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X-ORIGINAL-URL:https://aero.iisc.ac.in
X-WR-CALDESC:Events for Department of Aerospace Engineering
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TZID:Asia/Kolkata
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DTSTART:20240101T000000
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BEGIN:VEVENT
DTSTART;TZID=Asia/Kolkata:20240304T200000
DTEND;TZID=Asia/Kolkata:20240304T213000
DTSTAMP:20260517T193843
CREATED:20240324T084614Z
LAST-MODIFIED:20240802T165719Z
UID:10000002-1709582400-1709587800@aero.iisc.ac.in
SUMMARY:Nonequilibrium reacting flows: First principles based modeling for chemical kinetics and hydrodynamics
DESCRIPTION:Predicting state of the gas hitting vehicles flying at hypersonic speeds (Mach ~5) is challenging and is an exciting area of research. Hypersonic flows create shock waves\, which compress and heat the surrounding gas to high-temperatures\, nearly thousands of Kelvins. At these high temperatures\, air molecules (nitrogen and oxygen) dissociate into atomic species. Predicting the extent of dissociation and recombination of atomic species is important since the state of the gas near the vehicle surface determines heating rates and gas-surface chemistry that damages the heat shield. Since experiments in ground test facilities do not mimic such extreme flight conditions\, numerical simulation plays an important role. Predictive numerical simulations require accurate reaction chemistry models. Computational models developed thus far range from simple empirical models fit to limited experimental data to models with millions of input parameters that track individual quantized energy state transitions. The level of model fidelity required for accurate engineering analysis remains an open question of active research. Models coupling internal energy and dissociation chemistry tend to be developed at either the kinetic scale or the continuum scale. In this work\, we develop new nonequilibrium models for shock heated flows that are analytically consistent between kinetic and continuum scales and are based on recent ab-initio data\, applicable to large-scale CFD and direct simulation Monte Catlo (DSMC) simulations. \nNonequilibrium Hydrodynamics: The Navier-Stokes equations\, typically employed even at strong non-equilibrium conditions\, wherein thermodynamic fluxes such as stresses and heat flux vector are based on linear irreversible thermodynamics\, not be accurate in multiscale and multiphysics scenarios encountered in hypersonic flows. Similarly\, the Navier-Stokes equations are known to breakdown in rarefied (low density) gas flows. Therefore\, a new formalism is proposed to circumvent these issues\, which can also benefit\, hybrid methods that can combine continuum description using the Navier-Stokes equations and microscopic description\, necessary for efficient high-fidelity numerical simulations. Other wide range of physics problems such as nano-scale flows\, plasma physics modeling\, and general complex gas flows can also benefit from the proposed new non-equilibrium hydrodynamic formalism. \n  \nSpeaker: Dr. Narendra Singh \nBiography: Dr. Narendra Singh graduated with a PhD (and MS) in Aerospace Engineering (with minor in Mathematics and Chemistry) from University of Minnesota. Narendra obtained his undergraduate degree (with Honors) in MechE from IIT Bombay. In his doctoral thesis\, Narendra developed chemical kinetics models for DSMC and CFD using first principles-based approach. In addition\, Narendra (along with Prof.Agrawal) has developed higher order equations for rarefied and strong nonequilibrium flows\, known as O-13 and O-Burnett equations\, where O ‘refers’ to Onsager due to the consistency of equations with Onsager’s reciprocity principle. Narendra Singh did his 2 years postdoc in MechE at Stanford\, where his research spanned particle-laden flows\, carbon sequestration\, and ultrafast chemistry at SLAC. Currently\, he is a postdoc research associate at Center for Hypersonic\, UIUC\, and developing reduced order models for chemical kinetics. \n 
URL:https://aero.iisc.ac.in/event/nonequilibrium-reacting-flows-first-principles-based-modeling-for-chemical-kinetics-and-hydrodynamics/
LOCATION:STC Seminar Hall\, Dept. of Aerospace Engineering
CATEGORIES:AE Seminar
ATTACH;FMTTYPE=image/jpeg:https://aero.iisc.ac.in/wp-content/uploads/2024/04/AE-Seminar.jpg
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BEGIN:VEVENT
DTSTART;TZID=Asia/Kolkata:20240313T073000
DTEND;TZID=Asia/Kolkata:20240313T203000
DTSTAMP:20260517T193843
CREATED:20240312T225849Z
LAST-MODIFIED:20240803T053029Z
UID:10000003-1710315000-1710361800@aero.iisc.ac.in
SUMMARY:[PhD Colloquium] Asymptotic Modelling of Carbon Nanotube (CNT) and CNT-reinforced composite structures using strain gradient formulations
DESCRIPTION:Carbon nanotubes (CNTs) have garnered attention for their remarkable mechanical\, thermal\, and electrical properties\, making them valuable in various applications. CNTs are particularly advantageous in aerospace structures as reinforcements in polymer matrix composites\, enhancing structural strength while reducing weight. Furthermore\, they offer the potential for multifunctionality\, integrating structural\, thermal\, and electrical functionalities within components like wings. However\, accurately modelling CNT behaviour poses challenges\, especially considering their application in larger-scale aerospace structures. While accurate\, molecular dynamics and molecular structural mechanics are computationally intensive and limited in length scale. In this context\, the present research proposes reduced-order continuum structural models using the Variational Asymptotic Method (VAM) to study CNT and its composite structures while incorporating length scale effects using strain-gradient formulations. \nUsing VAM\, single-walled CNTs (SWCNTs) were first analysed by considering them as straight\, hollow\, circular tubes in a local continuum framework. This tube model accounts for the geometrically nonlinear behaviour of standalone CNT when subjected to bending and buckling loads. Cross-sectional ovalisation leading to nonlinear bending and buckling behaviour has been studied. Combined loading cases of bending and compression and torsion and compression and bending and torsion have been examined. The study aims to provide insights into the 3-D nonlinear deformation behaviour of SWCNTs\, offering a more efficient approach for evaluating CNTs in aerospace composite applications. \nIn the next step\, recognising the significance of the structure’s small size (such as used in MEMS\, NEMS\, and sensors)\, the non-classical theories\, such as the Modified Strain Gradient Theory\, which account for the size effect in the material\, have been employed to develop a pioneering beam and plate models tailored for CNT-reinforced composite structures. Emphasising the critical nature of size effects\, characterised by length scale parameters\, this study delves into the nuances of the length scale effects in nanoscale structures. To develop the asymptotically-correct strain-gradient beam model\, a prismatic beam with a rectangular cross section has been considered to derive zeroth-order and subsequent higher-order models while capturing the strain-gradient effects. Notably\, this work is the first application of non-classical theories in developing VAM-based beam models. Different orders for length scale parameters have been considered\, and the validity of each choice is scrutinised\, followed by guidance on the appropriate choice of the length scale parameters. \nFollowing the development of the strain-gradient beam model\, a modified strain gradient theory-based plate model has also been developed using VAM\, which is again a first-of-its-kind work in the context of VAM and reduced-order structural models. Using the variational methods\, fourth-order ordinary differential equations were obtained for the non-classical case\, and similarly\, an additional set of boundary conditions (non-classical) were also derived. The warping solutions and the plate stiffnesses are obtained by solving these governing differential equations and boundary conditions. It was noted that the material length scale parameters appear only in the bending and twist stiffness terms. Further\, the classical results can be derived by setting the material length scale parameters as zero. Zeroth- and first-order approximations have been derived\, followed by detailed validation of the results with literature for bending and buckling load cases. Parametric studies involving variations in thickness and plate width have been conducted to assess their influence on mechanical behaviour. The developed plate model is then applied to CNT-reinforced composites\, and their bending and buckling studies have been carried out. The parametric studies have also considered evaluating all influencing parameters like CNT volume fraction\, material length scale parameter\, plate thickness and width. \n  \nSpeaker: Renuka Sahu
URL:https://aero.iisc.ac.in/event/asymptotic-modelling-of-carbon-nanotube-cnt-and-cnt-reinforced-composite-structures-using-strain-gradient-formulations/
LOCATION:STC Seminar Hall\, Dept. of Aerospace Engineering
CATEGORIES:Thesis Colloquium / Defence
ATTACH;FMTTYPE=image/jpeg:https://aero.iisc.ac.in/wp-content/uploads/2024/04/Thesis-Colloquium-Defence.jpg
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