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Published Articles

The Volume 10, No 2, June 2005

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Measurements of Tyre/Road Noise and of Acoustical Properties of Porous Road Surfaces

Malcolm J. Crocker, Zhuang Li, Jorge P. Arenas


turbulence. Tyre/road interaction noise is receiving increasing attention. The main tyre/road interaction mechanisms consist of: 1) impacts between the tyre tread and the road, which cause radial, tangential, and sidewall tyre tread and carcass vibration and consequent noise radiation, and 2) air displacement mechanisms caused by the tyre, the major one probably being the so-called ?air pumping? in, or between, the tyre tread and the road surface. In this paper, the results of tyre/road interaction noise measured on different types of road pavement surfaces are presented. The results were obtained by means of the close proximity method. The sound absorption coefficients of dense and porous road surfaces were measured in the Sound and Vibration Research Laboratory at Auburn University 1) using core samples with 102 and 153 mm diameter impedance tubes and 2) with the same two impedance tubes mounted vertically on pavement slabs with surfaces similar to those of the core samples. In addition, the sound absorption coefficient of road surfaces of similar type to those of the cores and slabs was measured in situ, also with the tubes mounted vertically. The peak sound absorption coefficient measured of the fine and coarse mix aggregate porous surfaces suggests that the first peak frequency and peak absorption coefficient magnitude is only slightly different for the two types of porous surfaces. Since the fine mix aggregate porous surface is smoother, it is preferred since it should result in less tyre tread impact noise and thus lower overall tyre noise than the coarse aggregate surface. A porous surface of between 38 and 50 mm thickness is recommended for the type of porous surface examined, if a peak absorption frequency of about 1000 Hz is desired. Such a surface would be most effective at reducing interstate highway noise of automobiles. In addition, porous road pavement surfaces have the further advantage that they drain water well and reduce the splash up behind vehicles during heavy rainfalls.

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Numerical Modelling of the Vibro-acoustic Behaviour of a Vehicle Gearbox

Newton S. Soeiro, Elias B. Teodoro, Samir N.Y. Gerges, Roberto Jordan, Jorge P. Arenas


In this article, a global vibro-acoustic method to model gearboxes, which is based on the finite element and boundary element methods, is presented. The final aim of the method is to investigate the vibration and noise transmitted to the gearbox structure casing, which originate from the excitation caused by the gear train, in order to predict the vibro-acoustic parameters. Thus, the mathematical formulae that allow the determination of generalised stiffness matrices are presented in terms of the bearing and gear elements. A numerical model of the geared axle system that allows the estimation of the bearing reactions due to the gear forces transmitted is developed. This model takes into account the influence of modifying the gears teeth profile. The finite elements and boundary meshes were devised and generated in order to represent the gearbox. These meshes were used for the estimation of the acoustic parameters and for vibro-acoustic predictions.

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Parameter Characterisation of the Bouc/Wen Mechanical Hysteresis Model for Sandwich Composite Materials using Real Coded Genetic Algorithms

Klaus H. Hornig and George T. Flowers


One major advantage of composite materials for structural and machinery applications is their relatively high energy dissipation characteristics. Accordingly for advanced design applications, it is important to have a thorough understanding of the material damping behaviours. In general, material damping tends to be a complex nonlinear function of vibration amplitude, frequency, loading, and material formulation. One approach for identifying damping characteristics uses mechanical hysteresis curves. It is well recognised that the area enclosed by such curves is proportional to the energy dissipation per cycle of oscillation. However, the specific shape of the curve also has important implications for characterising the specific functional form of the damping. Therefore, it is important to develop methods for accurately accounting for such effects. The current work explores the application of Real Coded Genetic Algorithms (RCGA) for curve-fitting a nonlinear mathematical model (the Bouc/Wen Hysteresis Model) to synthetic (computer-generated) and experimentally obtained hysteresis loops for a sandwich composite material. The model depends on seven parameters, for which patterns and tendencies are searched as functions of the type of material. The solutions of the model enable us to determine also the contributions of the nonlinearities to the energy dissipation.

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Startup Dynamic Behaviour of a Jeffcott Rotor

H. Diken and K. Alnefaie


In this study, the dynamic behaviour of a Jeffcott rotor during startup is analysed. Equations of a Jeffcott rotor model are obtained assuming that rotor speed is not constant. Startup speed is assumed to have a second order control system transfer function. Numerical calculations show that if the rotor is running in a subcritical condition, maximum whirl radius is reached before the rotor reaches the critical speed. If the rotor is running in a supercritical condition, the maximum whirl radius is reached after the rotor passes the critical speed. An overshoot of the startup speed significantly increases the value of the maximum whirl radius. It is also observed that, for a supercritical startup, the whirl radius has a cyclic behaviour before it reaches a steady state value.

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Vibration Diagnosis of Failure of Mechanical Coupling between Motor and Pump Rotors

Jyoti K. Sinha and A. Rama Rao


A failure of the mechanical coupling between the rotors of the pump and motor for two pump assemblies was observed since the pumps commissioned in 1984. The use of vibration based conventional condition monitoring during the pump operation could not identify the root cause, though high levels of vibration were observed. Modal tests conducted on the complete assembly of pumps and piping layout identified resonance as the root cause. Vibration measurements, data analysis, and observations that led to the identification of the root cause for the failure of the mechanical coupling have been reported here as a case study.

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Effect of Composite Material Parameters on Vibrational Behaviour of Pipes Conveying Fluid

E. Rabeih, M. El-Maddah, R. Gadelrab and A. Atwa


High flow velocity causes instability in pipes. The critical flow velocity, which causes the onset of the pipe?s instability, depends on the mechanical and physical parameters of its material. For pipes made of fibre composite materials, these properties depend on composite material parameters such as the fibre orientation angle and fibre volume fraction. The effect of these parameters on the natural frequencies and critical flow velocities of composite material pipes has been investigated for different pipe configurations. A finite element model derived based on the Timoshenko beam theory for a generally orthotropic material pipe has been used in this paper. The results showed that the critical flow velocity is greatly affected by the composite material parameters.

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