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

A three-dimensional molecular dynamics simulation of a rarefied gas flow confined between two parallel solid walls has been carried out to study the gas transport behavior in nanoscale pressure-driven flows. To simulate the effects of pressure-driven flows in nanoscale systems; a reservoir is created at the beginning of the channel. A force, in the form of gravity, is applied to every gas molecule occupying a specific region in the reservoir thereby facilitating to establish a streamwise inhomogeneous flow in a finite length nanochannel. Further, the model is tested for its structural stability and steady-state characteristics. The flow characteristics are evaluated at various bins (A, B, C, and D) along the length of the channel. The presence of a pressure drop established along the length of the channel results in a significant variation of flow properties in the channel. The characteristics of the system are further studied using the spatial distribution of flow properties. To investigate the streamwise variation, thermal accommodation coefficients (TACs) at various sections of the channel are calculated. The results indicate that the TACs vary along the length. Further, the effect of pressure drop on TACs is also analysed. The effect of confinement is also studied with velocity autocorrelation function (VACF) and mean squared displacement (MSD). The effect of confinement is evident in the fluid region away from the wall too. © 2021

World University root node

International Journal of Heat and Mass Transfer

Transport behavior of pressure-driven gas flow in a nanochannel and the variation of thermal accommodation coefficient

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.

AIAA Scitech 2021 Forum

Time series behaviour of laminar separation bubble at low reynolds number

Small and micro-scale energy harvesting is an essential and viable option for the powering of portable and maintenance free electronic devices, wireless sensor nodes, and similar applications. In this regard, piezoelectric harvesters have presented promising outcomes. This article provides a sequential, comprehensive, and informative survey of potential well based models and studies related to piezoelectric harvesters (PEH). Piezoelectric materials used for energy harvesting are discussed briefly, following which a non-dimensional generalized model is derived to set the discussion on a common platform. Dynamics of various potential well configurations are presented using the generalized model before discussing specific models and related studies. The survey is classified into symmetric and asymmetric potential well categories. Under the symmetric head, lumped and distributed parameter linear models and tuning methods for improving the broadband response are discussed. Subsequently, studies related to nonlinear mono-stable, bi-stable, and tri-stable potentials showing interwell, multi-periodic and chaotic oscillations with improved broadband response are discussed. The asymmetric section studies the influence of asymmetries on the performance of the mono-stable, bi-stable, and tri-stable configurations. Few other configurations outside the cantilever type PEH were mentioned, realizing the widespread research in this field. Important observations and future challenges for performance improvement are also discussed. © The Author(s) 2020.

Journal of Intelligent Material Systems and Structures

Dynamics of symmetric and asymmetric potential well-based piezoelectric harvesters: A comprehensive review

Magnetoelectric (ME) effect is a product property arising out of the interactions between the piezoelectric and the magnetostrictive phase. Multi-phase ME composites being multifunctional materials find use in myriad of applications. In this work, epoxy free two phase and three phase embedded ring ME composites have been fabricated by the press-fit technique. For a comparative study, three phase conventional epoxy bonded ring shaped composite of same dimensions have also been fabricated. Dynamic ME experiment has been conducted at room and elevated temperatures on all the prepared composites. It is shown that the epoxy free composite by virtue of the absence of epoxy shows a better resonant ME response at all temperatures. The significance of the Electromechanical Resonance (EMR) in the resonance behavior of the composites has also been highlighted. An analytical model in cylindrical coordinate system incorporating the temperature effects on the individual composite constituents and their interface coupling has been developed based on the concentric ring approach to predict the dynamic ME behavior of the epoxy free ring composite at different temperatures. The model has been further used to study the effect of volume fraction of the constituents on the ME response.&nbsp;

Department of Aerospace Engineering

European Journal of Mechanics - A/Solids

Modeling of resonant magnetoelectric response in press-fit embedded ring composite

In this paper, numerical analysis is conducted using a local camber correction approach called “decambering” to predict pre and post-stall aerodynamic characteristics of multiple lifting surfaces operating in formation. A three wings Chevron formation and five and nine wings V-formation are studied. NACA2412 wing section is used and experimental validation is provided with Cessna 172 aircrafts flying in Chevron formation. Effect of wing incidence and shifting of stall angles is looked at along with changes in geometric offsets between the wings in formation. The spanwise distribution of coefficients of lift and induced drag at different angles of attack, including high and post-stall angles of attack is studied for all the wings. The span efficiency factor, which represents the correction in drag due to change in lift as compared to that of an ideal wing of the same aspect ratio but with elliptical lift distribution is calculated. The maximum possible efficiency is then used to estimate the maximum reduction in drag possible for individual wings in different formations. The change in efficiency with number of lifting surfaces in a formation is also estimated. © 2020 Elsevier Masson SAS

European Journal of Mechanics, B/Fluids

Aerodynamic analysis of wings in Chevron and V formation flights

We study the distribution of eigenvalues of the 2D strain rate tensor in a horizontal plane close to the hot plate in Rayleigh B\'{e}nard Convection (RBC). The regions of negative dominant eigenvalues are shown as attracting Lagrangian Coherent structures that govern material folding in the instantaneous limit. Deriving the relation between horizontal divergence, total strain and eigenvalues, we show that these regions are also the regions with negative horizontal divergence. We propose these regions to be thermal plumes, arguing based on earlier visualisations that fluid elements transform from dominant extension to dominant compression in a horizontal plane as they traverse from boundary layers to plumes. We thereby propose two alternate, equivalent, velocity based criteria - namely regions with negative dominant eigenvalues and regions with negative horizontal divergence - to detect thermal plumes in a horizontal plane close to the hot plate in RBC. We then compare the extent of these regions with available theoretical relations and with the regions detected by different temperature based plume detection criteria.

Bulletin of the American Physical Society

<a href="https://ui.adsabs.harvard.edu/abs/2020APS..DFDF16023S/abstract">Strain Rate Signatures of Plumes in Rayleigh Bénard Convection</a>

This manuscript proposes an iterative scheme for geometrically large deflection analysis of corrugated structures using the nonlinear shooting method. The corrugated structure is modeled by discretizing it in several corrugated units. The solution of each unit is obtained assuming it to be consistering of several beam elements. Finally, the deflection of a corrugated structure is calculated assembling the deflection of each of the corrugated units. The formulation has been extended to various boundary conditions (fixed–fixed and fixed–hinged) and loading conditions (point loads and uniformly distributed load). This shows the versatility of the methods in solving various problems. Furthermore, two prototypes of the corrugated structure are fabricated using aluminum and carbon fiber reinforced polymer (CFRP) laminate, and a moment actuation test is performed. The deflections of these prototypes obtained using the proposed iterative scheme are compared with the numerical model and validated with experiments, and results are found to be in good agreement. © 2020, Springer-Verlag GmbH Austria, part of Springer Nature.

Department of Ocean Engineering

Acta Mechanica

Studies on large deflection of geometrically nonlinear corrugated structures

This work proposes a novel computational model for estimating stochastic buffeting loads on an aircraft fin-like structure. Fin buffeting refers to the response of an aircraft fin to the aerodynamic excitation by separated flow from the upstream components like wing, foreplane, fuselage, etc. Depending on flight conditions and aircraft configurations, the buffeting response can be significantly large, leading to structural failure due to fatigue. Through this work, a thorough survey of the sources of fin buffeting has been performed, and each source is identified to have distinct spectral characteristics. Using available experimental data of power spectra for different buffeting sources, temporally consistent velocity fields upstream of the fin have been reconstructed using the Spectral Representation Method (SRM). In this study, we have proposed a novel implementation of the stochastic input velocity, modelled through SRM as a random process with a stipulated correlation, as an inlet boundary condition in a finite volume method-based Navier–Stokes solver. A computational study using the novel boundary condition has been performed on a symmetric NACA airfoil located in the wake of an idealised delta wing to estimate the buffeting loads. The power spectra for the lift coefficient obtained using the proposed method have been compared with Liepmann’s analytical model for buffeting. © 2021, The Editor(s) (if applicable) and The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd.

Department Of Chemical Engineering

Lecture Notes in Mechanical Engineering

Computational Modelling of Stochastic Buffeting of Fin-Like Structures

The study focuses on the design of an energy harvesting nonlinear dynamic vibration absorber (DVA) for possible vibration attenuation and energy generation. As an application vibration mitigation of a base-excited single degree of freedom (SDOF) system is considered. Conventional DVAs are widely used as vibration control devices that undergo large displacements in order to dissipate the energy from the primary structure. For an energy harvester higher the vibration higher is the energy generated. Therefore, if an energy harvester is attached to the DVA, the primary structure DVA interaction can be used for dual purposes. In this study, a duffing-type nonlinear DVA system with a piezo patch is proposed as energy harvesting nonlinear DVA to mitigate the vibration and to obtain electricity. The modeling of the total system is carried out considering the electromechanical interactions between the harvester-DVA and structural system. The formulation is done in time domain and a simulation study is carried out for harmonic base excitation to understand the effect of nonlinearity in voltage generation. A frequency sweep study is carried out to locate the frequency band in which the system responses are consistently higher. Further, the important design parameters are identified. A parametric study to obtain optimal design parameters is also reported. The advantages of nonlinear energy harvesting DVA over the linear ones are many. A nonlinear harvester provides power over a broad range of frequencies and, therefore would be able to dissipate energy from the primary structure over wideband excitations. Finally, the performance of the designed nonlinear DVA system with harvester is examined for vibration mitigation of SDOF primary system. © 2021, The Editor(s) (if applicable) and The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd.

Department of Metallurgical and Materials Engineering

Design of a Nonlinear Energy Harvesting Dynamic Vibration Absorber

In this manuscript, a concept flow control valve is designed, exploiting the bistable characteristics of a special class of hybrid laminates made of glass epoxy and carbon epoxy prepregs. The principal structural element of the device is a hybrid bistable laminate, having a multi-section layup laid in a symmetric configuration. The thermal curing process responsible for the inherent bistability is simulated in ABAQUS(Formula Presented) and the equilibrium shapes hence obtained using the FEA scheme is validated against an existing semi-analytical technique based on the Rayleigh-Ritz minimization of potential functional. These multi-stable elements are then studied for their potential in controlling a flowing stream. Toward that, the snapping response of these laminates in a flow stream is analyzed using a combination of XFOIL and ABAQUS(Formula Presented). The pressure distribution on the laminate is estimated using XFOIL, which is an interactive program for analysis of subsonic isolated airfoils in viscous/inviscid low Reynolds number flow. The pressure distribution hence obtained is used to evaluate the load-displacement characteristics of the laminate using post-buckling regime analysis capabilities of ABAQUS(Formula Presented). Using these analysis tools, the design space is explored and the possibility of using the proposed bistable design elements for flow regulation is established. © 2021, The Editor(s) (if applicable) and The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd.