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 focuses on characterising numerically the attractor volume in the state space of dynamical systems excited by additive white noise. A definition for stochastic attractors is introduced in terms of probability measure and numerical methodologies are presented to characterise them. The study is limited to investigating the effects of additive noise on fixed point and limit cycle attractors of the corresponding noise free system. The effect of noise intensity on the definition and validity of the proposed methodology is also discussed. © 2021 Elsevier B.V.

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Communications in Nonlinear Science and Numerical Simulation

Characterising stochastic fixed points and limit cycles for dynamical systems with additive noise

The present work investigates impact behaviour of additively manufactured AlSi10Mg alloy and ballistic limit of projectiles using FEM simulations. Tensile tests, dynamic tests and elevated temperature tensile tests simulations were performed on smooth and notched specimens to calculate Johnson–Cook material and damage model parameters, which are subsequenty given as inputs for impact simulation. The relationship between residual velocity versus initial projectile velocity is expressed using Jonas–Lambert’s model for calculating ballistic limit. The effects of projectile velocity, its shape, thickness and material property of AlSi10Mg on ballistic limit were thoroughly investigated. C3D8R elements are used to discretize the target plate and mesh transition zone was created in impact region. Johnson–Cook elasto-viscoplastic model was employed to study the ballistic resistance behaviour of AlSi10Mg alloy. Fracture energy value of 43.6 kN/m for AlSi10Mg alloy is used to initiate the damage in target plate. All FE simulations were performed by using ABAQUS/Explicit. It is observed that ballistic impact on 3D printed AlSi10Mg has shown plugging and petaling failure when hemispherical projectile was used while plugging failure in the case of blunt projectiles. The ballistic limit of hemispherical projectiles is found to be higher (311 m/s, 400 m/s) compared to the blunt projectiles (216.5 m/s, 245 m/s). The impact velocity to completely penerate 6 mm thick target plate is relatively higher as compared to 3 mm thick target plate for both projectiles. © 2021, Society for Experimental Mechanics, Inc.

Department Of Physics

Department of Engineering Design

Journal of Dynamic Behavior of Materials

FEM Simulation of High Speed Impact Behaviour of Additively Manufactured AlSi10Mg Alloy

We study the effect of shear by the inherent large-scale flow in the bulk on the boundary layers on the hot plate in Rayleigh–Bénard convection for a range of Prandtl numbers 4.69 ≤ Pr ≤ 5.88 and Rayleigh numbers 105 ≤ Ra ≤ 109. We observe that, at each Ra, at an instant, the distribution of horizontal velocities within the boundary layer in a horizontal plane is either of a unimodal nature or of a bimodal nature. Unimodal distributions occur either at low Ra or at high Ra while the bimodal distributions occur more at intermediate Ra. The peak of the unimodal distribution at low Ra occurs at values at around Vbl, the natural convection boundary layer velocity while the peak of the unimodal PDFs at high Ra occur at values greater than or equal to Vsh, the large-scale flow velocity. In the case of bimodal distributions, the first peak occurs in between Vbl and Vsh while the second peak occurs after Vsh. We show that the second peak of the bimodal distribution and the unimodal peak which occur at ≥Vsh scales as Vsh scales with Ra. The first peak of bimodal distribution and the single peak occurring at around Vbl scales with Ra as the natural convection boundary layer velocity forced by shear. © 2021, Springer Nature Singapore Pte Ltd.

Lecture Notes in Mechanical Engineering

Effect of Large-Scale Flow on the Boundary Layer Velocity Field in Turbulent Convection

We report a novel approach for the fabrication of porous polymer films and their self-folding behavior in response to water. In this approach, the poly(vinyl alcohol) (PVA) films of tunable porosity are prepared by direct casting of aqueous PVA solution into a nonsolvent, isopropyl alcohol (IPA). The method developed is simple, efficient and low-cost. The results presented provide a modular route to tune the distribution of pores across the film thickness by varying the volume of nonsolvent and the polymer solution. We show that asymmetric porous polymer films (which consist of pores across a certain thickness of the film in the plane perpendicular to its surface) as well as symmetric porous polymer films (which have pores across the entire film) can be fabricated by this versatile method. The percentage of pores in the polymer film calculated as , wheretpis the thickness of the film across which the pores exist andttotalis the total thickness of the film, can be tuned over a wide range. The emanated porous PVA films are found to show self-folding behaviour in response to water. Our results indicate that the pore architecture in the films significantly enhances the actuation speed. The self-folding originating due to the diffusion of water molecules across the film is observed to occur in a controlled and predictable manner for the films with 60% pores and above. A detailed study of the folding characteristics and actuation speed in relation to folding time is substantiated. © The Royal Society of Chemistry 2021.

Department Of Chemical Engineering

Soft Matter

Engineering polymer film porosity for solvent triggered actuation

Studies on entomopter’s performance under the influence of gust have received impetus in the past decade. There exists a dire need to ascertain the threshold of the frontal gusty conditions which would destabilize these anthropogenic flyers. This would help to devise methods to mitigate the detrimental effects of gust. In light of this aspect, the present study aims at analyzing the onsets of instability in a flapping wing system subjected to temporal gust by employing recurrence period density entropy (RPDE) and detrended fluctuation analysis (DFA). Simulation of the flapping wing along inclined stroke is carried out for a Reynolds number of 150. This Reynolds number lies in the typical operating regime of fruit flies and entomopters like the Pico aerial vehicle. Numerical simulations are carried out to solve the laminar, unsteady, and incompressible Navier–Stokes equations. The dynamic meshing technique is employed to model flapping kinematics. Nine gusts with a combination of frequency and velocity ratios of 0.1, 0.5, and 1.0 are considered. Instantaneous horizontal and vertical forces are estimated. Time series of these forces are analyzed using RPDE and DFA paradigms. These analyses indicate that gust frequency of an order of magnitude higher than flapping frequency and gust amplitude of the order of magnitude as the wing’s root mean square velocity induces a possible onset of instability. © IMechE 2021.

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

Entropy and fractal perspectives of a flapping wing subjected to gust

This paper approaches the problem of analyzing the bifurcation phenomena in three-dimensional discontinuous maps, using a piecewise linear approximation in the neighborhood of a border. The existence conditions of periodic orbits are analytically calculated and bifurcations of different periodic orbits are illustrated through numerical simulations. We have illustrated the peculiar features of discontinuous bifurcations involving a stable fixed point, a period-2 cycle, a saddle fixed point, etc. The occurrence of multiple attractor bifurcation and hyperchaos are also demonstrated. © 2021 Author(s).

Chaos

Local and global bifurcations in 3D piecewise smooth discontinuous maps

Aneurysms are bulges in arteries which reflect unhealthy state of conduit in which blood is flowing. In the aorta, they are typically found in the abdominal region as well as thoracic region. Understanding the rupture risk of these vessels is critical to preventing failure and fatalities. In the current clinical practice, treatment modalities are initiated, when the out-pouching exceeds maximum diameter (Dmax). However this approach is very crude as it does not account for the fluid mechanical forces and the attendant stresses. Since it is medically and ethically not possible to follow the patients to study the rupture risk potential, fluid structure interaction (FSI) modelling would be an apt tool to develop adequate understanding on various hemodynamic parameters. On the other hand, performing patient-specific studies would demand adequate lead time and they are computationally expensive as well. In the present study, the shape of the aneurysm and its interaction with the flowing fluid are accounted through the shape indices to study the FSI effects on the hemodynamic parameters. Numerical simulation of Newtonian flow through five axi-symmetric geometries with different shape indices coupled with a linear elastic vessel wall model is considered. From these simulations, it was observed that (Dmax) to height ratio (DHr) is the most significant shape index which influences the variation of all hemodynamic parameters, which makes it a potential candidate for predicting rupture risk. Wall acceleration due to pulsatile flow was found to cause the onset of re-circulation zones at the centre of the aneurysm during early systole and the temporal deceleration resulted in the generation of near wall eddying structures during late diastole. Investigation of turbulence carried out with k-ω Shear Stress transport turbulence model, predicts a turbulence intensity of greater than 1.5% in the diseased segment as well as the distal end of the aneurysm. © 2020 John Wiley &amp; Sons, Ltd.

International Journal for Numerical Methods in Biomedical Engineering

Fluid structure interaction study in model abdominal aortic aneurysms: Influence of shape and wall motion

Development of clinically amenable bio-implants with silk-fibroin (SF) necessitates characterization of cellular-traction generated between cells and the substrate. However, studies on the biomechanical response of cells on SF substrates are limited. In this study, we prepared SF hydrogels of varying compliance (SF30 and SF50) and varying surface-ligands (derivatized with poly-L-lysine (PLL) or Arg-Gly-Asp (RGD) peptide). Subsequently, NIH-3T3 fibroblast cells were grown on these substrates, and the morphological changes was examined. It was observed that the increase in SF stiffness from 0.7 kPa to 3.1 kPa decreased nucleus-to-cytoplasm area-ratio and increased asymmetricity along the major-axis of cells. Moreover, while functionalization of SF with RGD induced increase in cell-area and circularity, functionalization with PLL did not cause any change. Next, using traction-force-microscopy (TFM), we quantified 2D cell-traction for NIH-3T3 cells cultured on SF hydrogels. Cells plated on SF50 hydrogel exhibited significantly high traction stress as compared to SF30; change of functionalization did not show significant change. Also, protrusion traction stress was found to be greater than nuclear traction stress. Put together, our results suggest that surface-stiffness of SF-hydrogel, rather than nature of surface-ligand, regulates both cellular morphology and cellular traction stresses. © 2021 Taylor & Francis Group, LLC.

Department Of Civil Engineering

Soft Materials

Morphology and cellular-traction of fibroblasts on 2D silk-fibroin hydrogel substrates

Numerical studies on pumps emphasize mainly on modelling the interactions between the impeller and the volute to obtain an accurate understanding of the physics involved. However, the importance of modelling leakage paths, which is known to have a significant influence on the flow structure in the pump, necessitates an in-depth analysis. This activity is undertaken in this paper by investigating a specific case of a centrifugal pump. Numerical studies have been conducted on the pump modelled with and without leakages for the design condition. The sliding mesh method is used to obtain single phase pressure pulsations data at some important locations in the volute and the leakage path, and transient Multiple Reference Frame (MRF) modelling is utilized to conduct the cavitation analysis. It is observed that for the case under study, the pressure pulsations pattern and the cavitation behaviour varies significantly due to the inclusion of leakage paths in the analysis. © Published under licence by IOP Publishing Ltd.

Fulltext

Journal of Physics: Conference Series

Numerical investigation of the effect of leakage flow on cavitation in centrifugal pump

In this paper, we discuss a CFD model to predict vapor condensation on walls in the presence of non-condensable gases, with a specific focus on large scale applications, such as accidental flows in a nuclear reactor containment. It is conclusive from the previous works that the heat and mass transport resistance due to the diffusion boundary layer in the gas phase overwhelms the liquid film thermal resistance. Therefore, the two-phase wall condensation phenomenon is treated with a single-phase (gas) model. For the numerical implementation, the containmentFOAM CFD package, based on OpenFOAM is used. For the first time, the model implementation is discussed for arbitrary multi-component mixtures, and performances of two commonly used approaches – Volumetric source terms and Face-fluxes – are compared; the Face-flux model proved to be more accurate, computationally cheaper, and less grid-dependent. Concluding, the Face-flux approach was validated against the experimental database for forced convection flows, obtained at the SETCOM facility in Forschungzentrum Jülich, Germany. The results demonstrate the model's predictiveness and robustness for a wide range of cases in the forced convection regime. © 2021 Elsevier Ltd