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 presents an in situ growth technique to develop highly sensitive plasmonic fiber optic sensors with an excellent control over the plasmonic properties of gold (AuNPs) and silver nanoparticles (AgNPs). Here, we exploit the dual functionality of the U-bent fiber optic sensor (FOS) probes, where the probe acts as, firstly, the substrate for nanoparticles’ growth and, secondly, an invaluable tool to monitor as well as control the gold and silver seed binding to the surface amine groups and subsequently their growth in real time by means of the evanescent wave absorbance (EWA) spectral response. Au and Ag seeds (&lt; 5&nbsp;nm) with a peak absorbance at 510 and 390&nbsp;nm, respectively, were used. The NP growth kinetics from the probes for different seed densities with a peak EWA response of 0.05, 0.1, and 0.15&nbsp;optical density (OD) were observed in the presence of the respective metal precursor, cetyltrimethylammonium bromide (CTAB), and ascorbic acid. In comparison with AuNP grown FOS, a significant anisotropic growth was observed for AgNP with a redshift and spectral width as high as 215&nbsp;nm and 425&nbsp;nm, respectively, for a peak EWA response of 2.0&nbsp;OD. The localized surface plasmon resonance (LSPR) activity of the AuNPs and AgNP grown FOS probes was evaluated for seed density of 0.1&nbsp;OD. These proof-of-the-concept studies show significantly high RI sensitivity and surface-enhanced Raman scattering (SERS) enhancement factor for AgNP probes at 15.8 ΔA/RIU (for 22 AgNPs/μm2) and 1.3 × 107, respectively, in comparison with 18.9 ΔA/RIU (for 1424 AuNPs/μm2) and 1.1 × 106, respectively, for AuNP FOS probes. In addition, these plasmonic probes were stable in organic solvent (hexane) but its stability was deteriorated in alkaline solution (1&nbsp;M NaOH).

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Plasmonics

Controlled In Situ Seed-Mediated Growth of Gold and Silver Nanoparticles on an Optical Fiber Platform for Plasmonic Sensing Applications

In this work, an attempt is made to distinguish nucleolar and centromere staining patterns using Bag-of-Keypoint Features (BoKF) model and Binary Grey Wolf Optimization (BGWO) based feature selection. Fluorescent staining patterns are produced by Indirect Immunofluorescence (IIF) Imaging and the patterns considered for this study are taken from a publicly available online database. The IIF images are pre-processed using edge-aware local contrast enhancement method. The contrast enhanced images are subjected to BoKF framework and Speeded up Robust Feature keypoints are extracted. Further, the most significant features are identified using BGWO and are fed to k-Nearest Neighbor (kNN) for classification. The results show that the BGWO features are able to classify the nucleolar and centromere patterns with an average accuracy of 91.6%. Results also indicate that the prominent features obtained using BGWO can improve the discrimination performance of IIF staining patterns. Hence it appears that the BGWO based feature selection could enable the computer aided diagnosis of autoimmune diseases. © 2019 IEEE.

Proceedings of the Annual International Conference of the IEEE Engineering in Medicine and Biology Society, EMBS

Binary Grey Wolf Optimizer based Feature Selection for Nucleolar and Centromere Staining Pattern Classification in Indirect Immunofluorescence Images

In this work, an attempt is made to characterize the variation in the complexity of the surface electromyography (sEMG) signals in fatigue. For this, sEMG signals from 58 healthy volunteers are recorded from the biceps brachii muscle under well-defined dynamic contraction protocol. The contractions are segmented, and the initial and final curls are extracted. These are considered as nonfatigue and fatigue respectively. Further, visibility graphs are constructed at multiple scales, and median degree centrality (MSMC) is calculated in them. To quantify the variations in the MSMC, two features namely, the average and standard deviation are calculated. The results reveal that the recorded signals are non-stationary. The constructed networks form distinct clusters in space. The MSMC feature shows a decreasing trend with scale in both nonfatigue and fatigue conditions. Additionally, the extracted features have higher values in fatigue. This may be due to the motor unit synchronization, which causes an increase in connectivity between nodes. All the extracted features showed statistical significance with p<0.005. This approach of analysis can be extended to characterize muscle in other neuromuscular conditions. © 2019 IEEE.

Analysis of Dynamic Contractions from Biceps Brachii Muscle using Surface Electromyography signals and Multiscale Visibility Graph Features

Surface Electromyogram (sEMG) is an indicator of fatigue progression during isometric or dynamic contraction of skeletal muscle. Estimation of fatigue index provides clinically relevant data for the diagnosis of neuromuscular disorders. The major challenge is that the signal is highly nonstationary upon dynamic contraction of muscles. Therefore, an advanced signal processing method is essential for the analysis of such signals to measure fatigue indices. Cyclo-nonstationary (CNS) analysis reveals the hidden periodicities of a highly nonstationary signal which is not firmly established for muscle fatigue analysis. In this work, an attempt has been made for the cyclo-nonstationary analysis of sEMG signal in biceps brachii muscle using Order-Frequency Spectral Correlation function (OFSC) method. For this, signals are recorded from fifty healthy volunteers with well-defined protocol. The preprocessed signals are equally partitioned into three segments namely, nonfatigue, progression of fatigue and fatigue. Further, OFSC is computed using the Welch-based estimator. In addition, the OFSC statistical features such as area under the curve, skewness, kurtosis and six entropies are estimated to evaluate fatigue condition with CNS analysis. The preliminary results show that OFSC features are able to differentiate the fatigue condition. The obtained results are statistically significant with p < 0.002. Therefore, OFSC-based CNS analysis can be used for the fatigue index estimation to diagnose neuromuscular disorders. © 2019 IEEE.

Order Frequency Spectral Correlation Based Cyclo-nonstationary Analysis of Surface EMG Signals in Biceps Brachii Muscles

Crawley and Luis ("Use of Piezoelectric Actuators as Elements of Intelligent Structures," AIAA Journal, Vol. 25, No. 10, 1987, pp. 1373-1385) presented in the year 1987 a classic one-dimensional (1-D) quasi-static shear-lag model for the stress transfer between piezoelectric actuators and the host beam to which they are bonded through adhesive layers. Since then, it has been the backbone in modeling piezoelectric actuation and sensing. However, even after 30 years of its existence, the model remains to be extended to incorporate the inertia terms of the system, which is important for high-frequency applications, such as structural health monitoring. This work presents a consistent and generic extension of the 1-D shear-lag model for the dynamic stress transfer of a piezoelectric wafer transducer bonded to a thin isotropic plate, incorporating the inertia of the transducer, host plate, and the adhesive. The transducer and the plate were considered to be under plane strain condition. The plate was modeled using the classical Kirchhoff's plate theory, whereas the wafer transducer was considered to undergo only extensional deformation. The model led to a simple closed-form solution for the shear stress induced at the transducer-plate interface under harmonic electric potential excitation. The results were compared with detailed two-dimensional finite element dynamic simulations. A detailed numerical study was conducted to illustrate the influence of various transducer, plate, and adhesive parameters, as well as the excitation frequency on the inertia effect on the interfacial shear stress. © 2018 by the American Institute of Aeronautics and Astronautics, Inc.

AIAA Journal

Dynamic shear-lag model for stress transfer in piezoelectric transducer bonded to plate

This study focuses on numerically analyzing the transition from periodic to chaotic dynamics in the fluid-elastic response of a 2-dof flexibly-mounted airfoil with chord-wise rigidity. The computational framework is composed of a high fidelity Navier–Stokes solver, weakly coupled with a structural model having geometric nonlinearity represented by cubic order stiffness terms. A low Reynolds number flow regime and a very low structure-to-fluid added mass ratio have been considered to simulate the flying conditions of very light-weight unmanned devices. A bifurcation analysis of the system, in the absence of actuation or control forces, is undertaken with the wind velocity as the control parameter. The route to chaos – identified to be the Ruelle–Takens–Newhouse quasi-periodic route – is established for the first time for a flexible pitch–plunge flapping system. Robust nonlinear time series analysis techniques have been implemented to characterize different complex dynamical states present in the system. © 2018 Elsevier Ltd

GENERAL

Department of Aerospace Engineering

International Journal of Non-Linear Mechanics

Transition to chaos in the flow-induced vibration of a pitching–plunging airfoil at low Reynolds numbers : Ruelle–Takens–Newhouse scenario

Haptic feedback in immersive virtual reality (IVR) systems is critical to enable a more intuitive and natural way of interacting with virtual objects. IVR-based haptic medical simulations such as needle insertion procedures have the potential to enhance clinicians’ haptic expertise. This work is a preliminary study on the use and implementation of IVR for needle simulators. Although few studies have quantified haptic skills such as force Just Noticeable Difference (JND) with the single finger, none have measured the force JND as recommended in the standard needle insertion protocol in an IVR environment. The hypothesis of this study is that there will be an improvement of force perception in the IVR, compared to that of the non-immersive virtual reality (NIVR) which facilitates the use of IVR for medical simulations. This paper emphasized on two objectives: firstly, the development of the observer state model for both the IVR and NIVR and the theoretical analysis of the psychophysical measures in both of the environments. Secondly, measures of force JND with the three fingers and comparison of these measures in NIVR to that of the IVR using psychophysical study with the force matching task, constant stimuli method, and isometric force probing stimuli to validate the model. Twenty voluntary subjects performed the experiment in both of the environments. Mean force JND and standard deviation of the JND were found to be 9.12% and 3.75% in the NIVR and 5.91% and 3.65% in the IVR (p value < 0.0001) which are in the same range of JNDs found in the literature (5–10%) for the NIVR using a single finger. Surprisingly, the results showed a better force JND in the IVR compared to that of the NIVR. Also, a simple state observer model was proposed to explain the improvement of force JND in the IVR. This study would quantitatively reinforce the use of IVR for the design of various medical simulators. © 2018, Springer-Verlag London Ltd., part of Springer Nature.

Virtual Reality

Improved force JND in immersive virtual reality needle insertion simulation

This paper focusses on investigating how high-frequency (fast) excitations affect the aeroelastic instability of a spinning disc immersed in a compressible fluid-filled enclosure. The method of multiple scales is used to recast the governing equations of motion into separate equations for fast and slow motions. The slow motions represent the dynamic behaviour of the non-autonomous coupled system. The stability boundaries of the coupled system are investigated through a bifurcation analysis with respect to the mean disc rotation speed and the forcing amplitude. The study reveals that an increase in the forcing amplitude of the fast parametric excitation results in a corresponding increase in the frequencies and the critical speeds of the coupled disc modes associated with the slow motions. Moreover, it is shown that the aeroelastic stability can be postponed or suppressed due to the stiffening and gyroscopic effects induced by the fast excitations. © 2019, Springer Nature B.V.

Nonlinear Dynamics

Effect of fast parametric excitation on the instability behaviour of a spinning disc bounded in a compressible fluid-filled enclosure

Two-dimensional laminar fluid flow and heat transfer characteristics have been investigated numerically for a oscillating fin mounted on the top wall of backward facing step with constant bottom wall temperature. OpenFOAM is used to solve the governing equation of mass, momentum and energy conservation with the appropriate boundary conditions. Air is used as a working fluid with constant thermo-physical property (Pr = 0.71). It is found that the oscillating fin is the most effective method with highest average Nusselt number and lowest pressure drop, to enhance the mixing and heat transfer when it is compared to the different types of stationary fin arrangement. Further, the effect of frequency (which is directly proportional to the amplitude of velocity) and oscillation have been investigated and found that the average Nusselt number increases with the increase in velocity amplitude. It is also observed that the change in average Nusselt number is negligible with the increase in the amplitude of oscillation for a constant velocity amplitude. A correlation is also presented to express the effectiveness of the fin (ηf) in terms of ratio (Kv) of velocity amplitude (Vo) to the flow velocity (Uf) and is observed to follow the power law with constant exponent as ηf=cKv 0.3. © 2018 Elsevier Ltd

International Journal of Heat and Mass Transfer

The effect of fin oscillation in heat transfer enhancement in separated flow over a backward facing step

Flow past two tandem cylinders near a free surface is studied numerically at a Reynolds number of 180 using level set method and immersed boundary method. Values of Froude number are varied as 0.3,0.4,0.6; inter-cylinder distance varied as 2,3,4,5,6,10; submergence depth varied as 0.3,0.55. Flow characteristics and mean forces are noted with the variation of these parameters. Upon examination, it is observed that cylinder-to-cylinder proximity along with increased Froude number reduces the instabilities in flow. It is also found that mean drag of the rear cylinder reduces or increases at certain inter-cylinder distance depending on the submergence depth. At the same time, mean lift is observed to be sensitive to variation in submergence depth for flows with low Froude number. © 2019