ACCELERATION TESTS OF LONG-TERM OPERATION FOR GIANT MAGNETOSTRICTIVE UNITS OF THE SOURCE FOR GLOBAL OCEAN CLIMATE CHANGE

摘要

A sound source with the frequency below 70 Hz and transmitting level over 195 dB is required to investigate global ocean climate change by acoustic monitoring like the A TOC project for long-range sound propagation of 5-10 Mm of gyre scale. Long-term operation of the source over ten years is also required for this purpose. A low frequency sound source of 70 Hz is planned using the same driving units of giant magnetostrictive type as the units used in the 200 Hz source for our ocean acoustic tomography system . Acceleration tests of long-term operation of the driving units were conducted to realize the equivalent operation to ten years of the 70 Hz source in a shorter period. As the resonance frequency of the driving unit is about 1 kHz, the acceleration rate is 1000/70. The driving unit was operated 40,000 times for one minutes which corresponds to 30 minutes operation for the 70 Hz source every four hours for ten years. Variation of strain, impedance and displacement-current sensitivity of five driving units were measured every 10,000 time drives. It was found there was no significant variation for these parameters during the tests.