The size effects of some permanent magnet on vibration characteristics of magnetic fluid adsorbed to a permanent magnet subject to vertical oscillation were studied. Some disk type permanent magnet-magnetic fluid elements were oscillated vertically with an electrodynamic shaker. The amplitude of the oscillation of the permanent magnet was measured with an optical displacement detector system. It was found that the resonant frequency of the magnet-magnetic element system depends on the size of permanent magnet. The dynamic repsonse of the element system was analyzed with a FFT analyzer. The shift hysteresis for the harmonic and subharmonic responses of the element system was revealed.

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The profile drag of circular cylinders with v-type grooves in the circumferential, spiral direction and crossing at the angles of 60゜ was measured in the range of Reynolds number Re=1.5×(10)^4 to 7×(10)^4 in a uniform flow. An Eiffel type low speed wind tunnel in an experimental apparatus produces a muximum velocity of 21m/s at the blow down section of width 300mm and height 400mm. The effects of the groove direction and the roughness on the drag coefficient were examined experimentally. The measurement of profile drag was carried out a direct method using the strain gauge load cells. The roughness of the cylinder surface was shown by the ratio h/d of v-type groove depth h and the diameter d of test cylinder. V-type grooves crossing at the angles of 60゜ have a great effect on the profile drag of circular cylinders. As h/d increases, the drag coefficient for the circular cylinders dercreases abruptly at lower Re. The drag coefficient for the circular cylinders with v-type grooves in the circumferential and spiral direction did not show the characteristic change in the present experiment range.

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