Underwater probe for deep sea exploration : Long range acoustic underwater communication system

This was a thesis that was commissioned by Researcher Peter Sigray at the Royal Institute of Technology (KTH) in Stockholm and was based on an idea by Professor Thomas Rossby, University of Rhode Island (URI). The idea was to further develop the existing Expendable Bathythermograph (XBT), which has been in use since the 1960s. This by first and foremost replacing existing transfer technology, which involved using a thin copper wire when communicating with the recipient remaining on the ship. The new way in which communication is to take place, is by acoustic signals transmitted from the freely descending probe. The goal is to be able to measure down to greater depth compared to the previous type. The aim is to increase today's in-depth measuring capacity of about 900 meters, down to depth of at least 2000 meters, preferably even deeper. The thesis project was divided into several smaller parts, some of which went on in parallel, while others had to have the preceding portion completed, in order for them to take place, i.e., to begin. Initially – and in parallel during the rest of the thesis work – their were studies of two selected books and a set of documents. This to ensure the understanding of all the concepts to be used during the development of the probe. In parallel with the studies, simulations in the computer program COMSOL Multiphysics began. The model probe geometry and material parameters were programmed. An important task was to implement and verify that the so called Perfectly Matched Layer (PML) performed as expected. This was of crucial importance, as different implementations of the PML turned out to result in different outcomes of the simulations’ data. With the results from Perfectly Matched Layer tests verified, the actual simulations could be initiated. Two different pipes were evaluated; one made of stainless steel and the other made of aluminum alloy. Their proportions were slightly different regarding diameter and length. The simulations led to the makings of plots/diagrams over the Transmission Voltage Response (TVR) over a certain frequency range (3000-17000 Hz). Directivity polar plots were also created for both pipes in the program MATLAB and by using a MATLAB. The actual assessment of the probes began in the latter part of the simulation work. There were several different steps in the process of assembling the probes. Finally, the tests in the water tank at The Defense Research Institute (FOI) could take place. For three days all the simulated results were “put to test.” The results during the tests in the water tank at FOI were promising and the remaining challenges, before a complete probe is developed, are achievable. The hypothesis that initially was set got proven, and it can be argued that the thesis as a whole successfully demonstrated it to be true. The idea of the probe is definitely worth further development, in the making of the new version of the Expendable Bathythermograph