Faculty of Engineering
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Publication Open Access Entrance zone effect on the sediment trapping efficiency in desilting tanks of run-of-river type mini-hydropower plants(The University of Peradeniya, Peradeniya, Sri Lanka, 2007-11-30) Rathnayake, U. S; Harishchandra, M. R. T. S; Weerakoon, S. BDevelopment of run-of-river type minihydropower plants is receiving increased attention in Sri Lanka at present owing to the incentives announced for developers of renewable power generation projects during the last decade by the Sri Lankan government. The sources for most of the run-of-river type mini hydropower plants are mountainous streams where the discharges experience significant seasonal variation with frequent flash floods. The catchments of these streams are generally steep and face an increasing trend of soil erosion due to cultivation and other human activities. Therefore, the stream flows carry high sediment loads during seasonal floods. This sediment-laden flow enters the headrace canals feeding water to the turbines of the rninhydropower plants. Sediment in the water passing through the turbines with high velocity erode the contact surfaces of turbine components. The erosion of turbine components leads to a drop in hydraulic efficiency and to a high maintenance cost of the turbines. Removal of sand carried with the flow in the headrace canals of run-of-river mini hydropower plants is therefore an important issue for the developers to reduce the maintenance cost of the turbines (Singal and Ranendra, 2006). Introduction of a de-silting tank in series with the headrace canal is one of the commonly used techniques for this purpose. De-silting tanks are designed as settling basins to settle sediment greater than a targeted size (Janssen, 2004). The shape and the size of the de-silting tank are major factors affecting the sand trapping efficiency of the desilting tank. Several empirical and semiempirical relations for the efficiency of …Publication Open Access Experimental investigation of hyporheic interactions(2010) Rathnayake, U. S; Izumi, NResearch on hyporheic interactions is not new to the present world, but most of the previous research is in the environmental and ecological points of view. This study was to understand the hyporheic interactions by means of engineering perspectives. Several experiments were carried out at laboratory scale to identify the relationships between important non-dimensional river parameters and non-dimensional interaction parameters. Results can be concluded to show some clear relationships among the non-dimensional parameters.Publication Open Access Impact of urbanization on earth resources in suburbs of Colombo, Sri Lanka(NSF: Colombo, 2019) Rathnayake, U. SClimate change is believed to be a critical issue and there is enough evidence to identify the impact of climate change. Sri Lanka is expected to be one of the most affected countries from adverse impact of climate change. Various climatic models propose a rise of rainfall intensity to south Asian region while the number of rainy days are to be reduced. Therefore, the necessity is raised to find the clear trends in climatic factors in the region. However, a very few research work was carried out to see the climatic changes over the last few decades in Sri Lanka. Temporal variation of precipitation (rainfall) can be a good indicator to identify the trends in climate. In addition, these rainfall variations are used in many engineering aspects, including design of massive civil engineering structures like dams, design of water supply networks, etc. Furthermore, the rainfall variations are not only important in engineering aspects but also heavily in agriculture. Therefore, this research work targets to find the temporal variations of rainfall n Sri Lanka and then, to project the results to the available water resources.Publication Open Access Scientific Investigation of Ancient Sri Lankan Private Labor Room (Thimbiri Geya)(Department of Archaeology, University of Kelaniya, 2020) Rathnayake, U. S; Suratissa, D. M; Hashan, T; Siriwardena, K. N. T; Udugama, D. CSri Lanka is a proud nation in the world for its ancient architectural and irrigational structures. Unlike today, the hospitals were not served for purpose of natural labor and delivery. Most of the houses have had a private labor room (Thimbiri Geya) for the purpose. However, the architectural plan of the labor room was different from the other bedrooms of the house. The room had provided the better quality of hygienic level and health conditions to the expecting mothers and the newborn babies. The room was sometimes used for other functions including the control of epidemic diseases, control of post childbirth psychosis and for healing wounds. It is interested to understand the scientific concepts behind this labor room and then, to learn and practice them if possible, for today’s world. Therefore, experiments were carried out using three sample labor rooms (3×4 square feet sized) under the same environmental conditions to scientifically investigate the ancient architecture. Unit A were constructed similar to the ancient labor room while unit B was constructed similar to the ancient labor room, but the walls were built by cement blocks and unit C was constructed according to the modern-day room with cement floors. These three rooms were monitored for atmospheric temperature, atmospheric humidity, dissolved oxygen (DO) of water samples of well water and pipe born water and microbial actions on some selected food (bread, meat and fish). It was found out that the room temperature and humidity levels of unit A were much lower to the other rooms and the three strata of floor in unit A could be reason for those. In addition, higher DO levels and lower microbial activities were recorded in unit A. The results suggest the usage of ancient system is a way forward approach in the path of sustainability in health care facilities in the modern world. However, it is also advised to have more experiments in a longer time span to reveal more interesting features of the ancient labor room (Thimbiri Geya) in Sri LankaPublication Open Access Regression-Based Prediction of Power Generation at Samanalawewa Hydropower Plant in Sri Lanka Using Machine Learning(Hindawi, 2021-07-31) Ekanayake, P; Wickramasinghe, L; Jayasinghe, J. M; Rathnayake, U. SThis paper presents the development of models for the prediction of power generation at the Samanalawewa hydropower plant, which is one of the major power stations in Sri Lanka. Four regression-based machine learning and statistical techniques were applied to develop the prediction models. Rainfall data at six locations in the catchment area of the Samanalawewa reservoir from 1993 to 2019 were used as the main input variables. The minimum and maximum temperature and evaporation at the reservoir site were also incorporated. The collinearities between the variables were investigated in terms of Pearson’s and Spearman’s correlation coefficients. It was found that rainfall at one location is less impactful on power generation, while that at other locations are highly correlated with each other. Prediction models based on monthly and quarterly data were developed, and their performance was evaluated in terms of the correlation coefficient (R), mean absolute percentage error (MAPE), ratio of the root mean square error (RMSE) to the standard deviation of measured data (RSR), BIAS, and the Nash number. Of the Gaussian process regression (GPR), support vector regression (SVR), multiple linear regression (MLR), and power regression (PR), the machine learning techniques (GPR and SVR) produced the comparably accurate prediction models. Being the most accurate prediction model, the GPR produced the best correlation coefficient closer to 1 with a very less error. This model could be used in predicting the hydropower generation at the Samanalawewa power station using the rainfall forecast.Publication Embargo A new hybrid fuzzy time series model with an application to predict PM10 concentration(www.elsevier.com/locate/ecoenv, 2021-10-28) Alyousifi, Y; Othman, M; Husin, A; Rathnayake, U. SFuzzy time series (FTS) forecasting models show a great performance in predicting time series, such as air pollution time series. However, they have caused major issues by utilizing random partitioning of the universe of discourse and ignoring repeated fuzzy sets. In this study, a novel hybrid forecasting model by integrating fuzzy time series to Markov chain and C-Means clustering techniques with an optimal number of clusters is presented. This hybridization contributes to generating effective lengths of intervals and thus, improving the model accuracy. The proposed model was verified and validated with real time series data sets, which are the benchmark data of actual trading of Taiwan Stock Exchange Capitalization Weighted Stock Index (TAIEX) and PM10 concentration data from Melaka, Malaysia. In addition, a comparison was made with some existing fuzzy time series models. Furthermore, the mean absolute percentage error, mean squared error and Theil's U statistic were calculated as evaluation criteria to illustrate the performance of the proposed model. The empirical analysis shows that the proposed model handles the time series data sets more efficiently and provides better overall forecasting results than existing FTS models. The results prove that the proposed model has greatly improved the prediction accuracy, for which it outperforms several fuzzy time series models. Therefore, it can be concluded that the proposed model is a better option for forecasting air pollution parameters and any kind of random parameters.Publication Open Access Hydrologic utility of satellite-based and gauge-based gridded precipitation products in the Huai Bang Sai watershed of Northeastern Thailand(https://www.mdpi.com/journal/hydrology, 2021-11-01) Gunathilake, M; Zamri, M. N. M; Alagiyawanna, T; Samarasinghe, J; Baddewela, P; Babel, M; Jha, M; Rathnayake, U. SAccurate rainfall estimates are important in many hydrologic activities. Rainfall data are retrieved from rain gauges (RGs), satellites, radars, and re-analysis products. The accuracy of gauge-based gridded precipitation products (GbGPPs) relies on the distribution of RGs and the quality of rainfall data records obtained from these. The accuracy of satellite-based precipitation products (SbPPs) depends on many factors, including basin climatology, basin topography, precipitation mechanism, etc. The hydrologic utility of different precipitation products was examined in many developed regions; however, less focused on the developing world. The Huai Bang Sai (HBS) watershed in north-eastern Thailand is a less focused but an important catchment that significantly contributes to the water resources in Thailand. Therefore, this research presents the investigation results of the hydrologic utility of SbPPs and GbGPPs in the HBS watershed. The efficiency of nine SbPPs (including 3B42, 3B42-RT, PERSIANN, PERSIANN-CCS, PERSIANN-CDR, CHIRPS, CMORPH, IMERG, and MSWEP) and three GbGPPs (including APHRODITE_V1801, APHRODITE_V1901, and GPCC) was examined by simulating streamflow of the HBS watershed through the Soil & Water Assessment Tool (SWAT), hydrologic model. Subsequently, the streamflow simulation capacity of the hydrological model for different precipitation products was compared against observed streamflow records by using the same set of calibrated parameters used for an RG simulated scenario. The 3B42 product outperformed other SbPPS with a higher Nash–Sutcliffe Efficiency (NSEmonthly>0.55), while APHRODITE_V1901 (NSEmonthly>0.53) performed fairly well in the GbGPPs category with closer agreements with observed streamflow. In addition, the CMORPH precipitation product has not performed well in capturing observed rainfall and subsequently in simulating streamflow (NSEmonthly<0) of the HBS. Furthermore, MSWEP and CHIRPS products have performed fairly well during calibration; however, they showcased a lowered performance for validation. Therefore, the results suggest that accurate precipitation data is the major governing factor in streamflow modeling performances. The research outcomes would capture the interest of all stakeholders, including farmers, meteorologists, agriculturists, river basin managers, and hydrologists for potential applications in the tropical humid regions of the world. Moreover, 3B42 and APHRODITE_V1901 precipitation products show promising prospects for the tropical humid regions of the world for hydrologic modeling and climatological studies.Publication Open Access Trend analysis and change point detection of air pollution index in Malaysia(Springer Berlin Heidelberg, 2021-11-21) Alyousifi, Y; Ibrahim, K; Zin, W. Z. W; Rathnayake, U. SParametric methods are commonly used to conduct the trend analysis of air pollution. These methods require certain statistical assumptions, such as stationarity and normality of the data. However, such assumptions are usually not applicable to trends in Air pollution index (API). In addition, the change points in the time series have not been taken into consideration by most of the analysis of API. Therefore, this study presents a comprehensive investigation of the trend analysis and change point detection of the mean and maximum of API series in Malaysia. The hourly, daily, weekly, monthly, seasonal, and annual API data series were considered in the analysis. The fner time intervals were used to detect any signifcant increasing or decreasing trends of the API series for Malaysia. The API data were collected from 37 air monitoring stations in Peninsular Malaysia. The nonparametric tests, including Mann–Kendall test, Pettitt test, and innovative trend analysis were used to examine the contribution presented herein. Various aspects of API data were studied, including upward trends, downward trends, and change points. Several signifcant monotonic trends and changing points in some of the API measuring stations were found from the Mann–Kendall test results. Signifcant increasing trends of the monthly and seasonal mean, as well as maximum API, were found in the years 2013 and 2014 for some stations. In addition, the magnitudes of the increasing trends in maximum API are larger than the mean API. The detection points captured by the Pettitt test are possibly related to the El-Nino events. In general, the results of the study provide comprehensive information on air quality trends and their atmospheric aspects, which can help in developing strategies to address air quality problems and provide meaningful opportunities to mitigate air pollution problems in Peninsular Malaysia.Publication Open Access Projected Moisture Index (MI) for tropical Sri Lanka(Hindawi, 2021-12) Wickramarachchi, C; Samarasinghe, T; Alyousifi, Y; Rathnayake, U. SAtmospheric moisture loading can cause a great impact on the performance and integrity of building exteriors in a tropical climate. Buildings can be highly impacted due to the changing climate conditions over the world. Therefore, it is important to incorporate the projected changes of moisture loads in structural designs under changing climates. The moisture index (MI) is widely used in many countries as a climate-based indicator to guide the building designs for their durability performance. However, this was hardly considered in structural designs in Sri Lanka, even though the country is one of the most affected countries under climate change. Therefore, this study investigates future climate change impacts on the environmental moisture in terms of MI, which can be used in climate zoning, investigating indoor air quality, understanding thermal comfort and energy consumption, etc. The moisture index was found as a function of the drying index (DI) and wetting index (WI) to the whole country for its four rainfall seasons. The temporal and spatial distributions were plotted as MI maps and showcased under two categories; including historical MI maps (1990–2004) and future projected MI maps (2021–2040, 2041–2070, and 2071–2100). Future projected MI maps were constructed using bias-corrected climatic data for two RCP climatic scenarios (RCP4.5 and RCP8.5). Results showed that the temporal and spatial variations of MIs are justifiable to the country’s rainfall patterns and seasons. However, notable increases of MIs can be observed for future projected MIs in two seasons, and thus a careful investigation of their impacts should be assessed in terms of the construction of buildings and various agricultural activities. Therefore, the outcome of this research can be essentially used in policy implementation in adapting to the ongoing climate changes in Sri Lanka.Publication Open Access Theoretical analysis for the interaction between the river flow and the seepage flow(Proceedings of the 6th WSEAS International Conference on FLUID MECHANICS, 2009) Rathnayake, U. S; Izumi, NMany previous studies have been carried on the interaction between river flow and the seepage flow in the environmental point of view, but these hardly touch on the boundary conditions or the limitations for the interactions. The subsurface layer below the river is known as the hyporheic layer and it is a saturated band of sediment that surrounds river flow and forms a linkage between the river and the aquifer. 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. Linear stability analysis technique is used to understand the stability of the natural flows in rivers as well as the flows occurred in the air by many researchers. In this study a linear stability analysis is carried out to presents the interaction between the river flow and seepage flow. Reynolds averaged Navier-Stokes equations and Brinkman-Forchheimer equations are used in order to formulate the river flow and seepage flow interaction. The open channel flow is analyzed by mixing length turbulent model and Spectral collocation method incorporated with the Chebyshev polynomials are used to perform the numerical solution of the perturbed equations. Instability diagrams are discussed with several slopes of the layers against the dimensionless particle diameter and wave numbers. It has been noted that the instability occurs even in the range of small dimensionless particle diameter with relatively high wave numbers if there is a seepage layer beneath the flow and the instability region increases with the slope when the wave numbers are at small values.