- Sayan Gupta

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# Sayan Gupta

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Sayan Gupta

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Sayan Gupta

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Gupta, S.

Gupta, Sayan

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- PublicationEstimation of modal characteristics of a reduced-order fluidâ€“structure interaction system(01-01-2019)
;Lal, Hridya P. ;Dheelibun Remigius, W.; Show more Understanding of modal characteristics of fluid–structure interaction (FSI) systems plays a vital role in avoiding large oscillations and instabilities. Further, with parametric uncertainties, the onset of the instabilities may change and hence it is important to know the statistics of the modal characteristics of the coupled system to avoid system failures. The primary objective of the study is to estimate the statistics of modal characteristics of the stochastic FSI system which demands intensive computation resources especially for large ordered FSI systems. The present study also focusses on developing and implementing a stochastic reduced-order model to resolve pressure-induced oscillations of a disc-like structure as a generic fluid–structure interaction system. The stochastic reduced-order model uses a modal reduction approach together with spectral projection-based polynomial chaos expansion (PCE) to truncate both the system degrees of freedom (dofs) and the random modes. Interfacing algorithms have also been developed that enable finite element (FE) modelling of the FSI system using commercial software and in-house developed codes.Show more - PublicationInteraction of a flexible splitter plate with vortex shedding past a rigid circular cylinder(01-01-2019)
;Bose, Chandan ;Krishna Kumar, S.; Show more This study deals with energy harvesting from vortex-induced vibration (VIV) of a flexible cantilever plate placed in the wake of a rigid cylinder. Conventionally, the plate is designed to resonate with the vortex shedding frequency behind the cylinder at a given flow velocity. The experimental results presented here show that the frequency of the plate oscillations undergoes an abrupt increase from a low value to a higher value at a critical flow velocity. Numerical simulations carried out in the present study suggest that this jump is due to the transition between two modes of wake oscillations in the system, one with a low Strouhal number range accompanied by impeded shedding and the other being the natural vortex shedding with a higher Strouhal number range. It is also found that the mode of vortex shedding depends on the flow velocity as well as the gap between the cylinder and the plate. There exists a critical gap for every flow velocity below which vortex shedding is inhibited resulting in reduced plate vibrations. The results indicate that the position of the plate in the wake affects the shedding frequency significantly and thus the gap between the plate and cylinder needs to be considered as a key parameter in design of such flow-induced energy harvesters.Show more - PublicationExplosive death transitions in complex networks of limit cycle and chaotic systems(01-03-2023)
;Pranesh, SamanaShow more The conditions for explosive death transitions in complex networks of oscillators having generalized network topology, coupled via mean-field diffusion, are derived analytically. The network behaviour is characterized using three order parameters that define the average amplitude of oscillations, the mean state and the fraction of dead oscillators. As the mean field coupling is changed adiabatically, the amplitude order parameter undergoes explosive death transitions and the nodes in the network collectively cease to oscillate. The transition points in the parameter space and the boundaries of amplitude death regime are derived analytically. Sub-critical Hopf bifurcations are shown to be responsible for amplitude death transition. Explosive death transitions are characterized by hysteresis on adiabatic change of the bifurcation parameter and surprisingly, the backward transition point is shown to be independent of network topology. The theoretical developments have been validated through numerical examples, involving networks of limit cycle systems — such as the Van der Pol oscillator and chaotic systems, such as the Rossler attractor for both random and small world networks.Show more - PublicationTransitional Flow Dynamics Past aÂ Passively Flapping Airfoil in Gusty Flow(01-01-2021)
;Bose, Chandan; Show more This paper investigates the transitional flow dynamics behind a passively flapping airfoil supported by nonlinear springs in the presence of gusty inflow. The fluid-structure interaction (FSI) framework is composed of an incompressible Navier-Stokes solver weakly coupled with a two degree-of-freedom (dof) nonlinear structural model. The fluid-elastic system shows a rich bifurcation behavior in terms of successive Hopf bifurcations in uniform flow condition as the mean wind speed is increased. Presence of gusty fluctuations in the inflow makes the dynamics more complex through transitional states that we refer to as ‘intermittency’ between different dynamical states. A regular intermittent state between quasi-periodic dynamics and low amplitude aperiodic response has been observed when the FSI system is subjected to a time harmonic gust in terms of sinusoidal fluctuation. A parametric study has been carried out for various amplitudes and frequencies of the sinusoidal fluctuation to demarcate the transitional regimes. Thereafter, the system is subjected to random gusts modeled as Ornstein-Uhlenbeck process and ‘on-off’ and ‘burst’ type intermittent dynamics have been observed for long time-scale and short time-scale input fluctuations respectively. The intermittent states have been characterized through time series analyses tools and the corresponding flow-field dynamics has been investigated in detail.Show more - PublicationCrossing statistics of quadratic transformations of LMA processes(15-03-2013)
;Jith, Jithin; Rychlik, IgorShow more Random loads that exhibit significant non-Gaussianity in terms of asymmetric distributions with high kurtosis can be modeled as Laplace Moving Average (LMA) processes. Examples of such loads are the wave loadings in ships, wind loads on wind turbines, loads arising due to surface roughness in vehicular systems, etc. The focus of this paper is on estimating the crossing statistics of second-order response of structures subjected to LMA loads. Following the Kac-Siegert representation, a second order approximation of the Volterra expansion of the system enables representing the response as a quadratic combination of vector LMA processes. The mean crossing rate of the response is then computed using a hybrid approach. The proposed method is illustrated through two numerical examples. © 2013 Elsevier Ltd.Show more - PublicationThe use of polynomial chaos for parameter identification from measurements in nonlinear dynamical systems(01-12-2015)
;Pandurangan, Rangaraj; Show more This study focuses on the development of a computationally efficient algorithm for the offline identification of system parameters in nonlinear dynamical systems from noisy response measurements. The proposed methodology is built on the bootstrap particle filter available in the literature for dynamic state estimation. The model and the measurement equations are formulated in terms of the system parameters to be identified - treated as random variables, with all other parameters being considered as internal variables. Subsequently, the problem is transformed into a mathematical subspace spanned by a set of orthogonal basis functions obtained from polynomial chaos expansions of the unknown system parameters. The bootstrap filtering carried out in the transformed space enables identification of system parameters in a computationally efficient manner. The efficiency of the proposed algorithm is demonstrated through two numerical examples - a Duffing oscillator and a fluid structure interaction problem involving an oscillating airfoil in an unsteady flow.Show more - PublicationProbabilistic residual life assessment against thermal fatigue and creep(01-12-2013)
;Appalanaidu, Y.Show more This study focuses on the residual life assessment of nuclear power plant components carrying high temperature fluids, which exhibit random temporal fluctuations about a mean value. The primary mechanisms of damage in the components are due to thermal fatigue and creep. First, based on available data, a stochastic model for the random temporal fluctuations is developed. The thermal stresses generated due to the loadings are multiaxial in nature and are random processes in time. The von Mises stress, obtained as a nonlinear combination of the components of the stress tensor, is considered for estimating the expected fatigue damage. Analytical expressions are developed for estimating the expected fatigue damage. For estimating the expected creep damage, it has been shown that even though creep growth is a slow process and the temporal fluctuations do not appear in the growth trajectories, random variable models are not sufficient. Finally, estimates of the failure probability are obtained by considering different models for the creep-fatigue interaction effects. This study is currently in progress. © 2013 Taylor & Francis Group, London.Show more - PublicationDynamical Stability Analysis of a Fluid Structure Interaction System Using a High Fidelity Navier-stokes Solver(01-01-2016)
;Bose, Chandan ;Badrinath, Sandeep; Show more The present paper investigates the flow induced dynamics of a non-linear fluid-structure interaction (FSI) system comprising of a symmetrical NACA 0012 airfoil supported by non-linear springs. Two methods are used in calculating the aerodynamic loads: a linear analytical approach and a full Navier-Stokes (N-S) solution. The analytical approach is based on the assumption of potential flow theory and a rigid wake. Wind velocity as a bifurcation parameter shows that the structural response undergoes a supercritical Hopf bifurcation. However, the analytical loads predict unrealistic bifurcation onset at low values of solid to fluid added mass ratio (μ) relevant to the application of flapping wing micro air vehicles (MAVs), showing the extremely large amplitude of oscillations. These observations render the use of an inviscid approach meaningless at such parametric regimes. Hence, we propose to use a N-S solver to emphasize the limit of applicability of the linear aerodynamic theory. Moreover, the inclusion of the viscous effects can potentially result in interesting dynamical behavior that has not been captured by the analytical approach. A bifurcation and stability analysis has been carried out for different parametric variations of μ in the fluid structure interaction system.Show more - PublicationRoute to synchronization in coupled phase oscillators with frequency-dependent coupling: Explosive or continuous?(01-10-2022)
;Kumar, MohitShow more Interconnected dynamical systems often transition between states of incoherence and synchronization due to changes in system parameters. These transitions could be continuous (gradual) or explosive (sudden) and may result in failures, which makes determining their nature important. In this study, we abstract dynamical networks as an ensemble of globally coupled Kuramoto-like phase oscillators with frequency-dependent coupling and investigate the mechanisms for transition between incoherent and synchronized dynamics. The characteristics that dictate a continuous or explosive route to synchronization are the distribution of the natural frequencies of the oscillators, quantified by a probability density function g(ω), and the relation between the coupling strength and natural frequency of an oscillator, defined by a frequency-coupling strength correlation function f(ω). Our main results are conditions on f(ω) and g(ω) that result in continuous or explosive routes to synchronization and explain the underlying physics. The analytical developments are validated through numerical examples.Show more - PublicationBifurcation and response analysis of a nonlinear flexible rotating disc immersed in bounded compressible fluid(31-03-2017)
;Remigius, W. Dheelibun; Show more Use of heavy gases in centrifugal compressors for enhanced oil extraction have made the impellers susceptible to failures through acousto-elastic instabilities. This study focusses on understanding the dynamical behavior of such systems by considering the effects of the bounded fluid housed in a casing on a rotating disc. First, a mathematical model is developed that incorporates the interaction between the rotating impeller - modelled as a flexible disc - and the bounded compressible fluid medium in which it is immersed. The nonlinear effects arising due to large deformations of the disc have been included in the formulation so as to capture the post flutter behavior. A bifurcation analysis is carried out with the disc rotational speed as the bifurcation parameter to investigate the dynamical behavior of the coupled system and estimate the stability boundaries. Parametric studies reveal that the relative strengths of the various dissipation mechanisms in the coupled system play a significant role that affect the bifurcation route and the post flutter behavior in the acousto-elastic system.Show more