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(1998)Journal ArticleA recent publication says that the primary spelling of the word for the depth of water required to float a ship is draught, with draft as the secondary spelling. A survey of thirty practising naval architects was made to check the claim, and found that a large majority of Australian-educated naval architects spell it draft. The overall results are interesting and are given here.
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(1998)Journal ArticleThe two types of marine hydrometer commonly used by naval architects and surveyors measure two distinct, but related, properties. The properties have different units and are used for different purposes. Some users may not be aware of the two types of hydrometer, the properties measured, or the errors which can significantly affect the end result. The relationships between the measured properties are discussed, together with the specific applications of the two types of hydrometer. The conversion of measurements made on one type of hydrometer to the other type is given, with examples of the conversions. Application of the principles presented here will prevent confusion and ensure the use, rather than abuse, of the two types of marine hydrometer.
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(1999)Conference PaperPipe laggings are used as a means of inhibiting the transmission of sound radiated from pipes. They are usually formed of porous jackets such as fibreglass or rockwool blankets and impervious jackets such as cladding sheets. Sometimes air spaces are used to separate these jackets from the pipe and each other. Papers in the readily available literature relating to the acoustic performance of pipe laggings are generally concerned with presenting experimental results such as frequency dependent insertion losses. The authors have developed a model to calculate the insertion losses produced by such laggings when the lagged pipes are vibrating in their low order structural modes. The results of the model indicate that negative insertion lossess are not unexpected with conventional pipe laggings, particularly at low frequencies.
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(1999)ThesisInvestigations were made into how squared envelope analysis and Self Adaptive Noise Cancellation (SANC) can be used to improve the reliability of bearing diagnostics in gearboxes. Present models of bearing fault signals were improved by incorporating slight random fluctuations into the spacings between bearing fault impulses. This allowed simulated signals to be used for the investigation of squared envelope analysis and the optimisation of SANC. The values for the three variables which affect the adaptation process of S~L\.NC are optimised for removing discrete frequency noise from bearing fault components; this was done by using simulated bearing fault and gear signals. The recommended values were then applied to enhance the bearing fault signals recorded from an actual helicopter gearbox. Analysis of the squared envelope can give an improvement in bearing diagnostics if the signal-to-noise ratio is greater than unity. The MSR (Mean Squared Ratio) of signal to noise in the demodulation band and the percentage fluctuation of the bearing fault impulses were found to influence this factor and their values determined for a SNR of unity. Phase demodulation around a bearing frequency component in the envelope spectrum can be used to obtain a value for the percentage fluctuation in spacing of bearing fault impulses. Signals measured from a helical gear rig, spur gear rig, planetary gear rig arid helicopter gearboxes were used to test the performance of SANC. From the analyses, the combinations of modulations and carrier components can be categorised into four types. Bearing fault components from additive impulse responses (the classic model) appear in the spectrum as random frequency components and remain after SANC. Bearing fault components which modulate discrete frequency carriers appear in the spectrum as discrete frequency components, and thus are removed by SANC. Gearmesh harmonics which appear in the spectrum as discrete frequency carriers are also removed by SANC. However gearmesh frequency components which modulate random carriers appear in the spectrum as random components and thus are not removed by SANC. Although in this research the SANC technique did not provide an improvement in all bearing diagnostic cases, it provided a deeper insight into how bearing faults may manifest themselves in the spectrum.
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