Vortex-Induced Vibration of a Rectangular Cross Section With Transverse and Rotational Modes

Abstract Periodic vortex shedding downstream of a rectangular cross-section can result in excessive vibration, reducing fatigue life. Accurate characterization of the fluid-structural interaction can help develop models to predict the excitation of vibration at different flow velocities. These models can help develop methods to avoid the excitation of significant vibrations, ensuring structural integrity and preventing fatigue failure. In this work, the vibration response of a structure with a rectangular cross-section with an aspect ratio of four is numerically investigated when susceptible to both transverse and rotational vibration modes. A coupled two-dimensional fluid-structural model is used to solve the equations of structural vibration and fluid flow. The model provides predictions of the rectangular cross-section vibration under forces induced by vortex shedding. The amplitude, frequency, and phase characteristics of the coupled cross-flow and rotational modes are presented and compared to vortex-induced vibration in a single degree-of-freedom system. The coupling between modes at different flow velocities lock-in is investigated for cases where the two modes have equal or different natural frequencies. Although the two modes are structurally independent, results show that fluid forces introduce modal coupling if the two modal frequencies are equal, leading to elevated vibration levels away from the expected vortex-induced vibration lock-in range. However, this coupling effect did not materialize for cases where the two modal frequencies were not equal.