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 empirical study aims to characterize the dynamical behaviour of sprays using time-series analysis of the size-velocity data acquired using a phase Doppler particle analyser. The prime motivation of this analysis is to capture the spatio-temporal correlations using time-series modelling paradigms that provide valuable new insights into spray dynamics. As a first step, we study long-held assumptions, especially on stationarity and time unsteadiness. We show that air-blast sprays have increased drop size as well as velocity ordering near the edge of the spray. Analysis of the inter-particle time of the droplets shows non-Poisson behaviour where droplets that are closely spaced in time are also closely spaced in the size and velocity coordinates. Temporal auto-correlation and partial auto-correlation calculations reveal the presence of inherent correlated features in the spray. This correlation is stronger and short lived in an air-blast spray and weaker but more persistent in a pressure swirl spray. These correlations render the probability density function (p.d.f.) estimate obtained from standard methods inaccurate; therefore, we propose a technically correct way of estimating the p.d.f. using a suitable downsampling and averaging method. Statistical analysis of residuals (from appropriate autoregressive integrated moving average time-series models) uncovers an interesting feature of spray data pertaining to heteroskedasticity (stochastically changing variance) of the diameter series. In order to account for heteroskedasticity, appropriate generalized autoregressive conditional heteroskedasticity models are developed. Finally, we present a utilitarian view of these results as an empirically consistent boundary condition implementation tool for computational fluid dynamics (CFD). © 2021 American Medical Association. All rights reserved.

World University root node

Department Of Chemical Engineering

Journal of Fluid Mechanics

Spatio-temporal microstructure of sprays: Data science-based analysis and modelling

Gypsum scaling over a RO membrane significantly reduces the permeate flux. Since, the phenomenon is linked to concentration polarization; the present study aims to understand the effect of high shear rates over the membrane in reducing gypsum scaling of cross-flow RO filters. We have proposed an integrated CFD and moment-based population balance (MPB) formulation which is less complex than tracking the growth of individual particles. Most of the previous studies on modeling of scaling and permeate flux decline employing MPB formulation were limited to dead-end filters. The present numerical model for cross-flow RO filter has been verified by comparing the precipitate mass and permeate flux decline with the published results for channel filter. This model has been employed for different cross-flow conditions and geometries. We have demonstrated that scaling can be mitigated by increasing the shear rate over the membrane surface. In roto-dynamic RO filters, a 50% increase in the initial permeate discharge can be achieved, and permeate flux decline in time can be restrained if the shear rate is increased by rotating the disk. For a channel of identical membrane area, a similar improvement of permeate discharge requires an approximately two orders of magnitude higher feed discharge. In a channel, gypsum scale formation is significant at larger distances from the inlet. While for roto-dynamic filters, scaling occurs at the stagnation zone near the axis of rotation, the scaling potential decreases with radius. Additionally, we have also discussed some striking differences between fouling and scaling patterns in cross-flow RO filters. © 2020 Elsevier Ltd.

Department of Mechanical Engineering

Journal of Environmental Chemical Engineering

CFD modeling of gypsum scaling in cross-flow RO filters using moments of particle population balance

A Transcritical Regenerative Series Two stage <a href="https://www.sciencedirect.com/topics/engineering/organic-rankine-cycle">Organic Rankine Cycle</a> (TR-STORC) is proposed to improve the efficiency of existing Series Two stage ORC (STORC) architecture by combining <a href="https://www.sciencedirect.com/topics/engineering/supercritical">supercritical</a> heating in the high pressure (HP) stage and partial evaporation with regeneration in the low pressure (LP) stage. Exhaust gas and jacket water from a stationary <a href="https://www.sciencedirect.com/topics/engineering/internal-combustion-engine">IC engine</a> is used as the primary and secondary heat source respectively. Using cyclopentane as working fluid, system exergy performance is analysed for a range of heat source temperatures and for different ratios of heat available between the heat sources. At lower <a href="https://www.sciencedirect.com/topics/engineering/pressure-evaporator">HP evaporator</a> pressures, lower values of vapour outlet temperatures lead to <a href="https://www.sciencedirect.com/topics/engineering/maximum-power-output">maximum power output</a>. For a wide range of heat ratios and temperatures, TR-STORC delivers improved exergetic performance over STORC and pre-heated ORC. It is the recommended choice for all scenarios of dual source heat recovery. For the engine design point, TR-STORC delivers increased power output by up to16% and 23% than STORC and pre-heated ORC respectively. TR-STORC maintains exergetic superiority for all the working fluids investigated with maximum <a href="https://www.sciencedirect.com/topics/engineering/net-power-output">net power outputs</a> exceeding STORC by15–34% and preheated ORC by 15–52%.

Design and performance analysis of a novel Transcritical Regenerative Series Two stage Organic Rankine Cycle for dual source waste heat recovery

A detailed measurement of rainfall is an important input to various climate models. Accuracy of rainfall measurements also has a socio-economic impact since it forms an important constituent in the region-wise and seasonal water budget. Radar measurements are most promising in this direction since they provide the detailed spatiooral data than any conventional method. However, it also has the disadvantage that rainfall estimation using radar is an indirect measurement and often involves the use of a number of correlations. The amount of scattered radiation is directly related to the raindrop size and shape distribution. Therefore, this project is aimed at solving Maxwell's equations of electromagnetism using the lattice Boltzmann method with the intention of accurately relating the size and shape distribution of falling raindrops to scattered intensity and thus improving the rainfall measurement. Towards this objective, a D3Q7 code for a pseudo vector discrete Boltzmann distribution function has been developed following the work of Hauser and Verhey (2017) [1]. Standard validations involving scattering of electromagnetic waves by a dielectric interface and a circular scatterer have been performed. Error in the solutions was found to be minimal on comparing with analytical solutions. The applicability of the proposed numerical method towards analyzing scattering of electromagnetic waves by a three-dimensional scatterer, modelled on realistic hydrometeors, will be discussed.. © 2020 IEEE.

Proceedings of the 2020 IEEE International Conference on Computational Electromagnetics, ICCEM 2020

A lattice boltzmann method for electromagnetic wave propagation in medium

Measurement of the viscoelastic properties of a cell using microscopic tracer particles has been complicated given that the medium viscosity is dependent upon the size of the measurement probe leading to reliability issues. Further, a technique for direct calibration of optically trapped particles in vivo has been elusive due to the frequency dependence and spatial inhomogeneity of the cytoplasmic viscosity, and the requirement of accurate knowledge of the medium refractive index. Here, we employ a recent extension of Jeffery's model of viscoelasticity in the microscopic domain to fit the passive motional power spectra of micrometer-sized optically trapped particles embedded in a viscoelastic medium. We find excellent agreement between the 0 Hz viscosity in MCF7 cells and the typical values of viscosity in literature, between 2 to 16 mPa sec expected for the typical concentration of proteins inside the cytoplasmic solvent. This bypasses the dependence on probe size by relying upon small thermal displacements. Our measurements of the relaxation time also match values reported with magnetic tweezers, at about 0.1 s. Finally, we calibrate the optical tweezers and demonstrate the efficacy of the technique to the study of in vivo translational motion. © 2020 IOP Publishing Ltd.

Department Of Physics

Journal of Physics Condensed Matter

Measurement of viscoelastic properties of the cellular cytoplasm using optically trapped Brownian probes

In conventional linear array (CLA)–based elastography tissue compression in one direction (e.g., axial) leads to an expansion in all other directions (lateral, elevation). Therefore, the estimation of the lateral displacements and strains may provide additional information on the tissue mechanical properties. However, these are not exploited fully due to the inherent limitation in lateral sampling. Recently, a method named actuator-assisted beam translation (ABT) was demonstrated to address this issue, wherein the focused beam was translated at subpitch locations using an external bench-top setup. However, because such bench-top setup may be impractical for routine clinical use, an ultrasound transducer was customized to have an internal actuator. The performance of the customized transducer was studied through experiments on phantoms for rotation elastography application, which requires precise lateral displacement estimation. Furthermore, the results obtained from ABT was compared against the currently practiced spatial displacement compounding (SDC) method, which is known to yield better quality lateral displacement estimates than conventional approaches. The results show that the ABT method yields a full-width half-maximum (FWHM) value, taken from the lateral profile across a point scatterer, which is 65% and 24% smaller than that obtained using CLA and SDC methods, respectively. Furthermore, the contrast-to-noise ratio (CNR) estimated from rotation elastogram obtained using ABT method is better by 300% and 35% compared with that obtained by using CLA and SDC methods, respectively. Furthermore, the results demonstrate an additional advantage of having larger field of view (FoV) for the ABT method compared with spatial compounding approach. © The Author(s) 2019.

Ultrasonic Imaging

Actuator-assisted Subpitch Translation-capable Transducer for Elastography: Preliminary Performance Assessment

In this paper, the effect of porosity on the ductility of as-cast AA7075 (a commercial highstrength aluminum alloy) was investigated. The as-cast material was processed through hot upsetting, and specimens with different porosity content were achieved. These were then subjected to tensile and compression tests. It was shown that the tensile ductility exhibited a near sigmoidal dependence on the porosity content. Compressive ductility, on the other hand, was not affected by the initial porosity content. In addition, direct observations, on an X-ray microscope (XRM), enabled 3-dimensional imaging of the porosity evolution during plastic deformation. Numerical simulations using a homogenized damage model, the Gurson-Tvergaard-Needleman (GTN) approach, was used for predicting the mechanical responses. The continuum model, which accounted for the growth and coalescence of spherical voids, captured the overall experimental patterns reasonably well. © 2020 by ASME.

Department of Aerospace Engineering

Journal of Engineering Materials and Technology, Transactions of the ASME

Relating porosity with ductility in a commercial AA7075 alloy: A combined experimental and numerical study

A Spoken dialogue system for an unseen language is referred to as Zero resource speech. It is especially beneficial for developing applications for languages that have low digital resources. Zero resource speech synthesis is the task of building text-to-speech (TTS) models in the absence of transcriptions. In this work, speech is modelled as a sequence of transient and steady-state acoustic units, and a unique set of acoustic units is discovered by iterative training. Using the acoustic unit sequence, TTS models are trained. The main goal of this work is to improve the synthesis quality of zero resource TTS system. Four different systems are proposed. All the systems consist of three stages- unit discovery, followed by unit sequence to spectrogram mapping, and finally spectrogram to speech inversion. Modifications are proposed to the spectrogram mapping stage. These modifications include training the mapping on voice data, using x-vectors to improve the mapping, two-stage learning, and gender-specific modelling. Evaluation of the proposed systems in the Zerospeech 2020 challenge shows that quite good quality synthesis can be achieved. © 2020 ISCA

Department of Computer Science and Engineering

Proceedings of the Annual Conference of the International Speech Communication Association, INTERSPEECH

Exploration of end-to-end synthesisers for zero resource speech challenge 2020

Failure of bioengineered meniscus implant after transplantation is a major concern owing to mechanical failure, lack of chondrogenic capability and patient specific design. In this article, we have, for the first time, fabricated a 3D printed scaffold with carbohydrate based self-healing interpenetrating network (IPN) hydrogels-based monolith construct for load bearing meniscus tissue. 3D printed PLA scaffold was surface functionalized and embedded with self-healing IPN hydrogel for interfacial bonding further characterized by micro CT. Using collagen (C), alginate (A) and oxidized alginate (ADA), we developed self-healing IPN hydrogels with dual crosslinking (Ca2+ based ionic crosslinking and Schiff base (A-A, A-ADA)) capability and studied their physicochemical properties. Further, we studied human stem cells behaviour and chondrogenic differentiation potential within these IPN hydrogels. In-vivo heterotopic implantation confirmed biocompatibility of the monolith showing the feasibility of using carbohydrate based IPN hydrogel embedded in 3D printed scaffold for meniscal tissue development. © 2020 Elsevier B.V.

Department Of Biotechnology

Department of Ocean Engineering

International Journal of Biological Macromolecules

Meniscal tissue engineering via 3D printed PLA monolith with carbohydrate based self-healing interpenetrating network hydrogel

Microwave hyperthermia makes use of microwaves to deliver heat to biological tissues. Real time temperature monitoring during treatment is important for efficacy and effectiveness of the treatment. Non-invasive methods such as CT, MR and ultrasound (US) have been actively researched for use in hyperthermia monitoring. US has inherent advantages of real-time imaging, portability and non-ionizing nature. It is also known from the literature that acoustic properties of tissue are sensitive to temperature and this has been harnessed to track the evolution of hotspot and temperature in high temperature zones encountered in ablation treatments. However, their usage in low temperature zones typically observed in hyperthermia appears to be less explored. This study introduces an improved method of regularized Kurtosis imaging (RKI) and compares its performance against regularized log spectral difference (RLSD) and regularized Nakagami imaging methods. The performance of these methods is compared against the ground truth estimated from IR thermal images in an experimental study on tissue-mimicking PAG-agar based phantoms. The error in the area estimated by RKI was 10.6%. The error in the lateral and axial co-ordinate of the centroid was 5.92% and 0.47%, respectively. The structural similarity index was 0.82 for RKI when compared with RLSD and RNI having score of 0.76 and 0.72, respectively. The results are promising and offer an alternative way to track the hotspot during microwave hyperthermia treatment. © 2020 IEEE.

Department of Engineering Design

Proceedings - International Symposium on Biomedical Imaging

Regularized Kurtosis Imaging and its Comparison with Regularized Log Spectral Difference and Regularized Nakagami Imaging for Microwave Hyperthermia Hotspot Monitoring