Theses
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Postgraduate students are required to submit a thesis as part of fulfilling the requirements of their respective postgraduate degree programmes. This community features merit-based graduate theses submitted by SLIIT postgraduate students. Abstracts are available for public viewing, while the full texts can be accessed on-site within the library.
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Publication Open Access Shear capacity of composite deck slabs with concrete filled steel tubes(University of Moratuwa, 2008) Perera, S. V. TSteel and concrete composite systems are generally used as major structural components in multi-storey buildings. Composite construction in buildings is more popular with profiled steel sheeting (steel decking) since it serves as a working platform to support the construction loads and also as permanent formwork for concrete. To achieve large column free spans (in the range of 8m-12m), as often demanded for multi-storey office buildings, "steel and concrete composite floor trusses" may form economical solutions since they provide the facility to accommodate various service ducts within the structural zone. The concept of introducing a concrete filled steel tube (CFST), instead of the conventional open flanged steel section, as the top chord of these floor trusses has been discussed. However, the viability of this new concept should be ensured by experimental evidence on the longitudinal shear transfer capacity at the composite stage. This study discusses the experimental results of a series of push-off tests conducted on CFST embedded composite slab panels. The effect of providing different concrete top covers and effect of different concrete strengths have been investigated. With headed shear studs (two studs per sample, Configuration 3) 23%- 29% and 20%- 53% of increase in shear carrying capacity were achieved by increasing the concrete top cover from 20mm to 30mm and the concrete cube strength from grade 20 to grade 45 respectively. Composite slabs with CFSTs were 131% (only steel tube, Configuration 1) - 385% (steel tube with welded two steel strips, Configuration 2) higher than composite slabs with headed shear studs (two studs per sample). Then results of composite slabs with headed shear studs were compared with Eurocode-4 and it was at least 22% conservative. Keywords: composite slab, steel, concrete, concrete filled steel tubes, steel deckingPublication Open Access Trajectory Planners for Cooperative Control of Two Industrial Robots and Belt Drives(School of Science and Engineering, Saga University, 2005-03) Jayawardena, T. S. SThis thesis focuses on trajectory planning strategies for high-speed, vibration restrained position control of belt drives and cooperative contour control of two robots in view of increasing the speed of cooperative task. The proposed solutions have been devised, implemented and verified for effective functionality. The trajectory planning in this context is carried out considering the relevant kinematic constraints met in actual practice; the maximum joint velocity constraints and the maximum joint acceleration constraints. The proposed planners are based on the principles of kinematics and the trajectory planning scenarios and, the issues are critically reviewed. For belt driven machine, a fourth order kinematic model integrating belt reaction torque is systematically derived, and thereby explained the spiky phenomenon in velocity profile of motor position, when an acceleration change is experienced. Further, a feed forward dynamic compensator is proposed to restraint vibration and to improve dynamic characteristics of the belt drives. The proposed feed forward compensator is a combination of inverse dynamics of the system and a desirable dynamic filter, which reforms the dynamic characteristics of the existing system. The planned trajectories at low speeds and high speeds are extensively tested for accurate performance with an actual belt driven machine and the results are illustrated. The proposed trajectory planners for two-robot cooperation are basically of two types. 1) Given objective cooperative trajectory exceeding the dynamic bounds of a single robot is decomposed into two concurrent complementary trajectories of two robots maneuvered simultaneously 2) For a specified objective locus, the minimum time complementary trajectories for cooperation are planned. The objective locus used to exemplify the concept of trajectory planners in both cases is an Sshaped locus and realization of the trajectories are carried out under maximum joint acceleration constraints. In the former cooperative trajectory planner, a fair task distribution is accomplished by minimizing the difference in maximum joint velocities of two robots. The complexities in planning trajectories are coped with a two-stage trajectory-planning paradigm backed with a short-listing criterion. A fourth order spline technique for position, minimizing the joint acceleration is also derived theoretically. The latter, minimum time cooperative trajectory planner, is of bang-bang type in acceleration profile and the fairness of each robot contribution is achieved through an additional contribution constraint for each robot to the cooperative task. The applicability of the trajectory-planning concept has been verified with cooperative trajectories having sharp corners. Since the proposed trajectory planners concerned under the thesis work are off-line and therefore they can be conveniently applied to existing servo systems irrespective of the computational power of in-use controller. Neither, a dramatic change in the existing hardware setup nor a considerable reconfiguration of the system is demanded in instrumentation point of view. This requirement of minimal changes in adaptation enhances the pragmatic significance of the proposed schemes.Publication Open Access Lightning warning system based on slow fields and fast transient variations, suitable for oceanic tropics(http://dl.lib.mrt.ac.lk/handle/123/1958, 2007) Abhayasinghe, NLightning causes a lot of property and human damage all over Sri Lanka. It has been a major requirement to develop a low cost lightning warning system. The environmental vertical static electric field changes from 0.1 kVm-1 under fair weather conditions to extreme values like 10 kVm-1 under thunderstorm conditions. Also, lightning discharges generate electromagnetic radiation from ultra low frequency (ULF) through ultra high frequency (UHF) with peak energy emission at 10 kHz. The work discussed in this thesis uses both the static field variation and the electromagnetic radiation emitted by lightning discharges to predict a thunderstorm. A portable transient detector using an envelope detector tuned to 1600 kHz is used to detect electromagnetic radiation emitted by lightning discharges. An operational amplifier circuit having a slow response with a horizontal plate antenna is used to detect the static field variation. Final decision is made by a third circuit and three levels of alarms are released accordingly. Using the transient detector only, a warning can be released 25 minutes before the close by thunderstorm with 95% level of confidence. With the entire system, the confidence of the warning further increases. The cost of the transient detector is about 2500 Sri Lankan rupees with a rechargeable battery bank. The entire system with a battery backup costs about 5000 Sri Lankan rupees. According to the observations made by the transient detector the delay between cloud flashes and ground flashes shows a distribution of the form of a fractional function with a maximm at 27.52 minutes. The newly designed lightning warning system shows an acceptable grade of performance with its low cost.Publication Embargo Characterization of winged bean (Psophocarpus Tetragonolobus (L.) DC.) Accessions using Isoenzyme profiles and morphological characteristics (Electrophoresis, starch Gel …(The Pennsylvania State University, 1986) Peiris, C. NThe winged bean, a tropical legume, is rich in protein, minerals, vitamins, and carbohydrates. It is unique among leguminous plant kinds in that every part of the plant except the roots can be eaten. There are over a thousand accessions and cultivars of winged bean. Therefore, the use of classical methods of describing and identifying genotypes based on morphological characteristics has become increasingly difficult.Publication Open Access IT management sophistication in small business: its definition, measurement and relationship with IT impact(University of Canterbury. Accountancy, 2004) Suraweera, TThis research deals with information technology (IT) management in small businesses. Although IT management in large businesses has been extensively researched, only a handful of studies have focused on the small business sector. There are three specific objectives of this research: (a) to characterise IT management sophistication in small business, (b) to develop and validate a comprehensive instrument to measure this construct, and (c) to develop a model that explains the relationship between IT management sophistication and the IT impact, in the context of small business. The characterisation of the construct is based on the work of Raymond and Pare (1992) who explored the concept of IT sophistication within the context of small businesses. This study adopted a multi-method investigative approach, combining both case study research and survey methods. The study population was New Zealand's small chartered accountancy firms. Initially, a pool of indicators representing IT management sophistication in small business was derived on the basis of case study analysis. These indicators were used as the basis for drafting the measurement instrument which was tested within a wider population in the quantitative phase of the investigation. The second generation multivariate analytical technique, Partial Least Square (PLS) modelling, was used in the study's survey data analysis phase. This research characterised IT management sophistication in small business under three sub-dimensions: IT planning, IT controlling and IT leading. These factors were represented by nineteen indicators. The validity and reliability of the measurement instrument was examined in the PLS data analysis. A PLS model explaining the relationship between IT management sophistication, technological sophistication, and informational sophistication on one hand with IT impact on the other, in the context of small business was derived. The characterisation of IT management sophistication in small business will be useful for the researchers to understand this complex construct more clearly. The measurement instrument can be used to examine further the different aspects of IT management in small businesses. The model that related the study constructs will aid understanding the associated links between them. Practitioners will be able to use these results to improve upon their IT managerial practices to derive a greater impact of IT, which can, in tum, result in achieving higher organisational performance.Publication Embargo Representation of evidence from bodies with access to partial knowledge(University of Miami, 2001) Kulasekere, E. CProblem solving and decision making are often carried out in environments where no single decision agent has access to the complete scope of information and the available information is either partial or approximate. An appropriate framework for modeling partial knowledge is crucial for understanding the various types of uncertainties that are generated and making decisions in such environments. When the complete scope of information is unavailable, the logical approach is to focus on the information that is common to all decision agents. For this purpose, it is necessary that an appropriate notion of conditional knowledge be developed. In this work, we propose a suitable conditional framework that is capable of extracting relevant information from a given body of evidence. A new combination function that allows the combination of evidence generated from two or more sources possessing non-identical scopes of information is also proposed in the context of this conditional framework. The proposed theory circumvents many of the difficulties and conflicting issues related to the traditional Dempster-Shafer theory of evidence and counter-intuitive results drawn from it. New measures for information embedded in the uncertainties generated from randomness and non-specificity of bodies of evidence are also proposed. These measures are shown to converge to the traditional Bayesian uncertainty measure in a probabilistic environment. The results of this research work are used to arrive at a unified strategy for intelligent resource management and congestion control of distributed sensor networks. Viable alternatives for analyzing common data mining tasks using subjective knowledge rather than the more traditional query processing methods are also proposed.Publication Open Access Interactions between river flow and seepage flow(M. Sc. Thesis, Hokkaido University, Japan, 2009-09) Rathnayake, U. SMany previous studies have been carried on the interactions between river flow and the seepage flow in the environmental and biological point of view. Even though the interactions between river flow and seepage flow is recognized as an important process in rivers, previous literature hardly touches on the stability or the limitations for the interactions. Since these interactions are occurred frequently at least in mountainous regions, the river flow cannot be well treated as a lined cannel flow. Understanding the stability of these interactions among river flow and the seepage flow would be advantages for several research areas; including river environmental engineering, ecological and biological studies. The subsurface layer below the river is known as the “hyporheic zone” and it can be defined as a saturated band of sediment that surrounds river flow and forms a linkage between the river and the aquifer. The zone facilitates to have bidirectional interactions as up-welling interactions and downwelling interactions. The origin of these interactions is due to the pressure and velocity differences between the two layers. The large velocity difference between the river flow layer and the seepage flow layer causes the instability of the flows. Due to this flow instability, a reciprocating flow motion is generated between the hyporheic layer and the above. In addition flow obstructions create an upstream high-pressure zone and a downstream low-pressure zone, resulting in hyporheic circulation under the object. The stability of these hyporheic interactions is analyzed using the linear stability analysis technique. Linear stability analysis technique is used to understand the stability of the natural phenomenon by many researchers. Navier-Stokes equations and Brinkman-Forchheimer equations are used in order to formulate the river flow and seepage flow interactions respectively. The open channel flow in river is analyzed using the mixing length turbulent model and spectral collocation method incorporated with the Chebyshev polynomials are used to perform the numerical solution of the perturbed equations. Stability diagrams are discussed with several slopes of the layers against the dimensionless particle diameter and wave number. It has been understood that the range for the occurrence of instability region increases with the slope of the combined river and seepage layers. However it is important to recognize another instability region which occurs even in the range of small dimensionless particle diameter with relatively high wave numbers. Several experiments are carried out, in order to understand the hyporheic interactions. Seepage layer is modeled using a Hele-Shaw which is a longitudinal parallel plate model. Methylene blue is used as the tracer to understand the hyporheic interactions and the experiment is conducted for two slopes as 0.1% and 0.2%. It can be concluded that the dimensionless dominant wave numbers have an effect on the combined channel slope and the Froude number of the river flow. In addition, it can be concluded that the residence time of hyporheic interactions are increased with the height of the river layer. Rough comparison between the theoretical analysis and the experimental observations is carried out. It can be concluded that the same tendency in the theoretical analysis and the experimental observations from the comparison figuresPublication Open Access Multiple-input multiple-output wireless system designs with imperfect channel knowledge(Queen's University, 2008-07) Ding, MEmploying multiple transmit and receive antennas for wireless transmissions opens up the opportunity to meet the demand of high-quality high-rate services envisioned for future wireless systems with minimum possible resources, e.g., spectrum, power and hardware. Empowered by linear precoding and decoding, a spatially multiplexed multiple-input multiple-output (MIMO) system becomes a convenient framework to offer high data rate, diversity and interference management. While most of the current precoding/decoding designs have assumed perfect channel state information (CSI) at the receiver, and sometimes even at the transmitter, in this thesis we will design the precoder and decoder with imperfect CSI at both the transmit and the receive sides, and investigate the joint impact of channel estimation errors and channel correlation on system structure and performance. The meansquare error (MSE) related performance metrics will be used as the design criteria. We begin with the minimum total MSE precoding/decoding design for a single-user MIMO system assuming imperfect CSI at both ends of the link. Here the CSI includes the channel estimate and channel correlation information. The closed-form optimum precoder and decoder are determined for the special case with no receive correlation. For the general case with correlation at both ends, the structures of the precoder and decoder are also determined. It is found that compared to the perfect CSI case, linear filters are added to the transceiver structure to balance the channel noise and the additional noise caused by imperfect channel estimation, which improve system robustness against imperfect CSI. i Furthermore, the effects of channel estimation error and channel correlation are coupled together, and are quantified by simulations. With imperfect CSI at both ends, the exact capacity expression for a single-user MIMO channel is difficult to obtain. Instead, upper- and lower-bounds on capacity have been derived, and the lower-bound has been used for system design. The closed-form transmit covariance matrix for the lower-bound has not been found in literature, which is referred to as the maximum mutual information design problem with imperfect CSI. Here we transform the transmitter design into a joint precoding/decoding design problem. The closed-form optimum transmit covariance matrix is then derived for the special case with no receive correlation, whereas for the general case with non-trivial correlation at both ends, the optimum structure of the transmit covariance matrix is determined. The close relationship between the maximum mutual information design and the minimum total MSE design is discovered assuming imperfect CSI. The tightness and accuracy of the capacity lower-bound is evaluated by simulation. The impact of imperfect CSI on single-user MIMO ergodic channel capacity is also assessed. For robust multiuser MIMO communications, minimum average sum MSE transceiver (precoder-decoder pairs) design problems are formulated for both the uplink and the downlink, assuming imperfect channel estimation and channel correlation at the base station (BS). We propose improved iterative algorithms based on the associated Karush-KuhnTucker (KKT) conditions. Under the assumption of imperfect CSI, an uplink–downlink duality in average sum MSE is proved, which is often used to simplify the more involved downlink design. As an alternative for solving the uplink problem, a sequential semidefinite programming (SDP) method is proposed. Simulations are provided to corroborate the analysis and assess the impacts of channel estimation errors and channel correlation at the base station on both the uplink and the downlink system performances.