Showing papers on "Vortex-induced vibration published in 1991"

Coriolis-effect in mass flow metering

Abstract: The paper aims at a detailed description of the physical background, for the so-called Coriolis mass flow meter. It presents essentially an analysis of the (free) vibration modes of a fluid conveying straight pipe segment. Due to the inertial effects of the flowing fluid, mainly the Coriolis force, these modes deviate in shape (and in frequency) from those appearing in the absence of fluid motion. The effect of fluid inertia may, therefore, be exploited for the purpose of flow measurement. The analysis is performed under a simplifying approximation: The pipe is considered as a beam, the fluid as a moving string. This approximation leaves the fluid with only one degree of freedom, connected with its mean velocity, and eliminates an infinity of degrees of freedom of the pipe. Yet it keeps, the essential features of the phenomenon. The equations describing the vibrations are derived variationally, with the constraint of a common vibration amplitude of both fluid and pipe. The Lagrange multiplier associated with the constraint gives the interaction force between pipe and fluid. The modes are determined by a perturbation procedure, wherein the small (perturbation) parameter is related to the fluid velocity. The analysis shows, as main result, how the time delay between the vibrations of two appropriately chosen points of the pipe may serve to determine the mass flow rate of the fluid. Other aspects of the problem, like the precise role of the Coriolis force, are considered. The possible improvement of the used approximation is discussed.

Vortex-Induced Vibration of Flexible Cylinders Having Different Mass Ratios

Abstract: A series of experiments were performed to see the dependence of the response characteristics of vortex-induced vibration of flexible cylinders on mass rations for marine applications. Experiments were conducted in the test section of the cavitation tunnel at the Korea Research Institute of Ships and Ocean Engineering using 5 test rods of 60cm length and 6mm diameter with different mass ratios. It was confirmed quantitatively from the experiments that the low mass ratio cylinders have much broader flow velocity range of large amplitude vibrations than high mass ratio ones.

Effects of Secondary Injection on the Cross Flow Induced Vibration of a Single Cylinder

Abstract: This paper represents an experimental investigation on the effect of a secondary injection in the vicinity of an elastically mounted smooth cylinder, on the flow induced vibration of such cylinder with the possibilities of using such injection for controlling the flow induced vibration. It was found that the effect is very much dependent on the blowing rate (ρiUi/ρU), the location of injection downstream, the cylinder and the range of reduced velocities in question. The results obtained suggest that at certain combination of injection velocities, location of injection downstream and reduced velocity, the dimensionless amplitude of vibration can be reduced by as much as 50%. However, there seems to be other blowing rates, i.e. blowing rates greater than 1, which may lead to an increase in the vibration amplitude of the cylinder. The results of this investigation show that secondary flow, if properly used, can be utilized as an effective means for controlling practical flow induced vibration.

Application Of A General Prediction Method For Vortex Induced Vibrations Of Catenary Risers

Abstract: This paper presents the application of a general vortex induced vibration model for catenary flexible risers. A time domain simulation is performed using a modal analysis approach. The numerical calculation procedure allows fluid and structural non-uniformities in time as well as in space. Two realistic configurations are considered, a Lazy-S in 350m water depth and a Lazy-wave in 110m water depth. Wave only and current only flows in and normal to the riser plane are investigated. The effects of physical parameters of the risers and flows are demonstrated as leading to very low amplitudes of vibration in service environments. The reasons for this are explained.

Experimental studies on shedding vortex frequency of a circular cylinder in a pulsating flow.

Abstract: Vortex shedding frequency was measured in the downstream of a circular cylinder in a pulsating flow. A hot-wire anemometer was used for the velocity measurement. The Strouhal number was calculated based on the measured shedding frequency. The constancy of the Strouhal number was also retained in the pulsating flow, though the Strouhal number itself was substantially higher than that in the steady flow.

Analysis of flow on cones and cylinders using discrete vortex methods

Abstract: Discrete vortex methods have been developed to investigate the vortex flows on cones and two-dimensional cylinders. The cone problem was solved by assuming that, to meet conical flow and zero-force conditions, the vortices move radially away from the body at a given cross-section. The two-dimensional cylinder problem was solved by limiting the velocity along the zero streamline surrounding the vortex field to two times freestream velocity and by limiting the lateral movement of the vortices. Variations in vortex position and strength with time were determined by taking into account the rate at which circulation is generated at separation points on the body. The calculated vortex positions and strengths were in good agreement with available experimental data. Viscous effects could be accounted for by adding empirically determined damping terms to the velocity equations. The models indicate that different types of asymmetry occur for the cone and two-dimensional cylinder. Asymmetry onset boundaries determined by the discrete vortex method show the same trend as experiment.

Flow Transition in a Symmetric Sinusoidal Wavy-walled Channel for Oscillatory Flow

Abstract: Oscillatory flow is examined experimentally in a two-dimensional furrowed channel. We show the transition of two-dimensional to three-dimensional flow due to instability of the flow at moderate Reynolds numbers. The critical value of the Reynolds number at the onset of three-dimensional flow strongly depends on the Strouhal number. The fluid motion is found to be most unstable in the limited Strouhal number range of 0.02 to 0.03. Two distinct three-dimensional flows are discovered and their boundary is determined only by the Strouhal number, i. e. St≒0.02.

Vortex-Induced Vibration of Flexible Cylinders Having Different Mass Ratios

Abstract: A series of experiments were performed to see the dependence of the response characteristics of vortex-induced vibration of flexible cylinders on mass rations for marine applications Experiments were conducted in the test section of the cavitation tunnel at the Korea Research Institute of Ships and Ocean Engineering using 5 test rods of 60cm length and 6mm diameter with different mass ratios It was confirmed quantitatively from the experiments that the low mass ratio cylinders have much broader flow velocity range of large amplitude vibrations than high mass ratio ones

シェル形長径間ゲートの流体関連振動 : 第2報, アンダーフロータイプの基本的な自励振動特性に関する検討

Abstract: This study examines the fundamental characteristics for a flow-induced vibration of shell-type long-span gates which have a gate front consisted of vertical and inclined weir plates. The shell-type gates possess two freedoms to vibrate in the streamwise and vertical directions due to their bending flexibility. Both streamwise and vertical vibrations couple well each other through hydrodynamical forces acting on the weir plates, thus resulting in a severe self-excited vibration. A two-dimensional model test for a shell-type long-span gate under small gate-openings was performed and a previous study reported the experimental results in detail. Here, the obtained results for the vibration frequency, the added mass of water and the dynamic press-shut gate trajectories are carefully studied. Moreover, the self-excited vibration mechanism is studied and the self-excited vibration possibility of Shell-type long-span gates under practical uses is examined. Finally a design criterion for dynamic stability is presented.

Experimental study on flow induced vibration criteria of gates through forced oscillation of model with submerged outlet flow

Abstract: ゲートの自励振動発生限界の把握を目的として, 模型ゲートをモータとクランクで強制的に加振し, ゲートに取りつけた圧力センサーにより, ゲートが振動状態にあるときの流体力を計測した. 流体力は自励振動発生域ではゲートの変位よりも進み位相で出現し, 制振域では遅れ位相で出現する状況が明確に捉えられ, この実験法の有効性を示すことができた. この方法は, 流体力の正・負減衰作用の定量評価にも供し得る.

Instability of multi-layer fluid configurations in the presence of time-dependent accelerations in a microgravity environment

Abstract: The increasing number of research opportunities in a microgravity environment will benefit not only fundamental studies in fluid dynamics, but also technological applications such as those involving materials processing. In particular, fluid configurations which involve fluid-fluid interfaces would occur in a variety of experimental investigations. This work investigates the stability of a configuration involving fluid-fluid interfaces in the presence of a time-dependent forcing. Both periodic (g-jitter) and nonperiodic accelerations are considered. The fluid configuration is multilayered, and infinite in extent. The analysis is linear and inviscid, and the acceleration vector is oriented perpendicular to each interface. A Floquet analysis is employed in the case of the periodic forcing. In the problem of nonperiodic forcing, the resulting system of equations are integrated in time. Specific nondimensional parameters appear in each problem. The configuration behavior is investigated for a range of parameter values.

On Flow-Induced Vibration of a Circular Cylinder Placed near a Plane Boundary

Abstract: Experimental investigations were carried out to examine the flow features around an elastically supported circular cylinder placed near a plane boundary in a uniform stream and the associated flow-excited vibrations. The experiment was conducted in a recirculating water channel. The undisturbed uniform cross stream is parallel to the plane boundary and normal to the axis of the cylinder. The flow field was visualized using hydrogen bubble technique. Time sequential photography was used to quantify the development of the vortex pattern and the vibrational characteristics of the cylinder.