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

We report an experimental study on the near injector structure of spray exiting a Gas Centered Swirl Co-axial (GCSC) injector, where the effect of ambient pressure has been investigated. Cold flow tests were conducted with a conventional GCSC injector in an optically accessible high pressure chamber. Water and gaseous Nitrogen were the fluids used. The parameters varied during the study were the gas Reynolds number (0 − 46908) and ambient pressure (1 − 9bar). The liquid Reynolds number was kept constant at 2275. Spray characteristics have been analyzed at different operating conditions with the aid of high speed visualization. Qualitative analysis shows that ambient pressure exerts a strong influence on the morphology of the annular sheet. Mean spray cone angle increases and intact sheet length decreases with increase in ambient pressure at a particular gas Reynolds number. A higher flapping of the annular sheet is observed at elevated ambient pressures. The non-intrusive method of Feature Correlation Velocimetry (FCV) has been used for quantitatively characterizing the liquid sheet at a particular spatial location. This method relies on the advection of naturally formed features/corrugations on the surface of the annular sheet for retrieving the sheet velocity. The axial and swirl velocities remain relatively unchanged at high ambient pressures. In conclusion, the sheet thickness based on axial velocity values obtained from FCV analysis remains unaltered at elevated ambient conditions. © 2018 Solar Turbines Incorporated.

World University root node

ICLASS 2018 - 14th International Conference on Liquid Atomization and Spray Systems

Effect of back pressure on the near injector spray structure of a gas centered swirl co-axial injector

Department Of Chemical Engineering

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Fast transport of water in carbon nanotubes: a review of current accomplishments and challenges

Recently, researchers have shown an increased interest in ultrasound imaging methods alternate to conventional focused beamforming (CFB). One such approach is based on the synthetic aperture (SA) scheme; more popular are the ones based on synthetic transmit aperture (STA) schemes with a single-element transmit or multielement STA (MSTA). However, one of the main challenges in translating such methods to low-cost ultrasound systems is the tradeoffs among image quality, frame rate, and complexity of the system. These schemes use all the transducer elements during receive, which dictates a corresponding number of parallel receive channels, thus increasing the complexity of the system. A considerable amount of literature has been published on compressed sensing (CS) for SA imaging. Such studies are aimed at reducing the number of transmissions in SA but still recover images of acceptable quality at high frame rate and fail to address the complexity due to full-aperture receive. In this work, we adopt a CS framework to MSTA, with a motivation to reduce the number of receive elements and data. The CS recovery performance was assessed for the simulation data, tissue-mimicking phantom data, and an example in vivo biceps data. It was found that in spite of using 50% receive elements and overall using only 12.5% of the data, the images recovered using CS were comparable to those of reference full-aperture case in terms of estimated lateral resolution, contrast-to-noise ratio, and structural similarity indices. Thus, the proposed CS framework provides some fresh insights into translating the MSTA imaging method to affordable ultrasound scanners. © 1986-2012 IEEE.

IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control

Compressed Sensing Approach for Reducing the Number of Receive Elements in Synthetic Transmit Aperture Imaging

In this study we report polarization resolved intensity measurements for flyash and water aerosol, respectively, in an industrial stack like environment, for the purpose of developing a methodology for in-situ PM measurements in wet stacks. Flyash and water aerosols up to 4 (Formula presented.) mass concentration were seeded in a lab scale simulated industrial stack operated at velocities up to 15 m/s. Scattering of non-polarized (NP) and horizontally polarized light by these two aerosols were observed at (Formula presented.) back-scatter and (Formula presented.) forward-scatter angles for horizontal and vertical polarization states at the detector. Complete depolarization of horizontally polarized incident light was observed for ash at (Formula presented.) while negligible effects were observed for water. Thus the cross-polarization measurement in this angle, where the scattering energy from the mixed flow could directly represent the flyash concentration, can be the best possible measurement configuration for minimizing the impact of interference from water carryover in industrial emission stacks. Further, the change in depolarization ratio of the mixture (δm) when compared to flyash (δa) alone is proportional to the scattering intensity ratios of ash and water, respectively, and could be used to estimate the individual mass concentrations. With this development, we could propose the design of an instrument that can in-situ correct for errors from counting water droplet, and also enable real time estimation of individual mass concentrations. Copyright © 2020 American Association for Aerosol Research. © 2020, © 2020 American Association for Aerosol Research.

Aerosol Science and Technology

A polarization-resolved light scattering method for eliminating the interference of water aerosol in industrial stack PM measurement

Flexible structures are continuum modeled as infinite degrees of freedom. Most of the time finite element models are made with large number of degrees-of-freedom to analyse flexible structures. Continuous monitoring, analysis and control of dynamics of flexible structures need simulation of large degrees of freedom in real time. This is computationally expensive and realtime control fails. This study focuses on the development of a reduced order framework for dynamics of flexible structures and use the reduced order model for controlling the structure. Essentially, in the proposed framework, full order state space obtained from finite element modeling of the flexible structure has been reduced to lower subspace using a reduced order algorithm keeping the dynamical characteristic intact. The transformation matrix for reduction has been calculated using system equivalent reduction expansion process (SEREP). Traditionally, full order dynamical system is being used to find the gain matrix to suppress the uncontrolled dynamics associated with the dynamical system. Here in this methodology, the reduced dimension of state space of the system is used for estimating the gain matrix using optimal linear quadratic regulator (LQR). The gain obtained through the reduced system is subsequently used as a feedback to the attached actuators which produce the required force to control the system. A numerical example of a flexible cantilever beam has been shown to investigate the effectiveness of the algorithm. © 2020, IFAC (International Federation of Automatic Control) Hosting by Elsevier Ltd. All rights reserved.

IFAC-PapersOnLine

SEREP Integrated Control of Flexible Structures

Improvement in performance of Organic Rankine Cycle (ORC) systems, particularly in the context of dual heat sources such as IC engines, leads to better return on investments. However, the choice of architecture to achieve the best performance is not evident from available literature. When two separate heat sources are present concurrently at different temperature levels with heat contents such as in IC engines, single stage pre-heated ORC and dual loop ORC are the two commonly deployed ORC architectures. In this study, two stage architectures: Series two stage ORC (STORC) and Parallel two stage ORC (PTORC) are analysed and their performance is compared against a single stage pre-heated ORC at sub-critical conditions in the utilization of high temperature (primary) exhaust gases (573–773 K) and low temperature (secondary) jacket water (353–393 K) representing IC engine waste heat conditions. Results show that STORC and PTORC are able to achieve the maximum net power output for an intermediate utilization of secondary heat source. The power output gains from two stage layouts improves significantly with a reduction in heat source temperature difference and for lower ratios of the heat available between the primary to secondary heat source. For a 2.9 MW natural gas IC engine operating at its design point, STORC delivers 8.5% more power output whereas PTORC delivers 0.3% less power output than pre-heated ORC. Compared to a dual–loop ORC, STORC presents a less complex and improved cycle architecture with a 13.1% increased power output and a 27.9% reduced heat exchanger requirements. © 2020

Energy Conversion and Management: X

Performance investigation of two stage Organic Rankine Cycle (ORC) architectures using induction turbine layouts in dual source waste heat recovery

Multistable laminates have been widely analyzed in the recent past for their potential in morphing applications. However, all the analytical models developed up until now have taken into account only the free-free boundary condition. In this work two objectives are met: (a) an analytical model is developed, which extends the previously available models in literature to account for the cantilever boundary condition for a special class of hybrid bistable symmetric laminates (HBSL); (b) the previously proposed HBSL is modified by replacing the aluminum layers with bi-direction glass-epoxy prepregs in the layup. It is observed that the modified layup has a curvature similar to the previously proposed HBSL while maintaining bistability. The analytical model developed here successfully captures the equilibrium shapes and the snap-through behavior for this special class of laminates which is validated against the results obtained using ABAQUS® and experiments. The developed model is then subsequently used to study the design space and bistability characteristics of the HBSL and the proposed modified layup (m-HBSL) in the cantilever boundary condition. © 2020 Elsevier Ltd

Composite Structures

Modeling and design of a class of hybrid bistable symmetric laminates with cantilever boundary configuration

This work presents an experimental comparative study of the frequency-dependent response of the epoxy-free magnetoelectric (ME) composite against epoxy-bonded two-phase and three-phase ME composites of various configurations at varying operating temperatures. Conventionally, ME composites are prepared by bonding the piezoelectric and magnetostrictive material phases by means of an epoxy material. Therefore, the response of the composite becomes a function of the properties of the epoxy used. Since the epoxy properties degrade significantly with increase in temperature, the ME response of the ME composite becomes poor at elevated temperatures. In this work, two-phase and three-phase epoxy-free ME composite has been fabricated by employing a press-fit embedded structure and compared with similar epoxy-bonded embedded structure as well as conventional layered ME composite. Frequency-dependent experiments have been conducted at various temperatures and the responses from the two types of composites have been compared. Magnetostriction measurements at different temperatures have been conducted on individual magnetostrictive constituents to observe the effect of piezomagnetic coefficient on the ME response. It is observed that the ME responses of the epoxy-free composites at room temperature are nearly equivalent to their epoxy-bonded counterparts, whereas at higher temperatures the epoxy-free ring composite offers a much better response. The effect of demagnetizing field on the response of composites of various configurations is studied at different temperatures and a similar result is obtained. The resonant frequency of the ME composite is seen to decrease with an increase in temperature owing to the decrease in the effective Young's modulus of the composite. © 2020 IOP Publishing Ltd.

Smart Materials and Structures

Temperature-dependent dynamic response in epoxy-free and epoxy-bonded ME composite: A comparative study

Brainstem texture analysis can provide valuable information in the diagnosis of Early Mild Cognitive Impairment (EMCI) condition. In this work, 3D brainstem structure is segmented and analysed for texture alterations using multifractal features to differentiate EMCI from other Alzheimer's disease stages. The images obtained from public domain database are preprocessed for spatial registration, skull stripping and contrast enhancement. White matter volume is segmented from the preprocessed images using fuzzy ‘C’ means clustering algorithm. Midsagittal white matter tissue is used as the initial seed to segment the brainstem volume using sparse field level set method. Multifractal detrended moving average algorithm is used to compute the fluctuation function, generalized Hurst exponent and mass exponent to study the multifractal characteristics of brainstem structure. Features extracted from the multifractal spectrum are analysed to differentiate the images pertaining to EMCI subject group. Results indicate that the proposed technique is able to segment the brainstem structure from all the considered images. The fluctuation function is observed to have linear relationship with scale. The generalized Hurst exponent decreases with order and mass exponent follows a non-linear trend demonstrating the multifractal nature of brainstem. Singularity spectral features namely strength of multifractality, Holder exponent at f(2.8), tangent slope and maximum Holder exponent are found to be most significant in differentiating EMCI from subject groups. As this complex EMCI distinction is clinically important, the proposed approach is useful for early diagnosis of Alzheimer's condition. © 2019 Elsevier Ltd

Department of Mathematics

Biomedical Signal Processing and Control

Differentiation of early mild cognitive impairment in brainstem MR images using multifractal detrended moving average singularity spectral features

Fluid–elastic systems nearing dynamic instabilities are known to be sensitive to fluctuations in fluid flow. A cantilever plate in axial flow with random temporal fluctuations, is examined numerically for its dynamical behaviour. The numerical model comprises of a nonlinear structural model for the flexible plate, coupled with unsteady lumped vortex model for the fluid forces. As the mean flow velocity is increased, the system transitions to limit cycle oscillations from a state of rest, through a regime of intermittent oscillations. The conditions for onset and disappearance of intermittency are discussed and are interpreted using stochastic bifurcation theories. While the onset of intermittency is found to be unaffected by the time scales of the flow fluctuations, they are observed to affect the length of the intermittency regime. The effect of plate flexibility on intermittency is also discussed. © 2019 Elsevier Ltd