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Title: Numerical modelling of wave interactions with a vertical surface-piercing column
Author: Kasiman, Erwan Hafizi
ISNI:       0000 0004 8504 4570
Awarding Body: Imperial College London
Current Institution: Imperial College London
Date of Award: 2018
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This thesis concerns the numerical modelling of the wave interactions with a vertical, surface-piercing, column. The study focuses on the unexpected high-frequency wave scattering and the nonlinear loading of columns located in the inertia regime. The test cases include both regular and irregular incident waves. With the wave-column interactions involving highly nonlinear free-surface effects, the two-phase Volume of Fluid (VOF) model adopted. This choice was based upon preliminary calculations in which the model was shown to be capable of simulating appropriate extreme wave conditions. These calculations involved a wide range of incident wave conditions including as standing, regular, irregular and breaking waves. In all cases, comparisons with existing theory and lab data confirmed that the waves were successfully simulated. The numerical method was first employed in the simulation of Type-1 and Type-2 scattered waves due to the interaction between incident regular waves and a vertical column. Comparisons to the laboratory data presented in Swan & Sheikh (2015) allowed a rigorous validation of the proposed method. Further investigation to determine the dependency of the scattered waves on the size of the column and the incident wave steepness was undertaken. For wave-structure interactions involving irregular focused waves, an additional wave scattering mechanism was also identified. The physical origins of this new mechanism were carefully investigated and shown to be closely linked to the increased steepness of the wave cases. The nonlinear wave-wave interactions between the incident and scattered wave fields, for both regular and irregular waves, were examined and their practical implications discussed. The nonlinear loading, in particular, the secondary loading cycle was successfully predicted using the numerical model. Frequency analysis and comparisons with available analytical force models were carried out to highlight important changes in the higher order force components, particularly in respect of increasing wave steepness and varying column diameter. A clear linkage between the secondary loading cycle and high-frequency wave scattering has been established and the physical origins of the former studied and explained. Finally, the importance of the secondary loading cycle in provoking a dynamic excitation was investigated using a simple single degree of freedom model. The results reveal a large dynamic excitation in both regular and irregular waves in the presence of the secondary loading cycle. This has important practical implications, not least because the load models commonly applied in design are not able to predict the secondary loading cycle. As such, they will undoubtedly under-estimate both the magnitude and occurrence of dynamic excitation. Key insights into this important problem are provided.
Supervisor: Swan, Chris ; van Reeuwijk, Maarten Sponsor: Universiti Teknologi Malaysia
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral