Master of Science By Research

Permanent URI for this collectionhttp://192.248.9.226/handle/123/11526

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item: Thesis-Abstract
A Molecular dynamics study on viscous and thermal properties of Nanofluids
(2023) Somarathna CN; Samaraweera N; Jayasekara S; Perera K
The aim of this study is to understand the microscopic behavior of heat and momentum transfer in nanofluids. With nanofluids reporting enhanced thermal conductivities (𝜅) and viscosities (𝜂), a microscopic understanding is essential for engineering nanofluids to be practical in heat transfer applications. Therefore, to study the microscopic transport behavior, copper-argon nanofluids simulated by classical molecular dynamics are employed. The Applicability of the Green-Kubo (GK) method in nanofluid 𝜅 evaluation is questioned as the calculated thermal conductivities through the GK method are considerably higher than the direct method in Non-EquilibriumMolecular-Dynamics (NEMD). Green-Kubo calculations are found to be very sensitive to the ill-defined partial enthalpy computation, resulting in an overestimation of the 𝜅. However, the Green-Kubo and the direct method viscosity calculations demonstrate a reasonable agreement. Following the more reliable method, the NEMD direct approach, 𝜅 of the nanofluids consisting of spherical nanoparticles with different diameters are investigated. The computational results are compared with the classical effective medium theories and no anomalous 𝜅 enhancements are observed in the nanofluids having fully dispersed spherical particles. Various microscopic mechanisms such as liquid layering and micro-convection are found to be ineffective for 𝜅 enhancements in nanofluids. However, greatly enhanced 𝜅 are achieved, a maximum of 63% relative to pure argon, in nanofluids consisting of chain-like particle arrangements. This demonstrates the potential origin of anomalous 𝜅 enhancements in experimental measurements and the capability of nanofluids with extended nanostructures to deliver better 𝜅 enhancements. Further investigating the capability of extended nanostructures in nanofluid thermal transport, 𝜅 enhancements of nanofluids consisting of nanowires with different lengths and diameters are evaluated. It is shown that the heat conduction in the parallelly arranged liquid and the nanowires exhibit a coupled thermal behavior owing to the interface thermal resistance (R b ). This contradicts with the predictions of the classical parallel heat conduction model and therefore, a novel model is proposed taking this coupled behavior into account. New heat transfer characteristics at the nanoscale are identified including the R b -driven coupled heat conduction, the reduced 𝜅 of suspended nanowires, and the solid-like liquid layering. Using the new model, the importance of these microscopic thermal characteristics in accurately predicting the effective 𝜅 is shown. The sole contribution from the solid-like liquid layer to the 𝜅 enhancement is found to be in between 20-30% for the nanofluids considered. Extending the investigation of heat transfer phenomena in nanofluids based on spherical nanoparticles, 𝜂 of nanofluids with different nanoparticle sizes, concentrations, and arrangements are evaluated. Both the Green-Kubo and the direct methods are employed and unlike the 𝜅, both methods show a reasonable agreement with one another. Viscosity is observed to decrease as the particle diameter increases in fully dispersed nanofluids. The ratio 𝐶 ⁄ shows a decreasing trend indicating better heat transfer performance in nanofluids with large particles. Nanofluid 𝜂 is 𝜂 𝐶 𝜅 observed to increase rapidly as the concentration increase. This makes 𝐶 ⁄ to increase as well indicating the diminished heat transfer performance in nanofluids with high particle concentrations. As the particles in the nanofluid arrange into chain-like structures, 𝜂 remains unaffected. This makes 𝐶 ⁄ to decrease rapidly indicating the greater heat transfer performance in nanofluids with chain-like nanoparticle arrangements or in general, extended nanostructures.
item: Thesis-Abstract
Assessment of environmental performance of milling machining
(2022) Priyankara KPM; Gamage JR
The manufacturing industry largely contributes to the economy of a country. Thus, manufacturing by material removal processes leaves a significant environmental footprint. This is caused by the influence of process energy, resources, and releases. Due to that, increased attention on sustainable means of machining operations can be seen today. Thus, environmental sustainability assessments and preventive measures are being researched for promoting green manufacturing. In conventional machining, milling is a widely used machining method in the production and manufacturing industries. Thus, the purpose of this study is to assess the environmental performance of milling machining in an industrial setup. A literature review is conducted to understand the requirement of empirical assessment on sustainable milling and to identify the factors contributing to environmental damage while identifying sustainable machining practices. To conduct the empirical assessments, an industrial milling operation is monitored. At the experiment stage, different consumables and releases are identified and monitored such as power consumption, workpiece material usage, tool material, and coolant while controlling the machining parameters and the tool path. Design of Experiments were used to efficiently manage the controllable machining parameters relevant to environmental performance. The contribution to the environmental damage is analysed and quantified according to the ReCiPe endpoint impact assessment method using SimaPro® (Version 8) life cycle assessment (LCA) software following the guidelines of ISO 14044. The review revealed several factors that are significantly contributing to the environmental impact. Further, a number of operational level improvements were identified to improve the environmental performance. The results identified the electrical energy consumption and workpiece material usage as the most influencing contributing factors to the adverse environmental impact. Further, an operator‟s guide was also developed to harness the operational level savings to ensure the better environmental performance of milling.
item: Thesis-Abstract
Development of conductive polymer based tactile sensors for wearable bio-medical devices
(2021) Sampath WHP; Amarasinghe YWR; Dao DV; Mitani A
Tactile sensors are devices which acquire data from the physical world through sense of touch. These acquired data may be related to either, surface roughness, texture, force, or any other tactile parameter. Even though, tactile sensor systems are identiﬁed as a feasible method to acquire force feedback in robotics and automation systems, due to the requirement of physical interaction between the sensor and application, development of tactile sensors does not come to the spotlight during the past decades. Rather, researchers were more focused on developing non-contact sensors for various sensing modalities when comparing with the tactile sensors. Currently, importance of tactile sensors has come to the spotlight, as development of robotics, automation and biomedical applications are limited due to lack of tactile feedback. Also, many application areas are identiﬁed, where tactile sensors can be incorporated such as robotics, industrial automation, biomedical imaging, biomedical robotics, etc. With the recent advancements of the medical industry, wearable devices are used to support in controlling long-term or repetitive diseases or a disease that comes with time (i.e. chronic diseases) such as heart related diseases, diabetes and asthma by providing information on vital signs. Those vital signs can be heart rate, blood pressure, temperature in the body, blood oxygen level, etc. Other than that wearable biomedical devices are capable of producing smart and intelligent patient monitoring required for several diseases that capable of providing real-time feedback and assist in clinical based decision making. Tactile sensors are useful in measuring and monitoring point based and an area based force/pressure values in biomedical industry. Under this research, a novel tactile sensor has been developed using a conductive polymer-based sensing element. The incorporated sensing element is manufactured by polymer compression moulding, where the compound is based on silicone rubber and has enhancements by silica and carbon black, with Silane-69 as the coupling agent. Characteristics of the sensing element have been observed using its sensitivity and range. For the force scaling purpose and point based force/pressure measuring, a novel 3D printed cylindrical arch spring structure was developed for this highly customizable tactile sensor by adopting commonly available ABSplus material in 3D printing technology. By considering critical dimensions of the structure, ﬁnite element analysis was carried out to achieve nearly optimized results. A special electrical routing arrangement was also designed to reduce the routing complexities. A microcontroller based signal conditioning circuit was introduced to the system for the purpose of acquiring data. The concept was further improved to use as a tactile sensor array and hence a 3-DoF tactile sensor with a 3D printed square type spring system was also developed in this research. Under this research, a ﬂexible conductive polymer based sensor that consists of a ﬂexible electrodes sewn on a garment using conductive yarns, also developed. The ﬂexible tactile sensor has been incorporated into a knee brace and tested for its performances of monitoring forces generated at the patella of the knee. The developed sensor attached knee brace is capable of differentiating human activities and posses.
item: Thesis-Abstract
Development of a real-time grasping pattern classification system by fusing EMG-vision for hand prostheses
(2021) Perera GDM; Punchihewa HKG; Madusanka DGK
The Electromyography (EMG) based trans-radial prostheses have revolutionized the prosthetic industry due to their ability to control the robotic hand using human intention. Although recently developed EMG-based prosthetic hands can classify a signi cant number of wrist motions, classifying grasping patterns in real-time is challenging. However, the wrist motions alone cannot facilitate a prosthetic hand to grasp objects properly without performing appropriate grasping pattern. The collaboration of EMG and vision has addressed this problem to a certain extent. However they have not been able to achieve signi cant performance in real-time. This study proposed a vision-EMG fusion method that can improve the real-time prediction accuracy of the EMG classi cation system by merging a probability matrix that represents the usage of the six grasping patterns for the targeted object. The You Only Look Once (YOLO) object detection algorithm was utilized to retrieve the probability matrix of the identi ed object, and it was used to correct the classi cation error in the EMG classi cation system by applying Bayesian fusion. Experiments were carried out to collect EMG data from six muscles of 15 subjects during the grasping action for classi er development. In addition, an online survey was conducted to collect data to calculate the respective conditional probability matrix for selected objects. Finally, the ve optimized supervised learning EMG classi ers; Arti cial Neural Network (ANN), K-nearest neighbor (KNN), Linear Discriminant Analysis (LDA), Naive Bayes (NB), and Decision Tree (DT) were compared to select the best classi er for fusion. The real-time experiment results revealed that the ANN outperformed other selected classi ers by achieving the highest mean True Positive Rate (mTPR) of M = 72:86% (SD = 17:89%) for all six grasping patterns. Furthermore, the feature set identi ed at the experiment (Age, Gender, and Handedness of the user) proved that their in uence increases the mTPR of ANN by M = 16:05% (SD = 2:70%). The proposed system takes M = 393:89 ms (SD = 178:23 ms) to produce a prediction. Therefore, the user did not feel a delay between intention and execution. Furthermore, proposed system facilitated the user to use suitable multiple grasping patterns for a single object as in real life. In future research works, the functionalities of the system should be expanded to include wrist motions and evaluate the system on amputees.
item: Thesis-Abstract
Investigation of effect of human robot interaction with lower limb exoskeletons
(2021) Chandrasiri MDSD; Gopura RARC
Continuous development of exoskeletons (wearable robots) is essential to enhance the user experiences and performances of the wearable device. Therefore, it is necessary to determine human ergonomics and the comfort levels of wearable robots. These aspects can be analyzed by determining human-robot interaction (HRI). HRI is classified in cognitive- HRI (cHRI) and physical-HRI (pHRI) in the literature. cHRI involves the identification of complex human expression and physiological aspects. These pieces of information can be observed using a human-robot cognitive interface. Electroencephalogram (EEG) and electromyography (EMG) are mainly used sensing methods in cHRI. EEG is used to identify electrical activities of brain, while EMG is used to identify electrical activities of muscles. Furthermore, pHRI involves evaluating physical quantities such as position, force, and pressure between humans and robots. In order to identify pHRI with wearable robotic interfaces, a novel surface muscle pressure (SMP) sensory system was developed. The SMP sensor was calibrated and evaluated using surface electromyography (sEMG ) data for two separates experimental scenarios. Hence the system was proposed to determine the pHRI of wearable robotics. In order to determine HRI, a dummy lower limb exoskeleton was designed and manufactured in compliance with human ergonomics and biomechanics. The exoskeleton consists of 8 degrees of freedom (DoF) motions with variable limbs and weight attachment locations. Furthermore, sEMG, motion analysis, and SMP sensory systems were used to carry out the experiments. Moreover, a human lower limb model simulation with ground force reaction prediction was developed to determine the inverse dynamics. The experiments were carried out without exoskeleton, with the exoskeleton, and with exoskeleton weight attachments with six healthy subjects for the walking motion. A qualitative, comfortable level analysis was carried out simultaneously for each experiment. Captured SMP, sEMG, inverse dynamics and qualitative results were processed and feature extracted to evaluate HRI for different weight distributions and attachment locations. The relationship between exoskeleton attachments and locations was observed. The experiment results have provided an improved understanding of HRI for developing practical and ergonomically comfortable lower limb exoskeleton devices.
item: Thesis-Abstract
Development of a soft muscle actuator embedded with sensors
(2021) Arumathanthri RB; Chathuranga KVDS
Soft robotics plays a vital role in modern day robotics as day by day demand for soft robotic devices increases. To fulﬁll this demand more research are now focused on soft robotics and soft actuators are one of the main focus area. Soft robotic applications, such as soft robotic exoskeletons, often use pneumatic artiﬁcial muscle actuators. Soft robotic systems utilizing pneumatic artiﬁcial muscle actuators are a popular area of study as compactness, lightweight, high power-to-weight ratio, and great safety are just a few of the beneﬁts. Having sensors embedded to this soft muscle actuators are important as it would make close loop control of the actuators possible. Despite the beneﬁts of pneumatic artiﬁcial muscles, they lack sensory feedback for controlling force and displacement. To achieve close loop control, sensors are rarely incorporated into the actuator design. The major drawbacks of currently available sensor feedback systems are that they increase weight of the system and, in some circumstances, cause structural deformations. The design and fabrication of a displacement sensor to use in a novel soft robotic muscle actuator is presented in this study. Several advantages of this actuator and displacement sensor over conventional sensors and soft muscle actuators include ease of manufacture and negligible effect on actuator performance owing to sensor. Furthermore, as compared to soft actuators and sensors that are already available, the proposed soft actuator and sensor are affordable. The displacement of the actuator was determined using a novel inductance sensing approach, allowing closed loop control of the actuator. The performance of the soft robotic muscle actuator and displacement sensor was evaluated experimentally by the author. The prototype actuator is light in weight (14g) compared to other actuators and has a high strain (65%) and force-to-weight ratio (Capable of lifting 160 times of its self-weight). The dimensions of actuator are 110mm in length and 31mm in width. The sensitivity of the suggested sensor is 0.0022 mH=mm and the hysteresis is less than 1.5 percent, with an average error of less than 4%. Controlling the actuator over a square wave as a reference curve using the built-in displacement sensor was used to test and validate feedback control of the actuator. According to the results, this sensor can accurately determine the displacement of the soft muscle actuator and can be employed in a variety of soft robotic applications.
item: Thesis-Abstract
Optimising the operational parameters and conditions to enhance the environmental sustainability of turning operation
(2021) Fernando WLR; Gamage JR; Karunathilake HP
The manufacturing sector accounts for nearly 40% and 25% of global energy and resources consumption respectively. The die and mould manufacturing (DMM) sector, contributes largely to the energy and resource consumption in emerging economies. Turning is a popular and essential mode of machining within this sector. Furthermore, operational energy usage and metalworking fluid (MWF) consumption of turning have been identified as the key sources of environmental impacts in this process. However, there is a lack of evidence on analysing environmental impacts of lathe operations in the DMM sector compared to milling operation. Therefore, the purpose of this study is to identify and analyse the life cycle environmental impacts of the commercial turning operation. A series of case studies was conducted in DMM centres to explore the state-of-the-art industrial turning operation. Then, a set of experiments was designed using the Taguchi L 9 method, considering the mostly used workpiece material, cooling condition and cutting parameters. Experiments were performed to evaluate the energy consumption, metalworking fluid (MWF) consumption, surface roughness and material removal rate during turning of AISI P20 with both wet and dry machining. A life cycle assessment (LCA) was performed using SimaPro LCA software with Ecoinvent database version 8.5 to assess the environmental performance of turning. A multiresponse optimisation was performed using Grey-based Taguchi method to identify the optimum operating conditions. The results show that turning with wet machining yields better machining and environmental performances compared to dry machining. The largest portion of the energy is consumed for non-productive operations. The LCA results reveals electrical energy as the highest contributor under most of the impact categories. The workpiece material, AISI P20 and cutting insert material show significant contributions to aquatic ecosystems and resource consumption. However, the contribution of MWF on the midpoint impact categories is negligible. Further, the research presents optimum turning parameters to obtain better machining performances while maintaining lower environmental footprint in the context of turning of AISI P20 with wet machining.
item: Thesis-Abstract
Development of a multi-rotor aerial vehicle with top mounted counter balanced robotic manipulator
(2020) Wijayathunga ND; Lalitharatne SWHMTD; Chathuranga KVDS; Jayasekara AGBP
Aerial manipulation has been a growing research area within the past few years. This research area was associated with various application ideas and industries. Researchers implemented different aerial vehicle designs and manipulation techniques to accomplish these tasks in complex environmental conditions. Majority of conducted aerial manipulation research was composed of aerial vehicle bottom-mounted manipulators. These kind of aerial manipulation systems were not generally capable of achieving manipulator movements in an environment above the propeller disc plane. A few research projects were carried out by researchers to identify the performance of aerial vehicle top-mounted manipulators. Therefore, the manipulator mechanical designing step plays a challenging role in keeping the dynamic stability within the proper tolerances for manipulation systems. Center of Mass (COM) position and inertia of an aerial manipulation system become variables with respect to an inertial coordinate frame when a manipulator is attached to a multirotor. The manipulator, environmental reaction forces and torques are transferred on to the aerial vehicle as the system interacts with the external environment. Researchers had conducted a limited number of aerial manipulator system related projects with top-mounted manipulators which were capable of inspecting both vertical and overhead structures. The set of aerial manipulator systems capable of inspecting overhead structures are a small subset of the universal set of multirotor mounted manipulator projects. The literature suggests COM of an aerial manipulator system need to be placed in the propeller disc plane and closer to the central axis of a multirotor to achieve a better dynamic performance of that system. If a designer attaches manipulator on the top or bottom surface of a multirotor, the COM position moves vertically up or down from the propeller disc plane respectively. Generally, aerial vehicle top-mounted manipulators have generated more dynamic instabilities compared to manipulators mounted on the underside of multirotors. This thesis introduces a 2 Degrees of Freedom (DOF) serial link planar manipulator which has been mounted on top of a hexacopter by the rigid manipulator base. The research focused on inspection purposes of tall structures that human reach may be costly or vulnerable to physical injuries. The developed system included a novel serial link manipulator design and a force sensor as the end effector of the manipulator. This end-effector sensor would be able to identify the contact with surfaces of high-rise buildings or structures. The manipulator consisted of a separate controller apart from the flight controller. When this manipulator achieved different poses in its planar workspace, COM position of the system varied as a result. Therefore, a novel controller strategy was developed by the author in the research to compensate for the system attitude variations. Variation of the COM position caused attitude fluctuations. The thesis proposes a specifically designed manipulator mechanical design configuration to reduce the inherent COM position variation. Another concept was introduced by the author to counterbalance the COM position variation by synchronizing the motions of the system battery. A variable gain Proportional (P) controller, followed by a Proportional Integral Derivative (PID) controller was presented in the research to maintain the aerial manipulator system attitude. This research introduces novel concepts of designing, disturbance compensation and controlling of the aerial vehicle top-mounted manipulation systems. Theoretical simulations showed the COM, inertia, joint torque, disturbance torque variations of the manipulator. Experiments were carried out by the author considering the manipulator separately and the overall system in-flight to identify the performance of the developed system.
item: Thesis-Full-text
Development and characterization of a tactile array sensor for parallel grippers for use in object manipulation
(2020) Weerasinghe DLM; Chathuranga D
Within the era of modern robotics, during research as well as in industry, it is often the case to build robots that can mimic human-object interaction closely. To accom- plish this goal, excellence is required in many technological aspects, where one is tactile sensing. Tactile sensing is the ability of a system to measure information arising from physical interaction with its immediate environment. These include static & dynamic force/torque sensing, vibrations sensing and thermal sensing. To ful ll these require- ments, numerous types of sensors have been developed, which include but not limited to piezoresistive sensors, piezoelectric sensors, capacitive sensors and hall e ect based sensors. With any of the above sensors, it is necessary to accomplish mainly three tasks; at least one, if not all. These include contact point localization, dynamic sensing and tactile force measurement. These functionalities play a crucial role when developing human like grasping and manipulation capabilities. However, many problems arise during the design and manufacturing of these sensors due to the complexity of design, cost and di culties in practical implementation due to size. In order to overcome these di culties and ful ll the above mentioned requirements, this thesis presents a tactile gripper that has been developed based on hall e ect. An array of magnets and hall sensors create a unique combination of outputs for each di erent deformation of the dual layered silicon elastomer which houses the magnets. While allowing the interaction with non-planar surfaces due to the compliant nature of the silicon material, the sensor also facilitates accurate force recognition and contact localization using sensor readings and geometric properties of the silicon layer. This tactile gripper can be used for object manipulation and many other forms of tactile sensing requirements with necessary modi cations. Several experiments have been carried out to test and validate the operation of the sensor with successful results. This thesis aims to provide the entire design and development of the sensor & gripper, experimentation process, results, limitations and possible future improvements to the reader with the expectation that this development will aid current research in research community and industry. The end goal is to contribute to the process of developing tactile sensors which aids the progression of robotics technology that plays a crucial role in modern scienti c advancement.
item: Thesis-Full-text
Remanufacture for sustainability:
(2020) Gunasekara HNW; Gamage JR; Punchihewa HKG
Remanufacturing is the only end-of-life process where used products are brought back to the Original Equipment Manufacturers’ (OEM) performance specification from the customers’ perspective. At the same time, it offers a warranty equal or better to that of corresponding new products. During this process, products are returned to their original state with minimum waste of material and energy. Moreover, the benefits of remanufacturing are not only limited to ecological aspects but also it provides benefits for both the customer and the remanufacturer. There are barriers which hinder the remanufacturing activities globally. Thus, the purpose of this research is to investigate the present barriers of remanufacturing and propose solutions to the major barriers pertinent to the automotive remanufacturing industry in Sri Lanka. Thematic analysis of related literature, Semi-structured interviews, and industrial case studies was conducted to identify the barriers. Pair-wise comparison was used to prioritise them. The prioritised barriers were listed out, and solutions are proposed to promote local/regional automotive remanufacturing. Moreover, this research develops a business model for automotive parts remanufacturing by identifying suitable automotive parts. Initially, a review of the basic business components of a remanufacturing business was investigated. Then, a survey on the eBay online marketplace and local markets were performed to develop a Remanufacturability Index (RI) for automotive parts. Thematic analysis of related literature with the Business Model Canvas was integrated to generate the business model. These findings are significant for the entrepreneurs, other stakeholders of automotive parts remanufacturing business and other interest groups.
item: Thesis-Full-text
Computational tool to model and simulate solar assisted organic rankine cycle with a thermal energy storage
Gamage, SVR; Perera, KKCK.
The Organic Rankine Cycle (ORC) is considered as one of the most promising methods to convert low grade heat into the power. The ORC energy conversion process is much similar to the typical Rankine cycle except for the working fluid. The ORC applicability with low critical point organic fluids enables the operation of the system with low temperature heat sources. This makes low grade solar thermal, waste heat and geothermal suitable heat sources for power generation. Moreover, this applicability of small scale power generation makes it popular for standalone and low quantity heat source applications. This thesis presents a novel design of solar collector field along with a thermal energy storage to generate electrical power using an ORC. Concentric and non-concentric solar collectors were used to design the cascade collector array considering two collector operating temperatures. Several different collector arrangements of flat plate, evacuated tube, compound parabolic trough and parabolic trough solar collectors were considered. To overcome the intermittent nature of solar irradiation and to extend the number of operational hours, a thermal energy storage system was integrated to the system. Encapsulated phase change materials submerged in a thermal oil bath was considered for this thermal energy storage. For this investigation, the ORC system was designed according to the maximum load required. However, for the performance evaluation, part load system parameters variation was considered. Two systems were proposed for the evaluation process named system-1 and system-2. The system-1 consists with flat plate and evacuated tube solar collectors with low temperature thermal energy storage and system-2 contains evacuated and parabolic trough solar collectors with medium temperature thermal energy storage. The mathematical model is developed in this research to evaluate the energy flow through system components on an hourly basis. Hourly and seasonal variation of solar energy potential and energy demand were taken and used to simulate the mathematical model using a novel computational tool developed in this study. The system performances were evaluated based on collector area, the capacity of thermal energy storage and ORC thermal efficiency. Results from the investigation depict the performance of the proposed cascaded solar collector field with different ORC working conditions in a Sri Lankan context. The system performance evaluation was done for five different organic fluids identify optimal working fluids for different system parameters. The evaluated results show the variation of power output, plant factor and system efficiency with different system configurations. The identification of best system performance should be based on both power output and plant factor. However, identification of optimal system depends on both thermodynamic and economic factors. Therefore based on an economic analysis, normalized energy costs can be calculated to identify the best operating conditions along with economic considerations.
item: Thesis-Full-text
An Inviscid model for predicting unsteady forces in doubly connected domains
Gunarathna, MACK; Wimalsiri, WK; Dassanayake, VPC
Inviscid analytical-numerical model for predicting unsteady forces on two aerofoil configurations is developed and validated with the past literature. First the unsteady inviscid, incompressible and irrotational, except the logarithmic singularities at vortex points, flow field around the doubly connected domain is evaluated using a conformal mapping method. A discrete vortex shedding mechanism is incorporated to model the free shear layers of the real fluid flow. The complex potential associated with uniform flow and the vortex motion is obtained using elliptic functions and the modified Green’s function respectively. The strengths of the vortices are evaluated using Kutta condition which keeps the regularity of the flow field. Circulation development around the aerofoils is quantified by utilizing Kelvin’s circulation theorem. The unsteady forces are obtained using the unsteady version of the Blasius equation. Both trapezoidal rule and finite difference method are incorporated to solve the unsteady Blasius equation. The developed inviscid model is applied to various aerofoil configurations to predict the unsteady forces on the aerofoils. The results obtained were validated to the past relevant literature. Results showed a good agreement with the past literature.
item: Thesis-Full-text
Numerical evaluation of energy labeling test setups of ceiling fans
(2019) Casseer DR; Ranasinghe RACP
Ceiling fans are widely used as a means of providing thermal comfort to occupants in an indoor environment all around the world and it contributes to a significant portion of annual energy consumption throughout the world. A number of standards for efficiency analysis of ceiling fans are employed by many countries, with the intention of making ceiling fans more efficient. In these test standards, different test setups have been utilised. Work performed on analysis of the effect of these setups on performance evaluation of ceiling fans is currently unavailable. Further, there is a scarcity of research work performed on analysis of flow characteristics around a rotating ceiling fan. Understanding the proper flow around a rotating ceiling fan can lead to designing more efficient fan blades, which can lead to significant energy savings. Therefore, this study is split into two sections. In section one, a systematic investigation of the different test standards available for performance analysis of ceiling fans is performed, namely standards considered are ANSI/AMCA 230 standard, IEC 60879: 1986 standard, SLS 1600:2011 standard and Energy Star v1.2 standard for performance testing of ceiling fans. In section two, a flow physics analysis around a ceiling fan is carried out. For these, a CFD model was developed and it was validated using experimental results. The analysis of test standards was carried out by using a RANS method whereas the analysis of flow physics was carried out by using LES method. The numerical results obtained shows that the test cylinder present in some of the standards mentioned above, does not have a significant impact on the measured performance of the tested ceiling fan (variation is less than 2%), therefore having a test cylinder at an extra cost have no benefit on the measured results of ceiling fan testing. On the other hand, maintaining test cylinders for every fan size would impart a significant cost on the testing process and having a cylinder which is not correctly aligned can lead to inaccurate readings. From the flow results of the LES simulations, creation of two major vorticial structures is seen arising from the tip and the root of the blade. As these vorticial structures move further downward, more vortices were formed due to the action of these and the number of vortices keep growing with flow time, resulting the flow to become turbulent with the flow time. Furthermore, it was seen that the flow transition from laminar to turbulent occurred at the mid chord section, starting from the deflected section of the blade
item: Thesis-Full-text
Development of a robotic ortho-prosthesis for trans-humeral amputees
(2019) Abayasiri RAM; Gopura RARC
Over the years trans-humeral prostheses have been developed as a remedy for trans-humeral amputation: the amputation occurs between shoulder and elbow. For thebest usage of the trans-humeral prostheses, amputee should have a strong residual arm(stump arm) after the amputation. Furthermore, the ranges of motions and also thefull functionality of the prosthesis will be limited if the amputee has a weak stump arm.Moreover, prolonged applying of the loads on the stump arm can cause musculo-skeletaldisorders.In order to improve the dexterity of the prosthesis, they are developed with more jointsand actuators. Hence, the weight of the prosthesis increases. There is a need forpower assisting the weak stump arm while the prosthesis is at work. Trans-humeralortho-prosthesis is a device which assists the power of stump arm from an orthosis whilereplacing the missing upper limb with trans-humeral prosthesis. This research is carriedto develop a 9 Degrees of Freedom trans-humeral ortho-prosthesis. It consists of 4 DoFmotions: shoulder horizontal flexion/extension, shoulder vertical flexion/extension,shoulder abduction/adduction and shoulder internal/external rotation, at the ortho-sis and 5 DoF motions: elbow flexion/extension, forearm supination/pronation, wristulnar/radial deviation, wrist flexion/extension and compound motion of thumb andindex finger, at the prosthesis. Moreover, shoulder abduction/adduction is supportedas a passive DoF in order to compensate the misalignments of the joints caused bythe motions of clavicle and the scapula in the sagittal plane while enabling shoulderabduction/adduction . Even though the orthosis is designed to achieve 4 DoF motions,it contains 6 DoF motions. Therefore, the whole ortho-prosthesis becomes a redundantmanipulator.Simulation experiments have been carried out to determine the workspace of the handof the ortho-prosthesis and to determine the manipulability of the ortho-prosthesis.Workspace plots show that it can reach the workspace of a human hand. Manipu-lability measures: manipulability index, minimum singular values, condition numberand manipulability ellipsoids verify that the trans-humeral ortho-prosthesis would notreach singular configurations. Furthermore, it is confirmed that the ortho-prosthesis iscapable of performing dexterous motions due to its high manipulability after carryingout experiments with the fabricated prototype of the trans-humeral ortho-prosthesis.
item: Thesis-Full-text
Design and development of intelligent home automation system (IHAS) for enhanced energy performance
(2019) Basnayake BADJCK; Attalage RA; Amarasinghe YWR; Jayasekara AGBP
With the growing distresses on carbon emission and sustainable energy concepts, the whole world appreciates the movements towards sustainable energy consumption. Statistics point out that over 50% of total electricity generation is consumed by three sectors, namely residential, commercial and public services. Among them, the residential sector alone consumes over 25% of total energy consumption which can possibly be attributed to heating, ventilation, air-conditioning (HVAC) and lighting used for occupants’ comfort. However, over 65% of global electricity generation is based on fossil fuel and natural gases, residential electricity consumption is accountable for a substantial extent of global carbon emission, consequently the present climate calamity. Researchers across the globe have figured out that the theories on sustainable energy consumption should start with our own home. It is required to focus on reducing the energy consumption by home HVAC systems, lighting systems and other appliances while keeping residential comfort level untouched. Home automation systems have shown their success towards the goal amidst several drawbacks. This research, proposes an intelligent home automation system (IHAS) with a real-time sensor network. The system has the ability to perform user preference based automation on the premises based on user comfort, safety and energy efficiency. The proposed system consists of a wireless sensor network, intelligent controller and device control interface. The sensory system monitors the environment and the identified information transferred to the intelligent central controller, which makes the accurate decision on most efficient configurations for the home appliances. It includes HVAC system, lighting systems and multimedia systems thus optimizing power consumption and improving user comfort. Finally, the device control interface delivers the obtained control decisions to the appliances through the default control interface. The developed non-interactive user identification system will recognize individual users within the premises and track their activities to obtained individual user preferences related to the comfort and multimedia devices. Based on those preferences and real-time ambient conditions measured through climatic sensor systems, the central controller will decide the configurations for the home appliances. The entire work includes the design and fabrication of different hardware systems and firmware implementations based on 8-bit and 16-bit microcontrollers. The central controller was developed on a single board computer which is powered by 32 Bit ARM Cortex A11 CPU. Fuzzy inference systems were used to implement the intelligent control algorithms of different control application of the proposed system.
item: Thesis-Full-text
Development of an EEG signal based brain machine interface for a meal assistance robot
(2018) Perera, KDCJ; Lalitharathne, T
Most of the countries in the world are facing the problems of aging population and disabilities among the population. Among di erent problems faced by these individuals, self feeding can be identi ed as an important aspect that should get more attention from the research community. In addition, self feeding re ects the interdependency of an individual and thus relate to their mental health. Taking care of these individuals using care takers is becoming more and more di cult due to diminishing workforce for such tasks. Therefore assistive robotic technologies play a major role in providing feeding solutions to these individuals with disabilities. Meal assistance robot is a device designed to assist the individuals in need with self feeding. The research work of this thesis is focused on developing an EEG signal based Brain Machine Interface for a meal assistance robot. Meal assistance robot is capable of handling solid food items using the spoon mounted on the end e ector. Identifying user's food selection is carried out using a Steady State Visually Evoked Potential based Brain Machine Interface where 3 LED matrices icking at 6Hz, 7Hz and 8Hz are used to generate the stimulations in the brain. User has to gaze at a LED panel to activate the motion path of the robot which will feed the solid food from the container associated with the gazed LED panel. System is incorporated with a visual servoing algorithm to identify the user's mouth position and adapt the food feeding location according the mouth location. Further, Mouth open/close status detection system is developed to measure the user's willingness to intake the food. The developed meal assistance robot is experimentally validated using 15 subjects in di erent experiments. After detailing the research methods carried out, discussion of the results obtain are presented at the end of the thesis with limitations of the research and possible future improvements.
item: Thesis-Full-text
Application of Zimont's turbulent flame speed closure for combustion modeling of a single cylinder spark ignition engine
(2018) Eranga, JKL; Ranasinghe, RACP
Increasing need to get the maximum power out from fuels while maintaining less amount of toxic emissions has created the requirement of making an optimum IC engine. Numerical simulations play a vital part in determining those design and operating parameters which make that idea of an optimum engine a reality. In the present work applicability of two well-known turbulent flame speed models: Namely Peters and Zimont in premixed charge gasoline spark ignition (SI) engines were evaluated. Their ability to predict the characteristics of premixed turbulent combustion process of an SI engine in the RANS context was first assessed and based on those results Zimont model was used to evaluate the applicability of Smagorinsky-Lilly Large eddy simulation (LES) model in engine simulations. Several simulations were done to identify and implement required modifications to get correct solutions from the LES model. Combustion of the Ricardo E6 single cylinder test engine was modeled with the above two turbulent flame speed closure models implemented to a commercial computational fluid dynamics (CFD) code. Full cycle simulations, covering all four strokes including the valve motion, spark discharge, flame kernel development and fully developed combustion, were performed using different engine operating conditions. Engine was fueled with gasoline. Obtained results were compared with experimental values obtained using the same operating conditions of the E6 engine to evaluate the prediction ability of the different models. Accordingly, In-cylinder pressure variation and the combustion heat release rate versus crank angle were compared with measured values. In general, predictions, of both models were found to be in reasonable agreement with experiment values, but significant discrepancies could be observed in certain operating conditions.
item: Thesis-Full-text
Design and development of miniaturizes tactile sensors for tactile imaging
Thotegodage, DIU; Amarasinghe, YWR
Tactile sensors are devices which acquire data from the physical world through sense of touch. These acquired data may be related to either, surface roughness, texture, force, or any other tactile parameter. Even though, tactile sensor systems are identified as a feasible method to acquire force feedback in robotics and automation systems, due to the requirement of physical interaction between the sensor and application, development of tactile sensors does not come to the spotlight during the past decades. Rather, researchers were more focused on developing non-contact sensors for various sensing modalities when comparing with the tactile sensors. Currently, importance of tactile sensors has come to the spotlight, as development of robotics, automation and biomedical applications are limited due to lack of tactile feedback. Also, many application areas are identified, where tactile sensors can be incorporated such as robotics, industrial automation, biomedical imaging, biomedical robotics, etc. Tactile imaging is one of the medical imaging technique, which mimic manual palpitation to diagnose diseases such as breast cancer, prostate cancer, etc. Tactile sensor is the foremost element in a tactile imager. Comparing with the other medical imaging techniques, it was found that tactile imaging is the most cost effective method to screen breast cancers. Also it has other advantages such as minimum exposure to radiation, simple and easy operation, etc. Hence, main aim of this research is to develop miniaturized tactile sensors for tactile imaging applications. Working with that aim, miniaturized tactile sensors were developed during this research. In these developed sensors, Quantum Tunnelling Composite (QTCTM), which is a conductive polymer composite, has been used as the sensing element. A novel structure was proposed to be incorporated with the sensing elements and analysis of the structure discussed. Proposed sensor was developed and calibrated. In the next stage of this research, a novel enclosed tactile sensor was designed and developed utilizing the same sensing and working principle as the developed 1-DOF tactile sensor. Main motive of developing this sensor is to include the proposed improvements for the 1-DOF tactile sensor based on its experimental results. An enclosed novel structure was proposed so that the sensing element and spring will be omitted from the environmental effects. Sensor was developed and calibrated so that it could be integrate with tactile imaging applications. Sensitivity of this developed tactile sensor, calculated to be 0.02 V/N and sensor displayed repeatability of ±3 N. An experiment was carried out to evaluate the usability of developed sensors in tactile imaging applications. Using the developed sensor pressure variation of a human left hand was mapped and visual images were constructed. Applicability of sensor arrays instead of a single sensor in tactile imaging applications and miniaturization techniques to be used to construct tactile sensor arrays with high Taxel density is discussed. A MEMS based tactile sensor design was proposed to be developed to construct tactile sensor arrays with good performance for tactile imaging applications. Proposed sensor design analysed and simulated to validate the proposed working and sensing principles. Fabrication steps for the designed MEMS sensor was proposed.
item: Thesis-Full-text
Numerical modeling of the flow field for indoor thermal comfort of a building under stack effect
(2015-11-27) Nimarshana, PHV; Attalage, RA; Perera, KKCK
In recent years natural ventilation is widely recognised as excellent contributing towards in design low energy buildings. The main challenge in natural ventilation is identified as lack of knowledge in providing acceptable thermal comfort in an occupied space to meet the internal requirements against the prevailing climatic conditions variations. Numerical investigations of the indoor thermal comfort condition in a simple office space governed by the solar chimney stack effect have been undertaken using CFD techniques. A mathematical model was developed based on the relevant analytical framework governing the phenomena to simulate the velocity flow field and temperature distribution on the designated plane within the indoor space. Boussinesq approximation was incorporated to numerical scheme with realistic boundary conditions for flow simulation. The model was enriched by incorporating a sufficient fluid volume to represent environment surrounding the space and thereby eliminating the entry effect to the flow. Hexahedral cells were used in a non-uniform grid distribution to minimise numerical diffusion. A fine mesh is used near the walls to enhance the resolution and accuracy resolving the problems under the turbulent flow conditions. Grid independence analysis was carried out to ensure the accuracy of the numerical results. Under-relaxation factors 0.3, 1, 2, 0.8, 0.8, 1, 0.9 for pressure, density, momentum, turbulence kinetic energy, turbulence dissipation rate, turbulent viscosity, energy respectively were used. The model outputs were compared with the available experimental measurements taken under the same condition to calibrate the numerical scheme. A parametric study was carried out using the calibrated model to assess the distribution of thermal comfort index against the changes in geometrical and solar radiation parameters. The values of activity, metabolic rate for seated activity and clothing insulation were selected as 0, 60 W/m2 and 0.5 Clo respectively for thermal performance analysis. The effect of each input parameter was investigated in terms of mean value and standard deviation corresponding to the flow velocity and the PPDNV value. It can be concluded that the present model is capable of predicting the indoor thermal performance of a building under stack effect.
item: Thesis-Abstract
Development and clinical testing of a negative pressure wound therapy device
(2015-09-16) Welgama, WPD; Gray, HA; Amarasinghe, YWR; Sugathapala, AGT
Negative Pressure Wound Therapy (NPWT) is a type of treatment in which suction is applied to a wound bed in combined with a specialized dressing to increase the wound healing rate. This study aims to develop a fully automated, portable and user friendly NPWT device and it is capable of increasing the healing rate of wounds, which cannot be healed by only using conventional wound treating methods. The pressure of the developed device can be controlled within the range of -25 mmHg to -250 mmHg with an accuracy of ± 3 mmHg. Pressure controlling is done by controlling rpm of the motor in the vacuum of the device. Dimensions of the developed device are 30 cm x 20 em x 15cm, voltage is 12 V and power consumption range is 4 W to lOW. The satisfactory level of user friendliness of the device was shown when it was being clinically tested by non-technical medical staff. To evaluate the performance of the device, it was clinically tested and validation was done by analyzing the clinical results. It was proved that this device has the same performance as previously validated NPWT devices, during the clinically testing. Reliability of the device was validated by longer period clinical testing at hospital. Portability, size reduction and possibility to operate using battery power supply are the other advantages of the device compared to other NPWT devices developed in Sri Lanka.