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 paper identifies the laminar separation bubble at the root or span-wise midsection of a rectangular wing using direct surface pressure measurements and analyses their behavior. The locations of separation, transition, and reattachment are identified from surface pressure measurements and oil flow visualizations. Surface oil flow visualization results also clarified the wing-tip and separation bubble interactions near the leading edge of the wing. The transition structure and turbulence characteristics in the separated shear layer locations are studied using Laser Doppler Velocimetry. Time series analysis is carried out to distinguish the flow patterns of transition and later transition locations along with chordwise locations of the root section of the wing. © 2021, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.

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AIAA Scitech 2021 Forum

Time Series Behaviour of Laminar Separation Bubbles at Low Reynolds Number

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.

Plasmonics

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

Ground resonance is an aero-mechanical instability in helicopters that use soft in-plane rotors. Traditionally, ground resonance is mitigated by using passive lead–lag dampers that provide sufficient in-plane damping. However, these dampers because of their passive nature cannot adapt to all operating conditions. In this work, a magnetorheological fluid–based semi-active lead–lag damper is proposed to offer controllable damping. Two nonlinear control strategies are reported to operate the voltage to be supplied to the magnetorheological damper. The first strategy is a model-based control using dynamic inversion. The second is a fuzzy logic control integrated with a particle swarm optimization algorithm to optimize the control parameters. Both control strategies are shown to be effective in eliminating ground resonance. Unlike bang–bang control, the prescribed control algorithms can make use of complete voltage level available in the magnetorheological damper with smooth voltage updates. A comparative study of the controller performances is made through appropriate performance indices and system responses. Finally, the most optimum control strategy to mitigate ground resonance is inferred. © The Author(s) 2021.

JVC/Journal of Vibration and Control

Nonlinear dynamics and control of helicopter ground resonance

Amorphous thin film metallic glasses (TFMGs) have given rise to a widespread research interest due to their technological promise for practical applications and scientific importance in the biomedical field. As a result of their disordered atomic structure (leading to amorphicity), these TFMGs symbolize a new class of structural and functional materials with extraordinary properties, including exciting strength along with superior mechanical properties and biological properties. TFMG top-coats have the potential to improve the strength, corrosion resistance, biocompatibility, and life span of potential biomaterials (metallic, ceramics, or polymers). This article reviews the mechanical properties and biological behavior of TFMGs as well as the current progress in Zr-based, Ti-based, Fe-based, and Mg-based TFMGs for biomedical applications. © 2021 Elsevier B.V.

Journal of Alloys and Compounds

Thin film metallic glasses for bioimplants and surgical tools: A review

Collisions in a dilute polydisperse suspension of spheres of negligible inertia interacting through non-continuum hydrodynamics and settling in a slow uniaxial compressional flow are studied. The ideal collision rate is evaluated as a function of the relative strength of gravity and uniaxial compressional flow and it deviates significantly from a linear superposition of these driving terms. This non-trivial behaviour is exacerbated by interparticle interactions based on uniformly valid non-continuum hydrodynamics, that capture non-continuum lubrication at small separations and full continuum hydrodynamic interactions at larger separations, retarding collisions driven purely by sedimentation significantly more than those driven purely by the linear flow. While the ideal collision rate is weakly dependent on the orientation of gravity with the axis of compression, the rate including hydrodynamic interactions varies by more than with orientation. This dramatic shift can be attributed to complex trajectories driven by interparticle interactions that prevent particle pairs from colliding or enable a circuitous path to collision. These and other important features of the collision process are studied in detail using trajectory analysis at near unity and significantly smaller than unity size ratios of the interacting spheres. For each case analysis is carried for a large range of relative strengths and orientations of gravity to the uniaxial compressional flow, and Knudsen numbers (ratio of mean free path of the media to mean radius). © 2021 The Author(s),. Published by Cambridge University Press.

Journal of Fluid Mechanics

Collision rate of bidisperse spheres settling in a compressional non-continuum gas flow

A non-planar mixing layer observed between parallel Couette flows by Narasimhamurthy et al. (Phys Rev E 85:036,302, 2012) is considered. Direct numerical simulation is chosen, and simulations are run in order to determine the critical Reynolds number at which the interface between the co-flowing laminar and non-laminar flow becomes unstable exhibiting a meandering motion. The necessary conditions required to trigger the shear-layer instability were also discussed. Different combinations of Reynolds numbers are chosen keeping the Reynolds number ratio between the laminar and non-laminar flows as constant. Preliminary results indicate that the onset of instability occurs, and a meandering motion is observed at the interface when Reynolds number for the non-laminar flow corresponds to 650. © 2021, Springer Nature Singapore Pte Ltd.

Lecture Notes in Mechanical Engineering

DNS of an Oscillating Shear Layer Between Two Parallel Couette Flows

Flow separation over a two dimensional geometry such as aerofoil is defined as a point where shear stress goes to zero. For a three-dimensional boundary layer, separation is along a line and universally accepted definition of such lines do not exist for 3D geometry. Any flow leaves behind a wall signature on the surface which can be visualized by plotting velocity or skin-friction vector field over the surface. In our present work, critical point theory is used to explain the observations of vector fields over a finite wing surface and in particular, determine pattern in separation lines for 3D geometry. Oil flow experiments were carried out on a finite wing with NACA 0012 as cross-section for 0.085 and 0.1 million Reynolds number. Some of the results of wind tunnel experiments are discussed along with need for computational solution. Numerical simulations were carried out for sphere, spheroid, torus and 3D wing at different angles of attack at 1 million Re and separation lines are plotted over the surface. These lines are studied in pre-and post-stall angles of incidence to understand the nature of separation in three-dimensional boundary layer. © 2021, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.

Study of separation of three-dimensional boundary layer using critical point theory

Tissue simulating optical multilayer phantoms that closely mimic optical properties of specific tissues are used to evaluate and calibrate spectral imaging studies in clinical diagnostics. Consistency in phantom layer thickness, fabricated through the spin coating method is crucial in using the methodology to create large datasets to facilitate artificial intelligence (AI) based optical diagnostic systems. These phantoms are usually imaged under a scanning electron microscope to verify layer dimensions, varying with the amount of used materials, changes in sample parameters, and spin speed. Imaging a considerable number of phantoms under SEM for different applications is challenging. This paper addresses the automated detection of layered skin phantom thickness acquired from light microscopy images. The thickness estimation reported in this work is also useful in optimizing the sample and spin coating parameters to achieve a predefined sample dimension during the fabrication procedure. © COPYRIGHT SPIE. Downloading of the abstract is permitted for personal use only.

Progress in Biomedical Optics and Imaging - Proceedings of SPIE

Automated detection of optical phantom layer thickness using image analysis

Viscosity variation of solvent in local regions near a solid surface, be it a biological surface of a protein or an engineered surface of a nanoconfinement, is a direct consequence of intermolecular interactions between the solid body and the solvent. The current coarse-grained molecular dynamics study takes advantage of this phenomenon to investigate the anomaly in a solvated protein's rotational dynamics confined using a representative solid matrix. The concept of persistence time, the characteristic time of structural reordering in liquids, is used to compute the solvent's local viscosity. With an increase in the degree of confinement, the confining matrix significantly influences the solvent molecule's local viscosity present in the protein hydration layer through intermolecular interactions. This effect contributes to the enhanced drag force on protein motion, causing a reduction in the rotational diffusion coefficient. Simulation results suggest that the direct matrix-protein non-bonded interaction is responsible for the occasional jump and discontinuity in orientational motion when the protein is in very tight confinement. © 2021 IOP Publishing Ltd.

Nanotechnology

Rotational dynamics of proteins in nanochannels: Role of solvent's local viscosity

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.