底層流による海底地震計周囲の渦の発生の実験的観察

概要

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Oscillational noise has frequently been observed by pop-up ocean bottom seismometers (OBS). The major cause of the noise is supposed to be bottom currents. When the relationship between current speed and shape of the OBS was examined experimentally, Karman vortexes were found to develop about the L-shaped frames, the pressure case of the radio transmitter and the antenna of the transmitter when the current exceeded 20 cm/sec. The Karman vortexes which formed about the antenna were found to be the most undesirable. The frequency of the antenna oscillation was from 3.20 to 3.70 Hz for current speeds of 18 cm/sec and 30 cm/sec, and the amplitude was large enough to saturate the seismometers in the OBS. The frequency was nearly equal to the resonance frequency of the antenna in air and half of the excitation frequency of the Karman vortex. This suggests that the oscillation is the result of resonance in the antenna due to an external force. The use of a fin was effective in reducing the oscillation.
1980-08-25