The Tension Buoyant Tower: A Design for Deep Water

The Tension Buoyant Tower (TBT) consists of a cylindrical spar type buoyancy module moored to the sea bottom by a group of tendons arranged in a pattern close to the centreline of the buoyancy module. The buoyancy module consists of buoyant hard tanks extending to a depth of 250 feet or more depending on the specific requirements of the design. An upper stem extends below this point to a depth of 500 feet or more. Seven tendons pass through a centrewell in the buoyancy module and extend to the seafloor, passing through a lower stem before latching to a bottom template. Local tendon bending stresses are limited by tapered tendon sleeves at the entrance points to the upper and lower stems. The tendons and sleeves are allowed to pivot at these points, eliminating the need for elastomeric flex joints. Coupled analysis of the design was performed using the finite element program COPIPE. The key parameters in the design include: base tension, location of platform CG and CB, sleeve design and location of tendon support points within the stems. The results of analysis showing the sensitivity of the design to these and other parameters will be discussed. Application of the TBT to Gulf of Mexico applications ranging from 1,000 feet to 10,000 feet will be reviewed.