Doctor of Philosophy (Ph.D.)

Permanent URI for this collectionhttp://192.248.9.226/handle/123/2055

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Browsing Doctor of Philosophy (Ph.D.) by Subject "Doctor of Philosophy (PhD)"

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    item: Thesis-Abstract
    Development of a bio-inspired lower extremity exoskeleton with a passive-powering system
    (2023) Ranaweera, RKPS; Gopura RARC; Jayawardena TSS; Mann GKI
    Manual 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
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    item: Thesis-Abstract
    Improvement of thermoelectric properties in nanostructures with constrictions
    (2023) Henadeera, PB; Samaraweera N; Ranasinghe C; Wijewardane A
    The 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