17,581 research outputs found
Effective conductivity of composites of graded spherical particles
We have employed the first-principles approach to compute the effective
response of composites of graded spherical particles of arbitrary conductivity
profiles. We solve the boundary-value problem for the polarizability of the
graded particles and obtain the dipole moment as well as the multipole moments.
We provide a rigorous proof of an {\em ad hoc} approximate method based on the
differential effective multipole moment approximation (DEMMA) in which the
differential effective dipole approximation (DEDA) is a special case. The
method will be applied to an exactly solvable graded profile. We show that DEDA
and DEMMA are indeed exact for graded spherical particles.Comment: submitted for publication
Gear wear process monitoring using acoustic signals
Airborne acoustic signals contain valuable information from machines and can be detected remotely for condition monitoring. However, the signal is often seriously contaminated by various noises from the environment as well as nearby machines. This paper presents an acoustic based method of monitoring a two stage helical gearbox, a common power transmission system used in various industries. A single microphone is employed to measure the acoustics of the gearbox under-going a run-to-failure test. To suppress the background noise and interferences from nearby ma-chines a modulation signal bispectrum (MSB) analysis is applied to the signal. It is shown that the analysis allows the meshing frequency components and the associated shaft modulating components to be captured more accurately to set up a clear monitoring trend to indicate the tooth wear of the gears under test. The results demonstrate that acoustic signals in conjunction with efficient signal processing methods provide an effective monitoring of the gear transmission process
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