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U n i v e r s i t y of P e r a d e n i y a

The Institutional Repository of the University of Peradeniya is the University's digital gateway to scholarly knowledge and research excellence. Established as the next phase of the Digital Library initiative launched by the University Library in 2011, it preserves, showcases, and provides open access to the intellectual output of the University community.

Through a rich collection of research articles, conference proceedings, theses, dissertations, and other scholarly works, the repository enhances the visibility, accessibility, and long-term preservation of knowledge, extending the global reach and impact of the University of Peradeniya’s academic and research contributions.

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Palibhasajjhayanabhiyoga
(University of Peradeniya, Sri Lanka, 2015-10-20) Ayasma Mirisvattagamajo Vimalanano
Uddeso Imam pariyesanalekhanam pana imasmimsamaye Palibhasayauggahana-ugganhapanapatisamyuttassa "New Trends in the Study of Poli Language since 20 Century and their Long-term Effects" iti imassapariyesanalekhane antogadhanam matinam vivaranaya, vibhajanaya, uttanikaranaya tathapi dos@paharanaya ca hoti. Tam kho pana lekhanam Sanat Nanayakldira (Sanath Nanayakkara) iti pandito so mahasayo 2007 vasse Pali-sogatadhamma ajjhayananvopadhi-ayatanena pakasite Vimamsa iti pariyesanalekhanasamuccaye argaliya-bhasaya pakatikatam hoti. Tasmirp Lekhane paridipita ekacce matT saddahanto, ekacce mati vicarayanto ca ayam pariyesako tassa lekhane ajjatana palibhasa- ajjhayane parihani dassento uddittha mai ca taya parihaniya niddittha-hetu ca vittharakarena vimarpsati ca paridipayati ca.
Flow in s-shaped open channel bends
(University of Peradeniya, 1983) Keerthisena, Hewa Henipelle Jeevananda
The understanding of the physical processes governing the flow in meandering bends is rather poor. This is mainly as a result of a lack of reliable and detailed information on S-shaped open channel bends. Such information is invaluable in interpreting results of distorted scale models of river bends and in improving the design of S-shaped passages used in various duct systems. In the work reported here three S-bend configurations are investigated over a wide range of flow conditions. Through detailed measurements of the water surface elevations, bed shear stresses and velocity field, the influence of the relevant geometric and flow parameters is analysed and the main features of the flow in open channel S-bends of moderate curvature are explained. It is found that the reversal of curvature in S-bends leads to significant deformation of the water surface and that the attendant transverse variations of longitudinal pressure gradients have a dominant influence on the redistribution of velocity and of bed shear stress, and on the development and decay of helical flow in S-bends of moderate curvature. Unlike in shallow bends of mild curvature at low Froude numbers, where the flow adjusts freely to the demands of the induced secondary flow, in moderately curved S-bends, at moderate aspect ratios and Froude numbers, the flow is constrained by the strong longitudinal pressure gradients. At high aspect ratios and Froude numbers the secondary flow is found to be weak and the maximum velocity is located close to the inner wall. The trace of maximum bed shear race stress does not follow the trace of maximum velocity and is out of phase with the trace of maximum bed skew angle in the early parts of the bends. Unlike in the exit region of a single bend leading to a straight channel, the flow in the crossover region of an S-bend is severly deformed and strong lateral nonuniformities are observed. A pair of counterrotating vortices appearing in the second half of an S-bend gives rise to higher skew angles in the central part of the vertical and the streamline pattern near the bed does not fairly represent the helical flow in S-bends. Simplified mathematical descriptions are presented for the skew angle variation in S-bends, for the deduction of secondary flow profiles from main velocity profiles and for the effects of streamwise acceleration and deceleration of main flow. Using the findings of the present study, several conflicting results in earlier investigations are satisfactorily explained.
Investigations into Alkali-Aggregate Reaction in concrete structures
(University of Peradeniya, 2013) Pathirana, Chintha Kusumlatha
Alkali Aggregate Reaction (AAR) is a chemical reaction taking place in concrete between alkalis in pore solution of cement paste and reactive phases in aggregates, with mechanical implications. It causes the concrete concerned to undergo expansion with time, resulting in premature cracking of concrete, and unwarranted deformations in structures which could shorten their service lifetime. In Sri Lanka, so far there has been no documented evidence of systematic investigations on AAR in structures. Nevertheless there are a few old concrete structures which are still being used, but showing symptoms similar in nature to those of AAR. Since characteristics of aggregate mainly contribute to AAR a substantial part of the present study is devoted to investigate the potential alkali-silica reactivity of Sri Lankan aggregates. In this study, the standard tests, ASTM C289 - 07 for potential alkali-silica reactivity of aggregates (chemical method) and ASTM C295 - 07 for petrographic examinations, have been performed on samples collected from numerous locations spreading over Sri Lanka, representing a wide range of morphological types of coarse and fine aggregates. Based on the results of these tests, as the next step, ASTM C1260 - 7 for the potential alkali reactivity of aggregates (mortar-bar method) was performed on selected samples. Based on the results, a new parameter named, 'Potential Reactivity Index' (PRI), has been proposed as an index to rank slowly reactive aggregates. The degree of reactivity has been quantified by extending the rapid chemical test covered by ASTM C289. A correlation was established between the expansion of aggregates and PRI. The degradation of concrete was assessed by ultrasonic and acoustic tests. The results of ultrasonic pulse velocity and vi resonant frequency testing have shown that the dynamic modulus of elasticity of the concretes is affected by AAR. If AAR takes place in an existing concrete structure it might become necessary to implement remedial measures which can vary from blocking moisture ingress to introducing stress-relief cuts in concrete. To initiate remedies, the presence of AAR in a structure has to be detected. Then the progress of AAR along with its potential for causing structural distress needs to be predicted. To understand the structural implications of AAR, computer simulations can be performed. The present study uses a methodology for using a general purpose finite element program package to simulate AAR numerically. AAR is considered as a thermal equivalent expansion process, in which the expansion of the concrete due to the equivalent temperature rise is equal to the expansion due to AAR. A computer code has been developed for this purpose and validated using analytical solutions to several benchmark problems. A real structure under alkali-aggregate reaction, found in literature has been analyzed using the proposed numerical procedure.
Capability limits of doubly fed induction generator wind turbines
(University of Peradeniya, 2012) Tennakoon, A. P.
The research investigates mainly the capability of Doubly Fed Induction Generator (DFIG) wind turbines to meet the grid code requirements with special emphasis on stability. A complete modelling of the DFIG was carried out for this purpose for both transient and steady state analysis. A controller was designed with a novel technique for tracking the rotor angle. The performance of the DFIG with battery as an energy storage device connected to the DC link was investigated. A method was formulated using the wind data for the derivation of battery capacity that should be used. Eigen value analysis was undertaken to determine the influence of connecting battery at the DC link and a comparison was made with the DFIG model with capacitor connected at the DC link. Since having a battery as an energy storage device connected to the DC link had many advantages this was chosen for the final DFIG model with the controller. A laboratory set up of a prototype DFIG was done similar to the derived model with a battery connected to the DC link. Tests were carried out using the control techniques derived during the modeling. The methods developed for tracking the rotor angle for rotor current injection were tested. Adjustments were made where necessary during testing and a final controller model was validated experimentally. The behavior of the DFIG output with rotor current injection were checked and investigated. Then using the model of the DFIG with the developed controller, dynamic behaviour of the DFIG with and without energy storage was investigated. A comparison for response to wind fluctuations and fault ride through operation was compared for DFIG with battery and DFIG with Capacitor connected to DC link. Using the derived and validated DFIG model and the controller, an investigation was carried out on capability limits of the DFIG, when operating within the specified speed range taking in to consideration the limitations on the rotor power, stator current and the stability. It was investigated on how the stability could be improved by selecting wound rotor induction machine with different machine parameters and reactive power exchange with the power system. A capability chart of the DFIG was prepared using an iteration method. A small signal model of the DFIG wind farm, connected with the power system, was used for the stability studies with Eigen value analysis. Finally, a case study was carried out to find the feasibility of connecting a DFIG based wind farm with energy storage at Puttalam area in Sri Lanka. Dynamic studies were carried out and the performance was compared with a DFIG wind farm with and without energy storage. The impact on the present power system for wind fluctuations and fault ride through operation was investigated.
Improvements in stress life approach for fatigue damage assessment of steel structures and components
(University of Peradeniya, 2015) Bandara, A. M. A. C. S.
Fatigue is a common problem in steel structures and components when they are subjected to cyclic loading. Fatigue assessments require testing. As fatigue testing (cyclic testing) is costly and time consuming, analytical models with a few monotonic tests are usually used for fatigue assessments. However, still there are areas in fatigue studies where not enough research has been done. Therefore, some of these research areas were studied to close existing research gaps and to solve the problems in metal fatigue to some extent. The main fatigue areas studied were: very high cycle fatigue (VHCF); full range stress - life models (S- N curves); nondestructive methods for developing full range S-N curves; effects of corrosion on full range S-N curves and fatigue damage assessment procedures for steels. First, a simple strength based model was proposed for predicting the critical size of fracture origins after an extensive study on very high cycle fatigue of steels. Experimental fatigue data of a number of various steels were used in this study. Then, using the proposed model and existing S-N relations, a new fatigue strength prediction formula was proposed for the very high cycle fatigue region (new VHCF model). The applicability of the new VHCF model for low carbon structural steels was verified using laboratory fatigue testing. Next, a model for a full range S-N curve was proposed for steels using the new VHCF model, existing low and high cycle stress life relationships and a mathematical function. This S-N model proposed (new full range S-N model) describes the entire stress and cycle range from the 1st cycle to very high cycles (gigacycles). The new full range S-N model was verified using experimental fatigue data of seven medium strength steels. Salient features of the new full range S-N model are that it requires only monotonic strength and hardness properties of steels to predict the S-N curves of steels. Highlighting the importance of nondestructive methods for damage assessments, a nondestructive full range S-N model for steels was proposed using the new full range S-N model. Material hardness was used as the only nondestructive test parameter in this model (hardness based S-N model). The hardness based S-N model too was verified using experimental fatigue data of seven medium strength steels. This hardness based S-N model is iii special because it only requires material hardness for predicting the S-N curve and that it is able to describe the entire fatigue range from the 1st cycle to gigacycles fairly accurately. Corrosion is unavoidable in most structures and components exposed to a corrosive atmosphere. Therefore, the new full range S-N model was modified to take into account the effects of corrosion (corrosion based S-N model). The corrosion based S-N model was verified using three medium strength steels tested in laboratory. Apart from hardness and strength parameters, the only parameter required to predict a full range S-N curve using this model is the fatigue strength of the steel in the high cycle region in the corrosive media. The S-N models proposed in this study are equivalent to axial, fully reversed, constant amplitude mean S-N curves. Therefore, modifications are necessary for the proposed full range S-N models when using them in real structures with various geometries and loading conditions. Therefore, a new damage assessment procedure was proposed using existing damage assessment methods. This new procedure takes into account the stress concentration effects, different cyclic loading ratios and variable amplitude loading. The proposed assessment procedure was verified using experimental fatigue data. Finally, a connection detail of a steel bridge was used as a case study to show the efficiency of the proposed damage assessment procedure and S-N models against the methods used in design codes.