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 manuscript discusses a magnetically coupled nonlinear hybrid piezo-electromagnetic energy harvester under harmonic base motion. Linear energy harvester works optimally when the natural frequency of the harvester meets the resonating frequency, elsewhere harvested power falls drastically. Most of the ambient vibration sources are random in nature. Hence, considering the realistic application, narrowband linear vibration energy harvesters are inefficient. Alternatively, nonlinear energy harvesters are capable of producing the electrical power over a broad frequency range. Hence, to acquire the optimum power in the broader frequency range, a magnetically coupled hybrid piezo-electromagnetic energy harvester is developed. In this current work, a tip loaded unimorph piezo cantilever beam configuration is used to scavenge electrical energy from the strain developed in the piezoelectric patch and spring-magnetic mass attached to another end of the cantilever beam with solenoid arrangements are used to scavenge electrical energy from the relative motion between magnetic mass and solenoid. This hybrid harvester is coupled with magnetic oscillators to introduces nonlinearity in the developed harvester. This paper compares, the energy harvested from the hybrid harvester with that of conventional piezoelectric and electromagnetic harvesters for both linear and nonlinear systems. © Springer Nature Singapore Pte Ltd 2020.

World University root node

Lecture Notes in Mechanical Engineering

A nonlinear hybrid energy harvester

This manuscript analyzes the performance of a tristable vibration energy harvester under Gaussian white noise excitation. Broadband vibration energy harvesting has attracted significant research attention and is targeted toward obtaining large power output over a wide range of frequencies. Nonlinearity can be introduced into vibration energy harvesting systems through multi-stability. In cantilever-type vibration energy harvesters, multi-stability could be achieved by the introduction of magnetic interactions. When two external magnets are used, the harvester can have up to three stable static equilibrium positions. The harvester with two stable states has been explored widely, both theoretically and experimentally. Recently, the harvester with three stable states is shown to perform better than its bistable counterpart in the presence of a linearly increasing harmonic sweep excitation. Ambient vibrations are random in nature, and the performance of tristable energy harvesters under such excitations needs to be studied. To begin with, we study the performance of tristable energy harvesters under Gaussian white noise excitation through numerical simulations. The simulations show that beyond a certain critical amplitude of excitation, the harvesters undergo inter-well oscillations and harvest more power. This implies that if the variance of the random ambient excitation is known, then the harvester could be optimized so that the mean harvested power is maximized. © Springer Nature Singapore Pte Ltd 2020.

Analysis of tristable energy harvesters under random excitations

An energy harvesting device built on the lines of capitalizing the linear resonance of the system works well only when the natural frequency is close to the excitation frequency. To overcome this limitation of the linear harvester, this work investigates the prospect of using an array of mistuned cantilevers for broadband energy harvesting. The common device configuration of inverted beams with tip masses has been adopted in this study. The considered system is highly nonlinear for tip masses beyond Euler buckling load, and it has two potential wells on either side of the unstable zero position. The non-linear characteristics of the harvester are studied as a preliminary investigation to identify the values of mistuning parameters used in the current work. Numerical simulations have been carried out to understand the influence of mistuning parameters such as length of the beams and tip masses on the frequency band of the harvester power. Comparative studies on the power bandwidth of array of mistuned linear and non-linear harvesters are performed. Observations show that an array of non-linear harvesters enhanced the frequency bandwidth of the power more than that of its linear counterpart. © Springer Nature Singapore Pte Ltd 2020.

Broadband Piezoelectric Energy Harvesting Using an Array of Mistuned Inverted Cantilever Beams

In this study, wake of an elliptic cylinder is analyzed in the presence of a fluid–fluid interface. The interactions between the interface and flow affect each other and hence different wake dynamics and interface topologies are observed. The numerical solver developed for this study has immersed boundary method (IBM) coupled with level-set method (LSM). The proximity of the elliptical cylinder to the interface (H/D), Froude number (Fr), and angle of incidence (AOI) are the parameters considered. Three different Froude number regimes are considered for this study, namely, subcritical (Fr &lt; 1), critical (Fr = 1.0), and supercritical (Fr &gt;1) regime. In this paper, the interface topology, wake dynamics, and force values are compared for the variation of these parameters.

Shear Layer Interactions With Fluid–Fluid Interface in the Wake of an Elliptical Cylinder

This work involves an experimental investigation of the static and fatigue behavior of patch repaired laminates under flexural loading. At first, a static flexural study is conducted for two types of parent laminates comprising 4-plies ([0°]4 &amp; [45°]4) and 8-plies ([0°]8 &amp; [45°]8) of woven carbon fiber. The repair is conducted by two types of patches with stacking sequence [0°]2 and [45°]2. Three different repair configurations involving patch bonded on the compressive side, tensile side, and both the sides of the parent specimens, have been tested. Digital image correlation has been employed to capture the deflection of the specimens. In order to understand the vulnerability of patch repaired laminates to cyclic loading, the load controlled constant amplitude fatigue tests have been conducted on 8-ply repaired laminates. Different failure modes, distinctive to each type of repair configurations have been observed. The results of this work provide more insight to the influence of various parameters viz. number of plies, fiber orientation, patch placement, and so forth, on the flexural behavior of repaired laminates. © 2020 Society of Plastics Engineers

Polymer Composites

Flexural static and fatigue response of patch repaired laminated composites for different patch-parent configurations

The nonstationarity measure of surface Electromyography (sEMG) signals provide an index for muscle fatigue conditions. In this paper, a new framework has been proposed for the analysis of sEMG signal using Instantaneous Spectral Centroid (ISC). The novelty of the proposed work is use of topological signal processing method to quantify the nonstationarity of sEMG signal. For this, the signals are recorded from the biceps brachii muscles of 25 healthy subjects in isometric contraction. The analytical signals corresponding to nonfatigue and fatigue segments are computed using Hilbert Transform. Further, topological features such as center of gravity (CoG), triangular area function (TAF) and ISC are calculated from the geometrical representation of a transformed signal. The result indicates the increase of TAF in fatigue condition and the significant right shift of CoG in x-axis for 80% of subjects. Importantly, the ISC estimate is decreased by 17% upon fatiguing for 84% of subjects. The obtained results show statistical significance with p < 0.05. It is observed that the shape parameters are varied in accordance with the changes observed in global characteristics of sEMG signals during muscle fatigue. The preliminary results show that the topological features are able to quantify the nonstationarity in sEMG signal. Therefore, the proposed method can be used as a fatigue index for diagnosing various neuromuscular disorders.Clinical Relevance - This method can be used to establish metrics of muscle fatigue for the benefit of physicians especially in the field of fitness, sports, pre and post-surgery surveillance and rehabilitation. © 2020 IEEE.

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

A Method to Differentiate Fatiguing Conditions in Surface Electromyography Signals using Instantaneous Spectral Centroid

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.

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.