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Understanding the anomalous mechanical behavior of Monel K500 at cryogenic temperatures: The defining role of twinning

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Journal of Alloys and Compounds 2025年 1032卷

作者： Kumar, Ravi Ranjan Dey, Soumyajyoti Florist, Varsha Pai, Namit Sadhasivam, M. Tripathy, Debasis Pradeep, K.G. Murty, SVS Narayana Liquid Propulsion Systems Centre Thiruvananthapuram695547 India Indian Institute of Space Science and Technology Thiruvananthapuram695547 India Indian Institute of Technology Bombay Mumbai400076 India Correlative Microscopy Lab Department of Metallurgical and Materials Engineering Indian Institute of Technology Madras Chennai600036 India

Monel K500 alloy has been processed through double melting wherein the primary melting was performed through vacuum induction melting followed by secondary electro-slag remelting. The nominal composition of the alloy was Ni-28.67Cu-2.53Al-0.77Ti-0.16 C and a three-step age hardening was imparted to achieve the required balance of tensile strength (0.2 % YS ≥ 585 MPa, UTS ≥ 895 MPa) and ductility (≥ 20 %). Detailed microstructural characterization of the material was performed in both solution-treated and precipitation hardened (aged) conditions using optical microscopy, scanning electron microscopy fitted with an electron back scatter diffraction (EBSD) detector. Further, transmission electron microscopy (TEM) and atom probe tomography (APT) of aged specimens were performed to understand the evolution of precipitates and their interactions with dislocations. The tensile and impact property of both solution-treated and aged specimens was evaluated in both longitudinal and transverse directions, at room temperature and at 77 K. It is interesting to note that specimens tested at cryogenic temperatures (77 K) not only exhibited higher tensile strength but also showed a remarkable increase in ductility. This is contrary to the well-known behavior of increase in strength at the cost of ductility at cryogenic temperatures, observed in many of structural materials such as stainless steel SS321, SS316L and nickel-based superalloy Inconel 718, all of which are based on austenitic FCC microstructure. The results were further correlated with detailed EBSD analysis and fractography of tested specimens. © 2025 Elsevier B.V.

关键词： Tensile strength

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Robust Aeroelastic Response Estimation for Flexible Aircraft

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IFAC-PapersOnLine 2024年 57卷 95-100页

作者： Lagnesh Mahapatra Omkar Halbe Department of Aerospace Engineering Indian Institute of Technology Bombay Mumbai 400076 India Flight Mechanics & Control Division CSIR-National Aerospace Laboratories Bengaluru 560017 India

Elastic deformations of flexible aircraft significantly affect its stability, control, and performance. This paper proposes an observer-based approach to estimate the elastic motion of flexible aircraft under uncertainty. Based on an accurate aeroelastic model and primary sensors providing reliable rigid-body measurements, two full-order observers are synthesized to estimate both rigid-body and elastic modes. The first is a classical Luenberger observer with pole placement method for the observer gain selection. The second is a full-order discontinuous sliding mode observer that is robust to bounded exogenous disturbance, such as gust effects. The observer-based approach is demonstrated on a generic flexible hypersonic aircraft model to robustly estimate longitudinal elastic deformation in the presence of moderate gusts

关键词： aeroelasticity flexible aircraft observer state estimation

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Rate Constrained Discrete-time Maximum Principle ⁎

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IFAC-PapersOnLine 2021年第19期54卷 346-351页

作者： Siddhartha Ganguly Souvik Das Debasish Chatterjee Ravi Banavar Systems and Control Engineering Indian Institute of Technology Bombay India

Actuators in real-world systems operate under limited bandwidth and saturation constraints. Mathematically, these limitations manifest as certain types of constraints being imposed on the sequence of control action. While saturation constraints have been studied extensively, bandwidth limitations in the actuators have received very little attention in the control community. While an attempt has been made in the direction of incorporating frequency constraints at the synthesis stage, rate constraints on the control at the design stage has not been studied extensively in the regime of discrete-time. This article tries to fill in that gap by incorporating rate constraints on the control trajectories. We propose a new discrete-time Pontryagin maximum principle (PMP) with rate constraints being imposed on the control and derive a set of first order necessary conditions for optimality. As an illustration, the linear quadratic (LQ) optimal control problem under rate constraints has been considered.

关键词： Rate constraints optimal control Pontryagin maximum principle

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Decentralized Cooperative Guidance for Time-constrained Rendezvous with Non-Accelerating Targets

Decentralized Cooperative Guidance for Time-constrained Rend...

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control Conference (ICC), 2019 Sixth indian

作者： Rasesh Tabiyar Abhinav Sinha Shashi Ranjan Kumar Department of Aerospace Engineering Intelligent Systems & Control Lab Indian Institute of Technology Bombay India Unmanned Systems Lab The University of Texas at San Antonio USA

This paper addresses cooperative guidance for multiple interceptors targeting fast-moving non-accelerating targets. It proposes a strategy using arbitrary time consensus to establish unanimous agreement on interceptors' time-to-go values early on. This parameter is crucial for successful simultaneous target interception. The paper introduces two salvo guidance strategies based on deviated pursuit and true proportional navigation (TPN), which are modified using a definitive consensus protocol to achieve consensus on time-to-go values. By integrating this consensus mechanism into the guidance laws, interceptors can maneuver to adjust trajectories to rendezvous with targets. The paper also emphasizes collaborative decision-making through neighbor-to-neighbor communication to enhance overall guidance performance. Extensive numerical simulations validate the proposed approach, high-lighting its ability to achieve simultaneous target interception consistently and emphasizing the importance of cooperative time-constrained guidance for successful mission outcomes.

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Impact of the Phase Change Contributing Factors on the Dynamical Characteristics of a Pulsating Heat Pipe

SSRN

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SSRN 2024年

作者： Kumar, Alok Singh, Suneet Fluid Flow Systems Simulation Lab Department of Energy Science and Engineering Indian Institute of Technology Bombay Mumbai400076 India

A theoretical investigation of the effect of the factors contributing to the phase change in the operation of a pulsating heat pipe has been conducted using a nonlinear mathematical model. With the help of bifurcation analysis and eigenvalue analysis, the identification of sudden change in the dynamic behaviour for varying factors (namely, phase change limit, wall temperature gradient, and evaporation rate) provides insightful revelations on the suitable combinations of these factors to harvest an optimized output to enhance the heat transfer mechanism. In accordance with the eigenvalue analysis, codimension one bifurcation analysis provides different regions with varying operating characteristics. In addition, codimension two bifurcation analysis has partitioned the parameter space into distinct regimes. The temporal evolution of the position of the liquid slug, which is determined by the phase change of the system, has shown that the evaporation rate has a very small unstable oscillatory regime, and therefore, is necessary to be kept in the unstable region to harvest a maximum heat output through the self-sustained oscillation. It has also indicated that any combination of the other two parameters provided that one of them is in an unstable region, is feasible for the continuous operation of PHP. © 2024, The Authors. All rights reserved.

关键词： Heat pipes

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Balancing Priorities in Patrolling with Rabbit Walks

arXiv

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arXiv 2023年

作者： Katole, Rugved Mallya, Deepak Vachhani, Leena Sinha, Arpita Systems and Control Engineering Indian Institute of Technology Bombay India Dept. of Mechanical Engineering Birla Institute of Technology and Science Pilani K.K. Birla Goa Campus India

In an environment with certain locations of higher priority, it is required to patrol these locations as frequently as possible due to their importance. However, the Non-Priority locations are often neglected during the task. It is necessary to balance the patrols on both kinds of sites to avoid breaches in security. We present a distributed online algorithm that assigns the routes to agents that ensures a finite time visit to the Non-Priority locations along with Priority Patrolling. The proposed algorithm generates offline patrol routes (Rabbit Walks) with three segments (Hops) to explore non-priority locations. The generated number of offline walks depends exponentially on a parameter introduced in the proposed algorithm, thereby facilitating the scalable implementation based on the onboard resources available on each patrolling robot. A systematic performance evaluation through simulations and experimental results validates the proportionately balanced visits and suggests the proposed algorithm’s versatile applicability in the implementation of deterministic and non-deterministic scenarios. © 2023, CC BY-SA.

关键词： Location

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A Transactive Energy Framework for Real-Time Primary Frequency Support by Active Distribution Networks

A Transactive Energy Framework for Real-Time Primary Frequen...

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IEEE Innovative Smart Grid Technologies - Asia (ISGT Asia)

作者： Abhishek Mishra Arghya Mallick Ashish R. Hota Deepak Pullaguram Prabodh Bajpai Department of Electrical Engineering Indian Institute of Technology Kharagpur India Delft Center for Systems and Control Delft University of Technology Netherlands Department of Sustainable Energy Engineering Indian Institute of Technology Kanpur India

ISBN: (数字)9798350373929

ISBN: (纸本)9798350373936

Modern active distribution networks possess significant potential to deliver ancillary services to transmission networks owing to the rising integration of renewable energy sources. This study explores the provision of primary frequency support from active distribution network to transmission network via price-based transactive control of microgrid inverters. The proposed method aims to achieve efficient coordination among microgrids, optimizing their utility, while also assisting the active distribution network in optimal primary frequency support provision to transmission network. The feasibility of this approach for real-time application is validated using a real-time simulator.

关键词： Transactive energy Supply and demand Simulation Asia Microgrids Real-time systems Inverters Smart grids Active distribution networks Frequency control

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Information Revelation Through Signalling

arXiv

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arXiv 2022年

作者： Deori, Reema Kulkarni, Ankur A. Systems and Control Engineering Indian Institute of Technology Bombay Powai Maharashtra Mumbai400076 India

This paper studies a Stackelberg game wherein a sender (leader) attempts to shape the information of a less informed receiver (follower) who in turn takes an action that determines the payoff for both players. The sender chooses signals to maximize its own utility function while the receiver aims to ascertain the value of a source that is privately known to the sender. It is well known that such sender-receiver games admit a vast number of equilibria and not all signals from the sender can be relied on as truthful. Our main contribution is an exact characterization of the minimum number of distinct source symbols that can be correctly recovered by a receiver in any equilibrium of this game;we call this quantity the informativeness of the sender. We show that the informativeness is given by the vertex clique cover number of a certain graph induced by the utility function, whereby it can be computed based on the utility function alone without the need to enumerate all equilibria. We find that informativeness characterizes the existence of well-known classes of separating, pooling and semi-separating equilibria. We also compare informativeness with the amount of information obtained by the receiver when it is the leader and show that the informativeness is always greater than the latter, implying that the receiver is better off being a follower. Additionally, we also show that when the players play behavioral strategies, an equilibrium may not *** Codes 91A28, 91A65 Copyright © 2022, The Authors. All rights reserved.

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A Methodology Establishing Linear Convergence of Adaptive Gradient Methods under PL Inequality

arXiv

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arXiv 2024年

作者： Chakrabarti, Kushal Baranwal, Mayank Tata Consultancy Services Research Mumbai India Department of Systems & Control Engineering Indian Institute of Technology India

Adaptive gradient-descent optimizers are the standard choice for training neural network models. Despite their faster convergence than gradient-descent and remarkable performance in practice, the adaptive optimizers are not as well understood as vanilla gradient-descent. A reason is that the dynamic update of the learning rate that helps in faster convergence of these methods also makes their analysis intricate. Particularly, the simple gradient-descent method converges at a linear rate for a class of optimization problems, whereas the practically faster adaptive gradient methods lack such a theoretical guarantee. The Polyak-Lojasiewicz (PL) inequality is the weakest known class, for which linear convergence of gradient-descent and its momentum variants has been proved. Therefore, in this paper, we prove that AdaGrad and Adam, two well-known adaptive gradient methods, converge linearly when the cost function is smooth and satisfies the PL inequality. Our theoretical framework follows a simple and unified approach, applicable to both batch and stochastic gradients, which can potentially be utilized in analyzing linear convergence of other variants of Adam. Copyright © 2024, The Authors. All rights reserved.

关键词： Cost functions

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Signalling for Electricity Demand Response: When is Truth Telling Optimal?

arXiv

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arXiv 2023年

作者： Aïd, René Kowli, Anupama Kulkarni, Ankur A. University Paris Dauphine PSL Research University LEDa UMR Paris8007-260 France Electrical Engineering Indian Institute of Technology Bombay Powai Maharashtra Mumbai400076 India Systems and Control Engineering Indian Institute of Technology Bombay Powai Maharashtra Mumbai400076 India

Utilities and transmission system operators (TSO) around the world implement demand response programs for reducing electricity consumption by sending information on the state of balance between supply demand to end-use consumers. We construct a Bayesian persuasion model to analyse such demand response programs. Using a simple model consisting of two time steps for contract signing and invoking, we analyse the relation between the pricing of electricity and the incentives of the TSO to garble information about the true state of the generation. We show that if the electricity is priced at its marginal cost of production, the TSO has no incentive to lie and always tells the truth. On the other hand, we provide conditions where overpricing of electricity leads the TSO to provide no information to the *** Codes 91A27, 91A25, 91A28 © 2023, CC BY.

关键词： Costs

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