The Experts below are selected from a list of 267 Experts worldwide ranked by ideXlab platform
Mark C. Thompson - One of the best experts on this subject based on the ideXlab platform.
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Vortex-induced vibration of a transversely Rotating Sphere
Journal of Fluid Mechanics, 2018Co-Authors: Methma M. Rajamuni, Mark C. Thompson, Kerry HouriganAbstract:Vortex-induced vibration (VIV) of a Sphere is one of the most basic fluid-structure interaction problems. Since such vibrations can lead to fatal structural failures, numerous studies have focused on suppressing such flow-induced vibrations. In this study, for the first time, the effect of an imposed transverse rotation on the dynamics of the VIV of an elastically mounted Sphere has been investigated. It was observed that the non-dimensional vibration amplitude for a Rotating Sphere (A∗ = √2yrms/D, where yrms is the root mean square of the displacement in the transverse direction and D = Sphere diameter) exhibits a bell-shaped evolution as a function of reduced velocity, similar to the classic VIV response of a non-Rotating Sphere. The Sphere is found to oscillate freely up to a rotation ratio α (ratio of the equatorial velocity of the Sphere to the free-stream velocity) close to 0.5. For lower rotation ratios (α ≤ 0.3), the response looks similar to the non-Rotating case but with slightly smaller vibration amplitude. For higher α values, the amplitude was found to decrease significantly with the rotation up to α = 0.5. The amplitude dropped drastically after it reached the peak amplitude. This is unlike the VIV response of a Rotating circular cylinder where the vibration amplitude increases up to three times the maximum vibration amplitude in the non- Rotating case due to a novel asymmetric wake pattern (see [1])
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Vortex-induced vibration of a Rotating Sphere
Journal of Fluid Mechanics, 2018Co-Authors: Anchal Sareen, Kerry Hourigan, Jisheng Zhao, David Lo Jacono, John Sheridan, Mark C. ThompsonAbstract:Vortex-induced vibration (VIV) of a Sphere represents one of the most generic fundamental fluid–structure interaction problems. Since vortex-induced vibration can lead to structural failure, numerous studies have focused on understanding the underlying principles of VIV and its suppression. This paper reports on an experimental investigation of the effect of imposed axial rotation on the dynamics of vortex-induced vibration of a Sphere that is free to oscillate in the cross-flow direction, by employing simultaneous displacement and force measurements. The VIV response was investigated over a wide range of reduced velocities (i.e. velocity normalised by the natural frequency of the system): 3 U∗ 18, corresponding to a Reynolds number range of 5000 < Re < 30 000, while the rotation ratio, defined as the ratio between the Sphere surface and inflow speeds, α = |ω|D/(2U), was varied in increments over the range of 0 α 7.5. It is found that the vibration amplitude exhibits a typical inverted bell-shaped variation with reduced velocity, similar to the classic VIV response for a non-Rotating Sphere but without the higher reduced velocity response tail. The vibration amplitude decreases monotonically and gradually as the imposed transverse rotation rate is increased up to α = 6, beyond which the body vibration is significantly reduced. The synchronisation regime, defined as the reduced velocity range where large vibrations close to the natural frequency are observed, also becomes narrower as α is increased, with the peak saturation amplitude observed at progressively lower reduced velocities. In addition, for small rotation rates, the peak amplitude decreases almost linearly with α. The imposed rotation not only reduces vibration amplitudes, but also makes the body vibrations less periodic. The frequency spectra revealed the occurrence of a broadband spectrum with an increase in the imposed rotation rate. Recurrence analysis of the structural vibration response demonstrated a transition from periodic to chaotic in a modified recurrence map complementing the appearance of broadband spectra at the onset of bifurcation. Despite considerable changes in flow structure, the vortex phase (φvortex), defined as the phase between the vortex force and the body displacement, follows the same pattern as for the non-Rotating case, with the φvortex increasing gradually from low values in Mode I of the Sphere vibration to almost 180◦ as the system undergoes a continuous transition to Mode II of the Sphere vibration at higher reduced velocity. The total phase (φtotal), defined as the phase between the transverse lift force and the body displacement, only increases from low values after the peak amplitude response in Mode II has been reached. It reaches its maximum value (∼165◦) close to the transition from the Mode II upper plateau to the lower plateau, reminiscent of the behaviour seen for the upper to lower branch transition for cylinder VIV. Hydrogen-bubble visualisations and particle image velocimetry (PIV) performed in the equatorial plane provided further insights into the flow dynamics near the Sphere surface. The mean wake is found to be deflected towards the advancing side of the Sphere, associated with an increase in the Magnus force. For higher rotation ratios, the near-wake rear recirculation zone is absent and the flow is highly vectored from the retreating side to the advancing side, giving rise to large-scale shedding. For a very high rotation ratio of α = 6, for which vibrations are found to be suppressed, a one-sided large-scale shedding pattern is observed, similar to the shear-layer instability one-sided shedding observed previously for a rigidly mounted Rotating Sphere.
Kerry Hourigan - One of the best experts on this subject based on the ideXlab platform.
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Vortex-induced vibration of a transversely Rotating Sphere
Journal of Fluid Mechanics, 2018Co-Authors: Methma M. Rajamuni, Mark C. Thompson, Kerry HouriganAbstract:Vortex-induced vibration (VIV) of a Sphere is one of the most basic fluid-structure interaction problems. Since such vibrations can lead to fatal structural failures, numerous studies have focused on suppressing such flow-induced vibrations. In this study, for the first time, the effect of an imposed transverse rotation on the dynamics of the VIV of an elastically mounted Sphere has been investigated. It was observed that the non-dimensional vibration amplitude for a Rotating Sphere (A∗ = √2yrms/D, where yrms is the root mean square of the displacement in the transverse direction and D = Sphere diameter) exhibits a bell-shaped evolution as a function of reduced velocity, similar to the classic VIV response of a non-Rotating Sphere. The Sphere is found to oscillate freely up to a rotation ratio α (ratio of the equatorial velocity of the Sphere to the free-stream velocity) close to 0.5. For lower rotation ratios (α ≤ 0.3), the response looks similar to the non-Rotating case but with slightly smaller vibration amplitude. For higher α values, the amplitude was found to decrease significantly with the rotation up to α = 0.5. The amplitude dropped drastically after it reached the peak amplitude. This is unlike the VIV response of a Rotating circular cylinder where the vibration amplitude increases up to three times the maximum vibration amplitude in the non- Rotating case due to a novel asymmetric wake pattern (see [1])
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Vortex-induced vibration of a Rotating Sphere
Journal of Fluid Mechanics, 2018Co-Authors: Anchal Sareen, Kerry Hourigan, Jisheng Zhao, David Lo Jacono, John Sheridan, Mark C. ThompsonAbstract:Vortex-induced vibration (VIV) of a Sphere represents one of the most generic fundamental fluid–structure interaction problems. Since vortex-induced vibration can lead to structural failure, numerous studies have focused on understanding the underlying principles of VIV and its suppression. This paper reports on an experimental investigation of the effect of imposed axial rotation on the dynamics of vortex-induced vibration of a Sphere that is free to oscillate in the cross-flow direction, by employing simultaneous displacement and force measurements. The VIV response was investigated over a wide range of reduced velocities (i.e. velocity normalised by the natural frequency of the system): 3 U∗ 18, corresponding to a Reynolds number range of 5000 < Re < 30 000, while the rotation ratio, defined as the ratio between the Sphere surface and inflow speeds, α = |ω|D/(2U), was varied in increments over the range of 0 α 7.5. It is found that the vibration amplitude exhibits a typical inverted bell-shaped variation with reduced velocity, similar to the classic VIV response for a non-Rotating Sphere but without the higher reduced velocity response tail. The vibration amplitude decreases monotonically and gradually as the imposed transverse rotation rate is increased up to α = 6, beyond which the body vibration is significantly reduced. The synchronisation regime, defined as the reduced velocity range where large vibrations close to the natural frequency are observed, also becomes narrower as α is increased, with the peak saturation amplitude observed at progressively lower reduced velocities. In addition, for small rotation rates, the peak amplitude decreases almost linearly with α. The imposed rotation not only reduces vibration amplitudes, but also makes the body vibrations less periodic. The frequency spectra revealed the occurrence of a broadband spectrum with an increase in the imposed rotation rate. Recurrence analysis of the structural vibration response demonstrated a transition from periodic to chaotic in a modified recurrence map complementing the appearance of broadband spectra at the onset of bifurcation. Despite considerable changes in flow structure, the vortex phase (φvortex), defined as the phase between the vortex force and the body displacement, follows the same pattern as for the non-Rotating case, with the φvortex increasing gradually from low values in Mode I of the Sphere vibration to almost 180◦ as the system undergoes a continuous transition to Mode II of the Sphere vibration at higher reduced velocity. The total phase (φtotal), defined as the phase between the transverse lift force and the body displacement, only increases from low values after the peak amplitude response in Mode II has been reached. It reaches its maximum value (∼165◦) close to the transition from the Mode II upper plateau to the lower plateau, reminiscent of the behaviour seen for the upper to lower branch transition for cylinder VIV. Hydrogen-bubble visualisations and particle image velocimetry (PIV) performed in the equatorial plane provided further insights into the flow dynamics near the Sphere surface. The mean wake is found to be deflected towards the advancing side of the Sphere, associated with an increase in the Magnus force. For higher rotation ratios, the near-wake rear recirculation zone is absent and the flow is highly vectored from the retreating side to the advancing side, giving rise to large-scale shedding. For a very high rotation ratio of α = 6, for which vibrations are found to be suppressed, a one-sided large-scale shedding pattern is observed, similar to the shear-layer instability one-sided shedding observed previously for a rigidly mounted Rotating Sphere.
Vikas S. Krishnamurthy - One of the best experts on this subject based on the ideXlab platform.
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Stuart-type polar vortices on a Rotating Sphere
Discrete & Continuous Dynamical Systems - A, 2021Co-Authors: Adrian Constantin, Vikas S. Krishnamurthy, Darren Crowdy, Miles H. WheelerAbstract:Stuart vortices are among the few known smooth explicit solutions of the planar Euler equations with a nonlinear vorticity, and they can be adapted to model inviscid flow on the surface of a fixed Sphere. By means of a perturbative approach we show that the method used to investigate Stuart vortices on a fixed Sphere provides insight into the dynamics of the large-scale zonal flows on a Rotating Sphere that model the background flow of polar vortices. Our approach takes advantage of the fact that while a Sphere is spinning around its polar axis, every point on the Sphere has the same angular velocity but its tangential velocity is proportional to the distance from the polar axis of rotation, so that points move fastest at the Equator and slower as we go towards the poles, both of which remain fixed.
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Stuart-type vortices on a Rotating Sphere
Journal of Fluid Mechanics, 2019Co-Authors: Adrian Constantin, Vikas S. KrishnamurthyAbstract:Stuart vortices are among the few known smooth explicit solutions of the planar Euler equations with a nonlinear vorticity, and they have a counterpart for inviscid flow on the surface of a fixed Sphere. By means of a perturbative approach we adapt the method used to investigate Stuart vortices on a fixed Sphere to provide insight into some large-scale shallow-water flows on a Rotating Sphere that model the dynamics of ocean gyres.
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The vorticity equation on a Rotating Sphere and the shallow fluid approximation
Discrete & Continuous Dynamical Systems - A, 2019Co-Authors: Vikas S. KrishnamurthyAbstract:The material conservation of vorticity in fluid flows confined to a thin layer on the surface of a large Rotating Sphere, is a central result of geophysical fluid dynamics. In this paper we revisit the conservation of vorticity in the context of global scale flows on a Rotating Sphere. Starting from the vorticity equation instead of the Euler equation, we examine the kinematical and dynamical assumptions that are necessary to arrive at this result. We argue that, in contrast to the planar case, a two-dimensional velocity field does not lead to a single component vorticity equation on the Sphere. The shallow fluid approximation is then used to argue that only one component of the vorticity equation is significant for global scale flows. Spherical coordinates are employed throughout, and no planar approximation is used.
Anchal Sareen - One of the best experts on this subject based on the ideXlab platform.
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Vortex-induced vibration of a Rotating Sphere
Journal of Fluid Mechanics, 2018Co-Authors: Anchal Sareen, Kerry Hourigan, Jisheng Zhao, David Lo Jacono, John Sheridan, Mark C. ThompsonAbstract:Vortex-induced vibration (VIV) of a Sphere represents one of the most generic fundamental fluid–structure interaction problems. Since vortex-induced vibration can lead to structural failure, numerous studies have focused on understanding the underlying principles of VIV and its suppression. This paper reports on an experimental investigation of the effect of imposed axial rotation on the dynamics of vortex-induced vibration of a Sphere that is free to oscillate in the cross-flow direction, by employing simultaneous displacement and force measurements. The VIV response was investigated over a wide range of reduced velocities (i.e. velocity normalised by the natural frequency of the system): 3 U∗ 18, corresponding to a Reynolds number range of 5000 < Re < 30 000, while the rotation ratio, defined as the ratio between the Sphere surface and inflow speeds, α = |ω|D/(2U), was varied in increments over the range of 0 α 7.5. It is found that the vibration amplitude exhibits a typical inverted bell-shaped variation with reduced velocity, similar to the classic VIV response for a non-Rotating Sphere but without the higher reduced velocity response tail. The vibration amplitude decreases monotonically and gradually as the imposed transverse rotation rate is increased up to α = 6, beyond which the body vibration is significantly reduced. The synchronisation regime, defined as the reduced velocity range where large vibrations close to the natural frequency are observed, also becomes narrower as α is increased, with the peak saturation amplitude observed at progressively lower reduced velocities. In addition, for small rotation rates, the peak amplitude decreases almost linearly with α. The imposed rotation not only reduces vibration amplitudes, but also makes the body vibrations less periodic. The frequency spectra revealed the occurrence of a broadband spectrum with an increase in the imposed rotation rate. Recurrence analysis of the structural vibration response demonstrated a transition from periodic to chaotic in a modified recurrence map complementing the appearance of broadband spectra at the onset of bifurcation. Despite considerable changes in flow structure, the vortex phase (φvortex), defined as the phase between the vortex force and the body displacement, follows the same pattern as for the non-Rotating case, with the φvortex increasing gradually from low values in Mode I of the Sphere vibration to almost 180◦ as the system undergoes a continuous transition to Mode II of the Sphere vibration at higher reduced velocity. The total phase (φtotal), defined as the phase between the transverse lift force and the body displacement, only increases from low values after the peak amplitude response in Mode II has been reached. It reaches its maximum value (∼165◦) close to the transition from the Mode II upper plateau to the lower plateau, reminiscent of the behaviour seen for the upper to lower branch transition for cylinder VIV. Hydrogen-bubble visualisations and particle image velocimetry (PIV) performed in the equatorial plane provided further insights into the flow dynamics near the Sphere surface. The mean wake is found to be deflected towards the advancing side of the Sphere, associated with an increase in the Magnus force. For higher rotation ratios, the near-wake rear recirculation zone is absent and the flow is highly vectored from the retreating side to the advancing side, giving rise to large-scale shedding. For a very high rotation ratio of α = 6, for which vibrations are found to be suppressed, a one-sided large-scale shedding pattern is observed, similar to the shear-layer instability one-sided shedding observed previously for a rigidly mounted Rotating Sphere.
Adrian Constantin - One of the best experts on this subject based on the ideXlab platform.
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Stuart-type polar vortices on a Rotating Sphere
Discrete & Continuous Dynamical Systems - A, 2021Co-Authors: Adrian Constantin, Vikas S. Krishnamurthy, Darren Crowdy, Miles H. WheelerAbstract:Stuart vortices are among the few known smooth explicit solutions of the planar Euler equations with a nonlinear vorticity, and they can be adapted to model inviscid flow on the surface of a fixed Sphere. By means of a perturbative approach we show that the method used to investigate Stuart vortices on a fixed Sphere provides insight into the dynamics of the large-scale zonal flows on a Rotating Sphere that model the background flow of polar vortices. Our approach takes advantage of the fact that while a Sphere is spinning around its polar axis, every point on the Sphere has the same angular velocity but its tangential velocity is proportional to the distance from the polar axis of rotation, so that points move fastest at the Equator and slower as we go towards the poles, both of which remain fixed.
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Stuart-type vortices on a Rotating Sphere
Journal of Fluid Mechanics, 2019Co-Authors: Adrian Constantin, Vikas S. KrishnamurthyAbstract:Stuart vortices are among the few known smooth explicit solutions of the planar Euler equations with a nonlinear vorticity, and they have a counterpart for inviscid flow on the surface of a fixed Sphere. By means of a perturbative approach we adapt the method used to investigate Stuart vortices on a fixed Sphere to provide insight into some large-scale shallow-water flows on a Rotating Sphere that model the dynamics of ocean gyres.
