Showing papers by "S. P. Harsha published in 2009"

Fault diagnosis of a rotor bearing system using response surface method

Abstract: Dynamic analysis of a high-speed rotor bearing systems is challenged by their highly nonlinear and complex properties. Hence, an approximate response surface method (RSM) is utilized to analyze the effects of design and operating parameters on the vibration signature of a rotor-bearing system. This paper focuses on accurate performance prediction, which is essential to the design of high performance rotor bearing system. It considers distributed defects such as internal radial clearance and surface waviness of the bearing components. In the mathematical formulation the contacts between the rolling elements and the races are considered as nonlinear springs, whose stiffnesses are obtained by using Hertzian elastic contact deformation theory. The governing differential equations of motion are obtained by using Lagrange's equations. In terms of the feature that the nonlinear bearing forces act on the system, a reduction method and corresponding integration technique is used to increase the numerical stability and decrease computer time for system analysis. Parameters effects are analyzed together and its influence considered with DOE and Surface Response Methodology are used to predict dynamic response of a rotor-bearing system.

Non-linear vibration signature analysis of a high-speed rotating shaft due to ball size variations and varying number of balls

Abstract: In this article, a mathematical model has been developed to predict the non-linear dynamic behaviour of a high-speed unbalanced rotating shaft due to ball size variations and varying number...

Chaos and Nonlinear Dynamic Analysis of High-Speed Rolling Element Bearings due to Varying Number of Rolling Elements

Abstract: This paper presents a mathematical model to investigate the nonlinear dynamic behavior of a rotorbearing system due to varying the number of rolling elements. In the formulation, the contacts between rolling elements and inner/outer races are considered as nonlinear springs. A nonlinear damping formula, correlating the contact damping force with the equivalent contact stiffness and contact deformation rate is used in the derivation. The effects of varying number of rolling elements on periodic, quasi-periodic and chaotic behavior are analyzed. Results presented in form of frequency response, Poincare maps and Orbit plots to show the vibration characteristics of the rotor and its bearings.

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

Abstract: In this paper an analytical model has been developed to investigate the nonlinear dynamic behavior of an unbalanced 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 Poincare maps. The highest radial vibrations due to ball-size variation were at a speed of the number of balls multiplied by the cage speed (ω = kωcage Hz). The other vibrations due to ball-size variation occurred at V C ± kωcage, where k was a constant. The current study provides a powerful tool for design and health monitoring of machine systems.

The Dynamic Behaviour of Chiral, Fixed-Free, Single-Walled Carbon Nanotube-Based Nanomechanical Mass Sensors Due to Atomic Vacancies:

Abstract: The dynamic analysis of single-walled carbon nanotubes (SWCNTs) with chiralities has been performed using an atomistic finite element method. SWCNTs with different chiral angles are considered for the resonant frequency analysis. The cantilever carbon nanotube (CNT) is modelled by considering it as a space frame structure similar to three-dimensional beams and point masses. The beam element elastic properties are calculated by considering the mechanical characteristics of covalent bonds between the carbon atoms in the hexagonal lattice. The mass of each beam element is assumed as a point mass at nodes coinciding with carbon atoms. This atomistic simulation approach is used to visualize the effect of defects such as atomic vacancies in the CNT on the resonant frequency. The variation of the atomic vacancy is performed along the length and the response is obtained for different chiralities. It is observed that there is a reduction in the simulated natural frequency due to the atomic vacancy. This has a sign...

Fault Diagnosis of Ball Bearings Using Soft Computing

Abstract: This paper presents the condition monitoring and fault diagnosis of rolling element bearings using Support Vector Machines (SVM). The vibration response of healthy bearings and bearings with various component defects such as outer race, inner race, balls and their combination have been analyzed. From the obtained vibration spectrum, it is clearly seen that a discrete peak of excitation appeared for the specific defect of bearings. In this paper, various faults of the bearings has been simulated and classified. The process includes, data acquisition, feature extraction from time response and a knowledge based system to classify faults. Features defining feature vectors are formed using statistical techniques and are fed as input to the support vector machine (SVM) classifiers. Knowledge based system developed for classification can be used for automatic recognition of machinery faults based on feature vector.Copyright © 2009 by ASME

Vibration signature analysis of high speed unbalanced rotating shaft supported on ball bearings

Abstract: In this paper, non-linear dynamics of a high speed unbalanced rotor supported on ball bearings is analysed. The approach presented here accounts for contacts between balls and inner/outer races. The non-linearity in the rotor bearing system has been considered mainly due to Hertzian contact, unbalanced shaft and radial internal clearance. In the formulation, the contacts between balls and inner/outer races are considered as non-linear springs and also used non-linear damping, which is developed by correlating the contact damping force with the equivalent contact stiffness and contact deformation rate. The results show the appearance of instability and chaos in the dynamic response as the speed of unbalanced shaft is varied. The appearance of the regions like periodic, sub-harmonic and chaotic behaviour is observed to be strongly sensitive to the speed of the rotating shaft. Techniques like Poincare maps and frequency spectra are used to elucidate and to illustrate the diversity of the system behaviour.