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Published Articles

The Volume 11, No 4, December 2006

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Two- and Three-dimensional Methods for the Assessment of Ballast Mats, Ballast Plates and Other Isolators of Railway Vibration

Lutz Auersch


This contribution gives a simple two-dimensional method to calculate the dynamics of railway tracks which have been checked against the results of completely three-dimensional finite-element boundary-element calculations. The forces generated by the train are modified, amplified or reduced, by the vehicle-track interaction and the force transfer of the track, yielding the forces that are acting on the ground and exciting the ground-borne vibration. The overall force transfer function, which is the integral of all forces acting on the soil divided by the input force on the vehicle, is presented for a number of different track systems. Details are given for the track with ballast mats where the influence of wheel mass, track mass, subsoil condition, and the stiffness of the mat have been analysed. Experimental results of the Federal Institute of Materials Research and Testing and literature are used to check the theoretical results about ballast mats.

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On the Mode-Coupling Instability of Mechanical Systems Due to Sliding Friction Constraint

S. Chatterjee


A general lumped parameter model with two modes of vibration coupled through sliding friction constraint is considered. Stability analysis is carried out considering perfectly rigid and compliant contact models. The linear viscoelastic model and the non-linear Hunt-Crossley model of compliant contact are used to study the influence of the model of contact damping on stability. Influences of the contact parameters and the ratio of the modal parameters on the stability of sliding have been discussed in details. Mainly, three types of instabilities specifically, low-frequency flutter, high-frequency flutter, and divergence are found to exist in the class of systems considered. The condition of the existence of high-frequency flutter is shown to coincide with the condition of the Painleve paradox. Perfectly rigid contact consideration fails to provide qualitative as well as quantitative description of sliding instability in a specific parameter zone, where only a compliant contact model can properly describe the instability phenomenon. For low contact damping, stability boundary obtained from the perfectly rigid contact consideration is not the limit of that obtained from a compliant contact model, even with very high contact stiffness. Contact damping plays an important role in ascertaining the shape, size, and characteristics of the stability boundary.

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The Reduction of Jet Noise with Spherical Reflector and Evaluation of its Performance Compared to a Flat Reflector

Kunisato Seto, Md. Tawhidul Islam Khan and Kenbu Teramoto


A method of jet screech suppression with a spherical reflector has been proposed. The reflector was placed at the nozzle exit. Accurate placement of the reflector controlled the location of image sound source and reduced the sound pressure at the nozzle exit. The muted sound did not excite the unstable disturbance at the nozzle exit and the loop of the feedback mechanism disappeared, thus the generation of jet screech was cancelled. It was indicated that the new technique suppressed not only the screech tones, but also shielded the upstream radiation of the broadband noise components. Hence, the proposed spherical reflector technique protects the upstream noise propagation, and therefore protects the upstream structures of the nozzle exit from the acoustic fatigue. Optical investigations were carried out by using the Schlieren apparatus along with a high-speed video camera and it was observed that the jet was modified and became stable by the attachment of the spherical reflector at the nozzle exit. The performance of noise reduction with a flat reflector was also compared with the proposed technique. It was found that the method of noise suppression of a supersonic jet with the technique of the spherical reflector was more effective than that of the flat reflector.

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Forced Vibration for Electromechanical Integrated Toroidal Drive

Lizhong Xu, Xiuhong Hao and Hongbin Wang


In this paper, the forced vibration of the drive system is investigated. The mesh stiffness fluctuations caused by changes of the mesh tooth pair number and the fluctuations of the polar mass moment of inertia caused by the residual unbalance in the rotor are considered. For the drive system with fluctuations of the time-varying stiffness and polar mass moment of inertia, the time-dependent coefficient dynamic equations are required. Generally, the dynamic equations can be simplified as the constant coefficient dynamic equations by transforming the fluctuations of the time-varying stiffness into equivalent exciting forces. The forced vibration of the drive system to the mesh stiffness excitation is presented by use of the constant coefficient dynamic equations. The influences of the system parameters on the forced vibration are also discussed. Under certain conditions, unstable vibrations will occur and the time-dependent coefficient dynamic equations are used to obtain the stable conditions of the system vibrations under the mesh stiffness disturbance and the unbalance disturbance in the rotor.

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