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Drilling operation in deep water, harsh environment and remote locations becomes a key trend for the offshore industry to fulfil increasing demand for energy. For operational conditions wave induced loads are more significant for the offshore installations. Therefore, to ensure integrity and structural safety, the wave induced loads have to be taken into account. One of the approaches to accomplish this task is to perform a fatigue analysis with the extreme environmental loading on the offshore platform using rules and practices recommended by classification societies. The main objective of the thesis has been to present a case study of a semisubmersible drilling unit regarding the fatigue analysis. The applied approach consisted in finite element modelling of the global structure, applying hydrodynamic loads using recommended offshore design codes, transferring wave loads from hydrodynamic model to structural model and perform the fatigue analysis with most unfavorable combination of environmental conditions. Among different methods of fatigue analysis, the spectral method is considered as most suitable in which long term distribution of stresses is calculated using wave scatter data. 

For finite element modelling SESAM Genie was used while HydroD Wadam was used to analyze hydrodynamic loads and also transfer the loads to the finite element model for subsequent structural analysis. These hydrodynamic loads were applied for a number of wave directions and for a range of wave frequencies covering the necessary sea states and the results in form of stresses were obtained. These results were then used to calculate fatigue damages at given points in the structural model using another software – Stofat.

Ingénierie, informatique & technologie > Ingénierie civile