scispace - formally typeset
Search or ask a question
Author

A. S. Sekhar

Bio: A. S. Sekhar is an academic researcher from Indian Institute of Technology Madras. The author has contributed to research in topics: Rotor (electric) & Helicopter rotor. The author has an hindex of 29, co-authored 109 publications receiving 2757 citations. Previous affiliations of A. S. Sekhar include Indian Institute of Technology Kharagpur & Indian Institutes of Technology.


Papers
More filters
01 Jan 2015
TL;DR: In this paper, a computational framework based on a combined 3D-CFD/FE along with a second order rotor dynamics model is employed to assess a six-tooth straight through rotating labyrinth seal for a varying flow and operating conditions.
Abstract: A computational framework based on a combined 3D-CFD/FE along with a second order rotor dynamics model is employed to assess a six-tooth straight through rotating labyrinth seal for a varying flow and operating conditions. Three-dimensional Reynolds Averaged NavierStokes compressible equations are solved to obtain the circumferential pressure distributions and are integrated further to calculate the seal fluid forces. Subsequently, the extracted rotor dynamic coefficients are compared to the one without considering centrifugal growth. All the six rotor dynamic coefficients shows distinct characteristics when the centrifugal growth is accounted for. The centrifugal growth has a substantial reduction on cross-coupled stiffness and direct damping and the influence increases with speed. The stability aspects of the seal are examined in terms of whirl frequency ratio and effective damping coefficient, presuming synchronous whirl. The results emphasis the consideration of the seal centrifugal growth effects, while conducting rotor dynamic stability analysis for a typical rotor system.

1 citations

Journal ArticleDOI
TL;DR: In this article, the stability characteristics of journal bearings using the finite element method have been investigated using two different elements, a 3-node linear triangle and a 6-node quadratic triangle, and the results show a significant difference in stiffness and damping coefficients and stability characteristics at high eccentricity ratios.
Abstract: This study deals with the stability characteristics of journal bearings using the finite element method. Two different elements, a 3-node linear triangle and a 6-node quadratic triangle, have been used. The results show a significant difference in (1) stiffness and damping coefficients and (2) stability characteristics at high eccentricity ratios due to the use of the two different elements.

1 citations

Book ChapterDOI
01 Jan 2021
TL;DR: In this article, the effect of thermal growth of labyrinth seal on the leakage flow rates and effect on vibration characteristics of the system is evaluated. But the main design concern is to prevent the seal rub with the stator in the range of operating conditions and to control the system rotordynamics.
Abstract: Labyrinth seals are the most widely used non-contact-type turbine seals. The main design concern is to prevent the seal rub with the stator in the range of operating conditions and to control the system rotordynamics. This work aims at experimentally evaluating the effect of thermal growth of labyrinth seal on the leakage flow rates and effect on vibration characteristics of the system. An experimental seal test rig for teeth on rotor (TOR)-type straight labyrinth seal with four flat tip teeth has been developed. Constant clearance between seal and stator is maintained and tested at different speeds and temperatures by varying the inlet air pressure. Leakage results are compared for the seal for the range of operating conditions and for a given seal radial clearance. In addition, vibration data are measured at various locations to understand the influence of seal on the vibration characteristics of the rotor system. It is seen that flow leakage rate and vibration of system are influenced by the pressure difference and the temperature.
Book ChapterDOI
01 Jan 2021
TL;DR: In this paper, the in-plane elastic properties at different fiber volume fractions of 3D composite tube shafts are obtained from the literature and modal analysis is carried out, and bending natural frequencies are calculated for different 3D composites with E-glass, carbon and kevlar fibers and epoxy as matrix materials.
Abstract: Three-dimensional (3D) composites have good delamination resistance along with high specific stiffness and high specific strength. Composite tube shafts are modeled with different reinforcement architecture such as multi-axial, stitched, knitted, braided, orthogonal woven, interlock and z-pinned. The in-plane elastic properties at different fiber volume fractions of these composites are obtained from the literature. 3D composite tube shafts are modeled with length: 1 m, internal radius: 25 mm and thickness: 4 mm using modified equivalent modulus beam theory formulation. Modal analysis is carried out, and bending natural frequencies are calculated for different 3D composite tube shafts with E-glass, carbon and kevlar fibers and epoxy as matrix materials. The natural frequency reduces with through thickness reinforcement for orthogonal, knitted, z-pinned and stitched composites. Braided composites tube shafts have higher natural frequencies compared to that of other types.

Cited by
More filters
Journal ArticleDOI
TL;DR: This paper attempts to summarise and review the recent research and developments in diagnostics and prognostics of mechanical systems implementing CBM with emphasis on models, algorithms and technologies for data processing and maintenance decision-making.

3,848 citations

Journal ArticleDOI
TL;DR: This paper attempts to present a comprehensive review of AI algorithms in rotating machinery fault diagnosis, from both the views of theory background and industrial applications.

1,287 citations

Journal ArticleDOI
TL;DR: In this paper, a crack in a structural member introduces a local flexibility that affects its vibration response, and the crack will open and close in time depending on the rotation and vibration amplitude.

1,080 citations

Journal ArticleDOI
TL;DR: A systematic review of over 20 major time-frequency analysis methods reported in more than 100 representative articles published since 1990 can be found in this article, where their fundamental principles, advantages and disadvantages, and applications to fault diagnosis of machinery have been examined.

719 citations

Journal ArticleDOI
TL;DR: In this paper, a new scheme for the prediction of a ball bearing's remaining useful life based on self-organizing map (SOM) and back propagation neural network methods is presented.

502 citations