Thesis
Nonlinear hydrodynamic interaction analysis of multi-platform system
- Creator
- Rights statement
- Awarding institution
- University of Strathclyde
- Date of award
- 2022
- Thesis identifier
- T16186
- Person Identifier (Local)
- 201861814
- Qualification Level
- Qualification Name
- Department, School or Faculty
- Abstract
- Along with the technological development of ocean engineering, offshore platforms are gradually becoming larger and more complex. The recent development in the deep water region often involves multiple floating platforms adjacent to each other to perform more complex functions. Several aspects should be concerned due to the larger and more complex offshore structures in the offshore area, like water surface elevation and wave run-up around structures, motion characteristics of platforms in the multi-platform system and wave loads on platforms in multi-platform system. 3D potential flow method is applied in the present study. The perturbation theory is employed to divide the velocity potential into first-order and second order potential. The boundary value problem at each order is solved by boundary element method. This research describes the investigation carried out on the surface elevation around single column and multiple columns structures since the peak surface elevation often impacts the offshore structures with nonlinear wave loads and potentially causes slamming to platforms. The near-trapping frequency mode for circular columns is extended and applied for the rounded corner square columns and validated. The characteristics of different mechanism (superposition and near-trapping) for peak surface elevation are identified in the present thesis. The peak value of the second-order surface component caused by superposition decreases with higher corner ratio of column. However, for the peak surface elevation caused by near-trapping, the second order surface component decreases with lower corner ratio of column. Additionally, the peak surface elevation caused by near-trapping is located at the area enclosed by columns. These characteristics are applied to distinguish the mechanism of peak surface elevation. This thesis also contains the study on dynamic responses of a two platforms system containing a Tension Leg Platform (TLP) and a tender assisted drilling (TAD) with a flexible connection between the two platforms. The mooring lines and tendons are taken into consideration in the coupled analysis of the multi-body platform's system. The numerical model is validated by the published experimental result. Both frequency domain analysis and time domain coupled analysis are conducted. The motion responses and wave load characteristics on the two platforms in the multi-platform coupled model are investigated in the numerical simulation. It is found that the nonlinear wave force on TLP (Sum-frequency wave force) and TAD (Drift force) are changed significantly due to the existence of adjacent platform. The impact of hydrodynamic interaction on each platform is primarily determined by the incident wave direction and the arrangement direction of the platforms. The multi-platform system is not only applied in the oil and gas area but also in the renewable energy area. Research of interaction between an offshore wind turbine and support vessel is contained in the present study. The relative distance and the force along the connecting lines between the wind turbine and support vessel are investigated under different wind-wave misalignment conditions during the operation period. The maximum relative distance and tension in the connecting lines are significantly influenced by the wind-wave misalignment under the low environmental condition (LC) and medium condition (MC). However, there is little impact of misalignment under high condition (HC). For floating wind turbine, the impact of wind-wave misalignment for the floating wind turbine is rather small when the environmental condition is medium and high condition. There is also an interesting discovery that increasing wind speed and wind-wave misalignment evidently leads to a jump of maximum relative distance and maximum tension in the connecting lines.
- Advisor / supervisor
- Tao, Longbin
- Resource Type
- DOI
- Date Created
- 2021
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PDF of thesis T16186 | 2022-04-08 | Public | Download |