This continued research will improve the current state of understanding regarding the basic mechanisms affecting the seafloor stiffness within the Steel Catenary Riser (SCR) touchdown zone, and develop a means for providing quantitative estimates of seafloor stiffness and damping and their variation over the life of the project for various soil and site conditions.
The geotechnical studies in this project will use finite element analyses to develop load deformation relationships to describe soil-pipe interactions for various conditions of soil properties, trench conditions, and characteristics of riser motions. The hydrodynamic studies will investigate riser-structure fluid interactions for various sea states, floating system characteristics, and seafloor conditions. The parallel studies will be coordinated throughout the project to ensure proper accounting of interaction effects.
Phase 1 of this project has provided an overall study framework and plan, validation of FEM tools for use in this project, and an initial identification and assessment of the important parameters for modeling SCRs and developing boundary conditions in the touchdown area for use in estimating the fatigue life of SCRs.
Phase 2 developed a numerical model, performed parametric studies, and identified conditions most influential on the magnitude of bending stresses in the riser pipe. The parameters evaluated included soil strength and stiffness, trench geometry, the effects of trench collapse and infilling, strain rate effects, and non-linear effects associated with a range of amplitudes and velocities of riser motions. The range of riser motions near the touchdown zone were analyzed using a numerical code accounting for the interaction among a floating structure, its riser/mooring system and the seafloor.
The project's final report is currently under review by MMS and will be posted upon project completion.
Project completed in September 2006. See the following Final Report for additional information.