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Hugh E.M. Hunt, University of Cambridge
Jonathan E. May, University of Cambridge
The control of vibration generated by railways in tunnels is complicated by the dynamic interaction between tunnel and track. Conventional methods (floating slab track, ballast mats, under-sleeper pads) do not perform as well as might be expected and it is the purpose of this paper to explore the sources of error. The major factors which must be taken into account pertain to the three-dimensional vibration modes of the tunnel and their interaction with the track and with the surrounding soil. These factors are usually omitted under existing design methodologies and supposed improvements in track design are often not effective. The model used to quantify tunnel effects is based on exact solutions to the 3-dimensional wave equation as applied to a tunnel of infinite length. For a typical tunnel there are many resonance frequencies to be found in the range from 5 to 100Hz, most significant for railway vibration calculations.
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Lyudmila Ph. Drozdova, Baltic State Technical University (Russia)
Nikolay I. Ivanov, Baltic State Technical University (Russia)
Alexander V. Omelchenko, Baltic State Technical University (Russia)
Vyacheslav V. Potekhin, Baltic State Technical University (Russia)
The reduction of noise of movable compressors (MC) is a problem of great importance in Russia. Today most leading foreign compressor-manufacturing firms produce MC in sound-proofed varieties. Different methods can be used for the noise and vibration reduction of compressors depending on their types, such as: installation of sounf-proofed enclosures, mufflers, sound buffles, sound-absorbing and vibration-damping constructions, etc. Each approach when used separately or together with the others can provide a reduction in the noise to the noise limit. Therefore the designer always faces the problem of choosing the optimum approach. In this paper authors solved the problem of optimization of the noise and vibration protection approaches by choosing the noise reduction procedures using the cost and efficiency criteria for a given noise limit at a specified point.
sv970465.pdf (Scanned) TOPJames A. Forrest, University of Cambridge
Floating slab track is a popular approach used to try to reduce vibration transmitted from underground railways into the surrounding soil and thence into nearby buildings. The rails are fixed to a concrete slab foundation which is supported on a resilient mounting, so isolating the track from the tunnel invert. However, the effectiveness of the vibration attenuation does not compare well with the simple mass-spring models typically used in the design of these tracks. This paper uses models of infinite length to investigate the performance of floating slab track in more detail. A track model constructed from an infinite series of repeating units is presented, each unit being two beams (for the rail and the slab) separated by elastic layers (for the resilient elements used in the track construction). An improved model consisting of an infinite slab beam mounted inside a tunnel of infinite length in soil of infinite extent is also presented.
sv970526.pdf (Scanned) TOPYue Qi Zhou, Nippon Otis Elevator Company (Japan)
Many proposals have been made in recent years for building skyscrapers with heights in excess of 300 meters. For elevators in high buildings, the torque ripples generated by the traction motors can cause the cars to oscillate vertically due to the existence of the long ropes from which the elevator car hangs. In this study, a simplified 8-degrees-of-freedom model, which assumes the ropes to be spring and dashpot elements by neglecting the rope mass, is created for an elevator hoistway vertical dynamic system. The solutions are obtained by solving the 8 linear differential equations using MATLAB. In addition, an FEA model using computer code of ANSYS is also created for studying the dynamic behaviors of the long ropes. The results from those two models are compared and discussed, which gives the conclusion that it is necessary to use the FEA model for the analysis of elevator hoistway vertical dynamic system for high buildings.
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Hirokazu Takemiya, Okayama University (Japan)
Kazuya Goda, Toyo Construction Co. Ltd. (Japan)
Connecting cities by high speed trains is pursued in view of the increasing mass transportation of people and cargo. Speeding up of the train operation on track may produce some unexpected environmental problems like vibrations to propagate toward the neighborhood, disturbing people and giving trouble to sensitive machines along the track. The prediction and the countermeasure of vibrations by such moving source is of essential interest. In this paper, theoretical approach is first made for the induced wave propagation by a moving oscillatory load on layered soil, The three-dimensional analysis is conducted by taking Fourier transform of the governing equation with respect to time and space coordinates along the moving direction and the perpendicular to it. The solution satisfying the given boundary condition is obtained in the transformed domain. Since the concerned phenomenon does not require the causality, the back transformation from frequency-wave number to time-space coordinates along the moving direction is carried out analytically. The back transformation in the remaining coordinates is resorted to the discrete wave number method with application of the FFT algorithm. In order to disclose the fundamentals in wave field in the layered soil in the above situation, the dispersion curve e is obtained and interpreted, focusing on the Airy phase for predicting the dominant wave propagation. The embankment track on layered soil is then analyzed. The Green function for a layered soil is developed for certain distributed load in order to avoid the involvement of the singularity otherwise, The interaction of the embankment and the underlain soil is treated by the hybrid method by BEM and FEM. The field measurements are conducted on ground vibrations along the Shinkansen track and in nearby locations. This enables us to do an inverse analysis for predicting the train induced vibrations near the track. Results from the present study are summarized as follows: 1. The speed of the train operation is important when it approaches the Rayleigh wave of the soil. The transient vibration due to the train passage generates not only the Doppler effect but also the layer vibration, 2. The dynamic characteristics of the embankment and the interaction between the embankment and the underlain soil are important for the vibration assessment in train operation. 3. The inverse analysis was executed for the vibration prediction near the Shinkan-sen track to determine the parameters involved appropriately,
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Masaharu Aisaka, ISUZU Motors Limited (Japan)
Isao Yokomichi, Kitakyushu College of Technology (Japan)
Yoshiaki Araki, Kyushu Institute of Technology (Japan)
Takeshi Inoh, ISUZU Motors Limited (Japan)
This paper presents some results of a theoretical study of random impact vibrations of the engine-mounting system of heavy-duty trucks. The dynamic model of a vehicle is reduced to five degree-of-freedom system equipped with stoppers to limit the engine-body movement when traveling on rough roads. The impact force is reduced to the linear restoring and damping forces using by statistically equivalent coefficients of stiffness and damping. The responses of the system to road surface undulations are determined from the moment equation. These theoretical results are confirmed by the digital simulation.
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