Hybrid Method using CFD and Analytical Solutions for Evaluation of Fluid Elastic Vibration of Cylinder Arrays

Flow-induced vibrations occur in general heat exchangers and nuclear reactors. They cause the tube failures through fretting wear or fatigue. Fluid elastic instability may lead to vibration amplitudes large enough to cause tube-to-tube clashing and in such cases will lead to relatively rapid failures. Therefore mechanisms of elastic vibration induced by cross flow are significant problems for large vibration amplitudes. The aims of this study are to analyze the vibration of cylinders at various flow velocities and to get the fundamental data of design for the prevention of accidents in heat exchanger. In this study, the experimental apparatus was built so that cylinder tip motions could be measured at various flow velocities. The experiments were conducted in different cylinder arrays. The cylinder vibration was induced in normal direction to flow by an alternate vortex. Moreover, once the flow velocity was increased to a certain value, the cylinder oscillation amplitude increased rapidly with flow and had a maximum. When five cylinders were arranged in a row normal to flow, the wandering of energy was generated between the two cylinders. For three cylinders arranged in tandem, two cylinders in upstream and downstream positions mutually vibrated out of phase. For many cylinders, the entropy had the maximum at a specific flow velocity and oscillating behavior of cylinders became chaotic state which could not predict its behavior.

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Research on Fluid Elastic Vibration of Cylinder Arrays by Computational Fluid Dynamics. (Analysis of Two Cylinders and a Cylinder Row)

JSME International Journal Series B ◽

10.1299/jsmeb.40.16 ◽

1997 ◽

Vol 40 (1) ◽

pp. 16-24 ◽

Cited By ~ 14

Author(s):

Takehiko ICHIOKA ◽

Yutaka KAWATA ◽

Tomomichi NAKAMURA ◽

Hajime IZUMI ◽

Toshio KOBAYASHI ◽

...

Keyword(s):

Fluid Dynamics ◽

Computational Fluid Dynamics ◽

Elastic Vibration ◽

Dynamics Analysis ◽

Cylinder Arrays ◽

Computational Fluid Dynamics Analysis

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A Hybrid Method for Estimating Modal Damping in Sag Cable with Oil Damper

Advances in Structural Engineering ◽

10.1177/136943329800100401 ◽

1998 ◽

Vol 1 (4) ◽

pp. 221-236

Author(s):

Z. Yu ◽

Y.L. Xu ◽

J.M. Ko

Keyword(s):

Analytical Solutions ◽

Hybrid Method ◽

Equations Of Motion ◽

Orthogonal Transformation ◽

Internal Damping ◽

System Matrix ◽

Analytical Formulation ◽

Modal Damping ◽

Complex Eigenvalues ◽

Local Solutions

A hybrid method, combining analytical formulation with numerical computation, is developed for estimating the modal damping in a sag cable with oil damper. The sag cable is such divided into a series of segments that the damper is located at a joint between two segments. An orthogonal transformation is performed to decouple the equations of motion and find local analytical solutions for each segment. Then, a transfer matrix procedure is employed to assemble these local solutions to form a system matrix. From the system matrix and the boundary conditions of the cable, the complex eigenvalues including the modal damping of the cable are finally numerically estimated. Using the hybrid method, an extensive parametric study is carried out to investigate the modal damping of the system with respect to cable sag, cable internal damping, damper direction, damper stiffness, and others. The results show that for a taut cable, the obtained curves for the modal damping are very much compatible with the previous results, but much less computation effort is required. It is also shown that the disparity of modal damping between the previous theoretical values and experimental results may be attributed to the ignorance of the frequency crossover of a sag cable, damper stiffness, or damper direction.

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