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

Manual segmentation of brain tumor is often time consuming and the performance of the segmentation varies based on the operators experience. This leads to the requisition of a fully automatic method for brain tumor segmentation. In this paper, we propose the usage of the 100 layer Tiramisu architecture for the segmentation of brain tumor from multi modal MR images, which is evolved by integrating a densely connected fully convolutional neural network (FCNN), followed by post-processing using a Dense Conditional Random Field (DCRF). The network consists of blocks of densely connected layers, transition down layers in down-sampling path and transition up layers in up-sampling path. The method was tested on dataset provided by Multi modal Brain Tumor Segmentation Challenge (BraTS) 2017. The training data is composed of 210 high-grade brain tumor and 74 low-grade brain tumor cases. The proposed network achieves a mean whole tumor, tumor core &amp; active tumor dice score of 0.87, 0.68 &amp; 0.65. Respectively on the BraTS ’17 validation set and 0.83, 0.65 &amp; 0.65 on the Brats ’17 test set.

Department of Engineering Design

World University root node

Department of Applied Mechanics

Department of Mechanical Engineering

International MICCAI Brainlesion Workshop

Brain Tumor Segmentation Using Dense Fully Convolutional Neural Network

Numerous studies have been carried out in the past few decades to investigate the radial oscillations of encapsulated microbubbles (MBs). Nonspherical oscillations also have gained attention, being unavoidable in actual applications of these bubbles. The present paper is intended to describe the nature of resonance trends of such spherical and nonspherical modes of a thick encapsulated MB filled with air and suspended in water. The shell material is assumed to be linear viscoelastic and quasi-incompressible. The considered isotropic and spherically isotropic material parametric range is limited to thick polymer shelled MBs. For the case of an isotropic material, shell viscosity has a major influence on the fundamental modes with meridional wave number n = 0, 4, especially for thicker bubbles, unlike for the case of the spherically isotropic material case considered, where the viscosity has very little influence. For most of the parametric range, n = 2, 3 modes are underdamped and their frequency is found to be lower than the n = 0, 4 modes, for both material cases. An interesting case is found for a spherically isotropic quasi-incompressible material case, where the first few nonspherical mode resonances are very close to radial mode resonance frequency. © 2016 Acoustical Society of America.

Journal of the Acoustical Society of America

Modeling and parametric investigation of thick encapsulated microbubble's nonspherical oscillations

Tensegrities are cable-strut assemblies which find their stiffness and self-equilibrium states from the integrity between tension and compression. Low stiffness and coinciding natural frequencies are known issues. Their stiffness can be regulated and improved by changing the level of pre-stress. In vibration health monitoring, the first natural frequency is used as an indicator of better stiffness, but coinciding natural frequencies will be an obstacle in measuring and analysing the correct resonance. In this paper, the above two issues have been considered for modular tensegrity structures. The finite element model used considers not only the axial vibration of the components, but also the transversal vibration where non-linear Euler–Bernoulli beam elements are used for simulations. A genetic algorithm is used to solve the optimization problem, with a multi-objective criterion combination. The optimum self-stress of the tensegrity structures can be chosen such that their lowest natural frequency is high, and separated from others. Two approaches are used to find the optimal self-stress vector: scaling from a base module or considering all modules at once. Both approaches give the same optimum solutions.

Fulltext

Optimization of modular tensegrity structures for high stiffness and frequency separation requirements

Motivated by the numerous applications of spherical shell models in micro and nano scales (such as microbubbles, bacterial cells, and viral capsids), we have considered the axisymmetric free vibrations of a spherically isotropic fluid-filled thick microspherical shell suspended in another unbounded fluid. A partial-slip condition is considered at the solid-fluid interface(s). Three-dimensional linear elasticity equations for the spherically isotropic shell dynamics and linearized Navier-Stokes equations for the two compressible viscous fluids are used in the analysis. The eigenvalue problem is discretized and solved to find the resonances and quality factors. A perfectly matched layer technique is used to separate the solid driven spectrum from the boundary reflecting spectrum. An example of air filled polymer shell suspended in water is presented. The added mass effect and partial-slip condition from water (air) on the frequencies and quality factors are found to be significant (negligible). Spherical isotropy is found to have major influence on the low frequency and large meridional wave number region of the resonance spectrum. High quality eigenmodes are observed due to very small viscous penetration depth compared to the shell size. In the thin-shell limit, the eigenvalue problem can have only two modes of vibration for any meridional wave number greater than or equal to two. This explains the reason for the second resonance frequency found for the quadrupole shape oscillations of various bacterium cells in the earlier work. The partial-slip condition is found to have very small influence on the first few modes of vibration. Surface tension is found to have significant influence only on the lowest frequency trend of the eigenspectrum. Perfectly matched layer technique used in the present analysis is found to be very effective in handling the boundary truncated problems. © 2015 AIP Publishing LLC.

Journal of Applied Physics

Resonances of a submerged fluid-filled spherically isotropic microsphere with partial-slip interface condition

The problem of finite inflation of a hyperelastic toroidal membrane under uniform internal pressure is considered in this paper. The work consists of the following two aspects of the inflation problem. Firstly, a formulation for solving the inflation problem efficiently by directly integrating the differential equations of equilibrium without <a href="https://www.sciencedirect.com/topics/engineering/discretization">discretization</a> is proposed. The results obtained are compared with those obtained using a <a href="https://www.sciencedirect.com/topics/engineering/discretization">discretization</a> method proposed earlier. Secondly, the effects of the geometric and material parameters of the membrane and the internal pressure on the inflation and its stability are studied. The roles of the curvature (specifically, the <a href="https://www.sciencedirect.com/topics/engineering/eigenvector">eigenvalues</a> of the shape operator) of the toroidal geometry and the <a href="https://www.sciencedirect.com/topics/engineering/artificial-membrane">membrane material</a> parameter on the distortion of the cross-section and occurrence of wrinkling instability are clearly brought out. Based on the Cauchy stress resultants, the limits on the inflation to avoid wrinkling are determined. It is observed that the limit point pressure of the membrane is inversely proportional to the geometric parameter of the torus. The <a href="https://www.sciencedirect.com/topics/engineering/proportionality-constant">proportionality constant</a> involved is found to vary linearly with the material parameter of the membrane, and involves two universal constants for the toroidal geometry.

Department of Electrical Engineering

Effect of curvature and anisotropy on the finite inflation of a hyperelastic toroidal membrane

The present paper is devoted to the study of finite inflation of a hyperelastic toroidal membrane on a cylindrical rim under uniform internal pressure. Both compliant and rigid frictionless rims have been considered. The compliant cylindrical rim is modeled as a linear distributed stiffness. The initial cross-section of the torus is assumed to be circular, and the membrane material is assumed to be a homogeneous and isotropic Mooney–Rivlin solid. The problem is formulated as a two point boundary value problem and solved using a shooting method by employing the Nelder–Meads search technique. The optimization function is constructed on a two (three) dimensional search space for the compliant cylinder (rigid cylinder). The effect of the inflation pressure, material properties and elastic properties of the rim on the state of stretch and stress, and on the geometry of the inflated torus have been studied, and some interesting results have been obtained. The stability of the inflated configurations in terms of occurrence of the impending wrinkling state in the membrane has also been studied.

Finite inflation of a hyperelastic toroidal membrane over a cylindrical rim

A finite inflation analysis of two circumferentially bonded hyperelastic circular flat membranes with uniform internal pressure is presented. The governing equations of equilibrium are obtained using the variational formulation. By making a suitable change in the field variables, the problem is formulated as a set of two coupled nonlinear two point boundary value problem (TPBVP) and is solved using the shooting method. Membranes of identical and dissimilar material properties are considered in the analysis. For dissimilar membranes, asymmetric inflation, and remarkably, deflation (after an initial phase of inflation) in one of the membranes in certain cases, has been observed. The effect of inflation pressure and material properties on the geometry of inflated configuration, state of stress, and the impending wrinkling condition of the membranes are also studied. This work has relevance to tunable inflated reflectors and lenses among other applications. Copyright © 2014 by ASME.

Journal of Applied Mechanics, Transactions ASME

Finite inflation analysis of two circumferentially bonded hyperelastic circular flat membranes

In this work, we have studied the finite inflation of a hyperelastic toroidal membrane with an initially circular cross-section under internal pressure. The <a href="https://www.sciencedirect.com/topics/engineering/artificial-membrane">membrane material</a> is assumed to be a Mooney–Rivlin solid. The inflation problem is formulated as a variational problem for the total potential energy comprising the membrane strain energy and internal energy of the gas. The problem is then discretized and solved up to a high degree of accuracy through a sequence of approximations based on the Ritz expansion of the field variables combined with a potential <a href="https://www.sciencedirect.com/topics/physics-and-astronomy/flux-density">energy density</a> perturbation and Newton–Raphson method. The effects of the inflation pressure and material properties on the state of stretch and geometry of the inflated torus have been studied, and some interesting results have been obtained. The stability of the inflated configurations in terms of impending wrinkling of the membrane has been investigated on the principal stretch parameter plane for both isotropic and <a href="https://www.sciencedirect.com/topics/engineering/anisotropic">anisotropic</a> (transversely isotropic) material cases. Certain shape factors quantifying the geometry of the membrane have been defined and calculated which characterize the cross-sectional shape and size of the torus during inflation.

Finite inflation analysis of a hyperelastic toroidal membrane of initially circular cross-section

The occurrence of the limit-point instability is an intriguing phenomenon observed during stretching of hyperelastic membranes. In toy rubber balloons, this phenomenon may be experienced in the sudden reduction in the level of difficulty of blowing the balloon accompanied by its rapid inflation. The present paper brings out a link between the geometry and strain-hardening parameter of the membrane, and the occurrence of the limit-point instability. Inflation of membranes with different geometries and boundary conditions is considered, and the corresponding limit-point pressures are obtained for different strain-hardening parameter values. Interestingly, it is observed that the limit-point pressure for the different geometries is inversely proportional to a geometric parameter of the uninflated membrane. This dependence is shown analytically, which can be extended to a general membrane geometry. More surprisingly, the proportionality constant has a power-law dependence on the nondimensional material strain-hardening parameter. The constants involved in the power-law relation are universal constants for a particular membrane geometry. © 2013 American Physical Society.

Physical Review E - Statistical, Nonlinear, and Soft Matter Physics

Geometrical feature of the scaling behavior of the limit-point pressure of inflated hyperelastic membranes

We have studied the dynamics of in-plane displacement of a class of two-dimensional homogeneous and isotropic elastic membranes having constant curvature. The equation of motion of a general in-plane displacement field has been derived in covariant form using the variational formulation. The contribution of curvature on the dynamics of the field variable is clearly observed in the field equation. We observe that for certain membranes with constant curvature, the curvature term introduces a quadratic potential with the sign of the coupling constant being decided by the Ricci curvature of the membrane. Using the Helmholtz theorem, we reduce the field equation to two decoupled scalar equations which exhibit an interesting structure. We consider some examples of membranes with positive, and negative curvatures and comment on the nature of solutions expected. We analyze the deformation of the membranes in terms of the dilatation, shear and vorticity of the displacement field. © 2012 Elsevier Masson SAS. All rights reserved.

European Journal of Mechanics, A/Solids

In-plane dynamics of membranes having constant curvature

In this work, the dynamics of in-plane surface deformation modes of an inflated toroidal membrane has been studied. We have considered both isotropic and anisotropic but homogeneous material properties. The covariant form of the equation of motion assuming a general in-plane small amplitude displacement field has been derived from the variational formulation which clearly shows the effect of curvature on the dynamics. The curvature term in the equation of motion may be interpreted as an effective quadratic potential in the Lagrangian with a coupling proportional to the Ricci curvature scalar of the membrane. The variational problem is discretized, and is subsequently analyzed to obtain the eigenfrequencies and modes of vibration. The effect of geometric and material properties on the modal dynamics has been studied. The effect of anisotropy on the modal dynamics of the torus has also been studied. Certain invariant deformation measures have been defined which are found to characterize the modes in terms of presence or absence of nodal curves/points. © 2012 Elsevier Ltd. All rights reserved.

International Journal of Engineering Science

In-plane surface modes of an elastic toroidal membrane

The purpose of this paper is to understand non-linear processes occurring during the coupling of twin jet plumes using higher order spectral methods. To the best of our knowledge, most previous studies have used linear spectral analysis to document coupling and have focused on identifying configurations and conditions that produce coupling, without much knowledge of the 'why' and 'how.' Our work demonstrates the inadequacies of linear spectral analysis when closely spaced multiple screech sources exist in complex configurations. We use the cross-bicoherence for identifying the non-linear interactions. In order to evaluate the efficacy of the tool in identifying non-linear coupling we chose rectangular nozzles with spanwise oblique exit geometries. Jets from such nozzles are known to be rich in closely spaced complex screech source structures. In addition, they can produce multiple screech tones with the simultaneous presence of multiple feedback loops. The twin jets could be placed in two configurations, one that produced a 'V' shape in the inter-nozzle region and another that produced an 'arrow head' shape. The following significant findings emerged from our study: (i) some configurations that were apparently uncoupled by linear spectral analysis metrics were found to be non-linearly coupled. (ii) two types of non-linear coupling were observed – one dominated by the fundamental and its interaction with higher modes, and another that displayed clusters of interactions between a frequency component and its sidebands. (iii) a new interaction density metric was developed to quantify non-linear coupling. (iv) a second metric known as the average interaction density was shown to increase sharply during coupling mode transition. Our results indicate that nonlinear spectral analysis has the potential to uncover twin jet coupling mysteries that have eluded researchers for many years.