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

Amongst the available methods to model fracture processes, the phase field approach has proved to be efficient and has received extensive attention. However, the approach is computationally demanding as it requires a very high resolution, both in space and time to resolve the fracture characteristics. In this paper, a novel adaptive phase field method is proposed for modelling quasi-static crack propagation in brittle materials. The adaptive refinement is based on the stability analysis which is combined with the quadtree decomposition. The stability analysis is based on a linear perturbation method that is used herein to determine the onset of fracture initiation on the fly. Three standard benchmark problems are solved to show the efficiency and the robustness of the proposed method. It is shown that the proposed framework does not require any post processing technique for adaptive refinement and yet is effective. © 2021 Elsevier B.V.

World University root node

Computer Methods in Applied Mechanics and Engineering

Adaptive phase field method using novel physics based refinement criteria

In this paper, an adaptive phase-field scaled boundary finite element method for fracture in functionally graded material (FGM) is presented. The model accounts for spatial variation in the material and fracture properties. The quadtree decomposition is adopted for refinement, and the refinement is based on an error indicator evaluated directly from the solutions of the scaled boundary finite element method. This combination makes it a suitable choice to study fracture using the phase field method, as it reduces the mesh burden. A few standard benchmark numerical examples are solved to demonstrate the improvement in computational efficiency in terms of the number of degrees of freedom. © 2021 World Scientific Publishing Company.

International Journal of Computational Methods

Application of Adaptive Phase-Field Scaled Boundary Finite Element Method for Functionally Graded Materials

Problems involving material interfaces are challenging, owing to the cumbersome requirements in meshing such as a fine matching mesh on both sides of the interface. Often one does not require very fine meshes on either side of the interface owing to different geometric and material properties. If the interface meshes are finer on either side, the degrees of freedom (DOFs) increases substantially. To address this difficulty, in this work the benefits of polygonal elements constructed based on the cell-based smoothed finite element method (SFEM) are explored and an alternate approach for modelling fracture along cohesive interfaces is introduced. The proposed approach greatly reduces the DOFs in the system by allowing for more nodes along the required interface region, whilst allowing for a coarse mesh elsewhere in an elegant way, without compromising the accuracy compared with the conventional finite element method. The proposed framework enables the interface to be represented independent of the meshes at the interface giving complete freedom on meshing. The robustness, accuracy and the convergence properties are demonstrated with a few numerical tests involving straight, curved and multiple interfaces. © 2020 Elsevier Ltd

Department of Ocean Engineering

Engineering Fracture Mechanics

Cell-based smoothed finite element method for modelling interfacial cracks with non-matching grids

In this work, we extend the recently proposed adaptive phase field method to model fracture in orthotropic functionally graded materials (FGMs). A recovery type error indicator combined with quadtree decomposition is employed for adaptive mesh refinement. The proposed approach is capable of capturing the fracture process with a localized mesh refinement that provides notable gains in computational efficiency. The implementation is validated against experimental data and other numerical experiments on orthotropic materials with different material orientations. The results reveal an increase in the stiffness and the maximum force with increasing material orientation angle. The study is then extended to the analysis of orthotropic FGMs. It is observed that, if the gradation in fracture properties is neglected, the material gradient plays a secondary role, with the fracture behaviour being dominated by the orthotropy of the material. However, when the toughness increases along the crack propagation path, a substantial gain in fracture resistance is observed. © 2020 The Authors

Fulltext

Defence Technology

Adaptive phase field modelling of crack propagation in orthotropic functionally graded materials

Abstract: The southern peninsular India is characterized by unique climatology with rainfall processes throughout the year from land–ocean contrasts. In addition, the complex terrain induces localized effects causing huge spatial and temporal variability in the observed precipitation. This study aims at evaluating the sensitivity of the high-resolution Weather Research and Forecasting (WRF) model (4 km) to multi-physics parameterizations, 3D variational data assimilation, and domain configuration, in the study domain covering southern peninsular India. Furthermore, the study focusses on the formulation of an ensemble method to improve the simulation of precipitation across seasons. A total of 120 experiments were set up across four crucial rainfall events, of varying spatial extent and duration, dominated by different rainfall generation mechanisms. The assessment of the experiments shows that the model’s cumulus and microphysics schemes have the highest impact on the location, intensity, and spread of the simulated 4-day long Quantitative Precipitation Forecasts (QPFs). Applying cumulus schemes at all domains represented the variability in the QPFs, across space and time, for the precipitation events dominated by convective activity. The cases without cumulus schemes at the convective scale domain (4 km), captured the higher intensity rains during organized cyclonic circulations in the north-east monsoon period. Hence, a 10-member multi-physics ensemble approach including members with and without cumulus parameterization at the fine resolution domain was adopted. The preliminary results demonstrate that the mean from the suggested ensemble approach (n-MPP) performed well in capturing the dynamics of QPFs across the rainfall events, as opposed to a single-member deterministic simulation and mean from larger member conventional multi-physics ensemble approach (c-MPP) without cumulus parameterization at the convective scale. The rank histogram, delta semi-variance plots, and outlier statistics at various lead times clearly showed that the suggested n-MPP was able to capture the high-intensity rainfall, increasing the spread of precipitation forecasts and consequently reducing the occurrence of outliers. Highlights: Evaluated the sensitivity of a high-resolution Numerical Weather Prediction (NWP) model (4 km) with 120 experiments in generating short-term (4-day long) quantitative precipitation forecasts (QPFs).The cumulus and microphysics schemes have the highest impact on the location, intensity, and spread of the simulated rainfall across events dominated by different rainfall generation mechanisms.A 10-member multi-physics ensemble approach including members with and without cumulus parameterization at the fine resolution domain was able to capture the high-intensity rainfall, increasing the spread of precipitation forecasts and consequently reducing the occurrence of outliers. © 2021, Indian Academy of Sciences.

Department Of Civil Engineering

Journal of Earth System Science

A multi-physics ensemble approach for short-term precipitation forecasts at convective permitting scales based on sensitivity experiments over southern parts of peninsular India

Three-wheeled vehicles are used both for public and private transport. A 6 degrees of freedom (DOF) mathematical model of a three wheeled vehicle is developed for predicting its ride behaviour. Simulations are carried out on this model and responses of the sprung and unsprung masses are found on different tracks like; i) Half circular bump; and ii) Trapezoidal. Sprung mass and unsprung mass accelerations are compared with experimental results and discrepancies between simulation and experiments are found. In order to bridge this gap, the paths traced by the tyre for the two different profiles are obtained as 2D layouts and differences between the analytical road input and the actual input traced by the tyre are found out. The simulated responses of the 6 DOF model are validated on the two different tracks using the paths traced by the tyres as input and good correlation is found between experimental results and simulations. Copyright © 2021 Inderscience Enterprises Ltd.

International Journal of Vehicle Performance

Simulation and experiments on three-wheeled vehicle on different tracks

Metal powders are often made by gas atomization of liquid metal. During the process, liquid metal which flows from a melt delivery tube (MDT) is atomized by high speed gas discharging from a gas nozzle. In this work, the effect of the melt delivery tube position on atomization outcomes such as the yield, mass median diameter, and spread of the particle size distribution, is studied experimentally. A melt atomization setup (pilot-scale) is used to produce tin powder by gas-atomization. Three MDT positions, namely, intruded, extruded and flush with respect to the gas nozzle, are chosen for this study. Three pressure regimes (atmospheric, aspiration and pressurization) are established by varying the relative distance between the MDT and the gas nozzle exit for the three positions. Experimental investigations revealed that the intruded position produces powder with lower mean particle sizes and lower spread than the extruded configuration. The intruded position also gives a significantly higher yield compared to the extruded and flush positions at low gas flow rates, and hence appears to be the most suited for metal atomization using a free-fall configuration. © 2021 The Society of Powder Technology Japan

Advanced Powder Technology

Experimental investigation on the effect of melt delivery tube position on liquid metal atomization

Artificial intelligence (AI) and more specific subsets of AI such as machine learning (ML) and deep learning (DL) have become widely available in recent years. Open source software packages and languages have made it possible to implement complex AI based data analysis and modeling techniques on a wide range of applications. The application of these techniques can expedite existing models or reduce the amount of physical testing required. Two data sets were utilized to examine the effectiveness of multiple ML techniques to estimate experimental outcomes and to serve as a substitute for additional testing. To achieve this complex multi-variant regressions and neural networks were utilized to create estimating models. The first data sets of interest consist of a pool fire experiment that measured the flame spread rate as a function of initial fuel temperature for 8 different fuels, including Jet-A, JP-5, JP-8, HEFA-50, and FT-PK. The second data set consists of hot surface ignition data for 9 fuels including 4 alternative piston engine fuels for which properties were not available. When properties were not available multiple imputation by chained equations (MICE) was utilized to estimate fluid properties. 10 different ML techniques were implemented to analyze the data and R-squared values as high as 92% were achieved. © 2021, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.

AIAA Scitech 2021 Forum

Artificial intelligence application in combustion modeling

This work was carried out to bring out the differences in drop weight low velocity impact behavior of two quasi-isotropic (QI) laminates. These laminates were made of AS4/914 carbon fiber reinforced plastic (CFRP). The layup sequence chosen was [0/45/-45/90]2Sand [0//90/45/-45]2S.Two types of impactors were employed for the impact tests. One is a hemispherical-end and the other is of a conical-end. Coupon level specimens were supported on all four sides during the impact test. The impact energy was calculated for the laminates and the difference, as a comparison, in each case is presented. It has been observed that the layup sequence has a significant effect on the impact resistance of the laminates under hemispherical impactor. In the case of conical impactor, both the laminates were perforated while absorbing similar energy levels. © 2021 Elsevier Ltd. All rights reserved.

Materials Today: Proceedings

An experimental study on impact behavior of quasi-isotropic CFRP laminates

The National Science Foundation’s Daniel K. Inouye Solar Telescope (DKIST) will revolutionize our ability to measure, understand, and model the basic physical processes that control the structure and dynamics of the Sun and its atmosphere. The first-light DKIST images, released publicly on 29 January 2020, only hint at the extraordinary capabilities that will accompany full commissioning of the five facility instruments. With this Critical Science Plan (CSP) we attempt to anticipate some of what those capabilities will enable, providing a snapshot of some of the scientific pursuits that the DKIST hopes to engage as start-of-operations nears. The work builds on the combined contributions of the DKIST Science Working Group (SWG) and CSP Community members, who generously shared their experiences, plans, knowledge, and dreams. Discussion is primarily focused on those issues to which DKIST will uniquely contribute. © 2021, The Author(s).