The noise of an automobile alternator generally increases with rotating speed. However, at some low rotating speeds, the alternator generates tonal noise in the frequency range of 1 to 3 kHz, which is the most irritating to the human ear. These tonal noises annoy the driver as well as passengers, especially at low speeds where background noise is relatively insignificant. Experiments were conducted to identify these noise sources by analyzing the noise and vibration signals. Modal tests were also performed using impact testing to study the modal vibrations of the stator. The source of tonal noises was identified as the magnetic noise which was caused by the strong alternating magnetic force on the stator. The magnetic noise increased abnormally at some specific rotating speeds when its frequency coincided with one of the modal frequencies of the stator.Volume 37/Number 1 31
An elastic cantilever is used for the measurement of the mass of a small quantity, by measuring the shifted resonant frequency when the unknown mass is attached to the free end of the cantilever. The measurements of resonant frequencies of the cantilever with and without an attached mass should allow the calculation of mass. An optical glass fibre is used as the cantilever and is excited by an acoustic wave. The resonant frequency of the optical glass-fibre cantilever is determined by measuring the maximum displacement by optical means while the exciting frequency is swept. Since the optical glass-fibre is chemically stable, this system can be used to measure a chemically active viscous fluid as well as small soft materials because it is easy to attach these materials to the end of the glass fibre without any glue joint. The experimental results obtained by this method for small masses (10-300 mu g) are in good agreement with those measured by the commercially available microbalance.
A bilateral comparison of pressure sensitivity calibration of an LS2P microphone has been performed between the Korea Research Institute of Standards and Science (KRISS, Korea) and the Research and Development Center for Calibration Instrumentation and Metrology (KIM-LIPI, Indonesia), in 2008, with KRISS acting as the pilot laboratory. The results have been linked to the CCAUV.A-K3 comparison with degrees of equivalence for the KIM-LIPI.Main text.
To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/.The final report has been peer-reviewed and approved for publication by the CCAUV, according to the provisions of the CIPM Mutual Recognition Arrangement (MRA).
The measurements of acoustically generated temperature difference between the two ends of a TAC (thermoacoustic couple) in a resonant tube are made using the similar method suggested by Atchley et al. [J. Acoust. Soc. Am. 88, 251–263 (1990)] with a ceramic TAC cylinder. The linear duct was made of PVC pipe with an inner diameter of 30 mm and 680 mm long. Measurements are made for a frequency range of 150–350 Hz in atmospheric air along the TAC length from 2.5 to 10 cm with a 1-cm step. The unknown information of ceramic can be obtained from nonlinear fitting of experimental data with the equation reported by Atchley et al. From the result of this experiment and prediction by theory it is found that the direction of acoustic heat transport is altered at the point of a quarter of a wavelength. From the hint of the above experiment, a newly designed thermoacoustic refrigerator having two regererator stacks is tested.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.