・ ti・ 9 ・fi ・w , t。 investig ・t ・ amodulation of drag force, As a result , a reduction of drag force is found and it depends on period and arnplitude of the rotatiQn or the oscillat 正 Qn , A reason of the reduction of drag force is caused by a reduction of friction force on the particIe . And the reducti n Qf the friction force is induced by aconcent 「ation of the fluctuation energy of the How by the rotation or the oscillation on the vicinity of the particle in case Stokes layer thickness , which is estimated using a frequency of the roLation or the osciUatiQn , is comparable or smaller than the thickness of boundary layer of thc particle that is estimated in a larninar now .