Department of Applied Mechanics

IIT Madras is a public technical and research university located in Chennai, Tamil Nadu. Founded in 1959, it is recognised as an Institute of National Importance.

IIT Madras has been ranked as the top engineering institute in India for four years in a row by the National Institutional Ranking Framework of the MHRD

It currently offers undergraduate, postgraduate and research degrees across 16 disciplines in Engineering, Sciences, Humanities and Management. About 596 faculty belonging to science and engineering departments and centres of the Institute are engaged in teaching, research and industrial consultancy.

IIT Madras

In the current study, experiments are performed on the aero-engine compressor blade model which is fastened to the disc using dovetail joint. Using the technique of photoelasticity, the highly stressed zone is found to be at the interface of the disc and the blade. Cyclic loading is then applied to the disc-blade assembly. Initial experimental observations showed formation of small cracks leading to crack growth and subsequent failure. In this region, a small crack is put and then the growth of crack during cyclic loading is studied till the failure of the specimen. The variation of stress intensity factor with respect to crack length and the number of cycles is evaluated for crack perpendicular to the contact length. Â© 2020, Society for Experimental Mechanics, Inc.

World University root node

Conference Proceedings of the Society for Experimental Mechanics Series

Analysis of Crack Growth in Compressor Blade Root Subjected to Fatigue

Event-related patterns (EPs) play an essential role in detecting motor imagery (MI) movements of the subject. Due to the difference in the spatial and temporal distribution of brain signals among the subjects, the extraction of EP is a major issue. To rectify this problem, the Hilbert transform (HT) was used for the detection of EPs, and the machine learning (ML) models were implemented for decoding MI movements. The proposed method comprises two steps: initially, μ (8–12 Hz) and β (12–30 Hz) frequency bands were extracted from the raw electroencephalogram (EEG) signal. The HT was implemented on extracted μ and β bands signals and the EPs were calculated. Finally, the EPs were fed into two ML models such as support vector machine (SVM) and logistic regression (LR) for the detection of MI movements. The proposed method was tested on two benchmark datasets (BCI competition-III and IV). The results show that the mean classification accuracy (%CA) and Cohen's kappa coefficient (K) for BCI competition-III and IV were 86.11% & 0.72 and 82.50% & 0.65 respectively, which are higher than several existing methods. © 2020 Elsevier Ltd

Biomedical Signal Processing and Control

Hilbert transform-based event-related patterns for motor imagery brain computer interface

We experimentally study thermoacoustic transitions in an annular combustor consisting of sixteen premixed, swirl-stabilized turbulent flames. We show the changes in the characteristics of bifurcations leading to the state of longitudinal thermoacoustic instability (TAI) when equivalence ratio and bulk velocity are systematically varied. Depending upon the bulk velocity, we observe different states of combustor operation when the equivalence ratio is varied. These states include combustion noise, intermittency, low-amplitude TAI, mixed-mode oscillations (MMO), and high-amplitude TAI. We closely examine the special case of MMO that is encountered during the transition from low-amplitude TAI to high-amplitude TAI. We also discuss the global and local flame dynamics observed during the state of MMO. We find that during epochs of low-amplitude oscillations of MMO, all the flames are partially synchronized, while during epochs of high-amplitude oscillations, all the flames are perfectly synchronized. Finally, we replicate the criticalities of bifurcation of the annular combustor in a phenomenological model containing sixth-order nonlinearities. Copyright © 2020 ASME.

Department of Aerospace Engineering

Department Of Civil Engineering

Proceedings of the ASME Turbo Expo

Intermittency, secondary bifurcation and mixed-mode oscillations in a swirl-stabilized annular combustor: experiments and modeling

In this study, an attempt has been made to analyze uterine Electromyography (uEMG) signals during Term conditions (pregnancy duration more than 37 weeks of gestational age) using Empirical Mode Decomposition based Detrended Fluctuation Analysis (EMD-DFA). The Term delivery signals are considered from a publicly available database, grouped as T1 (<26 weeks gestational age) and T2 (≥26 weeks gestational age) based on the time of recording, and are subjected to an EMD-DFA algorithm. The double logarithmic plot of the detrended fluctuation function against the scale is analyzed, and the Hurst exponent feature is computed for both groups. The features are statistically analyzed using the Student s t-test. Results show that the EMD-DFA method is able to capture the variations in the fluctuations of uEMG signals under these conditions. The Hurst exponent feature is found to be statistically significant (p-value < 0.005) for both groups. There is an increase in the Hurst exponent feature value in the T2 group, which indicates that T2 signals possess smoother characteristics than T1 signals. Hence, it appears that the proposed approach could aid in investigating variations in the fluctuations of Term delivery signals, differentiating T1 and T2 conditions.. © 2020 Institute of Electronics and Information Engineers. All rights reserved.

IEIE Transactions on Smart Processing and Computing

Empirical Mode Decomposition based Detrended Fluctuation Analysis of Uterine Electromyography Signals in Term Conditions

In this work, an attempt has been made to assess the texture variations of brainstem occurring in the Early Mild Cognitive Impairment (EMCI) condition. Fractal dimension is calculated for the segmented brainstem volume using Higuchi's and Detrending moving average (DMA) method. These measures are validated using Random forest classifier. DMA shows better performance when compared to Higuchi's method in categorising EMCI stage. Thus, the proposed approach using brainstem image's DMA fractal measures with random forest can be used in diagnosis of EMCI. © 2020 European Federation for Medical Informatics (EFMI) and IOS Press.

Studies in Health Technology and Informatics

Identification of EMCI in MR brainstem structure using fractal measures and random forest approach

The mechanistic aspects of process of initiation of a mode-I fatigue crack in an aluminium alloy (AA 2219-T87) are studied in detail, both computationally as well as experimentally. Simulations are carried out under plane strain conditions with fatigue process zone modelled as stress-state–dependent cohesive elements along the expected mode-I failure path. An irreversible damage parameter that accounts for the progressive microstructural damage due to fatigue is employed to degrade cohesive properties. The simulations predict the location of initiation of the fatigue crack to be subsurface where the triaxiality and the opening tensile stresses are higher in comparison with that at the notch surface. Examination of the fracture surface profile of fracture test specimens near notch tip reveals a few types of regions and existence of a mesoscopic length scale that is the distance of the location of highest roughness from the notch root. A discussion is developed on the physical significance of the experimentally observed length scale. © 2019 Wiley Publishing Ltd.

Fatigue and Fracture of Engineering Materials and Structures

Mesoscopic mechanisms in fatigue crack initiation in an aluminium alloy

Department of Electrical Engineering

Collagen‐I/silk‐fibroin biocomposite exhibits microscalar confinement of cells and induces anisotropic morphology and migration of embedded fibroblasts

Normal thermal fluctuations of the cell membrane have been studied extensively using high resolution microscopy and focused light, particularly at the peripheral regions of a cell. We use a single probe particle attached non-specifically to the cell-membrane to determine that the power spectral density is proportional to (frequency)-5/3 in the range of 5 Hz to 1 kHz. We also use a new technique to simultaneously ascertain the slope fluctuations of the membrane by relying upon the determination of pitch motion of the birefringent probe particle trapped in linearly polarized optical tweezers. In the process, we also develop the technique to identify pitch rotation to a high resolution using optical tweezers. We find that the power spectrum of slope fluctuations is proportional to (frequency)-1, which we also explain theoretically. We find that we can extract parameters like bending rigidity directly from the coefficient of the power spectrum particularly at high frequencies, instead of being convoluted with other parameters, thereby improving the accuracy of estimation. We anticipate this technique for determination of the pitch angle in spherical particles to high resolution as a starting point for many interesting studies using the optical tweezers. This journal is © The Royal Society of Chemistry.

Department Of Physics

Fulltext

Soft Matter

Detection of sub-degree angular fluctuations of the local cell membrane slope using optical tweezers

Two-dimensional (2D) materials such as graphene, molybdenum sulfide, and hexagonal boron nitride are widely studied for separation applications such as water desalination. Desalination across such 2D nanoporous membranes is largely influenced by the bulk transport properties of water, which are, in turn, sensitive to the operating temperature. However, there have been no studies on the effect of temperature on desalination through 2D nanopores. We investigated water desalination through hydrogen functionalized graphene nanopores of varying pore areas at temperatures 275.0 K, 300.0 K, 325.0 K, and 350.0 K. The water flux showed a direct relation with the diffusion coefficient and an inverse relation with the hydrogen-bond lifetime. As a direct consequence, the water flux was found to be related to the temperature as per the Arrhenius equation, similar to an activated process. The results from the present study improve the understanding on water and ion permeation across nanoporous 2D materials at different temperatures. Furthermore, the present investigation suggests a kinetic model, which can predict the water and ion permeation based on the characteristics of the nanopore. © 2020 American Institute of Physics Inc.. All rights reserved.

Journal of Chemical Physics

The effect of temperature on water desalination through two-dimensional nanopores

Accommodation coefficients (ACs) are the phenomenological parameters used to evaluate gas-wall interactions. The gas transport through a finite length nanochannel will confront the variation of properties along the length of the channel. A three-dimensional molecular dynamics simulation has been carried out to examine this streamwise inhomogeneity of flow characteristics in a nanochannel. The rarefaction of the flow to the downstream direction is a crucial behavior in a pressure-driven nanochannel flow. This is manifested as the variation in velocity and temperature along the length of the channel. Subsequently, the interactions between the gas and wall particles will get reduced considerably. Moreover, the characteristics near the wall are examined in detail. A nonhomogeneous behavior in density and velocity profile near the wall is reported. Further, the momentum accommodation coefficient (MAC) in both the tangential and normal directions is examined along the lengthwise sections of the channel. The results show a significant variation of tangential and normal MACs along the length. Further, three channels with different length-to-characteristic dimension (L/H) ratios are considered to investigate the effect of L/H ratio. All three channels are subjected to the same pressure drop along the length. It is observed that the MACs and slip length show distinct behavior for different (L/H) ratios. The work establishes that the variation of MAC along the length of the channel has to be considered in modeling the nano- A nd microtransport systems. © 2020 American Physical Society.