Hydrodynamic forces on monopiles with secondary structures. Numerical approach

Nygaard, Michael

4. term

Structural and Civil Engineering, Master

2016

2016-06-07

53 pages

The main purpose of this project was to investigate the usability of numerical models in order to determine the hydrodynamic forces on a monopile with a secondary structure. The numerical models used was BEM models and CFD models. In the analysis, a analytical solution by MacCamy and Fuchs was used to calibrate the BEM models because they are based on the same theory and should trend towards the same results. This was done with a convergence analysis. Skewness of the elements was also considered. For the CFD models the Volume of Fluid (VOF) method was used and using the program Star-CCM+ it is possible to generate waves in the domain. Models with and without the secondary structure was analysed using nine different wave conditions with varying wave height and wave period. The wave conditions are based on waves used in physical model tests. Finally the different methods are compared to each other and physical model tests. The comparison shows that BEM might not be a suitable method to determine forces because drag is a factor when considering monopiles. CFD consider drag and gives results closer to the model tests. But there are still further studies to be made in order to determine the viability of numerical models, but there is potential.

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