Doctor of Philosophy (Ph.D.)
Permanent URI for this collectionhttp://192.248.9.226/handle/123/2055
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- item: Thesis-AbstractImprovement of thermoelectric properties in nanostructures with constrictions(2023) Henadeera, PB; Samaraweera N; Ranasinghe C; Wijewardane AThe results of a study into the development of novel Thermoelectric (TE) materials by engineering nanoscale constrictions are presented in this thesis. The aim of this investigation lies in the development of an enhanced TE material. To achieve this, the dependence of TE properties, specifically the TE figure of merit (𝑍𝑇) on the material properties has been considered. The enhancement of the 𝑍𝑇 was achieved by reducing the thermal conductivity (𝑘) of the material. During this phase, the effects of different nanoscale modifications to the material structure on its electrical properties are contemplated to ensure that the TE 𝑍𝑇 does not get vitiated. Here, a novel nanostructure formed by the sintering of individual Silicon nanoparticles in a linear fashion has been used and is referred to as a Nanoparticle Chain (NPC) structure. The nanoparticle arrangement in an NPC structure causes nanoscale constrictions to be formed along the transport direction of the structure. This is seen to cause extremely low lattice 𝑘 (reaching 0.614 W/mK) while preserving a considerable amount of crystallinity. The fabrication procedure of the NPC structure has also been considered through this study thereby ensuring that results can be translated to real-world applications using existing technologies. During the investigation, an interesting competing effect between two, phonon transport aspects has been observed to cause a nonmonotonic trend in the 𝑘 of the structure, while a variation in the phonon density of states along the transport direction was identified to cause a 𝑘 reduction to values lower than those attained with comparably sized nanowires. Further variations of the structure are obtained by expanding the zero-dimensional constriction of NPC structures to a one-dimensional form referred to as Nanowire Chain (NWC) structures. Subsequently, the electrical properties of the structures in consideration are evaluated, and a three-order of magnitude enhancement in the TE ZT is observed in comparison to the bulk material. Thus, it is shown that nanoscale constrictions can be engineered to enhance the TE performance of materials. Keywords: Nanoparticles, Thermoelectric, Phonon transport, Electron transport, Ab-initio modelling, Constriction engineering
- item: Thesis-AbstractDevelopment of a bio-inspired lower extremity exoskeleton with a passive-powering system(2023) Ranaweera, RKPS; Gopura RARC; Jayawardena TSS; Mann GKIManual handling is an indispensable activity in any occupational setting. It is any activity that requires the use of human force for lifting, carrying or moving an object. Such repetitive and tiring tasks may cause work-related musculoskeletal disorders and adversely affect productivity of manual workers. In that context, the goal of this research was to develop a wearable device or exoskeleton for providing lift assistance during squat lifting. The outcome of the research was to reduce human effort and improve human comfort. The objectives or contributions of the work include conceptualization of a biomechanical energy management approach for squat lifting, development of an anthropomorphic passively powered multi-joint lower extremity exoskeleton for lift assistance, and investigation of the effectiveness of the proposed lift-assist system. Initially, a literature review was conducted on lower extremity exoskeletons to identify the research gap. The analysis on the state-of-the-art of exoskeletons revealed the need for introducing sustainable powering systems and minimizing interference issues at the human robot interface. Next, the biomechanical energy management approaches were conceptualized. The work includes the biomechanical modelling of squat lifting activity and the investigation of feasibility of proposed energy recycling strategies. Subsequently, design of anthropomorphic mechanical structure for the exoskeleton, design of bio-inspired passive-dynamic powering system for ankle and knee joints, and design of passive and active controlling systems were carried out. Thereafter, prototype of the ankle knee exoskeleton was fabricated as per the design specifications. Finally, performance with the proposed lift-assist system was experimentally evaluated. Results from the biomechanical analysis show that, when wearing the exoskeleton, energetic consumption at ankle and knee got reduced by 23-24% and 38-40%, respectively. The effectiveness of proposed system was also verified by evaluating muscle activities of lower and upper leg. All in all, the ankle knee exoskeleton with proposed passive actuators made a positive influence on the lower limb’s muscular system. Therefore, the proposed exoskeleton has proven to be an effective solution for industrial use. Keywords: Bio-inspired Design, Biomechanical Energy Harvesting, Lower Extremity Exoskeleton, Leg/Squat Lifting, Motion Analysis, Passive Actuator, Power Assistance, Surface Electromyography
- item: Thesis-Full-textDevelopment of a soft linear actuator to use in wearable assistive exosuits(2023) Kulasekera AL; Chathuranga KVDS; Gopura RARC; Lalitharatne SWHMTDWearable exosuits require flexible, linearly contractile, and lightweight actuators to provide sufficient force to move the respective limb. This thesis presents the concept, design, fabrication, experimental performance characterization, and numerical modeling of two types of respectively thin and low-profile vacuum-driven, soft, linearly contractile actuators. The proposed soft actuators are made of an inextensible yet flexible thin-skinned pouch supported by a collapsible skeleton that orients the collapse of the actuator in the longitudinal axis upon the evacuation of the air within the pouch. The proposed novel soft, lightweight, contractile actuators are thin (ThinVAc) and lowprofile (LPVAc). Both these actuators are lightweight (ThinVAc: 0.75 g; LPVAc: 14 g), provide high maximum blocked forces (ThinVAc: 5.2 N; LPVAc: 39 N), provide maximum stresses similar to that expected from biological muscles (ThinVAc: 184 kPa; LPVAc: 117 kPa) and have high force-to-weight ratios (ThinVAc: 477; LPVAc: 285). The ThinVAc can combine to create multifilament actuators for force scaling. Combining 15 units of 500 mm ThinVAcs generates a maximum blocked force of 54 N (Max. stress: 62 kPa), 290 times the self-weight. The LPVAc integrates a position sensor based on an inductive sensor allowing closed-loop control with minimal error at 0.25 Hz. Numerical models for the contraction and blocked force of mono- and multifilament actuators allow for predicting their behavior independent of external sensors. The proposed actuators are tested in wearable applications to check their suitability. The ThinVAc is integrated into a knee rehabilitation assist device, and the LPVAc is incorporated into a novel mono-articular sit-to-stand transition (StSt) assist exosuit, helping to reduce muscle activity by 45%. These actuators have the potential to be integrated into a wide range of assistive devices and orthoses, such as knee or ankle braces, exoskeletons, and prosthetics, to provide the necessary support for people with mobility impairments.
- item: Thesis-AbstractModeling of ground - level ozone formation in urban air - sheds of Sri Lanka(2022) Perera GBS; Sugathapala AGT; Manthilake MMID; Lee SCPhysical phenomenon of the relation among ground-level ozone (O 3 ), oxides of nitrogen (NO X ) and volatile organic compounds (VOC) is governed by complex nonlinear photochemistry. To predict and control O 3 concentration, it is vital to know, how O 3 concentration changes in response to prescribed changes in source emissions of NO X and VOCs. In this research, a theoretical model was developed and validated for ground-level O 3 formation in urban air-sheds of Sri Lanka. Hourly averaged weekly results of ambient pollutant concentration data of eleven cities in the base years 2013, 2014 and 2015 in Sri Lanka was assessed and an urban air shed model was developed. The model was calibrated using influential parameters measured. Then Colombo as the most complicated urban air-shed in Sri Lanka was analyzed in detail. Model was validated using measured 24-hour air quality monitoring data from the mobile air quality monitoring stations at major traffic locations in Colombo in the year 2018 and 2019. Operational schedules of emission sources including train scheduled data, working hours of the thermal power plants, and vehicle counts were conducted at identified critical locations in Colombo to investigate the responsible sources. Gases from the exhaust line of different types of vehicles was collected and analyzed using Gas Chromatography Mass Spectroscopy (GCMS). Results confirm that there exist two regimes of NO X -VOC-O 3 sensitivity as NO x sensitive regime and VOC-sensitive regime. The urban air-shed model is capable of estimating the ground-level steady state ozone concentration (O 3ss ) and contributions from each regime. The univariate linear regression model using predicted and observed O 3 values confirmed that O 3ss concentration was significantly correlated with the predicted O 3 concentration. Analysis of urban air shed in Colombo also confirms the predicted and observed O 3ss concentration were significantly correlated. This research provides a detailed understanding of photochemical degradation on formation of ground-level O 3 in urban air-sheds of Sri Lanka and provides critical information for the scientific community and decision-makers to formulate air pollution mitigation policies.
- item: Thesis-Full-textA framework developed using ergonomic principles and modified per- determined motion time systems ( PMTS ) to increase the opportunities for physically disabled population to work in industry(2020) Abeykoon KMW; Punchihewa HKG; Nanayakkara LDJFOne billion of the world population are estimated to have some form of disability, and governments spend huge amounts of money to provide welfare facilities to protect their rights and make them inclusive. The literature reveals that people with disabilities (PWDs) are willing to work if they are provided with necessary job support. People with only mobility impairments are commonly named as people with physical disabilities (PPDs). It is a subset of PWDs. PPDs can effectively contribute towards economic growth if their residual physical capabilities are correctly identified. However, employers as well as PPDs themselves find it difficult to identify their residual physical capabilities. Work norms explained in Pre-Determined Motion Time Systems (PMTS) such as Method Time Measurement (MTM) is present for the normal people. These work norms assume that the people have normal capabilities and that they do not have any physical disability. However, there are no such work norms developed to cater for the PPDs. Therefore, the aim of the research was to develop a framework to increase the ability of PPDs to work in industry. The objectives were to explore typical manual work-activities (WAs) similar to those prescribed in PMTS that could potentially be carried out by PPDs, with their residual physical capabilities, explore essential range of movement (RM) of each of the body regions/joints required to perform the identified WAs, formulate a framework mapping RMs of each body regions/joints required to perform typical manual WAs and finally to evaluate and validate it for its purpose, user-friendliness and functionality. In this pursuit, research was carried out in five distinct phases. In the first phase, typical manual WAs were identified that can be performed by upper and lower extremities using industrial engineering experts (n=3). Then, essential RM of each body region/joint required to perform the identified WAs were determined using relevant medical experts (n=9). Orthopaedic surgeons (n=4) then mapped the RMs that are needed to carry out the WAs to form a framework. These three phases used a modified delphi approach for data collection. In the fourth phase, the framework was evaluated for its purpose and user-friendliness by the intended users of the framework (n=22) in different industries. In the fifth and final study, the functionality of the framework was evaluated with PPDs (n=92) and mapped the work capability of a randomly selected sample of PPDs (n=6) using the framework. The results were compared against the WAs that they were engaged in at the time of the study. The developed guide was named as the WARM mapping tool. Ethical clearance was granted from the Medical Research Institute (MRI), Sri Lanka to carry out the study. This research proposes a novel philosophical work-related capability and limitations analysis tool to help employ PPDs by identifying suitable WAs based on the degree of disability of the body regions/joints in terms of the corresponding RMs. It is a step towards extending the work norms for PPDs. WARM mapping tool has been developed to guide the employers to recruit PPDs to carryout physical work tasks. All that participated in the usability study proved that it is a convenient and simple tool to use. All 22 practitioners also said that it can also be used as a self-assessment tool by the PPDs. The usability was rated over 60% by all the participants. This tool may be used as a platform to decide on the equipment, facilities, procedures and training that the PPDs will need for effective performance in industry.
- item: Thesis-Full-textOptimizing energy performance and indoor environmental quality of buildings using energy simulation, generic optimization and computational fluid dynamicsBandara, RMPS; Attalage, RAA building is a complex system with multiple interacting physical processes taking place simultaneously. Various aspects influence the performance of buildings and the building envelope is one of the major contributors in this regard. Building orientation, Aspect ratio, Window to wall ratio, Location and types of fenestration, Envelope materials and their characteristics etc. can have a major impact on the energy consumption and life cycle cost of buildings. However, the best combination of the said envelope elements for optimizing the performance of buildings is difficult to determine and is not known. Whole building simulation tools are often used in making building performance predictions. Building energy simulation is generally used on a scenario-by-scenario basis, with the designer generating a solution and subsequently having the computer evaluating it. This is however, a slow and a tedious process and only a few cases are evaluated in a large range of scenarios, possibly leading to sub-optimal envelope designs. By coupling a generic optimization tool with a whole building energy simulation tool, it is possible to optimize the performance of buildings by determining the best combination of envelope elements, subject to predefined constraints. First part of the thesis explains optimization of energy performance and life cycle cost of buildings through this methodology. Secondly, drawbacks of whole building simulation tools that lead to issues in energy performance predictions of buildings are discussed in detail. The issues have been addressed by coupling the whole building simulation tool with a computational fluid dynamics tool on a complementary data exchange platform. It is observed that with this approach more reliable building performance predictions can be made. Final section of the thesis discusses on optimizing indoor environmental quality using computational fluid dynamics with respect to identified mechanical ventilation configurations. Model predictions have been validated using a detailed experimental design where computational model predictions closely agree with the actual measurements.
- item: Thesis-Full-textDevelopment of a vision aided reach-to-grasp path planning and controlling method for trans-humeral robotic prosthesesMadusanka, DGK; Gopura, RARC; Amarasinghe, YWR; Mann, GKIThis study proposes a reach-to-grasp path planning and controlling method for trans- humeral prostheses. Trans-humeral prostheses are used to replace the missing body part after the loss of upper limb (UL) above elbow. Reach-to-grasp paths refers to the paths taken by the human UL to reach towards an object with the intention of grasping. A trans-humeral prosthesis has been designed and fabricated with 5DOF. A simulation environment has been proposed using the design. Simulation environment consists of a virtual shoulder joint which can be actuated according to a natural human shoulder using an Inertial Measurement Unit (IMU). Prosthesis and the simulation environment has been used to experimentally evaluate the proposed path planning method. A reach-to-grasp path planning method combining Electromyography (EMG) signals and vision signals has been proposed. EMG Based Module (EBM) is capable of con- trolling prosthesis elbow motion e ectively with an accuracy of 92%. Visual Servoing Module (VSM) consists of a 2-1/2D visual servoing system to center the object of in- terest to the hand of the prosthesis and to correct the orientation. An object reaching algorithm has been proposed to reach towards the object. Later, the EBM and the VSM has been fused using an fusion lter. An improvement to the above method has been proposed to make the paths straight. It consists of a path generation module and a path tracking module. Path generation module is capable of generating a path towards the object. The object position is located and a path is generated from the current position of the prosthetic hand to the object position with the aid of vision. Path tracking module takes the prosthetic hand on the generated path considering shoulder motions. Two path tracking methods has been proposed: spatial path following method and Model Predictive Controller (MPC) based path tracking method. Proposed path planning method has been experimentally evaluated.