China 
Africa 
Explore chapters and articles related to this topic
A Systems Analysis of Rail Level Crossings
Published in Gemma J.M. Read, Vanessa Beanland, Michael G. Lenné, Neville A. Stanton, Paul M. Salmon, Integrating Human Factors Methods and Systems Thinking for Transport Analysis and Design, 2017
Christine Mulvihill, Guy Walker, Miranda Cornelissen
The first step in developing each CAT involved identifying the situations and control tasks within the rail level crossing system and determining how these should best be represented. The situations, shown along the horizontal axis in Figure 5.2, depict the spatially and temporally distinct approach phases that the road and rail users progress through as both approach the rail level crossing. For the rail user, the phases were defined as follows: pre-whistle board, at whistle board, at train detection device, at station pre-rail level crossing, traversing rail level crossing and post-rail level crossing.For the road user, the phases were defined as follows: pre-approach, on-approach, pre-boom gates, at boom gates/boom gates closing and on rail level crossing.
Sound and hearing
Published in John Watkinson, Audio for Television, 1997
Figure 1.24 shows that when standing, sounds from above reach the ear directly and via a ground reflection which has come via a longer path (there is also a smaller effect due to reflection from the shoulders). At certain frequencies the extra path length will correspond to a 180-degree phase shift, causing cancellation at the ear. The result is a frequency response consisting of evenly spaced nulls which is called comb filtering. A moving object such as a plane flying over will suffer changing geometry which will cause the frequency of the nulls to fall towards the point where the overhead position is reached. The result depends on the kind of aircraft. In a piston engined aircraft, the sound is dominated by discrete frequencies such as the exhaust note. When such a discrete spectrum is passed through a swept comb filter the result is simply that the levels of the various components rise and fall. The Doppler effect has the major effect on the pitch which appears to drop suddenly as the plane passes. In the case of a jet plane, the noise emitted on approach is broad band white noise from the compressor turbines. As stated above, the Doppler effect has no effect on aperiodic noise. When passed through a swept comb filter, the pitch of the output appears to fall giving the characteristic descending whistle of a passing jet.
Stereophony
Published in John Watkinson, The Art of Sound Reproduction, 2012
The result depends on the kind of aircraft. In a piston-engined aircraft, the sound is dominated by discrete frequencies such as the exhaust note. When such a discrete spectrum is passed through a swept comb filter the result is simply that the levels of the various components rise and fall. The Doppler effect has the major effect on the pitch which appears to drop suddenly as the plane passes. In the case of a jet plane, the noise emitted on approach is broadband white noise from the compressor turbines. As stated above, the Doppler effect has no effect on aperiodic noise. When passed through a swept comb filter, the pitch of the output appears to fall giving the characteristic descending whistle of a passing jet.
On the Development of a Novel Acoustic Flowmeter for High-Temperature Gas-Cooled Reactors
Published in Nuclear Technology, 2022
Jiaxin Mao, Victor Petrov, Annalisa Manera, Trevor K. Howard, Sacit M. Cetiner
The influence of the smooth pipe on the whistling can come from several factors. First, since the whistle is caused by the coupling between pipe acoustical resonance and vortex shedding, adding a longer tube will effectively increase the resonance length. On the other hand, this will also influence the velocity profile near the wall region. As vortex formation, shedding, and impinging on the edge of the cavity rely heavily on the velocity profiles, changing the velocity profile will alter the source strength and thus the whistle frequency. It then suggests separating the corrugated pipe from the piping system. A tube-in-tube configuration is thus proposed here as an optimization, as illustrated in Fig. 8. The corrugated section needed to generate the acoustic wave is mounted inside the main circulation pipe. An undisturbed inlet will be established in this way, and the corrugated section (necessary to establish an acoustic wave) will be independent of the piping system.