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Experimental Investigation on Drilling and Welding of Engineering Materials using Laser
No full textConventional drilling of advanced engineering materials is extremely difficult because of occurrence of rapid tool wear and frequent tool breakage. Likewise, conventional welding processes poses difficulty in fabrication works made of engineering materials such as stainless steel, titanium alloy and shape memory alloy due to excessive heat generation causing high risk of contamination and distortion of weldment. Therefore, Light Amplification by Stimulated Emission of Radiation (laser) is gaining popularity for micro-drilling as well as welding because a high intensity heat source is applied at the precise location to achieve the desired output. The present study focusses on application of laser during micro-drilling and welding of similar/dissimilar materials. In order to gain insight into effect of process parameters on output measures during microdrilling and welding on thin foils of 0.5 mm thickness, extensive experimental investigation is performed using millisecond pulsed Nd:YAG laser. During micro-drilling, it is observed that spatter area and heat affected zone (HAZ) increase with increase in laser current and pulse width because increase in heat input causing more material to melt but sufficient time is not available for completely flushing away the molten material. As a result, heat is not properly dissipated resulting in increase in spatter formation and heat affected zone. It is also observed that increase in pulse frequency and gas pressure leads to decrease in spatter area because of formation of laser supported absorption (LSA) wave which blocks the input energy to penetrate adequately. During laser welding of similar materials, it is found that micro-hardness value in the fusion zone of the weldment is much higher than the base material during welding of stainless steel in comparison to welding of titanium alloy. This phenomenon may be attributed to higher cooling rate observed in case of stainless steel as compared to titanium alloy. Drilling of titanium alloy and stainless steel have potential application in manufacturing of medical implant, compressor blading in gas turbine, turbochargers and steam turbine valve seat. Similarly, welding of thin sheets has potential applications in automobile, razor blades, jet planes, electrical circuits and micro-electromechanical systems.
Artificial intelligence (AI) techniques such as adaptive neuro-fuzzy inference system (ANFIS) and multi-gene genetic programming (MGGP) are used to predict the performance measures such as circularity (at entry and exit), heat affected zone, spatter area and taper for laser drilling process. Similarly, artificial intelligence techniques are used for the prediction of performance measures like bead width, heat affected zone, surface roughness and welding strength during laser welding.
Comparative study of AI models suggests that MGGP predicts the performance measures in an effective manner as root mean square error (RMSE) for testing data is less as compared to ANFIS in both laser drilling and welding operations and can be potentially used for accurate prediction of desired output.
Welding of dissimilar materials such as nitinol, a shape memory alloy, with stainless steel and titanium alloy is one of the challenging tasks because of formation of brittle intermetallic compounds. Therefore, the study is further extended to find the feasibility of welding of nitinol with stainless steel and titanium alloy separately providing copper foil as interlayer during fibre laser welding. Analysis of physical and mechanical properties of the weldments reveals crack-free surface in the weld pool and less percentage of porosity. The study indicates that minimum tensile strength of the welded joint is more than the ultimate tensile strength of the weakest intermediate material i.e. copper. The study examines the possibility of using high melting point intermediate layer material during welding of nitinol with other materials to avoid formation of unwanted phases.
Feasibility of welding of titanium alloy with stainless steel sheets having five millimetre thickness using CO2 laser providing copper as interlayer using electroplating process is explored in this work. Presence of copper provides compatibility between titanium alloy and stainless steel during laser welding process and reduces brittle intermetallic compounds. The study suggests that the presence of interlayer during joining of dissimilar materials provides stable, crack-free and less brittle joints as compared to joining of dissimilar materials without interlayer. The study also examines the possibility of providing interlayer using coating technology during dissimilar metal joining. Welding of dissimilar engineering materials helps to provide hybrid system performance finding potential application in the field of various industrial applications like seismic damping device, petrochemical devices, aerospace equipment and medical equipmen
Perturbations of Cellular Model Membranes Induced by Membrane Interacting Model Peptide, Protein and Proteoliposome
No full textThe cell membrane interface constantly encounters a highly crowded environment of membrane interacting biomolecular entities present, extracellularly and intracellularly, that both influence as well as exploit the physicochemical properties of membrane to execute key cellular functions. This thesis is majorly focused on the perturbation of the cellular membranes induced by three physiologically important membrane interacting model biomolecular entities, namely - Nisin (an antimicrobial peptide), a Hepatitis E virus-like particle (a globular viral coat protein) and bacterial membrane vesicle (secreted by E. coli).
Nisin is a 34-amino acid residue long peptide known to inhibit Gram positive bacteria viability by interacting with lipid II lead to pore formation and restriction of cell wall synthesis. Our findings suggest that nisin can inhibit Gram positive B. subtilis and also Gram negative E. coli bacteria (lipid II deprived) in high concentration regime. Using experimental and molecular dynamics simulations, we shown that high concentration regime of nisin can non-specifically interact with phospholipids and deform membrane in a lipid-II independent manner mechanism that depends on surface density and degree of peptide oligomerization. Furthermore, we dissect the attenuating role of nisin on neuroblastoma cell growth as observed by MTT assay. The underlying mechanism of attenuation of cancer cell growth was due to fluidizing effect of nisin on cancer cell membrane verified by decrease in anisotropy and in-plane elasticity of cell membrane.
The second model biomolecule, a globular viral coat protein Hepatitis E virus like particle (HEV-LP) was chosen which infects liver cells and we focussed on the entry mechanism through hepatic cell membrane. The binding and passive entry of HEV-LPs in hepatic cell model membrane was confirmed by the fluorescence microscopy and observed significant change in dipole potential, membrane fluidity and non-ideal mixing with hepatic cell model membrane. Specifically, lipids containing anionic lipid headgroups i.e. DOPS, DOPG and Liver PI and DOPE critical for the binding and membrane internalization of HEV along with low cholesterol content in membrane. Together, our findings suggest that the changes in the host cell membrane mechanical properties induced by HEV-LP crowding might facilitate virus penetration through host cell membranes.
The third biomolecular model system was proteoliposome - bacterial membrane vesicles (MVs) secreted by E. coli which facilitate long-distance delivery of bacterial virulence factors crucial for pathogenicity. Whether MVs modulate the physicochemical properties of xv
the host lipid membrane remains unknown. We quantitatively show that MV interaction increases the fluidity, dipole potential and elasticity of a biologically relevant multi-component host model membrane. Such modulation is facilitated by the presence of lipids containing head-groups such as phosphatidylcholine, phosphatidylglycerol and phosphatidylinositol as well as a moderate acyl chain length of C16. While significant binding of MVs to the raft-like lipid membranes with phase separated regions of the membrane was observed, however, the elevated levels of cholesterol tend to hinder the interaction of MVs.
Together, this thesis attempts to understand a broader picture of how cellular membranes respond to perturbation induced by biomolecular entities of diverse shapes and biochemical nature that are often encountered by the biological membrane interface. We find that phase boundary conditions, line tension, negatively charged lipids are some of the common parameters that come into play during membrane interaction of structurally different biomolecules, further, degree of membrane perturbance may be dependent on the magnitude of molecular dipoles and curvature of the interacting biomolecules
Development of IoT-Based Real-Time Monitoring System and Prediction of Blast-Induced Ground Vibrations in Opencast Mines using Soft Computing Techniques
No full textBlasting is an economical and viable operation for reliable excavation of hard rock in mining and civil construction. An ambiguous ground vibration generated by blasting is unenviable and causes grievous damage to nearby inhabitants, residential premises, and other sensitive sites. Consequently, proper monitoring and prediction of ambiguous ground vibration is an indispensable prerequisite to pinpoint the safe limits in and around mines to reduce their hazardous effects. Currently, conventional monitoring systems (seismographs) are widely used to measure the ground vibrations purposes. The existing systems have few limitations such as expensive, need an expert to operate, tedious, and time-consuming process. To mitigate the flaws of existing system, in this work, designed and developed a real-time, economical, reliable, continuous monitoring wireless system with Internet of Things (IoT) technology for blast-induced ground vibration (BIGV) measurement. The recent proliferation of wireless sensor networks (WSNs) evolution into the IoT vision enables a variety of low-cost monitoring applications which allows a seamless transfer of information via embedded computing and network devices. As Micro-Electro-Mechanical-System (MEMS) based accelerometer sensors are becoming widely prevalent in vibration and condition monitoring applications.
Additionally, these sensors are integrated within a wireless sensor network (WSN) to allow monitored data to be transmitted wirelessly. The developed system was integrated with threeaxis, low-g, cost-effective ICM-20600 MEMS accelerometer and 32-bit ATSAMV71N21B microcontroller. In addition, a General Pocket Radio Service (GPRS) for SIM800C device was used as a radio frequency module and integrated to design an effective prototype. The experiment has been carried out by installing IoT prototype at Dungri limestone of ACC Limited, Bargarh, India, and twenty-two blast-events PPV was recorded at variable distances from blast source. The experiment results ensure that the Peak Particle Velocity (PPV) ranges from 0.081 to 2.94 mm/s at different monitoring locations. Similarly, in this study, to evaluate and predict the ambiguous PPV, seven conventional predictor models proposed by the United States Bureau of Mines (USBM), Ambraseys–Hendron, Langefors–Kihlstrom, General predictor, Ghosh–Daemen predictor, Central Mining Research Institute (CMRI) predictor, Bureau of Indian Standards, as well as Multiple Linear Regression (MLR), were applied and established a relation between PPV and its influencing parameters. The results were compared based on evaluation performance models such as Coefficient of Determination (R2), Mean Absolute Deviation (MAD), Root Mean Square Error (RMSE), and Normalized Root Mean Vii Square Error (NRMSE) between monitored and predicted values of PPV. The outcomes of empirical predictors exhibit that the MLR model yields significant R2 (0.86420), MAD (0.24122), NRMSE (0.23539), and less RMSE (0.28940) as compared to other conventional predictor equations. Although, empirical predictor models have two major flaws such as lack of generalizability and a limited number of input variables. Therefore, a study on the development of an alternative method of accurate PPV prediction using soft computing techniques was undertaken. An endeavor has been made in this research to apply three soft computing prediction models, namely, Feed-Forward Back Propagation Multilayer Perception (MLP) Neural Network, Radial Basis Function Neural Network (RBFNN), and Support Vector Machine (SVM). In this context, eleven input parameters such as number of holes, average top stemming, average spacing, average burden, average hole depth, hole diameter, maximum charge per delay, powder factor, total explosive, total depth, as well as absolute distance, and one output: PPV, was used and trained. The obtained results reveal that the RBFNN approach provides high R2 (0.99891), Accuracy (99.62956), MAD (0.00370), NRMSE (0.02287), and low RMSE (0.04897) among all other soft computing techniques and empirical predictor approaches for accurate prediction of blast-induced ground vibration. Hence, the RBFNN model yielded better performance as compared to the other prediction models to estimate the PPV
Investigation of Micro-drilling of Aerospace Materials: Modeling and Optimization
No full textMicro-drilling is an emerging substantial elimination process in the field of precision manufacturing sectors. So countless challenges are involved in the micro-drilling application for machining aerospace alloys. Moreover, the assisted knowledge of macro-scale machining may not be directly transferable into the micromachining domain. The application of the Micro drilling process is commonly utilized in aviation, marine and insistence because of quality, impervious consumption capacity to withstand a raised temperature. Micro-holes are built-in characteristics in dissimilar micro products. Conventional micro-drilling is having some distinct benefits over other processes. It is a more established process. It may be applied to any material regardless of whether electrically conducting or non-conducting. The main drawback is the less quality of micro-drill bits. There is a chance of accidental breakage of the drill bits. The different engineering process is applied to improve the strength of drill bits. Physical vapour deposition (PVD) coated carbide tools are used due to the more excellent friction less and anti-sticking properties of TiAlN coating. The micro-drilling parameters have been optimized using a design of experiment technique the drilling torque and thrust have been measured. Finite element analysis modelling has been carried out using DEFORM ® software to study the mechanism of chip-formation and to determine torque and thrust. In this work, Mechanical micro-drilling has been supported in aviation materials like Inconel 718 and aluminium alloy (AISI 6061) alloy. The study revealed the influence of the cutting speed, feed, and drill bit diameter on the workpiece surface-enhanced micro-drilling with relation to improved surface finish and decrease of thrust force and torque. Different optimization techniques are also applied for controlling the input process parameters Simulation method of modelling was also used to control torque, thrust, circularity, temperature distribution, and stress, in micro-drilling of Inconel 718 and aluminium alloy (AISI-6061). Several trails are to be booked for experiments conducted for validation of the simulated process. The simulated and experimental results are compared and the results are found to be having a good agreement
Microbial Strategies for Decolorization of Anthraquinone Based Dyes in Batch and Continuous Systems
Get PDFEnvironmental pollution and human exposure to dyes have increased significantly in recent years due to their growing use in industries like textiles, paints, plastics, paper, and tannery. The textile industry in India is regarded as one of the significant sources of toxic waste. The effluent produced from the textile industry generates large quantities of unfixed dyes that are generally present in wastewater that poses a potential environmental risk. The Physico-chemical effluent treatment strategies are ineffective in degrading the recalcitrant synthetic dyes completely from effluents due to their light and colorfastness, stability, and resistance to degradation. Dye decolorization by biological treatment methods has recently achieved popularity, as these are cost-effective, environmentally friendly and thus can be applied to a wide variety of dyes. The isolation of microorganisms from contaminated sites is thought to become more effective in treating both recalcitrant and xenobiotic pollutants because they have been acclimatized to the toxic effect of the contaminants. Therefore, it is significantly necessary to have a comprehensive knowledge of the biological treatment strategies and various factors required to accomplish the desired performance. In the first part of the study, ten morphologically distinguishable bacterial strains were isolated from the textile wastewater sample collected from textile processing units outlet and dye polluted soil with a high possibility of contamination by anthraquinone vat dyes. Three potential isolates significantly varied from the other seven isolates were selected for further studies based on their high tolerance and maximum decolorization efficacy. Based on the morphological and biochemical characterization, 16S rRNA analysis, the three strains were identified as Bacillus flexus TS8, Proteus mirabilis PMS, and Pseudomonas aeruginosa NCH and the 16S rRNA gene sequence was deposited in the NCBI Gene bank database. The pure bacterial strains were evaluated for decolorization of four model anthraquinone vat dyes (Indanthrene Blue RS, Vat Green 1, Vat Brown R, and Vat yellow 5G). The three strains were found to be tolerant of high dye concentrations resulting in maximum decolorization for all the four model dyes. The effect of various Physico-chemical parameters on decolorization efficiency of the isolated strains shown that alkaline pH, ambient temperature, shaking, or aerobic incubation condition favors the growth and decolorization ability of the microorganisms. The second, third, and fourth part of the research work focused on the decolorization of different anthraquinone vat dyes by isolated strains. Response surface methodology was applied for the optimization of the process parameters such as pH, temperature, and inoculum size. Degradation kinetic studies were carried out using three different models, like Michaelis-Menten, Lineweaver-Burk, and Eadie-Hofstee model. Decolorization was validated through UV-vis spectroscopy and FT-IR analysis. The fifth part of the study focuses on enhanced decolorization of anthraquinone vat dye Indanthrene Blue RS by a developed bacterial consortium-BP. The physicochemical parameters were optimized to attain maximum decolorization efficacy. The agricultural residual wastes were supplemented to increase the decolorization efficiency of consortium-BP. The oxidoreductive enzymes involved in the decolorization was studied extensively. The phytotoxicity study of the original dye and its degraded metabolites formed on mineralization by consortium-BP was performed. The final part of the study focuses on the biodegradation of simulated textile wastewater containing Indanthrene Blue RS dye in an immobilized continuous packed bed bioreactor using corn-cob biochar. The adsorption studies were performed without microbes to evaluate the adsorption efficiency in the removal of the dye. The kinetic parameters were evaluated by using linear plots of pseudo-first-order, pseudo-second-order kinetic models. The Langmuir and Freundlich isotherm model was studied at 30°C. During the continuous operation, the effect of flow rate, initial substrate concentration, inlet loading rate on the elimination capacity and removal efficiency of Indanthrene Blue RS in the bioreactor was studied. The overall results of this research work suggested that bacterial strains isolated from dye contaminated textile wastewater can be used for the degradation of organic contaminants in the environment. The information gained from the biodegradation process and the mechanisms involved in the degradation of reactive dyes provide better knowledge of the transformation of anthraquinone based dyes in the environment
Stabilization of Dispersive Soil Using Industrial by-Products
No full textDispersive soils are highly susceptible to erosion due to higher sodium content, and it deflocculates in the presence of flowing water. Under saturated conditions, the attractive forces are less than the repulsive forces, and this will help the particle to segregate and to move in suspension. In the earlier days, it was said clayey soils are non-erodible. But recently it was found some clayey soils with low-to-medium plasticity (CL and CL-CH) that contain montmorillonite have the tendency to erode. The erosion due to the dispersion of soil depends on mineralogy and clay chemistry and the dissolved salts in pore water. Dispersive soils contribute to the failure of many conservative practices. The stabilization of dispersive soils is very important for the success of many geotechnical projects all across the world. In this investigation, an attempt has been made to stabilize the dispersive soil with cement clinker, ground granulated blast furnace slag (GGBS) and flyash. Samples were prepared with the different predetermined proportions of dispersive soil, cement clinker, GGBS, and flyash to determine the strength and durability of the stabilized soils. Results of unconfined compressive strength (UCS) are found to be increased significantly by mixing additives in different proportions. From the results of the UCS tests, the optimum mix proportion was obtained with the mixing of 20% of flyash, 15% of GGBS and 30% of cement clinker in dispersive soil. Outcomes of this study suggest that the combined mixture of cement clinker, flyash, and GGBS are more effective to improve the strength than an alone mix. To evaluate the effect of freeze-thaw cycles and water immersion aging on the strength properties of different mix proportion, 0, 1, 3, 6, 9 and 12 cycles freeze-thaw tests and 32 days water immersion tests were done on cylindrical samples at 7, 14, 28, 60 and 90 days curing periods. A coefficient of strength loss/gain was also defined to determine the influence of freezing-thawing and water immersion aging on the durability of the mix proportion. The scanning electron microscope (SEM) and X-ray diffraction tests (XRD) divulge the changes in microstructure and the formation of hydrated particles play a vital role to enhance the strength because of the reaction between the soil and the additives. The UCS of dispersive soil stabilized with cement clinker, GGBS and flyash were modeled and predicted using Gaussian Process (GP), Artificial Neural Network (ANN), Random Forest (RF), M5P, Linear Regression (LR) and Adaptive Neuro-Fuzzy Inference System (ANFIS). Three statistical performance evaluation parameters such as coefficient of correlation (R), Mean Square Error (MSE) and Root Mean Squared Error (RMSE) were used to evaluate the performance of the above-developed models. Results obtained from this study suggest that the RF-based model is most suitable than other discussed models for the prediction of is most suitable for UCS, UCSFT, and UCSWIT. Sensitivity analysis is also carried out to find the most influencing parameter for the best-developed model
Simultaneous Production of Antimicrobial Agent (2- hydroxyacetohydrazide) and Phenol Degradation Via Microbial Technology
No full textToxic pollutants of varying anthropogenic sources have been showing adverse effects on growth and survival of biological systems. Microorganisms play a vital role in the biotransformation of these toxic pollutants to less complex chemical compounds which can be used in various industrial applications. These organisms have been evolved to degrade pollutants in different metabolic pathways, and some of them have adapted to consume these chemicals as either growth supplements or elemental sources. The identification and investigation of such organisms is a great challenge and will be beneficial for recycling of pollutants to useful products, thereby reducing the need for expensive substrates. Phenol degrading organisms were effectively isolated from petroleum-contaminated soil. Based on their resistivity to phenol up to 1500 mg l-1, the bacterial strains were isolated as R1, R2, R3, R4, and R5. Morphological studies showed that most of these organisms as Grampositive, rod-shaped, and aerobic. These five isolated organisms showed maximum similarity with Pseudomonas stutzeri NCG1, Bacillus flexus strain MS14-1, Bacillus thuringiensis strain 2PR56-10, Bacillus anthracis strain IHB B 18197, and Bacillus thuringiensis strain Bt 2 based on 16S rRNA sequencing. Preliminary experimental conditions such as pH, temperature, aeration, inoculum age, and inoculum volume were studied for maximum phenol degrading organisms along with the mixed culture. Under optimized conditions, Gram-negative P. stutzeri (Genbank Ac. No. MG230258) showed the maximum capability to degrade phenol up to 81.8% at 500 mg l-1 initial concentration within 84 h.
Moreover, phenol degradation by Pseudomonas stutzeri was optimized using response surface methodology (RSM) for various parameters viz. pH, temperature, phenol concentration, and yeast extract concentration. Optimized conditions of pH, temperature, and yeast extract concentration were used to determine the kinetic parameters of phenol degradation using various models. The analysis of kinetic data suggests that the Haldane substrate inhibitory model can be used to fit experimental data. Additionally, phenol tolerant Pseudomonas stutzeri produced cis, cis-muconic acid, which is a metabolic intermediate signifying the organism followed ortho pathway. Pseudomonas stutzeri also exhibited antimicrobial activity against Gram-positive bacteria like Bacillus cereus (MTCC 430), Bacillus subtilis (MTCC 1133), etc. The culture medium of Pseudomonas stutzeri containing various metabolites was analyzed using Gas chromatography-mass spectrometry (GCMS), and 2-hydroxyacetohydrazide (HAH) was found to be active antimicrobial substance in the culture medium after 72 h of fermentation. The organism P. stutzeri is capable of producing HAH in the culture medium supplemented with 500 mg l-1 of phenol.
The HAH was purified using silica gel column chromatography by subsequent collection of fractions, and the purified HAH was analyzed using Fourier transform infrared spectroscopy (FTIR). Additionally, the concentration of HAH present in the culture medium was assayed using HPLC and found to be 357 μg ml-1. The action of HAH against B. subtilis (MTCC 1133) was determined using tunneling electron microscopy (TEM) analysis. The minimum inhibitory concentration (MIC) of the HAH was found to be 40 μg ml-1 against B. subtilis (MTCC 1133). The optimum parameters for the production of HAH and degradation of phenol were determined using strain improvement techniques. The resultant strain obtained from strain improvement was employed in a 2-liter batch reactor for phenol degradation and HAH production simultaneously
Development and Characterization of Biopolymer-based Composite Edible Films with Antimicrobial Functionality
No full textThe modern food processing industry has undergone various changes during the past decade in terms of preservation and food safety. Novel preservation strategies such as innovative thermal processing, microwaves, irradiation, high-pressure, and pulsed electric fields have become more prevalent in the recent past. Though these techniques have demonstrated certain advantages such as reduced processing times and maintenance of food quality, several disadvantages are associated. For example, such processing technologies involve a high start-up cost which might be a hindrance for small-scale food processors. In addition, post-processing contamination of foods from spoilage and pathogenic microbes have also posed an increased threat within the food supply. Therefore, in order to maintain food quality and safety standards, alternative strategies need to be developed. One viable option is by the development of edible films. Edible films are prepared from biodegradable polymers and can be made functional by the addition of active ingredients such as antimicrobial agents. Therefore, the overall goal of this work is geared towards formulation and characterization of antimicrobial, composite, edible films from biodegradable polymers.
In the first part of the work, a biphasic edible film based on sago starch and guar gum was developed, and thereafter, two essential oils, namely, carvacrol (0.75% w/w) and citral (1.0% w/w) were impregnated either individually or in combination into the blend. The morphology, optical, structural, and water barrier properties of the films were evaluated by various analytical techniques. Scanning electron micrographs exhibited the roughness on the top surface of the essential oil-incorporated blend films, whereas the confocal microscopy confirmed the dispersibility of essential oils into the blend. The tensile strength of films significantly reduced and Young’s modulus increased when essential oils were incorporated. The sago starch/guar gum/essential oil films exhibited excellent antimicrobial activity against Bacillus cereus and Escherichia coli. These results indicate that essential oils have the potential as antimicrobial agents in sago starch/guar gum films for use as active packaging materials in the food applications.
The aim of the second part of the work was to formulate antimicrobial films of guar gum, sago starch, and whey protein isolate. The essential oils, namely, carvacrol, citral and their combination were used as the model antibacterial compounds. The films became darker and brownish in color due to the entrapment of the oils. The surface of oil-entrapped films were more rough and coarse. Confocal micrographs affirmed the uniform distribution of the oil droplets within the biopolymeric network. However, the film formulation containing combination of carvacrol and citral demonstrated the lowest WVTR, highest tensile strength, and Young’s modulus. All oil-containing films demonstrated strong antibacterial potency against both Bacillus cereus and Escherichia coli.
In the final section of the work, essential oil containing ternary films of chitosan, guar gum, and whey protein isolate were prepared. Eugenol, carvacrol, and citral were used as the oil phase, either alone or in combination. The addition of essential oils decreased the water vapor transmission rate and tensile strength of the films. CLSM confirmed the presence of essential oil droplets within the biopolymer matrix. The essential oil containing films showed good antimicrobial activity, suggesting potential application in food packagin
Molecular Dynamics Simulation Based Study for Creep Deformation Behaviour of Nanocrystalline Nickel and Nickel-Zirconium Alloys
No full textThis thesis is an investigation of high temperature mechanical properties of nanostructure materials using atomistic simulation. Atomistic simulations are useful methods and techniques for obtaining beneficial information related to the study of materials phenomenon. The original contribution of this thesis is to provide an understanding of deformation behaviour of ultrafine-grained nanocrystalline (NC) material during creep process. The underlying deformation mechanism is revealed by dynamic characterization of structural evolution for ultrafine-grained NC Ni and ultrafine-grained NC NiZr alloys during creep process under various operative temperatures and applied stresses. The study of deformation mechanism for ultrafine-grained NC materials (grain size less than ten nanometres) by experimentation is difficult to perform, as it is very expensive as well as time consuming. Molecular dynamics (MD) simulation is a reliable and effective tool to identify the underlying deformation mechanism at nano scale. In this thesis, MD simulation based investigations have been carried out for a set of six research problems, and the first five are directly associated with the creep of ultrafine-grained NC Ni and NiZr alloys and the sixth one is the stress-induced solid-state amorphization (SSA) of ultrafine-grained NC Ni and NiZr alloys under static loading.
Creep deformation of ultrafine-grained NC materials controlled by lattice or grain boundary diffusion mechanism depends on the temperature, applied stress, grain size, and structural materials. The first work of the thesis is the study of the effect of different types of defects on creep properties of nano-sized single crystal and ultrafine-grained NC Ni. The detailed explanation of the nature of the creep curve and the structural evolution has been presented. The second work of this thesis is the investigation of the influence of bimodal grain size distribution on creep properties of ultrafine-grained NC Ni. The study of healing mechanism of nanocrack in ultrafine-grained NC Ni during creep process is discussed in the third chapter of the thesis. The fourth work of this thesis involves the study of the influence of Zr addition (accomplished in two different ways i.e. GB segregation and randomly distributed fashion in the specimen) on creep properties for ultrafine-grained NC Ni. The fifth work of the thesis includes the investigation of structural evolution and deformation features at the interface of the joint between two ultrafine-grained NC metallic systems at high-temperature. The sixth one encompasses the study of stress-induced SSA of NC Ni and NiZr alloys.
The principal deformation mechanisms promoting the creep process are dislocation motion, grain boundary diffusion, grain boundary sliding, lattice diffusion and grain rotation. In NC materials, either the diffusional flow of atoms or dislocation motion or both the above mentioned types of creep mechanisms are involved during deformation. An extensive investigation for ultrafine-grained NC Ni and ultrafine-grained NC NiZr alloys has been performed to establish the creep mechanism at various applied stresses and temperatures. Coble creep mechanism is dominant for both ultrafine-grained NC Ni and ultrafine-grained NC NiZr alloys specimens, (with grain sizes 4 nm, 6 nm, 7 nm, 8 nm, and 10 nm) during creep deformation occurring at low stresses (i.e., 0.5 GPa to 1.5 GPa) and high temperatures (i.e., 900 K to 1609 K). The various aspects of nanostructure models including bimodal structure, crack healing, NiZr alloys (Zr added in two different fashions such as GB segregation and random distribution in the specimen) and interfacial study between ultrafine-grained NC Ni and ultrafine-grained NC Fe-Cr-Ni system have been carried out to explain the underlying mechanisms during creep deformation process at various applied stresses and temperatures. Significant improvement in creep resistance for bimodal ultrafine-grained NC Ni specimens is observed with the increasing grain size at moderate creep temperatures (i.e. 900 K to 1300 K). Furthermore, applied stress is found to be a dominant contributory factor for crack healing during creep process. The creep properties of ultrafine-grained NC NiZr alloys having segregated Zr atoms at GB is found to be superior as compared to that of both ultrafine-grained NC Ni and ultrafine-grained NC NiZr alloy having randomly distributed Zr atoms. The calculation of activation energy for creep process and self-diffusion process has been studied to explain the possible controlling mechanism as well as the effect of external applied load on activation energy for ultrafine-grained NC materials. The stress-induced SSA and structural evolution of ultrafine-grained NC Ni and NiZr alloys under static loading as well as its underlying mechanism have also been studied using MD simulations. It is found that SSA for ultrafine-grained NC Ni and NiZr alloys are possible when specimens are subjected to high hydrostatic state of stress.
Hence, it can be encapsulated from the MD simulation results that the creep properties for ultrafine-grained NC Ni/NiZr alloys can be significantly altered by the variations in grain size, defects, applied stresses, operative temperatures and nature of solute atoms distribution. The creep resistant properties are found to be notably enhanced with the increasing size of coarse grain in bimodal structure. From the entire work of this thesis, it can be elucidated that the deformation of creep of ultrafine-grain is found to be majorly controlled by the grain boundary diffusion (i.e. Coble creep mechanism)
Robust Active and Reactive Power Controllers for a Grid Connected Wind Energy Conversion System
No full textPermanent Magnet Synchronous Generator (PMSG) is widely used in a Wind energy Conversion System (WECS) due to its several advantages, such as gear less construction, high power density, less noise, high torque and ease of maintenance. The control objective for a PMSG based WECS is to regulate the active power extraction from the wind and at the same time to maintain the reactive power at zero value in order to achieve unity power factor operation of WECS. A number of control algorithms have been proposed in the past to control the active power and reactive power of WECS. However, a WECS is subjected to a large number of parametric uncertainties and external disturbances. Thus, it is necessary to negate the effect of parametric uncertainties and external disturbances appearing in the WECS dynamics in order to achieve satisfactory performance by designing suitable robust control algorithms.
A lot of research works have been directed to control the active power and reactive power of WECS. But parametric uncertainties greatly influence the active power and reactive power control performance in a WECS. Thus, challenges in designing suitable controllers for
regulating active power and reactive power of the WECS in face of parametric uncertainties and disturbances.
The thesis focuses on development of different robust control algorithms for a PMSG based grid connected WECS to control both reactive power in face of parametric uncertainties and disturbances. Since both the active power and reactive power of the PMSG are coupled with each other, hence it is necessary to design controllers such that the active power and reactive power can be controlled independently by appropriately decoupling the active power and reactive power control loops.
The thesis begins with development of a robust H∞ controller to regulate the active power and reactive power of PMSG based WECS delivered to the grid. The detailed design of the inner current control loop and the outer speed control loop are also presented. The H∞ based
robust controller for the PMSG is synthesized using MATLAB/Simulink. The performance of the proposed controller is first verified at nominal conditions of PMSG and then in the presence of the parametric uncertainties. To investigate the robustness of the proposed H∞ controller, stator resistance and stator inductance of the PMSG are varied and efficiency of the proposed H∞ controller in rejecting the effect of the external disturbance is also evaluated. The peak overshoot and the settling times of the active power response obtained by applying the proposed H∞
controller with the variation in these aforesaid parameters are compared. From the comparison, it is observed that the proposed controller is efficient in regulating the active power and reactive power of PMSG in face of parametric uncertainty and also able to reject the adverse effect of external disturbance in set point tracking.The efficiency of the proposed H∞ controller is also evaluated experimentally. Comparing the simulation and experimentation results it is concluded that the proposed H∞ controller effectively handles the parametric variation for setpoint tracking of active power and reactive power of WECS.
Although the proposed H∞ controller exhibits robust performance in regulating both the active power and reactive power but, the controller has some drawback i.e. the nominal performance of the WECS may slightly degrade. The design of this controller involves complex
mathematical calculations. Further, the designed H∞ controller is of high order and thus necessitates reduction of the order. Even though the proposed H∞ controller is able to reject the disturbance but the active power tracking performance is poor when disturbance is present. Moreover, the effect of the external disturbance needs to be attenuated faster than obtained with the proposed H∞ controller to minimize its adverse effect. In view of this,a Multi loop Active Disturbance Rejection Controller (MADRC) is designed to resolve the above limitations of the proposed H∞ controller. The basic idea behind designing the Active Disturbance Rejection Controller (ADRC) is to consider the internal dynamics, parametric uncertainties, the coupling term and the external disturbances as a lumped disturbance which can be estimated by designing an Extended State Observe (ESO). Subsequently, these lumped disturbances can be rejected by designing a suitable control law. The proposed MADRC is designed for speed control loop, d-axis current control loop and q-axis current control loop. The performance of the proposed MADRC is verified at nominal condition of PMSG from which it is observed that the peak overshoot and the settling time yielded by applying MADRC are less compared to the corresponding values obtained with the proposed H∞ controller. Also, the efficacy of the proposed controller is evaluated for variation of stator resistance and stator inductance of PMSG. For this, a step and variable wind speeds are applied to the WECS. From the obtained results it is observed that the MADRC regulates both the active power and reactive power under the aforesaid conditions effectively by generating suitable control actions. The performance of the proposed MADRC in active power and reactive power tracking in face of parametric uncertainties is also compared with the Single loop Active Disturbance rejection Controller (SADRC) by applying a step change in wind speed. On comparing the results, it is found that in the case of MADRC, the peak overshoot and settling time are less than that of SADRC in q-axis current and in active power responses of the PMSG. Further, the effectiveness of the proposed MADRC to reject the effect of the disturbance is verified by applying a step change in wind speed. From the result analysis, it is observed that the proposed MADRC is efficient to reject the external disturbance faster as compared to the H∞ controller. The adverse effect of the disturbance is less visible in terms of lower values peak overshoot yielded by MADRC as compared to the H∞ controller.
Although, the performance MADRC is satisfactory in active and reactive power tracking of WECS in the presence of parametric variation and external disturbances, there lie some drawbacks in this control scheme are as well. The exact estimation of the lumped disturbance by the ESO is difficult. Moreover, if the total disturbance is not constant, the estimation error in ESO may not converge to zero. Hence, to resolve this problem a Two Degree of Freedom Internal Model Controller based Active disturbance Rejection Controller (TDFIMC-ADRC) is designed. In TDFIMC-ADRC, the exact mathematical model of WECS is not required when designing a controller for WECS. In TDFIMC-ADRC, the ESO is omitted and a set point and a disturbance rejection filters are incorporated in this control scheme. Hence, the setpoint tracking and disturbance rejection are achieved in two individual decoupled control loop. The design of setpoint tracking and disturbance rejection filters for all the control loops (speed, d-axis current and q-axis current) is presented. With these filters, the proposed TDFIMC-ADRC is designed and then the performance of the proposed TDFIMC-ADRC is evaluated for active and reactive power tracking in a PMSG based WECS. The performance of the controller is verified at nominal condition of the PMSG and subsequently by varying Rs and Ls of PMSG. From the results analysis, it is observe that the proposed TDFIMC-ADRC exhibits superior performance i.e. yielded less peak overshoot and less settling time as compared to the corresponding values obtained with MADRC with a step change in wind speed and a variable change in wind speed. The efficacy of the proposed TDFIMC-ADRC controller to attenuate the adverse effect of the external disturbance is also studied. It is observed that the proposed TDFIMC-ADRC rejects the disturbance faster compared to the both H∞ controller and MADRC.
From the simulation and experimental results obtained when by applying all the above three proposed controllers, it is observed that these controllers exhibit robust performance for set point tracking of active power and reactive power of the PMSG based WECS. The performance indices such as peak overshoot and settling time in the active power and reactive
power responses obtained by applying the proposed three robust controllers are compared in the presence of the parametric uncertainty. From the comparative assessment, it is envisaged that the TDFIMC-ADRC exhibits superior performance amongst the three in face of parametric
uncertainties. The effect of the disturbance in the active power and reactive power tracking performance for all the proposed controller are compared. From this comparison, it is also observed that the TDFIMC-ADRC rejects the disturbance accurately and quickly compared
to both H∞ and MADRC. Moreover, the proposed TDFIMC-ADRC has simple structure and its implementation in both simulation and experiment becomes less complex as compared to both H∞ controller and MADRC for a PMSG based WECS in face of parametric uncertainties and external disturbances.Thus it is concluded for achieving robust active power and reactive power control performances when parametric uncertainties and external disturbances exist, the TDFIMC-ADRC is the best choice amongst all the proposed controllers described in the thesis