Aanandh Manjunathan, Sujyesh (2021-11). Flow induced vibration of a circular cylinder with an attached elastic plate of high aspect ratio. Master's Thesis.
Thesis
We studied the flow induced transverse vibration of cylinder of reduced mass M_r = 2 with an attached flexible and elastic plate of high aspect ratio attached to the leeward side of cylinder and subjected to large scale flow-induced deformation at Re = 150. This problem statement was approached numerically using an in-house developed fluid solver based on curvilinear immersed boundary method strongly coupled with an open-source finite element based structural solver, using a partitioned approach. Further, the convergence of the fluid-structure solver was improved using dynamic under-relaxation. The coupled solver was also verified and validated using the method of manufactured solution and literature benchmarking cases. The vibration of cylinder with an attached elastic plate of aspect ratio of 20 was segregated into three categories as vortex induced vibration, transition and galloping. Lock-in in vortex induced vibration was observed when the non-dimensional natural frequency of elastic plate, cylinder undergoing vibration and vortex shedding nearly matched and came into resonance. The elastic plate at resonance was observed to be attaining very high modes of deformation leading to vortex to-vortex interaction with cylinder. The transverse displacement of the cylinder with an attached elastic plate of length twice the diameter of the cylinder was found to be nearly twice of an isolated cylinder for Ured = [5, 7]. Further, the lock-in regime in the presence of attached elastic plate was observed to be narrowed when compared to that of an isolated cylinder. Beyond this frequency, the cylinder was pushed into transition regime wherein the displacement of cylinder was nullified because of lack of vorticity interaction and out-of-phase deformation. Beyond U_r = 10, the cylinder was pushed into galloping regime wherein the cylinder was seen to be vibrating in frequency high than the reduced velocity. The elastic plate was restricted to the second mode of deformation and the transverse displacement of cylinder showed a linear increase with increase in U_r. The flow physics of the cylinder-plate system has been explained in detail using amplitude, frequency spectrum, force and phase characteristics. Modal analysis of deformation of attached elastic plate was performed to correlate it with agitation and subsidence of cylinder-plate system vibration.
