抄録
Mearsurements of unsteady hydrodynamic forces on a circular cylinder and a square cylinder are carried out. The motion of the cylinders are given by a forced oscillation mechanism with Reynolds numbers 35,000 to 50,000 and KC numbers 10 to 60. For the square cylinder attack angles are set to be 0, 30 and 45 degrees. For the analysis of the drag force, the authors attempt to clarify the magnitude of higher-order terms using Fourier expansions and a newly defined formula, in addition to the usual Morison's formula. It is found that there exists a considerable amount of the third-order force. The hydrodynamic lift is also found to be of the same order of magnitude as the drag. The lift frequency depends on the shape of the cylinder and the attack angle of the motion, although in the case of circular cylinder the frequency at high KC number is nearly equal to the value estimated from the steady-motion case.
