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

Global recurrence plots (GRPs) and windowed recurrence quantification analysis (WRQA) are two recurrence paradigms which find wide applications to detect the onset of instability in a dynamic system. The present work reports the attempt to employ these recurrence paradigms to assess the effect of frontal gust on the force patterns of an insect-sized flapping wing in the inclined-stroke plane. Horizontal and vertical forces generated by the flapping wing in the presence of gusts of the form uGuw=u∞uw+(uguw)sin(2πfgfwt) were numerically estimated in the 2D reference frame for Re = 150. Nine gusts with combinations of the ratio of gust frequency to wing’s flapping frequency, fg/fw = 0.1, 0.5 and 1 and ratio of gust velocity amplitude to root mean square averaged flapping velocity, ug/uw = 0.1, 0.5 and 1 were considered. Recurrence studies of the forces were carried out to find out the gusty condition, which would trigger an onset of unstable behaviour. Studies indicated a possible onset of instability in the force patterns for gust with fg/fw = 0.1 and ug/uw = 1. The onset of unstable behaviour was prominently captured by WRQA of the vertical force coefficient based on determinism (DET) and laminarity (LAM) series. © 2019, Indian Academy of Sciences.

Fulltext

Sadhana - Academy Proceedings in Engineering Sciences

Recurrence studies of insect-sized flapping wings in inclined-stroke plane under gusty conditions

Ductile crack growth in austenitic 316LN stainless steel weld joint has been studied using FEA simulations with Gurson-Tvergaard-Needleman (GTN) damage model. The material specific GTN damage parameters are assessed and calibrated based on coupled experimental and numerical simulations for tensile and compact tension specimens. The influence of initial crack tip at various locations across the weld thickness has been analysed using CT geometry. The simulated results reveal that the crack propagates along the initial crack line for centrally located welds and deviates from the crack line for interfacial welds. The crack growth path for all cases is explained with damage parameters like equivalent plastic strain and void volume fraction. Copyright © 2019 Inderscience Enterprises Ltd.

Department of Mechanical Engineering

International Journal of Materials and Structural Integrity

Numerical investigation of crack growth in AISI type 316LN stainless steel weld joint using GTN damage model

Coiling of steel sheet is one of the easiest methods adopted by steel mills for the compact transportation of bulk sheet material to truck manufacturers for making 'C' shaped side frame rails. The coiling-uncoiling operation induces residual stresses in the steel sheet due to plastic strain hardening. This initial imperfection in the form of residual stresses remains in the plain web and flange areas of the rail sections. In corner areas of frames, increase in residual stresses are observed due to severe plastic deformation from forming operation than the coiling-uncoiling operation. More accurate consideration of the residual stresses becomes necessary when the behaviour of truck side frame rail web and flange sections, derived from different coil diameters are assessed. In this work, micro-hardness measurement is employed to predict the extent of plastic deformation at different coil diameter locations. The residual stresses induced by the coiling-uncoiling operation is assessed using the X-ray diffraction technique for steel coil diameters ranging from 600 mm to 1800 mm. Fatigue tests on samples extracted from different coil diameters indicate that fatigue life increases with the increase in coil diameter of the sample. The fatigue life of the annealed flat test sample was found to be higher than the fatigue life of samples derived from different coil diameter locations of steel coils received from steel mills. © School of Engineering, Taylor’s University.

Journal of Engineering Science and Technology

Study of the influence of coiling-uncoiling induced residual stresses on the fatigue behavior of truck frame rail sections

This work presents a comparison of various combinations of patch and parent laminates with different orientations and stacking sequence, on the performance of adhesively bonded external patch-repaired carbon/epoxy laminates under quasi-static compressive loading. The compressive behaviour and failure modes of pristine, damaged and repaired specimens of four different parent laminates ([0]6, [45]6, [0/45/45]s, [45/45/0]s) are discussed. The repair of each parent laminate is carried out by bonding patches of four configurations ([0]2, [45]2, [45/0], [0/45]) having two plies on each side of the parent laminates. Real-time digital image correlation technique was employed to capture the development of the strain field with the increasing load. The results reveal the development of distinctive strain contours associated with different patch–parent configurations. The inspection of damaged specimens revealed the fiber micro-buckling as the dominant mode of failure. The orientation of plies influences the overall failure mode of the laminates. The clustering of 0° plies results in laminate possessing higher strength. The less stiff [45]2 patch shows higher compliance with the increasing load. © The Author(s) 2019.

Journal of Composite Materials

Experimental investigation on compressive behaviour of different patch–parent layup configurations for repaired carbon/epoxy composites

Motor neuron disease (MND) is a condition where voluntary muscle movements of the patient stop functioning due to progressively damage of motor neurons resulting paralyzed the patient. One of the solution of MND is motor imagery (MI) based brain-computer interface (BCI) which acts as an assistive device for motor disabled people. But it has limited applications due to its lower classification performance. To improve it, this paper introduces second order difference plot (SODP) for the detection of various MI activities. First, filter bank technique was implemented to the signals and set of multiple sub-bands were generated. In order to study MI activities effectively, SODP was applied to each sub-band and area of ellipse was calculated. The feature (area of ellipse) of all sub-bands were combined and the significant features (p <0.05) were extracted using one-way analysis of variance (ANOVA). These significant features were fed into multi-class support vector machine (SVM) for decoding MI activities. The Proposed method and classifier were tested on BCI competition 2008 MI dataset-II-a. The performance of the proposed method was evaluated in term of Cohen's kappa coefficient (K). Results show that the SVM improved the mean value of kappa (K=0.62) and outperformed the existing methods reported in the literature. © 2019 IEEE.

World University root node

2019 7th International Conference on Smart Computing and Communications, ICSCC 2019

Second Order Difference Plot to Decode Multi-class Motor Imagery Activities

Parallel computations of flow past a perforated plate of porosity 25% at Reynolds number 250 (based on plate width, d and inflow velocity, Uo) is carried out. The effect of aspect ratio is studied with different span-wise lengths of the domain (1d, 3d and 6d). Present results revealed that an aspect ratio of 6d is required to capture the transient wake dynamics. It was found that statistical quantities stemming from aspect ratio 3d and 6d cases agree with each other, though the dynamical behavior of the wake is very different. The signature period doubling effects associated with short constrained domains were visible in the 1d and 3d aspect ratio cases. Enforcing periodic boundary condition along the short span-wise domains may thus adversely affect the flow. © 2018 IEEE.

Proceedings - 25th IEEE International Conference on High Performance Computing Workshops, HiPCW 2018

Perforated bluff-body wake simulations: Influence of aspect ratio

In this study, a high performance electrooculogram (EOG) based synchronous and asynchronous visual keyboard system is designed with large number of targets. The proposed system overcomes the limitations in the conventional EEG based visual keyboard system which has to compromise with either accuracy or typing speed of the system. In this study, we first proposed a synchronous visual keyboard system with 36 targets which includes alphabets, numbers and space. Later, we proposed an asynchronous visual keyboard system where the user can have control on the system. Ten subjects were taken for evaluating the performance of the proposed keyboard systems. A cue guided online experimental procedure was conducted on all the subjects in synchronous and asynchronous case. The average classification accuracy of 94.2% and 98.79% were obtained in synchronous and asynchronous cases respectively. Four subjects show 100% accuracy in the asynchronous case with average information transfer rate (ITR) of 66.71 bits/minute. This result shows that the developed system outperforms conventional keyboard system. © 2019 IEEE.

2019 IEEE EMBS International Conference on Biomedical and Health Informatics, BHI 2019 - Proceedings

A novel EOG based synchronous and asynchronous visual keyboard system

We study the effect of shear on the coherent structures near the hot surface, namely, line plumes, in turbulent Rayleigh-Bénard convection (RBC) and turbulent mixed convection (MC) for the range of near-surface Rayleigh numbers 5.75×107≤Raw≤2.17×109 and shear Reynolds numbers 8.02×102≤Re≤15×103 for a Prandtl number range of 10.1≥Pr≥0.7 in water and air. Plumes are visualized by particle scattering in MC in air while they are extracted from the particle image velocimetry fields in RBC in water. We also use the planforms of plume structure obtained by Gilpin et al. [J. Heat Transfer 100, 71 (1978)JHTRAO0022-148110.1115/1.3450506] in MC in water using electrochemical visualization, as well as those obtained by Pirozzoli et al. [J. Fluid Mech. 821, 482 (2017)JFLSA70022-112010.1017/jfm.2017.216] in simulations. The planforms of plume structure show that shear aligns the line plumes and increases their mean spacing λ. An increase in Raw decreases λ, while the resulting increase in Re in RBC, due to the increase of larger large-scale flow strength, counteracts this effect. Further, plumes are seen more spaced and smeared in air, compared to that in water, due to the lower Pr. We show that these complex dependences of λ on Raw, Re, and Pr in RBC and MC can be described by a common scaling law λ∗=λ-λ0=SZsh/D, where λ0 is the mean plume spacing in the absence of shear, S=Re3/Raw is a shear parameter, Zsh=ν/Ush is the viscous-shear length, and D a function of Pr. © 2019 American Physical Society..

Physical Review Fluids

Effect of shear on coherent structures in turbulent convection

The use of theoretical calibration table for fringe pattern demodulation in isochromatic images is revisited and a sensitivity analysis of material stress fringe value to generate theoretical calibration table is studied. The influence of filter parameter ‘R’ in normalization is discussed and its nuances are brought out. A substitution for theoretical calibration table and a new normalization technique is proposed to alter the dynamic range over the entire model domain of the isochromatic image suitably. © The Society for Experimental Mechanics, Inc. 2019.

Conference Proceedings of the Society for Experimental Mechanics Series

Development of a new normalization technique for twelve fringe photoelasticity (TFP)

In this work, an attempt has been made to differentiate human epithelial type-2 (HEp-2) specimen images using Bag of Features (BoF) and Adaptive Cuckoo Search (ACS) feature selection. For this, 420 images consisting of homogenous and speckled patterns were obtained from a publicly available International Conference on Pattern Recognition (ICPR) 2016 database. These images are preprocessed using edge-aware local contrast enhancement and subjected to a speeded-up robust feature (SURF) descriptor for feature extraction. The optimal features are identified using the ACS method and are then fed into a support vector machine (SVM) for classification. The results show that the proposed approach is able to distinguish homogenous and speckled patterns. It is found that the features identified using ACS-based feature selection are significant. The proposed approach yields an average accuracy of 97.90% using the SVM classifier. Because automated analysis and classification of HEp-2 specimen images is important for the diagnosis of autoimmune diseases, this study seems to be clinically relevant. Copyrights © 2019 The Institute of Electronics and Information Engineers.