Yasser Amini

and two center-to-center distances between the cylinders (5D and 7D). In each center-to-center distance, the effects of reduced velocity on hydrodynamic coefficients, displacement amplitudes, and the vortex shedding pattern, are explored. Results indicate that the flexibility of the plate significantly affects the vibration regime of the cylinder, so that the cylinder vibrations at low flexibility values are of the FIV type, at medium flexibility values they are of the stable vibrations type and at high flexibility values they are of the galloping type. It was also observed that the trajectory motion of the upstream cylinder is mostly in the form of an apparent 8, but the trajectory motion of the downstream cylinder is very complicated.