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Oleg A Godin - One of the best experts on this subject based on the ideXlab platform.

  • recovering the acoustic green s function from ambient noise cross correlation in an inhomogeneous Moving medium
    Physical Review Letters, 2006
    Co-Authors: Oleg A Godin
    Abstract:

    We study long-range correlation of diffuse acoustic noise fields in an arbitrary inhomogeneous, Moving Fluid. The flow reversal theorem is used to show that the cross-correlation function of ambient noise provides an estimate of a combination of the Green's functions corresponding to sound propagation in opposite directions between the two receivers. Measurements of the noise cross correlation allow one to quantify flow-induced acoustic nonreciprocity and evaluate both spatially averaged flow velocity and sound speed between the two points. Introduction.—In recent experiments, Weaver and Lobkis (1,2) demonstrated that the cross correlation of the recordings of diffuse noise fields at two spatially sepa- rated points gives the time-domain Green's function be- tween the two points, i.e., the wave field that would be observed at one point if a source were placed at the other. Emergence of the Green's function from cross correlations of diffuse noise was demonstrated theoretically by a num- ber of researchers (1-8) under various assumptions, with the most rigorous and general proof being offered by Wapenaar (6). His reasoning is based on an application of the reciprocity principle and pertains to arbitrary inho- mogeneous solids. A similar proof pertaining to Fluids of constant density was independently given by Weaver and Lobkis (7). Proposed applications of noise cross- correlation measurements to passive remote sensing range from ultrasonics and acoustic oceanography to helioseis- mology and geophysics, at wave frequencies that differ by more than 10 orders of magnitude (see (1,3,5,6,8,9) and references therein). The work described here is motivated by possible appli- cations to remote sensing of inhomogeneous flows, includ- ing precise measurements of flow velocities that are small compared to sound speed, which can be used for environ- mental monitoring and medical purposes. In this Letter we apply the flow reversal theorem (10) to derive exact and asymptotic relations between the two-point correlation function of noise and the sum of the Green's functions, which correspond to sound propagation in opposite direc- tions between the two points. The cross-correlation func- tion of ambient noise is shown to contain the information necessary to retrieve the flow velocity and the sound speed from acoustic measurements. The flow reversal theorem.—Linear acoustic fields in an inhomogeneous Moving Fluid with sound speed cx� , mass density � � x� , and flow velocity uxare governed by the following equations ((10); (11), Chap. 8) � d 2 w

  • recovering the acoustic green s function from ambient noise cross correlation in an inhomogeneous Moving medium
    Physical Review Letters, 2006
    Co-Authors: Oleg A Godin
    Abstract:

    We study long-range correlation of diffuse acoustic noise fields in an arbitrary inhomogeneous, Moving Fluid. The flow reversal theorem is used to show that the cross-correlation function of ambient noise provides an estimate of a combination of the Green's functions corresponding to sound propagation in opposite directions between the two receivers. Measurements of the noise cross correlation allow one to quantify flow-induced acoustic nonreciprocity and evaluate both spatially averaged flow velocity and sound speed between the two points.

  • the kirchhoff helmholtz integral theorem and related identities for waves in an inhomogeneous Moving Fluid
    Journal of the Acoustical Society of America, 1996
    Co-Authors: Oleg A Godin
    Abstract:

    The Kirchhoff–Helmholtz integral theorem (KHT), which expresses the wave field in a volume inside (or outside) a given surface in terms of the field’s value on the surface, is well known and widely used in acoustics of motionless media. In this paper, an extension of the theorem to acoustic‐gravity waves in an arbitrary inhomogeneous Moving Fluid is obtained as a corollary of the reciprocity‐type relations constituting the recently established flow reversal theorem (FRT) [O. A. Godin, J. Acoust. Soc. Am. 97, 3396(A) (1995); 98, 2866(A) (1995)]. The KHT takes a concise form when stated in terms of acoustic pressure and oscillatory displacement of Fluid particles. The KHT is applied to study uniqueness of solutions to acoustic boundary value problems in Moving media and to establish unitarity and other general properties of the scattering matrix for surface and volume scattering as well as in an irregular (range‐dependent) waveguide with flow. Relation of the scattering matrix properties to the FRT and to wave‐action conservation is discussed. [Work supported by NSERC.]

Norfifah Bachok - One of the best experts on this subject based on the ideXlab platform.

  • A (2009) Mixed convection boundary layer flow over a horizontal plate with thermal radiation. Heat Mass Transfer 46: 147–151
    2016
    Co-Authors: Norfifah Bachok, Anuar Ishak, Ioan Pop
    Abstract:

    The steady boundary layer flow of a viscous and incompressible Fluid over a Moving vertical flat plate in an external Moving Fluid with viscous dissipation is theoretically investigated. Using appropriate similarity variables, the governing system of partial differential equations is transformed into a system of ordinary (similarity) differential equations, which is then solved numerically using a Maple software. Results for the skin friction or shear stress coefficient, local Nusselt number, velocity and temperature profiles are presented for different values of the governing parameters. It is found that the set of the similarity equations has unique solutions, dual solutions or no solutions, depending on the values of the mixed convection parameter, the velocity ratio parameter and the Eckert number. The Eckert number significantly affects the surface shear stress as well as the heat transfer rate at the surface

  • radiation effects on the thermal boundary layer flow over a Moving plate with convective boundary condition
    Meccanica, 2011
    Co-Authors: Anuar Mohd Ishak, Nor Azizah Yacob, Norfifah Bachok
    Abstract:

    The steady laminar boundary layer flow over a Moving plate in a Moving Fluid with convective surface boundary condition and in the presence of thermal radiation is investigated in this paper. Under certain conditions, the present problem reduces to the classical Blasius and Sakiadis problems. The effects of radiation and convective parameters on the thermal field are thoroughly examined and discussed. Dual solutions are found to exist when the plate and the Fluid move in the opposite directions.

  • the effects of suction and injection on a Moving flat plate in a parallel stream with prescribed surface heat flux
    WSEAS Transactions on Heat and Mass Transfer, 2010
    Co-Authors: Norfifah Bachok, Anuar Mohd Ishak
    Abstract:

    The effect of surface mass flux on a Moving flat plate in a Moving Fluid with prescribed surface heat flux is studied. The governing partial differential boundary layer equations are first transformed into ordinary differential equations before being solved numerically by a finite difference method. The features of the flow and heat transfer characteristics for different values of the governing parameters are analyzed and discussed. It is found that dual solutions exist when the plate and the free stream move in the opposite directions. The results indicate that the range of known dual solutions increases with suction and decreases with injection and the rate of heat transfer increases with increasing heat flux exponent parameter.

  • flow and heat transfer characteristics on a Moving flat plate in a parallel stream with prescribed surface heat flux
    Heat and Mass Transfer, 2010
    Co-Authors: Norfifah Bachok, Anuar Mohd Ishak
    Abstract:

    The boundary layer flow on a Moving flat plate in a Moving Fluid with prescribed surface heat flux is studied. A finite difference scheme is used to solve the system of transformed governing equations. The features of the flow and heat transfer characteristics for different values of the governing parameters are analyzed and discussed. It is found that dual solutions exist when the plate and the free stream move in the opposite directions. The rate of heat transfer increases with increasing heat flux exponent parameter.

Anuar Mohd Ishak - One of the best experts on this subject based on the ideXlab platform.

Esmaeal Ghavanloo - One of the best experts on this subject based on the ideXlab platform.

  • flow thermoelastic vibration and instability analysis of viscoelastic carbon nanotubes embedded in viscous Fluid
    Physica E-low-dimensional Systems & Nanostructures, 2011
    Co-Authors: Esmaeal Ghavanloo, Ahmad S Fazelzadeh
    Abstract:

    Abstract The flexural vibration of viscoelastic carbon nanotubes (CNTs) conveying Fluid and embedded in viscous Fluid is investigated by the nonlocal Timoshenko beam model. The governing equations are developed by Hamilton's principle, including the effects of structural damping of the CNT, internal Moving Fluid, external viscous Fluid, temperature change and nonlocal parameter. Applying Galerkin’s approach, the resulting equations are transformed into a set of eigenvalue equations. The validity of the present analysis is confirmed by comparing the results with those obtained in literature. The effects of the main parameters on the vibration characteristics of the CNT are also elucidated. Most results presented in the present investigation have been absent from the literature for the vibration and instability of the CNT conveying Fluid.

  • in plane vibration analysis of curved carbon nanotubes conveying Fluid embedded in viscoelastic medium
    Physics Letters A, 2011
    Co-Authors: Esmaeal Ghavanloo, Masoud Rafiei, Farhang Daneshmand
    Abstract:

    Abstract The effect of the induced vibrations in the carbon nanotubes (CNTs) arising from the internal Fluid flow is a critical issue in the design of CNT-based Fluidic devices. In this study, in-plane vibration analysis of curved CNTs conveying Fluid embedded in viscoelastic medium is investigated. The CNT is modeled as a linear elastic cylindrical tube where the internal Moving Fluid is characterized by steady flow velocity and mass density of Fluid. A modified-inextensible theory is used in formulation and the steady-state initial forces due to the centrifugal and pressure forces of the internal Fluid are also taken into account. The finite element method is used to discretize the equation of motion and the frequencies are obtained by solving a quadratic eigenvalue problem. The effects of CNT opening angle, the elastic modulus and the damping factor of the viscoelastic surrounded medium and Fluid velocity on the resonance frequencies are elucidated. It is shown that curved CNTs are unconditionally stable even for a system with sufficiently high flow velocity. The most results presented in this investigation have been absent from the literature for Fluid-induced vibration of curved CNTs embedded in viscoelastic foundations.

  • vibration and instability analysis of carbon nanotubes conveying Fluid and resting on a linear viscoelastic winkler foundation
    Physica E-low-dimensional Systems & Nanostructures, 2010
    Co-Authors: Esmaeal Ghavanloo, Farhang Daneshmand, Masoud Rafiei
    Abstract:

    Abstrac t Carbon nanotubes (CNTs) are used for a variety of technological and biomedical applications. Fluid flows inside CNTs have become an attractive research topic in recent years. In the present study, the vibration and instability analysis of a CNT resting on a linear viscoelastic Winkler foundation are investigated based on the classical Euler–Bernoulli beam model. The effect of internal Moving Fluid is characterized by two parameters, the steady flow velocity and the mass density of the Fluid. The finite element method is used to discretize the equation of motion, and the resonant frequencies are obtained by solving a quadratic eigenvalue problem. The lowest four frequencies are determined for different boundary conditions. The effects of the modulus and the damping factor of the linear viscoelastic Winkler foundation and the Fluid velocity on the resonance frequencies are also examined. The validity of the present analysis is confirmed by comparing the results with those obtained from the literature.

A Mioduchowski - One of the best experts on this subject based on the ideXlab platform.

  • flow induced flutter instability of cantilever carbon nanotubes
    International Journal of Solids and Structures, 2006
    Co-Authors: J Yoon, A Mioduchowski
    Abstract:

    Carbon nanotubes are finding significant application to nanoFluidic devices. This work studies the influence of internal Moving Fluid on free vibration and flow-induced flutter instability of cantilever carbon nanotubes based on a continuum elastic model. Since the flow-induced vibration of cantilever pipes is non-conservative in nature, cantilever carbon nanotubes conveying Fluid are damped with decaying amplitude for flow velocity below a certain critical value. Beyond this critical flow velocity, flutter instability occurs and vibration becomes amplified with growing amplitude. Our results indicate that internal Moving Fluid substantially affects vibrational frequencies and the decaying rate of amplitude especially for longer cantilever carbon nanotubes of larger innermost radius at higher flow velocity, and the critical flow velocity for flutter instability in some cases may fall within the practical range. On the other hand, a moderately stiff surrounding elastic medium (such as polymers) can significantly suppress the effect of internal Moving Fluid on vibrational frequencies and suppress or eliminate flutter instability within the practical range of flow velocity.