Trashracks in pumped storage systems with high flow rates can develop fatigue failures due to excessive vibration excited by the flow past the rods in the rack. An experimental study of trashrack vibration was made on a half-scale model of a prototype rack design for the TVA Raccoon Mountain pumped storage system. The natural frequencies and loss factors of the first dozen natural modes of the rack were determined in air before placing the rack in a water channel. Under normal flow rates the rack developed “locked-in” pure tone vibrations of sufficient amplitude to cause early fatigue failure. Unexpectedly, the frequency of the vibration was not close to the vortex-shedding frequency and the motion of the rods was not transverse to the flow. The “locked-in” modes were identified as modes in which the bending displacements of the rods were parallel to the flow. Further investigation showed that the excitation mechanism involved synchronization between the fluctuating drag involved in vortex shedding and the fore-and-aft motion of the rods in sharply resonant modes. Modifications of the original design were introduced to defeat the identified mechanism. In order to completely eliminate the “lock-in” phenomenon it was necessary to change the bar cross-sectional shape and to introduce additional damping into the rack structure. A half-scale model of the modified design was built and tested to verify the absence of destructive vibrations.
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November 1975
This article was originally published in
Journal of Engineering for Industry
Research Papers
Destructive Vibration of Trashracks due to Fluid-Structure Interaction
S. H. Crandall,
S. H. Crandall
Massachusetts Institute of Technology, Cambridge, Mass.
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S. Vigander,
S. Vigander
Engineering Laboratory, Tennessee Valley Authority, Norris, Tenn.
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P. A. March
P. A. March
Engineering Laboratory, Tennessee Valley Authority, Norris, Tenn.
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S. H. Crandall
Massachusetts Institute of Technology, Cambridge, Mass.
S. Vigander
Engineering Laboratory, Tennessee Valley Authority, Norris, Tenn.
P. A. March
Engineering Laboratory, Tennessee Valley Authority, Norris, Tenn.
J. Eng. Ind. Nov 1975, 97(4): 1359-1365
Published Online: November 1, 1975
Article history
Received:
May 27, 1975
Online:
July 15, 2010
Citation
Crandall, S. H., Vigander, S., and March, P. A. (November 1, 1975). "Destructive Vibration of Trashracks due to Fluid-Structure Interaction." ASME. J. Eng. Ind. November 1975; 97(4): 1359–1365. https://doi.org/10.1115/1.3438783
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