Abstract B8

Parametric studies of a drilling riser in approximately 5300 ft. of water have been conducted using the program ABAQUS to assess the general characteristics of the dynamic behavior, the accuracy of various models (number and type of finite elements) and the importance of several effects (inclined buoyancy forces and internal fluid). The riser has been studied both in the connected and hanging positions. The results indicate that the first case even the simplest finite elements provide relatively good solutions. The analysis in the hanging mode is, however, much more difficult requiring finer meshes (larger number of elements) for convergency and accuracy. Very significant high frequency components appear in the response. These sharp peaks are eliminated when artificial damping is introduced in the numerical integration scheme, but there is a need to determine whether these high frequency components are real or not. The existence of water inside the riser when it is disconnected and hanging from the vessel increases the stresses by about 30%. Substantial saving could be achieved if the riser could be pressurized with air to avoid collapse as the mud is expelled and closed at the bottom to prevent water from coming in.