This work is part of a research project on Dynamic Analysis of Risers and Tendons conducted at The University of Texas at Austin. The main objectives of this study were to gain a better understanding of the dynamic behavior of deep water drilling risers and of the importance of various parameters, and the assess the effect of different modeling options on the accuracy of the results. In addition, the results of the study were to serve as benchmark solutions to evaluate alternative formulations with simpler as well as more sophisticated models.
To conduct these studies a drilling riser in some 5300ft water was selected. No attempt was made to study any real riser but an effort was made to use general dimensions and properties realistic for such a water depth. The analyses were conducted using the program ABAQUS, developed by Hibbitt, Karlsson and Sorensen Inc., and extensively used in industry. This program was selected because of its powerful capabilities including special modules to simulate hydrodynamic forces with Morison’s equation. The riser was studied both in the connected and hanging positions. For each one of these two cases parametric studies were conducted to evaluate the effect of the number of finite elements used in the model, the types of elements and the inclusion of some artificial damping in the numerical integration scheme. In addition, the analyses were conducted to evaluate the importance of the inclined buoyancy forces resulting from the rotation of the riser from the vertical position and the effect of the internal fluid (mud in the connected position and water in the hanging mode.)