چكيده به لاتين
In present thesis, intelligentactive and semi-active control strategies are applied to suppress the two-dimensional vortex-induced vibrations (VIV) of an elastically mounted cylinder, at low Reynolds numbers using time domain collaborative simulations. In addition energy regenerating auxiliary system equipped with dual functional electromagnetic (EM) control device is investigated. In the first step, an adaptive fuzzy sliding mode control (AFSMC) scheme is applied to actively annihilate the2dof VIV of an elastically mounted circular cylinder, free to move in in-line and cross-flow directions. The strongly coupled unsteady fluid/cylinder interactions are captured by implementing the moving mesh technologythrough integration of an in-house developed User Define Function(UDF) into the main code of the commercial CFD solver Fluent. The AFSMC approach comprises of a fuzzy system designed to mimic an ideal sliding-mode controller, and a robust controller intended to compensate for the difference between the fuzzy controller and the ideal one. The fuzzy system parameters as well as the uncertainty bound of the robust controller are adaptively tuned online. In the second step,a self-powered active support system, which produces a control force using the energy regenerated by a transversely mounted linear electromagnetic damper,is considered.In addition, a passive energy generating system is devised that achieves a proper trade-off between VIV suppression and energy harvesting actions with the EM damper acting either in the regeneration or dissipation mode. Next as a third step, the concept of energy-regenerative damping is adopted in semi-active vortex induced vibration suppression of an elastically supported inclined impenetrable elliptical cylinder in laminar cross-flow at low Reynolds numbers.It is based on the intelligent control strategy in conjunction with switch-based energy regenerating circuit of a tunable electromagnetic damper.The AFSM controller initially calculates the desired transverse control force for suppression of the cylinder VIV. Consequently, by smart adjustment of the variable circuit load resistance, the current flow through EM damper circuit is adaptively modulated in such a way that the damping force continually tracks its active counterpart in a semi-active manner.Furthermore, when the damper is operating in the regeneration mode, the mechanical vibration energy that is traditionally dissipated as heat in conventional viscous dampers will be stored as electric charge in a capacitor. As a final step in present thesis, an active rotary oscillation feedback control methodology is investigated. The closed-loop VIV control action is realized by active forced rotational oscillations of the circular cylinder about its axis based on the feedback signal of lift coefficient. This prevents the occurrence of resonance by shifting the vortex shedding frequency away from the natural oscillator frequency. Three different active closed-loop proportional controllers are implemented and their superior performance in cylinder VIV suppression is demonstrated against that of a representative open-loop control system with pre-specified rotational oscillations
