Browsing by Author "Nickerson, Brendon Mark"

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    Development of an integrated numerical method for the fatigue analysis of railway bogies
    (Stellenbosch : Stellenbosch University, 2017-03) Nickerson, Brendon Mark; Venter, Gerhard; Stellenbosch University. Faculty of Engineering. Dept. of Mechanical and Mechatronic Engineering.
    ENGLISH ABSTRACT: This study focuses on the creation of a numerical simulation process that can be used to determine the fatigue life of railway bogies, using the Commonwealth railway bogie of the class 5M train in South Africa as example. The numerical simulation is intended for use in future research on railway bogies. The research is supported and funded by the Passenger Rail Agency of South Africa (PRASA) Engineering Research Group at Stellenbosch University. A finite element (FE) model of the bogie has been created using an accurate three dimensional computer aided drawing (CAD) model, supplied by the PRASA Engineering Research Group. The FE model has been used to determine stress distributions due to unit loads applied at the primary and secondary suspension attachment points. Dynamic load cases have been determined through simulation of spring-mass-damper models representing the train and track systems. The load cases have been applied to the FE model stress distributions and superimposed to obtain stress histories. A script has been coded in Python to determine fatigue life from the stress histories. The process has been designed in such a way that each component can be altered and refined, allowing future research opportunities and refinements such as expanding the process to be applied to other bogies or allowing actual measured track data to be used as input for determining dynamic loads. Further research is required to validate and improve the numerical process.
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    Inverse models for ice-induced propeller moments on a polar vessel.
    (Stellenbosch : Stellenbosch University, 2021-03) Nickerson, Brendon Mark; Bekker, Annie; Stellenbosch University. Faculty of Engineering. Dept. of Mechanical and Mechatronic Engineering.
    ENGLISH ABSTRACT: It is necessary to quantify the loads experienced by the propellers of ice-going vessels.Knowledge of these loads will serve to improve propulsion design specifications and maintenance strategies for polar class ships. Recent developments include the inverse solutions of the external ice-induced propeller moments from indirect measurements on the propulsion shaft. These inverse solutions are performed using models that account for the dynamic influence of the shaft. Although torsional vibration calculations are required by design rules there is little information on the methodology external propeller moments as their use, in this context, is still relatively new. Full-scale propulsion shaft measurements were conducted on board the S.A. Agulhas II, in which the torque and angular velocity were captured, to be trans-formed into external propeller moments. Two inverse models of the propulsion shaft were investigated. The first is an existing model which represents the shaft as a combination of lumped masses. The inverse problem in this case is ill-posed and requires regularization. It was found that the assumptions made in the derivation of this model, that both the hydrodynamic and motor torques were constant, and its computational expense made it ill-suited for use in the inverse estimation of propeller moments. The second inverse model is newly developed and based on the superposition of the shaft modes, resulting in a well-posed problem. This model accounts for the modal inertia in the flexible modes of the shaft, as full-scale data indicated that this was important, and has increased accuracy and efficiency. To the author’s knowledge, this is the first model that has been efficiently applied to determine the inverse propeller moments from full-scale measurements for a complete voyage. The derivation of the corresponding estimated propeller load profiles is presented. The new model is suitable for the real-time monitoring of propeller loads, which can assist in ship operation.