Fedem Technology has carried out several projects with the purpose of understanding Wellhead Systems behaviour and various parameters influence on fatigue life. A central part of these projects has also been development of simulation methods for such systems. Analyzes are executed both in the frequency- and time domain. Fedem has mainly worked with the time domain analysis. Time domain analysis has to variants, coupled and decoupled, where the decoupled analysis completely dominates today's analysis. Loads on the Wellhead System are calculated for a number of seastates described by metocean data for the relevant area and season. These seastates excites the model consisting of the riser and the rig and RAO'er. From an FE model of the Wellhead System, Stress Transfer Functions (STF = non-linear SCF) of all hotspots is extracted. Mapping the STF’s with the Load Time History gives a stress time history for each hotspots. Fatigue life of the hotspots is calculated based on rainflow counting of the stress ranges. The total fatigue life is calculated based on the probability distribution of the different seastates, described by the metocean data.
 

Currently state-of-the art simulation methods are under development here at Fedem Technology. Fully coupled models includes in addition to the riser, 3D FE-models for the top side and subsea systems. Advanced heave compensation modelling is enabled by the built-in control system. The use of dynamic superelement reduction enables simulation times from real-time up to 3 times real-time.