Computational methods are developed to simulate interactions of nonlinear waves with single- and multi-structures through the finite element method based on second order and fully nonlinear theories. The three dimensional (3D) mesh with prism elements is generated through an extension of a two dimensional (2D) unstructured mesh. The potential and velocity in the fluid field are obtained by solving finite element matrix equations at each time step using the conjugate gradient method with SSOR preconditioner. The combined Sommerfeld-Orlanski radiation condition and the damping zone method is used to minimize wave reflection. The regridding and smoothing techniques are employed to improve the stability of the solution and the accuracy of the result. The method is first used to simulate interactions of waves and an array of cylinders in the time domain based on the second order theory. It is shown that the interference between the cylinders has magnificent influence on the phase and amplitude of the waves and forces. The fully nonlinear problem is tackled first by considering the two dimensional problem, which allows the developed method to be properly tested and validated. Simulation is made for a body in a tank and a wedge-shaped body in oscillation. Comparison is made with results obtained from other methods. In the next application, the 3D interactions between single- and multi-cylinders with or without flare and waves generated by a wave maker in a rectangular tank are investigated based on the fully nonlinear theory. The effect of the flare on waves and hydrodynamic forces is analysed, and the mutual interference of multiple cylinders is also studied. The method is also employed to solve the 3D fully nonlinear radiation problems by single- and multi-cylinders undergoing oscillation in the open sea. The result is compared with those obtained from the linear and second order theories. It is concluded that the developed numerical approaches based on the finite element method can be used to effectively simulate interactions of waves and single- and multi- cylinders with or without flare, which can provide some valuable information to design of offshore structures.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:428774 |
| Date | January 2006 |
| Creators | Wang, Chizhong |
| Publisher | University College London (University of London) |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://discovery.ucl.ac.uk/1446187/ |
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