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Abstract
The objective of this thesis is to study the static, dynamic and fatigue response of the offshore pipelines (Riser/Spool) under the effect of the environmental wave force in the static analysis and the slug forces in the dynamic and fatigue analysis. A parametric study has been performed for three models with different pipe sizes. Each model has been studied with different parameters in two load cases for each model with the same pipe size. The static analysis has been performed under the effects of self-weight, buoyancy, design pressure, design temperature, environmental loading, pipeline thermal expansion and the jacket displacements due to environmental loads. The hydrodynamic forces calculations for the pipelines have been described in details in additional to the wave theories. The dynamic analysis has been studied for all the load cases; however the concentration is on the slug effect at the riser and spool, so it has been studied deeply in this thesis, as it is the most critical portion of the pipeline. It is found that the slugging inside the riser induces a large deflection, which is much more than the displacement results from the static analysis, also the stress induced by the slug should be studied in the fatigue analysis.
The fatigue analysis has been studied in different models with different slug parameters to get the dynamic response and how it affects the pipeline design life. The fatigue design life has been deduced based on the fatigue analysis and compared with different pipelines design life to show the importance of performing the dynamic and fatigue analysis in additional to the static analysis which cannot control the pipeline design life.
At the present practices, the slugging effect is not included in the fatigue analysis and when it is performed there are question marks about how representative the analysis is. As this area is important and require attention from the industry, so the slug effect, dynamic analysis and fatigue analysis have been studied in this thesis to reply on these questions and also the industry in this thesis is kindly requested to pay more attention to this point in future.
The results are discussed and the main conclusions and recommendations of the thesis are presented in the last chapter.