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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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TZOFFSETFROM:+0530
TZOFFSETTO:+0530
TZNAME:IST
DTSTART:20240101T000000
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BEGIN:VEVENT
DTSTART;TZID=Asia/Kolkata:20241108T150000
DTEND;TZID=Asia/Kolkata:20241108T170000
DTSTAMP:20260430T162832
CREATED:20241108T093028Z
LAST-MODIFIED:20241126T093831Z
UID:10000029-1731078000-1731085200@aero.iisc.ac.in
SUMMARY:MTech(Res): Deformation-based Topological Lattices and their Edge States
DESCRIPTION:Topological elastic metamaterials (TEMs) represent a novel class of elastic materials known for their unique ability to localize vibration energy at boundaries\, maintaining robustness against system disorders. These unconventional properties make TEMs highly attractive for applications in vibration isolation\, energy harvesting\, mechanical sensing\, and waveguiding. \nSpring-mass models are fundamental in designing TEMs\, capturing essential physics due to their structure of periodically repeating unit cells with lumped masses. The elastic coupling of these unit cells gives rise to unique wave propagation properties within the bulk material. Traditionally\, TEMs have been analyzed using mass displacements as degrees of freedom. However\, recent discoveries have shown that analyzing these models through the lens of spring deformations as degrees of freedom opens up new design possibilities for TEMs. \nIn this study\, we generalize the deformation framework in one dimension (1D). We introduce a novel 1D TEM that employs spinners with alternating moments of inertia coupled to their nearest neighbors through various types of spring connections. These connections result in different spring deformations\, thereby extending the deformation framework. Notably\, different localization profiles of boundary states emerge at opposite ends of the finite model\, explained by hidden chiral symmetry in the deformation framework. The results are validated experimentally using Laser Doppler Vibrometry. We further extend the deformation framework to two dimensions (2D) using a quasi-1D approach\, demonstrating the robustness of boundary waves against disorder. \nWe then explore the mathematical foundations of the deformation framework for a general 1D lattice\, emphasizing an underlying rank deficiency in the local stiffness matrices of spring-mass models. This leads to a special factorization of the global stiffness matrix that involves trapezoidal matrices\, thereby allowing the model to be represented in the deformation framework as an isospectral partner. We illustrate the utility of this approach with examples of disordered topological models\, generating a family of isospectral partners exhibiting boundary states and bandgaps. \nOur study introduces a non-standard approach to expressing the dynamics of spring-mass models of TEMs\, unlocking numerous research opportunities to construct periodic and aperiodic topological systems with a broader range of boundary conditions. Additionally\, the insights gained from this work can be extended to other classical domains\, such as acoustic\, photonic\, and electrical systems. \n  \nSpeaker: Udbhav Vishwakarma \nResearch Supervisor: Rajesh Chaunsali
URL:https://aero.iisc.ac.in/event/deformation-based-topological-lattices-and-their-edge-states/
LOCATION:STC Seminar Hall\, Dept. of Aerospace Engineering
CATEGORIES:Thesis Colloquium / Defence
ATTACH;FMTTYPE=image/jpeg:https://aero.iisc.ac.in/wp-content/uploads/2024/11/Udbhav-Vishwakarma1.jpg
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Asia/Kolkata:20241114T140000
DTEND;TZID=Asia/Kolkata:20241114T170000
DTSTAMP:20260430T162832
CREATED:20241114T083023Z
LAST-MODIFIED:20241126T093958Z
UID:10000030-1731592800-1731603600@aero.iisc.ac.in
SUMMARY:Ph.D. (Engg): 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 performance 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; torsion and compression; & 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)\, 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 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 this boundary value problem. 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 to 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 \nResearch advisor: Prof Dineshkumar Harursampath
URL:https://aero.iisc.ac.in/event/asymptotic-modelling-of-carbon-nanotube-cnt-and-cnt-reinforced-composite-structures-using-strain-gradient-formulations-2/
LOCATION:STC Seminar Hall\, Dept. of Aerospace Engineering
CATEGORIES:Thesis Colloquium / Defence
ATTACH;FMTTYPE=image/jpeg:https://aero.iisc.ac.in/wp-content/uploads/2024/11/renuka.jpg
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BEGIN:VEVENT
DTSTART;TZID=Asia/Kolkata:20241127T110000
DTEND;TZID=Asia/Kolkata:20241127T130000
DTSTAMP:20260430T162832
CREATED:20241126T094710Z
LAST-MODIFIED:20241126T094710Z
UID:10000032-1732705200-1732712400@aero.iisc.ac.in
SUMMARY:Ph.D. (Engg): On the nature of transonic buffet in a finite span wing
DESCRIPTION:Transonic buffet\, or shock oscillations\, is a pre-stall aerodynamic instability\, caused by shock boundary layer interaction\, of the flow over a wing. This aerodynamic instability occurs at critical combinations of transonic Mach number and angle of attack. Shock oscillations cause vibrations of the wing and is known as buffeting. Buffeting may cause fatigue of the wing\, and in an overall sense limit the flight envelope of the aircraft. Despite decades of study\, an unequivocal understanding of the physical mechanism of transonic buffet is lacking. In literature\, global stability analysis\, modal analysis\, and spatial correlation-based wave propagation analysis have been the tools of choice in understanding the mechanisms that cause transonic buffet. Here we present a perspective on transonic buffet\, using results from correlation analysis\, streamwise and spanwise pressure distributions\, and the temporal evolution of skin friction lines on the surface of the Benchmark Supercritical Wing (BSCW). Skin friction lines and critical point theory are well established to describe 3D separated flows over solid walls and bodies. Together with correlation analysis of time-resolved fluid dynamics\, the evolution of skin friction lines reveals a new perspective on the driving mechanism for shock oscillations. This viewpoint supports\, in some ways\, earlier observations on the drivers of shock-induced separation in a finite span and infinite span wing but also reveals new insights on 3D shock oscillations. The presence and distribution of these critical points—unstable foci\, saddle points\, and nodes—lead to the formation of buffet cells or pockets of streamwise shock oscillations along the span. The topology of skin friction lines in the presence of these critical points gives rise to separation and re-attachment lines. In particular\, the propagation of buffet cells is shown to be due to the self-induced motion of contra-rotating unstable foci in the skin friction lines. The self-induced motion of these unstable foci\, or vortices\, causes them to convect inboard or oscillate spanwise. This perspective on transonic buffet based on the distribution of critical points of the skin friction lines\, enables possibilities of buffet control using low-order nonlinear dynamical system models. \nSpeaker: Magan Singh \nResearch Supervisor: Prof Kartik Venkatraman
URL:https://aero.iisc.ac.in/event/ph-d-engg-on-the-nature-of-transonic-buffet-in-a-finite-span-wing/
LOCATION:Online
CATEGORIES:Thesis Colloquium / Defence
ATTACH;FMTTYPE=image/jpeg:https://aero.iisc.ac.in/wp-content/uploads/2024/11/magan.jpg
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Asia/Kolkata:20241129T150000
DTEND;TZID=Asia/Kolkata:20241129T170000
DTSTAMP:20260430T162832
CREATED:20241126T093642Z
LAST-MODIFIED:20241126T093642Z
UID:10000031-1732892400-1732899600@aero.iisc.ac.in
SUMMARY:MTech(Res): Adjoint-Based Aerodynamic Shape and Mesh Optimization with High-order Discontinuous Galerkin Methods
DESCRIPTION:The aerodynamic shape of an aircraft plays a critical role in its performance. Aerodynamic Shape Optimization (ASO) modifies the shape to achieve desired performance metrics\, such as reduced drag or increased lift. ASO integrates numerical optimization techniques with Computational Fluid Dynamics (CFD). Gradient-based optimization techniques are widely employed for ASO. The adjoint solution enables the accurate and efficient computation of the gradients of the performance metrics with respect to the shape parameters. Performance metrics are derived from CFD solutions\, which inherently contain inaccuracies. These inaccuracies can affect the reliability of the optimization process. High-order methods\, like Discontinuous Galerkin (DG)\, offer improved accuracy for a computational cost comparable to Finite Volume methods in compressible flows\, making them well-suited for ASO. Adaptive mesh refinement can further improve the accuracy of simulations. The adjoint solution used for computing gradients also finds application in mesh adaptation. Combining adjoint-based mesh adaptation with gradient-based ASO provides better control over the inaccuracies during optimization.\n\nTowards this\, the present work performs ASO using high-order DG methods and devises strategies for incorporating adaptive mesh refinement. The shape is defined using smooth splines\, and the Free Form Deformation (FFD) method controls shape changes. With changes in the geometry\, the mesh needs to move to be consistent with the modified shape. A mesh deformation strategy ensures that the mesh evolves smoothly with geometry. A gradient-based method employing the Sequential Quadratic Programming (SQP) algorithm is used for optimization. The adjoint solution computes the gradients and passes them to the optimization algorithm. Optimization for a set of drag minimization problems\, including benchmark Aerodynamic Design Optimization Discussion Group (ADODG) test case 1 and inverse design problems\, is performed on non-adapted meshes.\n\nFurthermore\, a strategy is formulated to incorporate adjoint-based mesh adaptation within the optimization process. Based on the value of adjoint-based error estimates\, the strategy decides on instances of the optimization process that require control of the errors and\, thus\, mesh adaptation. Such a strategy leads to automated control of errors in the performance metrics\, thus improving the reliability and efficiency of the optimization process.\n\n\nSpeaker: Pandya Kush Tusharbhai\n\nResearch Supervisor: Aravind Balan
URL:https://aero.iisc.ac.in/event/mtechres-adjoint-based-aerodynamic-shape-and-mesh-optimization-with-high-order-discontinuous-galerkin-methods/
LOCATION:STC Seminar Hall\, Dept. of Aerospace Engineering
CATEGORIES:Thesis Colloquium / Defence
ATTACH;FMTTYPE=image/jpeg:https://aero.iisc.ac.in/wp-content/uploads/2024/11/pandya.jpg
END:VEVENT
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