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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:20240705T163000
DTEND;TZID=Asia/Kolkata:20240705T173000
DTSTAMP:20260430T221209
CREATED:20240705T061014Z
LAST-MODIFIED:20240803T061218Z
UID:10000014-1720197000-1720200600@aero.iisc.ac.in
SUMMARY:[PhD Defense] Wave Propagation in Bio-Inspired Inhomogeneous waveguides for Impact  Mitigation Applications
DESCRIPTION:Decades of research aim to shield structures and people from impact and  shock\, mitigating damage and traumatic brain injuries. The development  of novel structures to absorb energy and reduce stress waves in  structures is indispensable. This thesis derives inspiration from the  biological structure of the woodpecker beak. The woodpecker pecking  generates very high amplitude impact loads causing stress waves to  propagate in its inhomogeneous beak structure\, without sustaining any  brain injury. The main aim of this thesis is to mimic such inhomogeneous  structures in the critical mechanical systems that require impact  mitigation. This dissertation focuses on comprehensive investigation of  computational and experimental wave propagation analysis in such  bio-inspired inhomogeneous structures\, which are often periodic\,  symmetric or anti-symmetric about the midplane\, while exhibiting both  the elastic and viscoelastic material behaviour. Importantly\, the goal  of these new bio-inspired designs is to control the wave propagation in  terms of increased attenuation\, reduction of group speeds and increase  in dispersion. \nFirstly\, the superconvergent finite elements (FE) for longitudinal and  flexural wave propagation analysis in the symmetrical sinusoidally  corrugated bio-inspired structures considering both elastic and  viscoelastic material models are developed\, whose accuracy is validated  using Abaqus. In addition to the wave propagation studies\, static and  free vibration analyses are also carried out in such structures. Next\,  the governing differential equations and the superconvergent FE are  derived for the wave propagation analysis in the shear-deformable  waveguides with anti-symmetric sinusoidal corrugations that introduce  coupling between the wave modes\, and it is validated using the  conventional FE. The study resulted in the development of the  methodology to easily manipulate wave propagation characteristics. Thus\,  a few optimised waveguide configurations that can reduce both group  speeds and wave amplitudes are presented. \nDue to the advantage of modeling viscoelasticity in the frequency  domain\, the frequency domain finite elements based on the spectral FE  are developed for both elastic and viscoelastic structures. Exploiting  the periodicity of the bio-inspired structures\, the dispersion plots are  obtained using the Floquet-Bloch theorem and the transfer matrix method.  The spectral FE and Bloch theorem-eigenvector methods are then used to  obtain the time-history responses in the semi-infinite as well as finite  structures. For dynamic and wave propagation analysis of viscoelastic  structures in the time domain\, a new direct time integration scheme is  also proposed. The stability analysis of the proposed scheme is carried  out using the spectral technique as well as the von Neumann stability  criteria. The responses obtained using the proposed time integration  scheme for various structures are validated with a commercial finite  element code. \nBased on the conducted research\, facesheets for honeycomb sandwich  structures as a practical application for blast wave mitigation are  developed. The suture structures in the facesheets are obtained with the  multi-objective structural optimization method using genetic algorithm  (NSGA-II)\, wherein the developed viscoelastic FE formulation is used.  The performance of this optimized suture-based face sheet is  experimentally tested in a vertical shock tube to validate the results  obtained using Abaqus.\nIn summary\, this thesis offers a multidisciplinary approach in  investigating and understanding wave propagation in the bio-inspired  inhomogeneous structures and its relevance to impact mitigation. \n  \n  \nSpeaker: Manish Suresh Raut
URL:https://aero.iisc.ac.in/event/phd-defense-wave-propagation-in-bio-inspired-inhomogeneous-waveguides-for-impact-mitigation-applications/
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
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Asia/Kolkata:20240716T160000
DTEND;TZID=Asia/Kolkata:20240716T170000
DTSTAMP:20260430T221209
CREATED:20240716T061914Z
LAST-MODIFIED:20240803T062047Z
UID:10000017-1721145600-1721149200@aero.iisc.ac.in
SUMMARY:[PhD Defense] Bearings-Only Quadrotor Guidance in Gap Traversal Scenarios
DESCRIPTION:In autonomous missions\, quadrotors are often required to safely fly through gaps or openings. Designing traversal guidance strategies becomes crucial in such scenarios\, especially when the quadrotor relies on the information obtained through onboard sensors. Lightweight and passive vision-based sensors can readily provide bearing information of the gaps using image features. This thesis addresses the quadrotor guidance problem of traversing gaps using only the relative bearing information. Specifically\, the work considers three scenarios: planar flight through gaps\, window traversal\, and moving gap traversal for lane transition in air corridors. \nThe first part of the thesis presents a planar gap traversal guidance law using bearings-only information. The main contribution in this part is a novel guidance method governing quadrotor heading direction using bearing information of the gap opening. The proposed heading direction is designed using an elliptic shaping angle derived from the angular bisector orientation of the gap-bearing angles. The stability of the resulting closed-loop kinematics is ascertained using Lyapunov’s direct method. Additionally\, a phase plane analysis is carried out to visualize the safe traversal characteristics of the proposed method considering all possible initial conditions around the gap. Combined with a tracking controller\, the proposed guidance strategy is applied to a six-degree-of-freedom (6-DOF) quadrotor model\, ensuring convergence towards the prescribed trajectory. The effectiveness of the proposed guidance method is validated with numerical simulations considering several initial conditions\, noisy bearing measurements\, and dynamic vehicle constraints. \nMoving beyond planar scenarios\, a three-dimensional window traversal problem is considered in the next part of the thesis and a guidance solution is proposed using bearing information of window extremities. The guidance logic governs the commanded flight path angle and heading angle of the vehicle. Again\, these commands comprise an angular bisector component with a shaping angle\, facilitating traversal along a direction normal to the window plane and passing through the centroid. A detailed stability analysis ascertains the convergence of vehicle trajectories to the desired traversal path. Simulation studies consider a 6-DOF quadrotor model\, dynamic attitude constraints\, and noise in bearing information. The robustness of the proposed method is demonstrated through a Monte-Carlo simulation study\, considering various initial conditions and noisy measurements. \nNext\, a new lane transition guidance method for a quadrotor flying in an air corridor system is introduced. Utilizing the bearing information of the neighboring vehicles\, the guidance method directs the quadrotor for a safe transition between two lanes. Comprising three sequential guidance phases\, the method includes discerning guidance for determining neighboring vehicle velocity\, longitudinal guidance to identify suitable gaps in the destination lane\, and transit guidance to maneuver the quadrotor into the desired gap. A detailed analysis deduces\, in closed-form\, the time duration for each of the three guidance phases. Additionally\, local asymptotic stability is ascertained for the proposed guidance phases. Simulation results and Monte-Carlo studies demonstrate the proposed method’s feasibility\, effectiveness\, and robustness for safe autonomous lane transition. \nOverall\, the proposed guidance methods present simple\, easily computable and closed-form analytic guidance inputs using only the passive bearing information. Further\, deterministic performance guarantees provide a sound theoretical foundation for the novel guidance solutions. The thesis also includes representative experimental studies using an indoor motion capture system and Crazyflie quadrotor platform. \n  \n  \nSpeaker: Midhun E K
URL:https://aero.iisc.ac.in/event/phd-defense-bearings-only-quadrotor-guidance-in-gap-traversal-scenarios/
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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BEGIN:VEVENT
DTSTART;TZID=Asia/Kolkata:20240731T150000
DTEND;TZID=Asia/Kolkata:20240731T160000
DTSTAMP:20260430T221209
CREATED:20240731T054804Z
LAST-MODIFIED:20240822T084630Z
UID:10000012-1722438000-1722441600@aero.iisc.ac.in
SUMMARY:[MTech(Res) Colloquium] 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.\n\n\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.\n\n\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.\n\n\nWe then explore the mathematical foundations of the deformation framework for a general 1D lattice\, revealing an underlying rank deficiency in the local stiffness matrices of spring-mass models. This leads to a unique factorization of the global stiffness matrix\, allowing the model to be represented in the deformation framework as an isospectral partner. We illustrate the utility of this approach with examples of spring-mass models for bars and beams\, generating a family of isospectral partners exhibiting disorder and boundary states.\n\n\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  \n  \n\nSpeaker: UDBHAV VISHWAKARMA
URL:https://aero.iisc.ac.in/event/mtechres-colloquium-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/2024/04/Thesis-Colloquium-Defence.jpg
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