The Experts below are selected from a list of 2435538 Experts worldwide ranked by ideXlab platform

Bruno Souza Carmo - One of the best experts on this subject based on the ideXlab platform.

  • Computational simulation of the flow-induced vibration of a circular cylinder subjected to wake interference
    Journal of Fluids and Structures, 2013
    Co-Authors: Bruno Souza Carmo, Gustavo R. S. Assi, Julio Romano Meneghini
    Abstract:

    In this work, we considered the flow around two circular cylinders of equal diameter placed in tandem with respect to the incident uniform flow. The upstream cylinder was fixed and the downstream cylinder was completely free to move in the cross-stream direction, with no spring or damper attached to it. The Centre-to-Centre Distance between the cylinders was four diameters, and the Reynolds number was varied from 100 to 645. We performed two- and three-dimensional simulations of this flow using a Spectral/hp element method to discretise the flow equations, coupled to a simple Newmark integration routine that solves the equation of the dynamics of the cylinder. The differences of the behaviours observed in the two- and three-dimensional simulations are highlighted and the data is analysed under the light of previously published experimental results obtained for higher Reynolds numbers.

  • Flow-induced vibration of a circular cylinder subjected to wake interference at low Reynolds number
    Journal of Fluids and Structures, 2011
    Co-Authors: Bruno Souza Carmo, Spencer J. Sherwin, Peter W. Bearman, Richard H. J. Willden
    Abstract:

    Abstract Two- and three-dimensional numerical simulations of the flow around two circular cylinders in tandem arrangements are performed. The upstream cylinder is fixed and the downstream cylinder is free to oscillate in the transverse direction, in response to the fluid loads. The Reynolds number is kept constant at 150 for the two-dimensional simulations and at 300 for the three-dimensional simulations, and the reduced velocity is varied by changing the structural stiffness. The in-line Centre-to-Centre Distance is varied from 1.5 to 8.0 diameters, and the results are compared to that of a single isolated flexible cylinder with the same structural characteristics, m ⁎ = 2.0 and ζ = 0.007 . The calculations show that significant changes occur in the dynamic behaviour of the cylinders, when comparing the flow around the tandem arrangements to that around an isolated cylinder: for the tandem arrangements, the lock-in boundaries are wider, the maximum displacement amplitudes are greater and the amplitudes of vibration for high reduced velocities, outside the lock-in, are very significant. The main responsible for these changes appears to be the oscillatory flow in the gap between the cylinders.

  • Numerical investigation of the flow around two circular cylinders in tandem
    Journal of Fluids and Structures, 2006
    Co-Authors: Bruno Souza Carmo, Julio Romano Meneghini
    Abstract:

    Abstract The incompressible flow around pairs of circular cylinders in tandem arrangements is investigated in this paper. The spectral element method is employed to carry out two- and three-dimensional simulations of the flow. The Centre-to-Centre Distance ( l cc ) of the investigated configurations varies from 1.5 to 8 diameters (D), and results thus obtained are compared to the isolated cylinder case. The simulations are in the Reynolds number (Re) range from 160 to 320, covering the transition in the wake. Our analysis focuses on the small-scale instabilities of vortex shedding, which occurs in the Re range investigated. With the aid of Strouhal data and vorticity contours, we propose mechanisms to explain the interference phenomenon and its interaction with the three-dimensional vortical structures present in the flow field. It is found that, for Re > 190 , when three-dimensional structures are present in the flow field, two-dimensional simulations are not sufficient to predict the ( Re , l cc ) pair of drag inversion.

Julio Romano Meneghini - One of the best experts on this subject based on the ideXlab platform.

  • Computational simulation of the flow-induced vibration of a circular cylinder subjected to wake interference
    Journal of Fluids and Structures, 2013
    Co-Authors: Bruno Souza Carmo, Gustavo R. S. Assi, Julio Romano Meneghini
    Abstract:

    In this work, we considered the flow around two circular cylinders of equal diameter placed in tandem with respect to the incident uniform flow. The upstream cylinder was fixed and the downstream cylinder was completely free to move in the cross-stream direction, with no spring or damper attached to it. The Centre-to-Centre Distance between the cylinders was four diameters, and the Reynolds number was varied from 100 to 645. We performed two- and three-dimensional simulations of this flow using a Spectral/hp element method to discretise the flow equations, coupled to a simple Newmark integration routine that solves the equation of the dynamics of the cylinder. The differences of the behaviours observed in the two- and three-dimensional simulations are highlighted and the data is analysed under the light of previously published experimental results obtained for higher Reynolds numbers.

  • Numerical investigation of the flow around two circular cylinders in tandem
    Journal of Fluids and Structures, 2006
    Co-Authors: Bruno Souza Carmo, Julio Romano Meneghini
    Abstract:

    Abstract The incompressible flow around pairs of circular cylinders in tandem arrangements is investigated in this paper. The spectral element method is employed to carry out two- and three-dimensional simulations of the flow. The Centre-to-Centre Distance ( l cc ) of the investigated configurations varies from 1.5 to 8 diameters (D), and results thus obtained are compared to the isolated cylinder case. The simulations are in the Reynolds number (Re) range from 160 to 320, covering the transition in the wake. Our analysis focuses on the small-scale instabilities of vortex shedding, which occurs in the Re range investigated. With the aid of Strouhal data and vorticity contours, we propose mechanisms to explain the interference phenomenon and its interaction with the three-dimensional vortical structures present in the flow field. It is found that, for Re > 190 , when three-dimensional structures are present in the flow field, two-dimensional simulations are not sufficient to predict the ( Re , l cc ) pair of drag inversion.

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

  • Magnetic field dependent small-angle neutron scattering on a Co nanorod array: evidence for intraparticle spin misalignment.
    Journal of applied crystallography, 2014
    Co-Authors: A Günther, J-p Bick, P Szary, D Honecker, C D Dewhurst, U Keiderling, A V Feoktystov, A Tschöpe, R Birringer, A Michels
    Abstract:

    The structural and magnetic properties of a cobalt nanorod array have been studied by means of magnetic field dependent small-angle neutron scattering (SANS). Measurement of the unpolarized SANS cross section dΣ/dΩ of the saturated sample in the two scattering geometries where the applied magnetic field H is either perpendicular or parallel to the wavevector ki of the incoming neutron beam allows one to separate nuclear from magnetic SANS, without employing the usual sector-averaging procedure. The analysis of the SANS data in the saturated state provides structural parameters (rod radius and Centre-to-Centre Distance) that are in good agreement with results from electron microscopy. Between saturation and the coercive field, a strong field dependence of dΣ/dΩ is observed (in both geometries), which cannot be explained using the conventional expression of the magnetic SANS cross section of magnetic nanoparticles in a homogeneous nonmagnetic matrix. The origin of the strong field dependence of dΣ/dΩ is believed to be related to intradomain spin misalignment, due to magnetocrystalline and magnetoelastic anisotropies and magnetostatic stray fields.

Ming Zhao - One of the best experts on this subject based on the ideXlab platform.

  • Vortex-induced vibration of four cylinders in an in-line square configuration
    Physics of Fluids, 2016
    Co-Authors: Ming Zhao, Kalyani Kaja, Yang Xiang, Liang Cheng
    Abstract:

    This paper presents a numerical study of vortex-induced vibration of four rigidly connected and four separately mounted circular cylinders in an inline square configuration at a Reynolds number of 150, a low mass ratio of 2.5, and a range of spacing ratio L from 1.5 to 4, where the spacing ratio is defined as the Centre-to-Centre Distance of two adjacent cylinders normalized by the cylinder diameter. For the rigidly connected cylinder array, the maximum and minimum response amplitudes occur at L = 1.5 and L = 2.0, respectively, for the range of spacing ratio covered in this study and the maximum response amplitude at L = 1.5 is accompanied by a wide lock-in range. The large response amplitude at a small spacing ratio L = 1.5 is because the cylinder array responds to the flow as a single cylinder with an overall size that is much larger than the diameter of the single cylinder while the small response amplitude observed at L = 2.0 is attributed to the strong interaction of the vortices through the gap betw...

  • Flow induced vibration of two rigidly coupled circular cylinders in tandem and side-by-side arrangements at a low Reynolds number of 150
    Physics of Fluids, 2013
    Co-Authors: Ming Zhao
    Abstract:

    Flow induced vibration of two rigidly coupled identical circular cylinders in tandem and side-by-side arrangements at a low Reynolds number of 150 is studied numerically. The two cylinders vibrate in the cross-flow direction and have the same displacement. The Navier-Stokes equations are solved by the finite element method and the equation of motion of the cylinders is solved by the fourth-order Runge-Kutta algorithm. Simulations are conducted for a constant mass ratio of 2 and the gap ratios (defined as the ratio of the Centre-to-Centre Distance between the two cylinders L to the cylinder diameter D) of 1.5, 2, 4, and 6. The reduced velocities range from 0.5 to 15 with an increment of 0.5 for the tandem arrangement and from 0.5 to 30 with an increment of 0.5 for the side-by-side arrangement. It is found that the gap between the two cylinders has significant effect on the response. For a tandem arrangement, the lock-in regime of the reduced velocity is narrower than that of a single cylinder for L/D = 1.5...

Dong Qiu - One of the best experts on this subject based on the ideXlab platform.

  • A small-angle neutron scattering study of poly(ethylene oxide) microstructure in aqueous poly(styrenesulfonate sodium) solutions
    Journal of colloid and interface science, 2011
    Co-Authors: Zewei Bai, Yue Xie, Chunhai Chen, Terence Cosgrove, Dong Qiu
    Abstract:

    Abstract Dilute aqueous solutions of d-PEO and PSSNa mixtures were studied by 2 H NMR spectroscopy and small-angle neutron scattering (SANS). The interactions between d-PEO and PSSNa were found to be negligible both in the presence and absence of NaCl. At very dilute concentration (0.7 mg mL −1 ), d-PEO chains were still found to be slightly collapsed at ambient temperature in water. Upon the addition of PSSNa, aggregates of d-PEO were observed with d-PEO coils loosely associated with each other. The average centre to centre Distance between d-PEO coils, which was calculated from the maxima in SANS spectra, was similar to the size of the individual coils. The effect of a simple salt, NaCl, on d-PEO-PSSNa interaction was investigated. Salt addition induced a breakdown of the dilute d-PEO aggregates.