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Hydrodynamically Coupled Shape-Morphing Beams Oscillating in a Viscous Fluid
AuthorGhani, Walid Abdel
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In this thesis, we study the fluid-structure interaction (FSI) of a pair of hydrodynamically coupled parallel beams immersed in a quiescent, incompressible, viscous, Newtonian fluid. The beams have two concurrent motions: a rigid oscillation in the vertical direction and a harmonic shape-morphing deformation to an arc of a circle. We perform a comprehensive computational fluid dynamics (CFD) simulation campaign to estimate the hydrodynamic function describing the added mass effect and hydrodynamic damping effect of the problem. Hydrodynamic loading increases when two beams are placed in close proximity due to the squeeze film effect. Our study found that the shape-morphing deformation is an effective strategy to reduce the hydrodynamic loadings on both beams. Previous literature introduced a simplified methodology based on the superposition principle to estimate forces for this class of problems with small amplitude oscillation. In this approach, one beam is in motion while the other beam remains stationary. Thus, a hydrodynamic function is calculated for the actions on the beam in motion (direct effect) and on the stationary beam (coupling effect). Any combination of motion can then be obtained by properly combining these two prototypical hydrodynamic functions. Our findings show that superposition methodology is an effective strategy for estimating the hydrodynamic loadings for small amplitude oscillation in the case of shape-morphing. We validate our findings from CFD simulations with the results obtained utilizing the superposition technique through a boundary element method (BEM), whose algorithm was previously developed by our group. We expand our simulation campaign to the moderately large amplitude oscillation to study the limits of applicability of the superposition treatment. Our findings show that due to the interplay of vortex shedding and convection phenomenon, the estimation of complex hydrodynamic loading using superposition strategy is not a reliable approach for moderately large oscillation amplitudes. We conclude this thesis with a qualitative comparison of the vortex shedding phenomenon between the cases of small and moderately large amplitude oscillations.