Browsing by Author "Hansameenu, W. P. T."

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Controllability of a system of coupled harmonic oscillators
(Research Symposium on Pure and Applied Sciences, 2018 Faculty of Science, University of Kelaniya, Sri Lanka, 2018) De Silva, R. N. S.; Hansameenu, W. P. T.
In general, it is worthwhile to understand and control the dynamics of an existing system whose output behaves somewhat closer to the desired output rather than developing a new system which tracks the desired output, since it is beneficial for industries in many aspects; low cost, less time, etc. In this research, we control the output of a couple harmonic oscillator which has been extensively used in many Engineering Models by mainly focusing on two types of control techniques, namely source term controlling and initial condition controlling. Numerical results using MATLAB validates that controlled system output tracks the desired output for these two types of controlling. Consider the governing equations:
Controllability of a system of coupled harmonic oscillators
(Research Symposium on Pure and Applied Sciences, 2018 Faculty of Science, University of Kelaniya, Sri Lanka, 2018) De Silva, R. N. S.; Hansameenu, W. P. T.
In general, it is worthwhile to understand and control the dynamics of an existing system whose output behaves somewhat closer to the desired output rather than developing a new system which tracks the desired output, since it is beneficial for industries in many aspects; low cost, less time, etc. In this research, we control the output of a couple harmonic oscillator which has been extensively used in many Engineering Models by mainly focusing on two types of control techniques, namely source term controlling and initial condition controlling. Numerical results using MATLAB validates that controlled system output tracks the desired output for these two types of controlling. Consider the governing equations: 𝑚𝑥̈1 = − 𝑚𝑔 𝑙 𝑥1 + 𝑘(𝑥2 − 𝑥1) ,𝑚𝑥̈2 = −𝑚𝑔 𝑙 𝑥2 + 𝑘(𝑥1 − 𝑥2) 𝑥1(0) = 𝛼,𝑥2(0) = 𝛽,𝑥̇1(0) = 𝛾,𝑥̇2(0) = 𝜇. (i) Controlling by the source term: Let the desired outputs 𝑥1 and 𝑥2 be given by 𝑥1 = 𝑟 sin(𝑝𝑡) + 𝑤 sin(𝑞𝑡),𝑥2 = −𝑟 sin(𝑝𝑡) + 𝑤 sin(𝑞𝑡) where r, w, p, and q are parameters. Then controlled system for the source term is given by 𝑚𝑥̈1 = − 𝑚𝑔 𝑙 𝑥1 + 𝑘(𝑥2 − 𝑥1) + 𝛼(𝑡), 𝑚𝑥̈2 = −𝑚𝑔 𝑙 𝑥2 + 𝑘(𝑥1 − 𝑥2) + 𝛽(𝑡) and the source terms are 𝛼(𝑡) = 𝐴 sin(𝑝𝑡) + 𝐵 sin(𝑞𝑡) and 𝛽(𝑡) = −𝐴 sin(𝑝𝑡) + 𝐵 sin(𝑞𝑡), where 𝐴 = −𝑟𝑚𝑝2 − 𝑠𝑟 + 𝑘𝑟, 𝐵 = −𝑤𝑚𝑞2 − 𝑘𝑤 − 𝑠𝑤 and 𝑠 = −(𝑚𝑔 𝑙 + 𝑘) for 𝑥1(0) = 0, 𝑥2(0) = 0,𝑥̇1(0) = 𝛾,𝑥̇2(0) = 𝜇. (ii) Controlling by the initial condition: Let the desired output 𝑥1 and 𝑥2 be given by 𝑥1 = 𝑎𝑒√𝜆+𝜙 𝑡 + 𝑏𝑒−√𝜆+𝜙 𝑡 + 𝑐𝑒√𝜆−𝜙 𝑡 + 𝑑𝑒−√𝜆−𝜙 𝑡, 𝑥2 = 𝑎𝑒√𝜆+𝜙 𝑡 + 𝑏𝑒−√𝜆+𝜙 𝑡 − 𝑐𝑒√𝜆−𝜙 𝑡 − 𝑑𝑒−√𝜆−𝜙 𝑡 , where 𝜆 = −(𝑔 𝑙 + 𝑘 𝑚 ) and 𝜙 = 𝑘 𝑚 . By considering the system (1) the controlled system for initial conditions is given by 𝑚𝑥̈1 = −𝑚𝑔 𝑙 𝑥1 + 𝑘(𝑥2 − 𝑥1) ,𝑚𝑥̈2 = −𝑚𝑔 𝑙 𝑥2 + 𝑘(𝑥1 − 𝑥2) with initial conditions: 𝑥1(0) = 𝛼 + (𝑎 + 𝑏 − 𝑐 − 𝑑) − (𝐴 + 𝐵 − 𝐶 − 𝐷),𝑥2(0) = 𝛽 + (𝑎 + 𝑏 + 𝑐 + 𝑑) − (𝐴 + 𝐵 + 𝐶 + 𝐷),𝑥̇1(0) = 𝛾 + ( (𝑎−𝑏)−(𝐴−𝐵) √𝜆+𝜙 + (𝐶−𝐷)−(𝑐−𝑑) √𝜆−𝜙 ),𝑥̇2(0) = 𝜇 + ( (𝑎−𝑏)−(𝐴−𝐵) √𝜆+𝜙 + (𝑐−𝑑)−(𝐶−𝐷) √𝜆−𝜙 ) where 𝐴 = 1 4 (𝛼 + 𝛽 + 𝛾 √𝜆+𝜙 + 𝜇 √𝜆+𝜙 ),𝐵 = 1 4 (𝛼 + 𝛽 − 𝛾 √𝜆+𝜙 − 𝜇 √𝜆+𝜙 ), 𝐶 = −1 4 (𝛼 − 𝛽 + 𝛾 √𝜆−𝜙 − 𝜇 √𝜆−𝜙 ) ,𝐷 = − 1 4 (𝛼 − 𝛽 − 𝛾 √𝜆−𝜙 − 𝜇 √𝜆−𝜙 ).
Convective heat transfer through a pipe with mixed boundary conditions
(Faculty of Science, University of Kelaniya Sri Lanka, 2023) Imeshan, W. U.; Hansameenu, W. P. T.
Convective heat transfer is crucial in various engineering applications, particularly in systems involving fluid flow through pipes. Understanding the heat transfer characteristics in such systems is essential for optimizing thermal performance and ensuring safe operation. The study of convective heat transfer through a pipe with mixed boundary conditions is significant for several reasons. It represents a more realistic representation of many industrial systems, where different pipe sections may experience diverse thermal environments. Also, accurately predicting heat transfer parameters under mixed boundary conditions is essential for designing and optimizing thermal systems, ensuring adequate heat dissipation or heat transfer efficiency. This study investigates convective heat transfer through a pipe with mixed boundary conditions: constant heat flux and variable wall temperature boundary conditions to examine the impact of temperature-dependent thermophysical properties on hydrodynamic and heat transfer characteristics. By conducting computational fluid dynamics (CFD) simulations, the velocity and temperature behaviours of the fluid are analysed under combinations of constant heat flux and variable wall temperature boundary conditions. The effects of fluid parameters are investigated to assess their influence on heat transfer performance. CFD analysis in COMSOL Multiphysics is carried out by coupling the continuity, momentum, and heat equations to determine the velocity and temperature profiles for a three-dimensional incompressible, steady, viscous laminar flow through a pipe with a diameter of 0.25𝑚 and length of 1𝑚. The mixed wall boundary conditions: linear temperature (0.5𝑚 ≤ 𝑧 ≤ 1𝑚) and constant heat flux (𝑧 < 0.5𝑚) were considered. The results show that velocity reduces with increasing values of viscosity and magnifies with increasing values of density and volume expansion coefficients. Moreover, the temperature reduces with the increasing value of density.
Design of heat sink and simulation of electronic cooling of power transistor circuit
(Faculty of Science, University of Kelaniya Sri Lanka, 2022) Gunasinghe, L. M.; Samaranayake, W. J. M.; Hansameenu, W. P. T.
Heat sinks are utilized in industrial equipment to disperse surplus heat from heat-generating components to the surrounding environment. In recent years, efforts have been made to develop mechanical or electronic devices that are lighter, smaller, and more affordable. Heat dissipation from the heat sink is a major issue that many researchers are attempting to address. In this work, a traditional heat sink design technique of computer power supplies, which is extending fin topology, is used with four power transistors. This study attempts to improve the cooling of power transistor circuits by designing a new heat sink attached to four power transistors and seeing how the joule heating profile of the power transistor circuit and heat sink are changed. COMSOL Multiphysics version 5.6 software is used to graphically design the heat sink, four-transistor circuit and simulate the heat profile of the design. An electric currents interface and a heat transfer in solids interface are included in the Multiphysics interface. The multiphysics couplings add electromagnetic power dissipation as a heat source and investigate the joule heating and the temperature distribution on power transistors without the heat sink and with the heat sink. Transistors without the new heat sink get heated more than the transistors with the new heat sink with the same applied current density to the circuit board. It shows that joule heating is minimized with the new heat sink design. Here, the results of several studies of a new geometrical 3D model that focus on four power transistors attached to an aluminium heat sink are discussed. The results show the impact of the heat sink area and surface-to-ambient radiation to the power transistors and the circuit board. Based on the simulation results, four transistors become very cooled with the new heat sink design. How the heat-sink thermal performance is affected by shapes and space between fins is also reviewed. It could be observed that in the proposed design, the joule heating was reduced remarkably.
The Holt-Winters’ method for forecasting water discharge in Attanagalu Oya
(Faculty of Science, University of Kelaniya, Sri Lanka., 2021) Anuruddhika, M. L. P.; Premarathna, L. P. N. D; Perera, K. K. K. R.; Hansameenu, W. P. T.; Weerasinghe, V. P. A.
Forecasting river water discharge is significant in developing flood and agriculture management plans. Annual flood events damage properties, agricultural field, and infrastructures, etc. can be observed in Attanagalu Oya catchment area in Sri Lanka. Therefore, the aim of this study is to forecast water discharge rates (m3/s) at the Dunamale gauging station of Attanagalu Oya using Holt-Winter's method. Holt-Winter's method was chosen because of its’ ability to model trend and seasonal fluctuations, less data requirements and simplicity. Time series models were fitted using the Holt-Winter's method to daily water discharge rates for the period of 2015 –2019 and water discharge was forecasted for the year 2020. The accuracy of the fitted time series models was tested using root mean squares error (RMSE) and mean absolute error (MAE) values. Results showed that the additive Holt-Winters’ method is more appropriate for future forecasting which gave the minimum RMSE and MAE values. Forecasted results will be useful to identify future flood events in advanced to take necessary actions to mitigate damages.
Maximising the total population in a diffusive predator-prey system using optimal control theory
(Faculty of Science, University of Kelaniya Sri Lanka, 2024) Senanayake, N. S.; Hansameenu, W. P. T.
Studying population dynamics provides insights into the behavioural patterns of species. Several scholars have introduced different physical systems to understand behavioural patterns of real-world phenomena. Predator-prey interaction is one of the most common interrelationships in nature. Studying a diffusive predator-prey model is significant for several reasons which represents a more realistic representation of population dispersal in space, where a heterogeneous population exists. In this study, optimal control theory has been applied to a diffusive predator-prey system in analysing the population model to achieve the maximum total population. By implementing a time-dependent control variable 𝛼(𝑡) which is the mixing rate, to the diffusive predator-prey system, our concern is to maximise both predator and prey populations in a final time 𝑇. According to optimal control theory, under mathematical formulation, the Pay-off functional and the Hamiltonian are introduced along with the adjoint dynamics and the terminal conditions where the optimality criterion is satisfied. The Pontryagin Maximum Principle has been introduced such that the Hamiltonian is maximised where 0 ≤ 𝛼(𝑡) ≤ 1. More interestingly, we determined that the Hamiltonian would get its maximum value when 𝑝2𝜇2 - 𝑝1𝜇1 ≤ 0, where the optimal value of the control variable is 𝛼∗(𝑡) = 0 and if 𝑝2𝜇2 - 𝑝1𝜇1 > 0 then 𝛼∗(𝑡) = 1, where 𝑝1, 𝑝2 are costate functional and 𝜇1, 𝜇2 are the rate of prey loss and the growth rate of predators respectively. Furthermore, the term 𝑝2𝜇2 - 𝑝1𝜇1 is analysed under three cases which are 𝜇2 < 𝜇1, 𝜇2 = 𝜇1 and 𝜇2 > 𝜇1. From the analytical approach, we obtained that for the cases 𝜇2 < 𝜇1 and 𝜇2 = 𝜇1 the system is uncontrollable, and a switching time does not exist. The study reveals that the system is considered controllable only when 𝜇2 > 𝜇1 where a switching time exists such that the total population is maximised. A simulation is conducted under the case 𝜇2 > 𝜇1 to depict the results, achieving the maximum population at 𝑡 = 16.5 while setting the switching time as 𝑡 = 11. Finally, the obtained results were validated. Therefore, using both numerical simulation and estimates we concluded that 𝛼∗(𝑡) = 0 when [0, 𝑡2] and 𝛼∗(𝑡) = 1 when (𝑡2, 𝑇], where 𝑡2 is the switching time. In future work, it is expected to improve the analysis by implementing both time and space dependent control variable 𝛼(𝑥, 𝑡).
Maximising the total population in a diffusive predator-prey system using optimal control theory
(Faculty of Science, University of Kelaniya Sri Lanka, 2024) Senanayake, N. S.; Hansameenu, W. P. T.
Studying population dynamics provides insights into the behavioural patterns of species. Several scholars have introduced different physical systems to understand behavioural patterns of real-world phenomena. Predator-prey interaction is one of the most common interrelationships in nature. Studying a diffusive predator-prey model is significant for several reasons which represents a more realistic representation of population dispersal in space, where a heterogeneous population exists. In this study, optimal control theory has been applied to a diffusive predator-prey system in analysing the population model to achieve the maximum total population. By implementing a time-dependent control variable 𝛼(𝑡) which is the mixing rate, to the diffusive predator-prey system, our concern is to maximise both predator and prey populations in a final time 𝑇. According to optimal control theory, under mathematical formulation, the Pay-off functional and the Hamiltonian are introduced along with the adjoint dynamics and the terminal conditions where the optimality criterion is satisfied. The Pontryagin Maximum Principle has been introduced such that the Hamiltonian is maximised where 0 ≤ 𝛼(𝑡) ≤ 1. More interestingly, we determined that the Hamiltonian would get its maximum value when 𝑝2𝜇2 - 𝑝1𝜇1 ≤ 0, where the optimal value of the control variable is 𝛼∗(𝑡) = 0 and if 𝑝2𝜇2 - 𝑝1𝜇1 > 0 then 𝛼∗(𝑡) = 1, where 𝑝1, 𝑝2 are costate functional and 𝜇1, 𝜇2 are the rate of prey loss and the growth rate of predators respectively. Furthermore, the term 𝑝2𝜇2 - 𝑝1𝜇1 is analysed under three cases which are 𝜇2 < 𝜇1, 𝜇2 = 𝜇1 and 𝜇2 > 𝜇1. From the analytical approach, we obtained that for the cases 𝜇2 < 𝜇1 and 𝜇2 = 𝜇1 the system is uncontrollable, and a switching time does not exist. The study reveals that the system is considered controllable only when 𝜇2 > 𝜇1 where a switching time exists such that the total population is maximised. A simulation is conducted under the case 𝜇2 > 𝜇1 to depict the results, achieving the maximum population at 𝑡 = 16.5 while setting the switching time as 𝑡 = 11. Finally, the obtained results were validated. Therefore, using both numerical simulation and estimates we concluded that 𝛼∗(𝑡) = 0 when [0, 𝑡2] and 𝛼∗(𝑡) = 1 when (𝑡2, 𝑇], where 𝑡2 is the switching time. In future work, it is expected to improve the analysis by implementing both time and space dependent control variable 𝛼(𝑥, 𝑡).
Numerical evaluation of wave energy absorption and performance of a selection of wave energy converters in southern sea conditions of Sri Lanka
(Faculty of Science, University of Kelaniya Sri Lanka, 2022) Vishvanath, N. A. V.; Weerasinghe, M. H. L.; Hansameenu, W. P. T.
Ocean wave energy is undoubtedly the next crucial step in Sri Lanka’s energy sector. The abundance of this source of green energy, mainly in the Southern seas of Sri Lanka, has been identified and estimated in a handful of preliminary studies. In the present work, three wave energy converters are numerically modelled with the objective of estimating annual average electrical power and variations in seasonal average electrical power. A 1-body point absorber, 2-body point absorber, and an oscillating surge flap are simulated in sea conditions native to Tangalle, Galle, and Matara generated using measured and re-analysis data. The selection of the devices is mainly based on the depth of the location at which the data is available. The open-source numerical wave energy converter simulating software WEC-Sim is used as the dynamic equation solver, while the open-source Boundary Element Method code NEMOH is used to calculate hydrodynamic parameters. The power take-off is modelled as a linear spring-damper system in all three cases. A damping coefficient optimisation procedure is carried out using samples drawn from each set of data in which a comparative analysis was done to select the damping values that give the maximum power output. Under the optimised damping conditions, mechanical power matrices are generated which are then converted to electrical power matrices using a PTO efficiency conversion factor. Annual and seasonal average power outputs are calculated utilizing both electrical power matrices and joint probability distributions of sea states. The electrical power matrices generated for the 2-body point absorber, and oscillating surge flap are a clear indication that both the devices are naturally tuned to the dominant wave frequencies of tested locations, while the 1-body point absorber is tuned to sea states with lower periods. The highest output power is observed for oscillating surge flap, the second highest for the 2-body point absorber, and the lowest for the 1-body point absorber. The variation of the seasonal average power is significant over the four climatic seasons of Sri Lanka. The highest power observed in South-West monsoon is more than twice the lowest observed in North-East monsoon. The calculated annual average power and seasonal average power outputs are a clear indication of Sri Lanka’s potential for wave energy harvesting, although the greater variation in seasonal average power poses a considerable challenge.
Study of the improvement of Ozone production: A simulation
(Faculty of Science, University of Kelaniya Sri Lanka, 2022) Amarakoon, A. M. M. N. B.; Hansameenu, W. P. T.; Samaranayake, W. J. M.
Ozone is an unstable, colourless gas that has a pungent odour which occurs naturally in small amounts in the stratosphere. Ozone is one of the strongest oxidants. Major applications of ozone are disinfection, deodorization, decolourization, bleaching processes, semiconductor industry, treatment of industrial wastes, treatment of flue gases, chemical synthesis, potable and wastewater treatments etc. In many industrial applications, ozone is being used as an alternative oxidant for chlorination processes. It has a minimal negative impact on the environment and the extra benefit of requiring less energy for its production than other alternatives. This work was focused on a numerical simulation using MATLAB software and this study was aimed at understanding the discharge phenomenon in the ozoniser in detail, which could not be observed by experiments. It considered the rate coefficients of different plasma chemical reactions as a function of time using a single pulse and multiple pulses. The simulation study was carried out using differential equations of the plasma chemical reactions with the peak pulsed voltage (42.5 kV), pulse repetition rate (100 pulses per second, pps), input energy per pulse (∼0.22 J), pulse width (FWHM 100 ns), flow rate (3.0 l/min), the gaseous gap spacing (36 mm), the reactor length (1 m) and 1 cm pitch length of the spiral wire forming the central electrode at a pressure of 1.01×105 Pa and a temperature of 293 K. A central copper wire (1 mm in diameter) made to a cylindrical configuration (22 mm in diameter) in a concentric coaxial electrode system without a dielectric barrier was considered. The concentration of ozone was found for a single pulse as well as for multiple pulses, and the production yield of ozone was found at different concentrations. The dependence of the densities of atomic oxygen, excited and ground state of molecular oxygen has been investigated. The concentration of ozone reached a saturated value of 137.2 ppm after about 18 μs when a single pulse was applied. When a large number of pulses (105 pulses) were used, ∼33% of ozone could be produced from oxygen. The production yield of ozone was found to be strongly dependent on the concentration of ozone and it showed an optimal behaviour for each and every repetitive pulse. The dependence of the concentration and production yield of ozone in oxygen on the parameters studied generally agreed with the published literature, thus confirming the validity of the simulation model. This study covered a wide range of ozoniser conditions, including low and high concentrations and low and high yields of ozone that can be applied to various industrial applications.
Tracking problem of 1D damped translational mechanical system for harmonic signals
(4th International Research Symposium on Pure and Applied Sciences, Faculty of Science, University of Kelaniya, Sri Lanka, 2019) Leelarathne, H. M. A. K.; Hansameenu, W. P. T.
The translational mechanical systems play a major role in engineering systems such as automobile shock absorbing system, stock bridge damper, motion sensor etc. However, the damping influence of the translational mechanical systems is a major concern of system engineers. In this study, we consider a damped translational mechanical system and find control parameters, source term (force) and initial conditions, which are needed to track a harmonic signal.
Viscous Dissipation and thermal radiation of Williamson fluid flow over an exponentially stretching sheet
(Karunathilake N. G. A.; Hansameenu W. P. T.; Wijesiri G. S. (2023), Viscous Dissipation and thermal radiation of Williamson fluid flow over an exponentially stretching sheet, Proceedings of the International Conference on Applied and Pure Sciences (ICAPS 2023-Kelaniya) Volume 3, Faculty of Science, University of Kelaniya Sri Lanka. Page 78., 2023) Karunathilake, N. G. A.; Hansameenu, W. P. T.; Wijesiri, G. S.
This study investigates the viscous dissipation and thermal radiation of Williamson fluid flow over an exponentially stretching sheet. The analysis has been started with the governing equations of the fluid flow derived from the conservation of mass, momentum, energy, and concentration. The internal heat generation and absorption effect in the view of getting the influence of temperature difference between the free stream and stretching sheet have been incorporated. The Rosseland approximation and Taylor series expansion formulate the radiative heat flux. The density difference which interacts with the gravitational force, resulting in a natural convection heat and mass transfer process is described by the mass transfer phenomenon with the homogeneous first-order chemical reaction effect. The boundary layer approximations have been introduced to focus on the fluid flow near the stretching sheet. Furthermore, the governing system of partial differential equations has been converted into a nonlinear ordinary differential equation by using similarity transformations. The resulting non-linear coupled system of ordinary differential equations has been solved numerically by shooting techniques. The graphs have simulated and presented the qualitative impact of different flow parameters such as magnetic field, Prandtl number, Williamson number, Grashof number, and thermal radioactive parameter on the radial velocity, temperature, and mass concentration profiles. The study reveals that the Prandtl number intensifies the radial velocity and has a mixed impact on the temperature and concentration, which decreases with an increase in the magnetic parameter but increases temperature and concentration. Further with the increase of the Prandtl number, the velocity and the temperature decrease in general but increase the concentration. The radial velocity increases with the Radioactive parameter but the temperature and the concentration display mixed reactions to the parameter. The Grashof parameter intensifies the radial velocity but reduces the temperature and the concentration. The Williamson parameter does not significantly impact radial velocity, temperature, and concentration.