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 shows development of highly sensitive and stable localized surface plasmon resonance (LSPR)-active U-bent glass and polymeric optical fiber (GOF and POF) sensor probes by a seed-mediated in situ growth technique. Here, the nickel/nickel oxide seeds (Ni/NiO, 3 to 5 nm size) were formed on the U-region of the fiber probe by sputter coating nickel under a low vacuum (3 Pa), and then, gold nanostructures (AuNSs) were grown over the Ni/NiO seeds. The evanescent wave absorbance (EWA) phenomenon in the U-bent fiber probe was exploited to monitor the growth kinetics of AuNSs in real-time. Experimental observations point to a potential galvanic replacement of Ni by Au. The newly formed AuNSs on U-bent GOF and POF probes gave rise to a LSPR-based refractive index sensitivity of 27.66 and 25.65 ΔA/ΔRIU with plasmonic peak at 600 and 570 nm, respectively. These plasmonic probes show an excellent chemical and mechanical stability, in addition to high surface enhanced Raman scattering (SERS) activity. This quick and facile technique is highly suitable for large-scale manufacture of reliable plasmonic fiber optic sensor probes for chemical and bio sensing applications. © 2021, The Author(s), under exclusive licence to Springer Science+Business Media, LLC part of Springer Nature.

World University root node

Plasmonics

Highly Stable Plasmonic Nanostructures on a Nickel-Sputtered Glass and Polymeric Optical Fiber Sensors

A novel non-linear beamforming method, namely, filtered delay optimally-weighted multiply and sum (F-DowMAS) beamforming is reported for conventional focused beamforming (CFB) technique. The performance of F-DowMAS was compared against delay and sum (DAS), filtered delay multiply and sum (F-DMAS), filtered delay weight multiply and sum (F-DwMAS) and filter delay Euclidian weighted multiply and sum (F-DewMAS) methods. Notably, in the proposed method the optimal adaptive weights are computed for each imaging point to compensate for the effects due to spatial variations in beam pattern in CFB technique. F-DowMAS, F-DMAS, and DAS were compared in terms of the resulting image quality metrics, Lateral resolution (LR), axial resolution (AR), contrast ratio (CR) and contrast-to-noise ratio (CNR), estimated from experiments on a commercially available tissue-mimicking phantom. The results demonstrate that F-DowMAS improved the AR by 57.04% and 46.95%, LR by 58.21% and 53.40%, CR by 67.35% and 39.25%, and CNR by 44.04% and 30.57% compared to those obtained using DAS and F-DMAS, respectively. Thus, it can be concluded that the newly proposed F-DowMAS outperforms DAS and F-DMAS. As an aside, we also show that the optimal weighting strategy can be extended to benefit DAS. © 2021, The Author(s).

Fulltext

Scientific Reports

Optimally-weighted non-linear beamformer for conventional focused beam ultrasound imaging systems

Compressed Sensing (CS) framework was reported previously to reduce the number of active receive elements in diverging beam-based multi-element synthetic transmit aperture imaging (MSTA). One major issue in that approach was that the active receive elements need to be selected randomly for every transmission. Recently, a methodology for an optimal selection of active receive elements once and using it for all the transmission of MSTA was shown using a genetic algorithm (GA). However, the number of physical transducer elements cannot be reduced due to the requirement of linear electronic scanning of the transmit beam. To overcome this limitation, the CS framework is adopted in this work for a limited-element compounded diverging wave (LeCDW), where the same set of sparse elements are used for all the transmissions and receptions. The simulation dataset for this study was obtained from Field II. The obtained results suggest that it is possible to reduce the number of receive elements by 50% without significant degradation in the image quality. These preliminary results indicated that it is possible to realize the CS framework using a customized transducer with physical elements at random locations. © 2021 IEEE.

IEEE International Ultrasonics Symposium, IUS

Compressed Sensing framework for Limited-element Compounded Diverging Waves: Initial Results

Polymeric gels, when made into thin films, are reported to depict a reversible folding behavior on exposure to favorable solvents as a result of the coupled diffusion–deformation mechanism. In this work, we develop a model based on the coupled diffusion–deformation mechanism which can predict the large deformation caused during this reversible folding behavior of a polymeric thin film. The formulation incorporates a concentration dependent Young's modulus variation. It is found that the incorporation of concentration dependent Young's modulus of the film in the formulation is essential to predict the folding curvatures accurately. The results obtained using this model are validated with the experimental results of the Chitosan–Water system by comparing the folding characteristics — intermediate folding stages and curvature, while accurately explaining the mechanism of reversible folding. The model is applied to other material systems such as PVA–Water and PDMS–Hexane systems. Furthermore, we demonstrate that the developed model successfully predicts the buckling and wrinkling phenomenon observed experimentally in stimuli-responsive polymer thin films. © 2020 Elsevier Ltd

Department of Mechanical Engineering

Mechanics of Materials

Coupled diffusion–deformation behavior of stimuli-responsive thin polymer films

Biological nanopores such as aquaporins combine the opposing functions of high water permeation and total ion exclusion in part by the virtue of their hourglass shape. Here, we perform molecular dynamics simulations to examine water and ion conduction through hourglass shaped nanopores created from carbon nanotubes (CNTs) of chirality (6,6), (8,8), and (10,10) in combination with carbon nanocones of half cone angles 41.8°, 30.0°, 19.45°, 9.6° and 0.0°. We observe large variations in flow through the nanopores with change in half cone angles and tube diameters. By computing the pore-water interactions we find a correlated change between the flux and the density profiles of water inside the nanopores. Further, from the orientation, and the hydrogen bonding characteristics of water, we uncover some unexplored facets of flow through hourglass shaped nanopores. The results are insightful for devising novel separation membranes based on nanopores that mimic the shape of biological nanochannels. © 2021 Elsevier B.V.

Department Of Civil Engineering

Desalination

Highly efficient water desalination through hourglass shaped carbon nanopores

The objective of this work is to determine the interfacial strength between cement paste and epoxy, coated at the different instant of time during the hydration. The factors influencing the magnitude of interfacial adhesive strength were also studied. To pursue this, the interfacial adhesive strength between cement paste and epoxy coated at different days of hydration was determined by performing macro-mechanical experiments such as slant shear and pull-off adhesion test. The various instant of hydration when epoxy was coated are 2, 7, 14, 21, and 28 days from the point of initiation of hydration. The possible influencing factors considered were water-cement ratio, curing time, and thickness of the coating. Results of macro-mechanical tests show that the average interfacial adhesive strength between cement paste and the epoxy coating was in the same range, irrespective of the instant of coating. Although the higher surface energy and work of adhesion should result in a higher interfacial strength for epoxy coated on 2nd day, the measured value of interfacial strength, however, did not show such. One of the possible reasons why interfacial strength of epoxy coated on the 2nd day is similar to 28th day coating in spite of higher surface energy and work of adhesion, is the presence of the larger amount of surface water during the earlier days. The effect of this excess water balances out the contributory effect of the physical interactions and mechanical interlocking. From the parametric study, it was observed that the factors considered in the present study play a major role, particularly when coated during the early days of hydration. © 2021 Elsevier Ltd

Construction and Building Materials

Evaluation of interfacial strength between hydrating cement paste and epoxy coating

Textile factories are usually batch plants. Their high freshwater consumption and large emissions of toxic wastewater present a threat to water availability and public health. Wastewater minimization can be used to reduce this impact. This paper presents a framework for combining the unit-specific continuous-time approach and the global continuous-time approach in batch water minimization. The unit-specific approach is used to obtain an optimal schedule, which is mapped onto a global time grid using a bridging algorithm before performing water minimization. The objectives are to minimize the process makespan and freshwater consumption, respectively. This research is applicable to large batch problems which are intractable using conventional techniques. An industrial case study from a textile factory in India is used to demonstrate the applicability of the formulation, followed by a sensitivity analysis to determine the number of storage tanks required to facilitate wastewater reuse. Results indicate freshwater savings of up to 94%. ©

Department Of Chemical Engineering

Industrial and Engineering Chemistry Research

Synthesis of an Optimal Schedule and Water Network for a Multipurpose Multiproduct Textile Industry through a Sequential MILP-NLP Technique

The specific role of disorder in the cell-wall material of a two-dimensional cellular solid on its deformation and crushing failure under uni-axial compression was examined numerically and validated with existing experimental data. A random spring network model with nearest and next-nearest neighbour interactions was developed for the representative cellular architecture of staggered-square honeycomb. The springs were taken to be quasi-brittle in nature and to account for the disorder, spring failure properties were taken to be statistically distributed. The model is shown to be capable of reproducing the non-linear behaviour of honeycombs resulting from the damage accumulation and results are shown to be in agreement with experimental measurements in terms of stiffness, strength and energy absorption. Further, the role of disorder in the material properties on the types of failure modes was investigated. Increasing disorder in the spring failure threshold was shown to result in decrease in the peak strength but a more stable crushing response resulting from the increased separation between the two primary cell wall failure modes. © 2021

Crushing of square honeycombs using disordered spring network model

This study focuses on characterising numerically the attractor volume in the state space of dynamical systems excited by additive white noise. A definition for stochastic attractors is introduced in terms of probability measure and numerical methodologies are presented to characterise them. The study is limited to investigating the effects of additive noise on fixed point and limit cycle attractors of the corresponding noise free system. The effect of noise intensity on the definition and validity of the proposed methodology is also discussed. © 2021 Elsevier B.V.

Communications in Nonlinear Science and Numerical Simulation

Characterising stochastic fixed points and limit cycles for dynamical systems with additive noise

We study the effect of shear by the inherent large-scale flow in the bulk on the boundary layers on the hot plate in Rayleigh–Bénard convection for a range of Prandtl numbers 4.69 ≤ Pr ≤ 5.88 and Rayleigh numbers 105 ≤ Ra ≤ 109. We observe that, at each Ra, at an instant, the distribution of horizontal velocities within the boundary layer in a horizontal plane is either of a unimodal nature or of a bimodal nature. Unimodal distributions occur either at low Ra or at high Ra while the bimodal distributions occur more at intermediate Ra. The peak of the unimodal distribution at low Ra occurs at values at around Vbl, the natural convection boundary layer velocity while the peak of the unimodal PDFs at high Ra occur at values greater than or equal to Vsh, the large-scale flow velocity. In the case of bimodal distributions, the first peak occurs in between Vbl and Vsh while the second peak occurs after Vsh. We show that the second peak of the bimodal distribution and the unimodal peak which occur at ≥Vsh scales as Vsh scales with Ra. The first peak of bimodal distribution and the single peak occurring at around Vbl scales with Ra as the natural convection boundary layer velocity forced by shear. © 2021, Springer Nature Singapore Pte Ltd.