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Towed array shape estimation aided with non-acoustic sensors is widely used for its rather low computational complexity of solutions and rather explicit results. In addition, previous studies have emphasised that depth sensors' distribution has a dramatic influence on the accuracy of this kind of array shape estimation method. Established on the basic theory of towed array shape estimation using Kalman Filters, the approximately optimal distribution of a certain number of depth sensors over a certain number of discretised towed arrays yields the approximately best achievable performance in terms of minimum space average mean square error (AMSE), is addressed in this study. The effect of depth sensors' distribution has been discussed. Then an exact expression for the space AMSE is derived. The expression is simplified in a reasonable way considering the practical issues in order to calculate the minimum space AMSE rapidly and effectively. The performance assessments demonstrate the effectiveness of the newly proposed method.

Proceedings of the ICA 2019 and EAA Euroregio : 23rd International Congress on Acoustics, integrating 4th EAA Euroregio 2019 : 9-13 September 2019, Aachen, Germany / proceedings editor: Martin Ochmann, Michael Vorländer, Janina Fels 23rd International Congress on Acoustics, integrating 4th EAA Euroregio 2019, ICA 2019, Aachen, Germany, 9 Sep 2019 - 13 Sep 2019; Aachen (2019)., Published by Aachen

Most of the non-acoustic methods for towed array shape estimation are based on the incorrect original Paidoussis equation. A comparison between solution to the original and revised Paidoussis equation is made to prove the significance of utilising the latter. In addition, considering relative characteristics of the revised Paidoussis equation and the critical point which exists on the cylinder, the minimum length of damping section added at the end of the cylinder is derived.

On the basis of phase relationships in the Ca–Si–Al–O–N system, a Ca–α–sialon ceramic was synthesized using the hot-pressing technique. The reaction sequences and densifications of the Ca–α–sialon vs. firing temperatures have been characterized in detail. The present experiments reveal a reaction sequence as follows: at 1250°C the reactant mixture started to soften, at 1300°C a gehlenite phase was produced, at 1500°C the gehlenite phase was resolved into a liquid phase and a Ca–α–sialon started to form, and at 1600°C the formation of Ca–α–sialon was complete. The product was stable and almost entirely single phase Ca–α–sialon. Accompanying to the above sequences, densification also proceeded via a liquid-phase sintering, particle rearrangement, solution–reprecipitation, and grain growth process. In the final microstructure elongated grains of Ca–α–sialon were obtained, improving the fracture toughness of this Ca–α–sialon ceramic.

Nucleation and growth behavior of the elongated α′-SiAlON grains have been studied in α′-SiAlON ceramic with an overall composition Y 0.48 Si 10.00 Al 2.30 O 1.17 N 15.29 prepared by hot-pressing at 1825 °C. Transmission electron microscopy (TEM) and high resolution electron microscopy (HREM) have shown that the elongated α′-SiAlON grains always contain an α-Si 3 N 4 core, implicating heterogeneous nucleation operating in the present system. The growth mode is epitaxial. Selected area diffraction (SAD) and HREM analyses reveal that the crystal structure of the elongated α′-SiAlON has dilated and does not strictly comply with the hexagonal construction, i.e. the c axis tilting by no more than 2 ° is no longer normal to (001) plane, giving a conclusion that the deformed structure, probably formed by local high stress at high temperatures, changes the chemical bonding conditions especially on (001) plane, leading to faster deposition of atoms on (001) plane than on other planes. Additionally, morphology and growth defects have been studied in this paper.