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Flow-Induced Vibration of Small Cylinders in the Shear Flow of a 2D JetHsin, Antai 13 August 2004 (has links)
Flow-induced vibration of small elastic cylinders mounted in the shear flow of a two-dimensional jet is investigated experimentally. There has been a great deal of work concerned with different vibrating conditions and practical dynamic responses by way of mass ratios and diameters of various different cylinders. In such cases, the amplitude of the cylinder oscillation changed along with the variation of the jet velocity is due to the influence of fluid elastic instability. The experiment is based on the method of the magnetic field induction to measure the motion of the small cylinder, and it involves measurements of the varying velocity in a jet through the hot- wire anemometer. The critical velocity of the cylinder vibration in the shear flow with different diameters, mass ratios and damping factors are examined. Moreover, the oscillation traces of the cylinder by fluid elastic instability were observed when the jet velocity was increased, and then decreased for examination of hysteresis phenomena. The results show that the bifurcation of the cylinder vibration traces is remarkable especially for cylinders with high mass ratios. By the amplitude diagrams of the cylinder vibration, the critical velocity for onset of fluid elastic vibration was determined. The dependence of the critical velocity and hysteresis phenomena on the mass ratio and damping factor are discussed.
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noneChen, Kuei-Hsiung 30 July 2001 (has links)
none
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FLOW-INDUCED VIBRATION OF CARBON NANOTUBESSlisik, Jeffrey A. 05 October 2006 (has links)
No description available.
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Two-dimensional Wakes and Fluid-structure Interaction of Circular Cylinders in Cross-flowYang, Wenchao 16 October 2018 (has links)
The wake of a bluff body is a representative issue in vortex dynamics that plays a central role in civil engineering, ocean engineering and thermal engineering. In this work, a flowing soap film was used to investigate the wakes of multiple stationary circular cylinders and of a single oscillating cylinder. Corresponding computer simulations were also conducted. Vortex formation of a stationary circular cylinder was analyzed by proper orthogonal decomposition (POD). The POD analysis was used to define an unsteady vortex formation length, which suggests a relationship between the vortex formation length of a single cylinder and the critical spacing of two cylinders in a tandem arrangement. A systematic parametric study of the wake structure was conducted for a controlled transversely oscillating cylinder. Neural network and support vector machine codes assisted the wake classification procedure and the identification of boundaries between different wake regimes. The phase map of the vortex shedding regimes for the (quasi) two-dimensional experiment qualitatively agrees with previous three-dimensional experiments. The critical spacings of two identical tandem circular cylinders in a flowing soap film system were determined using visual inspections of the wake patterns and calculations of the Strouhal frequencies. The dimensionless spacing was both increased and decreased quasi-statically. Hysteresis was observed in the flow patterns and Strouhal numbers. This study appears to provide the first experimental evidence of critical spacing values that agree with published computational results. The wake interaction between a stationary upstream circular disk and a free downstream circular disk was also investigated. With the ability to tie together the wake structure and the object motion, the relationship between energy generation and flow structure in the simplified reduced order model system was studied. The research results find the optimal efficiency of the energy harvesting system by a parametric study. / PHD / The wake of a bluff body is a classic issue in vortex dynamics that has been the subject of much research in civil engineering, ocean engineering and thermal engineering. Bluff bodies, especially circular cylinders, can be found extensively in heat exchangers, cooling systems and offshore structures. Flow-induced vibration of a bluff body due to the formation of a wake is an important problem in many fields of engineering. Flow-induced vibration determines the oscillation of flexible pipes that transfer oil from the seabed to the surface of the ocean, for example [71]. In civil engineering, flow-induced vibration affects the design of bluff structures in wind such as bridges, chimneys and buildings [62]. Flow-induced vibration caused by vortices being shed from a bluff body is also a promising way to extract energy from geophysical flows [10]. FIV energy harvesting systems are especially suitable for slow flow speeds in the range 0.5-1.5m/s which cannot be efficiently harvested by traditional hydroelectric power technologies. When a pair of tandem cylinders is immersed in a flow, the downstream cylinder can be excited into wake-induced vibrations (WIV) due to the interaction with vortices coming from the upstream cylinder.
In this work, a flowing soap film was used to investigate the flow-induced vibration of the downstream cylinder of a tandem pair. With the ability to tie together the wake structure and the object motion, we investigate the relationship between energy generation and flow structure in the reduced order model system. The research results find the optimal efficiency of the energy harvesting system by a parametric study. To get deep physical understanding of the flow-induced vibration, wake structures of a circular cylinder undergoing controlled motion and the critical spacing of two identical tandem circular cylinders were also investigated in this research. These research results can help not only the optimization of energy harvesting systems based on flow-induced vibration of the circular-cylinder system, but also will benefit the understanding of wake interactions between multiple bluff bodies such as schooling fish, natural draft cooling towers and wind turbine farms.
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Stochastic Stability of Flow-Induced VibrationZhu, Jinyu January 2008 (has links)
Flow-induced structural vibration is experienced in many engineering applications, such as aerospace industry and civil engineering infrastructures. One of the main mechanisms of
flow-induced vibration is instability which can be triggered by parametric excitations or
fluid-elastic forces. Experiments show that turbulence has a significant impact on the
stability of structures. The objective of this research is to bridge the gap between
flow-induced vibration and stochastic stability of structures.
The flow-induced vibration of a spring-supported circular cylinder is studied
in this research. The equations of motion for the
cylinder placed in a cross-flow are set up, in which the vortex force is modeled by a
bounded noise because of its narrow-band characteristics.
Since the vibration in the lift direction is more prominent in the lock-in region,
the system is reduced to one degree-of-freedom, i.e., only the vibration of
the cylinder in the lift direction is considered. The equation of motion for the
cylinder can be generalized as a two-dimensional system excited by a bounded noise.
Stochastic analysis is used
to determine the moment Lyapunov exponents and Lyapunov exponents for the generalized
system. The results are then applied to study the parametric instability of a cylinder in
the lock-in region.
Fluidelastic instability can occur when the cylinder is placed in a shear flow. The
equations of motion are established by using the quasi-steady theory to model the
fluid-elastic forces. To study the turbulence effect on the stability of the cylinder,
a real noise or an Ornstein-Uhlenbeck process is used to model the grid-generated
turbulence. The
equations of motion are randomized resulting in a four-dimensional system excited by a
real noise. The stability of the stochastic system is studied by determining the
moment Lyapunov exponents and Lyapunov exponents. Parameters of the system and the noise
are varied to investigate their effects on the stability. It is found that
the grid-generated turbulence can stabilize the system when the parameters take
certain values, which agrees with the experimental observations.
Many flow-induced vibration problems can be modeled by a two degrees-of-freedom system
parametically excited by a narrow-band process modeled by a bounded noise. The
system can be in subharmonic resonance, combination (additive or differential) resonance,
or both if the central frequency of the bounded noise takes an appropriate value.
The method for a single degree-of-freedom system
is extended to study the stochastic stability of the two degrees-of-freedom system. The
moment Lyapunov exponents and Lyapunov exponents for the three cases are obtained using
a perturbation method. The effect of noise on various types of parametric resonance,
such as subharmonic resonance, combination additive resonance, and combined
subharmonic and combination additive resonance, is investigated.
The main contributions of this thesis are stochastic stability analysis of
one-degree-of-freedom systems and two-degree-of-freedom systems.
Stability analysis for systems under the excitation of real noise and bounded noise
is carried out by determining the moment Lyapunov exponents and Lyapunov exponents.
Good agreement is obtained between analytical results and those obtained from Monte Carlo simulations.
In the two degrees-of-freedom case,
the effect of free stream turbulence on cylinder vibration and its stability is examined.
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Stochastic Stability of Flow-Induced VibrationZhu, Jinyu January 2008 (has links)
Flow-induced structural vibration is experienced in many engineering applications, such as aerospace industry and civil engineering infrastructures. One of the main mechanisms of
flow-induced vibration is instability which can be triggered by parametric excitations or
fluid-elastic forces. Experiments show that turbulence has a significant impact on the
stability of structures. The objective of this research is to bridge the gap between
flow-induced vibration and stochastic stability of structures.
The flow-induced vibration of a spring-supported circular cylinder is studied
in this research. The equations of motion for the
cylinder placed in a cross-flow are set up, in which the vortex force is modeled by a
bounded noise because of its narrow-band characteristics.
Since the vibration in the lift direction is more prominent in the lock-in region,
the system is reduced to one degree-of-freedom, i.e., only the vibration of
the cylinder in the lift direction is considered. The equation of motion for the
cylinder can be generalized as a two-dimensional system excited by a bounded noise.
Stochastic analysis is used
to determine the moment Lyapunov exponents and Lyapunov exponents for the generalized
system. The results are then applied to study the parametric instability of a cylinder in
the lock-in region.
Fluidelastic instability can occur when the cylinder is placed in a shear flow. The
equations of motion are established by using the quasi-steady theory to model the
fluid-elastic forces. To study the turbulence effect on the stability of the cylinder,
a real noise or an Ornstein-Uhlenbeck process is used to model the grid-generated
turbulence. The
equations of motion are randomized resulting in a four-dimensional system excited by a
real noise. The stability of the stochastic system is studied by determining the
moment Lyapunov exponents and Lyapunov exponents. Parameters of the system and the noise
are varied to investigate their effects on the stability. It is found that
the grid-generated turbulence can stabilize the system when the parameters take
certain values, which agrees with the experimental observations.
Many flow-induced vibration problems can be modeled by a two degrees-of-freedom system
parametically excited by a narrow-band process modeled by a bounded noise. The
system can be in subharmonic resonance, combination (additive or differential) resonance,
or both if the central frequency of the bounded noise takes an appropriate value.
The method for a single degree-of-freedom system
is extended to study the stochastic stability of the two degrees-of-freedom system. The
moment Lyapunov exponents and Lyapunov exponents for the three cases are obtained using
a perturbation method. The effect of noise on various types of parametric resonance,
such as subharmonic resonance, combination additive resonance, and combined
subharmonic and combination additive resonance, is investigated.
The main contributions of this thesis are stochastic stability analysis of
one-degree-of-freedom systems and two-degree-of-freedom systems.
Stability analysis for systems under the excitation of real noise and bounded noise
is carried out by determining the moment Lyapunov exponents and Lyapunov exponents.
Good agreement is obtained between analytical results and those obtained from Monte Carlo simulations.
In the two degrees-of-freedom case,
the effect of free stream turbulence on cylinder vibration and its stability is examined.
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Fluid-elastic vibration of a circular cylinder in the shear flow of an air jetYang, Chao-cong 11 September 2007 (has links)
In the study, vibrations of small elastic cylinders mounted in the shear flow of an air jet are investigated experimentally. In such cases, the amplitude of the cylinder oscillation changed along with the variation of the jet velocity gradient is due to the influence of fluid elastic instability. The experiment is based on the method of the magnetic field induction to measure the motion of the small cylinder, and it involves measurements of the varying velocity in a jet through the hot- wire anemometer. We focus on the fluid-elastic instability of a circular cylinder in shear flow. The vibration behaviors of the cylinder above the critical condition are be examined with different velocity gradients, mass ratios and damping factors. The vibration amplitude of the cylinder is also larger as velocity gradient is larger. With lower mass ratios and damping factor, moreover, the orbit of cylinder is larger. When the velocity gradient is increasing, the frequency of cylinder vibration becomes higher.
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Simulation of single circular cylinder in shear flowHsu, Jui-chen 12 August 2008 (has links)
The present study aims to explore dynamical behavior of the fluid-elastic instability of a circular cylinder in shear flow by numerical simulations. The theoretical model comprises two groups of transient conservation equations of mass and momentum and the governing equations are solved numerically with Fluent software to determine the flow property. The analysis presented that there exist both vortex-induced vibration and flow-elastic vibration for single cylinder in sear flow. The numerical results with a Harmonic Model built from Gambit indicate that there is a transverse force acting from high velocity side toward the low velocity side in shear flow. The transverse force make cylinder move periodically and thus go to a vibration. Furthermore, this study appraises the amplitude and orbit of fluid elastic vibration of a circular cylinder in shear flow and shows the effects of the shear velocity slope and damping factor on fluid elastic vibration of the cylinder.
Here in the thesis, as the function applied with Fluent of displaying dynamic mesh on-time, the movement and re-mesh of cylinder could be observed. A vibration expansion diagram was presented and the pictures of flow velocity and flow pressure were retrieved from Fluent.
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Wet Electrostatic Precipitator, Increasing the Efficiency of Collecting Dust Particlesthrough Vibrating Precipitator AnalysisLutfullaeva, Anbara 02 June 2020 (has links)
No description available.
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非対称分布声帯モデルによる疾患時の発声の数値解析 (第2報, 非対称な声帯振動の数値シミュレーション解析)青松, 達哉, AOMATSU, Tatsuya, 松崎, 雄嗣, MATSUZAKI, Yuji, 池田, 忠繁, IKEDA, Tadashige 03 1900 (has links)
No description available.
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