Department of Mechanical and Mechatronic Engineering

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https://scholar.sun.ac.za/handle/10019.1/109

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Browsing Department of Mechanical and Mechatronic Engineering by browse.metadata.advisor "Bekker, Anriette"

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    A human cyber-physical system to study the motion sickness of seafarers.
    (Stellenbosch : Stellenbosch University, 2023-11) Taylor, Nicole Catherine; Kruger, Karel; Bekker, Anriette; Stellenbosch University. Faculty of Engineering. Dept. of Mechanical and Mechatronic Engineering.
    ENGLISH ABSTRACT: Maritime 4.0 offers technical opportunities to digitally enable ships. Systems are equipped with virtual counterparts, forming cyber-physical systems, to manage operations. However, the human element remains constrained to the physical layer. This dissertation proposes the Mariner 4.0 concept that encourages equipping seafarers with virtual counterparts. Mariner 4.0 is a contribution formulated to serve as a branch of digitalisation that addresses opportunities and challenges associated with human factors in Maritime 4.0, such as a lack in accessibility of human-centric data during operation. Human cyber-physical systems offer a promising means for human-system integration and human digital representation amidst technically-centred developments. This dissertation contributes an architecture for a human cyber-physical system that defines core elements – a physical layer, where seafarers are present, a cyber layer, which contains virtual counterparts for seafarers, and communication between the layers. A human cyber-physical system for seafarers is implemented and deployed, which is the first objective of this dissertation. The trialled human cyber-physical system is a contribution that facilitated human-centric data acquisition and processing for seafarers on a ship over the course of a 20-day long voyage. The motion sickness of seafarers is monitored subjectively and objectively in near real time, a novel feat in shipping, in a case study with 63 participants on board. Seafarers recorded their subjective experiences of motion sickness through two methods. The first, traditional method used paper-based questionnaires, while the second, novel method used the human cyber-physical system. The second objective of this dissertation is to use the human cyber-physical system as a mechanism for advancing the study of motion sickness in shipping. The human cyber-physical system enables personalised data analysis as well as conventional aggregation of results. As such, novel understanding of motion sickness and the study thereof in shipping is uncovered. Measures of motion exposure are determined objectively according to recommended procedures in ISO 2631-1 (1997) and are integrated with the percentage of motion sick individuals on board, forming motion sickness criteria. The human cyber-physical system provides a platform for inspecting the evolution of criteria development during ship operation. The results contribute diagnostic thresholds that could be used beyond the operational stage to assess the levels of sickness that individuals or a cohort may present if exposed to certain measures of ship motion. The motion sickness criteria accommodates factors, such as exposure duration, for tailoring diagnostic thresholds to voyage missions – potentially applicable for voyage planning and ship design. The human cyber-physical system provides a customised platform for addressing challenges and opportunities associated with human factors in Maritime 4.0. Moreover, the human cyber-physical system extended the knowledge basis of motion sickness on ships innovatively. The human cyber-physical system served as a human-centric platform for seafarers that empirically revealed the importance of performing data acquisition and analysis at an individual level in addition to an aggregate level.
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    A laboratory-based verification rig for inverse models of ice-induced propeller moments on ship propulsion shafts
    (Stellenbosch : Stellenbosch University, 2023-03) Laas, Jacobus; Bekker, Anriette; Bredell, Johann; Stellenbosch University. Faculty of Engineering. Dept. of Mechanical and Mechatronic Engineering.
    ENGLISH SUMMARY: The rise in maritime traffic in icy polar regions, create hazardous conditions for ships that may require costly and time-consuming in-port repairs. The drive towards environmentally friendly, energy-efficient ships pressure ship builders to conform to stringent design guidelines, set by classification societies. Improving efficiency and production cost is often coupled with a reduction in over-designed components. As a result, there is a critical need for openly-available, accurate, measurement data to support theoretical computations. Due to cost, installation challenges, and harsh operating conditions, there are few openly-available shaft and propeller torque measurements during ice interaction. As such, available propulsion shaft response data, along with inverse models, are used to determine propeller torsional loads. It remains to verify and validate these models in a controlled environment. Common verification methods consist of subjecting the inverse models to standardised load cases which compare the resulting inverse to the input load cases by the classification society. The use of experimental data, however, quantifies actual ice-loading responses, as opposed to ideal load cases, and prevents inverse crime when implemented in inverse models. For this purpose, a laboratory rig was developed, manufactured and commissioned that is capable of exerting a measured external torque to the end of a shaft whilst performing conventional shaft measurements. A disc brake was implemented in the place of a propeller as load device. The laboratory rig is able to simulate important phenomena observed in ship shaft measurements during propeller-ice contact. A continuous, modal superposition model was adapted to the dynamics of the rig, and the inverse brake torque was calculated from shaft measurements. It was found that the first torque peak, of the inverse solution, is within 14% of the measured torque. Subsequent torque peaks, such as those from multi-impact ice milling cases, however, are not inverted successfully, as the free-response of the shaft contaminates the torque solution. Consequently, the nature of ice-loading is not adequately described by the continuous model. Recommendations are made to improve the laboratory rig and the continuous model investigated.
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    The numerical investigation of wave slamming on a polar supply and research vessel
    (Stellenbosch : Stellenbosch University, 2023-03) Van der Westhuizen, Alexander; Bekker, Anriette; Meyer, Christiaan J.; Stellenbosch University. Faculty of Engineering. Dept. of Mechanical and Mechatronic Engineering.
    ENGLISH SUMMARY: The SA Agulhas II is a polar supply and research vessel owned by the Department of Forestry, Fisheries and the Environment of South Africa. She facilitates and supports research in the Southern Ocean and Antarctica. The SA Agulhas II was designed to polar class 5 and experiences harsh seas and ice conditions during her voyages. The ship was designed with a raised transom which results in significant slamming during open water navigation. This can cause local damage to the hull as well as increased fatigue damage to the structure of the vessel. The ship was designed to manage ice passage which may be sub-optimal during open water navigation due to the increased slamming which results from the raised transom. An investigation into a monitoring scheme with the use of full-scale measurements and simulation software is instantiated to detect slamming pressures experienced by the hull of the vessel. The full-scale slam load measurement estimation is established with the use of plate theory and strain measurements on sections of the hull plating at the transom. The strain measurements are used to determine an estimate of the pressure loads experienced on the hull during slamming events. The results show promise in the technique used after some improvements in noise attenuation and error adjustment due to simplifying assumptions. A computational fluid dynamic model and simulation procedure is developed to analyse the validity of using simulation software to predict loading and vessel responses as well as inform hindsight investigations of the vessel responses to her environment. The simulation software does not capture the response of the vessel well in some seaways and hydrodynamic pressure estimates are not determined well for small sea states.