Dynamic analysis of ship collisions with offshore platforms

[Truncated] The work performed in this thesis is concentrated on the response of offshore facilities upon ship impacts, evaluated by means of non-linear dynamic FE code LS-DYNA. The numerical studies are carried out because of high-energy ship impacts on offshore structures that, despite their low chance of occurrence, are not totally covered/predicted by hand calculations according to the simplified plastic mechanisms as suggested and commonly adopted in the current design practice. Explicit FEA are known for being widely used in collision problems and offer a good alternative to the lack of experiments (especially full-scaled), which would still be extremely costly in comparison to the computational resources demanded by such numerical analyses. However, in order to be able to carry out a significant number of numerical simulations necessary to perform parametrical studies, some simplifications still need to be assumed while trying to keep the accuracy of the FEM. Therefore, an extensive literature review is presented in the thesis to review and discuss every main aspect involved in both internal and external mechanics of the collisions and its respective preponderance on the problem’s outcome. Likewise, special care is also devoted to the FEM techniques employed in both ship and installation structures, in particular modelling the members in the contact zone and its surroundings, subjected to significant plastic deformations. It is intended that the numerical study may constitute a solid base for the solutions eventually proposed for easy application in practical engineering problems.
The numerical assessment of the collisions considered in this study concentrates primarily on jacket based steel platforms as they are the most representative platform structures among the offshore installations. Based on the principles of strain energy dissipation, the results here obtained can be extrapolated, to some extent, to other platform types.