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

Non-invasive assessment of tissue perfusion has gained increased interest in the recent past for monitoring various physiological dysfunctions. Laser speckle imaging and associated processing techniques present useful and inexpensive methods of achieving this goal. However, differentiating the effects of static and dynamic scatterers from the captured speckle image is challenging and limits the sensitivity of such techniques. This paper presents a fractal analysis in the temporal domain to assess the various dynamic scattering features of tissue perfusion demonstrated on a perfusion model. We use detrended fluctuation analysis for the quantitative assessment of image fractal dimensions, which reflect the concentration and flow features of the moving scatterers in the perfusion model. © COPYRIGHT SPIE. Downloading of the abstract is permitted for personal use only.

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Progress in Biomedical Optics and Imaging - Proceedings of SPIE

Differential imaging of dynamic scattering from laser speckle images for applications in perfusion monitoring

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Journal of Rehabilitation and Assistive Technologies Engineering

Quantification of the relative arm use in patients with hemiparesis using inertial measurement units

A stress-state dependent cyclic cohesive model, which accounts for accumulation of plasticity, during both tensile as well as compressive deformations, and incorporates accumulation of irreversible damage due to macroscopic plasticity as well as microstructural mechanisms, is formulated. The model is implemented in mode-I plane strain fatigue crack growth simulations. The model is validated by reproducing the effect of retardation in crack growth rates after different combinations of tensile and compressive overloads. We show accurate description of the elastic–plastic behaviour of the process zone is vital, in particular for negative stress ratios subsequent to a tensile over-load, as considerable plasticity occurs in compression at the crack-tip, significantly reducing retardation effects. © 2020, Springer Nature B.V.

International Journal of Fracture

An incremental elastic–plastic triaxiality dependent fatigue model

We develop a passive control strategy for suppressing thermoacoustic instability in a bluff-body stabilized premixed turbulent combustor. When the equivalence ratio is varied, there is a transition from combustion noise to thermoacoustic instability via intermittency in the combustor. We perform simultaneous acoustic pressure, 2D-PIV, and CH* chemiluminescence measurements to capture the pressure fluctuations, the velocity field, and the heat release rate (HRR) field during the transition. We measure the spatial distribution of the amplitude of turbulent velocity at the acoustic frequency, time-averaged vorticity, time-averaged HRR, and Rayleigh index and identify various regions of significance. We implement a passive control strategy by targeting these regions with a steady injection of secondary micro-jet of air to optimize the injection location and determine the critical region. Targeting the critical region with secondary air leads to greater than 20 dB suppression of the dominant thermoacoustic mode. We observe that the coherent structure forming from the shear layer following the dump plane gets suppressed, leading to an incoherent spatial distribution of HRR fluctuations. We find that the turbulent velocity amplitude correctly identifies the critical region for optimized passive control during thermoacoustic instability. In contrast, the Rayleigh index identifies the region of the most significant acoustic driving; however, it does not identify the region most sensitive to control. Finally, we extend our analysis by determining the spatial distribution of the Hurst exponent measured from the turbulent velocity field. We show that the Hurst exponent identifies the critical region during thermoacoustic instability and intermittency, unlike the other physical measures. Thus, we develop a smart passive control method by combining the need for finding critical regions in the combustor with the predictive capabilities of the Hurst exponent. © 2020 The Combustion Institute

Department of Aerospace Engineering

Department Of Chemistry

Combustion and Flame

Critical region in the spatiotemporal dynamics of a turbulent thermoacoustic system and smart passive control

Deep CO2 storage reservoirs show a wide range of heterogeneous structures across different scales. Here, we show how high-resolution heterogeneity in both permeability and capillary entry pressure control dissolution and local capillary trapping of supercritical CO2 (ScCO2). Prior works mainly considered homogeneous reservoirs or simplified heterogeneity with horizontal and fixed capillary transition zones. Most of those studies ignored simultaneous free-phase ScCO2 spreading and solutal fingering. To advance understanding of heterogeneity effects, we have performed two-dimensional numerical simulations for ScCO2 injection into the middle of a storage reservoir. We have computed metrics including the spatial plume moments to compare the dissolution trapping and spreading of ScCO2 during the injection and post-injection period for different variances and correlation lengths of log-normal permeability and capillary entry pressure fields. The results show that the second-order spatial moment of the ScCO2 saturation field in the horizontal direction decreases by 10% as the permeability variance increases from 0.1 to 3.0. But it decreases by 50% as the capillary entry pressure variance becomes 1.1. For higher capillary entry pressure variance, the ratio of dissolved CO2 mass to free-phase ScCO2 mass decreases, showing higher local capillary trapping. The vertical distance between the centers of mass of the ScCO2 and dissolved CO2 plumes (representing the downward flow of dissolved CO2 through solutal fingering) is greater for heterogeneous reservoirs. © 2021

International Journal of Greenhouse Gas Control

Coupled multiphase flow and transport simulation to model CO2 dissolution and local capillary trapping in permeability and capillary heterogeneous reservoir

Pulsed laser diodes (PLDs) promise to be an attractive alternative to solid-state laser sources in photoacoustic tomography (PAT) due to their portability, high-pulse repetition frequency (PRF), and cost effectiveness. However, due to their lower energy per pulse, which, in turn, results in lower fluence required per photoacoustic signal generation, PLD-based photoacoustic systems generally have maximum imaging depth that is lower in comparison to solid-state lasers. Averaging of multiple frames is usually employed as a common practice in high PRF PLD systems to improve the signal-to-noise ratio of the PAT images. In this work, we demonstrate that by combining the recently described approach of subpitch translation on the receive-side ultrasound transducer alongside averaging of multiple frames, it is feasible to increase the depth sensitivity in a PLD-based PAT imaging system. Here, experiments on phantom containing diluted India ink targets were performed at two different laser energy level settings, that is, 21 and 27 μ \textJ. Results obtained showed that the imaging depth improves by 38.5% from 9.1 to 12.6 mm for 21- μ \textJ energy level setting and by 33.3% from 10.8 to 14.4 mm for 27- μ \textJ energy level setting by using λ /4-pitch translation and average of 128 frames in comparison to λ -pitch data acquired with the average of 128 frames. However, the achievable frame rate is reduced by a factor of 2 and 4 for λ /2 and λ /4 subpitch translation, respectively. © 1986-2012 IEEE.

IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control

Extending Imaging Depth in PLD-Based Photoacoustic Imaging: Moving beyond Averaging

This study presents a novel plasmonic fiber optic sandwich immunobiosensor for the detection of chikungunya, an infectious mosquito-borne disease with chronic musculoskeletal pain and acute febrile illness, by exploiting non-structural protein 3 (CHIKV-nsP3) as a biomarker. A plasmonic sandwich immunoassay for CHIKV-nsP3 was realized on the surface of a compact U-bent plastic optical fiber (POF, 0.5 mm core diameter) with gold nanoparticles (AuNPs) as labels. The high evanescent wave absorbance (EWA) sensitivity of the U-bent probes allows the absorption of the light passing through the fiber by the AuNP labels, upon the formation of a sandwich immunocomplex of CHIKV-nsP3 on the core surface of the U-bent probe region. A simple optical set-up with a low-cost green LED and a photodetector on either end of the U-bent probe gave rise to a detection limit of 0.52 ng mL-1 (8.6 pM), and a linear range of 1-104 ng mL-1 with a sensitivity of 0.1043A530 nm/log(CnsP3). In addition, the plasmonic POF biosensor shows strong specificity towards the CHIKV-nsP3 analyte in comparison with Pf-HRP2, HIgG, and dengue whole virus. The results illustrate the potential of plasmonic POF biosensors for direct and sensitive point-of-care detection of the chikungunya viral disease. © 2021 The Royal Society of Chemistry.

Analyst

Development of a U-bent plastic optical fiber biosensor with plasmonic labels for the detection of chikungunya non-structural protein 3

A dislocation density based crystal plasticity model is developed to account for the precipitate induced cyclic softening in IN718. The new model treats the interaction between the precipitates and the dislocations using a probabilistic approach. It is also capable of capturing the reduction in the effective size of the precipitates due to reversible dislocations shearing through them. Further, the phenomenological model accounts for the heterogeneous accumulation of dislocations in the microstructure (i) as a function of distance to the nearest grain boundary and (ii) the interparticle spacing within a grain. The developed model is used to simulate the macroscopic mechanical response of IN718 under a series of monotonic and cyclic loads at different strain rates and alternating strain levels, respectively. Model predictions of macroscopic behavior are shown to be in good agreement with experimental data. They can capture the initial hardening and subsequent softening during cyclic loading for several strain amplitudes. Sensitivity analyses have been performed to understand the influence of grain size, reversible dislocations, and the size of the precipitates. © 2021 Elsevier Ltd.

Department of Metallurgical and Materials Engineering

International Journal of Plasticity

Dislocation density based crystal plasticity model incorporating the effect of precipitates in IN718 under monotonic and cyclic deformation

Analysis of fluctuations of uterine contractions under varied gestational ages is clinically significant. In this work, fluctuations associated with Preterm pregnancies are analyzed. For this, uterine electromyography (uEMG) signals in Preterm condition with varied gestational ages are considered. The signals are subjected to Adaptive Fractal Analysis (AFA) where a global trend is identified using overlapping windows of varying orders. The signal is detrended and fluctuation function is estimated. Hurst exponent features are extracted and analyzed statistically. Results show that AFA is able to characterize the variations in the fluctuations of Preterm uEMG signals. The feature values are distinct and vary with gestational age. Coefficient of variation is observed to be low, indicating that these features could handle inter-subject variability of Preterm signals. As early diagnosis of premature delivery is imperative for timely medical intervention and treatment, it appears that the proposed features could aid in determining the changes in uterine muscle contractions in Preterm condition. © 2021 World Scientific Publishing Company.

Fluctuation and Noise Letters

Analysis of Fluctuations of Uterine Contractions in Preterm Pregnancies using Adaptive Fractal Features of Electromyography Signals

Accurate prediction of preterm birth is a global, public health priority. This necessitates the need for an efficient technique that aids in early diagnosis. The objective of this study is to develop an automated system for an effective detection of preterm (weeks of gestation < 37) condition using Electrohysterography (EHG) and topological features associated with the frequency components of signals. The EHG signals recorded prior to gestational age of 26 weeks are considered. The pre-processed signals are subjected to discrete Fourier transform to obtain the Fourier coefficients. The envelope is computed from the boundary of the complex Fourier coefficients identified using the α-shape method. Topological features namely, area, perimeter, circularity, convexity, ellipse variance and bending energy are extracted from the envelope. Classifications based on threshold-determination method and machine learning algorithms namely, naïve Bayes, decision tree and random forest are employed to differentiate the term and preterm conditions. The results show that the Fourier coefficients of EHG signals exhibit different shapes in the term and preterm conditions. The regularity of signals is found to increase in preterm condition. All the features are found to have significant differences between these two conditions. Bending energy as a single biomarker achieves a maximum accuracy of 80.7%. The random forest model based on the topological features detects the conditions with the maximum accuracy and positive predictive value of about 98.6%. Therefore, the proposed automated system seems to be effective and could be used for the accurate detection of term and preterm conditions. © 2021 Nalecz Institute of Biocybernetics and Biomedical Engineering of the Polish Academy of Sciences