Forced oscillation experiments for each vibration mode of closely spaced parallel pipes in steady flow

Abstract

In the industrially widespread use of multiple bundled pipes, the effects of mutual interference, in addition to the vibrations generated in single columns, must be considered, and estimating their behavior is critical to the design. In this study, based on previous research that identified the vibration modes occurring in two bundled pipes placed in a steady flow, such as (1) translational motion in the crossflow direction, (2) approaching and moving away, and (3) torsional motion, we developed four types of oscillators that can emulate the oscillation patterns (mode (2) uses different mechanisms for in-line and crossflow direction oscillation.), conducted forced oscillation experiments, and measured fluid forces. The mechanism of generation of the behavior patterns, measured in the towing and vibration measurement experiments of the elastic body model, was examined from the viewpoint of fluid force. A database of added mass and linear damping coefficients with parameters of distance between the center of the column and flow direction, in addition to oscillation patterns, was compiled for the development of a future two-tube behavior estimation program.A comparison of the measured fluid force of two columns with that of a single column, obtained by forced oscillation experiments for three vibration modes, showed that two closely spaced columns may vibrate over a wider frequency band and have larger amplitudes than a single column because of the expanded region of negative linear damping coefficients. Based on the results of the fluid force measurements for each vibration mode, rotational motion is more likely to occur in the tandem configuration, whereas approaching and moving away motion is more likely to occur in the side-by-side configuration because of the interchanged positive and negative added mass coefficients and strength of the negative linear damping coefficient.