Elastically mounted cylinder undergoing 1DOF vortex induced vibrations near profiled walls*

Vortex-induced vibrations near planar and curved solid walls are investigated for a 1DOF elastically mounted rigid cylinder of diameter D. The experimental system parameters are m*ζ = 3.08, 2.5 ≤ U* ≤ 11.5, and 0.0 ≤ e/D ≤ 1.0, 1600 < Re_D  < 7500,  with m*ζ  the non-dimensional mass damping of the system, U* the reduced velocity, Re_D the Reynolds number based on D, and e the neutral cylinder-wall gap. Considered are baseline (no wall), planar wall, and scour wall profiles mimicking riverbeds. The presence of a wall has a major impact on the structural response.  The extent of the lock-in region, 4.8 < U* < 8.5, the peak amplitude, A* = 0.7, and peak C_L = 0.87 for the baseline increases by more than 20% (4.5 < U* < 10; A* = 0.85; C_L = 1.0). Within the initial branch, the vortex shedding frequency is undetectable in the force and position response spectra, indicating fundamental changes in the vortex formation dynamics compared to the baseline.  The excitation of inter-harmonic and subharmonic frequencies in the response spectra suggest that the wall and its shape reinforce nonlinear interactions with the wake flow.