Flow velocity mapping in a circular experimental wave/current basin with small scale underwater acoustic tomography method
Several researches normally use the rectangle tank for ocean device testing in laboratory trails. Rectangle experimental tanks, however, can only generate normalized flow in one or some fixed directions with limited testing area. Meanwhile, the appearance of the flow will be in large extent affected by boundary. This thesis study flow details in a 25m diameter circular testing facility Flowave TT, which can generate combined wave and current in any relative direction. The spatial of flow current velocity obtained by fixed point direct measurement is insufficient if the quantity of test points is not enough. Acoustic tomography is used here for flow internal structure visualizing in the experimental basin by transmitting sound wave with acoustic transducer. Using acoustic tomography method, one could get real-time mapping of parameter variation by installing detect devices outside or at the boundary of interested region without interrupting original field. Two sets of underwater acoustic tomography system that developed in cooperation with Hiroshima University were used for sound wave emitting and acoustic signal receiving. Travel time of acoustic signal in the interested region is analysed to reconstruct flow velocity by solving inverse problems. Multi-path arrivals that propagated by different ray paths are identified by ray tracing. Flow details in the circular basin is studied in a horizontal plane and along a vertical slice using acoustic method. Besides acoustic tomography experiments in the Flowave, a field work was conducted in the Bali Strait, Indonesia. This trail explores the remote sensing of tide progress in the Bali strait with coastal acoustic tomography systems. This study is for the first time to conduct multi-station acoustic tomography experiment for flow velocity reconstructing with only two stations. This study demonstrates that small scale flow profiles in the experimental tank can be reconstructed with acoustic tomography method. The real time monitoring of small-scale flow details can be accomplished with multi-station network, which is one of the further research topics for small scale underwater acoustic tomography research.