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MOSES Minimizes Redundant Steel in ORCA Offshore’s Analysis of Self-installing Platform

MOSES Minimizes Redundant Steel in ORCA Offshore’s Analysis of Self-installing Platform
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MOSES Minimizes Redundant Steel in ORCA Offshore’s Analysis of Self-installing Platform - 1

CASE STUDY Project Summary Organization: ORCA Offshore Solution: Offshore Engineering Location: Dutch sector of the North Sea Project Objective: • Safely deploy the F3-FA self-installing offshore platform on time and on budget. • Utilize the best available analytical tools to minimize redundant steel. • Minimize the size of the sea fastening to allow for safe handling. Products used: MOSES Minimizes Redundant Steel in ORCA Bentley InRoads of Self-installing Platform Offshore’s Analysis ® Powerful tools Installation Specialist Demonstrates Validity of Dynamic Transport and for the design of civil infrastructure Load and Structural Strength Analysis Using Bentley Software Massive but Movable When Centrica acquired the F3-FA field in the Dutch sector of the North Sea, it planned to develop the field for four years of production and then relocate to another field. A EUR 200 million reusable platform was crucial to the project’s success. ORCA Offshore joined a team of design, fabrication, and installation contractors to provide the naval architectural analysis for transport and installation of the nearly 9,000-ton, self-installing platform. ORCA Offshore provided motion and stability analysis, multibody dynamic analysis, structural spectral analysis, and scale model testing. Bentley’s MOSES offshore platform design and installation software simulated and analyzed the transportation and installation of the unique production platform. transported by barge to the next location. The cost savings across three or four marginal fields would be significant. The F3-FA platform footprint measures 63-by-45 meters, and the structure reaches a height of 133 meters above the sea floor. Each of four 440-ton suction piles is 13 meters high and 15 meters in diameter. The design weighed in at about 8,800 tons. During transport, the platform’s piles would be raised and attached to the barge with temporary sea-fastening beams. Because of the size of the piles and the proximity to the wave zone, huge hydrodynamic loads would act on the piles. For the design to be viable, the team had to know the size of these loads at an early stage. Fast Facts Unconventional Analyses • Single-body marine transport analysis included ballast condition, intact and damaged stability, bollard pull analysis, motion analysis, and barge longitudinal loading. It quickly became clear that the F3-FA platform design posed a challenge in strength management, in part because the four legs were without braces and subject to the direct force of the waves. The team used finite element analysis to model the entire platform including about 200 load cases. These included the static and dynamic loads, which had to be balanced to optimize steel quantities. Bentley MOSES offshore analysis and design software was used for the static calculation, in combination with an ANSYS model. • Multi-body marine transport analysis resolved leg and deck support loads. • Structural transport and fatigue analysis looked at deck, joint, and leg-member utilization; and grillage and sea fastening. ROI • Complex analysis and model tests reduced both steel quantities and project risk. • The self-installing platform design was easy to install, which saved project-delivery time. Optioneering enabled by MOSES reduced material costs. Tapping Marginal Fields The F3-FA field was discovered in 1971, about two miles below the surface of the North Sea. Centrica is the third owner and acquired the field along with its acquisition of Venture Production in 2009. With only about four to five years of production life, it would be too costly to develop the F3-FA field by installing a conventional fixed platform. Instead, Centrica planned to deploy a self-installing platform that is constructed in harbor, transported by barge, and installed by putting down legs on the seabed and elevating the platform. When the field is exhausted, the supports are taken up, and the platform is ORCA Offshore used MOSES to provide the multi-body dynamic analysis for the extreme conditions during transport. The challenge was to convince the project stakeholders that this unconventional method would give reliable results. The loads during transport and upon lowering the suction piles and legs had to be accurate to size the steel to hold them. MOSES determined those loads using a five-body model, with each body having its own hydrodynamic database to derive the motions and loads acting between bodies. A model test verified the MOSES results to the stakeholders’ satisfaction. MOSES was also used to confirm the structural strength of the platform during transport and installation. The spectral structural analysis allowed ORCA Offshore to derive the structural loading without being unnecessarily conservative. Conventional methods would have determined the maximum load acting on each pile and combined that with maximum

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MOSES Minimizes Redundant Steel in ORCA Offshore’s Analysis of Self-installing Platform - 2

“MOSES software can perform real-integrated analysis for any type motion loads acting on the whole structure. The MOSES approach considered the natural relationship between loads to reduce the quantity of steel required for the platform itself and for the temporary sea fastenings. of marine structure in a dynamic sea environment, which contributes to the realization of innovative Find out about Bentley at: www.bentley.com Contact Bentley 1-800-BENTLEY (1-800-236-8539) Outside the US +1 610-458-5000 Global Office Listings www.bentley.com/contact Installation work in the 40-meter-deep water...

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