The introduction of urban railways is one of the most effective ways to deal with traffic problems in large cities. However, in the vicinity of railways, day-by-day vibrations from trains may cause discomfort to people, the malfunctioning of sensitive equipment, and even damage to old buildings, and railways therefore have serious environmental problems. The development of urban railways is now limited by such environmental vibrations.
Effective vibration-reduction technologies rely on a good understanding of the excitation source that generates the vibrations. "In recent years, substantial progress has been made in modeling the train–track–ground interaction, and consensus has been reached that the excitation source is the moving of constant loads and uneven contact between wheels and rails," according to background information in the article. "Nevertheless, the contact can hardly be measured directively, so its amplitude and frequency contents are not completely understood, and its quantitative expression remains a problem for further research to address.
Recently, a research group led by Prof. Tao Xiaxin at Harbin Institute of Technology, China, has made a breakthrough in revealing the excitation mechanism. Based on an inversion study in the frequency and wave-number domain, Dr. Wang Futong, a key research member in the group, has found that high-frequency contents are predominant in the excitation. A power spectral density function (PSD) of uneven wheel–rail contact, rather than the track PSD, was suggested to describe the random characteristics of the excitation source. An inversion strategy was then established to obtain the source function from vibration data recorded by an observation array at the ground surface. The wheel–rail unevenness PSD, being the source function for the No. 13 Beijing urban railway, was obtained by the inversion strategy. The result indicated that the source function properly described the track unevenness in the range of wavelengths over 1.2 m, and showed wheel irregularities in the range of wavelengths shorter than 1.2 m.
The researchers found that, in the range of short wavelengths under 1.2 m, the wheel–rail PSD maintained a value higher than the 6th class of the track PSD suggested by the Federal Railway Administration. As urban trains do not travel particularly quickly, this short wavelength range exactly corresponds to the main frequency band of environmental vibrations; i.e., the frequency components of the vibrations stem mainly from that range of uneven excitation. Taking account of only moving constant loads and track unevenness could result in a severe underestimation of the environmental vibrations.
"Whereas the track spectrum reflects only the evenness of the track, the wheel–rail spectrum expresses both the track unevenness and the irregularities of wheels, and it is therefore more suitable to be used as the source function of urban railway traffic," the researchers write. "It is also shown that inversion of the exciting source according to observed ground vibrations is an effective way to detect quantitatively the combined wheel–rail unevenness."
The research has been supported by the National Natural Scientific Foundation of China, under contract No. 50538030.
For more information, please see the original article.
Wang Futong, Tao Xiaxin, Zheng Xin. Inversion of Excitation Source in Ground Vibration from Urban Railway Traffic. Sci China Tech Sci, 55: 950-959, doi: 10.1007/s11431-011-4665-9
WANG Futong | EurekAlert!
The importance of biodiversity in forests could increase due to climate change
17.11.2017 | Deutsches Zentrum für integrative Biodiversitätsforschung (iDiv) Halle-Jena-Leipzig
Win-win strategies for climate and food security
02.10.2017 | International Institute for Applied Systems Analysis (IIASA)
The formation of stars in distant galaxies is still largely unexplored. For the first time, astron-omers at the University of Geneva have now been able to closely observe a star system six billion light-years away. In doing so, they are confirming earlier simulations made by the University of Zurich. One special effect is made possible by the multiple reflections of images that run through the cosmos like a snake.
Today, astronomers have a pretty accurate idea of how stars were formed in the recent cosmic past. But do these laws also apply to older galaxies? For around a...
Just because someone is smart and well-motivated doesn't mean he or she can learn the visual skills needed to excel at tasks like matching fingerprints, interpreting medical X-rays, keeping track of aircraft on radar displays or forensic face matching.
That is the implication of a new study which shows for the first time that there is a broad range of differences in people's visual ability and that these...
Computer Tomography (CT) is a standard procedure in hospitals, but so far, the technology has not been suitable for imaging extremely small objects. In PNAS, a team from the Technical University of Munich (TUM) describes a Nano-CT device that creates three-dimensional x-ray images at resolutions up to 100 nanometers. The first test application: Together with colleagues from the University of Kassel and Helmholtz-Zentrum Geesthacht the researchers analyzed the locomotory system of a velvet worm.
During a CT analysis, the object under investigation is x-rayed and a detector measures the respective amount of radiation absorbed from various angles....
The quantum world is fragile; error correction codes are needed to protect the information stored in a quantum object from the deteriorating effects of noise. Quantum physicists in Innsbruck have developed a protocol to pass quantum information between differently encoded building blocks of a future quantum computer, such as processors and memories. Scientists may use this protocol in the future to build a data bus for quantum computers. The researchers have published their work in the journal Nature Communications.
Future quantum computers will be able to solve problems where conventional computers fail today. We are still far away from any large-scale implementation,...
Pillared graphene would transfer heat better if the theoretical material had a few asymmetric junctions that caused wrinkles, according to Rice University...
15.11.2017 | Event News
15.11.2017 | Event News
30.10.2017 | Event News
20.11.2017 | Earth Sciences
20.11.2017 | Earth Sciences
20.11.2017 | Life Sciences