On-bottom stability design for pipelines and cables has until recently mainly been based on analytical methods or 1D and 2D computer tools which are incapable of accounting correctly for effects such as development of axial friction and associated change in tension, the presence of free spans, open trenches and curved sections along the route. These effects have been studied and addressed in the recent DROPS JIP Phase I where the results were implemented into the already broad capabilities of the SIMLA computer tool. The tool is a nonlinear 3D FE software tool for static and dynamic analysis of pipelines and cables. It was extended with a new hydrodynamic load model in which the well-known MOD-AGA database model was combined with a Morison formulation with gap-dependent hydrodynamic coefficients to account for free spans. Also included, was an improved algorithmic formulation of the pipe-soil interaction models developed by Verley and Sotberg and Verley and Lund.

SIMLA DROPS is therefore able to capture all relevant 3D effects such as actual seabed terrain, free spans, bending stiffness, axial tension, route curves, variation in soil conditions, wave phase variations along a section, boundary conditions at ends and along the section etc.

This paper discusses the new on-bottom stability capabilities of the SIMLA DROPS tool and the application of the tool to the design of the BM-C-33 gas export pipeline. The tool has been utilised for optimising the shallow water section of the BM-C-33 24" gas export pipeline located off the Brazilian coast.

The BM-C-33 Project

The BM-C-33 license is located in the southern part of Campos Basin offshore the Rio De Janeiro state of Brazil, approximately 200 km from shore in water depths of 2 600 to 2 861m MSL (Fig. 1). BM-C-33 is currently one of the deepest offshore fields under development.

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