review of using thermoelasticity for structural integrity assessment
Directory of Open Access Journals (Sweden)
L. Marsavina
2014-01-01
Full Text Available The advances in the use of thermoelastic stress analysis (TSA for fracture mechanics assessment are reviewed. The development of techniques to determine stress intensity factor is presented followed by the application of these techniques to fatigue crack growth, crack closure and the study of mixed mode cracks.
Loss of exponential stability for a thermoelastic system with memory
Directory of Open Access Journals (Sweden)
Bruno Ferreira Alves
2010-09-01
Full Text Available In this article we study a thermoelastic system considering the linearized model proposed by Gurtin and Pipkin [8] instead of the Fourier's law for the heat flux. We use theory of semigroups [9, 11] combining Pruss' Theorem [10] and the idea developed in [5] to show that the system is not exponentially stable.
Approximation in LQG control of a thermoelastic rod
Gibson, J. S.; Rosen, I. G.; Tao, G.
1989-01-01
Control and estimator gains are computed for linear-quadratic-Gaussian (LQG) optimal control of the axial vibrations of a thermoelastic rod. The computations are based on a modal approximation of the partial differential equations representing the rod, and convergence of the approximations to control and estimator gains is the main issue.
Santiago de Jesus, Diana
An effort to develop electrochemically smaller and well-dispersed catalytic material on a high surface area carbon material is required for fuel cell applications. In terms of pure metal catalysts, platinum has shown to be the most common catalyst used in fuel cells, but suffers from poisoning when carbon monoxide is strongly adsorbed on its surface when used for direct methanol fuel cell applications. The addition of a metal with the ability to form oxides, such as ruthenium, helps to oxidize the carbon monoxide, freeing the platinum surface for new methanol oxidation. The deposition of catalysts of PtRu onto a carbon support helps to increase the active surface area of the catalyst. Vulcan X is the most commonly used of the amorphous carbon materials for fuel cell applications. Also, a high-surface-area carbon material of interest is carbon nano-onions (CNOs), also known as multilayer fullerenes. The most convenient synthetic method for CNOs is annealing nanodiamond particles, thus retaining the size of the precursors and providing the possibility to prepare very small nanocatalysts using electrochemical techniques. A rotating disk-slurry electrode (RoDSE) technique was developed as a unique method to electrochemically prepare bulk Pt/Carbon and PtRu/Carbon nanocatalysts avoiding a constant contact of the carbon support to an electrode surface during the electrodeposition process. The nanocatalysts were prepared by using a slurry that was saturated with functionalized Vulcan XC-72R and the metal precursor in sulfuric acid. The electrochemically prepared Pt/C and PtRu/C catalysts were characterized by using TEM, STEM, XRD, XRF, TGA, XPS and electrochemical techniques. A computational analysis also was done.
A 2D Time Domain DRBEM Computer Model for MagnetoThermoelastic Coupled Wave Propagation Problems
Directory of Open Access Journals (Sweden)
Mohamed Abdelsabour Fahmy
2014-07-01
Full Text Available A numerical computer model based on the dual reciprocity boundary element method (DRBEM is extended to study magneto-thermoelastic coupled wave propagation problems with relaxation times involving anisotropic functionally graded solids. The model formulation is tested through its application to the problem of a solid placed in a constant primary magnetic field acting in the direction of the z-axis and rotating about this axis with a constant angular velocity. In the case of two-dimensional deformation, an implicit-explicit time domain DRBEM was presented and implemented to obtain the solution for the displacement and temperature fields. A comparison of the results is presented graphically in the context of Lord and Shulman (LS and Green and Lindsay (GL theories. Numerical results that demonstrate the validity of the proposed method are also presented graphically.
Ringed accretion disks: equilibrium configurations
Pugliese, D
2015-01-01
We investigate a model of ringed accretion disk, made up by several rings rotating around a supermassive Kerr black hole attractor. Each toroid of the ringed disk is governed by the General Relativity hydrodynamic Boyer condition of equilibrium configurations of rotating perfect fluids. Properties of the tori can be then determined by an appropriately defined effective potential reflecting the background Kerr geometry and the centrifugal effects. The ringed disks could be created in various regimes during the evolution of matter configurations around supermassive black holes. Therefore, both corotating and counterrotating rings have to be considered as being a constituent of the ringed disk. We provide constraints on the model parameters for the existence and stability of various ringed configurations and discuss occurrence of accretion onto the Kerr black hole and possible launching of jets from the ringed disk. We demonstrate that various ringed disks can be characterized by a maximum number of rings. We pr...
Results and applications in thermoelasticity of materials with voids
Directory of Open Access Journals (Sweden)
Michele Ciarletta
1991-05-01
Full Text Available We consider the linear theory of a thermoelastic porous solid in which the skeletal or matrix is a thermoelastic material and the interstices are void of material. We assume that the initial body is free from stresses. The concept of a distributed body asserts that the mass density at time t has the decomposition γν, where γ is the density of the matrix material and ν (0 In the first part, in order to derive some applications of the reciprocity theorem, we recall some results established by same authors in [3]. Then we obtain integral representations of the solution and prove that the solving of the boundary-initial value problem can be reduced to the solving of an associated uncoupled problem and to an integral equation for the volume fraction field.
[Thermo-elastic stress analysis of human bones].
Krüger-Franke, M; Heiland, A; Plitz, W; Refior, H J
1995-01-01
The Thermoelastic Stress Analysis (THESA) is a widely used procedure in motorcar- and airplane engineering. This study investigated the reliability of THESA for stress analysis of human bone. A human femur was cyclic stressed and the resulting stress pattern was scanned from the surface of the bone by means of the thermoelastic stress measuring instrument SPATE 9000. To proof whether the scan of SPATE 9000 is equivalent to the stress distribution of human femur surface, strain gauges are used to control the results at two different regions of the femur diaphysis under equal but static conditions. It could be shown, that both measuring methods lead to corresponding results of stress pattern on human femur surface.
Inverse transient thermoelastic deformations in thin circular plates
Indian Academy of Sciences (India)
A K Tikhe; K C Deshmukh
2005-10-01
This paper deals with the determination of unknown heating temperatures and temperature distributions on the upper surface of a thin circular plate, deﬁned as $0 \\leq r \\leq a,−b/2 \\leq z \\leq b/2$. The expressions of unknown heating temperatures and temperature distributions are obtained in series form, involving Bessel’s functions with the help of the integral transform technique. Thermoelastic deformations are discussed with the help of temperature and are illustrated numerically.
Global solutions to the equation of thermoelasticity with fading memory
Okada, Mari; Kawashima, Shuichi
2017-07-01
We consider the initial-history value problem for the one-dimensional equation of thermoelasticity with fading memory. It is proved that if the data are smooth and small, then a unique smooth solution exists globally in time and converges to the constant equilibrium state as time goes to infinity. Our proof is based on a technical energy method which makes use of the strict convexity of the entropy function and the properties of strongly positive definite kernels.
Axisymmetric free vibrations of infinite micropolar thermoelastic plate
Institute of Scientific and Technical Information of China (English)
Rajneesh Kumar; Geeta Partap
2007-01-01
The propagation of axisymmetric free vibrations in an infinite homogeneous isotropic micropolar thermoelastic plate without energy dissipation subjected to stress free and rigidly fixed boundary conditions is investigated. The secular equations for homogeneous isotropic micropolar thermoelastic plate without energy dissipation in closed form for symmetric and skew symmetric wave modes of propagation are derived. The different regions of secular equations are obtained. At short wavelength limits, the secular equations for symmetric and skew symmetric modes of wave propagation in a stress free insulated and isothermal plate reduce to Rayleigh surface wave frequency equation.The results for thermoelastic, micropolar elastic and elastic materials are obtained as particular cases from the derived secular equations. The amplitudes of displacement components, microrotation and temperature distribution are also computed during the symmetric and skew symmetric motion of the plate. The dispersion curves for symmetric and skew symmetric modes and amplitudes of displacement components, microrotation and temperature distribution in case of fundamental symmetric and skew symmetric modes are presented graphically. The analytical and numerical results are found to be in close agreement.
The VLab repository of thermodynamics and thermoelastic properties of minerals
Da Silveira, P. R.; Sarkar, K.; Wentzcovitch, R. M.; Shukla, G.; Lindemann, W.; Wu, Z.
2015-12-01
Thermodynamics and thermoelastic properties of minerals at planetary interior conditions are essential as input for geodynamics simulations and for interpretation of seismic tomography models. Precise experimental determination of these properties at such extreme conditions is very challenging. Therefore, ab initio calculations play an essential role in this context, but at the cost of great computational effort and memory use. Setting up a widely accessible and versatile mineral physics database can relax unnecessary repetition of such computationally intensive calculations. Access to such data facilitates transactional interaction across fields and can advance more quickly insights about deep Earth processes. Hosted by the Minnesota Supercomputing Institute, the Virtual Laboratory for Earth and Planetary Materials (VLab) was designed to develop and promote the theory of planetary materials using distributed, high-throughput quantum calculations. VLab hosts an interactive database of thermodynamics and thermoelastic properties or minerals computed by ab initio. Such properties can be obtained according to user's preference. The database is accompanied by interactive visualization tools, allowing users to repeat and build upon previously published results. Using VLab2015, we have evaluated thermoelastic properties, such as elastic coefficients (Cij), Voigt, Reuss, and Voigt-Reuss-Hill aggregate averages for bulk (K) and shear modulus (G), shear wave velocity (VS), longitudinal wave velocity (Vp), and bulk sound velocity (V0) for several important minerals. Developed web services are general and can be used for crystals of any symmetry. Results can be tabulated, plotted, or downloaded from the VLab website according to user's preference.
Global Models for Embedded, Accreting Protostellar Disks
Kratter, Kaitlin M; Krumholz, Mark R
2007-01-01
Most analytic work to date on protostellar disks has focused on disks in isolation from their environments. However, observations are now beginning to probe the earliest, most embedded phases of star formation, during which disks are rapidly accreting from their parent cores and cannot be modeled in isolation. We present a simple, one-zone model of protostellar accretion disks with high mass infall rates. Our model combines a self-consistent calculation of disk temperatures with an approximate treatment of angular momentum transport via several mechanisms. We use this model to survey the properties of protostellar disks across a wide range of stellar masses and evolutionary times, and make predictions for disks' masses, sizes, spiral structure, and fragmentation that will be directly testable by future large-scale surveys of deeply embedded disks. We define a dimensionless accretion-rotation parameter which, in conjunction with the disk's temperature, controls the disk evolution. We track the dominant mode of...
Magnetic interchange instability of accretion disks
Kaisig, M.; Tajima, T.; Lovelace, R. V. E.
1992-01-01
The nonlinear evolution of the magnetic interchange or buoyancy instability of a differentially rotating disk threaded by an ordered vertical magnetic field is investigated. A 2D ideal fluid in the equatorial plane of a central mass in the corotating frame of reference is considered as a model for the disk. If the rotation rate of the disk is Keplerian, the disk is found to be stable. If the vertical magnetic field is sufficiently strong, and the field strength decreases with distance from the central object, and thus the rotation of the disk deviates from Keplerian, if is found that an instability develops. The magnetic flux and disk matter expand outward in certain ranges of azimuth, while disk matter with less magnetic flux moves inward over the remaining range of azimuth, showing a characteristic development of an interchange instability.
Development of Powered Disk Type Sugar Cane Stubble Saver
Directory of Open Access Journals (Sweden)
Radite P.A.S.
2009-04-01
Full Text Available The objective of this research was to design, fabricate and test a prototype of sugar cane stubble saver based on powered disk mechanism. In this research, a heavy duty disk plow or disk harrow was used as a rotating knife to cut the sugarcane stubble. The parabolic disk was chosen because it is proven reliable as soil working tools and it is available in the market as spare part of disk plow or disk harrow unit. The prototype was mounted on the four wheel tractor’s three point hitch, and powered by PTO of the tractor. Two kinds of disks were used in these experiments, those were disk with regular edge or plain disk and disk with scalloped edge or scalloped disk. Both disks had diameter of 28 inch. Results of field test showed that powered disk mechanism could satisfy cut sugar cane’s stubble. However, scalloped disk type gave smoother stubble cuts compared to that of plain disk. Plain disk type gave broken stubble cut. Higher rotation (1000 rpm resulted better cuts as compared to lower rotation (500 rpm both either on plain disk and scalloped disk. The developed prototype could work below the soil surface at depth of 5 to 10 cm. With tilt angle setting 20O and disk angle 45O the width of cut was about 25 cm.
van der Kruit, P. C.; Freeman, K. C.
The disks of disk galaxies contain a substantial fraction of their baryonic matter and angular momentum, and much of the evolutionary activity in these galaxies, such as the formation of stars, spiral arms, bars and rings, and the various forms of secular evolution, takes place in their disks. The
Fabrication of Large YBCO Superconducting Disks
Koczor, Ronald J.; Noever, David A.; Robertson, Glen A.
1999-01-01
We have undertaken fabrication of large bulk items to develop a repeatable process and to provide test articles in laboratory experiments investigating reported coupling of electromagnetic fields with the local gravity field in the presence of rotating superconducting disks. A successful process was developed which resulted in fabrication of 30 cm diameter annular disks. The disks were fabricated of the superconductor YBa2Cu3O(7-x). Various material parameters of the disks were measured.
Vertical Structure of Magnetized Accretion Disks around Young Stars
Lizano, S; Boehler, Y; D'Alessio, P
2015-01-01
We model the vertical structure of magnetized accretion disks subject to viscous and resistive heating, and irradiation by the central star. We apply our formalism to the radial structure of magnetized accretion disks threaded by a poloidal magnetic field dragged during the process of star formation developed by Shu and coworkers. We consider disks around low mass protostars, T Tauri, and FU Orionis stars. We consider two levels of disk magnetization, $\\lambda_{sys} = 4$ (strongly magnetized disks), and $\\lambda_{sys} = 12$ (weakly magnetized disks). The rotation rates of strongly magnetized disks have large deviations from Keplerian rotation. In these models, resistive heating dominates the thermal structure for the FU Ori disk. The T Tauri disk is very thin and cold because it is strongly compressed by magnetic pressure; it may be too thin compared with observations. Instead, in the weakly magnetized disks, rotation velocities are close to Keplerian, and resistive heating is always less than 7\\% of the visc...
Mode-Ⅰ crack in a two-dimensional fibre-reinforced generalized thermoelastic problem
Institute of Scientific and Technical Information of China (English)
Kh. Lotfy
2012-01-01
A general model of the equations of the Lord-?ulman theory including one relaxation time and the Green-Lindsay theory with two relaxation times,as well as the classical dynamical coupled theory,are applied to the study of the influence of reinforcement on the total deformation for an infinite space weakened by a finite linear opening modeI crack.We study the influence of reinforcement on the total deformation of rotating thermoelastic half-space and their interaction with each other.The material is homogeneous isotropic elastic half space.The crack is subjected to prescribed temperature and stress distributions.The normal mode analysis is used to obtain the exact expressions for displacement components,force stresses,and temperature.The variations of the considered variables with the horizontal distance are illustrated graphically.Comparisons are made with the results obtained in the three theories with and without rotation.A comparison is also made between the two theories for different depths.
Compactness of the difference between the porous thermoelastic semigroup and its decoupled semigroup
Directory of Open Access Journals (Sweden)
El Mustapha Ait Benhassi
2015-06-01
Full Text Available Under suitable assumptions, we prove the compactness of the difference between the porous thermoelastic semigroup and its decoupled one. This will be achieved by proving the norm continuity of this difference and the compactness of the difference between the resolvents of their generators. Applications to porous thermoelastic systems are given.
Generalized thermoelastic diffusive waves in heat conducting materials
Sharma, J. N.
2007-04-01
Keeping in view the applications of diffusion processes in geophysics and electronics industry, the aim of the present paper is to give a detail account of the plane harmonic generalized thermoelastic diffusive waves in heat conducting solids. According to the characteristic equation, three longitudinal waves namely, elastodiffusive (ED), mass diffusion (MD-mode) and thermodiffusive (TD-mode), can propagate in such solids in addition to transverse waves. The transverse waves get decoupled from rest of the fields and hence remain unaffected due to temperature change and mass diffusion effects. These waves travel without attenuation and dispersion. The other generalized thermoelastic diffusive waves are significantly influenced by the interacting fields and hence suffer both attenuation and dispersion. At low frequency mass diffusion and thermal waves do not exist but at high-frequency limits these waves propagate with infinite velocity being diffusive in character. Moreover, in the low-frequency regions, the disturbance is mainly dominant by mechanical process of transportation of energy and at high-frequency regions it is significantly dominated by a close to diffusive process (heat conduction or mass diffusion). Therefore, at low-frequency limits the waves like modes are identifiable with small amplitude waves in elastic materials that do not conduct heat. The general complex characteristic equation is solved by using irreducible case of Cardano's method with the help of DeMoivre's theorem in order to obtain phase speeds, attenuation coefficients and specific loss factor of energy dissipation of various modes. The propagation of waves in case of non-heat conducting solids is also discussed. Finally, the numerical solution is carried out for copper (solvent) and zinc (solute) materials and the obtained phase velocities, attenuation coefficients and specific loss factor of various thermoelastic diffusive waves are presented graphically.
RINGED ACCRETION DISKS: EQUILIBRIUM CONFIGURATIONS
Energy Technology Data Exchange (ETDEWEB)
Pugliese, D.; Stuchlík, Z., E-mail: d.pugliese.physics@gmail.com, E-mail: zdenek.stuchlik@physics.cz [Institute of Physics and Research Centre of Theoretical Physics and Astrophysics, Faculty of Philosophy and Science, Silesian University in Opava, Bezručovo náměstí 13, CZ-74601 Opava (Czech Republic)
2015-12-15
We investigate a model of a ringed accretion disk, made up by several rings rotating around a supermassive Kerr black hole attractor. Each toroid of the ringed disk is governed by the general relativity hydrodynamic Boyer condition of equilibrium configurations of rotating perfect fluids. Properties of the tori can then be determined by an appropriately defined effective potential reflecting the background Kerr geometry and the centrifugal effects. The ringed disks could be created in various regimes during the evolution of matter configurations around supermassive black holes. Therefore, both corotating and counterrotating rings have to be considered as being a constituent of the ringed disk. We provide constraints on the model parameters for the existence and stability of various ringed configurations and discuss occurrence of accretion onto the Kerr black hole and possible launching of jets from the ringed disk. We demonstrate that various ringed disks can be characterized by a maximum number of rings. We present also a perturbation analysis based on evolution of the oscillating components of the ringed disk. The dynamics of the unstable phases of the ringed disk evolution seems to be promising in relation to high-energy phenomena demonstrated in active galactic nuclei.
Thermoelastic dissipation in MEMS/NEMS flexural mode resonators.
Yan, Jize; Seshia, Ashwin A
2009-02-01
Understanding the energy dissipation mechanisms in single-crystal silicon MEMS/NEMS resonators are particularly important to maximizing an important figure of merit relevant for miniature sensor and signal processing applications: the Quality factor (Q) of resonance. This paper discusses thermoelastic dissipation (TED) as the dominant internal-friction mechanism in flexural mode MEMS/NEMS resonators. Criteria for optimizing the geometrical design of flexural mode MEMS/NEMS resonators are theoretically established with a view towards minimizing the TED for single-crystal silicon MEMS/NEMS flexural mode resonators.
Chemistry in Protoplanetary Disks
Semenov, Dmitry
2010-01-01
Protoplanetary disks (PPDs) surrounding young stars are short-lived (~0.3-10 Myr), compact (~10-1000 AU) rotating reservoirs of gas and dust. PPDs are believed to be birthplaces of planetary systems, where tiny grains are assembled into pebbles, then rocks, planetesimals, and eventually planets, asteroids, and comets. Strong variations of physical conditions (temperature, density, ionization rate, UV/X-rays intensities) make a variety of chemical processes active in disks, producing simple molecules in the gas phase and complex polyatomic (organic) species on the surfaces of dust particles. In this entry, we summarize the major modern observational methods and theoretical paradigms used to investigate disk chemical composition and evolution, and present the most important results. Future research directions that will become possible with the advent of the Atacama Large Millimeter Array (ALMA) and other forthcoming observational facilities are also discussed.
Miyake, Tomoya; Inutsuka, Shu-ichiro
2015-01-01
We investigate the dynamics of dust grains with various sizes in protoplanetary disk winds driven by magnetorotational turbulence, by simulating the time evolution of the dust grain distribution in the vertical direction. Small dust grains, which are well coupled to the gas, are dragged upward with the upflowing gas, while large grains remain near the midplane of a disk. Intermediate--size grains float at several scale heights from the midplane in time-averated force balance between the downward gravity and the upward gas drag. For the minimum mass solar nebula at 1 AU, dust grains with size of 20 -- 40 $\\mu m$ float at 5-10 scale heights from the midplane. Considering the dependence on the distance from the central star, smaller-size grains remain only in an outer region of the disk, while larger-size grains are distributed in a broader region. This implies that the dust depletion is expected to take place in small-to-large and inside-out manners. We also discuss the implication of our result to the observat...
Accurate thermoelastic tensor and acoustic velocities of NaCl
Energy Technology Data Exchange (ETDEWEB)
Marcondes, Michel L., E-mail: michel@if.usp.br [Physics Institute, University of Sao Paulo, Sao Paulo, 05508-090 (Brazil); Chemical Engineering and Material Science, University of Minnesota, Minneapolis, 55455 (United States); Shukla, Gaurav, E-mail: shukla@physics.umn.edu [School of Physics and Astronomy, University of Minnesota, Minneapolis, 55455 (United States); Minnesota supercomputer Institute, University of Minnesota, Minneapolis, 55455 (United States); Silveira, Pedro da [Chemical Engineering and Material Science, University of Minnesota, Minneapolis, 55455 (United States); Wentzcovitch, Renata M., E-mail: wentz002@umn.edu [Chemical Engineering and Material Science, University of Minnesota, Minneapolis, 55455 (United States); Minnesota supercomputer Institute, University of Minnesota, Minneapolis, 55455 (United States)
2015-12-15
Despite the importance of thermoelastic properties of minerals in geology and geophysics, their measurement at high pressures and temperatures are still challenging. Thus, ab initio calculations are an essential tool for predicting these properties at extreme conditions. Owing to the approximate description of the exchange-correlation energy, approximations used in calculations of vibrational effects, and numerical/methodological approximations, these methods produce systematic deviations. Hybrid schemes combining experimental data and theoretical results have emerged as a way to reconcile available information and offer more reliable predictions at experimentally inaccessible thermodynamics conditions. Here we introduce a method to improve the calculated thermoelastic tensor by using highly accurate thermal equation of state (EoS). The corrective scheme is general, applicable to crystalline solids with any symmetry, and can produce accurate results at conditions where experimental data may not exist. We apply it to rock-salt-type NaCl, a material whose structural properties have been challenging to describe accurately by standard ab initio methods and whose acoustic/seismic properties are important for the gas and oil industry.
Large Deformation Constitutive Laws for Isotropic Thermoelastic Materials
Energy Technology Data Exchange (ETDEWEB)
Plohr, Bradley J. [Los Alamos National Laboratory; Plohr, Jeeyeon N. [Los Alamos National Laboratory
2012-07-25
We examine the approximations made in using Hooke's law as a constitutive relation for an isotropic thermoelastic material subjected to large deformation by calculating the stress evolution equation from the free energy. For a general thermoelastic material, we employ the volume-preserving part of the deformation gradient to facilitate volumetric/shear strain decompositions of the free energy, its first derivatives (the Cauchy stress and entropy), and its second derivatives (the specific heat, Grueneisen tensor, and elasticity tensor). Specializing to isotropic materials, we calculate these constitutive quantities more explicitly. For deformations with limited shear strain, but possibly large changes in volume, we show that the differential equations for the stress components involve new terms in addition to the traditional Hooke's law terms. These new terms are of the same order in the shear strain as the objective derivative terms needed for frame indifference; unless the latter terms are negligible, the former cannot be neglected. We also demonstrate that accounting for the new terms requires that the deformation gradient be included as a field variable
The Formation of Galactic Disks
Mo, H J; White, S D M; Mao, Shude; White, Simon D.M.
1997-01-01
We study the population of galactic disks expected in current hierarchical clustering models for structure formation. A rotationally supported disk with exponential surface density profile is assumed to form with a mass and angular momentum which are fixed fractions of those of its surrounding dark halo. We assume that haloes respond adiabatically to disk formation, and that only stable disks can correspond to real systems. With these assumptions the predicted population can match both present-day disks and the damped Lyman alpha absorbers in QSO spectra. Good agreement is found provided: (i) the masses of disks are a few percent of those of their haloes; (ii) the specific angular momenta of disks are similar to those of their haloes; (iii) present-day disks were assembled recently (at z3kpc/h and about 10% at r>10kpc/h. The cross-section for absorption is strongly weighted towards disks with large angular momentum and so large size for their mass. The galaxy population associated with damped absorbers should...
Generalized thermoelastic wave band gaps in phononic crystals without energy dissipation
Wu, Ying; Yu, Kaiping; Li, Xiao; Zhou, Haotian
2016-01-01
We present a theoretical investigation of the thermoelastic wave propagation in the phononic crystals in the context of Green-Nagdhi theory by taking thermoelastic coupling into account. The thermal field is assumed to be steady. Thermoelastic wave band structures of 3D and 2D are derived by using the plane wave expansion method. For the 2D problem, the anti-plane shear mode is not affected by the temperature difference. Thermoelastic wave bands of the in-plane x-y mode are calculated for lead/silicone rubber, aluminium/silicone rubber, and aurum/silicone rubber phononic crystals. The new findings in the numerical results indicate that the thermoelastic wave bands are composed of the pure elastic wave bands and the thermal wave bands, and that the thermal wave bands can serve as the low boundary of the first band gap when the filling ratio is low. In addition, for the lead/silicone rubber phononic crystals the effects of lattice type (square, rectangle, regular triangle, and hexagon) and inclusion shape (circle, oval, and square) on the normalized thermoelastic bandwidth and the upper/lower gap boundaries are analysed and discussed. It is concluded that their effects on the thermoelastic wave band structure are remarkable.
Institute of Scientific and Technical Information of China (English)
徐云兰; 贾金平
2012-01-01
采用溶胶-凝胶法制备了TiO2/Ti电极,X射线衍射(XRD)分析表明,TiO2主要为锐钛矿,晶粒尺寸约为46 nm.以TiO2/Ti电极作阳极,Cu电极作阴极,组装成转盘液膜反应器,考察了其光电催化处理染料罗丹明B(RhB)的影响因素(转盘转速、偏压、溶液初始pH、RhB初始浓度和电解质浓度).得到最佳处理条件为:转盘转速90 r/min,偏压0.4V,溶液初始pH2.5,电解质(硫酸钠)质量浓度0.5 g/L.在最佳处理条件下,处理20 mg/L RhB染料废水90 min的脱色率和总有机碳(TOC)去除率分别达到97.2％和72.7％.结果表明,由于同时强化了激发光源的利用率和溶液的传质效率,TiO2/Ti转盘液膜反应器可高效光电催化处理染料废水.%TiO2/Ti electrode was prepared by sol-gel method for photoelectrocatalysis treatment of the Rhoda mine B (RhB) solution in a rotating disk thin-film reactor. X-ray diffraction (XRD) analysis showed the TiO2 photo catast was anatase with grain size of 46 nm. The effect of rotating speed,bias potential,initial pH,initial RhB concen tration and supporting salt concentration on RhB degradation was investigated and the optimal treatment conditions were obtained as follow:rotating speed 90 r/min,bias potential 0. 4 V,initial pH 2. 5 and supporting salt concentration 0. 5 g/L. Under these conditions, color and TOC removal efficiency of 20 mg/L RhB solution reached 97. 2% and 72. 7% respectively after 90 min treatment. The perfect performance of TiO2/Ti rotating disk thin-film reactor for RhB degradation could be attribute to its enhancement to light utilization efficiency and mass transfer velocity.
RESTUDY OF COUPLED FIELD THEORIES FOR MICROPOLAR CONTINUA(Ⅰ)-MICROPOLAR THERMOELASTICITY
Institute of Scientific and Technical Information of China (English)
戴天民
2002-01-01
Problems of micropolar thermoelasticity have been presented and discussed by sone authors in the traditional framework of micropolar continuum field theory. In this paper the theory of micropolar thermoelasticity is restudied. The reason why it was restricted to a linear one is analyzed. The rather general principle of virtual work and the new formulation for the virtual work of internal forces as well as the rather complete Hamilton principle in micropolar thermoelasticity are established. From this new Hamilton principle not only the equations of motion, the balance equation of entropy, the boundary conditions of stress, couple stress and heat, but also the boundary conditions of displacement,microrotation and temperature are simultaneously derived.
Green's function for a prestressed thermoelastic half-space with an inhomogeneous coating
Belyankova, T. I.; Kalinchuk, V. V.
2016-09-01
A mathematical model is developed for an inhomogeneous thermoelastic prestressed half-space consisting of a stack of homogeneous or functionally graded layers rigidly attached to a homogeneous base. Each component of the inhomogeneous medium is subjected to initial mechanical stresses and temperature. Successive linearization of the constitutive relations of the nonlinear mechanics of a thermoelastic medium is performed using the theory of superposition of small deformations on finite deformations with the inhomogeneity of the medium taken into account. Integral formulas are derived to explore dynamic processes in inhomogeneous prestressed thermoelastic media.
van der Kruit, P C
2011-01-01
The formation and evolution of galactic disks is particularly important for understanding how galaxies form and evolve, and the cause of the variety in which they appear to us. Ongoing large surveys, made possible by new instrumentation at wavelengths from the ultraviolet (GALEX), via optical (HST and large groundbased telescopes) and infrared (Spitzer) to the radio are providing much new information about disk galaxies over a wide range of redshift. Although progress has been made, the dynamics and structure of stellar disks, including their truncations, are still not well understood. We do now have plausible estimates of disk mass-to-light ratios, and estimates of Toomre's $Q$ parameter show that they are just locally stable. Disks are mostly very flat and sometimes very thin, and have a range in surface brightness from canonical disks with a central surface brightness of about 21.5 $B$-mag arcsec$^{-2}$ down to very low surface brightnesses. It appears that galaxy disks are not maximal, except possibly in ...
Directory of Open Access Journals (Sweden)
Seokchan Kim
2013-01-01
Full Text Available A graded layer was introduced at the interface between the top and bond coats to reduce the risk of failure in a thermal barrier coating (TBC system, and the thermoelastic behavior was investigated through mathematical approaches. Two types of TBC model with and without the graded layer, subject to a symmetric temperature distribution in the longitudinal direction, were taken into consideration to evaluate thermoelastic behaviors such as temperature distribution, displacement, and thermal stress. Thermoelastic theory was applied to derive two governing partial differential equations, and a finite volume method was developed to obtain approximations because of the complexity. The TBC with the graded layer shows improved durability in thermoelastic characteristics through mathematical approaches, in agreement with the experimental results. The results will be useful in discovering technologies for enhancing the thermomechanical properties of TBCs.
Go, Jaegwi; Myoung, Sang-Won; Lee, Je-Hyun; Jung, Yeon-Gil; Kim, Seokchan; Paik, Ungyu
2014-10-01
The thermoelastic behaviors of such as temperature distribution, displacements, and stresses in thermal barrier coatings (TBCs) are seriously influenced by top coat thickness and edge conditions, which were investigated based on the thermal and mechanical properties of plasma-sprayed TBCs. A couple of governing partial differential equations were derived based on the thermoelastic theory. Since the governing equations are too involved to solve analytically, a finite volume method was developed to obtain approximations. The thermoelastic characteristics of TBCs with the various thicknesses and microstructures were estimated through mathematical approaches with different edge conditions. The results demonstrated that the top coat thickness and the edge condition in theoretical analysis are crucial factors to be considered in controlling the thermoelastic characteristics of plasma-sprayed TBCs.
Magneto-thermoelasticity with thermoelectric properties and fractional derivative heat transfer
Energy Technology Data Exchange (ETDEWEB)
Ezzat, Magdy A., E-mail: maezzat2000@yahoo.co [Department of Mathematics, Faculty of Education, Alexandria University (Egypt)
2011-01-01
In this work, a new model of the magneto-thermoelasticity theory has been constructed in the context of a new consideration of heat conduction with fractional derivative. A one-dimensional application for a conducting half-space of thermoelectric elastic material, which is thermally shocked in the presence of a magnetic field, has been solved using Laplace transform and state-space techniques (Ezzat, 2008). According to the numerical results and its graphs, a conclusion about the new theory of magneto-thermoelasticity has been constructed. The theories of coupled magneto-thermoelasticity and of generalized magneto-thermoelasticity with one relaxation time follow as limited cases. The result provides a motivation to investigate conducting thermoelectric materials as a new class of applicable materials.
Nonlinear Thermoelastic Model for SMAs and SMA Hybrid Composites
Turner, Travis L.
2004-01-01
A constitutive mathematical model has been developed that predicts the nonlinear thermomechanical behaviors of shape-memory-alloys (SMAs) and of shape-memory-alloy hybrid composite (SMAHC) structures, which are composite-material structures that contain embedded SMA actuators. SMAHC structures have been investigated for their potential utility in a variety of applications in which there are requirements for static or dynamic control of the shapes of structures, control of the thermoelastic responses of structures, or control of noise and vibrations. The present model overcomes deficiencies of prior, overly simplistic or qualitative models that have proven ineffective or intractable for engineering of SMAHC structures. The model is sophisticated enough to capture the essential features of the mechanics of SMAHC structures yet simple enough to accommodate input from fundamental engineering measurements and is in a form that is amenable to implementation in general-purpose structural analysis environments.
Dynamic ADI computations of thermoelastic stresses in crystalline laser media
Energy Technology Data Exchange (ETDEWEB)
Gelinas, R.J.; Doss, S.K.; Carlson, N.N.
1985-01-01
This article considers thermoelastic effects which influence both the thermal engineering design and optical propagation in solid state high average power laser (HAPL) systems. The methods and computations described here have been developed for applications, ultimately, to crystalline slabs with arbitrary symmetry properties and with arbitrary spatial orientations between crystalline axes and slab configurations. For this, accurate numerical solutions are required simultaneously for the heat equation and Hooke's law in thier most general tensor forms. Prompted by the optical problem requirements in HAPL systems, this work utilizes implementations of Eulerian discretizations and dynamic ADI methods for solving general fourth-order elliptic partial differential equations (PDE's) which describe stress potentials in anisotropic media. These formulations can provide both steady state and transient PDE solutions. This article concludes with computed results for trigonal Al/sub 2/O/sub 3/ crystal deformations in various crystal axes/slab orientations.
Laser-induced thermoelastic effects can evoke tactile sensations
Jun, Jae-Hoon; Park, Jong-Rak; Kim, Sung-Phil; Min Bae, Young; Park, Jang-Yeon; Kim, Hyung-Sik; Choi, Seungmoon; Jung, Sung Jun; Hwa Park, Seung; Yeom, Dong-Il; Jung, Gu-In; Kim, Ji-Sun; Chung, Soon-Cheol
2015-06-01
Humans process a plethora of sensory information that is provided by various entities in the surrounding environment. Among the five major senses, technology for touch, haptics, is relatively young and has relatively limited applications largely due to its need for physical contact. In this article, we suggest a new way for non-contact haptic stimulation that uses laser, which has potential advantages such as mid-air stimulation, high spatial precision, and long working distance. We demonstrate such tactile stimulation can be enabled by laser-induced thermoelastic effects by means of physical and perceptual studies, as well as simulations. In the physical study, the mechanical effect of laser on a human skin sample is detected using low-power radiation in accordance with safety guidelines. Limited increases (reports of the non-nociceptive sensation of laser stimuli.
Modelling Thermoelastic Distortion of Optics Using Elastodynamic Reciprocity
King, Eleanor; Veitch, Peter; Levin, Yuri
2015-01-01
Thermoelastic distortion resulting from optical absorption by transmissive and reflective optics can cause unacceptable changes in optical systems that employ high power beams. In advanced-generation laser-interferometric gravitational wave detectors for example, optical absorption is expected to result in wavefront distortions that would compromise the sensitivity of the detector; thus necessitating the use of adaptive thermal compensation. Unfortunately, these systems have long thermal time constants and so predictive feed-forward control systems could be required - but the finite-element analysis is computationally expensive. We describe here the use of the Betti-Maxwell elastodynamic reciprocity theorem to calculate the response of linear elastic bodies (optics) to heating that has arbitrary spatial distribution. We demonstrate using a simple example, that it can yield accurate results in computational times that are significantly less than those required for finite-element analyses.
Decay properties of linear thermoelastic plates: Cattaneo versus Fourier law
Said-Houari, Belkacem
2013-02-01
In this article, we investigate the decay properties of the linear thermoelastic plate equations in the whole space for both Fourier and Cattaneo\\'s laws of heat conduction. We point out that while the paradox of infinite propagation speed inherent in Fourier\\'s law is removed by changing to the Cattaneo law, the latter always leads to a loss of regularity of the solution. The main tool used to prove our results is the energy method in the Fourier space together with some integral estimates. We prove the decay estimates for initial data U0 ∈ Hs(ℝ) ∩ L1(ℝ). In addition, by restricting the initial data to U0 ∈ Hs(ℝ) ∩ L1,γ(ℝ) and γ ∈ [0, 1], we can derive faster decay estimates with the decay rate improvement by a factor of t-γ/2. © 2013 Copyright Taylor and Francis Group, LLC.
Directory of Open Access Journals (Sweden)
Chennakesava R Alavala
2016-01-01
Full Text Available The aim of the present work was to estimate non-linear thermoelastic behavior of three-phase AA5454/silicon nitride nanoparticle metal matrix composites. The thermal loading was varied from subzero temperature to under recrystallization temperature. The RVE models were used to analyze thermo-elastic behavior. The AA5454/silicon nitride nanoparticle metal matrix composites have gained the elastic modulus below 0oC and lost at high temperatures.
Assessment of foam fracture in sandwich beams using thermoelastic stress analysis
DEFF Research Database (Denmark)
Dulieu-Barton, J.M.; Berggreen, Christian; Mettemberg, C.
2009-01-01
Thermoelastic Stress Analysis (TSA) has been well established for determining crack-tip parameters in metallic materials. This paper examines its ability to determine accurately the crack-tip parameters for PVC foam used in sandwich structures.......Thermoelastic Stress Analysis (TSA) has been well established for determining crack-tip parameters in metallic materials. This paper examines its ability to determine accurately the crack-tip parameters for PVC foam used in sandwich structures....
Thermo-Elastic Nondestructive Evaluation of Fatigue Damage in PMR-15 Resin (Preprint)
2011-11-01
AFRL-RX-WP-TP-2011-4365 THERMO-ELASTIC NONDESTRUCTIVE EVALUATION OF FATIGUE DAMAGE IN PMR -15 RESIN (PREPRINT) J.T. Welter and E.A...Technical Paper 1 November 2011 – 1 November 2011 4. TITLE AND SUBTITLE THERMO-ELASTIC NONDESTRUCTIVE EVALUATION OF FATIGUE DAMAGE IN PMR -15 RESIN...largely been overlooked. In this paper we present studies of nondestructive evaluation of fatigue damage in a thermoset polyimide resin, PMR -15, performed
Directory of Open Access Journals (Sweden)
Costa A.
2010-06-01
Full Text Available Thermoelastic stress analysis (TSA has been applied to measure the first stress invariant on a composite helicopter component under load. The component comprised inner mono-directional glass fiber layers with an outer central plate in glass fiber cloth, covered by an anti-fretting surface coating. In order to obtain quantitative results, a previous calibration of the thermoelastic constant obtained on a composite sample with a similar anti-fretting coating has been necessary.
Study of Intrinsic Dissipation Due to Thermoelastic Coupling in Gyroscope Resonators.
Li, Changlong; Gao, Shiqiao; Niu, Shaohua; Liu, Haipeng
2016-01-01
This paper presents analytical models, as well as numerical and experimental verification of intrinsic dissipation due to thermoelastic loss in tuning-fork resonator. The thermoelastic analytical governing equations are created for resonator vibrating at drive-mode and sense-mode, and thermoelastic vibration field quantities are deduced. Moreover, the theoretical values are verified that coincided well with finite element analysis (FEM) simulation results. Also, the comparison of vibration field quantities is made to investigate the effect of different conditions on resonator thermoelastic vibration behavior. The significant parameters of thermoelastic damping and quality factor are subsequently deduced to analyze the energy dissipation situation in the vibration process. Meanwhile, the corresponding conclusions from other studies are used to verify our theoretical model and numerical results. By comparing with the experimental quality factor, the numerical values are validated. The combination of the theoretical expressions, numerical results and experimental data leads to an important insight into the achievable quality factor value of tuning-fork resonator, namely, that the thermoelastic damping is the main loss mechanism in the micro-comb finger structure and the quality factor varies under different vibration modes. The results demonstrate that the critical geometry dimensions of tuning-fork resonator can be well designed with the assistance of this study.
Accretion of solid materials onto circumplanetary disks from protoplanetary disks
Energy Technology Data Exchange (ETDEWEB)
Tanigawa, Takayuki [Institute of Low Temperature Science, Hokkaido University, Sapporo 060-0819 (Japan); Maruta, Akito; Machida, Masahiro N., E-mail: tanigawa@pop.lowtem.hokudai.ac.jp [Department of Earth and Planetary Sciences, Kyushu University, Fukuoka 812-8581 (Japan)
2014-04-01
We investigate the accretion of solid materials onto circumplanetary disks from heliocentric orbits rotating in protoplanetary disks, which is a key process for the formation of regular satellite systems. In the late stage of the gas-capturing phase of giant planet formation, the accreting gas from protoplanetary disks forms circumplanetary disks. Since the accretion flow toward the circumplanetary disks affects the particle motion through gas drag force, we use hydrodynamic simulation data for the gas drag term to calculate the motion of solid materials. We consider a wide range of size for the solid particles (10{sup –2}-10{sup 6} m), and find that the accretion efficiency of the solid particles peaks around 10 m sized particles because energy dissipation of drag with circum-planetary disk gas in this size regime is most effective. The efficiency for particles larger than 10 m becomes lower because gas drag becomes less effective. For particles smaller than 10 m, the efficiency is lower because the particles are strongly coupled with the background gas flow, which prevents particles from accretion. We also find that the distance from the planet where the particles are captured by the circumplanetary disks is in a narrow range and well described as a function of the particle size.
Numerical Investigation of Circumplanetary Disks
Mitchell, Tyler R.; Stewart, G. R.
2012-10-01
The regular satellites of Jupiter and Saturn are believed to have formed in circumplanetary disks that were present during the late stages of giant planet formation. At present, there is a large amount of uncertainly in both the structure of these disks and the nature of angular momentum transport within them. In circumstellar disks, magnetorotational rotational instability (MRI) is generally invoked as a mechanism to transfer angular momentum and drive accretion. It is unclear whether circumplanetary disks are sufficiently ionized for the MRI to be active. In an effort to better understand the physical nature of circumplanetary disks, we present 1+1D numerical models of Jovian and Saturnian circumplanetary disks. Our models include viscous diffusion, infall from the solar nebula and external photoevaporation. The combination of these three processes allow for steady-state, truncated disks roughly consistent with the present state of the regular satellite systems of Jupiter and Saturn (Mitchell & Stewart, 2011). Unlike recent models of tidal truncation (Martin & Lubow, 2010), our initial models showed that photoevaporation is able to truncate circumplanetary disks to a small fraction of the Hill radius. One goal of this work is to verify our previous results and confirm that truncated disks can be formed using models with more realistic viscous processes. In order to simplify the problem, our initial models employed a viscosity that was linearly dependent on radius. Our current disk models use a viscosity that is calculated locally based on the midplane temperature that is determined from detailed vertical structure calculations. These models are used to conduct an initial investigation of the viability of an active MRI as well as baroclinic instability and other instabilities that may exist.
Poynting Jets from Accretion Disks
Lovelace, R V E; Ustyugova, G V; Romanova, M M; Colgate, S A
2002-01-01
The powerful narrow jets observed to emanate from many compact accreting objects may arise from the twisting of a magnetic field threading a differentially rotating accretion disk which acts to magnetically extract angular momentum and energy from the disk. Two main regimes have been discussed, {\\it hydromagnetic outflows}, which have a significant mass flux and have energy and angular momentum carried by both the matter and the electromagnetic field and, Poynting outflows, where the mass flux is negligible and energy and angular momentum are carried predominantly by the electromagnetic field. Here we consider a Keplerian disk initially threaded by a dipole-like magnetic field and we present solutions of the force-free Grad-Shafranov equation for the coronal plasma. We find solutions with Poynting jets where there is a continuous outflow of energy and toroidal magnetic flux from the disk into the external space. This behavior contradicts the commonly accepted ``theorem'' of Solar plasma physics that the motio...
Swimming of a circular disk at low Reynolds number
Felderhof, B U
2014-01-01
The swimming of a circular disk at low Reynolds number is studied for distortion waves along its two planar surfaces with wavelength much smaller than the size of the disk. The calculation is based on an extension of Taylor's work for a planar sheet. It is shown that in general the disk performs both translational and rotational swimming, resulting in a circular orbit.
Thermoelasticity of hcp-Fe up to 171 GPa
Murphy, C. A.; Jackson, J. M.; Sturhahn, W.; Chen, B.
2012-12-01
Iron is thought to be the main constituent in Earth's core, along with ~5 to 10 wt% nickel and some light elements. The poorly constrained light element component in the core is due, in part, to uncertainties in the high-pressure thermoelastic and thermodynamic properties of both pure iron and iron-alloys. Therefore, it is important to firmly establish the properties of the end-member composition of pure iron at core conditions, which will serve as an important baseline against which to compare the properties of iron-alloys and those inferred for Earth's core. To further our understanding of hexagonal close-packed iron (hcp-Fe) at core pressures, we directly probed its total phonon density of states (DOS) up to 171 GPa and at 300 K, using nuclear resonant inelastic x-ray scattering (NRIXS) and in situ x-ray diffraction (XRD) experiments performed at Sector 3-ID-B of the Advanced Photon Source at Argonne National Laboratory (1, 2). Our use of a hydrostatic pressure medium for select measurements and determination of sample volume with in situ XRD at each of our eleven compression points distinguish our study from previous similar works. In addition, long data collection times resulted in a high statistical quality dataset that, in turn, allowed for our unique analyses of hcp-Fe's thermoelastic and vibrational thermodynamic properties. For example, we determined the Debye sound velocity of hcp-Fe at each compression point from our measured densities and a parabolic fit of the low-energy region of the phonon DOS. In addition, we obtained the vibrational entropy from the integrated total phonon DOS, and used its volume dependence to determine the thermal expansion coefficient of hcp-Fe at 300 K and up to 171 GPa (3). This parameter provides a means for converting between reported values for the isothermal bulk modulus (4) and the adiabatic bulk modulus, the latter of which we used with our measured Debye sound velocities to determine a new tight constraint on the
Modeling the Circumstellar Disk of $\\zeta$ Tauri
Carciofi, A. C.; Bjorkman, J. E.
2004-01-01
We present a model for the disk of the classical Be star $\\zeta$ Tauri. The model consists of a Keplerian rotating disk with a power-law surface density and a vertical density distribution that follows from the balance between the thermal gas pressure and the z-component of the stellar gravitation. The opening angle of such a disk is not a fixed value but increases with the distance to the star (flared disk). We use a Monte Carlo code that solves simultaneously the thermal equilibrium, the st...
The Dark Disk of the Milky Way
Purcell, Chris W; Kaplinghat, Manoj
2009-01-01
Massive satellite accretions onto early galactic disks can lead to the deposition of dark matter in disk-like configurations that co-rotate with the galaxy. This phenomenon has potentially dramatic consequences for dark matter detection experiments. We utilize focused, high-resolution simulations of accretion events onto disks designed to be Galaxy analogues, and compare the resultant disks to the morphological and kinematic properties of the Milky Way's thick disk in order to bracket the range of co-rotating accreted dark matter. We find that the Milky Way's merger history must have been unusually quiescent compared to median LCDM expectations and therefore its dark disk must be relatively small: the fraction of accreted dark disk material near the Sun is about 20% of the host halo density or smaller and the co-rotating dark matter fraction near the Sun, defined as particles moving with a rotational velocity lag less than 50 km/s, is enhanced by about 30% or less compared to a standard halo model. Such a dar...
Institute of Scientific and Technical Information of China (English)
王春明; 包永军; 杜永令
2001-01-01
用计时库仑法研究了Pb2+于旋转Ag盘电极(Ag-RDE)上的欠电位沉积(UPD)性质。实验证明，支持电解质(0.01 mol/LHN03+0.01 mol/L NaCl)中Cl-离子的存在有利于取得稳态条件下UPD-Pb的电量值。其氧化过程电量(Qa)，代表Pb2+吸附单层被定量转化为UPD Pb单层的量，Qa的平均值为393.3μC/cm2，相应于2×10-9 mol/cm2 Pb2+表面复盖量。%The monolayer charge of lead underpotential deposition (UPD) was studied by chronocoulometry. On the rotating silver disk electrode (Ag-RDE), the monolayer charge of UPD lead could reaches steady state at different Pb2+ concentration levels by changing reduction time of UPD Pb2+ . A supporting electrolyte solution of 0.01 mol/L HNO3 + 0.01 mol/L NaCl was used. The steady state charge measured was 393.3 μC/cm2, which corresponded to a surface cover of 2 × 10-9 mol/cm2 Pb2+ on the electrode surface.
Thermoelasticity of CaO from first principles
Institute of Scientific and Technical Information of China (English)
Liu Zi-Jiang; Qi Jian-Hong; Guo Yuan; Chen Qi-Feng; Cai Ling-Cang; Yang Xiang-Dong
2007-01-01
The thermoelastic properties of CaO over a wide range of pressure and temperature are studied using density functional theory in the generalized gradient approximation. The transition pressure taken from the enthalpy calculations is 66.7 GPa for CaO, which accords with the experimental result very well. The athermal elastic moduli of the two phases of CaO are calculated as a function of pressure up to 200 GPa. The calculated results are in excellent agreement with existing experimental data at ambient pressure and compared favourably with other pseudopotential predictions over the pressure regime studied. It is also found that the degree of the anisotropy rapidly decreases with pressure increasing in the B1 phase, whereas it strongly increases as the pressure increases in the B2 phase. The thermodynamic properties of the B1 phase of CaO are predicted using the quasi-harmonic Debye model; the heat capacity and entropy are consistent with other previous results at zero pressure.
The Spin History of Protostars: Disk Locking, Revisited
Matt, S.; Pudritz, R. E.
2004-12-01
In this talk, we take a new look at the theory of disk locking, which assumes that an accreting protostar rids itself of accreted angular momentum through a magnetic coupling with the accretion disk. We consider that differential rotation between the star and disk twists the field lines. For large enough twist, the magnetic field lines connecting the star and disk open and disconnect. This significantly reduces the spin-down torque on the star by the disk, and so we find that disk-locking theory predicts spin periods that are much too short to account for typical observed systems.
Counterrotating Stars in Simulated Galaxy Disks
Algorry, David G; Abadi, Mario G; Sales, Laura V; Steinmetz, Matthias; Piontek, Franziska
2013-01-01
Counterrotating stars in disk galaxies are a puzzling dynamical feature whose origin has been ascribed to either satellite accretion events or to disk instabilities triggered by deviations from axisymmetry. We use a cosmological simulation of the formation of a disk galaxy to show that counterrotating stellar disk components may arise naturally in hierarchically-clustering scenarios even in the absence of merging. The simulated disk galaxy consists of two coplanar, overlapping stellar components with opposite spins: an inner counterrotating bar-like structure made up mostly of old stars surrounded by an extended, rotationally-supported disk of younger stars. The opposite-spin components originate from material accreted from two distinct filamentary structures which at turn around, when their net spin is acquired, intersect delineating a "V"-like structure. Each filament torques the other in opposite directions; the filament that first drains into the galaxy forms the inner counterrotating bar, while material ...
Effect of thermoelastic damping on silicon, GaAs, diamond and SiC micromechanical resonators
Directory of Open Access Journals (Sweden)
Garuma Abdisa Denu
2017-05-01
Full Text Available The effect of thermoelastic damping as a main dissipation mechanism in single crystalline silicon, GaAs, diamond, SiC and SiO2 micromechanical resonators are studied. Numerical simulation is performed to compare quality factors of the given materials. Results using Zener’s well-known approximation and recent developments of Lifshitz and Roukes models were used to model thermoelasticity effects. In the later model, the effect of thermal diffusion length is taken into account for determination of thermoelastic damping. Our results show that larger discrepancy is obtained between the two models for SiO2. The difference is pronounced when beam aspect ratio (L/w is smaller. Such progresses will find potential applications in optimal design of high quality factor micrometer- and nanometer-scale electromechanical systems.
Photoacoustic generation by a gold nanosphere: from the linear to the nonlinear thermoelastic regime
Prost, Amaury
2015-01-01
We theoretically investigate the photoacoustic generation by a gold nanosphere in water in the thermoelastic regime. Photoacoustic signals are predicted numerically based on the successive resolution of a thermal diffusion problem and a thermoelastic problem, taking into account the finite size of the gold nanosphere, thermoelastic and elastic properties of both water and gold, and the temperature-dependence of the thermal expansion coefficient of water. For sufficiently high illumination fluences, this temperature dependence yields a nonlinear relationship between the photoacoustic amplitude and the fluence. For nanosecond pulses in the linear regime, we show that more than $90\\ \\%$ of the emitted photoacoustic energy is generated in water, and the thickness of the generating layer around the particle scales close to the square root of the pulse duration. The amplitude of the photoacoustic waves in the linear regime are accurately predicted by the point-absorber model introduced by Calasso and Diebold, but o...
Institute of Scientific and Technical Information of China (English)
Ibrahim A. Abbas
2015-01-01
The present work is concerned with the solution of a problem on thermoelastic interactions in a functional graded material due to thermal shock in the context of the fractional order three-phase lag model. The governing equations of fractional order generalized thermoelasticity with three-phase lag model for functionally graded materials (FGM) (i.e., material with spatially varying material properties) are established. The analytical solution in the transform domain is obtained by using the eigenvalue approach. The inversion of Laplace transform is done numerically. The graphical results indicate that the fractional parameter has significant effects on all the physical quantities. Thus, we can consider the theory of fractional order generalized thermoelasticity an improvement on studying elastic materials.
Thermoelastic stress analysis of multilayered films in a micro-thermoelectric cooling device
Institute of Scientific and Technical Information of China (English)
Yu-Mei Yang; Xing-Zhe Wang; Wen-Jie Zhang
2012-01-01
This paper presents an analytical solution for the thermoelastic stress in a typical in-plane's thin-film microthermoelectric cooling device under different operating conditions.The distributions of the permissible temperature fields in multilayered thin-films are analytically obtained,and the characteristics,including maximum temperature difference and maximum refrigerating output of the thermoelectric device,are discussed for two operating conditions.Analytical expressions of the thermoelastic stresses in the layered thermoelectric thin-films induced by the temperature difference are formulated based on the theory of multilayer system.The results demonstrate that,the geometric dimension is a significant factor which remarkably affects the thermoelastic stresses.The stress distributions in layers of semiconductor thermoelements,insulating and supporting membrane show distinctly different features.The present work may profitably guide the optimization design of highefficiency micro-thermoelectric cooling devices.
Self-consistent massive disks in triaxial dark matter halos
Bailin, Jeremy; Bolatto, Alberto D; Gibson, Brad K; Power, Chris
2007-01-01
Galactic disks in triaxial dark matter halos become deformed by the elliptical potential in the plane of the disk in such a way as to counteract the halo ellipticity. We develop a technique to calculate the equilibrium configuration of such a disk in the combined disk-halo potential, which is based on the method of Jog (2000) but accounts for the radial variation in both the halo potential and the disk ellipticity. This crucial ingredient results in qualitatively different behavior of the disk: the disk circularizes the potential at small radii, even for a reasonably low disk mass. This effect has important implications for proposals to reconcile cuspy halo density profiles with low surface brightness galaxy rotation curves using halo triaxiality. The disk ellipticities in our models are consistent with observational estimates based on two-dimensional velocity fields and isophotal axis ratios.
Heating of protostellar accretion disks
de Campos, R. R.; Jatenco-Pereira, V.
2017-07-01
The magneto-rotational instability (MRI) is believed to be the mechanism responsible for a magneto-hydrodynamic turbulence that could lead to the accretion observed in protoplanetary disks. The need of a minimum amount of ionization in protostellar accretion disks is necessary for the MRI to take place. There are in the literature several studies that include the damping of Alfvén waves as an additional heating source besides the viscous heating mechanism in a geometrically thin and optically thick disk. The damping of the waves transfers energy to the disk increasing the temperature and consequently its ionization fraction, making possible the presence of the MRI in a large part of the disk. We analyzed the contribution of non-ideal effects such as Ohmic and ambipolar diffusion for the disk heating and compare these heating rates with those obtained by damping of Alfvén waves. In order to study these non-ideal effects, we have estimated the radiation emission of each effect through the energy conservation equation, and associated each emission with a black body radiation, which enabled us to assign a temperature contribution of each effect. Using the ATHENA code we were able to simulate the disk at different radial distances, and estimate the electric current density needed to calculate the radiation emission associated with each effect. Once we have those data, we were able to compare the results with other heating sources, like viscosity and Alfvén waves damping, and we concluded that the Ohmic and ambipolar diffusions do not heat the disk in any significant way.
Quantifying Residual Stresses by Means of Thermoelastic Stress Analysis
Gyekenyesi, Andrew L.; Baaklini, George Y.
2001-01-01
This study focused on the application of the Thermoelastic Stress Analysis (TSA) technique as a tool for assessing the residual stress state of structures. TSA is based on the fact that materials experience small temperature changes when compressed or expanded. When a structure is cyclically loaded, a surface temperature profile results which correlates to the surface stresses. The cyclic surface temperature is measured with an infrared camera. Traditionally, the amplitude of a TSA signal was theoretically defined to be linearly dependent on the cyclic stress amplitude. Recent studies have established that the temperature response is also dependent on the cyclic mean stress (i.e., the static stress state of the structure). In a previous study by the authors, it was shown that mean stresses significantly influenced the TSA results for titanium- and nickel-based alloys. This study continued the effort of accurate direct measurements of the mean stress effect by implementing various experimental modifications. In addition, a more in-depth analysis was conducted which involved analyzing the second harmonic of the temperature response. By obtaining the amplitudes of the first and second harmonics, the stress amplitude and the mean stress at a given point on a structure subjected to a cyclic load can be simultaneously obtained. The experimental results showed good agreement with the theoretical predictions for both the first and second harmonics of the temperature response. As a result, confidence was achieved concerning the ability to simultaneously obtain values for the static stress state as well as the cyclic stress amplitude of structures subjected to cyclic loads using the TSA technique. With continued research, it is now feasible to establish a protocol that would enable the monitoring of residual stresses in structures utilizing TSA.
Propagation of plane waves in thermoelastic cubic crystal material with two relaxation times
Institute of Scientific and Technical Information of China (English)
Rajneesh Kumar; Manjeet Singh
2007-01-01
A problem concerned with the reflection and refraction of thermoelastic plane waves an imperfect interface between two generalized thermally conducting cutimes has been investigated.The generalized thermoelastic theory with two relaxation of retiected and refracted waves to the amplitude of incident waves are obtained for an imperfect boundary and deduced for normal stiffness,transverse stiffness,themlal contact conductance,slip and welded boundaries. Amplitude ratios of different reflected and graphically for different incident waves.It is observed that the amplitude ratios of reflected and refracted waves are affected by the stiffness and thermal properties of the media.
Deformation due to mechanical and thermal sources in generalised orthorhombic thermoelastic material
Indian Academy of Sciences (India)
Rajneesh Kumar; Leena Rani
2004-10-01
A dynamical two-dimensional problem of thermoelasticity has been considered to investigate the disturbance due to mechanical (horizontal or vertical) and thermal source in a homogeneous, thermally conducting orthorhombic material. Laplace–Fourier transforms are applied to basic equations to form a vector matrix differential equation, which is then solved by eigenvalue approach. The displacements, stresses and temperature distribution so obtained in the physical domain are computed numerically and illustrated graphically. The numerical results of these quantities for zinc crystal-like material are illustrated to compare the results for different theories of generalised thermoelasticity for an insulated boundary and a temperature gradient boundary.
Directory of Open Access Journals (Sweden)
Narottam Maity
2016-01-01
Full Text Available Reflection of longitudinal displacement waves in a generalized thermoelastic half space under the action of uniform magnetic field has been investigated. The magnetic field is applied in such a direction that the problem can be considered as a two-dimensional one. The discussion is based on the three theories of generalized thermoelasticity: Lord-Shulman (L-S, Green-Lindsay (G-L, and Green-Naghdi (G-N with energy dissipation. We compute the possible wave velocities for different models. Amplitude ratios have been presented. The effects of magnetic field on various subjects of interest are discussed and shown graphically.
Comparison of the thermoelastic phenomenon expressions in stainless steels during cyclic loading
Directory of Open Access Journals (Sweden)
M. Sapieta
2017-01-01
Full Text Available The main purpose of this paper is to compare the thermoelastic stress in specimens of stainless steel. As material specimens we chose stainless steel of AISI 304, AISI 316Ti and AISI 316L types. The specimens were cyclically loaded with three-point bending. The whole process was recorded using an infrared camera. The thermal differences that occurred during the test were evaluated based on the thermoelastic stress equations. Subsequently, stress distributions in the specimens were compared for different types of stainless steel.
Directory of Open Access Journals (Sweden)
Ibrahim A. Abbas
2016-06-01
Full Text Available In this article, we consider the problem of a thermoelastic infinite body with a spherical cavity in the context of the theory of fractional order thermoelasticity. The inner surface of the cavity is taken traction free and subjected to a thermal shock. The form of a vector–matrix differential equation has been considered for the governing equations in the Laplace transform domain. The analytical solutions are given by the eigenvalue approach. The graphical results indicate that the fractional parameter effect plays a significant role on all the physical quantities.
Generation and detection of thermoelastic waves in metals by a photothermal mirror method
Capeloto, O. A.; Zanuto, V. S.; Lukasievicz, G. V. B.; Malacarne, L. C.; Bialkowski, S. E.; Požar, T.; Astrath, N. G. C.
2016-11-01
We investigate the thermoelastic waves launched by a localized heat deposition. Pulsed laser excitation is used to generate mechanical perturbations in metals that are detected using the photothermal mirror method. This method detects the wavefront distortion of the probe beam reflected from the perturbed sample surface. Nanometer scale expansion of the material is induced just under the irradiated surface releasing transient thermoelastic waves of much smaller amplitudes on the surface. Numerical predictions and the experimental results are in a good agreement and represent both the thermal diffusion of the large amplitude, long-lasting outward bulge, and the released elastic waves.
Detection of Localized Heat Damage in a Polymer Matrix Composite by Thermo-Elastic Method (Preprint)
2007-02-01
AFRL-ML-WP-TP-2007-437 DETECTION OF LOCALIZED HEAT DAMAGE IN A POLYMER MATRIX COMPOSITE BY THERMO-ELASTIC METHOD (PREPRINT) John Welter...GRANT NUMBER 4. TITLE AND SUBTITLE DETECTION OF LOCALIZED HEAT DAMAGE IN A POLYMER MATRIX COMPOSITE BY THERMO-ELASTIC METHOD (PREPRINT) 5c...Include Area Code) N/A Standard Form 298 (Rev. 8-98) Prescribed by ANSI Std. Z39-18 1 DETECTION OF LOCALIZED HEAT DAMAGE IN A POLYMER MATRIX COMPOSITE BY
Ye, Xiaoliang; Du, Yongling; Lu, Daban; Wang, Chunming
2013-05-24
We proposed a green and facile approach for the synthesis of β-cyclodextrin-coated poly(diallyldimethylammonium chloride)-functionalized graphene composite film (β-CD-PDDA-Gr) by using L-ascorbic acid (L-AA) as the reducing agent at room temperature. The β-CD-PDDA-Gr composite film modified glassy carbon-rotating disk electrode (GC-RDE) was then developed for the sensitive simultaneous determination of two synthetic food colorants: sunset yellow (SY) and tartrazine (TT). By cyclic voltammetry (CV), the peak currents of SY and TT increased obviously on the developed electrochemical sensor. The kinetic parameters, such as diffusion coefficient D and standard heterogeneous rate constant kb, were estimated by linear sweep voltammetry (LSV). Under the optimal conditions, the differential pulse voltammetry (DPV) signals of SY and TT on the β-CD-PDDA-Gr modified GC-RDE were significantly enhanced. The enhanced anodic peak currents represented the excellent analytical performance of simultaneous detection of SY and TT in the range of 5.0×10(-8) to 2.0×10(-5) mol L(-1), with a low limit of detection (LOD) of 1.25×10(-8) mol L(-1) for SY and 1.43×10(-8) mol L(-1) for TT (SN(-1)=3). This proposed method displayed outstanding selectivity, good stability and acceptable repeatability and reproducibility, and also has been used to simultaneously determine SY and TT in some commercial soft drinks with satisfactory results. The obtained results were compared to HPLC of analysis for those two colorants and no significant differences were found. By the treatment of the experimental data, the electrochemical reaction mechanisms of SY and TT both involved a one-electron-one-proton-transfer process.
The early evolution of protostellar disks
Stahler, Steven W.; Korycansky, D. G.; Brothers, Maxwell J.; Touma, Jihad
1994-01-01
We consider the origin and intital growth of the disks that form around protostars during the collapse of rotating molecular cloud cores. These disks are assumed to be inviscid and pressure free, and to have masses small compared to those of their central stars. We find that there exist three distinct components-an outer disk, in which shocked gas moves with comparable azimuthal and radical velocities; and inner disk, where material follows nearly circular orbits, but spirals slowly toward the star because of the drag exerted by adjacent onfalling matter, and a turbulent ring adjoining the first two regions. Early in the evolution, i.e., soon after infalling matter begins to miss the star, only the outer disk is present, and the total mass acceration rate onto the protostar is undiminished. Once the outer disk boundary grows to more than 2.9 times the stellar radius, first the ring, and then the inner disk appear. Thereafter, the radii of all three components expand as t(exp 3). The mass of the ring increase with time and is always 13% of the total mass that has fallen from the cloud. Concurrently with the buildup of the inner disk and ring, the accretion rate onto the star falls off. However, the protostellar mass continue to rise, asymptotically as t(exp 1/4). We calculated the radiated flux from the inner and outer disk components due to the release of gravitational potential energy. The flux from the inner disk is dominant and rises steeply toward the stellar surface. We also determine the surface temperature of the inner disk as a function of radius. The total disk luminosity decreases slowly with time, while the contributions from the ring and inner disk both fall as t(exp -2).
Directory of Open Access Journals (Sweden)
Myongchol Ri
2013-01-01
Full Text Available We propose a disk encryption method, called Secure Disk Mixed System (SDMS in this paper, for data protection of disk storages such as USB flash memory, USB hard disk and CD/DVD. It is aimed to solve temporal and spatial limitations of existing disk encryption methods and to control security performance flexibly according to the security requirement of system.
A Supersymmetric Dark Disk Universe
Fischler, Willy; Tangarife, Walter
2014-01-01
We present a model of partially interacting dark matter (PIDM) within the framework of supersymmetry with gauge mediated symmetry breaking. Dark sector atoms are produced through Affleck-Dine baryogenesis in the dark sector while avoiding the production of Q-ball relics. We discuss the astrophysical constraints relevant for this model and the possibility of dark galactic disk formation. In addition, jet emission from rotating black holes is discussed in the context of this class of models.
Magnetohydrodynamic Origin of Jets from Accretion Disks
Lovelace, R V E; Koldoba, A V
1999-01-01
A review is made of recent magnetohydrodynamic (MHD) theory and simulations of origin of jets from accretion disks. Many compact astrophysical objects emit powerful, highly-collimated, oppositely directed jets. Included are the extra galactic radio jets of active galaxies and quasars, and old compact stars in binaries, and emission line jets in young stellar objects. It is widely thought that these different jets arise from rotating, conducting accretion disks threaded by an ordered magnetic field. The twisting of the magnetic field by the rotation of the disk drives the jets by magnetically extracting matter, angular momentum, and energy from the accretion disk. Two main regimes have been discussed theoretically, hydromagnetic winds which have a significant mass flux, and Poynting flux jets where the mass flux is negligible. Over the past several years, exciting new developments on models of jets have come from progress in MHD simulations which now allow the study of the origin - the acceleration and collima...
Hao, Zengrong; Gu, Chunwei; Song, Yin
2016-06-01
This study extends the discontinuous Galerkin (DG) methods to simulations of thermoelasticity. A thermoelastic formulation of interior penalty DG (IP-DG) method is presented and aspects of the numerical implementation are discussed in matrix form. The content related to thermal expansion effects is illustrated explicitly in the discretized equation system. The feasibility of the method for general thermoelastic simulations is validated through typical test cases, including tackling stress discontinuities caused by jumps of thermal expansive properties and controlling accompanied non-physical oscillations through adjusting the magnitude of IP term. The developed simulation platform upon the method is applied to the engineering analysis of thermoelastic performance for a turbine vane and a series of vanes with various types of simplified thermal barrier coating (TBC) systems. This analysis demonstrates that while TBC properties on heat conduction are generally the major consideration for protecting the alloy base vanes, the mechanical properties may have more significant effects on protections of coatings themselves. Changing characteristics of normal tractions on TBC/base interface, closely related to the occurrence of coating failures, over diverse components distributions along TBC thickness of the functional graded materials are summarized and analysed, illustrating the opposite tendencies in situations with different thermal-stress-free temperatures for coatings.
Nzodoum Fotsing, J. L.; Dietzel, D.; Chotikaprakhan, S.; Meckenstock, R.; Pelzl, J.; Cassette, S.
2005-06-01
In this contribution we report on combined investigations of hot areas in a high power high electron mobility transistor (HEMT) using a scanning thermo-elastic microscope and finite element simulations of the problem. The sample was a AlGaN/GaN-HEMT grown on sapphire substrate, with a gold coating for improved thermal management. The FE simulations were performed based on the ANSYS program version 5.7. The thermo-elastic response was detected with an Explorer AFM-head of Topometrix. To allow simultaneous detection of the topology and of the thermo-elastic expansion images, the explorer had been modified for AFM measurements in the DC mode and at the double frequency of the thermal sinus in AFM contact mode. The thermo-elastic image of the hot area of the HEMT recorded at 2f shows a bright line as the hot area which is located along the gate, between gate and drain. The absolute value of the vertical expansion has been calibrated from the measured diode signal by use of the microscope’s force-distance calibration curve. In order to obtain a reliable estimate of the maximum temperature on the hot line, the temperature image obtained by FE simulation is calibrated using the thermal expansion of the gold film of known thermal expansion coefficient.
Existence and Uniform Decay of Weak Solutions for Nonlinear Thermoelastic System with Memory
Directory of Open Access Journals (Sweden)
Liu Haihong
2009-01-01
Full Text Available A nonlinear thermoelastic system with memory is considered, which is derived from a physical model with vibration in temperature environment. By some skillful and technical arguments, results of existence, uniqueness, and uniform decay on this generalized system are obtained.
Initial-boundary value problems for a class of nonlinear thermoelastic plate equations
Institute of Scientific and Technical Information of China (English)
Zhang Jian-Wen; Rong Xiao-Liang; Wu Run-Heng
2009-01-01
This paper studies initial-boundary value problems for a class of nonlinear thermoelastic plate equations. Under some certain initial data and boundary conditions,it obtains an existence and uniqueness theorem of global weak solutions of the nonlinear thermoelstic plate equations,by means of the Galerkin method. Moreover,it also proves the existence of strong and classical solutions.
General Decay in some Timoshenko-type systems with thermoelasticity second sound
2015-01-01
In this article, we consider a vibrating nonlinear Timoshenko system with thermoelasticity with second sound. We discuss the well-posedness and the regularity of Timoshenko solution using the semi-group theory. Moreover, we etablish an explicit and general decay results for a wide class of relaxating functions which depend on a stability number $\\mu$.
Disk Winds Driven by Magnetorotational Instability and Dispersal of Proto-Planetary Disks
Suzuki, T K
2008-01-01
By performing local three-dimensional MHD simulations of stratified accretion disks, we investigate disk winds driven by MHD turbulence. Initially given weak vertical magnetic fields are effectively amplified by magnetorotational instability and winding due to differential rotation. Large scale channel flows develop most effectively at 1.5 - 2 times the scale heights where the magnetic pressure is comparable to but slightly smaller than the gas pressure. The breakup of these channel flows drives structured disk winds by transporting the Poynting flux to the gas. These features are universally observed in the simulations of various initial fields. This disk wind process should play an essential role in the dynamical evaporation of proto-planetary disks. The breakup of channel flows also excites the momentum fluxes associated with Alfvenic and (magneto-)sonic waves toward the mid-plane, which possibly contribute to the sedimentation of small dust grains in protoplanetary disks.
Bouwman, J.; Lawson, W. A.; Dominik, C.; Feigelson, E. D.; Henning, Th.; Tielens, A. G. G. M.; Waters, L. B. F. M.
2006-12-01
The formation of planets is directly linked to the evolution of the circumstellar (CS) disk from which they are born. The dissipation timescales of CS disks are therefore of direct astrophysical importance in evaluating the time available for planet formation. We employ Spitzer Space Telescope spectra to complete the CS disk census for the late-type members of the ~=8 Myr old η Chamaeleontis star cluster. Of the 15 K- and M-type members, eight show excess emission. We find that the presence of a CS disk is anticorrelated with binarity, with all but one disk associated with single stars. With nine single stars in total, about 80% retain a CS disk. Of the six known or suspected close binaries, the only CS disk is associated with the primary of RECX 9. No circumbinary disks have been detected. We also find that stars with disks are slow rotators with surface values of specific angular momentum j=2-15jsolar. All high specific angular momentum systems with j=20-30jsolar are confined to the primary stars of binaries. This provides novel empirical evidence for rotational disk locking and again demonstrates the much shorter disk lifetimes in close binary systems compared to single-star systems. We estimate the characteristic mean disk dissipation timescale to be ~5 and ~9 Myr for the binary and single-star systems, respectively.
Study of the Performance of Plane Seal Including Thermo-elastic Deformation%计入热弹变形的周隙密封性能研究
Institute of Scientific and Technical Information of China (English)
陈玲; 陈锦辉; 顾越; 王小静
2011-01-01
对周隙密封进行热弹流研究,分析周隙密封的流场、压力场和温度场.计入热弹变形的作用,比较不同参数如转速和小同密封瓦材料等因素对密封性能的影响.研究表明:密封瓦热膨胀变形非常显著,密封瓦体的热变形为向瓦体外部膨胀,使密封瓦油膜间隙变大,泄流量增大;随着转速的升高,密封瓦的侧泄流量和温升均迅速增加;使用热膨胀率较低的碳碳复合材料,将使密封瓦的侧泄流量和功耗大大降低.%The performance of plane seals was studied with thermo-elastic dynamic lubrication theory. The flow field,film pressure and film temperature of plane seals were analyzed including the thermo-elastie deformation. The effects of the seal material and rotating speed on the performance of the plane seal were studied. It is found that the sealing bush has obvious thermo-elastic deformation,which makes oil clearance increase and leakage increase. The side leakage and oil temperature increase rapidly with the increase of the rotating speed. The side leakage and power loss decrease by using C/C material significantly.
Vibro-Acoustic Model of a Disk Drive
Lee, Ming-Ran; Singh, Rajendra
A new mathematical model of the vibro-acoustic characteristics of a computer hard-disk drive is presented in this paper. In particular, a mobility transfer function is defined that links sound radiated by a stationary or rotating disk to electromagnetic torque pulsations and structural dynamics. A simplified disk-drive system consisting of a brushless d.c. motor driving a single disk-spindle assembly, which is mounted on a flexible casing, is considered as the example case. Parametric studies illustrate the roles of bearing stiffness and disk geometry on the vibration and radiated sound.
Numerical simulations of dissipationless disk accretion
Bogovalov, S. V.; Tronin, I. V.
2017-09-01
Our goal is to study the regime of disk accretion in which almost all of the angular momentum and energy is carried away by the wind outflowing from the disk in numerical experiments. For this type of accretion the kinetic energy flux in the outflowing wind can exceed considerably the bolometric luminosity of the accretion disk, what is observed in the plasma flow from galactic nuclei in a number of cases. In this paper we consider the nonrelativistic case of an outflow from a cold Keplerian disk. All of the conclusions derived previously for such a system in the self-similar approximation are shown to be correct. The numerical results agree well with the analytical predictions. The inclination angle of the magnetic field lines in the disk is less than 60°, which ensures a free wind outflow from the disk, while the energy flux per wind particle is greater than the particle rotation energy in its Keplerian orbit by several orders of magnitude, provided that the ratio r A/ r ≫ 1, where r A is the Alfvénic radius and r is the radius of the Keplerian orbit. In this case, the particle kinetic energy reaches half the maximum possible energy in the simulation region. The magnetic field collimates the outflowing wind near the rotation axis and decollimates appreciably the wind outflowing from the outer disk periphery.
Institute of Scientific and Technical Information of China (English)
明春英; 郑连存; 张欣欣
2011-01-01
The three-dimensional steady laminar flow of an incompressible non-Newtonian power-law fluid over a rotating infinite disk with heat transfer was studied. The governing partial differential equations, including the continuity equation, the momentum equation and the energy equation, were transformed to ordinary differential equations by utilizing the generalized Karman similarity transformation. The corresponding nonlinear two-point boundary value problem was solved by the multi-shooting method. Numerical re- sults were obtained for the shear-thinning fluid, the Newtonian fluid and the shear-thickening fluid. It is shown that the power-law character index and the Prandtl number affect the velocities in all directions and the temperature of the fluid in the boundary layer. The results are compared with those of Andersson et al. without considering heat transfer.%针对非牛顿幂律流体在无限大旋转圆盘上层流边界层内三维流动与传热问题,在普朗特数为常数的条件下,利用广义Karman相似变换,将连续方程、动量方程及能量方程形成的偏微分方程组化成常微分方程组,再采用多重打靶法数值求解非线性两点边值问题.分别针对剪薄型流体、牛顿流体和剪厚型流体,得到不同幂律指标下的速度和温度分布及不同普朗特数下温度场的结果.结果表明径向速度分量的峰值随幂律指标的增大而增大,轴向速度受边界层厚度的影响较突出,盘表面的传热随幂律指标和普朗特数都呈现递增趋势.最后将本文流场结果与Andersson等在不考虑传热情况下的结果进行比较表明吻合性较好.
Energy Technology Data Exchange (ETDEWEB)
Ye, Xiaoliang; Du, Yongling; Lu, Daban; Wang, Chunming, E-mail: wangcm@lzu.edu.cn
2013-05-24
Graphical abstract: -- Highlights: •A green and facile approach for synthesis of β-CD-PDDA-Gr at room temperature. •We present the β-CD-PDDA-Gr modified GC-RDE for simultaneous detection of SY and TT. •SY and TT's electrooxidations are both the one-electron-one-proton-transfer process. •Diffusion coefficients and standard rate constants of SY and TT were discussed. -- Abstract: We proposed a green and facile approach for the synthesis of β-cyclodextrin-coated poly(diallyldimethylammonium chloride)-functionalized graphene composite film (β-CD-PDDA-Gr) by using L-ascorbic acid (L-AA) as the reducing agent at room temperature. The β-CD-PDDA-Gr composite film modified glassy carbon-rotating disk electrode (GC-RDE) was then developed for the sensitive simultaneous determination of two synthetic food colorants: sunset yellow (SY) and tartrazine (TT). By cyclic voltammetry (CV), the peak currents of SY and TT increased obviously on the developed electrochemical sensor. The kinetic parameters, such as diffusion coefficient D and standard heterogeneous rate constant k{sub b}, were estimated by linear sweep voltammetry (LSV). Under the optimal conditions, the differential pulse voltammetry (DPV) signals of SY and TT on the β-CD-PDDA-Gr modified GC-RDE were significantly enhanced. The enhanced anodic peak currents represented the excellent analytical performance of simultaneous detection of SY and TT in the range of 5.0 × 10{sup −8} to 2.0 × 10{sup −5} mol L{sup −1}, with a low limit of detection (LOD) of 1.25 × 10{sup −8} mol L{sup −1} for SY and 1.43 × 10{sup −8} mol L{sup −1} for TT (S N{sup −1} = 3). This proposed method displayed outstanding selectivity, good stability and acceptable repeatability and reproducibility, and also has been used to simultaneously determine SY and TT in some commercial soft drinks with satisfactory results. The obtained results were compared to HPLC of analysis for those two colorants and no significant
Conservative GRMHD simulations of moderately thin, tilted accretion disks
Energy Technology Data Exchange (ETDEWEB)
Teixeira, Danilo Morales [Instituto de Astronomia, Geofísica e Ciências Atmosféricas, Universidade de São Paulo, São Paulo, SP 05508-090 (Brazil); Fragile, P. Chris [Department of Physics and Astronomy, College of Charleston, Charleston, SC 29424 (United States); Zhuravlev, Viacheslav V. [Sternberg Astronomical Institute, Moscow M. V. Lomonosov State University, Universitetskij pr. 13, 119992 Moscow (Russian Federation); Ivanov, Pavel B., E-mail: danilo.morales@iag.usp.br [Astro Space Centre, P. N. Lebedev Physical Institute, 84/32 Profsoyuznaya Street, 117810 Moscow (Russian Federation)
2014-12-01
This paper presents our latest numerical simulations of accretion disks that are misaligned with respect to the rotation axis of a Kerr black hole. In this work, we use a new, fully conservative version of the Cosmos++ general relativistic magnetohydrodynamics (GRMHD) code, coupled with an ad hoc cooling function designed to control the thickness of the disk. Together these allow us to simulate the thinnest tilted accretion disks ever using a GRMHD code. In this way, we are able to probe the regime where the dimensionless stress and scale height of the disk become comparable. We present results for both prograde and retrograde cases. The simulated prograde tilted disk shows no sign of Bardeen-Petterson alignment even in the innermost parts of the disk. The simulated retrograde tilted disk, however, does show modest alignment. The implication of these results is that the parameter space associated with Bardeen-Petterson alignment for prograde disks may be rather small, only including very thin disks. Unlike our previous work, we find no evidence for standing shocks in our simulated tilted disks. We ascribe this to the black hole spin, tilt angle, and disk scale height all being small in these simulations. We also add to the growing body of literature pointing out that the turbulence driven by the magnetorotational instability in global simulations of accretion disks is not isotropic. Finally, we provide a comparison between our moderately thin, untilted reference simulation and other numerical simulations of thin disks in the literature.
Long-term Evolution of Photoevaporating Protoplanetary Disks
Bae, Jaehan; Zhu, Zhaohuan; Gammie, Clarles
2013-01-01
We perform calculations of our one-dimensional, two-zone disk model to study the long-term evolution of the circumstellar disk. In particular, we adopt published photoevaporation prescriptions and examine whether the photoevaporative loss alone, coupled with a range of initial angular momenta of the protostellar cloud, can explain the observed decline of the frequency of optically-thick dusty disks with increasing age. In the parameter space we explore, disks have accreting and/or non-accreting transitional phases lasting of $\\lesssim20 %$ of their lifetime, which is in reasonable agreement with observed statistics. Assuming that photoevaporation controls disk clearing, we find that initial angular momentum distribution of clouds needs to be weighted in favor of slowly rotating protostellar cloud cores. Again, assuming inner disk dispersal by photoevaporation, we conjecture that this skewed angular momentum distribution is a result of fragmentation into binary or multiple stellar systems in rapidly-rotating c...
Reducing position error signal (PES) due to disk vibration using an air shroud
He, Zhimin; Du, Chunling; Mou, Jianqiang; Ong, Eng Hong
2008-04-01
The advances in magnetic recording technology demand higher magnetic head positioning accuracy and faster disk rotation speed. However, the higher rotational speed of disk generates the greater flow-induced vibration known as disk flutter, which causes the increase of the track misregistration (TMR). To overcome the issue, an air shroud is presented to reduce disk vibration and position error signal (PES) for magnetic recording. Computational fluid mechanics simulations are performed to study the flow pattern surrounding a disk with an air shroud for different openings. The air-bearing stiffness and damping effects of the disk spindle assembly with an air shroud are evaluated. Based on the computational fluid dynamics (CFD) simulation, the air shroud is prototyped and the disk vibrations with and without the air shroud at different disk rotation speeds are experimentally investigated using a laser Doppler vibrometer (LDV). Significant disk vibration reductions are attained while a shroud is installed onto a disk at certain disk rotation speeds. PESs are also measured for the cases with and without an air shroud during servo implementation. Reductions of PESs are observed when an air shroud is installed at some disk rotation speeds.
An alternative model for the origin of gaps in circumstellar disks
Vorobyov, Eduard I; Guedel, Manuel; Lin, D N C
2016-01-01
Motivated by recent observational and numerical studies suggesting that collapsing protostellar cores may be replenished from the local environment, we explore the evolution of protostellar cores submerged in the external counter-rotating environment. These models predict the formation of counter-rotating disks with a deep gap in the gas surface density separating the inner disk (corotating with the star) and the outer counter-rotating disk. The properties of these gaps are compared to those of planet-bearing gaps that form in disks hosting giant planets. We employ numerical hydrodynamics simulations of collapsing cores that are replenished from the local counter-rotating environment, as well as numerical hydrodynamic simulations of isolated disks hosting giant planets, to derive the properties of the gaps that form in both cases. Our numerical simulations demonstrate that counter-rotating disks can form for a wide range of mass and angular momentum available in the local environment. The gap that separates b...
Invariance of decay rate with respect to boundary conditions in thermoelastic Timoshenko systems
Alves, M. S.; Jorge Silva, M. A.; Ma, T. F.; Muñoz Rivera, J. E.
2016-06-01
This paper is mainly concerned with the polynomial stability of a thermoelastic Timoshenko system recently introduced by Almeida Júnior et al. (Z Angew Math Phys 65(6):1233-1249, 2014) that proved, in the general case when equal wave speeds are not assumed, different polynomial decay rates depending on the boundary conditions, namely, optimal rate {t^{-1/2}} for mixed Dirichlet-Neumann boundary condition and rate {t^{-1/4}} for full Dirichlet boundary condition. Here, our main achievement is to prove the same polynomial decay rate {t^{-1/2}} (corresponding to the optimal one) independently of the boundary conditions, which improves the existing literature on the subject. As a complementary result, we also prove that the system is exponentially stable under equal wave speeds assumption. The technique employed here can probably be applied to other kind of thermoelastic systems.
Three-dimensional fundamental thermo-elastic solutions applied to contact problems
Wang, Z. P.; Wang, T.; Li, P. D.; Li, X. Y.; Chen, W. Q.; Müller, R.
2016-11-01
This paper aims to develop three-dimensional fundamental thermo-elastic solutions for an infinite/half-infinite space of a two-dimensional hexagonal quasi-crystal, which is subjected to a point heat source. Starting from the newly developed general solution in terms of quasi-harmonic potential functions, the corresponding fundamental solutions are derived by means of the trial-and-error technique. Six appropriate potential functions involved in the general solution are observed. The present fundamental solutions are applied to construct boundary integral equations governing the contact problems. Numerical calculations are performed to show the distributions of the thermo-elastic coupling field variables in a half-space subjected to a point thermal source.
Analytical solution of thermoelastic interaction in a half-space by pulsed laser heating
Abbas, Ibrahim A.; Marin, Marin
2017-03-01
In this article, we consider the problem of a two-dimensional thermoelastic half-space in the context of generalized thermoelastic theory with one relaxation time. The surface of the half-space is taken to be traction free and thermally insulated. The solution of the considered physical quantity can be broken down in terms of normal modes. The nonhomogeneous basic equations have been written in the form of a vector-matrix differential equation, which is then solved by an eigenvalue approach. The exact analytical solution is adopted for the temperature, the components of displacement and stresses. The results obtained are presented graphically for the effect of laser pulse to display the phenomena physical meaning. The graphical results indicate that the thermal relaxation time has a great effect on the temperature, the components of displacement and the components of stress.
Two Temperature Magneto-Thermoelasticity with Initial Stress: State Space Formulation
Directory of Open Access Journals (Sweden)
Sunita Deswal
2013-01-01
Full Text Available Magneto-thermoelastic interactions in an initially stressed isotropic homogeneous elastic half-space with two temperatures are studied using mathematical methods under the purview of the L-S model of linear theory of generalized thermoelasticity. The formalism deals with the state space approach with the purpose of counteracting the difficulties of handling the displacement potential functions. Of specific concern here is the propagation of waves owing to ramp type increase in temperature and load. The medium is considered to be permeated by a uniform magnetic field. The expressions for different field parameters such as displacement, temperature, strain, and stress in the physical domain are obtained by applying a numerical inversion technique. Results of some earlier workers have been deduced from the present formulation. Numerical work is also performed for a suitable material with the aim of illustrating the results.
The thermoelastic excitation of air-solid interface waves using the pulsed laser
Institute of Scientific and Technical Information of China (English)
HU; Wenxiang; QIAN; Menglu
2004-01-01
Applying the integral transform to the coupled problem of thermoelastic and heat conduction equations, the integral representation of the normal displacement field for the air-solid interface waves excited by a pulsed laser line source is obtained. The pole residues of the integrand are performed analytically, and the transient displacement field is calculated by using FFT technique. The thermoelastic excitation and detection of the air-solid interface waves is carried out by a laser ultrasonic system, on which the pulsed laser is focused into a line source onto the interface to excite the air-solid interface waves:leaky Rayleigh wave and Scholte wave, and the interface waves displacement signal is detected successfully by a SH130 laser heterodyne interferometer. The theoretic and experimental results are in good agreement.
THERMOELASTICALLY COUPLED AXISYMMETRIC NONLINEAR VIBRATION OF SHALLOW SPHERICAL AND CONICAL SHELLS
Institute of Scientific and Technical Information of China (English)
王永岗; 戴诗亮
2004-01-01
The problem of axisymmetric nonlinear vibration for shallow thin spherical and conical shells when temperature and strain fields are coupled is studied. Based on the large deflection theories of von Krmn and the theory of thermoelasticity, the whole governing equations and their simplified type are derived. The time-spatial variables are separated by Galerkin's technique, thus reducing the governing equations to a system of time-dependent nonlinear ordinary differential equation. By means of regular perturbation method and multiple-scales method, the first-order approximate analytical solution for characteristic relation of frequency vs amplitude parameters along with the decay rate of amplitude are obtained, and the effects of different geometric parameters and coupling factors as well as boundary conditions on thermoelastically coupled nonlinear vibration behaviors are discussed.
Elastodynamics of axi-symmetric deformation in magneto-micropolar generalized thermoelastic medium
Institute of Scientific and Technical Information of China (English)
Rajneesh Kumar; Rupender
2009-01-01
The present investigation is concerned with an axiosymmetric problem in the electromagnetic micropolar thermoelastic half-space whose surface is subjected to the mechanical or thermal source. Laplace and Hankel transform techniques are used to solve the problem. Various types of sources are taken to illustrate the utility of the approach. Integral transforms are inverted by using a numerical technique to obtain the components of stresses, temperature distribution, and induced electric and magnetic fields. The ex-pressions of these quantities are illustrated graphically to depict the magnetic effect for two different generalized thermoelasticity theories, i.e., Lord and Shulman (L-S theory) and Green and Lindsay (G-L theory). Some particular interesting cases are also deduced from the present investigation.
Thermoelastic Femoral Stress Imaging for Experimental Evaluation of Hip Prosthesis Design
Hyodo, Koji; Inomoto, Masayoshi; Ma, Wenxiao; Miyakawa, Syunpei; Tateishi, Tetsuya
An experimental system using the thermoelastic stress analysis method and a synthetic femur was utilized to perform reliable and convenient mechanical biocompatibility evaluation of hip prosthesis design. Unlike the conventional technique, the unique advantage of the thermoelastic stress analysis method is its ability to image whole-surface stress (Δ(σ1+σ2)) distribution in specimens. The mechanical properties of synthetic femurs agreed well with those of cadaveric femurs with little variability between specimens. We applied this experimental system for stress distribution visualization of the intact femur, and the femurs implanted with an artificial joint. The surface stress distribution of the femurs sensitively reflected the prosthesis design and the contact condition between the stem and the bone. By analyzing the relationship between the stress distribution and the clinical results of the artificial joint, this technique can be used in mechanical biocompatibility evaluation and pre-clinical performance prediction of new artificial joint design.
Energy Technology Data Exchange (ETDEWEB)
Abbas, Ibrahim A., E-mail: aabbas5@kau.edu.sa [Department of Mathematics, Faculty of Science and Arts-Khulais, King Abdulaziz University, Jeddah (Saudi Arabia); Department of mathematics, Faculty of Science, Sohag University, Sohag (Egypt)
2015-03-01
In the present work, we consider the problem of fractional order thermoelastic interaction in a material placed in a magnetic field and subjected to a moving plane of heat source. The basic equations have been written in the form of a vector–matrix differential equation in the Laplace transform domain, which is then solved by an eigenvalue approach. The inverse Laplace transforms are computed numerically and some comparisons have been shown in figures to estimate the effect of each of the fractional order, heat source velocity, time and the magnetic field and parameters. - Highlights: • The problem of fractional order thermoelastic interaction in a material placed in a magnetic field and subjected to a moving plane of heat source. • The eigenvalue approach gives exact solution in the Laplace domain without any assumed restrictions on the actual physical quantities. • Numerical results for the temperature, displacement and the stress distributions are represented graphically.
Directory of Open Access Journals (Sweden)
A. M. Zenkour
2009-01-01
Full Text Available The quasistatic bending response is presented for a simply supported functionally graded rectangular plate subjected to a through-the-thickness temperature field under the effect of various theories of generalized thermoelasticity, namely, classical dynamical coupled theory, Lord and Shulman's theory with one relaxation time, and Green and Lindsay's theory with two relaxation times. The generalized shear deformation theory obtained by the first author is used. Material properties of the plate are assumed to be graded in the thickness direction according to a simple exponential law distribution in terms of the volume fractions of the constituents. The numerical illustrations concern quasistatic bending response of functionally graded square plates with two constituent materials are studied using the different theories of generalized thermoelasticity
Xiong, Q. L.; Tian, X. G.; Lu, T. J.
2012-07-01
The thermoelastic response of thin gold films induced by femtosecond laser irradiation is numerically simulated using a modified combined two-temperature model (TTM) and molecular dynamics (MD) method, with focus placed upon the influence of the electron relaxation effect. The validity of the numerical approach is checked against existing experimental results. While the electron relaxation effect is found negligible when the laser duration is much longer than the electron thermal relaxation time, it becomes significant if the laser duration matches the electron relaxation time, especially when the former is much shorter than the latter. The characteristics of thermo-mechanical interaction in the thin film are analyzed, and the influence of temperature-dependent material properties upon the thermoelastic response of the film quantified.
Wave Propagation in a Micropolar Transversely Isotropic Generalized Thermoelastic Half-Space
Directory of Open Access Journals (Sweden)
Gupta R.R.
2014-05-01
Full Text Available Rayleigh waves in a half-space exhibiting microplar transversely isotropic generalized thermoelastic properties based on the Lord-Shulman (L-S, Green and Lindsay (G-L and Coupled thermoelasticty (C-T theories are discussed. The phase velocity and attenuation coefficient in the previous three different theories have been obtained. A comparison is carried out of the phase velocity, attenuation coefficient and specific loss as calculated from the different theories of generalized thermoelasticity along with the comparison of anisotropy. The amplitudes of displacements, microrotation, stresses and temperature distribution were also obtained. The results obtained and the conclusions drawn are discussed numerically and illustrated graphically. Relevant results of previous investigations are deduced as special cases.
Directory of Open Access Journals (Sweden)
Rajneesh Kumar
2014-01-01
Full Text Available The present investigation deals with the propagation of Rayleigh type surface waves in an isotropic microstretch thermoelastic diffusion solid half space under a layer of inviscid liquid. The secular equation for surface waves in compact form is derived after developing the mathematical model. The dispersion curves giving the phase velocity and attenuation coefficients with wave number are plotted graphically to depict the effect of an imperfect boundary alongwith the relaxation times in a microstretch thermoelastic diffusion solid half space under a homogeneous inviscid liquid layer for thermally insulated, impermeable boundaries and isothermal, isoconcentrated boundaries, respectively. In addition, normal velocity component is also plotted in the liquid layer. Several cases of interest under different conditions are also deduced and discussed.
Generalised Thermo-Elasticity When the Material Coupling Parameter Equals Unity
Directory of Open Access Journals (Sweden)
D. Rama Murthy
1979-04-01
Full Text Available Analytical solutions of three problems using the theory of generalised thermo-elasticity are presented for the case when the material coupling parameter equals unity (lambda =1. The problems considered are (1 Constant velocity impact, (2 Daniloviskaya's problem, and (3 Step in strain. Solutions are presented for the case of thin bars (one dimensional stress and are obtained using Laplace transform. There is a great simplification in the equations of generalised thermo-elasticity when the material coupling parameter equals unity, which permits the straight forward inversion of the transformed solutions. The solutions obtained are more general which includes the effect of relaxation time also. The important feature of this paper is that the solutions of coupled theory can be readily obtained simply by putting the relaxation constant equals to zero (Beta=0.
Nonaxisymmetric evolution in protostellar disks
Laughlin, Gregory; Bodenheimer, Peter
1994-01-01
We present a two-dimensional, multigridded hydrodynamical simulation of the collapse of an axisymmetric, rotating, 1 solar mass protostellar cloud, which forms a resolved, hydrotastic disk. The code includes the effects of physical viscosity, radiative transfer and radiative acceleration but not magnetic fields. We examine how the disk is affected by the inclusion of turbulent viscosity by comparing a viscous simulation with an inviscid model evolved from the same initial conditions, and we derive a disk evolutionary timescale on the order of 300,000 years if alpha = 0.01. Effects arising from non-axisymmetric gravitational instabilities in the protostellar disk are followed with a three-dimensional SPH code, starting from the two-dimensional structure. We find that the disk is prone to a series of spiral instabilities with primary azimulthal mode number m = 1 and m = 2. The torques induced by these nonaxisymmetric structures elicit material transport of angular momentum and mass through the disk, readjusting the surface density profile toward more stable configurations. We present a series of analyses which characterize both the development and the likely source of the instabilities. We speculate that an evolving disk which maintains a minimum Toomre Q-value approximately 1.4 will have a total evolutionary span of several times 10(exp 5) years, comparable to, but somewhat shorter than the evolutionary timescale resulting from viscous turbulence alone. We compare the evolution resulting from nonaxisymmetric instabilities with solutions of a one-dimensional viscous diffusion equation applied to the initial surface density and temperature profile. We find that an effective alpha-value of 0.03 is a good fit to the results of the simulation. However, the effective alpha will depend on the minimum Q in the disk at the time the instability is activated. We argue that the major fraction of the transport characterized by the value of alpha is due to the action of
Kato, Shoji
2016-01-01
This book presents the current state of research on disk oscillation theory, focusing on relativistic disks and tidally deformed disks. Since the launch of the Rossi X-ray Timing Explorer (RXTE) in 1996, many high-frequency quasiperiodic oscillations (HFQPOs) have been observed in X-ray binaries. Subsequently, similar quasi-periodic oscillations have been found in such relativistic objects as microquasars, ultra-luminous X-ray sources, and galactic nuclei. One of the most promising explanations of their origin is based on oscillations in relativistic disks, and a new field called discoseismology is currently developing. After reviewing observational aspects, the book presents the basic characteristics of disk oscillations, especially focusing on those in relativistic disks. Relativistic disks are essentially different from Newtonian disks in terms of several basic characteristics of their disk oscillations, including the radial distributions of epicyclic frequencies. In order to understand the basic processes...
The DiskMass Survey : I. Overview
Bershady, Matthew A.; Verheijen, Marc A. W.; Swaters, Rob A.; Andersen, David R.; Westfall, Kyle B.; Martinsson, Thomas
2010-01-01
We present a survey of the mass surface density of spiral disks, motivated by outstanding uncertainties in rotation-curve decompositions. Our method exploits integral-field spectroscopy to measure stellar and gas kinematics in nearly face-on galaxies sampled at 515, 660, and 860 nm, using the custom
Long-time behavior of a class of thermoelastic plates with nonlinear strain
Fatori, L. H.; Jorge Silva, M. A.; Ma, T. F.; Yang, Zhijian
2015-11-01
In recent years a class of vibrating plates with nonlinear strain of p-Laplacian type was studied by several authors. The present paper contains a first thermoelastic model of that class of problems including both Fourier and non-Fourier heat laws. Our main result establishes the existence of global and exponential attractors for the strongly damped problem through a stabilizability inequality. In addition, for the weakly damped problem, we establish the exponential stability of its Galerkin semiflows.
Existence and stability results for thermoelastic dipolar bodies with double porosity
Marin, M.; Nicaise, S.
2016-11-01
This paper is concerned with the theory of thermoelastic dipolar bodies which have a double porosity structure. In contrast with previous papers dedicated to classical elastic bodies, in our context the double porosity structure of the body is influenced by the displacement field, which is consistent with real models. In this setting, we show instability of solution as the initial energy is negative while under an appropriated (and realistic) condition, we prove existence and uniqueness of solution using semi-group theory.
Global existence and decay of solutions of the Cauchy problem in thermoelasticity with second sound
Kasimov, Aslan R.
2013-06-04
We consider the one-dimensional Cauchy problem in non-linear thermoelasticity with second sound, where the heat conduction is modelled by Cattaneo\\'s law. After presenting decay estimates for solutions to the linearized problem, including refined estimates for data in weighted Lebesgue-spaces, we prove a global existence theorem for small data together with improved decay estimates, in particular for derivatives of the solutions. © 2013 Taylor & Francis.
A computational method for the solution of one-dimensional nonlinear thermoelasticity
Indian Academy of Sciences (India)
M Mirazadeh; M Eslami; Anjan Biswas
2015-10-01
In this paper, one of the newest analytical methods, new homotopy perturbation method (NHPM), is considered to solve thermoelasticity equations. Results obtained by NHPM, which does not need small parameters, are compared with the numerical results and a very good agreement is found. This method provides a convenient way to control the convergence of approximation series and adjust convergence regions when necessary. The results reveal that the proposed method is explicit, effective and easy to use.
Prawirodirdjo, Linette; Ben-Zion, Yehuda; Bock, Yehuda
2006-02-01
We suggest that strain in the elastic part of the Earth's crust induced by surface temperature variations is a significant contributor to the seasonal variations observed in the spatially filtered daily position time series of Southern California Integrated GPS Network (SCIGN) stations. We compute the predicted thermoelastic strain from the observed local atmospheric temperature record assuming an elastically decoupled layer over a uniform elastic half-space and compare the seasonal variations in thermoelastic strain to the horizontal GPS position time series. We consider three regions (Palmdale, 29 Palms, and Idyllwild), each with one temperature station and three to six GPS stations. The temperature time series is used to compute thermoelastic strain at each station on the basis of its relative location in the temperature field. For each region we assume a wavelength for the temperature field that is related to the local topography. The depth of the decoupled layer is inferred from the phase delay between the temperature record and the GPS time series. The relative amplitude of strain variation at each GPS station, calculated to be on the order of 0.1 μstrain, is related to the relative location of that station in the temperature field. The goodness of fit between model and data is evaluated from the relative amplitudes of the seasonal signals, as well as the appropriateness of the chosen temperature field wavelength and decoupled layer depth. The analysis shows a good fit between the predicted strains and the GPS time series. This suggests that the model captures the key first-order ingredients that determine the thermoelastic strain in a given area. The results can be used to improve the signal/noise ratio in GPS data.
Thermo-Elastic Nondestructive Evaluation of Fatigue Damage in PMR-15 Resin (Postprint)
2011-08-01
To) 25 June 2009 – 17 July 2011 4. TITLE AND SUBTITLE THERMO-ELASTIC NONDESTRUCTIVE EVALUATION OF FATIGUE DAMAGE IN PMR -15 RESIN (POSTPRINT) 5a...nondestructive evaluation of fatigue damage in a thermoset polyimide resin, PMR -15, performed by measuring the changes in the evolution of heat in the samples...discussed in reference to utilizing this technique for detection and evaluation of fatigue in PMR -15 resin and composites. 15. SUBJECT TERMS fatigue
Topology optimization for reduction of thermo-elastic dissipation in MEMS resonators
DEFF Research Database (Denmark)
Gerrard, Dustin D.; Chen, Yunhan; Chandorkar, Saurabh A.
2017-01-01
This paper presents a topology optimization approach for reducing thermo-elastic dissipation (TED) in MEMS resonators. This algorithm is applied to a clamped-clamped resonant beam to maximize the quality factor (Q). Optimal designs have a Q ten times higher than a solid beam and are 75% higher than...... previously optimized devices. Furthermore, new designs have intuitive topologies. Beams are fabricated in silicon wafers and experimental measurements of Q agree well with simulation....
Henry, Donald P., Jr.; Banerjee, Prasanta K.
1988-01-01
New two- and three-dimensional BEM formulations are developed for steady-state and transient uncoupled thermoelasticity. These new procedures differ from previous work in that additional surface of volume integration is not required to incorporate thermal loads in the analysis. Instead, thermal body forces are introduced in the BEM system via particular integrals. The present formulation is implemented in a general-purpose multiregion system, and examples are presented to demonstrate the accuracy and versatility of the method.
Rothe time-discretization method for a nonlocal problem arising in thermoelasticity
Directory of Open Access Journals (Sweden)
Nabil Merazga
2005-01-01
Full Text Available We investigate a model parabolic mixed problem with purely boundary integral conditions arising in the context of thermoelasticity. Using the Rothe method which is based on a semidiscretization of the given problem with respect to the time variable, the questions of existence, uniqueness, and continuous dependence upon data of a weak solution are proved. Moreover, we establish convergence and derive an error estimate for a semidiscrete approximation.
ASYMPTOTIC BEHAVIOUR AND EXPONENTIAL STABILITY FOR THERMOELASTIC PROBLEM WITH LOCALIZED DAMPING
Institute of Scientific and Technical Information of China (English)
GAO Hong-jun; ZHAO Yu-juan
2006-01-01
A semi-linear thermoelastic problem with localized damping is considered,which is one of the most important mathematical models in material science. The existence and decays exponentially to zero of solution of this problem are obtained. Moreover,the existence of absorbing sets is achieved in the non-homogeneous case. The result indicates that the system which we studied here is asymptotic stability.
Directory of Open Access Journals (Sweden)
Rajneesh Kumar
2014-01-01
Full Text Available The reflection of plane waves at the free surface of thermally conducting micropolar elastic medium with two temperatures is studied. The theory of thermoelasticity with and without energy dissipation is used to investigate the problem. The expressions for amplitudes ratios of reflected waves at different angles of incident wave are obtained. Dissipation of energy and two-temperature effects on these amplitude ratios with angle of incidence are depicted graphically. Some special and particular cases are also deduced.
Finite element investigation of thermo-elastic and thermo-plastic consolidation
Energy Technology Data Exchange (ETDEWEB)
Aboustit, B.L.
1984-01-01
The transient response of saturated continua due to thermal as well as mechanical loads is investigated in both elastic and plastic ranges. When the two phase saturated media are subjected to thermomechanical loading, the energy equation is coupled with the mass flow and solid deformation equations resulting in the initial boundary value problem of thermal consolidation. The solid behavior may be assumed to be either elastic or elastoplastic leading to the associated theories of thermoelastic and thermoelastoplastic consolidation. The governing equations for the quasi-static infinitesimal theory of thermoelastic consolidation are developed by using the theory of mixtures. An equivalent variational principle is developed along with associated finite element formulations. Two isoparametric elements of the composite type are employed for the spatial discretization. The formulation is extended to the plastic ranges by modeling the solid phase as an elastic work hardening material with an associated flow rule. An incremental iterative scheme is developed to solve this nonlinear transient problem. Several special purpose computer codes are developed for evaluating the isothermal, thermal, elastic and elastoplastic plane strain consolidation responses. These codes have been evaluated against limiting cases available in the literature. The effects of temporal and spatial interpolation schemes are investigated for one-dimensional thermoelastic consolidation problems. An application dealing with a plane strain underground coal gasification problem is also presented.
Study on generalized magneto-thermoelastic problems by FEM in time domain
Institute of Scientific and Technical Information of China (English)
Xiaogeng Tian; Yapeng Shen; Yunming Chen
2005-01-01
This paper presents an investigation of temperature, displacement, stress, and induced magnetic field in a half space perfectly-conductive plate. Finite element equations regarding generalized magneto-thermoelasticity problems with two relaxation times (i.e., the G-L theory) are derived using the principle of virtual work. For avoiding numerical complication involved in inverse Laplace and Fourier transformation and low precision thereof, the equations are solved directly in time-domain. As a numerical example, the derived equation is used to investigate the generalized magneto-thermoelastic behavior of a semi-infinite plate under magnetic field and subjecting to a thermal shock loading. The results demonstrate that FEM can faithfully predict the deformation of the plate and the induced magnetic field, and most importantly can reveal the sophisticated second sound effect of heat conduction in two-dimensional generalized thermo elastic solids, which is usually difficult to model by routine transformation methods. A peak can be observed in the distribution of stress and induced magnetic field at the heat wave front and the magnitude of the peak decreases with time, which can not be obtained by transformation methods. The new method can also be used to study generalized piezo-thermoelastic problems.
The effects of viscosity on circumplanetary disks
Institute of Scientific and Technical Information of China (English)
De-Fu Bu; Hsien Shang; Feng Yuan
2013-01-01
The effects of viscosity on the circumplanetary disks residing in the vicinity of protoplanets are investigated through two-dimensional hydrodynamical simulations with the shearing sheet model.We find that viscosity can considerably affect properties of the circumplanetary disk when the mass of the protoplanet Mp (＜) 33 M(⊙),where M(⊙) is the Earth's mass.However,effects of viscosity on the circumplanetary disk are negligibly small when the mass of the protoplanet Mp(＞) 33 M(⊙).We find that when Mp(＜) 33 M(⊙),viscosity can markedly disrupt the spiral structure of the gas around the planet and smoothly distribute the gas,which weakens the torques exerted on the protoplanet.Thus,viscosity can slow the migration speed of a protoplanet.After including viscosity,the size of the circumplanetary disk can be decreased by a factor of (＞) 20％.Viscosity helps to transport gas into the circumplanetary disk from the differentially rotating circumstellar disk.The mass of the circumplanetary disk can be increased by a factor of 50％ after viscosity is taken into account when Mp(＜) 33 M(⊙).Effects of viscosity on the formation of planets and satellites are briefly discussed.
Viscous Stability of Relativistic Keplerian Accretion Disks
Ghosh, P
1998-01-01
We investigate the viscous stability of thin, Keplerian accretion disks in regions where general relativistic (GR) effects are essential. For gas pressure dominated (GPD) disks, we show that the Newtonian conclusion that such disks are viscously stable is reversed by GR modifications in the behaviors of viscous stress and surface density over a significantly large annular region not far from the innermost stable orbit at $r=\\rms$. For slowly-rotating central objects, this region spans a range of radii $14\\lo r\\lo 19$ in units of the central object's mass $M$. For radiation pressure dominated (RPD) disks, the Newtonian conclusion that they are viscously unstable remains valid after including the above GR modifications, except in a very small annulus around $r\\approx 14M$, which has a negligible influence. Inclusion of the stabilizing effect of the mass-inflow through the disk's inner edge via a GR analogue of Roche-lobe overflow adds a small, stable region around \\rms~for RPD disks, but leaves GPD disks unchan...
Millimeter emission from protoplanetary disks : dust, cold gas, and relativistic electrons
Salter, Demerese Marie
2010-01-01
Star formation occurs when a dense cloud of interstellar gas and dust gravitationally collapses. Rotation during this collapse leads naturally to the formation of a flattened circumstellar disk around the forming star. These disks are additionally known as protoplanetary disks because the orbiting c
Estimation of Nonconservative Aerodynamic Pressure Leading to Flutter of Spinning Disks
DEFF Research Database (Denmark)
Hansen, Morten Hartvig; Raman, A; Mote Jr., C.D.
2001-01-01
An experimental method for predicting the onset of #utter of a disk spinning in a #uid medium is proposed. The method is based on a description of the aerodynamic loading on the disk as a distributed viscous damping force rotating relative to the disk. This model can arise from two aeroelastic...... theories described herein. It is shown analytically and experimentally that the few parameters of this model may be extracted from frequency response functions of the spinning disk. Parameters for a steel disk in air (with a near vacuum experiment as reference) are estimated at increasing rotation speeds...
Propulsion Health Monitoring of a Turbine Engine Disk Using Spin Test Data
Abdul-Aziz, Ali; Woike, Mark R.; Oza, Nikunj; Matthews, Bryan; Baaklini, George Y.
2010-01-01
This paper considers data collected from an experimental study using high frequency capacitive sensor technology to capture blade tip clearance and tip timing measurements in a rotating turbine engine-like-disk-to predict the disk faults and assess its structural integrity. The experimental results collected at a range of rotational speeds from tests conducted at the NASA Glenn Research Center s Rotordynamics Laboratory are evaluated using multiple data-driven anomaly detection techniques to identify abnormalities in the disk. Further, this study presents a select evaluation of an online health monitoring scheme of a rotating disk using high caliber sensors and test the capability of the in-house spin system.
NG7538 IRS1 N: modeling a circumstellar maser disk
Pestalozzi, M R; Conway, J; Booth, R
2004-01-01
We present an edge-on Keplerian disk model to explain the main component of the 12.2 and 6.7 GHz methanol maser emission detected toward NGC7538-IRS1 N. The brightness distribution and spectrum of the line of bright masers are successfully modeled with high amplification of background radio continuum emission along velocity coherent paths through a maser disk. The bend seen in the position-velocity diagram is a characteristic signature of differentially rotating disks. For a central mass of 30 solar masses, suggested by other observations, our model fixes the masing disk to have inner and outer radii of about 270 AU and 750 AU.
This model was a disk storage server used in the Data Centre up until 2012. Each tray contains a hard disk drive (see the 5TB hard disk drive on the main disk display section - this actually fits into one of the trays). There are 16 trays in all per server. There are hundreds of these servers mounted on racks in the Data Centre, as can be seen.
The Origin and Formation of the Circumstellar Disk
Machida, Masahiro N
2010-01-01
The formation and evolution of the circumstellar disk in the collapsing molecular cloud is investigated from the prestellar stage resolving both the molecular cloud core and the protostar itself. In the collapsing cloud, the first adiabatic core appears prior to the protostar formation. Reflecting the thermodynamics of the collapsing gas, the first core is much more massive than the protostar. When the molecular cloud has no angular momentum, the first core falls onto the protostar and disappears a few years after the protostar formation. On the other hand, when the molecular cloud has an angular momentum, the first core does not disappear even after the protostar formation, and directly evolves into the circumstellar disk with a Keplerian rotation. There are two paths for the formation of the circumstellar disk. When the initial cloud has a considerably small rotational energy, two nested disks appear just after the protostar formation. During the early main accretion phase, the inner disk increases its size...
Kuijken, K.; García, I.
2000-01-01
Abstract: This review addresses recent developments in the field of disk galaxy warps. Both results from a new HI survey of edgeon disk galaxies, and of simulations of the interaction between a disk+halo and an orbiting satelite, will be discussed.
Kuijken, K; Kuijken, Konrad; Garcia, Inigo
2000-01-01
This review addresses recent developments in the field of disk galaxy warps. Both results from a new HI survey of edgeon disk galaxies, and of simulations of the interaction between a disk+halo and an orbiting satelite, will be discussed.
Chemistry in Protoplanetary Disks
Henning, Thomas
2013-01-01
This comprehensive review summarizes our current understanding of the evolution of gas, solids and molecular ices in protoplanetary disks. Key findings related to disk physics and chemistry, both observationally and theoretically, are highlighted. We discuss which molecular probes are used to derive gas temperature, density, ionization state, kinematics, deuterium fractionation, and study organic matter in protoplanetary disks.
Abbott, George L.; And Others
1987-01-01
This special feature focuses on recent developments in optical disk technology. Nine articles discuss current trends, large scale image processing, data structures for optical disks, the use of computer simulators to create optical disks, videodisk use in training, interactive audio video systems, impacts on federal information policy, and…
Bar instability in disk-halo systems
Sellwood, J A
2016-01-01
We show that the exponential growth rate of a bar in a stellar disk is substantially greater when the disk is embedded in a live halo than in a rigid one having the same mass distribution. We also find that the vigor of the instability in disk-halo systems varies with the shape of the halo velocity ellipsoid. Disks in rigid halos that are massive enough to be stable by the usual criteria, quickly form bars in isotropic halos and much greater halo mass is needed to avoid a strong bar; thus stability criteria derived for disks in rigid halos do not apply when the halo is responsive. The study presented here is of an idealized family of models with near uniform central rotation and that lack an extended halo; we present more realistic models with extended halos in a companion paper. The puzzle presented by the absence of strong bars in some galaxies having gently rising inner rotation curves is compounded by the results presented here.
Inner edge of accretion disks in low mass X-ray binaries
Institute of Scientific and Technical Information of China (English)
李向东; 汪珍如
1995-01-01
The magnitude of the inner edge of accretion disks in low mass X-ray binaries is controversial in theoretical considerations and observations. Using the inner boundary conditions of accretion disks the inner disk radius has been calculated by taking into account the effect of feedback radiation and the deviation of disk rotation from Keplerian. Results have been applied to the observations and possible interpretations have been proposed for the X-ray spectra and quasiperiodic oscillations.
Kohler, Susanna
2016-07-01
Recent, unusual X-ray observations from our galactic neighbor, the Small Magellanic Cloud, have led to an interesting model for SXP 214, a pulsar in a binary star system.Artists illustration of the magnetic field lines of a pulsar, a highly magnetized, rotating neutron star. [NASA]An Intriguing BinaryAn X-ray pulsar is a magnetized, rotating neutron star in a binary system with a stellar companion. Material is fed from the companion onto the neutron star, channeled by the objects magnetic fields onto a hotspot thats millions of degrees. This hotspot rotating past our line of sight is what produces the pulsations that we observe from X-ray pulsars.Located in the Small Magellanic Cloud, SXP 214 is a transient X-ray pulsar in a binary with a Be-type star. This star is spinning so quickly that material is thrown off of it to form a circumstellar disk.Recently, a team of authors led by JaeSub Hong (Harvard-Smithsonian Center for Astrophysics) have presented new Chandra X-ray observations of SXP 214, tracking it for 50 ks (~14 hours) in January 2013. These observations reveal some very unexpected behavior for this pulsar.X-ray PuzzleThe energy distribution of the X-ray emission from SXP 214 over time. Dark shades or blue colors indicate high counts, and light shades or yellow colors indicate low counts. Lower-energy X-ray emission appeared only later, after about 20 ks. [Hong et al. 2016]Three interesting pieces of information came from the Chandra observations:SXP 214s rotation period was measured to be 211.5 s an increase in the spin rate since the discovery measurement of a 214-second period. Pulsars usually spin down as they lose angular momentum over time so what caused this one to spin up?Its overall X-ray luminosity steadily increased over the 50 ks of observations.Its spectrum became gradually softer (lower energy) over time; in the first 20 ks, the spectrum only consisted of hard X-ray photons above 3 keV, but after 20 ks, softer X-ray photons below 2 ke
Heating and Cooling Protostellar Disks
Hirose, S
2011-01-01
We examine heating and cooling in protostellar disks using 3-D radiation-MHD calculations of a patch of the Solar nebula at 1 AU, employing the shearing-box and flux-limited radiation diffusion approximations. The disk atmosphere is ionized by stellar X-rays, well-coupled to magnetic fields, and sustains a turbulent accretion flow driven by magneto-rotational instability, while the interior is resistive and magnetically dead. The turbulent layers heat by absorbing the light from the central star and by dissipating the magnetic fields. They are optically-thin to their own radiation and cool inefficiently. The optically-thick interior in contrast is heated only weakly, by re-emission from the atmosphere. The interior is colder than a classical viscous model, and isothermal. The magnetic fields support an extended atmosphere that absorbs the starlight 1.5 times higher than the hydrostatic viscous model. The disk thickness thus measures not the internal temperature, but the magnetic field strength. Fluctuations i...
Time Evolution of Relativistic Force-Free Fields Connecting a Neutron Star and its Disk
Asano, E; Matsumoto, R; Asano, Eiji; Uchida, Toshio; Matsumoto, Ryoji
2005-01-01
We study the magnetic interaction between a neutron star and its disk by solving the time-dependent relativistic force-free equations. At the initial state, we assume that the dipole magnetic field of the neutron star connects the neutron star and its equatorial disk, which deeply enters into the magnetosphere of the neutron star. Magnetic fields are assumed to be frozen to the star and the disk. The rotation of the neutron star and the disk is imposed as boundary conditions. We apply Harten-Lax-van Leer (HLL) method to simulate the evolution of the star-disk system. We carry out simulations for (1) a disk inside the corotation radius, in which the disk rotates faster than the star, and (2) a disk outside the corotation radius, in which the neutron star rotates faster than the disk. Numerical results indicate that for both models, the magnetic field lines connecting the disk and the star inflate as they are twisted by the differential rotation between the disk and the star. When the twist angle exceeds pi rad...
Variable Circumstellar Disks: Prevalence, Timescales, and Physical Mechanisms
Burrow, Anthony; Wisniewski, John P.; Lomax, Jamie R.; Bjorkman, Karen S.; Bjorkman, Jon Eric; Covey, Kevin R.; Gerhartz, Cody; Richardson, Noel; Thao, Pa
2017-01-01
Rapidly rotating B-type stars often experience mass ejection that leads to the formation of a circumstellar gas disk, as diagnosed by distinct emission lines present in their spectra. The mass ejection from these stars, known as classical Be stars, sometimes slows or stops, leading to the mass falling back onto the central star and the disk dissipating. The prevalence and time-scale of such disk-loss and disk-replenishment episodes, as well as the underlying physical processes that cause the underlying mass ejection, remain unknown. We are using multi-epoch broad- and narrow-band photometric observations of 12 young open clusters to characterize the prevalence and time-scale of disk-loss and disk-replenishment episodes. We use our observations to gauge which cluster objects exhibit H-alpha emission, which is a primary indicator of Be stars in our clusters. This program is supported by NSF-AST 1411563, 1412110, and 1412135.
On the gravitational stability of gravito-turbulent accretion disks
Lin, Min-Kai
2016-01-01
Low mass, self-gravitating accretion disks admit quasi-steady, `gravito-turbulent' states in which cooling balances turbulent viscous heating. However, numerical simulations show that gravito-turbulence cannot be sustained beyond dynamical timescales when the cooling rate or corresponding turbulent viscosity is too large. The result is disk fragmentation. We motivate and quantify an interpretation of disk fragmentation as the inability to maintain gravito-turbulence due to formal secondary instabilities driven by: 1) cooling, which reduces pressure support; and/or 2) viscosity, which reduces rotational support. We analyze the gravitational stability of viscous, non-adiabatic accretion disks with internal heating, external irradiation, and cooling. We consider parameterized cooling functions in 2D and 3D disks, as well as radiative diffusion in 3D. We show that generally there is no critical cooling rate/viscosity below which the disk is formally stable, although interesting limits appear for unstable modes wi...
Dynamo magnetic-field generation in turbulent accretion disks
Stepinski, T. F.
1991-01-01
Magnetic fields can play important roles in the dynamics and evolution of accretion disks. The presence of strong differential rotation and vertical density gradients in turbulent disks allows the alpha-omega dynamo mechanism to offset the turbulent dissipation and maintain strong magnetic fields. It is found that MHD dynamo magnetic-field normal modes in an accretion disk are highly localized to restricted regions of a disk. Implications for the character of real, dynamically constrained magnetic fields in accretion disks are discussed. The magnetic stress due to the mean magnetic field is found to be of the order of a viscous stress. The dominant stress, however, is likely to come from small-scale fluctuating magnetic fields. These fields may also give rise to energetic flares above the disk surface, providing a possible explanation for the highly variable hard X-ray emission from objects like Cyg X-l.
Extended HI disks in nearby spiral galaxies
Bosma, Albert
2017-03-01
In this short write-up, I will concentrate on a few topics of interest. In the 1970s I found very extended HI disks in galaxies such as NGC 5055 and NGC 2841, out to 2 - 2.5 times the Holmberg radius. Since these galaxies are warped, a ``tilted ring model'' allows rotation curves to be derived, and evidence for dark matter to be found. The evaluation of the amount of dark matter is hampered by a disk-halo degeneracy, which can possibly be broken by observations of velocity dispersions in both the MgI region and the CaII region.
Extended HI disks in nearby spiral galaxies
Bosma, A
2016-01-01
In this short write-up, I will concentrate on a few topics of interest. In the 1970s I found very extended HI disks in galaxies such as NGC 5055 and NGC 2841, out to 2 - 2.5 times the Holmberg radius. Since these galaxies are warped, a "tilted ring model" allows rotation curves to be derived, and evidence for dark matter to be found. The evaluation of the amount of dark matter is hampered by a disk-halo degeneracy, which can possibly be broken by observations of velocity dispersions in both the MgI region and the CaII region.
Relativistic Static Thin Disks of Polarized Matter
Navarro, Anamaria; Lora-Clavijo, F. D.; González, Guillermo A.
2017-03-01
An infinite family of exact solutions of the electrovacuum Einstein-Maxwell equations is presented. The family is static, axially symmetric and describe thin disks composed by electrically polarized material in a conformastatic spacetime. The form of the conformastatic metric allows us to write down the metric functions and the electromagnetic potentials in terms of a solution of the Laplace equation. We find a general expression for the surface energy density of the disk, the pressure, the polarization vector, the electromagnetic fields and the velocity rotation for circular orbits. As an example, we present the first model of the family and show the behavior of the different physical variables.
Energy Technology Data Exchange (ETDEWEB)
Ruzmaikin, A.A.; Sokolov, D.D.; Turchaninov, V.I.
1980-03-01
The large-scale magnetic field in a rotating, turbulent gaseous disk will be generated by a dynamo process (the ..cap alpha omega..-dynamo) determined by the differential rotation ..omega..(r) and the spirality function ..cap alpha..(z). The generation is best described by a difference approximation to the dynamo equations, using a step greater than the turbulence correlation length and a smooth function ..cap alpha..(z). The critical dynamo-number for exciting the lowest even quadrupole mode is D/sub q/ = -8. The odd dipole mode will be excited only for large dynamo-numberabsolute value (D/sub d/) > or approx. = 500. When absolute value (D) > or approx. = 20, all modes other than the lowest quadrupole mode (for which the threshold Dapprox. =-500) are oscillatory. The results are applied to the Galaxy (D approx. = -10; characteristic growth time, 3 x 10/sup 8/ yr) and to accretion disks in binary systems containing a black hole, where several oscillatory modes can be excited.
Star Counts and Nature of the Galactic Thick Disk
Yoshii, Yuzuru
Modern star counts at high Galactic latitudes played a major role in revealing the existence of a thick disk as the third stellar component of the Milky Way Galaxy in addition to the old thin disk and halo. A number of star count observations and models showed that the thick disk is represented well by a double exponential density law in the vertical and radial directions. The thick-disk structural parameters determined to date from star count analysis are reviewed, and their limitations are described in terms of the correlation among the derived parameters. The recent preference for h Z ˜ 0. 7 kpc for the scale height of the thick disk, associated with f thick ˜ 0. 1 for its normalization relative to the thin disk, is likely a consequence of the recent popularity of the flattened inner halo with an axial ratio of q ˜ 0. 6 prescribed in star-count modeling. This value of h Z for the thick disk is supported by the kinematic constraint of ˜ 40 km s- 1 for the measured vertical velocity dispersion of candidate thick-disk stars more than 1 kpc from the disk plane. Furthermore, star counts in multiple directions and from all-sky near-infrared surveys have arrived at a convergent result, indicating that the thick disk has a scale length h R ˜ 3. 5 kpc and has a greater radial extension compared to the thin disk, with h R ˜ 2. 5 kpc. Other constraints have arisen from high-resolution spectroscopic observations of the kinematics, chemical abundances, and ages of candidate thick-disk stars, confirming the rotational lag of ˜ 40 km s- 1 as well as the vertical gradients of the mean rotation and velocity dispersions in three directions, the constant ratio of alpha to the iron abundances [α/Fe] of ˜ +0.4 dex up to [Fe/H] ˜ - 0.4 dex, a large scatter of metallicity around the mean [Fe/H] ˜ - 0.8 dex with little or no spatial gradient, and a fairly old thick-disk age of ˜ 10 Gyr. The star counts and other constraints together indicate dissipational contraction and
Deswal, Sunita; Kalkal, Kapil Kumar; Sheoran, Sandeep Singh
2016-09-01
A mathematical model of fractional order two-temperature generalized thermoelasticity with diffusion and initial stress is proposed to analyze the transient wave phenomenon in an infinite thermoelastic half-space. The governing equations are derived in cylindrical coordinates for a two dimensional axi-symmetric problem. The analytical solution is procured by employing the Laplace and Hankel transforms for time and space variables respectively. The solutions are investigated in detail for a time dependent heat source. By using numerical inversion method of integral transforms, we obtain the solutions for displacement, stress, temperature and diffusion fields in physical domain. Computations are carried out for copper material and displayed graphically. The effect of fractional order parameter, two-temperature parameter, diffusion, initial stress and time on the different thermoelastic and diffusion fields is analyzed on the basis of analytical and numerical results. Some special cases have also been deduced from the present investigation.
Indian Academy of Sciences (India)
Ibrahim A Abbas
2011-06-01
The theory of thermoelasticity with energy dissipation is employed to study plane waves in a ﬁbre-reinforced anisotropic thermoelastic half-space. We apply a thermal shock on the surface of the half-space which is taken to be traction free. The problem is solved numerically using a ﬁnite element method. Moreover, the numerical solutions of the non-dimensional governing partial differential equations of the problem are shown graphically. Comparisons are made with the results predicted by Green–Naghdi theory of the two types (GNII without energy dissipation) and (GNIII with energy dissipation). We found that the reinforcement has great effect on the distribution of ﬁeld quantities. Results carried out in this paper can be used to design various ﬁbre-reinforced anisotropic thermoelastic elements under thermal load to meet special engineering requirements.
On the Gravitational Stability of Gravito-turbulent Accretion Disks
Lin, Min-Kai; Kratter, Kaitlin M.
2016-06-01
Low mass, self-gravitating accretion disks admit quasi-steady, “gravito-turbulent” states in which cooling balances turbulent viscous heating. However, numerical simulations show that gravito-turbulence cannot be sustained beyond dynamical timescales when the cooling rate or corresponding turbulent viscosity is too large. The result is disk fragmentation. We motivate and quantify an interpretation of disk fragmentation as the inability to maintain gravito-turbulence due to formal secondary instabilities driven by: (1) cooling, which reduces pressure support; and/or (2) viscosity, which reduces rotational support. We analyze the axisymmetric gravitational stability of viscous, non-adiabatic accretion disks with internal heating, external irradiation, and cooling in the shearing box approximation. We consider parameterized cooling functions in 2D and 3D disks, as well as radiative diffusion in 3D. We show that generally there is no critical cooling rate/viscosity below which the disk is formally stable, although interesting limits appear for unstable modes with lengthscales on the order of the disk thickness. We apply this new linear theory to protoplanetary disks subject to gravito-turbulence modeled as an effective viscosity, and cooling regulated by dust opacity. We find that viscosity renders the disk beyond ˜60 au dynamically unstable on radial lengthscales a few times the local disk thickness. This is coincident with the empirical condition for disk fragmentation based on a maximum sustainable stress. We suggest turbulent stresses can play an active role in realistic disk fragmentation by removing rotational stabilization against self-gravity, and that the observed transition in behavior from gravito-turbulent to fragmenting may reflect instability of the gravito-turbulent state itself.
Tsai, V.C.
2011-01-01
It is known that GPS time series contain a seasonal variation that is not due to tectonic motions, and it has recently been shown that crustal seismic velocities may also vary seasonally. In order to explain these changes, a number of hypotheses have been given, among which thermoelastic and hydrology-induced stresses and strains are leading candidates. Unfortunately, though, since a general framework does not exist for understanding such seasonal variations, it is currently not possible to quickly evaluate the plausibility of these hypotheses. To fill this gap in the literature, I generalize a two-dimensional thermoelastic strain model to provide an analytic solution for the displacements and wave speed changes due to either thermoelastic stresses or hydrologic loading, which consists of poroelastic stresses and purely elastic stresses. The thermoelastic model assumes a periodic surface temperature, and the hydrologic models similarly assume a periodic near-surface water load. Since all three models are two-dimensional and periodic, they are expected to only approximate any realistic scenario; but the models nonetheless provide a quantitative framework for estimating the effects of thermoelastic and hydrologic variations. Quantitative comparison between the models and observations is further complicated by the large uncertainty in some of the relevant parameters. Despite this uncertainty, though, I find that maximum realistic thermoelastic effects are unlikely to explain a large fraction of the observed annual variation in a typical GPS displacement time series or of the observed annual variations in seismic wave speeds in southern California. Hydrologic loading, on the other hand, may be able to explain a larger fraction of both the annual variations in displacements and seismic wave speeds. Neither model is likely to explain all of the seismic wave speed variations inferred from observations. However, more definitive conclusions cannot be made until the model
Studies on thermo-elastic heating of horns used in ultrasonic plastic welding.
Roopa Rani, M; Prakasan, K; Rudramoorthy, R
2015-01-01
Ultrasonic welding horn is half wavelength section or tool used to focus the ultrasonic vibrations to the components being welded. The horn is designed in such a way that it maximizes the amplitude of the sound wave passing through it. The ends of the horn represent the displacement anti-nodes and the center the 'node' of the wave. As the horns perform 20,000 cycles of expansion and contraction per second, they are highly stressed at the nodes and are heated owing to thermo-elastic effects. Considerable temperature rise may be observed in the horn, at the nodal region when working at high amplitudes indicating high stress levels leading to failure of horns due to cyclic loading. The limits for amplitude must therefore be evaluated for the safe working of the horn. Horns made of different materials have different thermo-elastic behaviors and hence different temperatures at the nodes and antinodes. This temperature field can be used as a control mechanism for setting the amplitude/weld parameters. Safe stress levels can be predicted using modal and harmonic analyses followed by a stress analysis to study the effect of cyclic loads. These are achieved using 'Ansys'. The maximum amplitude level obtained from the stress analysis is used as input for 'Comsol' to predict the temperature field. The actual temperature developed in the horn during operation is measured using infrared camera and compared with the simulated temperature. From experiments, it is observed that horn made of titanium had the lowest temperature rise at the critical region and can be expected to operate at amplitudes up to 77 μm without suffering failure due to cyclic loading. The method of predicting thermo-elastic stresses and temperature may be adopted by the industry for operating the horn within the safe stress limits thereby extending the life of the horn.
Planetesimal and Protoplanet Dynamics in a Turbulent Protoplanetary Disk: Ideal Stratified Disks
Yang, Chao-Chin; Menou, Kristen
2011-01-01
Due to the gravitational influence of density fluctuations driven by magneto-rotational instability in the gas disk, planetesimals and protoplanets undergo diffusive radial migration as well as changes in other orbital properties. The magnitude of the effect on particle orbits can have important consequences for planet formation scenarios. We use the local-shearing-box approximation to simulate an ideal, isothermal, magnetized gas disk with vertical density stratification and simultaneously evolve numerous massless particles moving under the gravitational field of the gas and the host star. We measure the evolution of the particle orbital properties, including mean radius, eccentricity, inclination, and velocity dispersion, and its dependence on the disk properties and the particle initial conditions. Although the results converge with resolution for fixed box dimensions, we find the response of the particles to the gravity of the turbulent gas correlates with the horizontal box size, up to 16 disk scale heig...
Tamma, Kumar K.; Railkar, Sudhir B.
1988-01-01
This paper represents an attempt to apply extensions of a hybrid transfinite element computational approach for accurately predicting thermoelastic stress waves. The applicability of the present formulations for capturing the thermal stress waves induced by boundary heating for the well known Danilovskaya problems is demonstrated. A unique feature of the proposed formulations for applicability to the Danilovskaya problem of thermal stress waves in elastic solids lies in the hybrid nature of the unified formulations and the development of special purpose transfinite elements in conjunction with the classical Galerkin techniques and transformation concepts. Numerical test cases validate the applicability and superior capability to capture the thermal stress waves induced due to boundary heating.
Han, Zhong-Jie; Xu, Gen-Qi
2015-08-01
In this paper, a transmission problem between elastic and thermoelastic material is considered. Assume that these two materials are connected by a vibrating concentrated mass. By a detailed spectral analysis, the asymptotic expressions of the eigenvalues of the system are obtained, and based on which, the Riesz basis property of the eigenvectors is deduced. It is proved that the total energy of this system cannot achieve exponential decay. However, by the frequency domain method together with some multiplier techniques, the polynomial decay of the system is showed and the optimal decay rate is estimated. Finally, some numerical simulations are given to support the results obtained in this paper.
Thermoelastic Thick Plate under Illumination of a Uniform Laser Beam with one Relaxation time
Directory of Open Access Journals (Sweden)
Ezzat. F. Henain
2013-05-01
Full Text Available The problem of thermoelasticity, based on the theory of Lord and Shulman (L-S with one relaxation time, is used to solve a one dimensional boundary value problem of a thick plate. The upper surface of the medium is taken as traction free and heated by a pulsed laser beam. The lower surface of the medium rests on a rigid and thermally isolated. The general solution is obtained in the Laplace transform domain. Approximate small time analytical solutions to temperature, stress and displacement are obtained. Results of this problem are presented graphically.
Directory of Open Access Journals (Sweden)
2006-01-01
Full Text Available The dynamic treatment of one-dimensional generalized thermoelastic problem of heat conduction is made for a layered thin plate which is exposed to a uniform thermal shock taking into account variable thermal conductivity. The basic equations are transformed by Laplace transform and solved by a direct method. The solution was applied for a plate of sandwich structure, which is thermally shocked, and is traction-free in the outer sides. The inverses of Laplace transforms are obtained numerically. The temperature, the stress, and the displacement distributions are represented graphically.
Interpolation/penalization applied for strength design of 3D thermoelastic structures
DEFF Research Database (Denmark)
Pedersen, Pauli; Pedersen, Niels L.
2012-01-01
illustrated with examples. In compliance minimization for thermoelastic structures it may be advantageous to decrease the total volume, but for strength maximization it is argued to keep the total permissible volume. Linear interpolation (no penalization) may to a certain extent be argued for 2D thickness...... optimized designs, but for 3D design problems interpolation must be included and not only from the penalization point of view to obtain 0-1 designs. Three interpolation types are presented in a uniform manner, including the well known one parameter penalizations, named SIMP and RAMP. An alternative two...
Reflection and transmission at the boundary surface of modified couple stress thermoelastic media
Directory of Open Access Journals (Sweden)
Kumar R.
2016-02-01
Full Text Available In this paper the reflection and transmission at a plane interface in modified couple stress generalized thermoelastic solid half spaces in the context of Loard-Shulman (LS and Green-Lindsay (GL theories in welded contact are investigated. Amplitude ratios of various reflected and transmitted waves are obtained due to incidence of a set of coupled longitudinal waves and coupled transverse waves. It is found that the amplitude ratios of various reflected and transmitted waves are functions of the angle of incidence, frequency and are affected by the couple stress properties of the media. Some special cases are deduced from the present formulation.
Thermoelastic Martensitic Transformations in Single Crystals of FeNiCoAlX(B) Alloys
Chumlyakov, Yu. I.; Kireeva, I. V.; Kuts, O. A.; Platonova, Yu. N.; Poklonov, V. V.; Kukshauzen, I. V.; Kukshauzen, D. A.; Panchenko, M. Yu.; Reunova, K. A.
2016-03-01
Using single crystals of Fe-based disordered alloys (Fe - 28% Ni - 17% Co - 11.5% Al - 2.5% X (0.05% B) (at.%) (X = Ti, Nb(B), (Ti + Nb)B), undergoing thermoelastic γ-α '-martensitic transformations (MTs), it is shown that precipitation of particles of the ordered γ'-phase in the course of aging at T = 973 K for 5 h results in the development of shape memory (SME) and superelasticity (SE) effects. It is experimentally found that variation in chemical composition and size of disperse particles of the γ'-phase allows controlling both mechanical and functional properties - SME and SE.
Thermoelastic investigation of a quartz tuning fork used in infrared spectroscopy
Energy Technology Data Exchange (ETDEWEB)
Spajer, M., E-mail: michel.spajer@univ-fcomte.fr; Cavallier, B.; Euphrasie, S.; Matten, G.; Vacheret, X.; Vairac, P.; Vernier, D. [Institut FEMTO-ST, Université de Franche-Comté, CNRS, ENSMM, UTBM, 32 avenue de l' Observatoire, F-25044 Besançon cedex (France); Jalocha, A. [CILAS, Département de Photonique, 8 avenue Buffon, BP 6319, F-45000 Orléans (France)
2013-11-11
The performances of quartz tuning forks (QTF) used in infrared spectroscopy for pollutant detection are investigated. The transduction between light and QTF vibration is elucidated, thanks to QTF encapsulation under vacuum. From the sensitivity enhancement which is obtained, we conclude that their interaction is photo-thermoelastic rather than photo-thermoacoustic. A mapping of the local sensitivity of the QTF is obtained by scanning its faces with the excitation probe beam. The comparison between the signal mapping and the theoretical strain mapping indicates that the most efficient areas of the QTF correspond to the areas where the strain or stress is the highest.
Directory of Open Access Journals (Sweden)
Andreev V.I.
2016-01-01
Full Text Available The article discusses the use of a numerical method the calculation of finite cylinders into account the dependence of physical and mechanical properties of the material on temperature. If we have two-dimensional temperature field characteristics of the material depends on two coordinates. - r and z from which follows that the problem of thermoelasticity is also a two-dimensional. Using the numerical method allows to solve the problem for any state of the cylinder (plane stress or plane strain and consider arbitrary boundary conditions at its ends.
Thermoelastic stresses in SiC single crystals grown by the physical vapor transport method
Institute of Scientific and Technical Information of China (English)
Zibing Zhang; Jing Lu; Qisheng Chen; V.Prasad
2006-01-01
A finite element-based thermoelastic anisotropic stress model for hexagonal silicon carbide polytype is developed for the calculation of thermal stresses in SiC crystals grown by the physical vapor transport method.The composite structure of the growing SiC crystal and graphite lid is considered in the model.The thermal expansion match between the crucible lid and SiC crystal is studied for the first time.The influence of thermal stress on the dislocation density and crystal quality iS discussed.
THE CAUCHY PROBLEM FOR THE SYSTEM OF EQUATIONS OF THERMOELASTICITY IN E^n
Directory of Open Access Journals (Sweden)
Ikbol E. Niyozov
2014-05-01
Full Text Available ABSTRACT: In this paper we consider the problem of analytical continuation of solutions to the system of equations of thermoelasticity in a bounded domain from their values and values of their strains on a part of the boundary of this domain, i.e., we study the Cauchy problem. ABSTRAK: Di dalam kajian ini, kami menyelidiki masalah keselanjaran analitik bagi penyelesaian-penyelesaian terhadap sistem persamaan-persamaan termoelastik di dalam domain bersempadan berdasarkan nilai-nilainya dan nilai tegasannya bagi sebahagian daripada sempadan domain tersebut, iaitu kami mengkaji masalah Cauchy.
On the spatial behavior in two-temperature generalized thermoelastic theories
Miranville, Alain; Quintanilla, Ramon
2017-10-01
This paper investigates the spatial behavior of the solutions of two generalized thermoelastic theories with two temperatures. To be more precise, we focus on the Green-Lindsay theory with two temperatures and the Lord-Shulman theory with two temperatures. We prove that a Phragmén-Lindelöf alternative of exponential type can be obtained in both cases. We also describe how to obtain a bound on the amplitude term by means of the boundary conditions for the Green-Lindsay theory with two temperatures.
Fejer, M M; Cagnoli, G; Crooks, D R M; Gretarsson, A M; Harry, G M; Hough, J; Penn, S D; Sneddon, P H; Vyatchanin, S P
2004-01-01
The displacement noise in the test mass mirrors of interferometric gravitational wave detectors is proportional to their elastic dissipation at the observation frequencies. In this paper, we analyze one fundamental source of dissipation in thin coatings, thermoelastic damping associated with the dissimilar thermal and elastic properties of the film and the substrate. We obtain expressions for the thermoelastic dissipation factor necessary to interpret resonant loss measurements, and for the spectral density of displacement noise imposed on a Gaussian beam reflected from the face of a coated mass. The predicted size of these effects is large enough to affect the interpretation of loss measurements, and to influence design choices in advanced gravitational wave detectors.
Institute of Scientific and Technical Information of China (English)
FENG Yongping; CUI Junzhi
2004-01-01
In this paper, the multi-scale computational method for a structure of composite materials with a small periodic configuration under the coupled thermoelasticity condition is presented.The two-scale asymptotic (TSA) expression of the displacement and the increment of temperature for composite materials with a small periodic configuration under the condition of thermoelasticity are briefly shown at first, then the multi-scale finite element algorithms based on TSA are discussed. Finally the numerical results evaluated by the multi-scale computational method are shown. It demonstrates that the basic configuration and the increment of temperature strongly influence the local strains and local stresses inside a basic cell.
Faraday Rotator Glass for Laser Application
Institute of Scientific and Technical Information of China (English)
JIANG Ya-si; ZHOU Bei-ming; WANG Biao; HU Li-li
2007-01-01
Glasses with strong Faraday rotation are interest for laser applications. The principles of diamagnetic and paramagnetic Faraday rotator glasses are described theoretically and experimentally. High performance Tb-paramagnetic glass series were developed and produced at Kigre in the US and SIOM in Shanghai. Large aperture glass disks have been used for high power laser fusion systems.
Institute of Scientific and Technical Information of China (English)
Chu Yuming; Cheng Jinfa; Wang Gendi
2009-01-01
Let D R2 be a Jordan domain, D* = -R2 \\ -D, the exterior of D. In this article, the authors obtained the following results: (1) If D is a John disk, then D is an outer linearly locally connected domain; (2) If D* is a John disk, then D is an inner linearly locally connected domain; (3) A homeomorphism f: R2→R2 is a quasiconformal mapping if and only if f(D) is a John disk for any John disk D(∈)R2; and (4) If D is a bounded quasidisk, then D is a John disk, and there exists an unbounded quasidisk which is not a John disk.
Exploring Disks Around Planets
Kohler, Susanna
2017-07-01
Giant planets are thought to form in circumstellar disks surrounding young stars, but material may also accrete into a smaller disk around the planet. Weve never detected one of these circumplanetary disks before but thanks to new simulations, we now have a better idea of what to look for.Image from previous work simulating a Jupiter-mass planet forming inside a circumstellar disk. The planet has its own circumplanetary disk of accreted material. [Frdric Masset]Elusive DisksIn the formation of giant planets, we think the final phase consists of accretion onto the planet from a disk that surrounds it. This circumplanetary disk is important to understand, since it both regulates the late gas accretion and forms the birthplace of future satellites of the planet.Weve yet to detect a circumplanetary disk thus far, because the resolution needed to spot one has been out of reach. Now, however, were entering an era where the disk and its kinematics may be observable with high-powered telescopes (like the Atacama Large Millimeter Array).To prepare for such observations, we need models that predict the basic characteristics of these disks like the mass, temperature, and kinematic properties. Now a researcher at the ETH Zrich Institute for Astronomy in Switzerland, Judit Szulgyi, has worked toward this goal.Simulating CoolingSzulgyi performs a series of 3D global radiative hydrodynamic simulations of 1, 3, 5, and 10 Jupiter-mass (MJ) giant planets and their surrounding circumplanetary disks, embedded within the larger circumstellar disk around the central star.Density (left column), temperature (center), and normalized angular momentum (right) for a 1 MJ planet over temperatures cooling from 10,000 K (top) to 1,000 K (bottom). At high temperatures, a spherical circumplanetary envelope surrounds the planet, but as the planet cools, the envelope transitions around 64,000 K to a flattened disk. [Szulgyi 2017]This work explores the effects of different planet temperatures and
Isolated unilateral disk edema
Varner P
2011-01-01
Paul VarnerJohn J Pershing VAMC, Poplar Bluff, MO, USAAbstract: Isolated unilateral disk edema is a familiar clinical presentation with myriad associations. Related, non-consensus terminology is a barrier to understanding a common pathogenesis. Mechanisms for the development of disk edema are reviewed, and a new framework for clinical differentiation of medical associations is presented.Keywords: disk edema, axoplasmic flow, clinical multiplier, optic neuritis, ischemic optic neuropathy, papi...
Isolated unilateral disk edema
Directory of Open Access Journals (Sweden)
Varner P
2011-07-01
Full Text Available Paul VarnerJohn J Pershing VAMC, Poplar Bluff, MO, USAAbstract: Isolated unilateral disk edema is a familiar clinical presentation with myriad associations. Related, non-consensus terminology is a barrier to understanding a common pathogenesis. Mechanisms for the development of disk edema are reviewed, and a new framework for clinical differentiation of medical associations is presented.Keywords: disk edema, axoplasmic flow, clinical multiplier, optic neuritis, ischemic optic neuropathy, papilledema
Galactic disks as reaction-diffusion systems
Smolin, L
1996-01-01
A model of a galactic disk is presented which extends the homogeneous one zone models by incorporating propagation of material and energy in the disk. For reasonable values of the parameters the homogeneous steady state is unstable to the development of inhomogeneities, leading to the development of spatial and temporal structure. At the linearized level a prediction for the length and time scales of the patterns is found. These instabilities arise for the same reason that pattern formation is seen in non-equilibrium chemical and biological systems, which is that the positive and negative feedback effects which govern the rates of the critical processes act over different distance scales, as in Turing's reaction-diffusion models. This shows that patterns would form in the disk even in the absence of gravitational effects, density waves, rotation, shear and external perturbations. These nonlinear effects may thus explain the spiral structure seen in the star forming regions of isolated flocculent galaxies.
An interferometric view of hot star disks
Faes, Daniel Moser
2015-01-01
Optical long baseline interferometry was recently established as a technique capable of resolving stars and their circumstellar environments at the milliarcsecond (mas) resolution level. This high-resolution opens an entire new window to the study of astrophysical systems, providing information inaccessible by other techniques. Astrophysical disks are observed in a wide variety of systems, from galaxies up to planetary rings, commonly sharing similar physical processes. Two particular disk like systems are studied in the thesis: (i) B He-rich stars that exhibits magnetic fields in order of kG and that trap their winds in structures called magnetospheres; and (ii) Be stars, fast rotating stars that create circumstellar viscous disks. This study uses the interferometric technique to investigate both the photosphere proper and the circumstellar environment of these stars. The objective is to combine interferometry with other observational techniques (such as spectroscopy and polarimetry) to perform a complete an...
Earth, Moon, Sun, and CV Accretion Disks
Montgomery, M M
2009-01-01
Net tidal torque by the secondary on a misaligned accretion disk, like the net tidal torque by the Moon and the Sun on the equatorial bulge of the spinning and tilted Earth, is suggested by others to be a source to retrograde precession in non-magnetic, accreting Cataclysmic Variable (CV) Dwarf Novae systems that show negative superhumps in their light curves. We investigate this idea in this work. We generate a generic theoretical expression for retrograde precession in spinning disks that are misaligned with the orbital plane. Our generic theoretical expression matches that which describes the retrograde precession of Earths' equinoxes. By making appropriate assumptions, we reduce our generic theoretical expression to those generated by others, or to those used by others, to describe retrograde precession in protostellar, protoplanetary, X-ray binary, non-magnetic CV DN, quasar and black hole systems. We find that differential rotation and effects on the disk by the accretion stream must be addressed. Our a...
Energy Technology Data Exchange (ETDEWEB)
Khayrullin, N.A.; Isayev, B.N.; Kruglov, S.A.; Molokanov, Yu.K.; Shchelkunov, V.A.; Shegay, V.R.; Vizhgorodskiy, B.N.
1982-01-01
A valve disk is proposed which includes a horizontal bed, on which there are laminar valves arranged in staggered order. To ensure the stable and effective operation of the disk in a broad range of loads by compensating for the direct flow and the partial sectioning of the disk bed, it is equipped with compensating elements installed in openings in the bed and hinged with it. They are made in the form of straight, triangular prisms with ports in the bases. The prisms are installed with the capability of movement relative to the disk bed. The valves are positioned on the upper lateral facets of the compensating elements.
Magnetic white dwarfs with debris disks
Külebi, Baybars; Lorén-Aguilar, Pablo; Isern, Jordi; García-Berro, Enrique
2012-01-01
It has long been accepted that a possible mechanism for explaining the existence of magnetic white dwarfs is the merger of a binary white dwarf system, as there are viable mechanisms for producing sustainable magnetism within the merger product. However, the lack of rapid rotators in the magnetic white dwarf population has been always considered a problematic issue of this scenario. In order to explain this discrepancy we build a model in which the interaction between the magnetosphere of the star and the disk induces angular momentum transfer. Our model predicts that the magnetospheric interaction of magnetic white dwarfs with their disks results in a significant spin down, and we show that the observed rotation period of REJ 0317-853, which is suggested to be a product of a double degenerate merger, can be reproduced.
Transient dynamics of perturbations in astrophysical disks
Razdoburdin, Dmitry N
2015-01-01
This paper reviews some aspects of one of the major unsolved problems in understanding astrophysical (in particular, accretion) disks: whether the disk interiors may be effectively viscous in spite of the absence of marnetorotational instability? In this case a rotational homogeneous inviscid flow with a Keplerian angular velocity profile is spectrally stable, making the transient growth of perturbations a candidate mechanism for energy transfer from the regular motion to perturbations. Transient perturbations differ qualitatively from perturbation modes and can grow substantially in shear flows due to the nonnormality of their dynamical evolution operator. Since the eigenvectors of this operator, alias perturbation modes, are mutually nonorthogonal, they can mutually interfere, resulting in the transient growth of their linear combinations. Physically, a growing transient perturbation is a leading spiral whose branches are shrunk as a result of the differential rotation of the flow. This paper discusses in d...
Directory of Open Access Journals (Sweden)
Sunita Deswal
2013-01-01
Full Text Available The aim of this paper is to study magneto-thermoelastic interactions in an initially stressed isotropic homogeneous half-space in the context of fractional order theory of generalized thermoelasticity. State space formulation with the Laplace transform technique is used to obtain the general solution, and the resulting formulation is applied to the ramp type increase in thermal load and zero stress. Solutions of the problem in the physical domain are obtained by using a numerical method of the Laplace inverse transform based on the Fourier expansion technique, and the expressions for the displacement, temperature, and stress inside the half-space are obtained. Numerical computations are carried out for a particular material for illustrating the results. Results obtained for the field variables are displayed graphically. Some comparisons have been shown in figures to present the effect of fractional parameter, ramp parameter, magnetic field, and initial stress on the field variables. Some particular cases of special interest have been deduced from the present investigation.
A High Order Theory for Linear Thermoelastic Shells: Comparison with Classical Theories
Directory of Open Access Journals (Sweden)
V. V. Zozulya
2013-01-01
Full Text Available A high order theory for linear thermoelasticity and heat conductivity of shells has been developed. The proposed theory is based on expansion of the 3-D equations of theory of thermoelasticity and heat conductivity into Fourier series in terms of Legendre polynomials. The first physical quantities that describe thermodynamic state have been expanded into Fourier series in terms of Legendre polynomials with respect to a thickness coordinate. Thereby all equations of elasticity and heat conductivity including generalized Hooke's and Fourier's laws have been transformed to the corresponding equations for coefficients of the polynomial expansion. Then in the same way as in the 3D theories system of differential equations in terms of displacements and boundary conditions for Fourier coefficients has been obtained. First approximation theory is considered in more detail. The obtained equations for the first approximation theory are compared with the corresponding equations for Timoshenko's and Kirchhoff-Love's theories. Special case of plates and cylindrical shell is also considered, and corresponding equations in displacements are presented.
Thermoelastic properties of sandwich materials with pin-reinforced foam cores
Institute of Scientific and Technical Information of China (English)
2008-01-01
Pin-reinforced foam is a novel type of sandwich core materials formed by inserting pins(trusses) into a foam matrix to create a truss-like network reinforced foam core.Upon loading,the pins deform predominantly by local stretching whilst the deformation of foam is governed by local bending.This paper presents a theoretical study on the thermoelasticity of pin-reinforced foam sandwich cores.To calculate the effective thermoelastic properties of pin-reinforced foam cores,the energy-based homogenization approach is employed to develop a micromechanics-based model,calibrated by the existing experimental data.It is found that the stiffness of the sandwich core is mainly governed by pin reinforcements:the foam matrix contributes little to sandwich stiffness.Compared with traditional foam cores without pin reinforcements,the changes in inplane thermal expansion coefficients are not vigorous as a result of pin reinforcements,while the through-thickness thermal expansion coefficient changes significantly.It is also demonstrated that it is possible to design materials with zero or negative thermal expansion coefficients under such a context.
The kinematic relationship between disk and jet in the DG Tauri system
Testi, L; Sargent, A I; Ray, T P; Eislöffel, J
2002-01-01
We present high angular resolution millimeter wavelength continuum and 13CO(2-1) observations of the circumstellar disk surrounding the TTauri star DG Tauri. We show that the velocity pattern in the inner regions of the disk is consistent with Keplerian rotation about a central 0.67 Msun star. The disk rotation is also consistent with the toroidal velocity pattern in the initial channel of the optical jet, as inferred from HST spectra of the first de-projected 100 AU from the source. Our observations support the tight relationship between disk and jet kinematics postulated by the popular magneto-centrifugal models for jet formation and collimation.
Stability of Galactic Gaseous Disks and the Formation of Massive Clusters
Escala, Andres
2008-01-01
We study gravitational instabilities in disks, with special attention to the most massive clumps that form because they are expected to be the progenitors of globular-type clusters. The maximum unstable mass is set by rotation and depends only on the surface density and orbital frequency of the disk. We propose that the formation of massive clusters is related to this largest scale in galaxies not stabilized by rotation. Using data from the literature, we predict that globular-like clusters can form in nuclear starburst disks and protogalactic disks but not in typical spiral galaxies, in agreement with observations.
Stability of Galactic Gas Disks and the Formation of Massive Clusters
Escala, Andres
2008-01-01
We study gravitational instabilities in disks, with special attention to the most massive clumps that form because they are expected to be the progenitors of globular-type clusters. The maximum unstable mass is set by rotation and depends only on the surface density and orbital frequency of the disk. We propose that the formation of massive clusters is related to this largest scale in galaxies not stabilized by rotation. Using data from the literature, we predict that globular-like clusters can form in nuclear starburst disks and protogalactic disks but not in typical spiral galaxies, in agreement with observations.
TLUSTY: Stellar Atmospheres, Accretion Disks, and Spectroscopic Diagnostics
Hubeny, Ivan; Lanz, Thierry
2011-09-01
TLUSTY is a user-oriented package written in FORTRAN77 for modeling stellar atmospheres and accretion disks and wide range of spectroscopic diagnostics. In the program's maximum configuration, the user may start from scratch and calculate a model atmosphere of a chosen degree of complexity, and end with a synthetic spectrum in a wavelength region of interest for an arbitrary stellar rotation and an arbitrary instrumental profile. The user may also model the vertical structure of annuli of an accretion disk.
Water Masers in AGN Accretion Disks
Braatz, J. A.; Reid, M. J.; Greenhill, L. J.; Kuo, C.-Y.; Condon, J. J.; Lo, K.-Y.; Henkel, C.
2009-08-01
Water vapor masers at 22 GHz have been detected in over 100 galaxies, most of them AGNs. High resolution VLBI observations of these masers provide the only opportunity for direct imaging of sub-parsec structure in AGN accretion disks. The key science goals associated with such observations are concentrated in two areas. First, observations of nearby, bright sources, exemplified by NGC 4258, enable unique investigations of accretion disk geometry, substructure, thickness, and rotation properties. Second, when combined with spectral line monitoring, VLBI imaging and subsequent disk modeling enables the estimation of a distance to the host galaxy independent of standard candle arguments. In this contribution we present VLBI observations of two maser disk systems in galaxies well into the Hubble flow, UGC 3789 and NGC 6323. A long term goal in these studies is to measure the Hubble constant with high precision and, as a complement to CMB observations, constrain several key cosmological parameters, including the equation of state for dark energy. Observations with VSOP-2 at 22 GHz will have the resolution critical for mapping substructure in these accretion disks and will contribute to reducing systematic errors in the measurement of distances to galaxies.
Radiative Ablation of Disks Around Massive Stars
Kee, N D
2015-01-01
Hot, massive stars (spectral types O and B) have extreme luminosities ($10^4 -10^6 L_\\odot$) that drive strong stellar winds through UV line-scattering. Some massive stars also have disks, formed by either decretion from the star (as in the rapidly rotating "Classical Be stars"), or accretion during the star's formation. This dissertation examines the role of stellar radiation in driving (ablating) material away from these circumstellar disks. A key result is that the observed month to year decay of Classical Be disks can be explained by line-driven ablation without, as previously done, appealing to anomalously strong viscous diffusion. Moreover, the higher luminosity of O stars leads to ablation of optically thin disks on dynamical timescales of order a day, providing a natural explanation for the lack of observed Oe stars. In addition to the destruction of Be disks, this dissertation also introduces a model for their formation by coupling observationally inferred non-radial pulsation modes and rapid stellar...
Youdin, Andrew N
2015-01-01
Planetesimals form in gas-rich protoplanetary disks around young stars. However, protoplanetary disks fade in about 10 Myr. The planetesimals (and also many of the planets) left behind are too dim to study directly. Fortunately, collisions between planetesimals produce dusty debris disks. These debris disks trace the processes of terrestrial planet formation for 100 Myr and of exoplanetary system evolution out to 10 Gyr. This chapter begins with a summary of planetesimal formation as a prelude to the epoch of planetesimal destruction. Our review of debris disks covers the key issues, including dust production and dynamics, needed to understand the observations. Our discussion of extrasolar debris keeps an eye on similarities to and differences from Solar System dust.
Testing protostellar disk formation models with ALMA observations
Harsono, Daniel; Bruderer, Simon; Li, Zhi-Yun; Jorgensen, Jes
2015-01-01
Abridged: Recent simulations have explored different ways to form accretion disks around low-mass stars. We aim to present observables to differentiate a rotationally supported disk from an infalling rotating envelope toward deeply embedded young stellar objects and infer their masses and sizes. Two 3D magnetohydrodynamics (MHD) formation simulations and 2D semi-analytical model are studied. The dust temperature structure is determined through continuum radiative transfer RADMC3D modelling. A simple temperature dependent CO abundance structure is adopted and synthetic spectrally resolved submm rotational molecular lines up to $J_{\\rm u} = 10$ are simulated. All models predict similar compact components in continuum if observed at the spatial resolutions of 0.5-1$"$ (70-140 AU) typical of the observations to date. A spatial resolution of $\\sim$14 AU and high dynamic range ($> 1000$) are required to differentiate between RSD and pseudo-disk in the continuum. The peak-position velocity diagrams indicate that the...
A SEMI-ANALYTICAL DESCRIPTION FOR THE FORMATION AND GRAVITATIONAL EVOLUTION OF PROTOPLANETARY DISKS
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Takahashi, Sanemichi Z.; Inutsuka, Shu-ichiro [Department of Physics, Nagoya University, Furo-cho, Chikusa-ku, Nagoya, Aichi, 464-8602 (Japan); Machida, Masahiro N., E-mail: takahashi.sanemichi@a.mbox.nagoya-u.ac.jp, E-mail: inutsuka@nagoya-u.jp, E-mail: sanemichi@tap.scphys.kyoto-u.ac.jp, E-mail: machida.masahiro.018@m.kyushu-u.ac.jp [Department of Earth and Planetary Science, Kyushu University, Higashi-ku, Fukuoka 812-8581 (Japan)
2013-06-10
We investigate the formation process of self-gravitating protoplanetary disks in unmagnetized molecular clouds. The angular momentum is redistributed by the action of gravitational torques in the massive disk during its early formation. We develop a simplified one-dimensional accretion disk model that takes into account the infall of gas from the envelope onto the disk and the transfer of angular momentum in the disk with an effective viscosity. First we evaluate the gas accretion rate from the cloud core onto the disk by approximately estimating the effects of gas pressure and gravity acting on the cloud core. We formulate the effective viscosity as a function of the Toomre Q parameter that measures the local gravitational stability of the rotating thin disk. We use a function for viscosity that changes sensitively with Q when the disk is gravitationally unstable. We find a strong self-regulation mechanism in the disk evolution. During the formation stage of protoplanetary disks, the evolution of the surface density does not depend on the other details of the modeling of effective viscosity, such as the prefactor of the viscosity coefficient. Next, to verify our model, we compare the time evolution of the disk calculated with our formulation with that of three-dimensional hydrodynamical simulations. The structures of the resultant disks from the one-dimensional accretion disk model agree well with those of the three-dimensional simulations. Our model is a useful tool for the further modeling of chemistry, radiative transfer, and planet formation in protoplanetary disks.
Protoplanetary Disks, Jets, and the Birth of the Stars
Anglada, G.
2017-03-01
Young stars are surrounded by rotating disks of gas and dust. These disks play an essential role in regulating the mass accretion onto the star and are the precursors of exoplanetary systems. Accretion disks also play an important role in driving the bipolar collimated ejections (jets) that remove the excess of angular momentum and allow the star to reach its final mass. Jets are partially ionized and their continuum free-free emission at centimeter wavelengths is a powerful tool to study at small scale (10-100 au) the region where they originate. Observations of the dust thermal emission at centimeter wavelengths are also well suited to study the distribution of dust grains that have evolved up to centimeter sizes and trace the signatures of planet formation in protoplanetary disks. I will present some recent results from VLA and ALMA observations of disks and jets in young stellar objects, and I will discuss future prospects with the SKA in this field.
Bouwman, J; Dominik, C; Feigelson, E D; Henning, T; Tielens, A G G M; Waters, L B F M; Henning, Th.
2006-01-01
The formation of planets is directly linked to the evolution of the circumstellar (CS) disk from which they are born. The dissipation timescales of CS disks are, therefore, of direct astrophysical importance in evaluating the time available for planet formation. We employ Spitzer Space Telescope spectra to complete the CS disk census for the late-type members of the ~8 Myr-old eta Chamaeleontis star cluster. Of the 15 K- and M-type members, eight show excess emission. We find that the presence of a CS disk is anti-correlated with binarity, with all but one disk associated with single stars. With nine single stars in total, about 80% retain a CS disk. Of the six known or suspected close binaries the only CS disk is associated with the primary of RECX 9. No circumbinary disks have been detected. We also find that stars with disks are slow rotators with surface values of specific angular momentum j = 2-15 j_sun. All high specific angular momentum systems with j = 20-30 j_sun are confined to the primary stars of ...
Destruction of Be star disk by large scale magnetic fields
Ud-Doula, Asif; Owocki, Stanley P.; Kee, Nathaniel; Vanyo, Michael
2017-01-01
Classical Be stars are rapidly rotating stars with circumstellar disks that come and go on time scale of years. Recent observational data strongly suggests that these stars lack the ~10% incidence of global magnetic fields observed in other main-sequence B stars. Such an apparent lack of magnetic fields may indicate that Be disks are fundamentally incompatible with a significant large scale magnetic field. In this work, using numerical magnetohydrodynamics (MHD) simulations, we show that a dipole field of only 100G can lead to the quick disruption of a Be disk. Such a limit is in line with the observational upper limits for these objects.
Three Dimensional Hydrodynamic Instabilities in Protostellar Disks with Cooling
Pickett, B. K.; Cassen, P.; Durisen, R. H.; Link, R.
1997-05-01
We present a series of extended three dimensional hydrodynamics calculations of protostellar cores in order to investigate the role of thermal energetics. One set of protostellar core models, denoted Hot Models, are isentropic equilibrium states formed by the axisymmetric collapse of uniformly rotating singular isothermal spheres. These objects are continuous star/disk systems, in which the star, the disk, and the star/disk boundary can be resolved in 3D in our hydrodynamics code. Since the disks of these equilibria are forced to have the same entropy as the stars, they are hotter than is typically considered appropriate for protostellar disks. Thus, the second set of models, denoted Cooled Models, are generated by first cooling the Hot Models in axisymmetry, and then calculating their subsequent nonaxisymmetric evolution. We compare evolutions of the Hot and Cooled models in which the disk is treated both adiabatically and isothermally, representing two extremes in cooling. The Hot models are marginally unstable to spiral disturbances that do not alter the protostellar core over many rotation periods. The Cooled models are highly unstable to multiple spirals, particularly two-armed spirals, which transport significant angular momentum and mass in a few dynamical times. In the isothermal evolution, the instability leads to the disruption of the disk and concentration of material into several dense, thin arcs. We compare these calculations with previous results and discuss the implications for star and solar system formation. This research is supported by grants NAGW-3399 DURISEN and RTOP 344-30-5101 CASSEN.
Kinematics of the Galactic disk from LAMOST Dwarf sample
Jing, Yingjie; Gu, Jiayin; Jia, Yunpeng; Peng, Xiyan; Chen, Yuqin; Wu, Zhenyu; Ma, Jun; Zhou, Xu; Cao, Zihuang; Hou, Yonghui; Wang, Yuefei; Zhang, Yong
2016-01-01
Based on the LAMOST survey and Sloan Digital Sky Survey (SDSS), we use low-resolution spectra of 130,043 F/G-type dwarf stars to study the kinematics and metallicity properties of the Galactic disk. Our study shows that the stars with poorer metallicity and larger vertical distance from Galactic plane tend to have larger eccentricity and velocity dispersion. After separating the sample stars into likely thin-disk and thick-disk sub-sample, we find that there exits a negative gradient of rotation velocity $V_{\\phi}$ with metallicity [Fe/H] for the likely thin-disk sub-sample, and the thick-disk sub-sample exhibit a larger positive gradient of rotation velocity with metallicity. By comparing with model prediction, we consider the radial migration of stars appears to have influenced on the thin-disk formation. In addition, our results shows that the observed thick-disk stellar orbital eccentricity distribution peaks at low eccentricity ($e \\sim 0.2$) and extends to a high eccentricity ($e \\sim 0.8$). We compare ...
Childhood to adolescence: dust and gas clearing in protoplanetary disks
Brown, Joanna Margaret
Disks are ubiquitous around young stars. Over time, disks dissipate, revealing planets that formed hidden by their natal dust. Since direct detection of young planets at small orbital radii is currently impossible, other tracers of planet formation must be found. One sign of disk evolution, potentially linked to planet formation, is the opening of a gap or inner hole in the disk. In this thesis, I have identified and characterized several cold disks with large inner gaps but retaining massive primordial outer disks. While cold disks are not common, with ~5% of disks showing signs of inner gaps, they provide proof that at least some disks evolve from the inside-out. These large gaps are equivalent to dust clearing from inside the Earth's orbit to Neptune's orbit or even the inner Kuiper belt. Unlike more evolved systems like our own, the central star is often still accreting and a large outer disk remains. I identified four cold disks in Spitzer 5-40 μm spectra and modeled these disks using a 2-D radiative transfer code to determine the gap properties. Outer gap radii of 20-45 AU were derived. However, spectrophotometric identification is indirect and model-dependent. To validate this interpretation, I observed three disks with a submillimeter interferometer and obtained the first direct images of the central holes. The images agree well with the gap sizes derived from the spectrophotometry. One system, LkH&alpha 330, has a very steep outer gap edge which seems more consistent with gravitational perturbation rather than gradual processes, such as grain growth and settling. Roughly 70% of cold disks show CO v=1&rarr 0 gas emission from the inner 1 AU and therefore are unlikely to have evolved due to photoevaporation. The derived rotation temperatures are significantly lower for the cold disks than disks without gaps. Unresolved (sub)millimeter photometry shows that cold disks have steeper colors, indicating that they are optically thin at these wavelengths, unlike
Finite element analysis of two disk rotor system
Dixit, Harsh Kumar
2016-05-01
A finite element model of simple horizontal rotor system is developed for evaluating its dynamic behaviour. The model is based on Timoshenko beam element and accounts for the effect of gyroscopic couple and other rotational forces. Present rotor system consists of single shaft which is supported by bearings at both ends and two disks are mounted at different locations. The natural frequencies, mode shapes and orbits of rotating system for a specific range of rotation speed are obtained by developing a MATLAB code for solving the finite element equations of rotary system. Consequently, Campbell diagram is plotted for finding a relationship between natural whirl frequencies and rotation of the rotor.
Analysis of Nonlinear Thermoelastic Dissipation in Euler-Bernoulli Beam Resonators.
Nourmohammadi, Zahra; Joshi, Surabhi; Vengallatore, Srikar
2016-01-01
The linear theory of thermoelastic damping (TED) has been extensively developed over the past eight decades, but relatively little is known about the different types of nonlinearities that are associated with this fundamental mechanism of material damping. Here, we initiate the study of a dissipative nonlinearity (also called thermomechanical nonlinearity) whose origins reside at the heart of the thermomechanical coupling that gives rise to TED. The finite difference method is used to solve the nonlinear governing equation and estimate nonlinear TED in Euler-Bernoulli beams. The maximum difference between the nonlinear and linear estimates ranges from 0.06% for quartz and 0.3% for silicon to 7% for aluminum and 28% for zinc.
Ebrahimi, Farzad; Reza Barati, Mohammad; Haghi, Parisa
2016-11-01
In this paper, the thermo-elastic wave propagation analysis of a temperature-dependent functionally graded (FG) nanobeam supported by Winkler-Pasternak elastic foundation is studied using nonlocal elasticity theory. The nanobeam is modeled via a higher-order shear deformable refined beam theory which has a trigonometric shear stress function. The temperature field has a nonlinear distribution called heat conduction across the nanobeam thickness. Temperature-dependent material properties change gradually in the spatial coordinate according to the Mori-Tanaka model. The governing equations of the wave propagation of the refined FG nanobeam are derived by using Hamilton's principle. The analytic dispersion relation of the embedded nonlocal functionally graded nanobeam is obtained by solving an eigenvalue problem. Numerical examples show that the wave characteristics of the functionally graded nanobeam are related to the temperature distribution, elastic foundation parameters, nonlocality and material composition.
Thermo-elastic induced phase noise in the LISA Pathfinder spacecraft
Gibert, F.; Nofrarias, M.; Karnesis, N.; Gesa, L.; Martín, V.; Mateos, I.; Lobo, A.; Flatscher, R.; Gerardi, D.; Burkhardt, J.; Gerndt, R.; Robertson, D. I.; Ward, H.; McNamara, P. W.; Guzmán, F.; Hewitson, M.; Diepholz, I.; Reiche, J.; Heinzel, G.; Danzmann, K.
2015-02-01
During the on-station thermal test campaign of the LISA Pathfinder, the diagnostics subsystem was tested in nearly space conditions for the first time after integration in the satellite. The results showed the compliance of the temperature measurement system, obtaining temperature noise around {{10}-4} K H{{z}-1/2} in the frequency band 1-30 mHz. In addition, controlled injection of heat signals to the suspension struts anchoring the LISA Technology Package (LTP) core assembly to the satellite structure allowed us to experimentally estimate, for the first time, the phase noise contribution through thermo-elastic distortion of the LTP interferometer, the satellite's main instrument. Such contribution was found to be at {{10}-12} mH{{z}-1/2}, a factor of 30 below the measured noise at the lower end of the measurement bandwidth (1 mHz).
Lotfy, K.; Sarkar, N.
2017-02-01
In this work, a novel generalized model of photothermal theory with two-temperature thermoelasticity theory based on memory-dependent derivative (MDD) theory is performed. A one-dimensional problem for an elastic semiconductor material with isotropic and homogeneous properties has been considered. The problem is solved with a new model (MDD) under the influence of a mechanical force with a photothermal excitation. The Laplace transform technique is used to remove the time-dependent terms in the governing equations. Moreover, the general solutions of some physical fields are obtained. The surface taken into consideration is free of traction and subjected to a time-dependent thermal shock. The numerical Laplace inversion is used to obtain the numerical results of the physical quantities of the problem. Finally, the obtained results are presented and discussed graphically.
Inverse thermoelastic analysis for thermal and mechanical loads identification using FBG data
Nakamura, Toshiya; Kamimura, Yukihiro; Igawa, Hirotaka; Morino, Yoshiki
2014-12-01
Fiber Bragg Grating (FBG) sensors have widely been used to monitor temperature and strain distributions as a part of the structural health monitoring system. Since FBG has the sensitivity to the variations in both temperature and strain, a compensation is required to separate the strain or temperature data from the sensor output which is the shift of the grating's Bragg wavelength. The present study develops a computational inverse thermoelastic analysis method to separately identify the thermal and mechanical boundary conditions (loads) from the output of the FBG sensor. Numerical study has been made for a corrugate-core sandwich integral thermal protection system (TPS) to examine the method. The discussion is focused on the computational stability. The results reveal that the identification of the mechanical load is less stable than that of the heat flux. It is also shown that the condition number of a coefficient matrix serves as the index of the stability of the inverse analysis.
Influence of thermal memory on the thermoelastic bending component of photoacoustic response
Directory of Open Access Journals (Sweden)
Nešić Mioljub V.
2011-01-01
Full Text Available In this work, thermoelastic component of the photoacoustic response is derived, including thermal memory of the material. The comparison between this model and the classic one, which does not account for the influence of thermal memory is made. It has been noticed that the two models tend to overlap at very high and very low frequencies of the light modulation spectrum, while in the middle range some deviations become more apparent, which proves that thermal memory must be taken into account. It has also been shown that the limits of this range are the function of heat propagation velocity and thickness of the sample. Based upon the processing of obtained data, it has been concluded that the characteristics of the output signal, in the range of the interest, are highly influenced by thermal dynamic qualities, like heat diffusivity and thermal relaxation time, as well as the sample thickness.
Directory of Open Access Journals (Sweden)
Repka M.
2015-11-01
Full Text Available The finite element method (FEM is developed for coupled thermoelastic crack problems if material properties are continuously varying. The weak form is utilized to derive the FEM equations. In conventional fracture theories the state of stress and strain at the crack tip vicinity is characterized by a single fracture parameter, namely the stress intensity factor or its equivalent, J-integral. In the present paper it is considered also the second fracture parameter called as the T-stress. For evaluation of both fracture parameters the quarter-point crack tip element is developed. Simple formulas for both fracture parameters are derived comparing the variation of displacements in the quarter-point element with asymptotic expression of displacement at the crack tip vicinity. The leading terms of the asymptotic expansions of fields in the crack-tip vicinity in a functionally graded material (FGM are the same as in a homogeneous one with material coefficients taken at the crack tip.
Kumar, Anil; Mukhopadhyay, Santwana
2017-08-01
The present work is concerned with the investigation of thermoelastic interactions inside a spherical shell with temperature-dependent material parameters. We employ the heat conduction model with a single delay term. The problem is studied by considering three different kinds of time-dependent temperature and stress distributions applied at the inner and outer surfaces of the shell. The problem is formulated by considering that the thermal properties vary as linear function of temperature that yield nonlinear governing equations. The problem is solved by applying Kirchhoff transformation along with integral transform technique. The numerical results of the field variables are shown in the different graphs to study the influence of temperature-dependent thermal parameters in various cases. It has been shown that the temperature-dependent effect is more prominent in case of stress distribution as compared to other fields and also the effect is significant in case of thermal shock applied at the two boundary surfaces of the spherical shell.
Weak Formulation Study For Thermoelastic Buckling Analysis Of Thick Laminated Cylindrical Shells
Directory of Open Access Journals (Sweden)
Kewei Ding
2015-08-01
Full Text Available Weak formulations of mixed state equations of closed laminated cylindrical shells are presented in the Hamilton System. The Hamilton canonical equation of closed cylindrical shell is established. By means of applying the transfer matrix method and taking the advantage of Hamiltonian matrix in the calculation, a unified approach and three-dimensional thermoelastic solutions are obtained for the buckling analysis of closed thick laminated cylindrical shells. All equations of elasticity can be satisfied and all elastic constants can be taken into account. Numerical results are given to compare with those of FEM calculated using SAP5. The principle and method suggested here have clear physical concepts. The equations and boundary conditions proposed in this paper are weakened. The solutions and results given here may serve as a benchmark for other numerical procedures.
Collier, Craig S.
2004-01-01
An emerging technology need for capturing 3-D panel thermoelastic response with 2-D planar finite element models (FEMs) is aided with an equivalent plate stiffness and thermal coefficient formulation. The formulation is general and applies to all panel concepts. Included with the formulation is the ability to provide membrane-bending coupling of unsymmetric sections and calculation of all thermal expansion and bending responses from in-plane and through-the-thickness temperature gradients. Thermal residual strains for both the laminates and plies are included. The general formulation is defined and then applied to a hat-shaped, corrugated stiffened panel. Additional formulations are presented where required to include all of the hat's unique characteristics. Each formulation is validated independently with 3-D FEA.
Generation of shear waves by laser in soft media in the ablative and thermoelastic regimes
Grasland-Mongrain, Pol; Lu, Yuankang; Lesage, Frédéric; Catheline, Stefan; Cloutier, Guy
2016-11-01
This article describes the generation of elastic shear waves in a soft medium using a laser beam. Our experiments show two different regimes depending on laser energy. Physical modeling of the underlying phenomena reveals a thermoelastic regime caused by a local dilatation resulting from temperature increase and an ablative regime caused by a partial vaporization of the medium by the laser. The computed theoretical displacements are close to the experimental measurements. A numerical study based on the physical modeling gives propagation patterns comparable to those generated experimentally. These results provide a physical basis for the feasibility of a shear wave elastography technique (a technique that measures a soft solid stiffness from shear wave propagation) by using a laser beam.
Thermo-elastic induced phase noise in the LISA Pathfinder spacecraft
Gibert, Ferran; Karnesis, Nikolaos; Gesa, Lluís; Martín, Víctor; Mateos, Ignacio; Lobo, Alberto; Flatscher, Reinhold; Gerardi, Domenico; Burkhardt, Johannes; Guzmán, Felipe; Heinzel, Gerhard; Danzmann, Karsten
2014-01-01
During the On-Station Thermal Test campaign of the LISA Pathfinder the data and diagnostics subsystem was tested in nearly space conditions for the first time after integration in the satellite. The results showed the compliance of the temperature measurement system, obtaining temperature noise around $10^{-4}\\,{\\rm K}\\, {\\rm Hz}^{-1/2}$ in the frequency band of $1-30\\;{\\rm mHz}$. In addition, controlled injection of heat signals to the suspension struts anchoring the LISA Technology Package (LTP) Core Assembly to the satellite structure allowed to experimentally estimate for the first time the phase noise contribution through thermo-elastic distortion of the LTP interferometer, the satellite's main instrument. Such contribution was found to be at $10^{-12}\\,{\\rm m}\\, {\\rm Hz}^{-1/2}$, a factor of 30 below the measured noise at the lower end of the measurement bandwidth ($1\\,{\\rm mHz}$).
Variational integrators for the dynamics of thermo-elastic solids with finite speed thermal waves
Energy Technology Data Exchange (ETDEWEB)
Mata, Pablo [Department of Mechanical Engineering, Stanford University, Stanford, CA 94305-4040 (United States); Centro de Investigación en Ecosistemas de la Patagonia (CIEP), Conicyt Regional/CIEP R10C1003, Universidad Austral de Chile, Ignacio Serrrano 509, Coyhaique (Chile); Lew, Adrian J., E-mail: lewa@stanford.edu [Department of Mechanical Engineering, Stanford University, Stanford, CA 94305-4040 (United States)
2014-01-15
This paper formulates variational integrators for finite element discretizations of deformable bodies with heat conduction in the form of finite speed thermal waves. The cornerstone of the construction consists in taking advantage of the fact that the Green–Naghdi theory of type II for thermo-elastic solids has a Hamiltonian structure. Thus, standard techniques to construct variational integrators can be applied to finite element discretizations of the problem. The resulting discrete-in-time trajectories are then consistent with the laws of thermodynamics for these systems: for an isolated system, they exactly conserve the total entropy, and nearly exactly conserve the total energy over exponentially long periods of time. Moreover, linear and angular momenta are also exactly conserved whenever the exact system does. For definiteness, we construct an explicit second-order accurate algorithm for affine tetrahedral elements in two and three dimensions, and demonstrate its performance with numerical examples.
Thermoelastic stresses induced by non-isothermal fluid injection into fractured rock
Mossop, A.; Matthai, S. K.
2003-04-01
The injection of cold water into hot fractured rock occurs in a number of industrial scenarios, most commonly in the recharge of geothermal reservoirs and during waterflood operations in hydrocarbon reservoirs. The cold water cools the rock local to the fracture flow pathways, the cooled rock contracts, causing localised stress perturbations. Essentially analogous physical processes are involved in the injection of hot fluids into cooler rock such as occur in steam flood operations in viscous oil recovery. In this study we investigate such thermoelastic stresses induced by non-isothermal injection into a three dimensional fractured rock mass. The starting point of our analysis is an idealized model of injection into a single, uniform, horizontal fracture. For this case we have previously found semi-analytic solutions and analytic estimates of the stress perturbation and these are in turn used for cross-verification of an isoparametric, quadratic, finite element model of the system. In the numerical model the fractures are treated as discrete conductive channels within the matrix and an additional feature is that the matrix itself can be assigned a non-zero permeability. As the numerical simulator follows a fundamentally different methodology for solving these thermoelastic problems, the results help to validate some of the scaling relationships and non-intuitive behaviour deduced from the analytic estimates (e.g. for a broad range of flow rates, fracture normal stress perturbations decrease with increasing injection rates). The finite element model is then used to explore progressively more complex fracture geometries and networks. Finally we investigate the validity of a continuum limit as fracture densities increase to the point that fracture separation length scales are comparable with thermal diffusion length scales.
Thermoelastic properties of grossular–andradite solid solution at high pressures and temperatures
Energy Technology Data Exchange (ETDEWEB)
Fan, Dawei; Kuang, Yunqian; Xu, Jingui; Li, Bo; Zhou, Wenge; Xie, Hongsen
2016-09-21
The pressure–volume–temperature (P–V–T) equation of state (EoS) of synthetic grossular (Grs)–andradite (And) solid-solution garnet sample have been measured at high temperature up to 900 K and high pressures up to 22.75 GPa for Grs50And50, by using in situ angle-dispersive X-ray diffraction and diamond anvil cell. Analysis of room-temperature P–V data to a third-order Birch–Murnaghan (BM) EoS yields: V0 = 1706.8 ± 0.2 Å3, K0 = 164 ± 2 GPa and K'0 = 4.7 ± 0.5. Fitting of our P–V–T data by means of the high-temperature third-order BM EoS gives the thermoelastic parameters: V0 = 1706.9 ± 0.2 Å3, K0 = 164 ± 2 GPa, K'0 = 4.7 ± 0.2, (∂K/∂T)P = -0.018 ± 0.002 GPa K-1, and α0 = (2.94 ± 0.07) × 10-5 K-1. The results also confirm that grossular content increases the bulk modulus of the Grs-And join following a nearly ideal mixing model. The relation between bulk modulus and Grs mole fraction (XGrs) in this garnet join is derived to be K0 (GPa) = (163.7 ± 0.7) + (0.14 ± 0.02) XGrs (R2 = 0.985). Present results are also compared to previously studies determined the thermoelastic properties of Grs-And garnets.
Thermoelastic properties of grossular-andradite solid solution at high pressures and temperatures
Fan, Dawei; Kuang, Yunqian; Xu, Jingui; Li, Bo; Zhou, Wenge; Xie, Hongsen
2017-02-01
The pressure-volume-temperature ( P- V- T) equation of state (EoS) of synthetic grossular (Grs)-andradite (And) solid-solution garnet sample have been measured at high temperature up to 900 K and high pressures up to 22.75 GPa for Grs50And50, by using in situ angle-dispersive X-ray diffraction and diamond anvil cell. Analysis of room-temperature P- V data to a third-order Birch-Murnaghan (BM) EoS yields: V 0 = 1706.8 ± 0.2 Å3, K 0 = 164 ± 2 GPa and K' 0 = 4.7 ± 0.5. Fitting of our P- V- T data by means of the high-temperature third-order BM EoS gives the thermoelastic parameters: V 0 = 1706.9 ± 0.2 Å3, K 0 = 164 ± 2 GPa, K' 0 = 4.7 ± 0.2, (∂K/∂T) P = -0.018 ± 0.002 GPa K-1, and α 0 = (2.94 ± 0.07) × 10-5 K-1. The results also confirm that grossular content increases the bulk modulus of the Grs-And join following a nearly ideal mixing model. The relation between bulk modulus and Grs mole fraction ( X Grs) in this garnet join is derived to be K 0 (GPa) = (163.7 ± 0.7) + (0.14 ± 0.02) X Grs ( R 2 = 0.985). Present results are also compared to previously studies determined the thermoelastic properties of Grs-And garnets.
Tong, Yujin; Guan, Mingzhi; Wang, Xingzhe
2017-04-01
The present study deals with the thermal characteristics and mechanical behaviors of low/high temperature superconducting (LTS/HTS) composite tapes during quench processes triggered by a spot heater. Based on the generalized thermoelastic theory, a dynamic thermoelastic model with a relaxation time is developed which takes into account the temperature dependence and finite speed of heat propagation for the superconducting tapes under cryogenic condition. The analyses were performed using the finite element method to solve the coupled differential equations of dynamic heat conduction and elastic equilibrium. The results show that the thermoelastic behaviors exhibit a strong relevance to quench characteristics of the superconductors. As a quench occurs, the thermoelastic strain-rate has an obvious jumping variation with the instant of time of its peak being fortunately coincident with the time at which the critical temperature is reached. Such a jumping change of strain-rate could be a way of estimation and detection of quench occurrence, and the theoretical predictions coincide with the existing experimental observations on thermoelastic strain-rate in LTS magnets. For a HTS tape, the thermoelastic strain-rate or temperature-rate variation and a small jump also are illustrated as the quench occurrence is determined. Additionally, the normal zone propagation velocities for the LTS/HTS tapes are predicted by the critical temperature and thermoelastic strain-rate to show quite good agreements with the results evaluated by Wilson’s formula for a LTS tape or the experimental measurements for a HTS tape. The influences of the relaxation time of heat conduction and thermoelastic coupling on the thermal distribution and strain profile are also discussed in details.
2005-07-01
thermo-elastic properties, stress concentration factors, and edge effect 5. FUNDING NUMBERS FA8655-05-1-5008 6. AUTHOR(S) 7...unbounded solids, Thermo-elastic properties, Stress concentration factors, edge effect , Non-linear elastic stress, Inclusion-reinforced materials...factors, and edge effect Project manager: Maslov Borys Petrovich, Dr. Sc. in Physics and Mathematics Phone: +380-44-454-7764, Fax: –, E-mail
National Aeronautics and Space Administration — How Data Was Acquired: The data presented is from a physical simulator that simulated engine disks. Sample Rates and Parameter Description: All parameters are...
Signs of Early-stage Disk Growth Revealed with ALMA
Yen, Hsi-Wei; Koch, Patrick M.; Takakuwa, Shigehisa; Krasnopolsky, Ruben; Ohashi, Nagayoshi; Aso, Yusuke
2017-01-01
We present ALMA 1.3 mm continuum, 12CO, C18O, and SO data for the Class 0 protostars Lupus 3 MMS, IRAS 15398‑3559, and IRAS 16253‑2429 at resolutions of ∼100 au. By measuring a rotational profile in C18O, a 100 au Keplerian disk around a 0.3 M⊙ protostar is observed in Lupus 3 MMS. No 100 au Keplerian disks are observed in IRAS 15398‑3559 and IRAS 16253‑2429. Nevertheless, embedded compact (<30 au) continuum components are detected. The C18O emission in IRAS 15398‑3559 shows signatures of infall with a constant angular momentum. IRAS 16253‑2429 exhibits signatures of infall and rotation, but its rotational profile is unresolved. By fitting the C18O data with our kinematic models, the protostellar masses and the disk radii are inferred to be 0.01 M⊙ and 20 au in IRAS 15398‑3559, and 0.03 M⊙ and 6 au in IRAS 16253‑2429. By comparing the specific angular momentum profiles from 10,000 au to 100 au in eight Class 0 and I protostars, we find that the evolution of envelope rotation can be described with conventional inside-out collapse models. In comparison with a sample of 18 protostars with known disk radii, our results reveal signs of disk growth, with the disk radius increasing as {{M}* }0.8+/- 0.14 or {t}1.09+/- 0.37 in the Class 0 stage, where M* is the protostellar mass and t is the age. The disk growth rate slows down in the Class I stage. In addition, we find a hint that the mass accretion rate declines as {t}-0.26+/- 0.04 from the Class 0 to the Class I stages.
Relativistic Effects on Neutrino Pair Annihilation above a Kerr Black Hole with the Accretion Disk
Asano, K; Asano, Katsuaki; Fukuyama, Takeshi
2001-01-01
Using idealized models of the accretion disk we investigate the relativistic effects on the energy deposition rate via neutrino pair annihilation near the rotation axis of a Kerr black hole. Neutrinos are emitted from the accretion disk. The bending of neutrino trajectories and the redshift due to the disk rotation and gravitation are taken into consideration. The Kerr parameter, $a$, affects not only neutrinos' behavior but also the inner radius of the accretion disk. When the deposition energy is mainly contributed by the neutrinos coming from the central part, the redshift effect becomes dominant as $a$ becomes large and the energy deposition rate is reduced compared with that neglecting the relativistic effects. On the other hand, for small $a$ the bending effect gets dominant and makes energy increase by factor 2 compared with that neglecting the relativistic effects. For the disk with temperature gradient, the energy deposition rate for a small inner radius of the accretion disk is smaller than that est...
Properties of Circumstelar Disks of Three Northern Galactic Be Stars
Ubaque Brito, K. Y.; Sabogal Martínez, B. E.; García-Varela, A.; Salas, L.; álvarez, M.
2017-07-01
Be stars have a very rapid rotation that leads, along with other mechanisms, to the generation of circumstellar decretion disks. Spectroscopic analysis of their Hydrogen emission lines in the infrared can be useful to understand the disk evolution. This is possible through characterizing the dependency with wavelenght of physical parameters of the lines, such as integrated flux and full width at half maximum. In this work, we obtained integrated fluxes for Humphreys, Pfund and Brackett spectral lines of a sample of 3 Be stars: γ Cas, φ Per and 28 Tau. With these data, we analized changes in optical depth and density of the disks. We found that the circumstellar disks of these stars are optically thin, based on a flux ratio diagram and from a qualitative description of the morphology found in the infrared spectra. We studied also the optical spectra of BeSS database of these stars and found that the variability of the Hα profile is correlated with the evolution and stages of stability in Be star disks. In our case, we could say that γ Cas and φ Per have circumstellar disks stable with a high density, which have remained almost constant. By contrast the remarkable variability of Hα profile for star 28 Tau lead us to believe that its disk has had episodes of dissipation and slight changes in density. All these results are in agreement with previous studies for different Be stars, confirming the mentioned aspects as general indicators of density changes suffered by circumstellar disks of Be stars.
1976-01-01
Introduced under the name "Verbatim", Latin for "literally", these disks that sized more than 5¼ inches have become almost universal on dedicated word processing systems and personal computers. This format was replaced more slowly by the 3½-inch format, introduced for the first time in 1982. Compared to today, these large format disks stored very little data. In reality, they could only contain a few pages of text.