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X-WR-CALDESC:Events for Department of Aerospace Engineering
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TZID:Asia/Kolkata
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TZOFFSETFROM:+0530
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DTSTART:20250101T000000
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BEGIN:VEVENT
DTSTART;TZID=Asia/Kolkata:20250203T153000
DTEND;TZID=Asia/Kolkata:20250203T170000
DTSTAMP:20260418T094803
CREATED:20250130T070018Z
LAST-MODIFIED:20250130T070404Z
UID:10000051-1738596600-1738602000@aero.iisc.ac.in
SUMMARY:Ph.D. (Engg): Ultrasonic Guided Wave-based Inspection of Additively Manufactured Components
DESCRIPTION:Layered structural components\, such as laminated composites and those made via Additive Manufacturing (AM)\, are widely used in aerospace and automotive industries due to their various advantages. The layer-wise approach allows for intricate and multifunctional designs\, but their performance depends on factors such as joining technique\, material properties\, manufacturing conditions\, and service environments. These layered components are susceptible to defects like delamination\, debonding\, porosity\, residual stress\, cracks\, and surface roughness\, affecting mechanical performance. In AM\, process parameters like laser power\, scan speed\, layer thickness\, hatch spacing\, scan strategies\, solidification strategies\, and build chamber conditions impact the quality of the produced parts. Optimizing these parameters and using in-process monitoring systems can minimize these defects. This thesis focuses on developing an ultrasonics-based monitoring system for AM processes.\nThis work involves the modeling and analysis of wave propagation in multi-layered structures. For this purpose\, three different approaches based on the modeling of interlayer interface bonding have been formulated. The developed models allow for the analysis of different levels of interface bonding\, including perfect bonding and complete debonding. The AM components are idealized as one-dimensional higher-order planar frame structures. The equations of motion are derived from Hamilton’s principle\, and the Fourier transform-based Spectral Finite Element Method (FSFEM) is used to perform the spectral analysis and the spectral elements formulation. The FSFEM formulation results in the dispersion curves and responses in frequency domain\, which is transformed into the time domain by performing the inverse Fast Fourier Transform. A concept of effective thickness is introduced to match the cut-off frequencies in the dispersion curves obtained from the developed approaches with those of exact Lamb waves\, which are used in determining the shear correction factors necessary for higher-order frame formulations.\nThe developed models undergo two levels of validation involving the validation of the dispersion curves\, and time-domain responses. Reference dispersion curves are computed from open-source software for dispersion curve computation\, while the reference time-domain responses are obtained from experiments and the Finite Element simulations.\nFurther\, this thesis focuses on examining the interaction of ultrasonic-guided waves (UGW) with two types of defects – porosity and delamination/debonding. The impact of porosity is analyzed through porosity-dependent constitutive models. Various levels of delamination/debonding are numerically simulated by varying the interface bonding strength in the defect region. Additionally\, the Semi-analytical Finite Element Method is employed to perform spectral analysis of defective structural waveguides with complex geometry\, where the impact of various defect parameters\, such as size\, depth\, and orientation\, have been investigated. Further\, the developed FSFEM models are employed to solve inverse problems for material property characterization\, porosity estimation\, and interface bonding strength characterization. Ultimately\, these models provide a framework for analyzing the dynamic behavior of multi-layered structures\, offering insights into the interaction of UGW with defects. \nAll are welcome. \n  \nSpeaker :   Anoop Kumar Dube \n  \nResearch Supervisor : Prof. S. Gopalakrishnan FNAE FASc\, FIMechE\, CEng
URL:https://aero.iisc.ac.in/event/ph-d-engg-ultrasonic-guided-wave-based-inspection-of-additively-manufactured-components/
LOCATION:Online
CATEGORIES:Thesis Colloquium / Defence
ATTACH;FMTTYPE=image/jpeg:https://aero.iisc.ac.in/wp-content/uploads/2025/01/Anoop-.jpg
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BEGIN:VEVENT
DTSTART;TZID=Asia/Kolkata:20250210T140000
DTEND;TZID=Asia/Kolkata:20250210T170000
DTSTAMP:20260418T094803
CREATED:20250206T052542Z
LAST-MODIFIED:20250206T052542Z
UID:10000052-1739196000-1739206800@aero.iisc.ac.in
SUMMARY:MTech (Res): Woven composite modeling
DESCRIPTION:In this work\, a novel sub-mesoscale model of woven fabrics is developed using nonlinear finite element methods. The main aim of the work is to develop a framework for modeling woven fabrics. The yarns are modeled as beam elements that move freely in space and undergo large deformations and rotations. A geometrically-exact beam theory (GEBT) used to model composite beams of arbitrary cross sections is considered to model the yarns. The variational asymptotic method (VAM)\, in tandem with the beam model\, offers the advantage of modeling beams of arbitrary cross sections. A surface-to-surface contact model is developed\, considering that the contact occurs at a point on the surface. The robustness of the contact model is tested by designing a patch test. The overall mesoscale model of woven fabric is validated using experimental results of biaxial tests performed on a plain glass weave woven fabric. The biaxial simulation is performed by varying the number of yarns in the mesoscale model to study the behavior of the model and demonstrate a representative volume element (RVE).\nThe yarns are made up of fibers twisted together. An isotropic model is an approximation that works well on the mesoscale\, but a more general model is needed to include fiber-level information. The yarns can be made of 10\,000 to 60\,000 fibers twisted together. Modeling individual fibers and the interaction between them can be computationally expensive. The variational asymptotic method-based homogenization (VAH) is used to get the homogenized properties of yarn. A representative volume element of woven fabric\, with yarns made of coated fibers\, is simulated by using homogenized properties obtained through VAH.\nThe framework can be extended by introducing friction between yarns in the contact. Further\, the uncertainty in the input parameters can be quantified by propagating the uncertainty through the system using uncertainty quantification (UQ) techniques.\n\n\nSpeaker: R Adhithya\n\nResearch Supervisor:  Dineshkumar Harursampath
URL:https://aero.iisc.ac.in/event/mtech-res-woven-composite-modeling/
LOCATION:STC Conference Hall\, Ground Floor\, Department of Aerospace Engineering
CATEGORIES:Thesis Colloquium / Defence
ATTACH;FMTTYPE=image/jpeg:https://aero.iisc.ac.in/wp-content/uploads/2025/02/Adhithya.jpg
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BEGIN:VEVENT
DTSTART;TZID=Asia/Kolkata:20250218T160000
DTEND;TZID=Asia/Kolkata:20250218T170000
DTSTAMP:20260418T094803
CREATED:20250212T065012Z
LAST-MODIFIED:20250212T065012Z
UID:10000053-1739894400-1739898000@aero.iisc.ac.in
SUMMARY:Ph.D. (Engg): Passive control and intermittent dynamics of the precessing vortex core oscillation in swirl flows
DESCRIPTION:Swirl is used in modern gas turbine combustor nozzles to achieve   reliable flame stabilization and efficient fuel-air mixing. The swirl   component in the nozzle jet flow induces an axial vortex. At high swirl   intensities\, vortex breakdown occurs\, creating a recirculation zone in   the flow known as the vortex breakdown bubble (VBB). VBB appearance is   typically accompanied by the emergence of a global self-excited   instability where the VBB precesses around the flow axis and causes the   axial vortex to form a co-precessing helical structure. This  instability  is referred to as the precessing vortex core (PVC). Several  prior  studies have shown that the PVC oscillation can significantly  impact  emissions and thermoacoustic stability characteristics of the  combustor.  This thesis studies the characteristics and passive control  of the PVC.  The non-reacting flow field in an axial entry swirl nozzle  combustor at  the Massachusetts Institute of Technology (MIT)\, USA\, is  investigated.  Planar three component time resolved velocity field  measurements in the  combustor for combinations of two swirl numbers\, S  = 0.67 and 1.17 and  centrebody diameters of Dc = 9.5 mm\, 4.73 mm and 0  mm (i.e. no centrebody) are analysed. All cases are at a fixed bulk  Reynolds number of 20\,000. A new modal decomposition method based on  wavelet  filtering and proper orthogonal decomposition (WPOD) is  developed in  this thesis to analyze the global non-stationary dynamics  of these  flows. WPOD analysis for configurations without a centrebody  for both  swirl conditions revealed a coherent PVC oscillation in the  flow. Large  eddy simulation (LES) is performed for configurations  without the  centrebody and with the Dc = 9.5 mm centrebody for both  swirl numbers.  For all four cases\, LES accurately captures flow  statistics and PVC  characteristics observed in the corresponding  experimental measurements.  Linear stability analysis (LSA) on the time  averaged flow for each value  of S in the configuration without a  centrebody yields a nearly neutrally  stable global mode whose  oscillation frequency and spatial flow  oscillation amplitude  distribution characteristics match those induced  by the PVC in each  case. The wavemaker region associated with the PVC  mode is shown to be  situated at the upstream end of the VBB on the flow  centreline.  Therefore\, the introduction of a centrebody disrupts the  wavemaker and  suppresses the PVC as the experiments verify. In both LES  and  experimental studies for the cases with the Dc = 9.5 mm centrebody\,  low  amplitude PVC like oscillations\, which are also intermittent in the   S=0.67 case\, are observed. Resolvent analysis (RA) for helical forcing   on the time averaged flow field from LES for these cases is performed.  RA reveals a low rank\, optimal helical mode pair at frequencies where   PVC like oscillations are observed. The output mode amplitude   distribution characteristics match those of the PVC like oscillations  at  both values of S. For the S=0.67 case\, the input mode structure  suggests  that intermittent separation between the centrebody wake and  the VBB\,  due to turbulence results in the startup of PVC oscillations\,  which  subsequent merger then suppresses. For the S=1.17 case\, the input  mode  structure shows that stochastic forcing of the flow by turbulence\,  generated by vortex shedding off the upstream swirler\, results in sustained PVC like oscillations due to a low-rank strongly amplified   flow response at the PVC frequency revealed by resolvent analysis. \n  \nSpeaker: Saarthak Gupta \nResearch supervisor: Prof. Santosh Hemchandra
URL:https://aero.iisc.ac.in/event/ph-d-engg-passive-control-and-intermittent-dynamics-of-the-precessing-vortex-core-oscillation-in-swirl-flows/
LOCATION:Online
CATEGORIES:Thesis Colloquium / Defence
ATTACH;FMTTYPE=image/jpeg:https://aero.iisc.ac.in/wp-content/uploads/2025/02/Saarthak-.jpg
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Asia/Kolkata:20250224T160000
DTEND;TZID=Asia/Kolkata:20250224T170000
DTSTAMP:20260418T094803
CREATED:20250221T055800Z
LAST-MODIFIED:20250221T055800Z
UID:10000054-1740412800-1740416400@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. \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. \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  \nSpeaker : Pandya Kush Tusharbhai \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-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/2025/02/Slide3.jpg
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