“As the oil and gas fields get deeper, the installations of deepwater platforms become more challenging. The coupling effects between a floater and its moorings become more pronounced and more important. Sesam is an excellent tool for analysing the interaction between hull, moorings and risers,” says Andy Kyriakides, Project Manager, MODEC International LLC.

The MODEC Central Pontoon (CP) Semi is an efficient new generation design for deepwater and ultra-deepwater offshore developments. This highly-efficient platform is designed to operate in hurricanes, cyclones, as well as in benign environments. It consists of an octagonal continuous central pontoon structure and four radially oriented columns outboard of the pontoon.

A box girder system at the top connects the four columns, which in turn support a conventional truss deck. Topsides are integrated quayside and the platform is stable at all times. The radial orientation of the columns enhances the stability of the platform during quayside integration of the topsides while minimising the displacement needed. The deep draft during operation results in SCR friendly motions.

Model tests in a wave basin and extensive analytical simulations using Sesam were performed, providing in-depth understanding of the vessel’s response and coupling effects between vessel, moorings and risers.

DeepC was extensively used in evaluating the response of the CP semi with moorings and risers for a variety of payloads, water depths and environments. The mooring lines and risers attached to the vessel were modelled as finite elements, while the vessel’s coefficients were computed by Wadam.

The agreement of results between model tests and DeepC provided additional confidence in the performance of the platform during the early design stage of future projects.

Author: Gang Miao and Qi Ling, MODEC

Founded in 1968, MODEC is a turnkey supplier of Floating Production, Storage and Offloading (FPSO) vessels, Floating Storage and Offloading (FSO) vessels, Tension Leg Platforms (TLPs) and production semisubmersibles (CP Semis) for the offshore oil and gas industry. MODEC is currently operating nine FPSOs/FSOs worldwide, and has two FPSOs and two FSOs under construction. MODEC has delivered four TLPs and has one under construction.