3. Electronic Theses and Dissertations (ETDs) - All submissions
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Item Thermal analysis of continuously moving solid and porous fins using approximate analytical methods(2019) Ndlovu, Partner LuyandaIn various industrial and engineering applications, fins (extended surfaces) are frequently adopted to enhance the rate of heat dissipation between a system and its surroundings. The heat transfer mechanism of a fin is to conduct heat from a heat source to the fin surface via conduction, and then dissipate heat to the surrounding fluid via convection, radiation, or simultaneous convection-radiation. In order to improve the rate of heat transfer through finned surfaces, it is necessary to understand a fin’s dynamic response to change in temperature. The study of heat transfer though fins continues to be of scientific interest and recently, the study of moving fins has attracted a lot of research interests. The study of heat transfer through fins is modeled by differential equations. In search for solutions to differential equations arising in physics and engineering, analytical methods are very useful as it is difficult if not impossible to find the exact solutions. In recent years, the availability of faster processing equipment further means that we are able to compute analytical solutions to highly nonlinear equations that are more accurate in representing the physical phenomena. The modeling of heat transfer through fins reduces the experimental costs and gives insight into various parameters influencing the heat transfer process. In this thesis, the Variational Iteration Method (VIM) and the Differential Transform Method (DTM) are used to solve the nonlinear boundary value problems describing heat transfer in solid and porous fins undergoing convective-radiative heat dissipation. Validation of analytical solutions is also obtained by comparison with numerical solutions. The aim is to derive mathematical models describing heat transfer though fins, analyze the impact of the embedding thermo-physical parameters, compare the accuracy and computational efficiency of these two modern day analytical methods. The study of porous fins is performed using Darcy’s model to formulate the governing heat transfer equations. As far as we know, the transient study of heat transfer through moving fins has not been performed anywhere in literature. Related work on finned heat transfer is modeled using steady state models with the assumption that the transient response dies out quickly. Since a broad range of governing parameters are investigated, the results could be useful in a number of industrial and engineering applications.Item Experimental investigation into a passive auto-tuning mass damper for structural vibration control of a MDOF system(2016) Naicker, Elizabeth NicoleA Passive Auto-Tuning Mass Damper with Pulley connections (PATPD) is a vibration control device that consists of a box filled with silica sand on roller supports. The silica sand provides the mass of the damper. The PATPD is connected to the structure to be controlled by a group of ropes and pulleys; it is free to move in any translational direction. The pulleys and rope transfer a driving force to the damper, caused by the movement of the structure. The mass provides an inertial force which, in addition to the driving force of pulleys, dissipates energy providing the vibration control of the structure. Firstly, the test model underwent ‘PATPD Efficiency tests’ where the model was subjected to free translational, torsional and coupled vibration both with and without damper. This procedure was then repeated for forced harmonic excitation and the control effect for both analysed. These tests aimed to demonstrate the effectiveness of the PATPD at controlling structural vibrations. The results indicate that the PATPD provided at least 99% reduction to first natural frequency Power Spectral Density (PSD) peak for all tests, with relatively minimal increases for others. The model then underwent ‘Parameter Tests’ where the damper characteristics were changed and test procedure above repeated. These tests aimed to investigate the effect of the property changes of the PATPD on its ability to control free and forced vibration. The results indicate that (a) the PATPD provided significant reduction to first natural frequency PSD peak for all tests and (b) the properties of the PATPD affected the amount of control provided to the structure thus optimization of the PATPD could result in improved control effect. The models’ ‘Dynamic Properties’ namely model mass and stiffness were changed and test procedure repeated. These tests aimed to demonstrate the auto-tuning or adaptivity of the PATPD in its ability to control free and forced vibration. The results indicate that for all tests performed the PATPD provided significant reduction to first natural frequency PSD peak for all tests, with relatively minimal increases for others. The PATPD worked over a wide frequency band and was able to adapt to frequency changes providing significant control effect. Additional forced vibration tests under specific frequencies close to and far away from the models’ natural frequency demonstrates PATPD adaptability and efficiency. In addition tests under random excitation (as could be expected for earthquake loading) demonstrated PATPD positive control effect, adaptability and efficiency.