A review on machinery diagnostics and prognostics implementing condition-based maintenance

Artificial intelligence for fault diagnosis of rotating machinery: A review

Vibration of cracked structures: A state of the art review

Recent advances in time–frequency analysis methods for machinery fault diagnosis: A review with application examples

Residual life predictions for ball bearings based on self-organizing map and back propagation neural network methods

Owing to increase in the demand for power, a number of power plants have been installed in the recent past. One of the vital components in these plants is gasketed flange joint. The behaviour of gasketed flange joint is highly dependent on the deformation characteristics of gasket material. In the present study, the deformation characteristic of spiral wound gasket along thickness direction is determined experimentally for different loading rates. Gasket has high nonlinearity under both loading and unloading, with hysteresis. Based on its characteristics, the flange joint is analysed to study its performance and leakage behaviour under static condition. 3D finite element model of flange joint is developed by considering the gasket as interface entity. Finite element analysis of flange joint is performed by including the nonlinear hysteretic behaviour of gasket, under different loading rate and frictional contact between joint members. The influence of different loading and unloading rates is emphasized on the sealing performance of flange joint using leakage pressure. The gasket deforms more when loaded at low rate. This phenomenon also affects the ability to withstand internal fluid without leakage. The maximum safe pressure without leakage increases, when gasket is loaded and unloaded at low rate.

Influence of Loading Rate on Deformation Behaviour and Sealing Performance of Spiral Wound Gasket in Flange Joint

In this study, displacement and strain energy mode shapes obtained from the structure, are processed using continuous spatial wavelet transforms for damage identification. A cantilever and simply supported beam are analysed in ANSYS to obtain mode shapes by performing modal analysis both for damaged and undamaged conditions. Different wavelets are processed to choose the best mother wavelet for detecting crack, a representation of damage. The dimensions of crack like depth are varied from 0.5 mm. Spatial distribution of wavelet coefficients obtained is used for identifying the damage. The quantification of the damage is done by using Lipchitz constant. It is observed that by using strain energy mode shapes the percentage of damage (crack) identification level can be improved than by using displacement mode shapes. The minimum damage level that the strain mode shape can identify is approximately 3% of the element thickness, whereas with displacement mode shapes, it is about 7% of the element thickness. Different types of crack configurations like single surface crack, double surface cracks and internal cracks are simulated and studied using both the modal methods. It is observed that the strain energy mode method could identify internal cracks also.

Damage Identification and Quantification in Structures Using Wavelet Analysis

Low stiffness bearings are useful to reduce the force transmitted from the vibrating rotor to the surrounding support structure. However, having low stiffness requires us to cross the low rigid body critical frequency while accelerating to operating rpm. In this work the stiffness of the bearing is changed online during operation by using an active magnetic bearing instead of a conventional constant stiffness rolling element bearing. This methodology is shown for a rigid rotor using both simulation and experimental techniques. During acceleration phase, a high stiffness is maintained, which gives us high critical frequency. After acceleration to operating rpm, the stiffness of the bearing is reduced at run time so that the bearing again becomes a soft support. In this work, a thrust magnetic bearing of variable stiffness is used to show that by changing the stiffness at run time, we can avoid crossing the rigid body critical frequency and hence reduce the amplitude of resonant vibrations.

Effecting Critical Frequency Shift in Rotors Using Active Magnetic Bearings

A defect-free rolling element bearing has a varying stiffness. The variation of stiffness depends on number of rolling elements, their configuration and cage frequency. The time-varying characteristics of the stiffness results in a parametric excitation. This may lead to instability which is manifested as high vibration levels. An FEM simulation is performed to evaluate stiffness in each configuration of rolling elements and is used to study the variation of direct stiffness and cross coupled stiffness. The obtained stiffness variation is expanded into a Fourier series to form the equation of motion for the bearing vibration. As the stiffness varies with cage frequency, stiffness term in the equation of motion is periodic with parametric excitation. Hence, the equation of motion is a 2-DOF coupled Mathieu equation. Based on Mathieu parameters and cage frequency there exists unstable rpm ranges for a particular bearing. Floquet theory is employed to find out the stable and unstable regions. This involves finding out maximum Floquet exponent using Monodromy matrix. The results obtained through Floquet theory are in agreement with the numerical solution of the governing equations.

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A. S. Sekhar

Papers

Influence of Loading Rate on Deformation Behaviour and Sealing Performance of Spiral Wound Gasket in Flange Joint

Damage Identification and Quantification in Structures Using Wavelet Analysis

Effecting Critical Frequency Shift in Rotors Using Active Magnetic Bearings

Parametrically Excited Vibration in Rolling Element Bearings

Effect of Twin Gasket and Internal Fluid on the Dynamic Behavior of Pipeline with Flange Joint