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Published Articles


The Volume 14, No 3, September 2009




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Dynamic Modeling of a Boring Bar Using Theoretical and Experimental Engineering Methods Part 1: Distributed-Parameter System Modeling and Experimental Modal Analysis

Tatiana Smirnova, Henrik Akesson, Lars Hakansson


https://doi.org/10.20855/ijav.2009.14.3243


Boring bar vibration is a common problem during internal turning operations and is a major problem for the manufacturing industry. High levels of boring bar vibration generally occur at frequencies related to the first two fundamental bending modes of a boring bar. This is the first of two companion papers that summarize the theoretical and experimental work carried out concerning modeling of dynamic properties of boring bars. This paper introduces the Timoshenko beam theory for the modeling of clamped boring bars. Also, the traditional Euler-Bernoulli beam theory is applied. These continuous system methods have been utilized to produce fixed- free beam models of the clamped boring bar. In order to improve accuracy of dynamic models of clamped boring bars, the modeling of the boring bar clamping is addressed by means of multi-span beam models with pinned boundary conditions. The derived boring bar models have also been compared with results obtained by means of experimental modal analysis, conducted on the actual boring bar clamped in a lathe. The multi-span beam boring bar models display higher correlation with experimental modal analysis results as compared to fixed-free beam models. For the fixed-free beams the Timoshenko model results in the highest correlation with the experimental results. On the other hand, the interval in frequency and the orientation of the two fundamental modes demonstrate differences, particularly between the continuous system models and the experimental results.


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Dynamic Modeling of a Boring Bar Using Theoretical and Experimental Engineering Methods Part 2: Finite Element Modeling and Sensitivity Analysis

Tatiana Smirnova, Henrik Akesson, Lars Hakansson


https://doi.org/10.20855/ijav.2009.14.3244


This is the second of two companion papers that summarize the theoretical and experimental work carried out concerning modeling of dynamic properties of boring bars. This paper introduces the finite element method for the modeling of clamped boring bars. The ?3-D? FE models of the system boring bar ? clamping house as well as the ?1-D? FE models of the clamped boring bar were derived. In particular, the modeling of the boring bar clamping is addressed. Dynamic properties predicted based on the developed FE models of the clamped boring bar were compared with the ones estimated by means of experimental modal analysis conducted on the actual boring bar clamped in the lathe. The ?3-D? FE models display substantially higher correlation with the experimental modal analysis results compared to the "1-D" FE models. A ?3-D? FE model of the boring bar ? clamping house manages to model the distance in frequency and the orientation of the two fundamental modes to a large extent. The importance of the modeling of the boring bar boundary conditions for the accuracy of dynamic models of boring bars is demonstrated. The sensitivity of the natural frequency estimates produced by means of the FE and the continuous system (presented in Part 1) boring bar models with respect to variations in material density and Young?s elastic modulus has been addressed.


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Evaluation of Whole-Body Vibration and Ride Comfort in a Passenger Car

Hassan Nahvi, Mohammad Hosseini Fouladi and Mohd Jailani Mohd Nor


https://doi.org/10.20855/ijav.2009.14.3245


Whole-body vibration transmission influences comfort, performance, and long-term health of the driver. This current study is an objective evaluation of vehicle comfort characteristics based on standard mathematical formulae and frequency analyses. A variety of road types were selected and quantified by using the International Roughness Index (IRI). To assess vibrations transmitted to the passengers, vibration dose values (VDV), kurtosis, frequency response functions (FRF), and power spectral densities (PSD) of the compartment recorded signals were evaluated. SEAT values based on VDV outputs qualified the seat suspension as a vibration isolator, whereas the FRF and PSD quantified that behaviour through frequency analyses. Results indicate that energy concentration is at frequencies lower than 30 Hz. Such low frequency excitations are well attenuated by seat suspension in the vertical direction but are amplified (up to five times in harsh conditions) by a backrest in the fore-aft trend. Signals are amplified beyond 30 Hz, but amplitudes are still very low. It seems that backrest assembly still can be improved to become a better isolator. However, T15 (time to reach severe discomfort), even in harsh conditions, is more than three hours, which exhibits the overall good quality of the vehicle suspension systems. Kurtosis and VDV correlate with IRI and may be used as two objective metrics, together with jury evaluation, to create a vehicle vibration-comfort index in the future.


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On Active Noise Reduction in a Cylindrical Duct with Flow

Louis M. B. C. Campos and Fernando J. P. Lau


https://doi.org/10.20855/ijav.2009.14.3246


An analytical approach to active-noise reduction is presented in the case of a line-source in a cylindrical enclosure, minimizing the noise in a sector, corresponding to (i) the passenger head area of an aircraft cabin for a cylindrical fuselage, in the absence of flow, and (ii) a sector or an annulus of noise reduction outside of a cylindrical duct carrying a uniform axial flow of an arbitrary Mach number. In both cases, the noise is assumed to consist of the superposition of modes, and the anti-noise is used to cancel the fundamental mode and/or specified harmonics. The total acoustic energy in the region of interest is calculated for the residual and original sound field, and their ratio specifies the noise-reduction function. The latter is minimized by adjusting the source position, and the noise reduction achieved is plotted versus the dimensionless radial wave number, taking into account mean flow effects. The case of the original noise field, consisting of the fundamental and the anti-noise source set to cancel this, is taken as the baseline for further comparison. Cases with several anti-noise line-sources set to cancel various combinations of the fundamental and harmonics are also considered; for example n anti-noise sources are used to cancel the fundamental and first n-1 harmonics. For a given noise field, the improvement in noise-reduction performance with the number of anti-noise sources is demonstrated, both for cylindrical and planar enclosures. The addition of anti-noise sources while reducing noise at low frequencies can cause an increase in noise at high frequencies; the latter may be countered by passive means. All results obtained follow from the calculation of the noise-reduction function in terms of Bessel functions, which can be evaluated with their zeros, using asymptotic methods, which are shown to be reasonably accurate.


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Vibration Signature Analysis of High-Speed Unbalanced Rotors Supported by Rolling-Element Bearings due to Off-Sized Rolling Elements

Sanjay H. Upadhyay, Suraj P. Harsha, and S. C. Jain


https://doi.org/10.20855/ijav.2009.14.3247


In this paper an analytical model has been developed to investigate the nonlinear dynamic behavior of an unbal- anced rotor-bearing system due to ball size variation of the rolling elements. Two cases of ball-size variation were considered: variations of 0.2 micron and 2 microns. In the analytical formulation, the contact between rolling elements and inner/outer races was considered a nonlinear spring, which became stiff using the Hertzian elastic deformation theory. A detailed contact-damping model reflecting the influences of the surface profiles and the speeds of both contacting elements was developed and applied in the rolling-element bearing model. The mathematical formulation accounted for the sources of nonlinearity, such as the Hertzian contact force, varying speed, and radial internal clearance. The equations of motion of a rolling-element bearing were formulated in generalized coordinates, using Lagrange's equations that consider the vibration characteristics of the individual constituents, such as inner race, outer race, rolling elements, and shaft, in order to investigate the structural vibration of the bearing. All results have been presented in form of Fast Fourier Transformations (FFT) and Poincar´e maps. The highest radial vibrations due to ball-size variation were at a speed of the number of balls multiplied by the cage speed (w = Kwcage Hz). The other vibrations due to ball-size variation occurred at VC =Kwcage, where k was a constant. The current study provides a powerful tool for design and health monitoring of machine systems.


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