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Experimental and Numerical Investigation of Wind Induced Pressure on C-shaped Building Models
No full textWind induced forces are significant for buildings and therefore their impact on such structures is essientally required during their design and analysis. For analytical solution of the wind load, estimations of the wind pressure coefficients on its faces are the pre requisite. Generally, there are three primary methods which are used to estimate pressure coefficient: full-scale building tests, model test in wind tunnel and parametric equations derived from experiments. Buildings shapes are changing with emerging demands of several aesthetical features. Developments of new building materials and construction techniques have enabled us to build new building, which are tall and unsymmetrical (irregular) but unfortunately such structures are susceptible to more complex wind loads. Thus, it becomes necessary to estimate the wind loads with higher degree of confidence. Although ample information regarding wind load on symmetrical and regular structure is available in various international codes, but they lack the study of wind forces on unsymmetrical structures.
Literature provides some information on L, T, E, Y, N, Plus (+) and also on U-shaped building plans with flat surface only i.e., without curvature. Although, there are many C-shaped buildings that exist in real practice, no work has been reported for C-shaped building models with variation in curvature. Wind pressure on the structures is affected by its geometry, the nature of the corner (with or without curvature), incidence angle of wind and flow features. The present work focuses on the outcome of experimental investigation of mean pressure coefficients on different faces of C-shaped building models. Distribution of wind pressure coefficient on the surfaces of C-shaped buildings models (irregular plan) through numerical and physical modelling are attempted. Experiments have been carried out on the different C-shaped building models with and without corner curvature along considering some other variables such as the angle of incidence, side ratio, frontal ratio and aspect ratio in a subsonic open circuit wind tunnel. All the experiments have been carried out at the Aerodynamics laboratory of the Department of Aerospace Engineering, Indian Institute of Technology Kharagpur (IITKGP), India.
One way to accurately estimate the wind pressure coefficients on the surfaces of C-shaped building is their model testings in a wind tunnel. The building models were made of 5 mm thick Perspex sheets. Recorded data of pressure at the located pressure taping points enabled to determine the pressure coefficient variation on the surfaces with wind angles and corner curvature. It has been observed that the pressure coefficient at a location on a surface varies significantly with the angle of incidence and the curvature of the surfaces. Also, the extent of (xii)
maximum and minimum pressure zones, and their locations have been observed to change with the curvature and the wind direction.
This work also presents numerical analysis through Computational Fluid Dynamics (CFD) technique to calculate wind effect used C-shaped buildings with varying aspect ratio and its optimization caused by the alteration of angle of incidence of the wind forces ranging from 00 to 1800 at an interval of 300. Further, results obtained through numerical simulation have been validated with the corresponding experimental results. Numerical analysis has been carried out using ANSYS Fluent with k-ε model of turbulence. This suggests the applicability of this technique to predict the wind pressures on the surfaces of the prototype building more accurately.
Further, analytical equations are developed for determining surface mean pressure coefficient (̅̅̅) on the face of the building structures using relevant experimental data obtained from laboratoary experiments. Various data driven techniques or artificial intelligence techniques such as group method of data handling neural network (GMDH-NN), multivariate adaptive regression spline (MARS) and gene-expression programming (GEP) approach are used to develop model equations of surface mean pressure coefficient (̅̅̅) using the non-dimensional parameters such as the side ratio, height ratio, curvature ratio, and wind incidence angle. Influence of each parameter for predicting the surface mean pressure coefficient on the surfaces of different C-shaped building models by the developed equations are tested through sensitivity analysis. Performance of all the developed models are evaluated by means of various statistical measures such as coefficient of determination (R2), root-mean-square-error (RMSE), mean absolute error (MAE), the mean absolute percentage error (MAPE), coefficient of efficiency (E), Akaike Information Criterion (AIC), and Scatter index (SI) and uncertainty analysis to determine the best predictable model equation. These developed model equations through GMDH-NN, MARS and GEP approaches can be used as a practical tool for the prediction of surface mean pressure coefficient (̅̅̅) on the face of the prototype buildings
Robust and Adaptive Grid Synchronization Control of a Two Stage Grid-Connected Photovoltaic System
No full textIn view of supplementing power generation to meet increasing load demand while minimizing environmental pollution, more attention is currently given to use renewable power extraction for Photovoltaic (PV) and Wind energy conversion system. Amongst all the renewable power generation options, PV power generation is being considered as the most suitable one owing to the abundant availability of solar irradiance with pollution¬free operation. A PV system can be operated as standalone or grid connected modes. The thesis focuses on design, development, and practical realization of robust and adaptive control schemes for effective synchronization of a two¬stage three¬phase Grid Connected Photovoltaic System (GCPVS) to the utility grid. The PV power varies continuously during the day, and PV current and voltage characteristics depend upon the irradiation and ambient temperature, respectively. Therefore, to track this random variation in the Maximum Power Point Tracker (MPPT), adaptive MPPT algorithms is necessary on the PV side. On the grid side, the grid voltage distortions, corrupts the grid synchronization controllers. To resolve these issues, a robust controller needs to be designed. The thesis first designs a Adaptive MPPT controller to improve the Maximum Power Point (MPP) tracking performance. The classical MPPT controllers such as P&O has fixed step size, and its MPP tracking performance is influenced by predefined parameters such as perturbation size, sampling time and initial duty ratio. Therefore, fast tracking of the MPP through these MPPT algorithms is difficult. To resolve these issues, a PI controller is employed to generate a variable step size duty ratio, to improve the tracking performance of this proposed Improved Adaptive Perturbed and Observed (IAPO) MPPT algorithm. In this algorithm, the step size is varied based on the PV power variation, which is embedded as an adaptive feature to a PI controller. This adaptive feature results in fast tracking of the MPP even during transients, less oscillations of DC link voltage during steady state, and least dependence on predefined parameters such as initial duty ratio. Subsequently, to achieve current control for synchronization, an Integral Sliding Mode Controller (ISMC) is designed in which issues regarding the harmonics in the grid injected current is reduced. The classical PI current controller performance deteriorates due to grid voltage distortions and hence there is a need to employ harmonic suppression schemes. But, this slows down the current controller dynamics. Whereas, the ISMC aids in achieving faster dynamics in face of modeling and parametric uncertainties. It also suppresses the harmonics in the injected grid current despite the presence of high Total Harmonic Distrotion (THD) vii content in the grid voltage. It is also found to have excellent decoupling of the cross coupling terms and provide independent control of active and reactive current. The ISMC based current controller is then integrated with the IAPO MPPT algorithm for a two stage GCPVS. Its performance is then compared with other control schemes, namely, SMC¬IAPO and PI¬IAPO control schemes. The comparison envisages that with ISMC¬IAPO control approach, the performance of the overall system improves, and this control strategy does provide faster dynamics despite rapid variations in the PV power, uncertainties owing to modeling and parametric variations in the PV system and grid disturbances. It is also found that this ISMC¬IAPO approach gives the best quality current in comparison to ISMC¬P&O, SMC¬IAPO, and PI¬IAPO. The robust performance of the ISMC is then evaluated in grid fault situations where a Vector Current Control with Feedforward (VCCF) control strategy is employed in the control of two stage GCPVS to deliver balanced three phase currents to the gird. The control of two stage GCPVS in the Low Voltage Ride Through (LVRT) situation becomes a real challenge. It is because the control operation needs to regulate the DC link voltage at its nominal value. Therefore, to transfer the reactive power, the PV panel is operated in the de¬rated mode of operation. This is only possible if MPPT operation is halted and boost converter is operated in constant duty ratio mode. This new duty ratio and reactive current reference are calculated based on the percentage of voltage dips. The ISMC based VCCF strategy is evaluated in the three phase symmetrical and two phase unsymmetrical fault. The ISMC provides both active and reactive current to the grid. The ISMC is compared with a PI controller based VCCF strategy and found to have good performance in damping the inrush currents that arise in the event of fault occurrence and fault clearance. All these control algorithms are simulated in MATLAB/Simulink environment followed real-time implementations on a prototype PV system. A prototype of 2 kW PV system is developed in the laboratory. The aforesaid grid synchronization algorithms were then implemented and verified in real-time on the prototype GCPVS, and results obtained are analyzed
Mitigating Challenges in Image Source Attribution through Digital Forensics
Get PDFThe study, analysis and investigation of digital evidences in relation to cybercrime investigation, constitutes the branch of science known as digital forensics. In today’s forensic world, images collected from electronic devices related to a crime scene are proven to be extremely useful elements in forensic investigations, and to trace perpetrators related to crime scenes. Digital images play a major role in forensic investigations today, and act as the primary elements to establish legal evidences. Mapping a contentious image correctly to its source of origin, hence attribution of an image collected from crime scene to a suspect’s device, is a crucial aspect of digital forensic investigation.
In this research, we focus on the problem of source camera identification in digital image forensics. In the forensic image source identification problem, the task at hand is to associate an image under question to a suspect’s camera, thus incriminating the suspect correctly. This is known as image source verification which answers the question of whether a particular camera device has indeed captured the query image. However, practically it may not always be feasible to obtain physical access to the devices owned by every suspect. In such cases, the traditional source verification mechanisms fail, and it becomes even more challenging to identify the correct image source (device make and model). In this thesis, we address the major present-day challenges associated with forensic source camera identification, aimed towards solving the practical problems encountered by a forensic analyst during image source attribution.
In this thesis, we also investigate the biggest threat to state-of-the-art forensic source attribution techniques, which is constituted of counter-forensic attacks on digital images. We propose efficient measures to distinctly identify counter-forensic images, as well as the class of attack that they have undergone, while accurately mapping such images back to their correct sources
Ti-6Al-4V alloy weld joint by variant of TIG welding method: Characterization and mechanical performance evaluation
No full textTi-6Al-4V alloy is an advance engineering material with excellent mechanical and metallurgical characteristic. However, joining of Ti-6Al-4V alloy by fusion welding methods has always been challenging because of its high affinity towards oxygen and nitrogen above 550 °C temperature. Therefore, shielding of weld pool during and after the welding process becomes essential for joining of Ti-6Al-4V alloy. In this work, autogenous butt weld joint of 3 mm thick Ti-6Al-4V alloy plate was performed by different variant of TIG welding, i.e., conventional TIG welding, pulse TIG welding and activated TIG welding methods with the aid of in-house fabricated shielding arrangements. The mechanical and metallurgical properties of the weld joints were analyzed through various characterization techniques and mechanical testing. The analysis of the weld bead geometry and microstructure was executed through optical microscopy and identification of metallurgical phase transformation, assessment of residual stress generated due to spatial thermal gradient and the texture evolution in the weldment were performed by X-ray diffraction (XRD) technique. The micro-hardness values of the weld joints at different locations were measured through Vickers micro indentation method. The tensile and flexural properties of the weld joints were analyzed through universal testing machine and the fracture surfaces were evaluated through scanning electron microscopy (SEM).
The experimental analysis revealed that with the use of pulse current, and TiO2 activated flux during TIG welding the mechanical properties of the weld joint improved significantly, which affirms that the proposed methods with appropriate parametric conditions can be adopted for industrial application of Ti-6Al-4V alloy
Utilization of Industrial Solid Wastes for Synthesis of Inorganic Polymer as a Soil Stabilizer
No full textSoils need to be stabilized to improve its geo-engineering properties before any construction of infrastructures. Conventional soil stabilizers such as cement and lime have environmental issues and uneconomical. Geopolymers are the new generation binder that has attracted considerable interest in modern construction industries due to their high engineering performance, less environmental impacts and cost-effectiveness. An investigation is made to explore the efficacy of geopolymer prepared by sodium hydroxide activated fly ash-slag in stabilizing the granular soil through a set of experimental studies.
The physical, mechanical and chemical properties of geopolymers are greatly influenced by the synthesis parameters. The fresh and hardened properties such as normal consistency, setting time, soundness, drying shrinkage, flow and compressive strength of the geopolymer paste and mortar are reported. The influence of synthesis parameters on the unconfined compressive strength of the geopolymer; synthesized under different processing conditions is investigated. The microstructural analysis is also made to correlate the reaction products with the observed strength. Statistical analyses are carried out to check the significance of the factors affecting the synthesis process. Also, mathematical relationships are established for factors influencing the mechanical behavior of the synthesized geopolymer. The compaction characteristics, unconfined compressive strength, bearing resistance, permeability characteristics, durability under wetting-drying, freezing thawing cycles and decay under chemical attacks of geopolymer modified granular soil are investigated experimentally in order to assess its suitability as a geotechnical construction material. Also, the effect of delayed compaction on density and strength has also been studied. Microstructural analysis has been carried out and correlated with the strength development.
The test results reveal that the dissolution of alumino-silicates is highly influenced by the alkali content and the reactive component of the source material. The experimental results indicated that the physico-mechanical properties of geopolymer binders are similar to that of conventional cement and are greatly influenced by the composition of the source material, concentration of the activator and processing conditions. The major reaction products were the hydrates of calcium and/or sodium based alumino-silicates and those were intensified with curing temperature and duration. Raw materials are optimized by the design of experiment and the fitted model shows a good relation with the experimental data. Based on the test results of geopolymer stabilized soil, a maximum unconfined compressive strength of about 7 MPa is attained. California bearing ratio ranging from 52 to 416% are obtained at different geopolymer contents and curing conditions. The geopolymer stabilized granular soil showed excellent stability against repeated wetting-drying, freezing-thawing cycles, slaking fluid and aggressive chemical environment. The microstructural developments in geopolymer stabilized granular soil are greatly influenced by the geopolymer content and curing period signifying the formation of hydration and geopolymeric reaction products
Performance Evaluation of Bentonite Embedded Pond Ash as Landfill Liner
No full textRapid urbanization and growth in population are key reasons for a massive increase in generation of solid wastes. This is becoming a major environmental concern. Landfilling is an extensively accepted practice for disposal of solid wastes. Conventionally, clay is used as a landfill liner due to its cost-effectiveness, high stability, and self-healing ability. The lack of suitable clay at a site often triggers the use of bentonite based materials as a substitute to since it is highly colloidal in nature with expanding lattice structure having high adsorption capacity and low hydraulic conductivity. However, compacted clays with higher bentonitic contents undergo extensive changes in properties when exposed to freeze-thaw or shrink-swell cycling. The problems associated with higher volume change and developments of cracks are found to be minimized by the addition of a substantial amount of non-swelling coarser fraction. Typically, soil-bentonite, sand-bentonite, zeolite-bentonite, etc. are used as an alternative liner material for waste disposal facilities. However, the scarcity of natural soil encourages the use of alternate materials as landfill liners.
In this context, the present research work focuses on assessing the suitability of pond ash-bentonite (PAB) mixture as an alternative to sand-bentonite (SB) mixture for liner material. As the coarse fraction of pond ash resembles natural sand in terms of gradation with higher interlocking and frictional properties, there is a potential for utilization of the coarser fraction of pond ash as a substitute to sand. The performance of the PAB mixtures is accessed by examining their physicochemical and hydro-mechanical properties. The physicochemical properties considered comprised of gradation, particle shape parameters, consistency limits, free swell index and cation exchange capacity, and the hydro-mechanical properties considered include unconfined compressive strength, shear strength parameters, hydraulic conductivity, compressibility and volumetric shrinkage characteristics. A comparative assessment is made between SB and PAB mixtures for a range of bentonite content varying from 0 to 30% by weight at an interval of 5% to ensure an effective substitution of sand with pond ash. The optimized bentonite contents are determined by examining the relevant properties of compacted PAB and SB mixtures as per the USEPA (1988) regulatory for liner material. Influential parameters such as clay content, molding water content, fibre content, and chemical environment on strength, durability, hydraulic and microstructural characteristics of PAB and SB mixtures have also been investigated.
The experimental results reveal that the addition of bentonite to sand or pond ash significantly influences the plasticity, strength, compressibility, permeability, and volumetric shrinkage properties. At comparable conditions, compacted PAB mixtures exhibit higher unconfined viii compressive strength (UCS), cohesion, frictional angle, hydraulic conductivity, and lower volumetric shrinkage than SB mixtures. Both PAB and SB mixtures met the liner requirements as per USEPA (1988) regulatory when compacted with modified Proctor energy at a minimum bentonite content of 20% and 15% respectively. Compression index (Cc) of the mixtures is found to maintain a linear relationship with liquid limit. Empirical equations have been developed to estimate the Cc and hydraulic conductivity of bentonite-based liner material from the basic parameters of the mixtures which have been compared and validated with existing corelations and experimental datasets. The compressive strength, failure strain, unit cohesion, and frictional angle of the compacted specimens are found to increase whereas the volumetric shrinkage strains are decreased with an increase in fibre content irrespective of the molding water content. With an addition of 1% Recron-3S polypropylene fibre, the UCS values are found to increase by 2 to 3 times as compared to those of unreinforced specimen. Both unreinforced and reinforced specimens exhibit the maximum UCS value at relative water content of 90% and 80% when compacted to standard and modified Proctor density respectively. Reinforced specimens compacted at dry of optimum did not show any significant variation in hydraulic conductivity whereas specimens compacted at wet of optimum exhibit an increased value of hydraulic conductivity with fibre content. The increase in volumetric shrinkage strain with relative water content is reduced as the fibre content increases. Furthermore, alternate freeze-thaw cycles are found to have a significant influence on volume, moisture content, unit weight, UCS, and hydraulic conductivity of the compacted mixtures. The changes in these properties are found to be stabilized after 10 freeze-thaw cycles. The rate of increment in hydraulic conductivity and reduction in compressive strength of compacted SB mixes are higher than those of compacted PAB mixes. Specimens compacted at dry of optimum exhibit lower reduction in compressive strength than those compacted at wet of optimum. In contrast, specimens compacted at dry of optimum show lower increment in hydraulic conductivity than those compacted at wet of optimum. The study on the effects of chemical environment on the engineering properties of PAB and SB mixtures reveals that the consistency limits, free swell indices, and volumetric shrinkage strain are reduced whereas the hydraulic conductivity increased as the concentration of salt solutions and their permeation time is increased. The UCS values are found to increase with the permeation of lower concentration of salt solutions and the same reduces substantially with further increase of concentration. Salt solutions of polyvalent cations are found to have more impact than those of monovalent cations. PAB specimens are less vulnerable to these changes as compared to those of SB specimens. The sorption concentrations of permeating cations are found to increase substantially in the liner materials with an increase of salt concentration and their permeation time, whereas the concentrations of inherently adsorbed elements decreased. The observed variations in the said ix properties associated with the influential parameters are correlated to the shape of coarse fraction particle and the corresponding microstructural arrangements of the compacted specimens.
Although, PAB mixtures experience marginally higher hydraulic conductivity than those of SB mixtures, the mixtures possess higher CEC, improved strength and lower volumetric shrinkage strain at a particular bentonite content and compactive effort. Further the engineering properties of PAB mixtures are less susceptible to adverse environmental conditions than SB mixtures. The use of pond ash as a coarse fractioned element in bentonite-based liner material will provide a greater avenue for its utilization as well as the preservation of the natural resource
Numerical and Experimental Analysis of Cryogenic Turboexpander
No full textCryogenic turboexpander is a device that is used for refrigeration and liquefaction cycles of various gases. The nozzle and radial inflow turbine are the critical components of such systems, and its performance has a significant effect on the overall efficiency of the system. Therefore, an optimum design procedure of such components is necessary to provide the maximum thermal efficiency and better cooling capacity.
In the present study, the design methodology of a non-axisymmetric convergent nozzle using a curve-fitting approach is proposed. The curves used for designing the nozzle are based on a combination of fifth and third-order polynomial at upper and lower surfaces respectively. Numerical simulations are conducted to visualize the fluid flow and thermal characteristics for two cryogenic fluids, nitrogen and helium at three different inlet pressure and temperature using computational fluid dynamics (CFD) tool ANSYS CFX®. Numerical results are further validated for medium and low-pressure helium by comparing it with the available experimental data.
After design of a convergent nozzle, an effective one-dimensional design methodology of a radial inflow turbine by considering different loss correlations is presented using nitrogen as a working fluid. A Sobol sensitivity analysis is carried out to determine the sensitivity index of major non-dimensional design variables, which have a significant effect on efficiency and total loss of the turbine. The optimal range of important non-dimensional variables such as blade speed ratio, pressure ratio, ratio of hub and shroud radius to turbine inlet radius are predicted using artificial intelligence techniques. This approach improves the turbine efficiency and power output by 4.00% and 18.90% respectively as compared to the existing model developed at NIT Rourkela. The three-dimensional numerical simulations are carried out to investigate the fluid flow, thermal characteristics, and critical properties that are extremely difficult to determine experimentally at different cryogenic temperatures.The obtained numerical results are validated with the experimental results.
The design procedure of nitrogen turboexpander is extended for high and low-pressure (16 and 4.5 bar) inlet fluids at different operating temperatures. The various losses obtained during the design process are discussed in detail. After that, a comparative numerical analysis is performed to visualize the effect of fluid flow and thermal performance at different spans and streamwise location of a nitrogen turboexpander.
The one-dimensional design is further extended for a helium turbine, where the optimal range of themost significant non-dimensional variables is identified through sensitivity analysis and artificial intelligence methods. Based on this approach, three turbines and nozzle (turboexpander) systems are designed for three operating conditions (high, medium, and low pressure). After that, a comparative numerical analysis is carried out to visualize the flow field and thermal performance of helium turboexpander at three different operating pressure and temperature. Furthermore, the numerical results are validated with the available experimental and numerical data from the literature. The variation of Mach number, Reynolds number, Prandtl number, static entropy, static enthalpy, temperature, and pressure inside the turboexpander are characterized at different spans and streamwise locations. The study also demonstrates the flow separation region, vortex formation, tip leakage flow, secondary losses, and its reasons along with the spanwise location.
Finally, the experimental test-rig is developed to understand the thermal performance of a nitrogen turboexpander at different operating pressure (6 −8 bar), rotational speed (60,914−120,529 rpm), inlet temperature (150−120 K), and mass flow rate (0.01−0.09 kg/s). The experimental results are presented to examine the isentropic efficiency, temperature drop, enthalpy drop, and power output of the turboexpander at different mass flow rate, rotational speed, and pressure ratio. The maximum temperature and enthalpy drops are 29.46 K and 34.5 kJ/kg respectively which is obtained for case 1 at a rotational speed of 119,614 rpm (75% of the designed rotational speed) and the mass flow rate of 0.08 kg/s and pressure ratio of 3.85. Based on the experimental data, an artificial intelligence model is developed to predict the optimal range in which the turboexpander has maximum isentropic efficiency and temperature drop. Also, the error analysis is carried out to measure the effectiveness of experimental parameter
Financial Integration of Corporate Bond Markets in India: Empirical Evidences
Get PDFConsidering the background of the global debt markets and India‗s competitive position, this research thesis assesses the state of the corporate bond markets in India and attempts to derive specific findings on the nature of its functioning. The macro-economic drivers of Corporate Bond Market along with the factors constraining development of Indian corporate bond markets are also determined. We have also highlighted a few models for the Corporate Bond Market as well as conducted yield estimation of bond portfolios and studied investor sentiments and its impact on integrated markets. This study has made an attempt to identify critical determinants and summarise isssues in the pricing of corporate bonds in India.
There are numerous studies which have identified the influence of macro factors on the capital markets, equity market and other financial markets. However, little attention has been drawn on its influence on the corporate bond market. Investor sentiment is a hugely researched area in behavioural finance but studies related to the impact of investor sentiment on corporate bond market participation are rare in global context and fewer in Indian context. The literature related to ratings led to the conclusion that there had existed few studies related to debt markets in general, but not many such were found to be related for corporate debts in the Indian context. Likewise, there have been a lot of studies on financial integration of equity markets to other domestic market segments or global peer markets, but only limited numbers of studies have focussed on financial integration of the corporate bond market in Indian context. This research study will try to plug holes in existing literature through the following objectives.
1. To study the development of the market of corporate bonds in India with special reference to current status and future challenges.
2. To examine the influence of macro-economic factors and related institutional factors on the corporate bond market in India.
3. To explore the antecedents influencing investor sentiment and to propose and validate a comprehensive empirical model in Indian corporate bond market.
4. To determine the premium of corporate bonds using idiosyncratic and liquidity factors, by presenting a simple, transparent and auditable model.
5. To estimate the yield of corporate bonds with respect to Liquidity conditions as a case for financial market integration.
The study reveals that foreign exchange reserve is important among the selected macroeconomic variables which affects the corporate bond market. Regarding Investor sentiment in the Corporate bond market, the results of this research affirm that market infrastructure, regulatory policy, risk appetite, and policy incentives significantly drive investor sentiment.
This study also dwells upon an important issue of arriving at the liquidity premium of corporate bonds are not easy to compute on account of the issues with liquidity of more than few corporate bonds. This section presents a simple, transparent and auditable model of the term structure of corporate bonds. The classic dynamic Nelson-Siegel method implemented by Diebold and Li (2012) is compared with our approach which is adaptive, parsimonious, simple and scalable. We find ratios of liquidity can explain the spread over 3.67 times more than an investment rating of corporate bonds, as compared to Li et al. (2016) who report the liquidity spread as 1/4th the spread for investment-grade bonds. This approach can enable practitioners to fit a yield curve to observed rates and produce a satisfactory curve. We also assessed the current level of integration using multiple regressions and error correction. The data include daily traded bonds reported in FIMMDA and NSE archives during a fifteen year period from January 1999 to December 2014. We found a significant bond yield with instruments of other markets such as domestic credit markets, money markets, and external credit markets. We also find relatively lower degrees with forex markets and no relationship with any of the commodity or economic indicators.
The study concludes that the bond markets in India continue to face the challenges of genuine and active invetor interests. Although, the importance of a deep and liquid market has been realized the response of participants has not been significant. Numerous policy initiatives to reduce the dominance of bank lending in the economy to the corporates has failed to desisit firms to seek bonds instead of primary debt
Estimation of Low-Frequency Oscillations Using Wide-Area Monitoring in Power System
No full textThe presence of high gain excitation system causes Low Frequency Oscillations (LFOs) in the interconnected power system, which leads the system contingencies and operative with stressed conditions. Traditional, model base off-line approaches utilized Small Signal Stability Analysis (SSSA) to linearized the non-linear power system, which involve computational complexity as well as large computational time. The real time LFOs detection and mode estimation is not possible using SSSA. Moreover, in the conventional Supervisory Control Data Acquisition/ Energy Management System (SCADA/EMS), these methods utilize the result of the state estimators, which at present, are run at a periodicity of few minutes. Besides, the data scan rate of the SCADA system is of the order of 2-10 sec. The slow refreshing rate of the SCADA/EMS system limits its application in on-line stability analysis. To improve the power system mode estimation by providing the synchronized and GPS time-stamped phasor data with higher refreshing rate a synchrophasor based Wide Area Monitoring Systems (WAMSs) is being developed.
The methods available in the literature, for identification of low frequency critical modes under small disturbances, are broadly classified into the ambient data and ringdown or probing data based methods. The methods, which utilize ambient data, require a time window of about 10-20 minutes and are not much accurate at estimating the damping of the modes, whereas, the methods based on the ringdown or probing data, are more accurate and require small time window of about 8-20 sec for the estimation of the low frequency modes. Most of the work on the use of ringdown data have assumed that the low frequency oscillations can be modeled as summation of the complex exponentials. Prony method and its variants have been widely applied in the literature to estimate these modes, but these methods are sensitive towards the presence of the noise. Most of these methods have used linear regression approach to estimate the modes, whereas the actual estimation problem can be formulated as non-linear least square regression problem. Also the sensitivity of these methods towards the presence of colored Gaussian noise has not been considered in the literature. Since the power system also experiences large disturbances, such as fault or outage of a major generating plant, it is important to predict the transient stability and the stability margin of the system in real time. The Phasor Measurement Units (PMUs), forming a part of the synchrophasor based WAMS, can estimate generator rotor angle in real-time for predicting the angular stability of the power system. Repeated off-line simulations are performed to get the critical clearing time, considered as one of the measures of the transient stability margin. However, the time required by these methods is considerably high and also, sometimes, have the problem of numerical instability. The above limitations have resulted in the development of energy function based direct method of stability analysis.
Recently, neural network based methods have been suggested for the on-line stability prediction utilizing synchrophasor measurements, but these methods also face the problem of insufficient training due to non availability of enough real time data. Because of the certain limitations of the existing methods, as discussed above, in the design of the low-frequency mode estimator, the small-signal and the transient stability prediction, the main objectives behind the research work carried out to develop an estimators, which can accurately estimate the low-frequency modes of oscillation in the presence of Additive White Gaussian Noise (AWGN) and Additive Colored Gaussian Noise (ACGN). The real-time execution of the estimator can be achieved by using an adaptive filtering approach based on Least Mean Squares Sign-Data(LMSSD) algorithm. This approach not only helps to reduce the noise but also helps to retain the information within the permissible limit. In addition, a more reliable estimator based on signal subspace approach i.e.
Karhunen-Loeve Transform (KLT) is proposed, which not only provided the accuracy in estimation of the low frequency oscillating modes of the power system by completely decorrelate the signal from the noise also maximally compact the information contained in the signal. KLT defines a new axis of reference to present the signal subspace and further, this signal subspace is processed to obtain the low-frequency oscillating modes of the power system Estimation of Signal Parameter using Rotational invariance technique (ESPRIT).
To improve the performance of the above estimator for a signal having low SNRs i.e. 5dB and 0.5dB a Hample filter (HF) is utilized. The signal filtered by using HF is further processed using Modified Karhunen-Loeve Transform (MKLT) to achieve final variance by differentiating the dominant eigenvalue of the auto-covariance matrix with respect to final instant "N". To develop an estimator that can work in a real-time environment quite nicely with less computational complicity and can be applicable to a large power system in both ambient and ring down conditions.
The thesis emphasizes on developing various robust mode estimation techniques for a small and large interconnected power system at different real-time conditions such as short circuit fault and sudden load removable. Therefore, when there are outliers and high noise interruption, the KLT-TLS-ESPRIT is the best choice among all the proposed estimation algorithms mentioned in the thesis to achieve robust effective LFO modes estimation in power system
Rational Design, Synthesis, Photophysical and Electroluminescence Study of Organic Fluorophores for Blue Organic Light Emitting Diodes
No full textThe present thesis works deals with molecular designing and synthesis of novel class of bipolar blue organic molecules and explores the possibility of using the same in blue Organic light emitting diodes (OLEDs) and white OLEDs. In chapter 1, a general overview of the development of new-generation optical phenanthroimidazole based fluorophores: introduction, literature survey of recent trends and brief objectives of the present thesis work was discussed. In the introduction, the main focus was enlighten on the design and synthesis of phenanthroimidazole based blue fluorescent materials and their applications in blue OLEDs. The main aim and importance of the proposed work of the thesis was summarized in this chapter