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 of asymmetric rotors has been investigated in the literature. However, considering the importance in the practical fields, the vibration characteristics of slotted shafts are not studied in detail. 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 slotted shafts including the compensatory inertia slots. Also, the slotted 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 slot parameters, stacking sequences and material properties have found to influence to great extent on the vibrational characteristics of rotors. The results are compared with those of isotropic slotted shaft.

World University root node

Journal of Sound and Vibration

Vibration characteristics of slotted shafts

We revisit the simplest walker studied earlier by Garcia and co-workers. We extend the small-slope stability analysis to second order, substantially improving accuracy, and also provide some details left out of the earlier work. We develop an alternative (reverse) approach for the stability analysis, which involves shorter calculations: for stability analysis upto any given order, the new procedure requires calculations to one order less than the previous (forward) procedure. The stability results obtained by the two methods are, nevertheless, equivalent.

Nonlinear Dynamics

An alternative stability analysis technique for the simplest walker

We study small perturbations of three linear Delay Differential Equations (DDEs) close to Hopf bifurcation points. In analytical treatments of such equations, many authors recommend a center manifold reduction as a first step. We demonstrate that the method of multiple scales, on simply discarding the infinitely many exponentially decaying components of the complementary solutions obtained at each stage of the approximation, can bypass the explicit center manifold calculation. Analytical approximations obtained for the DDEs studied closely match numerical solutions.

Multiple scales without center manifold reductions for delay differential equations near Hopf bifurcations

Bearing race faults have been detected by using discrete wavelet transform (DWT). Vibration signals from ball bearings having single and multiple point defects on inner race, outer race and the combination faults have been considered for analysis. The impulses in vibration signals due to bearing faults are prominent in wavelet decompositions. It is found that the impulses appear periodically with a time period corresponding to characteristic defect frequencies. It has been shown that DWT can be used as an effective tool for detecting single and multiple faults in the ball bearings. © 2002 Published by Elsevier Science Ltd.

Tribology International

Application of discrete wavelet transform for detection of ball bearing race faults

The vibrational characteristics of a slant-cracked rotor passing through its flexural critical speed have been analysed by using finite element method for flexural vibrations. The transient response of a cracked rotor has been obtained by applying an unbalance force and a harmonically varying torque on it. When a crack is present in the rotor, the sub and super harmonic frequency components at an interval frequency corresponding to torsional frequency were found to be centered on critical speed of the rotor system. A parametric study has been carried out for transient response of the rotor for different crack depths, rotor angular accelerations and torsional frequencies. Some suggestions for detection and monitoring of the slant cracks in the rotor are described. © 2002 Published by Elsevier Science Ltd.

Mechanism and Machine Theory

Transient lateral analysis of a slant-cracked rotor passing through its flexural critical speed

The transient response of a misaligned rotor-coupling-bearing system passing through the critical speed has been analysed by using the finite element method (FEM) for flexural vibrations. The coupling has been modelled in two ways: a frictionless joint and a joint with stiffness and damping. From the vibration analysis, the subcritical speeds at one-half, one-third and one-fourth the critical speed have been found when the misaligned rotor-coupling-bearing system passes through its critical speed. The continuous wavelet transform (CWT) has been used as a tool to extract the silent features from the time response of the rotor system. A parametric study has been carried out to investigate the transient response of this rotor system for different angular accelerations in different types of misalignment.

Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science

Vibration analysis of a misaligned rotor-coupling-bearing system passing through the critical speed

The dynamic behavior of structures, in particular, that of a rotor, containing cracks is a subject of considerable current interest. In the present study, the influence of a transverse surface crack, both open and breathing conditions, on the mechanical impedance of the rotor-bearing system, has been investigated by FEM analysis for flexural vibrations. The results show that the mechanical impedance changes substantially due to the presence of crack and follow definite trends with the crack parameters (depth and location) and force location. The normalized mechanical impedance of rotor system is more sensitive to the breathing crack when compared to the open crack. The sudden changes in mechanical impedance have been observed at the multiples of the running frequency for the breathing crack. The measurement of mechanical impedance has been suggested for crack detection and condition monitoring of rotor-bearing systems. © 2001 Acoustical Society of America.

Journal of the Acoustical Society of America

Detection and monitoring of cracks using mechanical impedance of rotor-bearing system

Mechanical Systems and Signal Processing

Detection and monitoring of cracks in a rotor-bearing system using wavelet transforms

Dynamic analysis of a cracked Jeffcott rotor has been carried out, considering the effects of fluid film bearings. Q factors and dissipation coefficients have been evaluated in addition to the harmonic responses of the rotor. The coast down phenomenon was analysed for the effects of crack depth. Sensitivity studies were carried out, considering dissipation, responses and the Q factor. Measurement of Q factors of second harmonics, Q(x2) and Q(y2), has been suggested for crack detection, while measurement of Q factors of first harmonics is recommended for crack monitoring as these proved to be more sensitive to cracks compared with other methods. Dynamic analysis of a cracked Jeffcott rotor has been carried out, considering the effects of fluid film bearings. Q factors and dissipation coefficients have been evaluated in addition to the harmonic responses of the rotor. The coast down phenomenon was analyzed for the effects of crack depth. Sensitivity studies were carried out, considering dissipation, response and the Q factor. Measurement of Q factors of second harmonics, Qx(2) and Qy(2), has been suggested for crack detection, while measurement of Q factors of first harmonics is recommended for crack monitoring as these proved to be more sensitive to cracks compared with other methods.

Detection and monitoring of cracks in rotors through Q factors

Non-linear transient stability analysis has been performed to study the sub-synchronous whirl stability of a rigid rotor supported on two symmetric hydrodynamic bearings with rough surfaces subjected to a unidirectional constant load. A Reynolds type equation for finite hydrodynamic bearings, with different models of rough surfaces, has been solved using the stochastic finite element method. The trajectories of the journal center have been obtained by solving the equations of motion of the journal center by the fourth-order Runge-Kutta method. Results show an increase in the stability with transverse roughness and a decrease in the stability with isotropic roughness. A small improvement in stability is obtained with longitudinal roughness. © 2000 Taylor & Francis Group, LLC.