Department of Mechanical Engineering

Indian Institute of Technology Palakkad&nbsp;(IIT Palakkad or IIT PKD) is a public autonomous&nbsp;engineering&nbsp;and&nbsp;research&nbsp;institute located in&nbsp;Palakkad,&nbsp;Kerala. It was&nbsp;one of the five new&nbsp;IITs&nbsp;proposed in the&nbsp;2014 Union budget of India. The campus was inaugurated on 3 August 2015. The institute has 94 faculty, 978 students, and 63 non-teaching staffs.

IT Palakkad currently offers four-year Bachelor of Technology (B.Tech) and two years MS programmes in 8 different engineering disciplines including&nbsp;Computer Science, Electrical, Mechanical, Civil among others.

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IIT Palakkad

Identification of crack location and magnitude through measurement in changes in system characteristics, such as modal measurements has been studied by various researchers. In the present work based on the new method proposed by Gounaris et al (1996) for crack detection through coupled response measurements, experiments were carried out on a cracked cantilever beam for eigenfrequencies, bending and axial response measurements. It has been observed that the rate of change of direct response (bending) is much less at small cracks while that of the coupled response (axial) changes substantially allowing diagnoses of smaller cracks.

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American Society of Mechanical Engineers (Paper)

Crack identification in a cantilever beam using coupled response measurements

The dynamic behaviour of structures - in particular, rotors containing cracks - is a subject of considerable current interest. Several researchers have developed models of cracked rotor systems considering mainly the transverse surface crack. In the present study finite element (FEM) analysis of a rotor-bearing system for flexural vibrations has been considered by including a shaft having a slant crack that has resulted from the fatigue of the shaft due to the torsional moment. A flexibility matrix for a slant crack and later the stiffness matrix of a slant cracked element have been developed to be used subsequently in the FEM analysis of the rotor-bearing system. The frequency spectrum of the steady state response of the cracked rotor was found to have sub-harmonic frequency components at an interval frequency corresponding to the torsional frequency, which can be used for crack detection. © 1997 Academic Press Limited.

Journal of Sound and Vibration

Dynamic analysis of a rotor system considering a slant crack in the shaft

A Reynolds-type equation for finite hydrodynamic bearings, (plane slider and cylindrical journal), with rough surfaces (longitudinal, transverse and isotropic roughnesses), has been solved using the stochastic finite element method considering film thickness to be a stationary, ergodic stochastic process with mean zero. Mean steady-state characteristics have been obtained and compared with those obtained by previous investigators. The effect of a spatially randomly varying component of roughness has been studied by giving different input standard deviations of film thickness and calculating output standard deviation of maximum pressure for different scales of fluctuation using the first-order second-moment method. © 1997 Taylor & Francis Group, LLC.

Tribology Transactions

Stochastic fem analysis of finite hydrodynamic bearings with rough surfaces

Identification of crack location and magnitude through measurement in changes in system characteristics, such as modal measurements has been studied by various researchers. In the present work based on the new method proposed by Gounaris et al (1996) for crack detection through coupled response measurements, experiments were . carried out on a cracked cantilever beam for eigenfrequencies, bending and axial response measurements. It has been observed that the rate of change of direct response (bending) is much less at small cracks while that of the coupled response (axial) changes, substantially allowing diagnoses of smaller cracks. Copyright © 1997 by ASME.

Proceedings of the ASME Turbo Expo

Usually, while modelling rotor-bearing systems the bearings are treated as point supports. In the present work using the finite element technique, the eigenvalue and stability analysis of rotors are studied by considering the distributed bearing stiffness and damping. Two models are considered: (i) uniform distribution model and (ii) parabolic distribution model. The results are compared with that of a rotor on point supports. Stability limits of a rotor supported on different types of bearings, viz. cylindrical journal bearings, tilting pad journal bearings, offset and three lobe journal bearings have been presented. Copyright © 1996 Elsevier Science Ltd.

Computers and Structures

Analysis of rotors considering distributed bearing stiffness and damping

The shaft misalignment, even being a common fault in rotating machinery, is not sufficiently studied. The present work addresses effects of misalignment in rotating machinery. An attempt to give a theoretical model for a rotor-coupling-bearing system has been done. The rotor-bearing system including the flexible coupling is modelled using the finite elements. The reaction forces and moments developed due to flexible coupling misalignment both for parallel and angular are derived and introduced in the model. Vibration analyses such as eigen value analysis and unbalance response are carried out for the rotor system with misaligned shafts.

Vibration analysis of rotor - coupling - bearing system with misaligned shafts

A stochastic finite element model of a one-dimensional hydrodynamic bearing with rough surfaces (longitudinal and transverse roughnesses), considering film thickness to be a stochastic variable, has been formulated and steady-state characterstics studied. The results expressed as mean values of load carrying capacity, flow rate, frictional force and coefficient of friction (in non-dimensional form) are in good agreement with those obtained by analytical methods by previous investigators. Further standard deviation of pressure, at a given node, has been calculated for different input standard deviations of stochastic variable and scales of fluctuation using the first-order (perturbation)-second moment method.

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Stochastic FEM model of one-dimensional hydrodynamic bearings with rough surfaces

The shaft misalignment, even being a common fault in rotating machinery, is not sufficiently studied. The present work addresses effects of . misalignment in rotating machinery. An attempt to give a theoretical model for a rotor-coupling-bearing system has been done. The. rotor-bearing system including the flexible coupling is modelled using the finite elements. The reaction forces and moments developed due to flexible coupling misalignment both for parallel and angular are derived and introduced in the model. Vibration analyses such as eigen value analysis and unbalance response are carried out for the rotor system with misaligned shafts. Copyright © 1996 by ASME.

ASME 1996 International Gas Turbine and Aeroengine Congress and Exhibition, GT 1996

Vibration analysis of rotor-coupling-bearing system with misaligned shafts

The equations of motion, with four degrees of freedom, taking into consideration the flexibility, damping and cross coupling of the fluid film bearings are derived for a cracked Jeffcott rotor supported on fluid film bearings. Dimensionless equations are developed for dynamic radial load, dynamic pressure developed in the fluid film bearings and coefficient of dissipation considering the journal vibrations in two harmonics; bearing fluid film stiffness and damping coefficients. These are applied to a cracked Jeffcott rotor supported on different types of bearings, i. e., cylindrical journal bearings, offset cylindrical bearings, tilting pad journal bearings and three-lobe bearings. Based on the allowable dynamic pressure developed in the fluid bearings, the severity of cracked shaft and allowable crack depths are estimated in this study. Measurement of dynamic pressure and dissipation for monitoring the crack growth is suggested. However, 2x vibration is the best indicator of cracks in the shafts. © 1995 Taylor & Francis Group, LLC.

Severity estimation of cracked shaft vibrations within fluid film bearings

Improper aligning of shafts through couplings often leads to severe vibration problems in many rotating machines. The rotor-bearing system is modelled using higher order finite elements by considering deflection, slope, shear force, bending moment with eight degrees of freedom per node. The reaction forces, moments developed due to flexible coupling misalignment are derived and introduced in the model. The imbalance response in two harmonics is evaluated. The increase in harmonics with misalignment can easily be modelled by using FEM analysis. The location of the coupling with respect to the bending mode shape has a strong influence on the vibrations. © 1995 Academic Press. All rights reserved.