Indian Institute of Technology Hyderabad (IITH) is a premier institute of science and technology established in 2008. IITH has been consistently ranked in the&nbsp;<a href="https://iith.ac.in/reports/" rel="noopener noreferrer">top 10 institutes</a>&nbsp;in India for Engineering&nbsp;<a href="https://www.nirfindia.org/2021/EngineeringRanking.html" rel="noopener noreferrer" target="_blank">according to NIRF</a>&nbsp;making it one of the most coveted schools for science and technology in the country.

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The very foundation of IIT Hyderabad is based on&nbsp;<a href="https://iith.ac.in/research/">research and innovation</a>. The vibrant research culture is evident from the number of patents and publications that IITH produces consistently every year. IITH offers&nbsp;<a href="https://iith.ac.in/academics/programmes-offered/">graduate programs</a>&nbsp;at both a masters, and a doctoral level, in several diverse areas. There are separate programs for technology, design, science, and liberal arts. The&nbsp;<a href="https://iith.ac.in/academics/post-graduate/">MTech program</a>&nbsp;is offered in various modes and durations to cater to the ever-growing need of postgraduate level professionals in the country.

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IITH creates a unique holistic ecosystem for education that offers interactive learning, a very flexible academic structure, cutting-edge research, strong industry collaboration, and entrepreneurship. This is an environment which enables students and faculty to translate their dreams into realities.

IIT Hyderabad

Department of Mechanical and Aerospace Engineering

The present work comprehensively addresses the hydrodynamic characteristics through microchannels with lotus leaf replica (exhibiting low adhesion and superhydrophobic properties) walls. The lotus leaf replica is fabricated following an efficient, two-step, soft-molding process and is then integrated with rectangular microchannels. The inherent biomimetic, superhydrophobic surface-liquid interfacial hydrodynamics, and the consequential bulk flow characteristics, are critically analyzed by the micro-particle image velocimetry technique. It is observed that the lotus leaf replica mediated microscale hydrodynamics comprise of two distinct flow regimes even within the low Reynolds number paradigm, unlike the commonly perceived solely apparent slip-stick dominated flows over superhydrophobic surfaces. While the first flow regime is characterized by an apparent slip-stick flow culminating in an enhanced bulk throughput rate, the second flow regime exhibits a complete breakdown of the aforementioned laminar and uni-axial flow model, leading to a predominantly no-slip flow. Interestingly, the critical flow condition dictating the transition between the two hydrodynamic regimes is intrinsically dependent on the micro-confinement effect. In this regard, an energetically consistent theoretical model is also proposed to predict the alterations in the critical flow condition with varying microchannel configurations, by addressing the underlying biomimetic surface-liquid interfacial conditions. Hence, the present research endeavour provides a new design-guiding paradigm for developing multi-functional microfluidic devices involving biomimetic, superhydrophobic surfaces, by judicious exploitation of the tunable hydrodynamic characteristics in the two regimes. This journal is © the Partner Organisations 2014.

World University root node

Soft Matter

Tunable hydrodynamic characteristics in microchannels with biomimetic superhydrophobic (lotus leaf replica) walls

The local equivalence ratio distribution in a flame affects its shape and response under velocity perturbations. The forced heat release response of stratified lean-premixed flames to acoustic velocity fluctuations are investigated via chemiluminescence measurements and spatial Fourier transfer analysis. A laboratory scale burner and its boundary conditions were designed to generate high-amplitude acoustic velocity fluctuations in flames. These flames are subject to inlet radial equivalence ratio distributions created via a split annular fuel delivery system outfitted with a swirling stabilizer. Simultaneous measurements on the oscillations of inlet velocity and heat release rate were carried out via a two-microphone technique, and OH∗ chemiluminescence. The measurements show that, for a given mean total power and equivalence ratio (Φg= 0.60), the flame responses vary significantly depending on forcing frequency, equivalence ratio split and velocity fluctuation amplitude, showing significant non-linearities with respect to forcing amplitude and stratification ratio. Furthermore, the spatial Fourier transfer analysis shows the underlying changes in the rate of heat release, including the direction and speed of the perturbation within the flame. Copyright © 2014 by ASME.

Proceedings of the ASME Turbo Expo

Spatial analysis on forced heat release response of turbulent stratified flames

Combustion in stratified mixtures is envisaged in practical energy systems such as direct-injection spark-ignited (DISI) car engines, gas turbines, for reducing CO2 and pollutant emissions while protecting their efficiency. The mixture gradients change the fundamental properties of the flame, especially by a difference in temperature and composition between the burnt gases and those of a flame consuming a homogeneous mixture. This paper presents an investigation of the properties of the flame propagating in a lean homogeneous mixture after ignition in a richer mixture according to the magnitude of the stratification. Three magnitudes of stratification are investigated. The local flame burning velocity is determined by an original PIV algorithm developed previously. The local equivalence ratio in the fresh gases is measured from anisole PLIF. From the simultaneous PIV-PLIF measurements, the flame burning velocities conditioned on the local stretch rate and equivalence ratio in fresh gases are measured. The flame propagating through the homogeneous lean mixture has properties depending on the ignition conditions in the stratified layer. The flame propagating in the lean mixture is back-supported longer for ignition under the richer condition. The change of stretch sensitivity and burning velocity of the flame in the lean mixture is measured over time for the three magnitudes of mixture stratification investigated. The ignition in richer mixtures compensates for the nonequidiffusion effect of lean propane flame and sustains its robustness to stretch. The flame propagation in the lean homogeneous mixture is enhanced by ignition in a richer stratified layer, as much by their robustness to stretch as by an increase in the flame speed or the burning velocity. The decay time of this influence of the stratification, called memory effect, is determined. © 2013 The Combustion Institute.

Combustion and Flame

Laminar propagation of lean premixed flames ignited in stratified mixture

Out-of-plane compression tests were conducted on six grades of ultra high molecular weight polyethylene fibre composites (Dyneema®) with varying grades of fibre and matrix, ply thickness, and ply stacking sequence. The composites with a [0°/90°] lay-up had an out-of-plane compressive strength that was dictated by in-plane tensile fibre fracture. By contrast, the out-of-plane compressive strength of the uni-directional composites was significantly lower and was not associated with fibre fracture. The peak strength of the [0°/90°] composites increased with increasing in-plane specimen dimensions and was dependent on the matrix and fibre strength as well as on the ply thickness. A combination of micro X-ray tomography and local pressure measurements revealed the existence of a shear-lag zone at the periphery of the specimens. Finite element (FE) and analytical micromechanical models predict the compressive composite response and reveal that the out-of-plane compression generates tensile stresses along the fibres due to shear-lag loading between the alternating 0° and 90° plies. Moreover, the compressive strength data suggests that the shear strength of Dyneema® is pressure sensitive, and this pressure sensitivity is quantified by comparing predictions with experimental measurements of the out-of-plane compressive strength. Both the FE and analytical models accurately predict the sensitivity of the compressive response of Dyneema® to material and geometric parameters: matrix strength, fibre strength and ply thickness. © 2014 Elsevier Ltd.

Journal of the Mechanics and Physics of Solids

The out-of-plane compressive response of Dyneema ® composites

Tactical Ballistic Missile (TBM) class target neutralization by the fragment spray of a Fragment Generator Warhead (FGW) calls for quantification of fragment projection angle scatter to finalize the end game engagement logic. For conventional axi-symmetric warhead, dispersion is assumed to be normal with a standard deviation of 30. However, such information is not available in case of FGW. Hence, a set of experiments are conducted to determine the dispersion of fragments. The experiments are conducted with a specific configuration of FGW in an identical arena to quantify the scatter and then verified its applicability to other configurations having a range of L/D and C/M ratios, and contoured fragmenting discs. From the experimental study, it is concluded that the scatter in projection angle follows normal distribution with a standard deviation of 0.75° at Chi-square significance level of 0.01(χ20.99). © 2014 China Ordnance Society

Defence Technology

Quantification of projection angle in fragment generator warhead

Tactical Ballistic Missile (TBM) class target neutralization by the fragment spray of a Fragment Generator Warhead (FGW) calls for quantification of fragment projection angle scatter to finalise the end game engagement logic. For conventional axi-symmetric warhead, dispersion is assumed to be normal with a standard deviation of 3°. However, such information is not available in case of FGW. Hence, authors have conducted a set of experiments to determine the dispersion of fragments. The first set of experiments were conducted with a specific configuration of FGW in an identical arena, to quantify the scatter and then verified its applicability to other configurations having a range of L/D and C/M ratios, and contoured fragmenting discs. From the experimental study, it is concluded that the scatter in projection angle follows normal distribution with a standard deviation of 0.75° at Chi-square significance level of 0.01(χ20.99).

Proceedings - 28th International Symposium on Ballistics, BALLISTICS 2014

Quantification of projection angle in fragment generator warhead

We propose simple approximate expressions for capacitance and electrostatic force for fixed-fixed beam-based MEMS/NEMS devices subjected to direct electrostatic and fringing field effects. The configuration that are considered for study are fixed-fixed beam and bottom electrode, fixed-fixed beam and side electrode, and a combination of beam, bottom electrode and side electrode. The expressions are evaluated based on the numerical result obtained using FEA analysis in COMSOL software. The accuracy of the proposed formulae is compared with available literature. The formulae proposed in this paper are valid for a wide operating range and they can also be used for array applications. © 2014 IEEE.

2014 IEEE 2nd International Conference on Emerging Electronics: Materials to Devices, ICEE 2014 - Conference Proceedings

Electrostatic forces in fixed-fixed microbeams under direct and fringing field effects

The ability of a multibody dynamic model to accurately predict the response of a physical system relies heavily on the use of appropriate system parameters in the mathematical model. Thus, the identification of unknown system parameters (or parameters that are known only approximately) is of fundamental importance. If experimental measurements are available for a mechanical system, the parameters in the corresponding mathematical model can be identified by minimizing the error between the model response and the experimental data. Existing work on parameter estimation using linear regression requires the elimination of the Lagrange multipliers from the dynamic equations to obtain a system of ordinary differential equations in the independent coordinates. The elimination of the Lagrange multipliers may be a nontrivial task, however, as it requires the assembly of an orthogonal complement of the Jacobian. In this work, we present an approach to identify inertial system parameters and Lagrange multipliers simultaneously by exploiting the structure of the index-3 differential-algebraic equations of motion. © 2013 Springer Science+Business Media Dordrecht.

Multibody System Dynamics

Parameter identification for multibody systems expressed in differential-algebraic form

Variable-stiffness shells are curved composite structures in which the fibre-reinforcement follow curvilinear paths in space. Having a wider design space than traditional composite shells, they have the potential to improve a wide variety of weight-critical structures. In this paper, a new method for computing the initial post-buckling response of variable-stiffness cylindrical panels is presented, based on the differential quadrature method. Integro-differential governing and boundary equations governing the problem, derived with Koiter's theory (Koiter, 1945), are solved using a mixed generalised differential quadrature (GDQ) and integral quadrature (GIQ) approach. The post-buckling behaviour is determined on the basis of a quadratic expansion of the displacement fields. Orthogonality of the mode-shapes in the expansion series is ensured by a novel use of the Moore-Penrose generalised matrix inverse for solving the GDQ-GIQ equations. The new formulation is validated against benchmark analytical post-buckling results for constant stiffness plates and shells, and compared with non-linear finite-element (FE) analysis for variable-stiffness shells. Stability estimates are found to be in good agreement with incremental FE results in the vicinity of the buckling load, requiring only a fraction of the number of variables used by the current method. © 2014 The Authors.

Fulltext

Initial post-buckling of variable-stiffness curved panels

Usage of lamination parameters for design of composite laminates significantly reduces the complexity of the optimisation problem and also allows gradient based methods to effectively be used in design. Lamination parameters are trigonometric functions of the stacking sequence of the laminate and are related to each other by a set of nonlinear con- straints which define their feasible region. The feasibility constraints have been derived for in-plane or out-of-plane lamination parameters separately. In the previous work by the authors, a set of nonlinear expressions were derived for two in-plane and two out-of-plane lamination parameters and were used for design of orthotropic variable angle tow laminates. In the present work, feasibility constraints are derived for a symmetric laminate which are functions of four in-plane and four out-of-plane lamination parameters. These nonlinear constraints were derived using the Cauchy-Schwarz inequality and algebraic identity rela- tions between in-plane, coupling and out-of-plane lamination parameters. The significance of the constraints in accurately defining the feasible region for different lamination parameters of a symmetric laminate is studied. Further, the derived nonlinear constraints are then used in the design of symmetrical variable angle tow laminate for maximising shear buckling performance.