Mohammad Vaghefi

In this paper, the effect of a significant phenomenon in fluid-structure interaction (FSI), known as vortex-induced vibrations (VIV), is numerically investigated for two fully submerged cylinders located near the free surface. The Volume of Fluid (VOF) method is used to track the free surface. The study is conducted for a range of reduced velocities from 2 to 14, Froude numbers of 0.3 and 1, and different distances between cylinders. The impact of the free surface, cylinder vibrations on vortex patterns, hydrodynamic characteristics, and the vibrational response of cylinders are studied. Findings indicate that the rear cylinder generally exhibits greater inline and transverse displacement amplitudes, along with more significant variations in lift and drag coefficients compared to the front cylinder. An increase in the Froude number contributes to free surface instability and suppresses vortex shedding. Furthermore, increasing the distance between the cylinders amplifies free surface instability and vortex interactions, underscoring the relevance of these factors for engineering applications in marine environments.