This is the accepted version of the paper.This version of the publication may differ from the final published version. A cascaded fibre optic acoustic sensor system, using optical filter signal demodulation has been developed and its performance extensively evaluated. To undertake this under standardized conditions, the optical sensor system was evaluated using a glass plate to detect the acoustic signal, followed by an evaluation using a metal plate to identify the location of acoustic sources, when subjected to sonotrode excitation, mimicking acoustic detection in cavitation detection. Under these circumstances, a very good agreement has been reached between the outputs of the optical acoustic sensors and of the co-located PZT acoustic sensors. This work confirms the utility of these sensors -they can detect not only weak AE signals, but also enable multipoint simultaneous measurement, showing their potential for condition monitoring applications, especially in the marine sector. Permanent repository link

This is the accepted version of the paper.This version of the publication may differ from the final published version. Permanent repository link:

No abstract

Ship components such as propellers and rudders are commonly operating in cavitation inducing conditions, therefore they are destined to experience the destructive effects of the phenomenon. Consequently, significant noise, as well as vibrations are commonly reported from ship operators. In addition, propellers and rudders also suffer from cavitation induced erosion, which in some cases can develop even within a few hours of operation, thus the expected service life of those components can be negatively influenced. This paper aims to present an ongoing research programme conducted by the Marine Engineering department of City, University of London which is oriented towards the evaluation of ultrasonically induced cavitation erosion in relation to materials commonly used in propellers and rudders, such as grade DH36 steel, stainless steel 254 and cupronickel 70-30, both from a quantitative and qualitative point of view. As such the relevant experimental procedures that were followed, including mass loss and acoustic emission measurements as well as microscopic and fractographic observations, along with the most important findings, are presented and explained. Results indicate that the proposed experimental procedure can form a baseline upon which efficient and effective evaluation of different materials in relation to ultrasonically induced cavitation erosion can be conducted. Moreover, the development of an acoustic emission-based cavitation erosion monitoring system for rudders, oriented towards the evaluation of erosion both in terms of intensity and location, is also presented. Results, from measurements conducted on small specimens and a reduced-scale model rudder, indicate that the system can potentially be used as means of cavitation erosion monitoring in full scale rudders.

This paper presents the results obtained from monitoring a simulated material cavitation process using both a fibre Bragg grating (FBG)-based acoustic sensor system developed at City University London and a commercial PZT (Piezoelectric Transducer) acoustic sensor, with an aim to identify the cavitation signatures. In the experiment, a sample metal plate with its back surface being instrumented with both sensors is positioned very close to an excitation sonotrode with a standard frequency of 19.5kHz. The data obtained from both sensors are recorded and analyzed, showing a very good agreement.