ياسين معصومي

Flow-induced vibration (FIV) is an area of great interest due to its widespread incidence in numerous practical engineering applications. Most of these applications involve suppression of structural FIV to inhibit the potential catastrophic damages imposed on the system as well as the associated environmental effects. Also, the recent growing concerns about irreversible depletion of fossil fuel reserves along with the ever more strict environmental emission standards of our modern society have triggered the use of sustainable kinetic energy of ambient fluid flow for generating electricity from the supposedly harmful FIV effects. The present thesis numerically implements three important classes of hybrid FIV control strategies for the standard linearly sprung cylinder. In the first problem, extensive two dimensional CFD simulations were carried out to investigate the hybrid active/semi-active cross-flow vortex induced vibration (VIV) suppression of a flexibly-mounted circular cylinder. The cylinder is equipped with two smart actively rotating control rods that are symmetrically oriented 120° apart in the near-wake region in real-time collaboration with an internally-fitted semi-active NES-based vibration absorber in the low Reynolds number flow regime (Re=100) over a typical range of lock-in reduced flow velocities (3≤U^*≤10). The control rods function as flow control actuators by enforcing the desired momentum injection into the near-wake region, while the semi-active structural control is realized by switching the nonlinear absorber force between some minimum and maximum values consistent with certain control logics. selected multi-input-multi-output (MIMO) feedback control laws are introduced into the coupled transient dynamic simulation framework through a manually hooked user defined function (UDF) subroutine. In the second problem, a two-dimensional numerical study on active flow induced vibration (FIV) suppression of an elastically suspended circular cylinder fitted with a thin smart flexural-mode (bender-type) piezoelectric bimorph splitter plate on its wake side in real-time collaboration with a conventional base force actuator is carried out in laminar cross-flow condition (Re=100) for a wide range of reduced flow velocities (4≤U^*≤40). The numerical model is based on a strongly-coupled partitioned two-way iteratively implicit Fluid-Structure Interaction (FSI) routine implemented in a multiphysics simulation framework that interactively connects a CFD-based finite volume solver with a nonlinear transient computational structural dynamics (CSD) finite-element solver. A single-input-multi-output (SIMO) direct displacement feedback control law is introduced into the coupled transient dynamic simulation framework through an internal subroutine written in APDL command language. Three distinct feedback control configurations are implemented and compared, namely, the force-actuated, the piezo-actuated, and the hybrid actuation control systems, primarily aiming at suppression of cylinder transverse displacement amplitude. Further improvements on the controller performance are achieved by incorporating two modified hybrid actuation control strategies particularly designed for mitigation of excessive temporal oscillations of the drag and lift coefficients. In the third problem, a novel high-performance dual-purpose FIV-based hydroelastic energy harvesting and cylinder response suppression strategy that functions based on the synergy of piezoelectric and electromagnetic transduction (EMT) mechanisms is proposed and numerically implemented. The hybrid harvester consists of a linearly sprung (1DOF) square cylinder fitted on the wake side with a thin flexural-mode cantilever bimorph piezoelectric splitter plate in real-time collaboration with a transversely hooked induction-based magnet-coil type transducer. The two-dimensional flow field distribution of the hybrid energy harvesting system is simulated through a partitioned two-way iteratively implicit fully coupled nonlinear transient fluid structure interaction (FSI) scheme implemented in a multiphysics CFD-FEM simulation framework. The Reynolds averaged Navier–Stokes (RANS) equations with the shear stress transport (SST) k-ω turbulence closure model were selected for qualitative/quantitative prediction of hydrodynamic flow behavior in the range of Reynolds numbers between 2×10^3and 4×10^5. The numerical simulation results for the first hybrid FIV-control problem indicate that notable reductions are obtained when a modified continuous feedback control strategy is directly applied in the NES-based semi-active vibration absorber (i.e., up to 55% in the displacements, and up to 11% in the drag coefficients). Furthermore, the superior performance of proposed smart hybrid active/semi-active VIV control system in comparison to the hybrid passive system is demonstrated (i.e., up to 68% reduction in the displacements, 61% in the lift amplitudes, and 12% in the drag coefficient). The numerical simulations for the second hybrid FIV-control problem show that the hybrid actuation control configurations provide a largely better displacement response control performance than the single-alone force-actuated or piezo-actuated systems. Also, it is concluded that if one primarily aims at pro‎mp‎t and forceful suppression of the base cylinder motion regardless of lift and drag force variations, the originally designed hybrid actuation control system is sufficiently adequate, while if one is specifically concerned with the severe temporal fluctuations in the lift and drag coefficients, the modified hybrid control configurations should be employed. Lastly, in the third hybrid FIV-control problem, the single-alone EMT-based conversion module moderately mitigates the key hydroelastic response parameters on top of capturing ample hydrokinetic energy based on the separate or combined vortex induced vibration (VIV)-galloping effects in the low to intermediate Reynolds number range (2×10^3≤Re≤3×10^4 ). The hybrid piezoelectromagnetic harvester, on the other hand, significantly suppresses the key response parameters and effectively improves the overall system electrical output performance in an expanded working bandwidth (3×10^4

شبيه سازي FSI چند فيزيك , ورق جداكننده بايمورف پيزوالكتريك هوشمند متصل به پشت استوانه , ميله‌هاي كنترل‌كننده فعال چرخان , انتقال انرژي هدفمند غيرخطي (TET) , جاذب ارتعاش نيمه‌فعال مبتني بر NES , كنترل و برداشت انرژي هم‌افزا همزمان از FIV , ناحيه‌هاي VIV، گلوپينگ و فلپينگ

Multiphysics FSI simulations , wake-mounted smart piezoelectric bimorph splitter plate , active rotating wake-control rods , nonlinear targeted energy transfer (TET) , NES-based semi-active vibration absorber , Dual-functional synergetic energy harvesting and FIV control , Vortex induced vibration, Galloping, and Flapping

Yasin Masoomi

Dr. Mohammad Hasheminezhad