Showing papers on "Vortex-induced vibration published in 1987"

Flow-Induced Vibration of Circular Cylindrical Structures

Abstract: This report summarizes the flow-induced vibration of circular cylinders in quiescent fluid, axial flow, and crossflow, and applications of the analytical methods and experimental data in design evaluation of various system components consisting of circular cylinders.

A Ring-Vortex Representation of an Axi-Symmetric Vortex Sheet

Abstract: We give a representation of an axi-symmetric vortex sheet by a set of vortex rings with precisely determined self-induced velocities. The representation loses accuracy at points near the axis of symmetry.

Three-in-one vortex shedding flowmeter

Abstract: This invention discloses a three-in-one flowmeter that measures volume flow rate, mass flow rate and the density of the fluid, which flowmeter comprises a vortex generator of an elongated shape having a blunt upstream side disposed across a first cross section of the flow passage, a vortex sensor having the shape of a wing disposed across a second cross section of the flow passage and a transducer converting the alternating lift forces exerted on the vortex sensor by the vortices generated by the vortex generator to an alternating electric signal, wherein the wing sensor is connected to a force receiving member extending from the transducer by a mechanical coupling. The volume flow rate is determined from the frequency of the signals as the fluid velocity is proportional to the frequency at which the vortices are generated by the vortex generator. The mass flow rate is determined by combining the frequency and the amplitude of the signals as the frequency is proportional to the fluid velocity and the amplitude is proportional to the dynamic pressure that is equal to one half of the fluid density times the square of the fluid velocity. The fluid density is obtained as the ratio of the mass flow rate divided by the volume flow rate. The combination of the wing sensor and the transducer includes self-calibrating means for accurately measuring the amplitude of the lift forces generated by the vortices independent of the drift in the characteristics of the transducer.

Stochastically Perturbed Linear Gyroscopic Systems

Abstract: Dynamic stability of linear conservative gyroscopic systems under stochastic parametric excitations of small intensity is examined. Conditions for mean square stability of dynamic response are obtained. Results are shown to depend only on those values of the excitation spectral density near twice the natural frequencies and the combination frequencies of the system. These results are applied to the problem of flow induced vibration in a supported pipe conveying fluid with pulsating velocity. The effects of mean flow velocity and virtual mass on the extent of parametric instability regions are then discussed.

On the Vortex-Induced Oscillation of Long Structural Elements

Abstract: Previous solutions to the vortex-induced vibration of structures have been primarily based on modal analysis, using a one or two-mode approximation. Such an analysis is generally meaningful only when the vortex shedding frequency is locked onto a natural frequency of the structure. In very large structures, typical of those found in some ocean engineering applications, modes are closely spaced, and it is not reasonable to assume total spanwise correlation in the fluid forces or response. The approach used herein avoids the limitations associated with the modal solution of such problems by implementing a solution based on the traveling wave nature of the response. Results presented indicate that the amplitude of response of a long cable is smaller than is predicted by a conventional modal analysis. The drag forces on such a structure may therefore be overestimated by current design approaches.

Vibrations of Circular Cylindrical Structures Subjected to Two-Phase Cross Flows

Abstract: This paper reviews a vibration problem relating to industrial energy equipment such as steam generators, heat exchangers. and condensers. It focuses on unstable vibrations in circular cylindrical structures immersed in two-phase cross flows, which are caused by unsteady fluid forces induced by the interaction between structural vibration and the fluid flow. Added mass and fluid damping induced by a vibrating circular cylinder in a two-phase bubble fluid are introduced, and then the effects of air bubbles on vortex-induced vibrations such as in-line and cross-flow oscillations of a single circular cylinder are reviewed experimentally. Finally, fluidelastic vibrations in a single row of cylinders as well as in cylinder arrays are discussed in relatlon to air bubble effects on instability criteria with respect to reduced velocity and mass-damping parameters.

Two-cylinder model for wind vortex-induced vibration

Abstract: A simple mathematical model for predicting the vortex‐excited resonant response of two cylinders in line with the wind direction is presented. For the model, a modified van der Pol equation is employed to account for the effect of fluctuating lift force on the cylinder, and this equation is coupled with the equation for the oscillatory motion of the cylinder. The governing equations are nonlinear in nature, and the solutions of these equations are assumed to be in the form of sinusoidal functions. Results obtained are in good agreement with the experimental data.

Vortex induced vibrations in sheared flow

Abstract: The paper presents the results of an experimental study on the vortex induced vibration of a flexible cantilevered cylinder in sheared approach flow. The modification of the vibration response due to changes in the stability parameter of the cylinder was investigated. See next Abstract.

Experimental Study on the Vibration of Circular Cylinders Subjected to Cross-flow : Case of Cross-flow Jetted from a Narrow Gap

Abstract: The vibrational phenomena of circular cylinders subjected to a cross-flow which is not uniform, but jetted from a narrow gap, were clarified experimentally in this paper. The simplified test apparatus was used for investigating the flow-induced vibration of circular cylinders. The vibrational behavior was measured by taking the following factors as the test parameters : the number of cylinders, the relative position of the cross-flow jetted from a narrow gap, and the fluid density. As a result, it was found that the vortex shedding vibration phenomena and the fluid elastic vibration phenomena could be observed in circular cylinders subjected to cross-flow jetted form a narrow gap, as well as in the case of uniform cross-flow, and that the particular vibrational phenomena, which were not observed in the uniform flow, existed in the gap flow.

Experimental Study on the Vibration of Circular Cylinders Subjected to Cross-flow : Relation Between Uniform Cross-flow and Gap Cross-flow : Vibration, Control Engineering, Engineering for Industry

Abstract: In this paper, the vibrational phenomena of circular cylinders in both uniform cross-flow and gap cross-flow were studied, and the similarities and the differences between them were clarified experimentally. The experiments were performed by utilizing the same simplified test apparatus employed in the previous report, besides expanding the flow band width of the cross-flow which was exerted on the circular cylinders from the extremely narrow width to the uniform flow width. As a result, it was found that the critical flow velocity for both the vortex shedding vibration and the fluid elastic vibration was almost constant, independent of the flow band width, when evaluated by the equivalent velocity which was calculated by applying the continuity condition and the momentum flux theory for the cross-flow jetted from a narrow gap.

Experimental study on the vibration of circular cylinders subjected to cross-flow. (Case of cross-flow jetted from a narrow gap).

Abstract: The vibrational phenomena of circular cylinders subjected to a cross-flow which is not uniform, but jetted from a narrow gap, were clarified experimentally in this paper. The simplified test apparatus was used for investigating the flow-induced vibration of circular cylinders. The vibrational behavior was measured by taking the following factors as the test parameters : the number of cylinders, the relative position of the cross-flow jetted from a narrow gap, and the fluid density. As a result, it was found that the vortex shedding vibration phenomena and the fluid elastic vibration phenomena could be observed in circular cylinders subjected to cross-flow jetted form a narrow gap, as well as in the case of uniform cross-flow, and that the particular vibrational phenomena, which were not observed in the uniform flow, existed in the gap flow.