A Numerical Study on Hydrodynamic Forces of an Oscillating Circular Cylinder in Harmonic Flow

概要

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The hydrodynamic forces acting on an oscillating circular cylinder in an uniform and harmonic flow are investigated through the use of direct solution of the incompressible Navier-Stokes equations in order to gain a deeper understanding of the nature of the slow-drift damping force of an ocean structure. In the calculations the time-dependent generalized coordinate system has been employed to obtain an accurate numerical representation of boundary conditions for a moving boundary, which is important for determining the hydrodynamic forces by integrating the pressure distribution on the cylinder surface. The computed results are compared with other experimental works and show good agreement. Several important conclusion regarding slow-drift damping and the characteristics of a two harmonic flow are obtained : in the range of small reduced velocity the high frequency oscillation of flow field obstructs the formation of an alternate vortex caused by steady flow or slow-drift oscillation, but in the range of large reduced velocity this oscillation excites the alternate vortex shedding. The values of the reduced velocity of the turning point can be determined from the Strouhal number of the cylinder in steady flow. An attempt to explain the mechanism of the viscous slow-drift damping force is also offered.
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