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The response of an oscillating circular cylinder at the wake of an upstream fixed circular cylinder was classified by different researchers as galloping, wake induced galloping or wake induced vibration. Furthermore it is already ...
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The response of an oscillating circular cylinder at the wake of an upstream fixed circular cylinder was classified by different researchers as galloping, wake induced galloping or wake induced vibration. Furthermore it is already known that a sharp edge square cylinder would undergo galloping if it is subjected to uniform flow. In this study the influence of the wake of a fixed circular cylinder on the response of a downstream square cylinder at different spacing ratios (S/D=4, 8, 11) is experimentally investigated. The subject appears not to have received previous attention. The lateral displacements, lift forces and the pressure data from gauges mounted in the wake of the oscillating cylinder are recorded and analyzed. The single degree of freedom vibrating system has a low mass-damping parameter and the Reynolds number ranges from 7.7 x 10(2) to 3.7 x 10(4).
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To date, it has been shown that the vibration response of an elastically mounted sphere undergoing vortex-induced vibration (VIV) can be controlled by imposing rotary oscillations at frequencies close to the vibration frequency. H...
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To date, it has been shown that the vibration response of an elastically mounted sphere undergoing vortex-induced vibration (VIV) can be controlled by imposing rotary oscillations at frequencies close to the vibration frequency. Here, we demonstrate that rotary oscillations imposed at significantly higher frequencies can be used to directly influence shear-layer vortex shedding and consequently reduce vibration. This approach contrasts with aiming to directly target the large-scale wake structures, using lower frequency perturbations. The oscillation frequencies imposed were between 5 and 35 times the natural frequency of the system and the amplitude of the rotational velocities were only 10% of the free-stream velocity. The effects of the rotary oscillations were found to vary significantly across sphere vibration modes. In the mode III transition regime significant attenuation of the vibration response was observed for a narrow band of rotary oscillation frequencies. Time-resolved particle image velocimetry revealed that the shear-layer vortex structures locked to the forcing frequency, where suppression of the vibration response occurred. Optimal tuning of the oscillation frequency reduced the vibration amplitude in the mode III transition regime by 84%, with a rotational velocity amplitude of only 10% of freestream. These results show low-amplitude shear-layer forcing is a promising method of more efficiently suppressing VIV of three-dimensional geometries. (C) 2021 Elsevier Ltd. All rights reserved.
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Flow around two cylinders with different diameters undergoing Flow-Induced Vibrations (FIV) in the subcritical flow regime is investigated using two-dimensional Unsteady Reynolds Averaged Navier-Stokes (URANS) approach. Physical p...
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Flow around two cylinders with different diameters undergoing Flow-Induced Vibrations (FIV) in the subcritical flow regime is investigated using two-dimensional Unsteady Reynolds Averaged Navier-Stokes (URANS) approach. Physical parameters of the system are chosen to represent the free spanning pipelines laid in proximity. The two cylinders are initially placed at various tandem and staggered positions with one in the wake of the other, and subject to steady current flows. The two cylinders are free to respond in both in-line and transverse directions. The investigated Reynolds numbers (Re) are Re-1 = 1.4 x 10(5) based on the diameter of the larger cylinder and Re-2 = 1.15 x 10(5) based on the diameter of the smaller cylinder. A parametric study investigating the effects of relative spacing of the cylinders on the vibration response of the system is performed. First and second order statistics of the flow, frequency domain analysis and flow field visualizations are used to characterize the dynamic behavior of the system. It is found that the motion trajectories of the downstream cylinder show a qualitative difference depending upon whether it is in tandem with the upstream cylinder or in the wake with a transverse offset. A large amplification of the in-line response is observed in the positions with a transverse offset. The vibration response of the upstream cylinder is affected by the presence of the downstream cylinder only when the horizontal center-to-center distance is small (L/D-1 = 2.06 where D-1 is the diameter of the larger cylinder) and is largely unaffected when the horizontal distance is increased to L/D-1 = 3.22.
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A two-dimensional numerical investigation of the flow-induced vibration of a circular cylinder held free to oscillate transverse to the free-stream direction has been performed. The simulations were performed over a Reynolds numbe...
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A two-dimensional numerical investigation of the flow-induced vibration of a circular cylinder held free to oscillate transverse to the free-stream direction has been performed. The simulations were performed over a Reynolds number range Re=[30,200] and for an infinite reduced velocity. Two regions of high amplitude oscillations are observed and are referred to as the viscous and higher Reynolds number range, respectively. The viscous range was observed for Re=[40,95] and the higher Reynolds number range was observed above Re=180. A critical mass ratio, below which appreciable amplitude oscillations are observed, is determined as a function of Reynolds number. For Reynolds numbers between the two ranges, only very small oscillations were observed for all mass ratios investigated. (C) 2005 American Institute of Physics.
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The objective of this paper is to numerically investigate the unsteady cavitating flow around a four-blade inducer, with focus on the cavitation instability and the flow-induced vibration characteristics. In the numerical simulati...
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The objective of this paper is to numerically investigate the unsteady cavitating flow around a four-blade inducer, with focus on the cavitation instability and the flow-induced vibration characteristics. In the numerical simulation, the modified rotation/curvature correction turbulence model and the Zwart cavitation model are used for the simulation of the flow field. The tightly coupled algorithm is adopted for the precise prediction of the fluid-structure interaction, including the calculation of the hydrodynamic loads based on the multiphase fluid dynamics and the computation of the structural displacement via the Finite Element Method (FEM). The results showed that good agreement has been obtained between the experimental and numerical results. The fluctuation of cavity volume is the main cause of the change in the head of the inducer, and the backflow vortex cavitation has little effect on that at this flow condition. The backflow vortex cavity develops and rotates with the blades of the inducer, but with a much lower rotational velocity than that of the blades. The flow-induced vibration of the inducer caused by the unsteady cavitating flow mainly manifests as a first-order bending mode. The backflow vortex cavitation has a significant impact on the vibration of both the blades and the guide-water cone. Besides, a cavitation auto-oscillation at the inlet of the inducer has also been detected based on the phase correlation analysis.
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A number of occurrences of flow-induced vibration in the power-generating industry are presented, many in nuclear plant where all incidents/problems have to be reported. Specifically, cases of (i) vortex-induced vibration (VIV), (...
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A number of occurrences of flow-induced vibration in the power-generating industry are presented, many in nuclear plant where all incidents/problems have to be reported. Specifically, cases of (i) vortex-induced vibration (VIV), (ii) fluidelastic instability in cylinder arrays, (iii) axial and (iv) annular-flow-induced vibration, (v) leakage-flow instability and (vi) shell-type ovalling are discussed. For items (ii), (v) and (vi), a few words on the mechanisms underlying the vibration are provided.
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Flow-induced resonance of a hinged bronze cable (length/diameter = 100) in uniform water flow at Reynolds number of Re{sub}D = 200 is simulated using a fluid-structure interaction code. At the periodically steady state, the cable ...
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Flow-induced resonance of a hinged bronze cable (length/diameter = 100) in uniform water flow at Reynolds number of Re{sub}D = 200 is simulated using a fluid-structure interaction code. At the periodically steady state, the cable vibrates as a standing wave at its resdnance frequency due to vortex shedding. It is found that, despite the higher streamwise fluid force, the amplitude of the cross-flow displacement is much higher than that of the streamwise displacement. This phenomenon is not observed at other states without resonance. The result is that the energy transfer from fluid to solid is maximized in the cross-flow direction.
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This paper presents high-fidelity simulations of the vortex induced vibration (VIV) phenomena using a new computational model based on the high-order spectral difference (SD) method on 2D and 3D unstructured grids. The SD method c...
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This paper presents high-fidelity simulations of the vortex induced vibration (VIV) phenomena using a new computational model based on the high-order spectral difference (SD) method on 2D and 3D unstructured grids. The SD method constructs continuous fields within each cell with a Riemann solver to compute the inviscid fluxes at the cell interfaces and an averaging mechanism to compute the viscous fluxes. This method has shown promise in the past as a highly accurate, yet sufficiently fast method for solving unsteady viscous compressible flows on moving and deforming grids. A 4th-order, 5-stage Runge-Kutta scheme is used to advance time. In this viscous, compressible flow solver the displacement of an elastically mounted bluff body has been coupled to the lift force created by unsteady vortex shedding. The solver is validated against previously published numerical and experimental data for a single, elastically mounted cylinder. Preliminary studies into 2 cylinder wake galloping and determining the energy transfer coefficient have been performed and comparisons between 2D and 3D predictions have been made.
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Flows past rows of elastically mounted cylinders display a number of flow-induced vibration phenomena that hitherto have proven difficult to categorise in a way that is independent of the number of cylinders in the row. Here, we i...
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Flows past rows of elastically mounted cylinders display a number of flow-induced vibration phenomena that hitherto have proven difficult to categorise in a way that is independent of the number of cylinders in the row. Here, we investigate the flow past six equispaced but independent elastically-mounted cylinders at Reynolds number Re = 200 using direct numerical simulations over a wide range of stiffnesses and for three values of the inter-cylinder spacing or pitch p. We make a first attempt at categorising the responses observed in terms of the framework of flow states linked to convective instabilities in rows of rigidly mounted cylinders recently presented in Hosseini, Griffith and Leontini (2020). We show that regardless of pitch, this framework has some success in explaining and collating the flow-induced vibration response for high to moderate stiffnesses (corresponding to low to moderate reduced velocities U*). Among others, one phenomenon observed that fits this framework is the fact that for some cases, the first and last cylinders in an array can vibrate, while the rest are almost stationary. However, at low stiffness/high U*, the arrays behave more like a single flexible structure that exhibits waves, which is an inherent fluid-structure mode with no root in the rigidly mounted case.
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Arterial stenosis is a vascular pathology which leads to serious cardiovascular diseases. Blood flow through a constriction generates sound and vibration due to fluctuating turbulent pressures. Generated vibro-acoustic waves propa...
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Arterial stenosis is a vascular pathology which leads to serious cardiovascular diseases. Blood flow through a constriction generates sound and vibration due to fluctuating turbulent pressures. Generated vibro-acoustic waves propagate through surrounding soft tissues and reach the skin surface and may provide valuable insight for noninvasive diagnostic purposes. Motivated by the aforementioned phenomena, vibration of constricted arteries is investigated employing computational models. The flow-induced pressure field in an artery is modeled as broadband harmonic pressure loading based on previous studies in the literature and applied on the inner artery wall. Harmonic analysis is performed for determining radial velocity responses on the outer surface of the models. Results indicate that stenosis severities higher than 70% lead to significant increase in response amplitudes, especially at high frequencies between 250 and 600Hz. The findings agree well with experimental and theoretical results in the literature considering bending mode frequencies, amplitude scales, and mainly excited frequency ranges. It is seen that artery vibration is sensitive to the phase behavior of pressure loading but its effect becomes less significant with the presence of surrounding tissue. As the surrounding tissue thickness increases, radial velocity response amplitudes decrease but the effect of changes in tissue elastic modulus is more pronounced.
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