Department of Mechanical Engineering

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

In many structural applications like bridges, arches, etc., frames are used, and it is important to study their dynamic behavior. Finite element method (FEM) is usually used for computational simulation of vibration for such frame structures. However, FEM simulations for high frequency are computationally intensive and lack accuracy. This paper proposes a wave propagation-based approach for the vibration analysis of a frame having angular and curved joints. The reflection and transmission matrices for the joints are derived using the kinematic compatibility and equilibrium conditions. Reflection, transmission, and propagation matrices are assembled leading to matrix equation terms of the wave amplitudes. Modal analysis and harmonic analysis of frames having curved and angular joints are performed using the present formulation. The frequency response function for point harmonic forcing acting on such structures is also presented. The formulation and the results are non-dimensionalized for wider applicability. The results obtained using the present formulation are compared with those obtained through FEM simulation in a commercial package. It is found that the results obtained using the two methods are in excellent correlation. The computational efficiency of the present method over FEM simulation is also reported. © 2021 American Society of Civil Engineers (ASCE). All rights reserved.

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Journal of Vibration and Acoustics, Transactions of the ASME

Wave analysis for in-plane vibration of angular and curved frames

The present study investigates the effect of inclination on the buoyancy driven systems. There are extensive studies on the cavity systems which exhibit a heat transfer coefficient jump upon the change in the inclination as the system moves from one steady state to another. The present numerical study makes use of 2-D and 3-D CFD simulations to investigate if a similar behaviour occurs in natural circulation systems such as a Natural Circulation Loop and a Coupled Natural Circulation Loop. The study identifies a combination of flow pattern rearrangement and flow direction reversal as the phenomena responsible for the heat transfer coefficient jump. The study also examines carefully as to why the same was not reported previously. The CFD study is validated thoroughly with the numerical and experimental data available in the literature. A parametric study is also conducted to examine the effects of the aspect ratio, the Rayleigh number, the Prandtl number and the inclination with the plane of the Natural Circulation Loop. © 2020 Elsevier Ltd

International Communications in Heat and Mass Transfer

Numerical investigation on the heat transfer coefficient jump in tilted single-phase natural circulation loop and coupled natural circulation loop

Filtering of the sub-band spectral radiation is an attractive technique to overcome the lower efficiencies of direct conversion thermophotovoltaic technology. The poor performance of these systems is due to the relatively small portion of the incident energy being above the bandgap of photovoltaic cell. To effectively filter the majority of the sub-bandgap radiation and re-employ it as regenerative heat, a viable solution is to design an efficient spectrally selective filter ideally matched to the photovoltaic cell's bandgap. Here, we have explored a high contrast amorphous silicon grating on a quartz substrate. Quartz due to its inherent nature inhibits transmission of sub-band gap radiation in the infrared (IR) region (>4.75 μm), whereas gratings further filter radiation above 1.8 μm suitable for GaSb photovoltaic cell. The optimized filter is fabricated using direct write laser lithography, and optical characterization result shows that 72% of incident radiation in unconvertible region (>1.80 μm) is filtered and recycled. Further, the thermal characterization results of IR filter carried out using a ceramic heater has shown the drop in effective temperature from 1074.9 to 813.2 K in above bandgap region. This suppressed radiation has contributed to an absolute increase in source body temperature by 16.0 K resulting in increase in the above bandgap radiation available for thermophotovoltaic conversion. The proposed spectral filtering design can be tailored to solar cells of any bandgap and is scalable for employment in various thermophotovoltaic applications. © 2021 Society of Photo-Optical Instrumentation Engineers (SPIE).

Department Of Civil Engineering

Journal of Photonics for Energy

Spectral filtering of sub-bandgap radiation using all-dielectric gratings for thermophotovoltaic applications

Machining of complex features and holes on superalloys is a topic of both industrial and academic interest. Though the demand for high aspect ratio holes on Ti-6Al-4V is high in aerospace, biomedical and chemical industries, machining the same is very challenging due to the low thermal conductivity and debris accumulation in the machining zone. The present-day methods of hole drilling by unconventional methods like Electric Discharge Machining (EDM) make use of electrodes with poor flushing capabilities. Hence the motivation of the present work is to develop a method to modify the geometry of Electric Discharge Drilling (EDD) tools in order to enhance debris removal. For the first time an attempt has been made to machine micro double-helical grooves on EDD tools in a single pass. Solid, single-helical and double-helical electrodes are developed and through-holes are drilled on a Ti-6Al-4V workpiece. A comparative analysis of the performance of these three types of tools with respect to the machining time, electrode wear rate and hole quality is carried out. From Computational Fluid Dynamics (CFD) simulations it is seen that the double-helical grooved tool is superior in debris removal. The best values of the machining time of 183.33 s, overcut of 2.19 mm, hole taper angle of 7.93° and area of recast layer of 6.66 mm2 are obtained on the holes machined using double-helical electrodes. The mentioned tool has the potential to overcome the problem of debris removal in high aspect ratio hole drilling and surpass the present-day electric discharge drilling tools. © IMechE 2021.

Proceedings of the Institution of Mechanical Engineers, Part B: Journal of Engineering Manufacture

Effect of micro double helical grooved tools on performance of electric discharge drilling of Ti-6Al-4V

In process industries, the study of granular mixing can substantially optimize energy costs and the quality of final products. In this work, we study the mixing of binary granular systems assisted by fluid flow through the assembly. The granular system is exposed to continuous fluid flow from the bottom to the top. Particle mixing is simulated by the coupling of Computational Fluid Dynamics (CFD) and the Discrete Element Method (DEM). Parameters like particle stacking order, density ratio, and size ratio show a significant influence on mixing. The presence of tilted plates as a geometric intervention with different configurations plays a critical role in mixing efficiency. A new mixing index which captures the nature of contact creation, and the degree of mixing is proposed. The present work helps develop efficient strategies for particle mixing in fluidized beds. © 2021 Elsevier B.V.

Powder Technology

Fluid flow assisted mixing of binary granular beds using CFD-DEM

In this paper, we propose a robust framework based on the scaled boundary finite element method to model implicit interfaces in two-dimensional differential equations in nonhomegeneous media. The salient features of the proposed work are: (a) interfaces can be implicitly defined and need not conform to the background mesh; (b) Dirichlet boundary conditions can be imposed directly along the interface; (c) does not require special numerical integration technique to compute the bilinear and the linear forms and (d) can work with an efficient local mesh refinement using hierarchical background meshes. Numerical examples involving straight interface, circular interface and moving interface problems are solved to validate the proposed technique. Further, the presented technique is compared with conforming finite element method in terms of accuracy and convergence. From the numerical studies, it is seen that the proposed framework yields solutions whose error is O(h2) in L2 norm and O(h) in the H1 semi-norm. Further the condition number increases with the mesh size similar to the FEM. © 2021 Elsevier Ltd

Engineering Analysis with Boundary Elements

Robust modelling of implicit interfaces by the scaled boundary finite element method

A recovery-based error indicator developed to evaluate the quality of polygonal finite element approximations is presented in this paper. Generalisations of the finite element method to arbitrary polygonal meshes have been increasingly investigated in the last years, as they provide flexibility in meshing and improve solution accuracy. As any numerical approximation, they have an induced error which has to be accounted for in order to validate the approximate solution. Here, we propose a recovery type error measure based on a moving least squares fitting of the finite element stress field. The quality of the recovered field is improved by imposing equilibrium conditions and, for singular problems, splitting the stress field into smooth and singular parts. We assess the performance of the error indicator using three problems with exact solution, and we also compared the results with those obtained with standard finite element meshes based on simplexes. The results indicate good values for the local and global effectivities, similar to the values obtained for standard approximations, and are always within the recommended range. © 2021 Elsevier Ltd

Computers and Mathematics with Applications

Error estimation for the polygonal finite element method for smooth and singular linear elasticity

This work presents a framework to study the quasi-static brittle fracture in functionally graded materials with random material properties using a non-intrusive phase field method. The model accounts for variation in the material and fracture properties. Further, the effective Young’s modulus, the gradient index and the fracture properties of the constituent materials are considered as random input variables. The output randomness is represented by polynomial chaos expansion. Two-dimensional benchmark numerical examples are presented to demonstrate the benefits of the non-intrusive approach to study fracture characteristics. The influence of the randomness in the material properties on the peak load carrying capacity is considered as a primary quantity of interest in this study. A systematic parametric study is carried out to bring out the sensitivity of the input randomness on the stochastic output response using Sobol indices. © 2021, The Author(s), under exclusive licence to Springer-Verlag GmbH Austria, part of Springer Nature.

Acta Mechanica

A non-intrusive stochastic phase field method for crack propagation in functionally graded materials

Numerical modeling of the thermo-elastic fracture using a hybrid phase-field method is presented. The model’s capability to simulate complex thermo-elastic crack propagation paths under the temperature and mechanical loads’ influence is demonstrated through a few example problems. The evolution of complex crack patterns in a ceramic plate subjected to quenching are simulated. Further, the behavior of functionally graded specimens with a spatial variation of material properties when subjected to thermal shock is investigated. A staggered solution scheme is used to solve the coupled system of multi-field partial differential equations using an open-source finite element software FEniCS. © 2021 Taylor & Francis Group, LLC.

International Journal for Computational Methods in Engineering Science and Mechanics

Hybrid phase-field modeling of thermo-elastic crack propagation

The onset of convection instability in a differentially heated layer consisting of gray and non-gray gaseous mixtures is studied numerically. The conditions investigated cover a wide range of Planck number values (Pl=κkT4σT03), from the conduction-dominated regime of Pl≫ 1 to the radiation-dominated regime of Pl≪ 1. The linear stability theory is applied to mass, momentum and energy balance equations and the resulting linear stability equations are solved by Chebyshev spectral collocation method. The divergence of radiative flux is solved by the finite-volume-based discrete ordinates method. The Spectral Line Weighted sum of gray gas (SLW) model is used to represent the fine spectral variation of absorption coefficient for a non-gray gas medium. The results indicate that the critical Rayleigh number (Rac) for the onset of convection increases with mean temperature (T) in the conduction-dominated regime at low values of T. In the radiation-dominated regime (Pl≪ 1), Rac decreases with T for gray media. If the medium is non-gray, the critical Rac reduces to even lower values (as compared with those of gray gases) due to the dependence of gas absorptivity on temperature T. A reduction in the wall emissivity value increases the stability of the fluid layer due to reflection of radiation from the wall, in the radiation-dominated regime. The reverse trend is seen for Pl≫ 1. The critical parameters also significantly depend on the concentrations of radiatively participating gases in the mixture. The temperature profile in the fluid layer transforms from a linear profile in conduction regime to a stratified profile with steep gradients near the walls, in the presence of non-gray participating gases. © 2021, Indian Academy of Sciences.