The flow-induced vibrations (FIV) of cylindrical structures subjected to a cross flow have been investigated in a number of studies owing to their practical importance. The results of these studies have been compiled into guidelines for the evaluation of FIV of cylindrical structures. However, the applicability of the guidelines to cases with upstream structures and with an oblique inflow has not been fully examined. In this paper, we describe the response characteristics of vortex-induced in-line vibration and random vibration of a circular cylinder under various inflow conditions. Water tunnel tests were conducted on a circular cylinder in a cross flow at three yaw angles of 0, 30 and 45 degrees to clarify the effects of the yaw angle on vortex-induced in-line vibration and random vibration. The vibration amplitudes of a circular cylinder downstream of another circular cylinder of five times larger diameter were also measured to investigate the effects of inflow turbulence generated by an upstream cylinder. The tests were conducted for two different relative locations of the upstream cylinder in the same reduced-velocity range as that of the single-cylinder tests. The response amplitudes and onset flow velocities obtained by the tests were compared with values predicted using the cosine law and the guidelines to verify the evaluation methods in the guidelines.

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