In this paper, non-planar vibrations of a cantilevered pipe, which is hung vertically with an end mass and conveys fluid with a flow velocity that is entirely constant, are examined. We are interested in such a case that a two-frequency oscillation of the pipe involving the two unstable vibration modes. This phenomenon will be called the mixed-mode flutter. The main purpose of this paper is to confirm some features of the mixed-mode flutter qualitatively in experiments. Experiments were conducted with a silicon rubber pipe conveying water. The non-planar behaviors of the vertical fluid-conveying pipe were observed using an image processing system that was based on the images captured by two CCD cameras. As a result, the second mode flutter, the mixed-mode flutter involving both the second mode and third mode and also the third mode flutter of a cantilevered pipe vibration were confirmed experimentally when the flow velocity was increased. Furthermore, we discussed the above phenomena, especially the mixed-mode flutter, using the basic equations of nonlinear non-planar vibration of a fluid-conveying pipe with an end mass from the viewpoint of nonlinear dynamics.

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