112 research outputs found
sj-docx-1-edq-10.1177_08912424231163151 - Supplemental material for COVID-19-Induced Automation: An Exploratory Study of Critical Occupations
No full textSupplemental material, sj-docx-1-edq-10.1177_08912424231163151 for COVID-19-Induced Automation: An Exploratory Study of Critical Occupations by Chun Song, Lionel J. Beaulieu, Indraneel Kumar and Roberto Gallardo in Economic Development Quarterly</p
Spatial and cross-sectoral relationships in business entry dynamics around a highway corridor: Supplementary Materials
No full textThis document is the supplementary material for our paper "Spatial and cross-sectoral relationships in business entry dynamics around a highway corridor" in Transportmetrica A: Transport Science.
Authors - Shagun Mittal, Takahiro Yabe, Indraneel Kumar, and Satish V. Ukkusuri</p
Task allocation for networked autonomous underwater vehicles
No full textUnderwater Acoustic Sensor Networks (UW-ASNs) consist of stationary or mobile nodes such as Autonomous Underwater Vehicles (AUVs), which may be classified as propeller-driven vehicles and gliders, that are equipped with a variety of sensors for performing collaborative monitoring tasks. UW-ASNs are envisioned for missions like oceanographic data collection, ocean sampling, offshore exploration, disaster prevention, tsunami and seaquake warning, assisted navigation, distributed tactical surveillance, and mine reconnaissance. A task allocation and optimization framework for networked AUVs that participate as a team to accomplish such missions is developed in this work. These missions entrusted to the AUVs are sometimes critical to human life and property, are bound by severe time and energy constraints, and involve a high degree of inter-vehicular communication. The objective of the framework is to form the best possible team, which is a subset of all deployed AUVs that is best suited to accomplish the mission, while adhering to the constraints. Successful completion of the mission is dependent on effective communication between the networked AUVs and to achieve this a geocasting based networking framework is also proposed. Research specific to this area has been limited. Hence, a framework based on energy minimization for the team of AUVs to complete the mission in given time bound is proposed. Further, the effect of size of geocast region, effect of underwater current on the choice of geocast region and on localized nature of the problem, and the performance of Propeller Driven Vehicles (PDVs) and gliders is compared.M.S.Includes abstractIncludes bibliographical referencesby Indraneel S. Kulkarn
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Rolling element bearing design through genetic algorithms
No full textThe design of rolling element bearings has been a challenging task in the field of mechanical engineering. While most of the real aspects of the design are never disclosed by bearing manufacturers, the common engineer is left with no other alternative than to refer to standard tables and charts containing the bearing performance characteristics. This paper presents a more viable method to solve this problem using genetic algorithms (GAs). Since the algorithm is basically a guided random search, it weakens the chances of getting trapped in local maxima or minima. The method used has yielded improved performance parameters than those catalogued in standard tables.
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Indraneel Chakraborty is currently with Massachusetts Institute of Technology and can be reached at [email protected]
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Vinay Kumar is currently with Mindtree Consulting, India and can be reached at [email protected]
Sedimentology and Stratigraphy of the Lower Cretaceous Viking Formation, Chigwell Field, Albert, Canada
No full textTitle: Sedimentology and Stratigraphy of the Lower Cretaceous Viking Formation, Chigwell Field, Albert, Canada, Author: Indraneel Raychaudhuri, Location: ThodeOngoing regional studies of the Viking Formation (Upper
Albian Stage, Lower Cretaceous) have revealed four regionally
extensive erosional bounding surfaces within the interval.
Examination of twenty-seven Viking cores from the Chigwell
field allowed the nature of the erosional surfaces to be
investigated. The examination of cores also permitted the
sequences of sediments between the erosional bounding
surfaces to be documented. Once documented in a series of
well log and core cross sections, an attempt to interpret the
nature and morphology of the erosional surfaces and the
sediments they envelope was made. The development of the erosion surfaces is problematic. It is suggested here that relative sea level fluctuations played
a major role in the formation of both the erosion surfaces
and the sediments found at Chigwell.ThesisBachelor of Science (BSc
Enhancement of Small Signal Stability in Power Systems: Novel Approaches
No full textThe modern power system is a highly nonlinear system that operates in a constantly changing environment. Power system, need to maintain more or less flat voltage profile across the grid and maintain stability for small and large disturbances. Traditionally, automatic voltage regulators (AVR) are used for voltage regulation and power system stabilizers (PSS) are used as auxiliary controllers in AVR to enhance the small signal stability of power system.
The conventional PSS design techniques require considerable expertise, full system information and extensive eigenvalue calculations, which increase the computational complexity with the increase in system size. The thesis proposes a novel approach to design a fixed parameter PSS utilizing only the local system information applicable for a wide range of operating and system conditions. The phase compensation requirements for a fixed parameter PSS significantly change with the generator loading and topology which degrades the PSS performance. The thesis proposes to augment a nonlinear gain to the existing static AVR structure so that the impact of the loading conditions is completely eliminated. It is shown that this modification produces a single phase-compensation curve for all loading levels which simplifies the PSS design and eliminates the PSS tuning requirements.
If the coupling between the voltage loop and the rotor angle loop is removed then the conflicting nature between them can be eliminated. This thesis shows that the rotor dynamics and voltage dynamics can be decoupled in a synchronous machine using a partial feedback linearization based nonlinear AVR. However, in such cases the damping is only dependent on the natural damping in the system. So, PSS is needed even in the case of a nonlinear AVR if the natural damping is insufficient. Consequently, a PSS design for a single machine infinite bus (SMIB) power system with the nonlinear AVR is proposed. The PSS design using local information is also extended to the nonlinear AVR scenario in a multi machine environment
Design Of Robust Power System Damping Controllers For Interconnected Power Systems
No full textSmall signal oscillation has been always a major concern in the operation of power systems. In a generator, the electromechanical coupling between the rotor and the rest of the system causes it to behave in a manner similar to a spring mass damper system, which exhibits an oscillatory behaviour around the equilibrium state, following any disturbance, such as sudden change in loads, fluctuations in the output of turbine and faults etc. The use of fast acting high gain AVRs and evolution of large interconnected power systems with transfer of bulk power across weak transmission links have further aggravated the problem of these low frequency oscillations. Small oscillations in the range of about 0.1Hz to 3.5Hz can persist for long periods, limiting the power transfer capability of the transmission lines. Power System Stabilizers (PSS’s) were developed as auxiliary controllers on the generators excitation system to produce additional damping by modulating the generator excitation voltage. Designing effective PSS for all operating conditions specially in large interconnected power systems still remains a difficult and challenging task.
The conventionally designed Power System Stabilizer (CPSS) is the most cost-effective electromechanical damping controller till date. However, continual changes in the operating condition and network parameters in large systems result in corresponding large changes in system dynamics. This constantly changing nature of power system makes the design of CPSS a difficult task. The design and tuning of PSS for robust operation is a laborious process. The existing PSS design techniques require considerable expertise, the complete system information and extensive eigenvalue calculations which increases the computational burden as the system size increases.
This thesis proposes a method for designing robust power system damping controllers that ensures a minimum robustness under model uncertainties. The minimum performance required for the PSS is set a priori and accomplished over a range of operating conditions.
A generalized robust controller design methodology has been first implemented on a Single Machine Infinite Bus (SMIB) power system model. The robust controller places the closed loop rotor modes of the system to the desire location while keeping the electrical modes intact. Unlike conventional lead/lag PSS design, the proposed PSS design is based on pole assignment technique which takes into account of various model uncertainties.
For the proposed stabilizer design in a multi-machine systems a new decentralized method has been used which requires system data only upto secondary bus of the unit transformer in a generating station. The proposed robust controller design based on modified Nevanlinna-Pick theory has been designed and tested extensively on SMIB and multi-machine systems to establish the efficacy of the controller in damping small signal oscillations.
The thesis is organized in four chapters as follows.
The first chapter discusses the basic concepts related to the rotor angle stability in power system. The conventional and other methods of countering this instability by power system stabilizers have been described. The relative merits of the various stabilization techniques have been discussed. The scope of present work, i.e design of decentralized robust power system controllers has been defined.
In second chapter a modified robust power system stabilizer for SMIB system is developed. It has been shown that under specific conditions the modified Nevanlinna-Pick theory can also be applied for designing damping controllers in system with lightly damped rotor modes.
Third chapter proposes a decentralized approach based on modified Nevanlinna-Pick theory for designing a power system stabilizer for interconnected power systems. The performance of the controller which is not based on external system information has been investigated on three widely used multi-machine test systems to established its efficacy in damping out low frequency oscillations.
The fourth chapter gives a brief summary of the work done and also includes a section on the scope of future work relating to design of power system stabilizers
Small Signal Stability Analysis of a Power System with a Grid Connected Wind Powered Permanent Magnet Synchronous Generator (PMSG)
No full textSmall signal oscillation has been always a major concern in the operation of power systems. In a generator, the electromechanical coupling between the rotor and the rest of the system causes it to behave in a manner similar to a spring mass damper system. Following any disturbance, such as sudden change in loads, actuations in the output of turbine and faults etc. it exhibits an oscillatory behaviour around the equilibrium state. The use of fast acting high gain AVRs and evolution of large interconnected power systems with transfer of bulk power across weak transmission links have further aggravated the problem of these low frequency oscillations. Small oscillations in the range of about 0.1Hz to 3.5Hz can persist for long periods, limiting the power transfer capability of the transmission lines. These oscillations can be reduced by incorporating auxiliary controllers on generator excitation system.
Power System Stabilizers (PSSs) were developed to produce additional damping by modulating the generator excitation voltage. Designing effective PSS for all operating conditions especially in large interconnected power systems still remains a difficult and challenging task.
More and more power electronic based controllers have been and will be used in power systems. Many of these controllers such as Static Var Compensators (SVCs), Static Synchronous Compensators (STATCOMs) and Unified Power Flow Controllers (UPFCs) etc., are incorporated in power transmission networks to improve its operational capability. In addition, some of the energy storage systems such as Battery Energy Storage systems (BESS), Super conducting Magnetic Energy Storage System (SMES) as well large non-conventional energy sources are also increasingly being integrated with the power grid. With large integration of these devices, there is a significant impact on system stability, more importantly on small signal oscillatory instability of the power system.
This thesis primarily focuses on impact of such devices on small signal oscillatory stability of the power systems. More specifically in this thesis small signal stability analysis of a Single Machine Infinite Bus (SMIB) system with a grid connected wind powered Permanent Magnet Synchronous Generator (PMSG) has been presented. A SMIB system has been purposely chosen so that general conclusions can be obtained on the behaviour of the embedded STATCOM/Energy Source (ES) system on system stability. With a better understanding of the impact of such a system it would be probably possible to analyze more complicated multimachine power system and their impact on system stability. Small signal model of the complete system which comprises the generator, transmission network, inter connecting STATCOM, the wind power generator and all associated controllers has been developed. The performances of the system following a small disturbance at various operating conditions have been analyzed.
To obtain quantitative estimates of the damping and synchronizing torques generated in the system, expressions for damping and synchronizing torque clients have been developed.
With these analyses, the relative impact of the STATCOM and STATCOM with ES on system performance have been assessed. It is shown that with active and reactive power modulation capabilities effective and efficient control of small signal oscillations in power systems can be achieved
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Essays in Financial Economics
No full textThis dissertation contains three essays in financial economics. The first essay shows that technology-driven innovations in credit markets have real and social implications. Using data from the largest online, peer-to-peer credit market in the United States, I find that borrowing increases when access to traditional credit is restricted, such as after bank mergers and natural disasters. Consequently, online borrowing moderates the diminished growth in business establishments and the heightened crime growth associated with credit scarcity. A percent increase in online lending offsets about 0.25% (0.22%) of the diminished establishment growth and 0.11% (0.18%) of the rise in crime associated with bank mergers (natural disasters). The effects are concentrated among small enterprises and property-related crimes. The second essay examines the impact of the visual representation of financial information on investors' decisions. Specifically, financial decisions are made in environments that involve color. However, perception of color influences behavior. We show that displaying losses in red reduces risk-taking. Presenting historical stock price paths in red reduces investors' expectations of returns and their propensities to purchase stocks. Salience effects alone do not drive the findings. The effects are not present in colorblind individuals and are muted in China, where red represents prosperity. Color also does not serve as an information-signaling mechanism. Rather, the findings are consistent with red causing "avoidance behavior." Overall, we draw from color psychology and visual science to further understand investors' behavior. The final essay shows that social factors impact households' financial decisions. Specifically, both experimental and field data suggest that exposure to social discrimination affects the risk perceptions and portfolio decisions of U.S. households. Experiments indicate that minorities perceive greater income risk. Minorities with relatively high risk perceptions are 10% less likely to invest. Discrimination further lowers the stock ownership of minorities by 2-5%. White heterosexual males exhibit no relations among perceived income risk, discrimination, and stock ownership. Results from field data support the experimental evidence, indicating that discrimination reduces stock ownership among minorities by 4-8%. The economic significance of socially-amplified risk perceptions is comparable to that of income and education.</p
Essays in Diversity and Behavioral Finance
No full textThis dissertation contains three essays in financial economics. The first essay examines whether financial market participants are able to assess the economic value of non-executive diversity. I construct a new measure of diversity among non-executive employees utilizing a large and unique resume-level dataset. Using this diversity measure, I find that non-executive diversity has a strong relation with longer-term corporate innovation and employee satisfaction, but it is unrelated to short-run financial performance. The market does not fully recognize the value of minority employees, potentially because it focuses more on tangible, short-term performance and pays relatively less attention on intangible, long-term human capital productivity. During the 1990 to 2021 period, a trading strategy that exploits this market misvaluation yields an annualized risk-adjusted return of over 7%. The second essay examines whether female sell-side equity analysts perform better in gender-supportive work environments, especially during economic downturns. While female analysts disproportionately exit the profession during economic downturns, their forecasting performance during recessions, as measured by forecast timeliness and thoroughness, is not as affected in gender-supportive brokerages. The third essay shows that diversity has diverse informational roles in financial markets. Focusing on racial/ethnic diversity among sell-side analysts, we find that informational habitats vary with race/ethnicity, which generate distinct forecasting styles.</p
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