Graduation - 2024 - March (Open Access)

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    A Study of the Longitudinal Open-water Performance of an Ice-class Ship
    (2024-02-26) Steyn, BJ; Bekker, A; Stellenbosch University. Faculty of Engineering. Dept. of Mechanical and Mechatronic Engineering.
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    Development of a test setup to determine frictional losses on bicycle drivetrains.
    (Stellenbosch : Stellenbosch University, 2024-02) Loedolff, C; Venter, G; Stellenbosch University. Faculty of Engineering. Dept. of Mechanical and Mechatronic Engineering.
    ENGLISH ABSTRACT: Cyclists compete purely under their own power, however the power output to the wheels is influenced by their equipment. Bicycle drivetrains are thus engineered to be as light and efficient as possible, but this may impact longevity without proper care and lubrication. Chain lubricants are developed for specific conditions, with characteristics resulting in better efficiency for shorter durations, or better resistance to contamination. To accurately determine the power losses in a given drivetrain for any given load condition, a test bench is required to simulate the real-world conditions these drivetrains are subjected to. This work presents the development of a test bench that is capable of performing three discreet tests: the frictional losses due the static radial loading on ball bearings used in the bottom brackets of bicycles, the isolated chain losses due to chain tension, and the complete system losses under full load conditions. All these tests require the measurement of speed and torque data to determine the power losses. In addition, the full load test requires a braking mechanism to supply the load. The speed and torque measurements were incorporated into a single, bespoke transducer. Strain gauge based torque transducers are the norm for industrial equipment, however a unique approach was pursued here. The transducer was constructed from a thin aluminium tube that deflects angularly under load. The ends of the tube were fitted with slotted disks which run through the line-of-sight path of a set of interrupter optical sensors. The sensor output signals were used to determine the angular velocity of each disk, as well as the relative angular deflection between the two disks. The angular deflection of the tube was used together with its known stiffness to determine the torque measured by the transducer. The sensor was calibrated and rated to measure torque above 0.2 Nm. Alongside the torque transducer, a custom eddy current brake was developed using permanent magnets with a spinning aluminium disk. This braking mechanism was chosen as it provides smooth loading and can be designed to accurately modulate the braking power. Control was successfully achieved by changing the relative position of the magnets to adjust the strength of the magnetic flux through which the disk is moving. The exact braking power of the eddy current brake is adjusted by using feedback control from the developed torque sensors. Filtering and smoothing of the measured speed and torque data was performed to ensure more stable control. Full system testing shows the torque induced by radially loaded bearings are lower than expected, while the developed sensor accurately measured the higher loading associated with full load conditions. Additionally, the eddy current brake is verified to supply the required braking power of 250Wduring full load testing. Drivetrain losses are seen to depend on the applied lubricant, with the highest efficiency measured to be 97.5 %.
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    Improvement of the acoustic properties of tonewoods
    (Stellenbosch : Stellenbosch University, 2024-02) Nefdt, Keenan Colin; Meincken, Martina; Stellenbosch University. Faculty of AgriSciences. Dept. of Forest and Wood Science.
    ENGLISH ABSTRACT: This work investigated different wood modification techniques to improve the acoustical properties of tonewoods, in particular the sound radiation ratio (R). The treatments used were heat-, fungal - and UV exposure, as well as immersion into NaOH and Na2SO3 solution and a combination of the most successful treatments. All initial experiments were performed on pine, before replicating the best performing treatment on spruce due to cost factors. The main objective was to reduce the hemicellulose content without severely degrading cellulose, which results in a reduction of density while maintaining, or even improving the elasticity (MOEL). The results indicated that it is possible to increase R and MOEL significantly with heat-, fungal – and sodium treatment. Overall, the combined heat-fungal and heat-sodium treatments performed the best and managed to increase R by up to 20 %. Sodium treatment led to the best increases in R, but compromised the wood structure and the treatment protocol needs to be developed further. Consequently, this study found the most successful wood treatment to be exposure to white rot combined with heat treatment.