Numerical simulation of dual oscillating cylinders under different angles for ocean engineering

Numerical simulations based on Boundary Data Immersed Method have been performed to study sinusoidal oscillation of an identical pair of circular cylinders under various angle and gap configurations in the still fluid. Simulations on single cylinder cases have also been performed for comparison. An obvious drag force coefficient's increase has been observed especially under large angles. This phenomenon has later been confirmed by calculating energy outflow through a selected control volume. Moreover, double oscillation frequency has been found for the lift force coefficient at all the angles except 45°, at which it has the same frequency as that of motion. Through flow field visualization, these phenomena are explained by discovering two different flow patterns that take place depending on the angle. The first pattern is the vortex circulation pattern when the angle is smaller than 45° while the second pattern is the jet flow pattern when the angle is bigger than 45°. The circulation of vortex around the upper cylinder after being shed out is observed in the vortex circulation pattern, while the jet flow pattern suggests that jet flow is generated in the gap which will be expelled far away and strengthen the energy outflow and dissipation. However, 45° is a critical condition under which the vortex can neither circulate nor shed far in the gap, making the oscillation frequency of lift force almost equal to that of motion.