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.

World University root node

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

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

In this paper, the development of modified beamforming methods, Filtered Delay Weight Multiply and Sum (F-DwMAS) and Filtered Delay Euclidian-Weighted Multiply and Sum (F-DewMAS), are reported. These methods were investigated on a minimum-redundancy synthetic aperture technique, called as 2 element Receive Synthetic Aperture Focusing Technique (2R-SAFT), which uses one element on transmit and two consecutive elements on receive, for reducing hardware complexity without compromising much on the image quality. The performance of the developed F-DwMAS and F-DewMAS methods were compared with Delay and Sum (DAS) and recently introduced F-DMAS beamforming methods. Notably, in the proposed methods, an additional aperture window function is designed and incorporated to the F-DMAS method. The different methods of F-DwMAS, F-DewMAS, 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), in simulation and experiments on tissue-mimicking phantoms. Experimental results show that (F-DwMAS) and F-DewMAS resulted in improvements of AR by (46.32% and 23.51%), 43.56% and 17.78%, LR by (47.81% and 30.27%), 44.26% and 26.14% and CR by (45.68% and 17.15%), 42.16% and 9.87% compared to those obtained using DAS and F-DMAS, respectively. However, CNR of F-DwMAS and F-DewMAS was found to be 31.19% and 21.16% less compared to DAS, but 4.89% and 18.64% more than F-DMAS, respectively. Hence, it can be concluded that the image quality improved by both F-DwMAS and F-DewMAS compared to DAS and F-DMAS. Also, between F-DwMAS and F-DewMAS, the later has the advantage of ready applicability to different acquisition schemes and settings compared to the former also having an additional advantage of better CNR compared to both F-DMAS and F-DewMAS. © 2020 Elsevier B.V.

Ultrasonics

Weighted non-linear beamformers for low cost 2-element receive ultrasound imaging system

In turbulent premixed flames, the fractal dimension of flame iso-surface is argued to be D=7/3 for Damköhler's large-scale limit (Da&gt;&gt;1) and D=8/3 for Damköhler's small-scale limit (Da∼O(1)) based on heuristic scaling arguments. However, such scaling arguments do not consider the effect of the intermittent nature of turbulent kinetic energy dissipation on the flame surface. In this paper, we account for the effects of intermittent dissipation on the fractal dimension of low Da turbulent premixed flames. Intermittent dissipation leads to variability in the inner cut-off, which then affects the scalar flux and total interface area. We account for these variabilities through two approaches: coarse-grained approach based on the moments of the dissipation and fine-scale analysis by adopting the multifractal formalism. We derive two corrections to the upper-limit of fractal dimension – D=8/3+3/4(1−D1/4) and D=8/3+2/3(3−D1/3). We further show that the second correction leads to an explicit dependence of the fractal dimension (D) on the scaling exponent (ξ) of the velocity structure function through the relation: D=7/3+ξ. Thus, we explicitly quantify the effect of the intermittent nature of turbulence upon low Da premixed combustion. © 2020 The Combustion Institute

Department of Aerospace Engineering

Combustion and Flame

Fractal dimension of premixed flames in intermittent turbulence

The numerical investigation of 2D insect wing kinematics in an inclined stroke plane is carried out using an immersed boundary solver. The effect of vortex shedding and dipole jet on the vertical force generation by the flapping wing due to change in the stroke plane angle is investigated in the vicinity of the ground. The results of instantaneous force and vorticity contours reveal the underlying lift enhancement mechanisms for the inclined stroke plane flapping wing. Moreover, they aid in the understanding of the wake-ground interaction and the associated shear layers. The calculated average vertical force delineates different force trends for the inclined stroke plane flapping near the ground. Furthermore, the dipole jet patterns are analyzed for different heights. These patterns are found to be a better tool to assess the kinematics for the vertical force enhancement and reduction, especially at intermediate heights. Vertical force enhancement is the critical parameter in the design of the micro aerial vehicle (MAV). Through this study, it is certain that the dipole jet has the potential to be used as a lift modification mechanism in MAVs. In summary, the study gives a holistic view of the physics of the inclined plane kinematics near the ground and serves as the basis for the design of MAVs. © 2021 IOP Publishing Ltd.

Bioinspiration & biomimetics

Can the ground enhance vertical force for inclined stroke plane flapping wing?

A composite of two different medium entropy alloys (MEAs, i.e., CoCrFeNi and AlCoCrFe) was synthesized using ball milling and spark plasma sintering. The composite microstructure contains a homogenous distribution of fcc and bcc phases with submicron-sized grains and exhibits excellent microstructural and phase stability even after 100 h heat treatment at 800 °C. The composite provides a combination of high compressive strength, adequate plastic strain, and multiple strain-hardening stages at room temperature. This first exploratory study on a MEA composite can be used as a template to other systems and illustrates the feasibility of combining two or more MEAs. © 2020 Acta Materialia Inc.