ABS Extends Offshore Structure Assessment Program to TLPs, Spars

Classification society ABS unveiled its ABS Eagle Offshore Structure Assessment Program (OSAP) Version 2.0 at the Offshore Technology Conference in Houston, TX, this week. This latest version now allows designers of tension leg platforms (TLPs) and spars to check the compliance of their designs with ABS class requirements. Initially the software was applicable only to semisubmersibles.

The evaluation of dynamic loads and site-specific fatigue assessments are key to developing appropriate design criteria for TLPs and spars. Using its market leading experience with both these types of structures, ABS issued specific industry guidance in its "Guide for Building and Classing Floating Production Installations" in 2004.

The new OSAP Version 2.0 software builds on this guidance by taking into account the sophisticated load modeling required for these two specialized floating structures to further simplify the verification of compliance by designers.

The various load cases that should be considered include: environmental loads, hydrostatic pressures and buoyancy, gravity and inclination-induced loads, inertia loads, operational loads, as well as mooring and riser loads during both transportation and operation and site-specific storm design levels.

"The software streamlines the complex design code check process by helping designers determine environmental loads, transfer hydrodynamic loads to a structural model and extract structural analysis results from a user selected finite element analysis program," explained Pao-Lin Tan, Director, ABS Corporate Offshore Engineering Support. "Simply put, the software acts like a data processing hub connecting the hydrodynamic and structural analysis software with analysis results to check against the design code," he added.

The six main functions of the program are: load generation, design wave calculation, load mapping and balancing, global strength assessment, fatigue assessment and buckling and ultimate strength analysis.

There are presently 22 TLPs and 18 spars installed worldwide. Of those 15 TLPs are ABS classed and 16 spars are ABS classed. Industry projections estimate 10 new TLPs and 10 new spars are expected over the next five years.