Modelling of Drilling Marine Riser: Comparisons in Static Analysis

For specific applications such as control of rigid riser angles, study of the riser fatigue, using suitable models that relate to accuracy and computation time is necessary. This study provides the formulations for a marine riser based on (a) large displacement cable mechanics, and (b) tensioned beam FE method. Numerical examples for risers subject to top tension force and current are presented and validated against published results. Results confirmed that the large displacement formulation is valid for risers in both shallow and deep waters, whereas the FE solution may only be suitable for risers in shallow water. The free vibration solution confirms that the system becomes more flexible with increasing water depth as well as smaller tension force at the top. The geometric effect on the dynamic characteristics is less obvious for higher vibration modes. Nevertheless, the differences obtained also indicate that if an assumed solution is needed to initiate an iterative computational process, such as control problem of marine risers, the simpler FE solution may be adequate.