The Experts below are selected from a list of 39105 Experts worldwide ranked by ideXlab platform
Suat Canbazoglu - One of the best experts on this subject based on the ideXlab platform.
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performance and flow Induced Vibration characteristics for conical ring turbulators
Applied Energy, 2004Co-Authors: Kenan Yakut, Bayram Sahin, Suat CanbazogluAbstract:In the present study, the performance characteristics of the conical-ring turbulators are determined by means of the entropy-generation minimization method based on the second law and enhancement efficiency based on the first law of thermodynamics. The relations between these performance and flow-Induced Vibration characteristics have been examined. The maximum entropy generation, at the same Reynolds number, occurs in sequence by the conical rings with 10, 20 and 30 mm pitches, respectively. The conical rings are thermodynamically advantageous (Ns,a
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performance and flow Induced Vibration characteristics for conical ring turbulators
Applied Energy, 2004Co-Authors: Kenan Yakut, Bayram Sahin, Suat CanbazogluAbstract:In the present study, the performance characteristics of the conical-ring turbulators are determined by means of the entropy-generation minimization method based on the second law and enhancement efficiency based on the first law of thermodynamics. The relations between these performance and flow-Induced Vibration characteristics have been examined. The maximum entropy generation, at the same Reynolds number, occurs in sequence by the conical rings with 10, 20 and 30 mm pitches, respectively. The conical rings are thermodynamically advantageous (Ns,a<1) up to 8000 Reynolds number with respect to entropy generation. The enhancement efficiency increases as the pitch decreases and varies between 0.86 and 1.16. The turbulators with 20 and 30 mm pitch, especially, produce vortices having low amplitudes up to a Reynolds number of 12,000.
John Sheridan - 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.
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Experimental investigation of flow-Induced Vibration of a rotating circular cylinder
Journal of Fluid Mechanics, 2017Co-Authors: K.w.l. Wong, Mark C. Thompson, Jisheng Zhao, David Lo Jacono, John SheridanAbstract:While flow-Induced Vibration of bluff bodies has been extensively studied over the last half-century, only limited attention has been given to flow-Induced Vibration of elastically mounted rotating cylinders. Since recent low-Reynolds-number numerical work suggests that rotation can enhance or suppress the natural oscillatory response, the former could find applications in energy harvesting and the latter in Vibration control. The present experimental investigation characterises the dynamic response and wake structure of a rotating circular cylinder undergoing vortex-Induced Vibration at a low mass ratio (m∗ = 5.78) over the reduced velocity range leading to strong oscillations. The experiments were conducted in a free-surface water channel with the cylinder vertically mounted and attached to a motor that provided constant rotation. Springs and an air-bearing system allow the cylinder to undertake low-damped transverse oscillations. Under cylinder rotation, the normalised frequency response was found to be comparable to that of a freely vibrating non-rotating cylinder. At reduced velocities consistent with the upper branch of a non-rotating transversely oscillating cylinder, the maximum oscillation amplitude increased with non-dimensional rotation rate up to α ≈ 2. Beyond this, there was a sharp decrease in amplitude. Notably, this critical value corresponds approximately to the rotation rate at which vortex shedding ceases for a non-oscillating rotating cylinder. Remarkably, at α = 2 there was approximately an 80% increase in the peak amplitude response compared to that of a non-rotating cylinder. The observed amplitude response measured over the Reynolds-number range of (1100 Re 6300) is significantly different from numerical predictions and other experimental results recorded at significantly lower Reynolds numbers.
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The interaction between flow-Induced Vibration mechanisms of a square cylinder with varying angles of attack
Journal of Fluid Mechanics, 2012Co-Authors: Andras Nemes, Jisheng Zhao, David Lo Jacono, John SheridanAbstract:This study examines the influence of angle of attack of a square section cylinder on the cylinder's flow-Induced Vibration, where the direction of the Vibration is transverse to the oncoming flow. Our experiments, which traversed the velocity-angle of attack parameter space in considerable breadth and depth, show that a low-mass ratio body can undergo combinations of both vortex-Induced Vibration and galloping. When the body has an angle of attack that makes it symmetric to the flow, such as when it assumes the square or diamond orientation, the two mechanisms remain independent. However, when symmetry is lost we find a mixed mode response with a new branch of vortex-Induced oscillations that exceeds the amplitudes resulting from the two phenomena independently. The oscillations of this higher branch have amplitudes larger than the 'upper branch' of vortex-Induced Vibrations and at half the frequency. For velocities above this resonant region, the frequency splits into two diverging branches. Analysis of the amplitude response reveals that the transition between galloping and vortex-Induced Vibrations occurs over a narrow range of angle of incidence. Despite the rich set of states found in the parameter space the vortex shedding modes remain very similar to those found previously in vortex-Induced Vibration.
Kenan Yakut - One of the best experts on this subject based on the ideXlab platform.
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performance and flow Induced Vibration characteristics for conical ring turbulators
Applied Energy, 2004Co-Authors: Kenan Yakut, Bayram Sahin, Suat CanbazogluAbstract:In the present study, the performance characteristics of the conical-ring turbulators are determined by means of the entropy-generation minimization method based on the second law and enhancement efficiency based on the first law of thermodynamics. The relations between these performance and flow-Induced Vibration characteristics have been examined. The maximum entropy generation, at the same Reynolds number, occurs in sequence by the conical rings with 10, 20 and 30 mm pitches, respectively. The conical rings are thermodynamically advantageous (Ns,a
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performance and flow Induced Vibration characteristics for conical ring turbulators
Applied Energy, 2004Co-Authors: Kenan Yakut, Bayram Sahin, Suat CanbazogluAbstract:In the present study, the performance characteristics of the conical-ring turbulators are determined by means of the entropy-generation minimization method based on the second law and enhancement efficiency based on the first law of thermodynamics. The relations between these performance and flow-Induced Vibration characteristics have been examined. The maximum entropy generation, at the same Reynolds number, occurs in sequence by the conical rings with 10, 20 and 30 mm pitches, respectively. The conical rings are thermodynamically advantageous (Ns,a<1) up to 8000 Reynolds number with respect to entropy generation. The enhancement efficiency increases as the pitch decreases and varies between 0.86 and 1.16. The turbulators with 20 and 30 mm pitch, especially, produce vortices having low amplitudes up to a Reynolds number of 12,000.
Z R Zhou - One of the best experts on this subject based on the ideXlab platform.
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experimental and numerical investigations of the piezoelectric energy harvesting via friction Induced Vibration
Energy Conversion and Management, 2018Co-Authors: D W Wang, Xiaofan Wang, Huajiang Ouyang, Z R ZhouAbstract:Abstract In this work, piezoelectric energy harvesting via friction-Induced Vibration is investigated experimentally and numerically. A test setup which is able to generate friction-Induced Vibration and simultaneously harvest Vibration energy is created. The experimental results verify the feasibility of energy harvesting via friction-Induced Vibration. They suggest that there is a critical driving speed for the friction system to generate strongest friction-Induced Vibration and output highest voltage; a larger normal load is beneficial for producing stronger Vibration and outputting higher voltage; the external electric resistance has little effect on the Vibration of the friction system, instead it will modify the output voltage amplitude within limits. To further understand the experimental findings, both the complex eigenvalue analysis and implicit dynamic analysis are performed in ABAQUS. The complex eigenvalue analysis further confirms the feasibility of energy harvesting by means of friction-Induced Vibration, and shows that the Vibration in both tangential and normal directions can be harvested. The implicit dynamic analysis verifies the effect of driving speed and normal load on the system dynamics and harvested energy. Accordingly, a two-degree-of-freedom friction system model is proposed to qualitatively characterise the effect of external electric resistance on the system dynamics and harvested energy. This investigation offers quite a new way of harvesting Vibration energy.
Marwan Hassan - One of the best experts on this subject based on the ideXlab platform.
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Two-phase flow Induced Vibration of piping structure with flow restricting orifices
International Journal of Multiphase Flow, 2019Co-Authors: Olufemi E. Bamidele, Wael H. Ahmed, Marwan HassanAbstract:Abstract In this paper, two-phase flow-Induced Vibration in a horizontal piping structure with flow restricting orifices has been experimentally investigated. The effect of flow patterns, void fraction, mass quality and orifice area ratio on Vibration response is evaluated in detail. The two-phase flow measurements and Vibration signals were analyzed simultaneously in order to understand the effect of two-phase flow behaviour on the governing factors responsible for flow-Induced Vibration mechanisms. The results show that the dynamic Vibration response of the structure increased with the increase in the liquid mass flux and upstream void fraction in the case of intermittent flow patterns. The flow pattern change across the orifice is found to strongly affect the magnitude of the resulting Vibrations. The maximum response was found in the region where a transition to slug flow occurred. Also, the RMS amplitude of Vibration increased with an increase in the gas flux for both stratified and annular flows. Flow pattern maps were therefore created for both horizontal and vertical dynamic responses. These maps can be used in evaluating the dynamic response of piping structures with flow restrictions which are commonly found in the power generation industry. This will allow for a better design and safe operation of systems suffering from multiphase flow-Induced Vibration.