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

The dynamics and diagnostics of cracked rotor have been gaining importance in recent years. Relatively few authors have addressed the problem of multi crack assessment for rotors. In the present study a model-based method is proposed for the on-line identification of two cracks in a rotor. The fault-induced change of the rotor system is taken into account by equivalent loads in the mathematical model. The equivalent loads are virtual forces and moments acting on the linear undamaged system to generate a dynamic behaviour identical to the measured one of the damaged system. The rotor has been modelled using finite element method, while the cracks are considered through local flexibility changes. The cracks have been identified for their depths and locations on the shaft. The nature and symptoms of the fault, that is crack, are ascertained using the FFT. © 2003 Elsevier Ltd. All rights reserved.

Mechanical Systems and Signal Processing

Model-based identification of two cracks in a rotor system

World University root node

Journal of Sound and Vibration

Comments on "vibration characteristics of slotted shafts" (multiple letter)

The vibration in rotating machinery is mostly caused by unbalance, misalignment, mechanical looseness, shaft crack and other malfunctions. Inspite of its importance and frequent observations in practice, only a few researchers have paid attention to misalignment. In the present study a model based method is proposed for the on-line identification of coupling misalignment in a rotor-coupling-bearing system. The fault-induced change of the rotor system is taken into account by equivalent loads in the mathematical model. The equivalent loads are virtual forces and moments acting on the linear undamaged system to generate a dynamic behaviour identical to the measured one of the damaged system. The rotor system, including flexible coupling has been modelled using finite element method (FEM). The reaction forces and moments due to misalignment have been estimated and are applied at the coupling nodes. Systematic fault identification is done with model-based approach. The nature and symptoms of the fault that is coupling misalignment are ascertained using the FFT. Copyright © 2003 by DEStech Publications, Inc. All right reserved.

Structural Health Monitoring 2003: From Diagnostics and Prognostics to Structural Health Management - Proceedings of the 4th International Workshop on Structural Health Monitoring, IWSHM 2003

Identification of coupling misalignment in a rotor-coupling-bearing system

The dynamics of cracked rotors has been the study for the last three decades. However, considering the importance in the practical fields, the vibration characteristics of cracked rotors are still under active investigation. It needs more attention, particularly with the emerging of new materials such as composites for shafts. The present study aims at the analysis of the cracked composite shafts. The composite shaft has been modelled based on first order shear deformation theory using finite element method with shell elements. Different materials such as, boron-epoxy, carbon-epoxy and graphite-epoxy have been tried for various stacking sequences. The influences of crack parameters, fibre orientation (stacking sequences) and material properties on the vibration characteristics of composite shafts have been studied.

Journal of Reinforced Plastics and Composites

Dynamics of cracked composite shafts

The dynamics and diagnostics of a cracked rotor have been gaining importance in recent years. Vibration monitoring during start-up or shut-down is as important as during steady-state operations to detect cracks especially for machines such as aircraft engines which start and stop quite frequently and run at high speeds. In the present study, a model-based method is proposed for the on-line identification of cracks in a rotor while it is passing through its flexural critical speed. The fault-induced change of the rotor system is taken into account by equivalent loads in the mathematical model. The equivalent loads are virtual forces and moments acting on the linear undamaged system to generate a dynamic behaviour identical to the measured one of the damaged system. The rotor has been modelled using FEM, while the crack is considered through local flexibility change. The crack has been identified for its depth and location on the shaft for different rotor accelerations. The nature and symptoms of the fault - crack - are further ascertained using the continuous wavelet transform. Copyright © 2003 Sage Publications.

Structural Health Monitoring

Identification of a crack in a rotor system using a model-based wavelet approach

Crack detection through wavelet transform for a run-up rotor

Crack detection and monitoring in a rotor supported on fluid film bearings: Start-up vs run-down

The method of multiple scales and the related method of averaging are commonly used to study slowly modulated oscillations. If the system of interest is a slightly perturbed harmonic oscillator, then these techniques can be applied easily. If the unperturbed system is strongly nonlinear (though possibly conservative), then these methods can run into difficulties due to the impossibility of carrying out required analytical operations in closed form. In this paper, we abandon the requirement of closed form analytical treatment at all stages. Instead, Galerkin projections are used to obtain approximate realizations of the method of multiple scales. This paper adapts recent work using similar ideas for approximate realizations of the method of averaging. A key contribution of the present work is in the systematic identification and removal of secular terms in the general nonlinear case, a procedure that is more difficult than for the perturbed harmonic oscillator case, and that is unnecessary for averaging. A strength of the present work is that the heuristics (Galerkin) and asymptotics (multiple scales) are kept distinct, leaving room for systematic refinement of the former without compromising the asymptotic features of the latter.

Nonlinear Dynamics

Multiple scales via Galerkin projections: Approximate asymptotics for strongly nonlinear oscillations

Measurements were done to determine the influence of a transverse crack on the mobility of a rotor-bearing system. The results show that the mobility changes substantially due to the presence of crack and follows definite trends with the crack depth and direction of force application. The significant changes in mobility were observed at the natural frequency and at the running frequency of the rotor system. Good agreement between the experimental results and numerical simulations has been observed. The measurement of mobility has been suggested for crack detection and condition monitoring of rotor-bearing systems. © 2002 Acoustical Society of America.