Flow-Induced Vibration of Bluff Bodies. Experiments on Flow-Induced In-Line Oscillation of a Circular Cylinder in a Water Tunnel. 1st-Report, The Difference of the Response Characteristics When a Cylinder is Elastically Supported at Both Ends and Cantilevered.

Abstract

Flow-induced in-line oscillation of a circular cylinder has been experimentally studied by free-oscillation tests in a water tunnel. Response amplitudes of a circular cylinder have been measured for determining the values of the reduced mass-damping parameter of less than 1.0. In the free-oscillation tests, the cylinder models were spring-mounted so as to oscillate as a two-dimensional rigid cylinder in the water tunnel. Two types of excitation phenomena appear at approximately half of the resonance flow velocity. The response amplitudes are sensitive to the reduced mass-damping parameter during the in-line oscillation of the first excitation region with a symmetric vortex street, and the alternate vortices are periodically shed, locking-in with the vibration of the cy]inder in the second excitation region. A hysteresis phenomenon is observed to appear in the in-line oscillation of the latter region. A cantilevered circular cylinder with a finite length aspect ratio of 10 was tested for fluid-elastic characteristics of the cylinder, and these characteristics are found to be quite different from those of the two-dimensional cylinder, having only one wide velocity region of excitation. The results of this study are providing important supporting data for the recent publication Guideline for Evaluation of Flow Induced Vibration of a Cylindrical Structure in a Pipe by the Japan Society of Mechanical Engineers, Standard JSME S()12 1998.