The effect of inclination on vortex-induced vibration of a circular cylinder with a base column

The vortex-induced vibration (VIV) of an inclined cylinder can be affected by its end condition. This paper numerically investigates the effect of inclination on the VIV of an elastically mounted rigid cylinder with a base column, which derives from a floating offshore wind turbine (FOWT). The numerical methods are validated against an existing VIV study of a finite-length cylinder. Two inclination angles, i.e. -5 degrees and -10 degrees, are studied to simulate the relatively small wind-induced inclination experienced by FOWTs. Results from stationary simulations show that differences between the force coefficients of inclined and upright cylinders are rather small. Nevertheless, contrary to the finding from previous VIV studies that the effect of inclination on the response of a cylinder with small inclination angles is limited, the present investigation reveals that the maximum response amplitude of the cylinder increases by about 20% when the inclination angle grows to -10 degrees due to the presence of the base column. Meanwhile, the inclination leads to a reduction in the width of the lock-in regime. The impacts of inclination are further discussed via forced vibration studies with same oscillation parameters, which show that the upper part of the cylinder is more affected by the inclination compared to the base column with a considerable decrease in the amplitude of lift coefficient. The discrepancies in fluid forces are substantiated by analysing the pressure distribution on specified spanwise sections of the cylinder surface.