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

This study examines the performance of the refined time-reversal method (RTRM), which recommends best reconstruction frequency as probing frequency and uses an extended mode of the reconstructed signal for computing the damage/similarity index for damage detection under a varying thermal environment. The experiments were performed on a 3 mm aluminum plate with a block mass-type damage at three excitation frequencies: the best reconstruction frequency, the sweet spot frequency at which only S0 mode is actuated, and an arbitrarily chosen frequency. Measurements were taken at two temperatures, 25∘ C and 50∘ C. The percent similarity between the reconstructed and original input signals showed a consistent decrease with the increase in damage height at the best reconstruction frequency. However, at the other excitation frequencies, the change in the similarity with the increase in damage height did not follow a consistent trend, which can lead to erroneous information about damage size. The percent similarity changes significantly with temperature rise at the sweet spot frequency and the arbitrarily chosen frequency. However, it showed minimal change with temperature rise at the best reconstruction frequency for undamaged and damaged states of different severity, making the RTRM suitable for baseline-free damage detection and sizing even under temperature variations. © 2023, The Author(s), under exclusive license to Springer Nature Switzerland AG.

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Lecture Notes in Civil Engineering

Damage Detection Using Refined Time Reversal Method of Lamb Waves Under Varying Temperatures

What makes Total fringe order photoelasticity (TFP) the ideal digital photoelastic technique for industrial applications is the sufficiency of a single colour isochromatic image for fringe order evaluation and the convenience of capturing this image using easily accessible, relatively cheap hardware. In TFP, the colour information in the application image is matched with an experimental colour calibration table. A simple least squares colour matching is insufficient for this due to errors caused by the repetition of colour in the isochromatics. This is rectified through a process called fringe order refinement. Among the existing fringe order refining methods, the combination of – flexible seeding, window search method, and FRSTFP scanning – has proved to be the best choice for solving a variety of problems for the complete model domain. The successful application of this combination requires the right choice of parameter values for its constituent methods. A systematic parametric study of these refining parameters is a lacuna in the literature, which is addressed in this work, by selecting a variety of problems. The study has revealed the interconnection between the refining parameters, which has helped to formulate a set of recommendations for selecting the same. It is found that some of the existing understandings on refining parameters require a relook. The difficulty in refining fringe fields having multiple fringe gradient reversals with a single set of parameters is illustrated, and how this can be overcome by local refinement is brought out. Additionally, a methodology to track the source of refining error is proposed. © 2022 Elsevier Ltd

Optics and Lasers in Engineering

Framework to select refining parameters in Total fringe order photoelasticity (TFP)

Objective: The first objective of this paper is to establish a relationship between brain activities and motor imagery (MI) movements through mapping functions. The second objective is to distinguish left and right hands MI movements of the subjects. Approach: In this paper, the dynamical behavior of brain activities is well explained by the discrete wavelet transform (DWT) and phase space reconstruction (PSR) techniques. The DWT is employed to identify μ and β frequency bands from raw electroencephalogram (EEG) signals. In order to extract rest and MI features and their corresponding brain patterns, a PSR-based common spatial pattern (CSP) technique is applied to both the frequency bands. The obtained MI features used to train a support vector machine (SVM) model to detect MI movements. Results: The proposed method is tested on benchmark BCI competition (II, III and IV) datasets. The mentioned technique yields a higher value of classification accuracy (%CA), Cohen's kappa coefficients (K) and information transfer rate (ITR) in bits per trial. Significance: The μ band is highly responsive than the β band in MI period. The PSR is a powerful graphical technique to investigate the brain activities. © 2022 Elsevier Ltd

Biomedical Signal Processing and Control

Investigation of the dynamical behavior of brain activities during rest and motor imagery movements

Gas hydrate sediments are considered as one of the potential sources of unconventional energy because of their high energy density and presence of abundant subsurface reserves in order to meet the rising global energy demand. Methane gas hydrate sediments generally occur naturally in permafrost regions and in deep-sea continental shelves where the water depth is more than 500 m below the mean sea level. These deep-water sediments have a high concentration of methane hydrates. Efficiently extracting (safe and economical) these unconventional energies will help in mitigating the energy demand of a country. The current study focuses on predicting the geo-mechanical response of gas hydrates using elastic-plastic constitutive relations and compare with the existing elemental experimental results. From the numerical integration of these advanced models, it is observed that the HISS-MH model could simulate realistic material response under triaxial conditions. Further, an investigation is also carried out to understand the effect of hydrate saturation and Over Consolidation Ratio (OCR) on the geo-mechanical response. There is an increase in stiffness, peak stress, stress dilatancy ratio and softening response with the increase in hydrate saturation. The response is due to the enhancement of cementation between soil particles with hydrate saturation. © 2023, The Author(s), under exclusive license to Springer Nature Switzerland AG.

Department Of Civil Engineering

Numerical Study on the Effect of Hydrate Saturation on the Geo-Mechanical Behavior of Gas Hydrate Sediments

Diffuser is a flow device which is used to reduce the velocity of flow. The performance of a diffuser is evaluated using metrics like flow uniformity and pressure recovery. The present work is part of development of a new compact diffuser design that can be incorporated in a heat exchanger for flow distribution. The design concept employs several baffles arranged as frustum of cones with an aerofoil cross-section along the flow direction. The performance enhancement is obtained by optimal positioning of these baffles, and this problem is solved as a numerical optimisation problem. The performance of the diffuser is evaluated using a CFD model, and the same is used for computing the design sensitivity and to perform optimisation. © 2023, The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd.

Department of Engineering Design

Department Of Chemical Engineering

Lecture Notes in Mechanical Engineering

Parametric Modelling, Analysis and Design of Compact Diffuser for Heat Exchanger

We present a new criteria to detect thermal plumes from the velocity field in a horizontal plane that pass from the local boundary layer to the plume close to the hot plate in turbulent Rayleigh Benard convection. Based on the characteristics of deformation of fluid elements, we propose that the negative dominant eigenvalues of the 2D strain rate picks up the thermal plume regions. We also show that the areas identified by this criteria match the areas identified by the horizontal divergence criteria ¯H.¯u &lt; 0 proposed by Vipin and Puthenveettil [4]

STRAIN RATE SIGNATURES OF PLUMES IN RAYLEIGH BENARD CONVECTION

SARS-CoV-2 nucleocapsid protein-based COVID-19 diagnosis is a promising alternative to the high-priced, time-consuming, and labor-intensive RT-PCR tests. Here, we developed a rapid, dip-type, wash-free plasmonic fiber optic absorbance biosensor (P-FAB) strategy for the point-of-care detection of SARS-CoV-2 N-protein, expressed abundantly during the infection. P-FAB involves a sandwich assay with plasmonic labels on the surface of a U-bent fiber optic sensor probe with a high evanescent wave absorbance (EWA) sensitivity. The SARS-CoV-2 N-protein is quantified in terms of the change in the intensity of the light propagating through the U-bent sensor probe coupled to a green LED and a photodetector. Firstly, the optical fiber material (silica vs. polymeric optical fiber), was evaluated to realize a sensitive sensor platform. The optimal size of AuNP labels (20, 40, and 60 nm) to achieve high sensitivity and a lower limit of detection (LoD) was investigated. Following the P-FAB strategy, fused silica/glass optical fiber (GOF) U-bent senor probe and citrate-capped AuNP labels (size ~40 nm) gave rise to an LoD down to ~2.5 ng/mL within 10 mins of read-out time. Further, studies on development and validation of a point of care (PoC) read-out device, and preclinical studies are in progress.

IEEE Sensors Journal

Plasmonic Fiberoptic Absorbance Biosensor (P-FAB) for Rapid Detection of SARS-CoV-2 Nucleocapsid Protein

The present study reports developing a bench-top Laser-Induced Breakdown Spectroscopy (LIBS) set up for the online analysis of powder samples without sample preparation. The powder particle blow-off during pulsed laser ablation was mitigated by adding a blow gas (an inert gas blown across the ablation surface) and a suction unit (for extraction of the blow gas and blown-off particle cloud) to the existing LIBS setup. The influence of a blow-gas combined with a suction unit on LIBS emission intensity from coal powder and flyash particles is studied in the present work. The effect of the blow gas flow rate and the suction pressure was studied on the LI-BS emission intensity and removal of the laser blown-off particle cloud. The combination gas flow at 2 lpm (liter per minute) flow rate and suction at 925 mbar (absolute) show an increase in the LIBS emission intensity and effective particle removal. The ratio of LIBS emission intensity of the powder sample and solid-target (pellet) sample improved from 0.25 without the Ar gas flow and the suction unit to 0.85, which is by a factor of 3.4 times with the proposed approach. © 2021 Elsevier B.V.

Spectrochimica Acta - Part B Atomic Spectroscopy

LIBS technique combined with blow gas and vacuum suction to remove particle cloud and enhance emission intensity during characterization of powder samples

Blunt-nosed launch vehicles featuring large nose-cone angles experience high levels of pressure fluctuations over the payload region at transonic Mach numbers due to shock-wave/boundary-layer interactions. The main cause for this phenomenon appears to be flow instability associated with separated flow and formation of a vortex pair. Interactions between the induced velocity of the vortex pair and oncoming mean flow cause oscillations of the&nbsp;𝜆<math xmlns="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll" altimg="eq-00001.gif"><mrow><mi>λ</mi></mrow></math>-shock system and high levels of fluctuating pressures. An aerospike causes flow separation at the nose and reattachment of the shear layer downstream, energizing the boundary layer. Consequently, flow separation and vortex formation are prevented: shock oscillations are stabilized. Dramatic reductions in the pressure fluctuations, around 95–35% in the low-frequency range, are observed along the payload region at small angles of attack. The observations are based on wind-tunnel tests involving unsteady pressure measurements, surface-flow patterns, and high-speed shadowgraph recordings on a blunt nose cone with various cone angles.

Journal Of Spacecraft and Rockets

Effect of Aerospike on Unsteady Transonic Flow over a Blunt Body

A benchtop laser-induced breakdown spectroscopy is demonstrated to determine the elemental carbon content present in raw coal used for combustion in power plants. The spectral intensities of molecular CN and C2 emission are measured together with the atomic carbon (C) and other inorganic elements (Si, Fe, Mg, Al, Ca, Na, and K) in the laser-induced breakdown spectroscopy spectrum of coal. The emission persistence time of C2 molecule emission is measured from the coal plasma generated by a nanosecond laser ablation with a wavelength of 266 nm in the Ar atmosphere. The emission persistence time of molecular C2 emission along with the spectral intensities of major ash elements (Fe, Si, Al, and Ca) and carbon emissions (atomic C, molecular CN, and C2) shows a better relationship with the carbon wt% of different coal samples. The calibration model to measure elemental carbon (wt%) is developed by combining the spectral characteristics (spectral intensity) and the temporal characteristics (emission persistence time of C2 molecule emission). The temporal characteristic studies combined with the spectroscopic data in the partial least square regression model have resulted in an improvement in the root mean square error of validation, and the relative standard deviation is reduced from 10.8% to 4.1% and from 11.3% to 6.0%, respectively. © The Author(s) 2021.