Ph.D.

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Analysis of Soft Ground Reinforced by Columnar Inclusions
(Saga University, Saga, Japan, 1996-03) Alamgir, Muhammed; Miura, Prof. Norihiko
A general method of analysis to solve an important class of problems encountered in the field of geotechnical engineering is developed in this dissertation. The analysis is formulated from the fundamental equation of equilibrium. It leads to develop a simple integro-differential equation to characterize the overall behaviour of the system. The behaviour of rigid columns (e.g. concrete/timber piles, lime/cement columns), deformable columns (e.g. stone columns/granular piles, sand compaction piles), pile groups, pile-raft foundations are the type of situations that can be analyzed by the proposed method. A numerical scheme using finite difference method is proposed to solve the governing equation with the aid of the. Relevant boundary conditions. A systematic process of trial is proposed to identify the possible slip and its magnitude developed at the column-soil interface. The numerical scheme can be used for end bearing and floating columns and for the situation involving stratified layers. The behaviour of soft ground reinforced by a group of columnar inclusions such as stone columns/granular piles, sand compaction piles and lime or cement columns, are predicted using the proposed method of analysis. The reinforced ground is covered by a layer of granular fill. The response of reinforced ground ranges from flexible to rigid loading conditions depending on the magnitude of thickness and deformation modulus of overlaying granular fill. The compacted granular fill over the column reinforced ground is very effective in reducing both the overall and the differential settlements of the composite ground. The compressibility of S the granular fill has an appreciable influence on the settlement response of the composite ground as long as the modulus of granular fill is less than approximately fifty times that of the soft ground. The depth of slip zone at column-soil interface increases with the decreasing value of limiting shear stress. It also increases with the increase of degree of penetration of column. Slip situation predicts higher depth of neutral plane than its no slip counterpart and it increases with the decreasing value of limiting shear stress. In case of end hearing column, a good portion of column sustains little or no interface shear stress at all but for floating column, the whole length of column is subjected to shear stress either positive or negative. The stress in column increases with depth and attains it high value at the bottom for end hearing columns. But in case of floating column, it increases up to the depth of neutral plane beyond which decreases up to the bottom of column. In both the cases no slip situation predicts higher depth of neutral plane than that of possible slip. The differential settlement of the composite ground is noticeable for the case of uniform flexible loading acting over the entire area. The overall and the differential settlements are more for slip analysis than that of no slip case. As the differential settlement does not reduce in case of floating column, end bearing column is more effective due to giving less overall settlement. The influence of soil stratification is evident in the predictions. This is, of course, as expected; the present analysis quantifies it. The spacing, length to diameter ratio, the degree of penetration of columns, the relative stiffness of column and soil, and the angle of friction between column and soil have a significant influence on the mobilization of shear stress, variation of normal stresses in column and soil and the settlement of the treated ground. But the Poisson's ratio of soil has little influence on them. A simple uncoupled consolidation model is proposed to determine the time-dependent response soft ground reinforced by columnar inclusions. This method is simple compared to Biot's coupled consolidation theory. The radial inhomogeneity of the soil properties such as deformation modulus and shear modulus and also soil stratification can be handled easily by the proposed method. From predicted results, it is realized that to evaluate the subsequent response of reinforced ground, the value of degree of consolidation predicted at every nodal points should be used rather than using the average value. The mobilization of shear stress at column-soil interface, the stress in column and soil and the settlement profile with time can be evaluated easily and reasonably accurately by the proposed method. The proposed foundation model has been compared with the existing approaches and verified by the finite element analysis as well as experimental results both in the laboratory and in the field. The existing approaches can be used for rigid loading condition but their application is restricted for flexible loading. In both cases flexible and rigid loading, the proposed model offers better solution as it can be used by taking account the role of overlaying granular fill, soil stratification, slip and no slip situations, can be used for both end bearing and floating columns and also for time-dependent analysis. The comparison of results obtained from finite element method and those of by the proposed model, indicates that the proposed model can be used with a reasonable degree of accuracy to depict the settlement behaviour of end bearing or floating columns reinforced ground subjected to either flexible or rigid loading. The prediction obtained from the proposed model show also good agreement with test results both in laboratory and field.
Development of Sustainable Cement Mortar Incorporating Rice Husk Ash
(Khulna University of Engineering & Technology (KUET), Khulna, Bangladesh, 2011-12) Rashid, Muhammad Harunur; Molla, Prof. Dr. Md. Keramat Ali
The study for the development of sustainable cement mortar incorporating rice husk ash was conducted by several approaches. Several researchers have been conducting research to replace the ordinary Portland cement by new materials with pozzolanic and cementitious properties. The aim of this study was to investigate the performance of cement mortar with rice husk ash for its sustainable development. A detail investigation was conducted to produce the rice husk ash with appropriate properties by effective incineration process. The fineness of rice husk ash based on different incineration systems, retention time and grinding time was determined. Characterization of rice husk ash was performed with XRD, SEM and chemical composition analysis. The effect of rice husk ash on heat of hydration was examined. Eventually, the performance of cement mortar with different proportions of rice husk ash was evaluated based on strength, permeability, sorptivity, salt crystallization, resistance to sulphate attack and effect of elevated temperature ranging from 200 to 700°C. The result shows that the highest fineness of 6894 cm2/gm was obtained for rice husk ash produced in laboratory burning system with 60 hours retention and 180 minutes grinding. The result of XRD confirmed the amorphous state of rice husk ash produced in laboratory burning system at 663.6°C. The maximum compressive strength of 33.09 MPa at 28 days was found for control sample. The highest compressive strengths at later age of 90, 350, 600 and 900 days were found to be 38.08, 38.80, 39.09 and 39.23 MPa respectively for 20% replacement with rice husk ash. The highest permeability of 4905 columbs was found in case of control sample at 28 days age. The result indicates that the permeability is inversely proportional to rice husk ash and curing age of sample. The trend of sorptivity was found similar to permeability and the highest value of control sample was found to be 0.214 kg/m2-min0.5. It was found that the mortar samples with 15% and 20% rice husk ash sustained up to standard 20 cycles in salt crystallization. No crack or spalling was observed due to sulphate attack on the mortar samples with 15 and 20% replacement of OPC with rice husk ash. The control sample exhibits the highest strength of 44.47 and 23.85 MPa at 200 and 700°C respectively. The sample having 15% rice husk ash shows maximum strength of 48.26 and 43.52 MPa at 300°C and 400°C respectively while the highest strength was obtained at 500°C for sample with 20% rice husk ash. The findings of the present study would contribute to the sustainable development of cement mortar incorporating rice husk ash.
Efficient Mode Selection Scheme for Video Coding
(Khulna University of Engineering & Technology (KUET), Khulna, Bangladesh., 2016-11) Yusuf, Md. Salah Uddin; Ahmad, Professor Dr. Mohiuddin
Video coding plays vital role in communications and multimedia applications. The appearance and development of various new multimedia services have need for higher coding efficiency. H.264/AVC is the latest international video coding standard that can achieve considerably highest coding efficiency than previous standards and uses rate-distortion optimized (RDO) mode selection technique. This means that the encoder has to code the video by exhaustively trying all the mode combinations including the different intra and inter prediction modes. However, this mode selection process also makes the encoding process extremely complex, especially in the computation of the rate-distortion cost function, which includes the computations of the sum of squared difference (SSD) between the original and reconstructed image blocks and context-based entropy coding of the block. So, the highly complex mode selection process limits the practical implementation of codec’s. This dissertation proposes six different fast and efficient schemes to reduce the computational complexity of mode (Intra and Inter) selection process. It also can effectively reduce the spatial and temporal redundancy. In H.264/AVC intra coding, DC mode is used to predict regions with no unified direction and the predicted pixel values are same and thus smooth the varying regions which are not well de-correlated. A modified DC prediction (MDCP) mode is suggested to replace the existing DC mode based on the distance between the predicted and reference pixels. By analyzing the impact of scanning, a new Z-scan scheme is proposed which can remarkably reduce bit rates compared with AVS codec using conventional zigzag scan, while the PSNR of video sequences are maintained. The entire macroblock is divided into simple motion or complex motion contents and their cost functions are calculated by using the developed rate-based fast and efficient mode selection scheme, which plays a vital role as no additional operation module is required. To avoid the entropy coding method during intra and inter mode decision, a rate estimation method proposed and readjusted to fit the characteristic of low complexity distortion functions of SATD and SAITD that use more accurate estimation while achieving higher prediction performance with low computational requirement of feature. In addition, a relative sum of absolute difference (RSAD) based inter mode decision algorithm is proposed to determine the best inter mode without calculating xiv rate-distortion costs. To further speedup SKIP mode early termination algorithm is adopted. Based on the probability characteristics, a fast inter mode decision algorithm is suggested which can determine the best inter mode only by calculating the Hadamard Transform (H-SAD) cost instead of rate distortion cost and avoid most of the complex computation processes like quantization, variable length coding, pixel reconstruction etc. To make the motion estimation process fast, a search point reduction scheme is introduced. Then the ranking and performance of the commonly used scheme are analyzed for different kinds of video. Experimental results indicate that the proposed efficient mode selection schemes reduce the computational complexity of H.264/AVC codec without sacrificing the quality of video which can be applied in implementing real time encoder for low-power mobile devices and general purpose computers.
Evaluation of Contamination Potential and Treatment Techniques of Leachate Generated from Landfill Lysimeter
(Khulna University of Engineering & Technology (KUET), Khulna, Bangladesh, 2014-08) Islam, Md. Rafizul; Alamgir, Prof. Dr. Muhammed
In this study one open dump lysimeter with leachate detection and collection system as well as two sanitary lysimeter having two different types of cap liner were simulated. After designing a reference cell, construction of landfill lysimeter was started in January 2008 and completed in July 2008. In all construction process locally available civil construction materials were used. The municipal solid waste (MSW) of 2800 to 2985 Kg having the total volume of 2.60 m3 (diameter 1.48 m; height 1 .6m) as well as moisture and organic content of 65, 52 %, respectively, was deposited in each lysimeter by applying required compaction energy. This study endeavors to characterize leachate and investigate the tropical climatic influence on leachate characteristics under different seasonal variation. The leachate characteristics, leachate generation and climatic influence parameter had been monitored since June 2008 to Dec. 2010. These periods covered both the dry and rainy season. The leachate generation followed the rainfall pattern and open dump lysimeter-A without top cover demonstrated more leachate generation due to percolation of rainfall than that of sanitary lysimeter-B and C. Open dump lysimeter-A showed lower concentration of TKN and NH4-N as well as TKN load, while both the concentration and load of COD higher in compared to sanitary lysimeter-B and C. Sanitary lysimeter-B, not only revealed lower leachate generation, but also produced reasonable lower concentration and load of COD in compared with open dump lysimeter-A. Result depicted that lysimeter operational mode had direct effect on leachate quality. In contrary, sanitary lysimeter-C showed higher composition of LFG in compared to sanitary lysimeter-B due to the providing of lower compaction of cap liner in sanitary lysimeter-C. in absence of compacted clay liner (CCL) and hence percolation of rainwater that facilitated rapid degradation of MSW in open dump lysimeter-A and resulted in higher settlement than that of sanitary lysimeter-B and C. In sanitary lysimeter-B and C, leachate generation showed lesser amount than that of open dump lysimeter-A due to the providing of cap liner in lysimeter-B and C, played an important role to reduce the percolation of rainwater. Study revealed leachate pollution index (LPI) and sub-pollution indices (sub-LPI) for lysimeter significantly higher and proper treatment to be necessary before discharging the leachate into the water bodies. To meet the standard discharge condition lysimeter leachate was treated in the laboratory through the phytoremediation treatment process by using aquatic reactors of duckweed, snail, helencha and topapana, but the removal efficiency was not satisfactory. Then the leachate was treated through the chemical coagulation process by using FeCl3, PAC, FeSO4 and Al2(SO4)3 in various dosages and pH. Result revealed that FeCl3 more effective for removing pollutant. In the laboratory, leachate was further treated by using FeCl3 at optimum dosage and the concentration and consequently the values of LPI of treated leachate were found within the limit of maximum discharge standards. Finally, it can be concluded that leachate generated from lysimeter may be discharge after required level of chemical treatment into the natural streams to maintain the limit of maximum discharge standards.
Heuristic Approaches for Maximin Distance and Packing Problems
(Università degli Studi di Torino, Torino, Italy, 2009-02-18) Jamali, Abdur Rakib Muhammad Jalal Uddin; Locatelli, Prof. Marco
In this thesis we mainly deal with two problems - experimental design and packing problems. In the field of experimental design problems we consider maximin Latin Hypercube Designs (LHDs). In the field of packing problems we consider those of packing n equal or unequal circles in a circular container with minimum radius. Both problems can be formulated as optimization ones. The former is a combinatorial problem, while the latter is a continuous one. We propose heuristic approaches to tackle these problems. These are Iterated Local Search (ILS) heuristics for maximin LHDs, and Basin Hopping (BH) heuristics for packing problems. Actually, ILS and BH approaches have strong similarities and could be described within an unified framework. However, following the literature, where ILS approaches are mainly applied to combinatorial problems, while BH approaches are mainly applied to continuous problems, we will keep them apart. In order to deal with maximin LHDs, we propose two ILS variants, corresponding to two distinct optimality criteria which are employed to drive the search among LHDs. Extensive experiments are performed for the investigation of the strengths and weaknesses of the algorithms. A remarkable finding is that the most efficient method, though time consuming, performs a non monotonic search, driven by an appropriate objective function, within the space of LHDs. The proposed approaches are extensively compared with the existing ones in the literature, and many improved results with respect to best known ones, are obtained. In particular, the proposed methods seem to outperform the existing ones when the dimension of the design points increases. Finally, we also discuss about the time complexity of the algorithms; by mixing theoretical results with experimental ones, we derive an empirical formula for each ILS variant, returning the expected run time as a function of the number of design points and of their dimension. To deal with the problem of packing equal circles in a circular container with minimum radius, we propose a variant of BH, namely Monotonic BH (MBH) and its population based counterpart, Population BH (PBH). Extensive computational experiments are performed both to analyze the problem at hand, and to choose in an appropriate way the parameter values for the proposed methods. Different improvements with respect to the best results reported in the literature are detected. The problem of packing unequal circles in a circular container with minimum radius is also attacked with the MBH and PBH approaches, but some components of these approaches are adapted in order to fully exploit the peculiarities of the problem with unequal circles (in particular, its combinatorial nature due to the different radii of the circles). Again extensive computational experiments are performed and improvements with respect to the existing literature are detected.
Investigation of Strength and Deformation Characteristics of Cement and Lime Treated Soft Clays
(Bangladesh University of Engineering & Technology (BUET), Dhaka, Bangladesh, 2008-07) Rahman, Md. Mokhlesur; Siddique, Prof. Dr. Abu
This thesis presents experimental and numerical investigations for the effects of cement and lime treatment on compressibility, permeability, stress-strain, strength and stiffness behaviour of three soft clays. Effects of cement treatment on physiochemical and micro-structural properties have also been investigated. X-ray Diffraction, Scanning Electron Microscopy, particle size distribution, pH measurement, organic content, electrical conductivity, cation exchange capacity, exchangeable cation, water content, unit weight, specific gravity, and Atterberg limits tests were conducted to examine physiochemical and micro-structural properties. Compressibility and permeability properties of untreatcd and, cement and lime treated clays were investigated by performing one-dimensional consolidation tests. Stressstrain, strength and stiffness behaviour of untreated and, cement and lime treated clays were evaluated by performing unconfined compression (UC) tests. Consolidated drained direct shear (OS), unconsolidated undrained (UU), isotropically consolidated undrained (CIU) and isotropically consolidated drained (CID) triaxial compression tests were also carried out to assess the stress, deformation and strength properties of cement treated clays. Sets of variables considered in the testing program include a wide range for type of clay (PI = 13% to 47%), type of admixture, clay-water/cement ratio (2 to 30), curing time (1 to 104 weeks), mixing water content (120% to 250%) and effective confining pressure (50 kPa to 400 kPa). Finally, applicability of different constitutive models and Cap models were assessed for the predictions of drained and undrained behaviour. It has been observed that pH value, electrical conductivity (EC), cation exchange capacity (CEC), increases with decreasing clay-water/cement ratio. pH value, however, decreases while EC and CEC value increases with increasing curing time. Loss on ignition and organic matter decreases due to increasing cement content and with increasing curing time. The relative amount of cementitious product (CSH + CASH) was identified by the XRD analysis and found to increase with the increase of cement content and curing time. Due to the formation of cementitious product, the fabric of the treated clays changed to flocculated type, comprising of clay-cement clusters separated by large inter-cluster voids with smaller intracluster pores as seen from the SEM images of treated clays. These changes were more pronounced with higher cement content and longer curing time. The significant increase in yield stress and reduction in compression index (Ce) and swell index (Cs) were observed with increasing admixture (cement/lime) content and increasing curing time. Ce and Cs for lime treated clays were found to be greater than those of cement treated clays. Ce and Cs values increase significantly with the increase of mixing clay-water content. The lime-treated clays gained comparatively higher void ratio and volumetric strains and lower yield stress than those of cement-treated clays. The effect of cementation is to increase the values of coefficient of consolidation (cv) and coefficient of volume compressibility (mv). The higher the admixture content and curing time, the lower is the values of cv and mv. cv and mv values for lime treated clay were found to be higher than those of cement treated clay. A substantial increase in the value of cv and mv was found to have occurred within higher mixing water content. At higher stress level, progressive destructuration of the treated clay particles occurred, which has been verified from the SEM images of cement treated clay compressed at different consolidation pressure. Addition of admixture to the clay increases the permeability and void of the soils, due to flocculation of the soil particles, which has been seen from SEM images. The Intrinsic Compression Line (ICL) and Generalized Compression Line (GCL) have been proposed for the untreated and treated clays. Coefficient of permeability (k) and void ratio relationships have also been proposed for cement and lime treated clays. The values of k of cement and lime treated clays have been found to reduce with increasing cement or lime content and curing period. Values of k for lime treated clays were found to be higher than those of cement treated clays. Based on the rate of strength development with time, the unconfined compressive strength and cement content relationships have been divided into 3 zones: Inactive Zone, Active Zone and Inert Zone. Since the behaviour of cement treated clays was remarkably governed by we/e, the strength prediction in terms of we/e as well as the interrelationship involving strength, curing time and clay-water content/cement content ratio (we/e) have been proposed. From stress-strain relationships, the overall behaviour has been categorized into brittle, quasi-brittle and ductile. Comparatively, brittle, quasi-brittle and ductile types for the cement treated clays, while quasi-brittle and ductile types for the lime treated clays have been found. The correlation between yield stress, (σy') and unconfined compressive strength (qu), τf0 and qu axial strain at failure (εf) and qu, and stiffness (Ei and E50) and qu have also been proposed. In direct shear test, for cement treated clays, vertical expansion (dilation) was observed at low normal stress and experienced vertical contractions or settlement throughout the shearing stage at higher normal stress. The cohesion and friction angle have been increased with increasing cement content and curing time. The undrained effective stress paths of the cement treated clays obtained from CIU triaxial compression tests indicate that the stress paths belong to different category of states such as normally consolidated, lightly, moderately and heavily over-consolidated state. The degree of alteration have been found different for different samples depending on the amount of cement content, curing time and pre-shear effective consolidation pressure. Upon reaching the peak deviator stress in CIU triaxial test, the progressive destructuration takes place and thus the stress path tends to move either on the I-Ivorslev envelope or envelope of strain softening behaviour. SEM results have been suggested that complete destructuration takes place only on the shear plane at which the clay-cement cluster crushes. The prevalent role of pre-shear effective consolidation pressure was manifested to annihilate the cementation effect attributing ductility to the treated matrix. The main effect of cement treatment was to modify the behaviour of the soft clay form normally consolidated to over-consolidated state. Similar natures of deviator stress-axial strain and volumetric strain-axial sirain relationships were observed for all samples having the identical wclc ratio in cm triaxial tests. So, the wclc is a prime parameter governing the engineering behaviour of cement treated samples having different mixing water content. For cement treated clays, peak deviator stress (qmax) criterion of failure envelopes can be used as obtained from CIU and CID triaxial compression tests. The degree of overall curvature of the failure envelope for each type of clay depends on the range of consolidation stresses and hence increases with increasing cement content and curing time. The values of soil constants λ and κ for the treated clays have been found to be less than those for the untreated clays while the values of the constant N and M are greater for the cement treated clays than those of untreated clays. At a particular curing time, the soil constants λ and κ decreased, while the constant N and M increased with increasing cement content. Correlations between the soil constants λ, κ and N with plasticity index have been proposed. Hvorslev surface was established for the cemented clays. No definite Roscoe surface could be found for cemented clays. For the untreated clay, it has been observed that the predicted stress paths, deviator stresses, volumetric strains and excess pore pressure responses at small strain levels using the MCC model appear to be significantly close to experimental curves. It appears from the present study that MCC, MMCC, EMMCC and Cap models (Plane Cap and Elliptic Cap) cannot be applied for predictions of drained and undrained behaviour of cemented clays at high water content.
Non-Linear Finite Element Analysis of Wall-Beam Structures
(Bangladesh University of Engineering and Technology (BUET), Dhaka, Bangladesh., 1997-05) Hossain, Dr. Md. Monjur; Rahman, Prof. M. Azadur; Ali, Prof. Sk. Sekender
The composite action between masonry wall and its supporting beam concentrates the vertical loading applied on the top of wall close to the beam supports. This produces bending moments much less than would be expected when the full load is acting directly on the beam. The study of this composite action is of economic importance since if the concept is utilised, a rational design of the beam will be achieved. This thesis presents a comprehensive material model and its incorporation into non-linear finite element computer model for the analysis of wall-beam structures made with brickwork of solid brick subjected to uniformly distributed load. The program is incremental in nature and capable of reproducing the non-linear behaviour caused by material non-linearity and progressive local cracking and crushing. The program is thus capable of modelling the behaviour of wall-beam structures subjected to non-linear load from first crack to final failure. The material model used in this program is derived from tests on representative samples of brick, mortar and small samples of brickwork. In the finite element model brick, mortar, concrete and steel are treated as separate materials along with the simulation of actual directional effects of mortar joints. A series of failure criteria have been adopted to model the different modes of failure experienced in the constituent materials. Due to the crack sensitive nature of the problem, particular emphasis has been given to the modelling of cracking and the post-cracking behaviour of the materials, especially the manner in which the local stresses in the fractured region are redistributed. The results of finite element model have been verified by comparison with experiments on brick masonry wall-beam structures subjected to uniformly distributed load applied at the top and extending over the full length and thickness of the wall. Comparison with published literature reveals that the present method can provide a more comprehensive prediction of behaviour of the wall-beam structure up to failure load. Sensitivity analyses of the various parameters defining the material model and the boundary conditions have been canied out. With the important parameters thus obtained, the finite element model has been used to carry out a comprehensive parametric study of the behaviour of storey height wall-beams subjected to uniformly distributed load. Based on the findings of this study, design recommendations have been proposed. As the computer program developed can handle general cases with arbitrary geometry, loading and boundary conditions, recommendations for investigations of various other wall-beam structures have been made.
Parameter Adaptive Vector Controller for CSI-fed Induction Motor Drive and Generalized Approaches for Simulation of CSI-IM System
(Indian Institute of Technology (IIT), Kharagpur, India., 1992-07) Ghosh, Dr. Bashudeb Chandra; Bhadra, Prof. S. N.
The main subject matter of this dissertation is to develop parameter adaptive rotor flux oriented current fed induction motor drive systems for controlled speed operation. The parameter adaptive approaches do not require special test signals and softwares in a big way. Three easy-to-implement schemes are suggested. One scheme is based on airgap power estimation method and takes into account of the non-linear magnetic state while tracking the actual rotor resistance. The other two methods constitute model reference adaptive controllers. They are based on the inverter input voltage and torque producing component of the stator current. The effectiveness of these methods is examined by extensive simulation and experimentation with two laboratory type induction machines. The experimental set up makes use of two microcomputers (i-8006 with i-6007) and a PC/AT with Burr Brown's PCI system having multi-channel 12 bit data acquisition modules for implementing the control algorithms. Prior to the description of parameter corrective algorithms, a control system suitable for a CSI-fed induction motor under rotor flux orientation is designed and tested by suitable simulation model. Then the influence of rotor resistance variation in the presence of magnetizing flux saturation has been extensively investigated. A two-parameter saturation model (two-term quintic non-linearity) is used in all these studies. It is further shown how the machine performances under field oriented condition are affected inclusion of saturation characteristics. Analytic expressions as well as digital simulation procedures are presented to study the performance of the drive system. Robustness of the drive system has been studied applying the concept of Kharitonov's theorem and then justified from the simulation results of the system for both parametric and torque disturbances. 'Bond Graph' and 'Nodal method' provide an organised way to write equations for a dynamic system. Tedious way of writing equations and their arrangement and re-arrangement for framing state equations can be avoided in the proposed simulation techniques. Simulation studies based on systematic modelling and framing of the system equations using the above two methods for the operation of a speed controlled CSI-IM system under normal and abnormal conditions have also been provided.
Planar Electromagnetic Bandgap Structures and Applications
(Nanyang Technological University, Nanyang Avenue, Singapore, 2005-03) Mollah, Md. Nurunnabi; Fu., Dr. Jeffrey S.
With the emergence of novel wireless technologies, the demands for larger bandwidth, high efficiency and high capacity RF and microwave devices have been growing tremendously. To satisfy the demand novel materials, new processing techniques and refinement of existing devices have been evolving. Using electromagnetic bandgap (EBG) is a new technology to improve the performances of existing RF active and passive devices. EBG structures (EBGSs) are periodic structures, which exhibit distinct passband and stopband characteristics. The passband can be used as phase shifters and slow wave structures. The stopband characteristics can be used to suppress surface waves in dielectric media. Due to these unique properties, EBGSs find potential applications in many active and passive RF and microwave devices including antennas, filters, amplifiers and oscillators. Recently, the dispersion properties in passband of EBGSs are used in the phased array antennas for wide angle beam steering. Among various EBG configurations, planar EBGSs become most popular due to their low profile, ease of fabrication and integration with monolithic microwave integrated circuits (MMICs). The thesis concerns the planar EBG structures in the forms of conventional circular and rectangular photonic bandgap structures (PBGSs) and defected ground structures (DGSs). Novel PBGSs in the form of non-uniform Binomial and Chebyshev distributions of unit PBG cells have been proposed. This novel PBGSs yield ripple free passband and wide stopband properties, which are very useful to suppress higher order harmonics in the bandpass filters. Next the chirped PBGSs are investigated that yield better passband return loss, low ripples and wider stopband than those for conventional PBGSs as well as non-uniform PBGSs mentioned earlier. The parametric study of dumbbell shaped DGSs has been conducted with the gap width and length and the size of dumbbell slots. Three novel designs are proposed: non-uniform dumbbell shaped DGSs with Chebyshev distribution, hybrid DGS and PBG and modified hybrid DGS and PBG configurations. The novel designs outperform the conventional DGSs reported in the literature. The DGSs yield perfect LPF responses with negligible passband ripples and extremely wide stopband. The modified hybrid DGS and PBG configuration yields dual stopbands that can be used as a dual stopband filter. The novel design are used in asymmetric coupled line bandpass filters, aperture coupled single band and dual-band patch antennas and finally in 4-element conventional and reconfigurable phased array antennas. For filters, PBGSs suppress second and third harmonics by about 40 dB, A comprehensive investigation of the number, filling factor and position of the PBGS under the filter has been conducted. The frequency response of the filter has been observed. This investigation is novel and illustrates the significance of PBGSs in suppression of higher order harmonics of the bandpass filters. It has been found that non-uniform distribution of PBGSs is more effective to suppress higher order harmonics than the conventional uniform PBGSs. DGSs are very effective for simultaneous suppression of both 2nd and 3rd harmonics due to their very wide stopband performances. This phenomenon of DGSs has been demonstrated in various designs of asymmetric coupled line bandpass filters. Finally, the passband phase properties of the PBG and DGS have been investigated. The comprehensive investigations of relative phase delays of PBGS and DGS assisted microstrip transmission lines have been performed. Such investigation is not found in the open literature. It is observed that DGSs yield much larger phase delay compared to a similar size PBG structure. Therefore, DGS assisted feed network can scan the beam over a wide angle. After thorough and satisfactory investigation of phase delays for PBGSs and DGSs, phased array theory is studied. The required phase delays for a 4-element phased array are calculated based on the element spacing and number of elements. A wide beam scanning up to approximately 60° is achieved with 0-8-16-24 DGS assisted corporate feed network for the 4-element patch antenna array. So far such wide angle scanning using DGS assisted beamforming network has not been reported in the open literature.
Protection of the Inter-Tie between an Industrial Cogenerator and a Utility
(Robert Gordon's Institute of Technology, Aberdeen, Scotland, 1990-11) Mollah, Abdur Rahim; Edwards, David C.; Deans, Prof. N. D.
The work presented in this thesis is concerned with the development of a microprocessor based technique to detect and locate symmetrical and unsymmetrical faults on the interfacing network of a utility interconnected industrial cogenerator system; and to identify the type of the detected fault. In order to provide operational flexibility and supply security to such an interconnected industrial cogenerator plant, fault location is regarded as being of prime importance. Current protection practices using conventional technology for this sort of interconnected cogeneration system were reviewed. A relay coordination study was carried out on a simulated utility interconnected cogeneration system. This resulted in identification of the problems and limitations of the application of standard IDMT relays for overcurrent protection of such a system. A review of digital protection, and its various algorithms, was undertaken. This provided the basis for a rational choice of algorithm for the proposed new technique. The sequence of functions of the protection scheme's algorithm, based on the proposed technique, can be presented in brief as follows: First, phase currents at selected positions on the system are sampled. The positive phase sequence (pps) currents at those positions are then obtained in digitised form from the sampled phase currents. Then, these pps currents, containing fundamentals along with other harmonics and dc offsets, are used in a Fourier filtering algorithm to extract only fundamental components in rectangular forms. Signs of imaginary parts of these components are then used to determine the directions of pps currents at the selected positions. The industrial bus voltage is used as the polarising reference. Finally these directions are based in a fault detection aridlocat1on subroutine to determine the location of any fault under such conditions. After detecting a fault and locating its position, the type of fault is determined from off-line analysis of the postfault phase currents. The analysis is based on identifying the phases carrying the maximum fault current and checking the presence of zero sequence current. The proposed protection scheme has been tested on a computer simulated system which consists of a utility interconnected to an industrial plant with cogeneration. The performance has been found to be satisfactory for all kinds of solid and low are resistance faults anywhere on the interfacing network between the systems.
Some Aspects of Generation Expansion Planning
(Indian Institute of Technology (IIT), Kharagpur, India., 1996-04) Azad, Dr. Md. Abul Kalam; Misra, Dr. R. B.
The primary objective of generation expansion planning is to meet the electrical energy needs of the customers as economically as possible with an acceptable degree of safety, reliability, and quality. Power system planning involves studies to determine the resources required to meet the growth in demand at the lowest possible cost considering environmental and financial constraints. A power utility should meet the demand under a wide range of normal, abnormal, and emergency conditions including the reasonable foreseeable failures and maintenance outages of facilities. This requires some generation system capacity reserve in excess of forecasted demand. The uncertainty associated with future demand projections could make the system facilities inadequate, or excessive and uneconomical, both cases being unacceptable. Purchasing cheaper power from other utility through interconnection is another alternative which improves system reliability. in this thesis, some studies have been made on generation expansion planning taking into account the above important criteria. The thesis contains a brief research background, motivation and objective to the modelling and analysis of some important requirements of generation expansion planning. The proposed techniques are implemented to an existing electric utility for generation expansion. The key to all generation expansion planning is a good forecast of load that reflects current and future trends, tempered with good judgment. This is quite important for financial success. Undoubtedly, the most obvious deficiency in any expansion plan is and eventually is seen to be, the accuracy of the demand forecasts. Four modules of Artificial Neural Network have been studied in detail, to forecast peak load of two distribution substations. It is observed from the sensitivity analysis that all modules are not valid for all systems. In other words, for a specific system only a particular module is suitable for load forecasting. It is also found that the predicted results of minimum mean absolute error (MAE) is dependent on learning rate and learning momentum. Using the findings of the sensitivity analysis, various modules of ANN are studied and the most suitable module found is used to forecast yearly peak load of an existing electric utility for fifteen years choosing an appropriate module for the system. Reliability criterion, the next aspect, is primarily used to determine the required S stein generating capacity reserve, to operate the system under equipment failures, equipment maintenance, and load variations. Probabilistic methods are used to evaluate reliability of generation expansion plans using stochastic representation of the generating unit failure-repair process, load variability and emergency help from interconnections. A modified FFT method has been proposed to evaluate the loss of load probability (LOLP) of a power generating system consisting of different types and sizes of unit. This approach uses hourly loads, or any suitable time interval for system demand, for a given period. Out of several properties of FFT scheme, some properties have been used for the reduction of computational complexity. The accuracy of the method has been illustrated using an example. This modified FFT algorithm is applied to IEEE Reliability Test System (IEEE-RTS). The modified approach improves the efficiency in comparison to the conventional FFT method. Further, another new approach has also been developed to evaluate the LOLP of a power generating system. This approach uses joint probability density function (PDF) concepts to convolve the unit outages and loads of the system. The reduction of computational effort for identical generating units is obtained using the binomial distribution. The method has been illustrated through an example and is applied to IEEE-RTS. This method is found efficient and easy to use as compared to other existing methods. In addition, the proposed approach can simulate multistate representations of generating units at less computational efforts. Exploiting these advantages of the proposed approach, generation expansion planning of an existing utility has been made based on levelized LOLP for projected future demand. In generation expansion planning, interconnected system may play an important role on system reliability. Reliability evaluation methodology of interconnected systems is different from that of a single area system. If the available capacity in one geographical region can be transmitted to other regions whenever it is needed without tie line restrictions then and only then, this system may be treated as a single area. Though it is possible to evaluate interconnected systems as a single system with some approximation, but, it is not in practice due to many obvious reasons. The improved modified FFT scheme, developed for single area, has been extended to evaluate LOLP of two area interconnected power systems. A stochastic procedure for interconnected systems is presented using improved two dimensional FF'T IMSL subroutine of Cyber 180/840A mainframe. This method can simulate multi-state generating units without affecting the computational complexity, whereas the computational complexity of other existing methods increases with the increase of number of outage states of generating units. The joint PDF approach, developed for single area, has also been applied to evaluate LOLP of two area interconnected power system consisting of different types and sizes of generating units considering independent as well as correlated system demands. The Probability Density Function (PDF) of equivalent load is obtained by convolving the PDF of generating unit outages with the PDF of system demands using the proposed approach. The LOLP values of each system are obtained from the PDF of equivalent load. The accuracy of the proposed method has been illustrated using a simple example. The results obtained for IEEE-RTS are compared with existing methods. In addition, the above approach is also implemented to an existing utility for which expansion planning studies were carried out. The system under study is considered to be interconnected with a hypothetical system. The benefits desired due to interconnection are evaluated and the impact of interconnection on expansion planning is studied. An efficient approach has been developed to evaluate the expected energy generation, expected unserved energy, production costs (in the thesis production cost is used for fuel cost) and loss of load probability of a power generating system. The expected energy generation of a given generating unit is obtained by evaluating the difference of unserved energy before and after the commitment of the unit. The method can evaluate expected energy generation and production costs of identical generating units at a time. This is not restricted to load duration curves and unit outage density function of any shapes, or size of the systems with a large number of generation units. Multiple generating units with same outage behavior can be committed with system demand efficiently. The new developed approach has been extended to evaluate the expected energy generation, expected unserved energy and production costs for two area interconnected power generating system. An example and IEEE-RTS have been used for illustration. Further, the proposed method has been used to evaluate expected energy generation, unserved energy and production cost of the generation expansion plan developed for existing utility under study. Based on the detailed study, addition of generating units for the existing utility has been recommended for the period under consideration. Reliability index is derived from the estimates of availabilities of generating units, forecasted loads and unit incremental costs. Uncertainty which results in an unacceptable estimates of system reliability is implicit in the estimates of availability of units and forecasted loads. The uncertainty in the availability of generating units is due to the variation of failure data for different reporting sources and fluctuation in environmental conditions. Fuzzy set theory provides optimistic and pessimistic values of the derived quantities, corresponding to the assumptions of the highest and lowest possibilities of concerned events. In many cases, these bounds provide excellent guidelines to the generation expansion planners. A model has been developed for fuzzy reliability to quantify the effect of uncertainty associated with unit capacity, FORs and the forecast loads on the LOLP of a power generating system. The model has been explained with the help of a simple generation system. Studies are also conducted on the IEEE-RTS to demonstrate effect of uncertainty on system parameters. Effects on the system reliability index due to variation in the amount of uncertainty of the parameters is studied. This proposed model has also been applied to a practical system to predict fuzzy LOLP.
Stress-Deformation Characteristics of Selected Coastal Soils of Bangladesh and their Sampling Effects
(Bangladesh University of Engineering & Technology (BUET), Dhaka, Bangladesh, 2002-03) Bashar, Md. Abul; Safiullah, Prof. Dr. A.M.M.
A considerable development activity within the Coastal Region of Bangladesh has necessitated an understanding of the geotechnical behaviour of soils from this region. With this objective in view a study into strength-deformation, compressibility and intrinsic properties of reconstituted samples of Chittagong coastal soils were undertaken. This thesis presents stress-deformation characteristics of three selected coastal soils and their sampling effects. The soils were collected from Banskhali, Anwara and Chandanaish in Chittagong coastal belt of Bangladesh. The soils are low to medium plasticity (Liquid limit = 34 to 45 and Plasticity index = 10 to 20). Reconstituted samples of the three soils were prepared in the laboratory by K0- consolidation of slurry in a large cylindrical consolidation cell using a consolidation pressure of 150 kN/m2. Overconsolidated samples were prepared in the triaxial cell by releasing the maximum isotropic consolidation pressure of 150 kN/m2 to appropriate values to achieve overconsolidation ratios (OCR) of 1.5, 2, 5, 10, 20 and 30. The stress-deformation-strength, stiffness and pore pressure characteristics of reconstituted isotropically normally consolidated and overconsolidated "block" samples of the three coastal soils were investigated in the laboratory by performing undrained triaxial compression tests. Models for the prediction of undrained shear strength of normally consolidated and overconsolidated samples have been developed. To develop intrinsic models of compressibility, intrinsic compression lines (ICL) for the three soils under K0 and isotropic stress conditions have been established which can be used to determine compressibility indices of soils at any depth of known overburden pressure. State boundary surfaces (Roscoe and Hvorslev state boundary surfaces) and critical state lines of the three coastal soils have been established. The critical state parameters of the soils have also been evaluated. Constitutive models relating critical state soil parameters and plasticity index of the soils have been proposed. Applications of these models to undisturbed naturaj clays will require further investigation. The experimentally observed stress-strain behaviour of reconstituted normally consolidated samples of the three coastal soils have been compared with those predicted using two critical state models, namely, "Cam clay model" and "Modified Cam clay model". It has been found that the results predicted by using "Modified Cam clay model" compared more favourably with the observed experimental results than "Cam clay model" for the three coastal soils. The present study has also been carried out to investigate the effects of "perfect" sampling disturbance and tube sampling disturbances on engineering properties of reconstituted normally consolidated samples of the three coastal soils. Undrained triaxial compression tests were carried out on "in situ", "perfect" and "tube" samples. "In situ" samples were prepared by consolidating reconstituted specimens of 38 mm diameter by 76 mm high under K0-condition in the triaxial cell to its in situ stress state. "Perfect" samples were prepared from "in situ" samples by undrained release of the total stresses in the triaxial cell. "Tube" samples were prepared from the large diameter consolidated samples by inserting samplers of different area ratios, external diameter to thickness ratio (De/t) but of constant outside cutting edge angle (OCA) and internal diameter (Di). Area ratio, De/t ratio, OCA and Di of the samplers were 16.4% to 73.1%, 27.3 to 8.3, 5° and 38 mm, respectively. Undrained triaxial compression tests were carried out on reconsolidated "perfect" and "tube" samples of the three coastal soils to assess the suitability of various reconsolidation techniques to minimize sampling disturbance effects. Experimental results indicate that disturbances due to perfect and tube sampling have significant influence on the mechanical properties of coastal soils. The nature of the effective stress paths and por' pressure responses of both "perfect" and "tube" samples are markedly different from those of the "in situ" samples. The "perfect" and "tube" samples adopted stress paths and showed pore pressure responses which are more typical of overconsolidated clays. Disturbances due to perfect sampling led to reduction in the values of undrained shear strength (se), Skempton's pore pressure parameter A at peak deviator stress (Ap), initial tangent modulus (Ei) and secant stiffiess at half the peak deviator stress (E50) whilr axial strain at peak deviator stress (εp) increased due to total stress relief. Due to total stress relief, the reduction Su, Ei and E50 increased with the decrease of plasticity while the increase in c. increased with the decrease of plasticity of the soils. It is also evident that the decrease in mean effective stress (p') due to perfect sampling increases with decreasing plasticity of the soils. The initial effective stress (σ՛i) of "tube" samples reduced considerably because of disturbance caused by penetration of tubes. Compared with the "in situ" samples, values of s, E1, E50 and A of the "tube" samples decreased while sp increased. The changes in measured soil parameters between the "in situ" and "tube" san )les have been found to depend significantly on the sampler characteristics, i.e., area ratio, De/t ratio, used for retrieving the "tube" samples. The values of σ՛i, su, Ei and E50 were decreased due to increase in area ratio (or reduction in De/t ratio). The values of εp, however, increased due to increasing area ratio. A quantitative increase in the degree of disturbance (Dd) has been obtained due to increase in area ratio, while the values of Dd increased with the decrease of De/t ratio of sampler. Disturbance due to tube sampling has been found to depend on the plasticity of the samples of the three coastal soils. The highest reductions in a', st,. Ei and E 0 occurred in the least plastic samples, whereas the minimum reduction in σ՛i, su, Ei and E50 occurred in the most plastic samples. Among the samples of the coastal soils, the least plastic sample produced higher degree of disturbance than the most plastic sample.