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

The spreading of a liquid on another is often encountered in oil spills and coatings and is also of industrial relevance in pharmaceuticals and petrochemicals. In this study, the spreading of oil drops on aqueous solutions containing cationic, anionic, and nonionic surfactants over a wide range of surfactant concentrations is investigated. The spreading behavior quantified by measuring the time evolution of the projected area of the oil lens reveals the occurrence of a maximum, which is strongly dependent on the concentration of the surfactant in the aqueous solution. Our experiments show that this dependence is different at concentrations above and below the critical micelle concentration (CMC) of the surfactant and can be captured by two straight lines of different slopes. Interestingly, these two straight lines intersect at a concentration that coincides with the CMC of the surfactants in solution. We find that this behavior is universal as shown by performing experiments with different types of surfactants, their purity, and other system variables. Thus, we propose a method to unambiguously determine the CMC of surfactant solutions compared to the conventional techniques. The proposed method is simple, versatile, and applicable for the determination of CMC of both ionic and nonionic surfactants.

World University root node

Department Of Chemical Engineering

Langmuir

Robust Method to Determine Critical Micelle Concentration via Spreading Oil Drops on Surfactant Solutions

Owing to their high energy densities, smart materials like shape memory alloys (SMAs), Macro-Fiber Composites (MFCs) and, electroactive polymers (EAPs) have massive potential as actuators in wing morphing applications. In this article, a detailed numerical model is developed for the shape prediction of an elastic base that is actuated by a combination of a shape memory alloy (SMA) wire and a Macro-Fiber Composite (MFC) bimorph. It has been demonstrated using the model that it is possible to achieve large deflections at low frequencies by virtue of the phase transformations in the SMA wire and rapid actuation with small deflections due to the MFC bimorph. In the developed scheme, the elastic base is modeled using non-linear Euler-Bernoulli beam theory. The influence of the non-linear hysteresis in the SMA wire and the linear actuation characteristics of the MFC is studied by incorporating thermo-mechanical and electro-mechanical constitutive behavior into the non-linear beam theory. The system of coupled equations hence obtained, is solved iteratively to obtain the deflected shape of the elastic base. The results from the developed numerical scheme are validated against the previously available studies in the literature and experiments. Additionally, the synergistic advantage of using the two actuators together has been shown through experiments. As an illustration, a smart trailing edge camber morphing concept is developed by integrating the flexible elastic structure along with the two smart actuators to a NACA 0012 airfoil as the trailing edge. © 2020 IOP Publishing Ltd.

Smart Materials and Structures

Modeling of integrated shape memory alloy and Macro-Fiber Composite actuated trailing edge

Polyvinylidene fluoride (PVDF) composite films have witnessed widespread applications in biomedical and flexible electronic devices in recent years. These applications require a material that has enhanced electrical properties, mechanical flexibility along with sufficient strength. A lot of research has been carried out to enhance the piezoelectric and dielectric properties of the PVDF composite films. However, the improvements in the mechanical properties of nano filler reinforced PVDF composite films has not received due attention. In this regard, the present work focuses towards enhancing the mechanical strength and load-bearing capability of PVDF, by preparing composites of PVDF films impregnated with Cellulose Nanocrystals (CNC) and Barium Titanate (BTO) nanoparticles. Solution casting method was adapted to fabricate the PVDF/BTO/CNC films. X-ray diffractograms and FTIR (Fourier Transform infrared spectroscopy) corroborate the presence of ferroelectric γ phase in PVDF. Mechanical and viscoelastic measurements have been carried out to examine the influence of CNC and BTO nano fillers in the PVDF matrix. The addition of CNC and BTO in PVDF film has improved the mechanical strength significantly. The stress achieved for PVDF/5% BTO and PVDF/5% BTO with 0.9% of CNC at 5% strain was 17% and 130% higher than the pristine PVDF, respectively. This study can be helpful for the design engineers to meet custom/specific requirements for a myriad of end-user applications such as piezoelectric nanogenerators.

Department of Electrical Engineering

Journal of Alloys and Compounds

PVDF/BaTiO films with nanocellulose impregnation: Investigation of structural, morphological and mechanical properties

Blunt nose cones used in launch vehicles can excite buffet due to shock oscillations over the payload fairing on the leeward side at transonic Mach numbers and small angles of attack. Wind-tunnel tests show that the overall aerodynamic characteristics, such as the pitching moment and location of the center of pressure, experience sudden jumps at these conditions. Thus, the longitudinal stability and controllability of a launch vehicle, as well as unsteady loading on the payload fairing, can be affected. The cause of these oscillations is found to be interactions between the streamwise flow and reverse flow induced by a pair of counter-rotating vortices over the payload fairing. An aerospike was found to prevent the formation of counter-rotating vortices, shock oscillations, as well as jumps in overall aerodynamic characteristics, with no significant changes in the drag coefficient. The observations are supported by high-speed shadowgraphs and surface-flow visualizations. Computational fluid dynamics studies suggest that the shear layer from the tip of the aerospike envelops a significant region of the heat shield in a reverse flow due to the formation of a separation bubble. Mean-flow models of the topologies of the flowfield for the model without and with aerospike are proposed.

Journal of Spacecraft and Rockets

Passive Control of Transonic Flow over a Blunt Body Using Aerospikes

Experimental investigation on two rectangular wings with NACA0012 and NACA4415 profiles is performed at different Reynolds numbers to understand their aerodynamic behaviours at a high α regime. In-house developed numerical code VLM3D is validated using this experimental result in predicting the aerodynamic characteristics of a rectangular wing with cambered and symmetrical wing profile. The sectional coefficient of lift ((Formula presented.)) obtained from the numerical approach is used to study the variation in spanwise lift distribution. The lift and moment characteristics obtained from wind tunnel experiments are plotted, and change in the maximum coefficient of lift ((Formula presented.)) and stall angle (αstall) are studied for both of the wing sections. A significant addition to the novelty of the present experiments is to provide some comparison of the numerical induced drag coefficient, (Formula presented.) with experimentally fitted model coefficients using least square technique. A novel method is used to examine the aerodynamic hysteresis at high angles of attack. The area included in the lift- Re curve loop is a measure of aerodynamic efficiency, and its variation with angle of attack and wing plan forms is studied. © IMechE 2020.

Proceedings of the Institution of Mechanical Engineers, Part G: Journal of Aerospace Engineering

Experimental validation of numerical decambering approach for flow past a rectangular wing

The dataset presented in the article includes the timestamp of key press and key release data of individual participants during a novel finger thumb opposition typing task. The novel task involves touching different segments (phalanges) of fingers with the thumb to type a specific symbol on the computer screen. This task involves learning of set of sequences by typing or touching them using the finger thumb opposition movements is termed as motor sequence learning task or paradigm. The symbol set comprised of nine most frequently used symbols in English. From the nine symbols, a set of 281 meaningful five lettered words (sequences) were formed. These sequences were presented to the participants in a game-like interface. Once a specific symbol was pressed and released the time stamp was registered in the computer as key (symbol) press and key release information. The dataset consists of three columns, first column shows the pressed key, second column the registered timestamp and final column shows the symbol activity with respect to the first symbol in terms of milliseconds. Key press information is followed by key release information. This is represented in the dataset as “LCONTROL” in the first column of the data. Changes of this key press and key release information over the course of practice can be used to understand change in performance of this novel tying task.&nbsp;

Fulltext

Motor sequence learning data collected continuously for fifteen days of practice using a novel glove-based typing device

The dataset presented in the article consists of finger forces of participants during a finger pressing task. The finger pressing task involves the production of fingertip forces using Index, Middle, Ring, and Little (I, M, R&amp;L) fingers of the right hand. The participant performed two types of task, namely MVC task and visual occlusion task. The participants completed the Maximum Voluntary Contraction (MVC) task first, where they were instructed to produce maximum possible force from each finger individually and all fingers together. The visually occluded finger pressing task followed the MVC task. In this task, the participant's visual feedback was removed after 8s. There were two conditions in this task, one with post-trial performance feedback (referred to as “epilogue” condition in this manuscript) and another that does not have this post-trial performance feedback (referred to as “no epilogue” condition in this manuscript). The epilogue condition is a particular case of post-trial visual feedback where, at the end of each trial, the performance in that trial is shown to the participant. This was followed by the next trial. Normalization of force levels for visual occlusion tasks was performed for the forces with the participants produced in the MVC task. Fourteen healthy participants were recruited for performing the experiments. For the experiments, they were instructed to produce fingertip forces using four fingers of the right hand with the target line at 15% MVC (15% of the force that they produced in the MVC task). The two visual occlusion conditions had 30 trials each. In both conditions, a single trial lasted 16 s. For the initial 8 s, there is visual feedback, which follows an eight-second visual occlusion period where there is no visual feedback. The dataset consists of three files; the first file has the data of Maximum Voluntary Contraction (MVC) data, the second file has the data for the “without epilogue” condition, and the third file has the data of “epilogue” case.

Finger pressing task data collected with and without post-trial performance feedback

Exercise-induced muscle damage is a condition which results in the loss of muscle function due to overexertion. Muscle fatigue is a precursor of this phenomenon. The characterization of muscle fatigue plays a crucial role in preventing muscle damage. In this work, an attempt is made to develop signal processing methods to understand the dynamics of the muscle’s electrical properties. Surface electromyography signals are recorded from 50 healthy adult volunteers under dynamic curl exercise. The signals are preprocessed, and the first difference signal is computed. Furthermore, ascending and descending slopes are used to generate a binary sequence. The binary sequence of various motif lengths is analyzed using features such as the average symbolic occurrence, modified Shannon entropy, chi-square value, time irreversibility, maximum probability of pattern and forbidden pattern ratio. The progression of muscle fatigue is assessed using trend analysis techniques. The motif length is optimized to maximize the rho value of features. In addition, the first and the last zones of the signal are compared with standard statistical tests. The results indicate that the recorded signals differ in both frequency and amplitude in both inter- and intra-subjects along the period of the experiment. The binary sequence generated has information related to the complexity of the signal. The presence of more repetitive patterns across the motif lengths in the case of fatigue indicates that the signal has lower complexity. In most cases, larger motif length resulted in better rho values. In a comparison of the first and the last zones, most of the extracted features are statistically significant with p &lt; 0.05. It is observed that at the motif length of 13 all the extracted features are significant. This analysis method can be extended to diagnose other neuromuscular conditions.&nbsp;

Proceedings of the Institution of Mechanical Engineers, Part H: Journal of Engineering in Medicine

Characterization of surface electromyography signals of biceps brachii muscle in fatigue using symbolic motif features

We study the effect of shear on the line plumes in turbulent mixed convection (MC) and Rayleigh Bénard convection (RBC) for a decade range of near-wall Rayleigh numbers (2.3 × 106 ≤ Raw ≤ 2.17 × 109) and shear Reynolds numbers (802 ≤ Re ≤ 15000) for a Prandtl number range of 0.7 ≤ Pr ≤ 10.1 in air and water. Plumes are visualised in mixed convection in air by smoke while the plumes in RBC in water are detected from the planar PIV fields using the horizontal divergence criteria [Vipin K. and Puthenveettil B. A., ExHFT-8, Lisbon, 2013]. In addition to our planforms we measure the plume spacings from the planforms of Gilpin et al. [J. Heat Transfer 100, 71 (1978)], Pirozzoli et al. [J. Fluid Mech. 821, 482 (2017)] and by Blass et al. [arXiv:1904.11400 , physics.flu-dyn]. The mean plume spacing λ increase with increase in Re while they decrease with increase in Raw, in addition to being a function of Pr. We propose a common scaling law that captures this complex dependence of the mean plume spacing on Raw, Re and Pr, λ* = λ− λo = SZsh/D, where S = Re3/Raw is the shear parameter, Zsh is the viscous shear length, D is a function of Pr and λ0 the plume spacing in the absence of shear.

Proceedings of the 25th National and 3rd International ISHMT-ASTFE Heat and Mass Transfer Conference (IHMTC-2019)

Quantifying Near-Wall Plumes in the Presence of Shear in Turbulent Convection

This study investigates the effect of randomness in the forcing on a harmonically excited bilinear impact oscillator with a soft barrier. The system parameter range considered coincides with regimes in which multiple stable attractors coexist. The random component superimposed on the harmonic excitations is shown to lead to qualitatively different dynamical behaviours at different parameter values, due to the presence of multiple coexisting attractors. This is classified as P-bifurcation. Wavelet analysis and recurrence quantification-based tools have been employed to show that these qualitative changes are due to noise-induced intermittency in the system. © 2020, Springer Nature B.V.