Two-degree-of-freedom flow-induced vibration suppression of a circular cylinder via externally forced rotational oscillations: comparison of active open-loop and closed-loop control systems

Abstract

In the current work, both active open-loop and closed-loop control approaches are considered to reduce two-degree-of-freedom vortex-induced vibration (VIV) of a circular-section cylinder, by means of externally imposed rotational oscillations. The open-loop control method utilizes pre-specified rotary oscillations, while the active closed-loop controller computes the proper angular velocity depending on the feedback signal of lift coefficient. The interactions between fluid and structure are realized by utilizing of the moving mesh methodology by means of user-defined function, which incorporated into the central code of computational fluid dynamic solver. According to the numerous set of numerical simulations, three optimum open-loop control systems for appropriate suppression of cylinder vibration are selected. In particular, it is observed that the VIV suppression capability of the closed-loop control strategy in comparison with optimum open-loop systems is more desirable despite the lower level of consuming control effort. Moreover, it is detected the excellent performance of selected closed-loop controller with constant proportional control gain in the entire range of reduced velocities, while the optimum open-loop systems are executable mainly near their corresponding reduced velocities. In particular, the selected closed-loop VIV control system (Kp = 10) is found to suppress the maximum transverse response amplitudes by 99.6%, 99.5%, and 99.3% for reduced velocities Vr = 5, 6, and 7, respectively, while the associated in-line displacement amplitudes decrease by 99.2%, 98.3%, and 96.2%. Also, the closed-loop controller does not require to find the “lock-on” frequency to execute appropriate de-synchronization type action and can effectively shift the C(2S)-mode vortices to the typical von Karman 2S-mode vortex shedding.