Bayliss, Clive (1999)
Ph.D. thesis, University of Birmingham.
Ocean acoustic tomography (OAT) is a method for mapping the physical characteristics of the world’s oceans. This technique enables the properties of a region of ocean – its temperatures, salinities, densities, and current speeds – to be inferred by measuring the propagation times of pulses transmitted between an array of transducers that surround the region. Central to the development of OAT is the availability of low frequency (< 500 Hz), low Q (< 4), light (< 250 kg), and efficient (> 50 %) sound sources that can operated at depths in excess of 500 m. Following a review of transducer motor and flextensional transformer technologies, the class I flextensional transducer driven by a piezoelectric ceramic stack is selected as being suitable for OAT. Finite element (FE) techniques are applied to the design of this transducer. By observing the change in pertinent performance characteristics of the device in response to altering various design parameters a set of design rules is established. In applying these rules an OAT projector has been designed. A scaled prototype has been constructed and the measured performance characteristics concur with FE predictions. Based on these results a full-scale device is expected to meet the requirements for an OAT projector, with the exception of weight, though this has to be verified. In order to accurately determine the performance characteristics of a transducer it is essential to know the phenomena that limit the acoustic power output of the transducer; these could be one or more of the following: (a) cavitation, (b) electrical failure, (c) mechanical failure, (d) thermal failure. Power limitations arising from (a) or (b) can be determined from empirical data, whilst those arising from (c) or (d) are best determined using numerical methods. FE software is readily obtainable for assessing the mechanical behaviour of transducers, however, no commercial software is currently available for determining thermal behaviour. To this end new FE software has been developed and applied to the analysis of various transducers. Experimental results are presented to validate the accuracy of this new software.
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