Browsing by Author "Omer, Hamza"

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    The impact of wave slamming indused vibration on human factors and equipment on board the SA Agulhas II
    (Stellenbosch : Stellenbosch University, 2016-03) Omer, Hamza; Bekker, Annie; Stellenbosch University. Faculty of Engineering. Dept. of Mechanical and Mechatronic Engineering.
    ENGLISH ABSTRACT: An investigation of wave slamming phenomenon was performed in the context of human factors on-board the S.A. Agulhas II, a South African Polar Supply and Research Vessel. Full scale vibration measurements were conducted during the vessel’s voyage to Marion Island in 2014 and Antarctica in 2014/15. The measurements captured vibrations in the vertical direction as per the directives of ISO 2631-1 (1997). A questionnaire survey was conducted on both voyages to acquire the human response to wave slamming. The study for the Marion Island voyage focused on measurement and analysis of vibration due to slamming using the metrics recommended by ISO 2631-1 (1997). The analysis revealed that slamming events produce impulsive accelerations of high magnitude resulting in broad band excitation of the vessel. The weighted r.m.s acceleration levels resulting from slamming exceeded the comfort threshold provided by the standard. The qualitative analysis of human response indicated that slamming not only caused discomfort on-board but also affected work and equipment. The study performed during the Antarctic voyage was designed to identify and correlate measured slamming vibration data with human response and to investigate their association. Statistical analysis, performed using Kendall’s coefficient, indicated that slamming vibration was correlated to human complaints on-board the S.A. Agulhas II. The highest correlation found was the cumulative Vibration Dose Values (VDV) which proved to be the best metric amongst all others to represent slamming vibration for human factors. In addition to that, the study evaluated the effects of some environmental factors such as swell height and wind speed on wave slamming. It was concluded that even moderate sea states can lead to heavy incidences of slamming. Finally, operational deflection shapes were calculated for the visualization of the structural response of the vessel during bow and a stern slamming event. Time domain response and frequency response was calculated to observe the motion of the ship as it undergoes a slamming event. The analysis indicated that the area of impact (bow or stern) comes under severe loading immediately. Both slamming events produce bending and twisting of the entire structure. It was also noted that the long duration of heavy oscillations produced by slamming may affect human comfort and performance on-board the vessel.