Atle Steen

Float Over Installation Method—Comprehensive Comparison Between Numerical and Model Test Results

Installing a large deck onto a platform, such as a spar, using the floatover method is gaining popularity. This is because the operational cost is much lower than other methods of installation, such as modular lifts or a single piece installation by a heavy lift barge. Deck integration can be performed on land, at quay side and will not depend on a heavy lift barge. A new concept for a floatover vessel has been developed for operations in the Gulf of Mexico and West Africa. In this application sea state conditions are essential factors that must be considered in the Gulf of Mexico, especially for transportation. In West Africa, swell conditions will govern floatover deck (FOD) installation. Based on these two different environmental conditions, Technip Offshore, Inc. developed the FOD installation concept using semi-submersible barge type vessels. A significant amount of development work and model testing has been done on this method in recent years on spar floatover. These tests have validated our numerical methods. Another test was conducted to investigate the feasibility of a deck float-over operation onto a compliant tower for a West Africa project. The project consists of a compliant tower supporting a 25,401 metric ton (28,000 s. ton) integrated deck. This paper will describe comparisons between model test data and numerical predictions of the compliant tower floatover operation.

Float Over Installation Method: Numerical and Model Test Data

Installing a large deck onto a platform, such as a spar, using the floatover method is gaining popularity. This is because the operational cost is much lower than other methods of installation, such as modular lifts or a single piece installation by a heavy lift barge. Deck integration can be performed on land, at quay side and will not depend on a heavy lift barge. A new concept for a floatover vessel has been developed for operations in the Gulf of Mexico and West Africa. In this application sea state conditions are essential factors that must be considered in the Gulf of Mexico, especially for transportation. In West Africa, swell conditions will govern floatover deck (FOD) installation. Based on these two different environmental conditions, Technip Offshore Engineering developed the FOD installation concept using semi-submersible barge type vessels. A significant amount of development work and model testing has been done on this method in recent years on spar floatover. These tests have validated our numerical methods. Another test was conducted to investigate the feasibility of a deck float-over operation onto a compliant tower for the Benguela Belize (BBT) project. The BBT project consists of a compliant tower supporting a 25,401 metric ton (28,000 s. ton) integrated deck. This paper will describe comparisons between model test data and numerical predictions of the compliant tower floatover operation.Copyright

Global Performance and Sloshing Analysis of a New Deep-Draft Semi-Submersible LNG FPSO

A new concept of LNG FPSO based on a deep-draft semi-submersible hull is introduced. With the deep draft, small water plane area, low center of gravity and large radius of gyration, the new LNG FPSO offers very low motions. This low-motion LNG FPSO platform provides more options and flexibilities in the selection of LNG liquefaction units, LNG containment systems, construction sites, installation methods, mooring systems (i.e. no requirements for weather-vaning), riser system and less down time compared with a conventional FPSO hull. Global performance and sloshing analyses for the new LNG FPSO hull and the conventional FPSO hull are performed to compare their operating performance for West Africa and the Northwest Australia environments.Copyright

New Buoy Designs for Ocean Observatories

The Ocean Research Interactive Observatory Networks (ORION - www.orionprogram.org) is a federally funded program that focuses the science, technology, education and outreach of an emerging network of science driven ocean observing systems. The objective of this initiative is to provide the scientific community with ocean observatories around the globe that will provide the infrastructure necessary to collect, among other things, time series data of oceanographic and geophysical phenomena which can’t be collected from vessel expeditions alone. The program calls for placing buoys in all water depths and a full range of metocean domains, from calm equatorial sites to high latitude deepwater southern ocean locations. Conventional oceanographic buoys will not meet all the requirements of this program, so new buoy designs are being developed. The authors have developed a variation of the spar buoy design for the more robust requirements, and are currently looking into other options. This paper will review the more demanding criteria for the Orion buoys, and the proposed solutions for new buoy designs.

Characterization of the Dynamic Loads Between Spar Top-Tensioned Riser Buoyancy Cans and Hull: Horn Mountain Field Data Measurements and Predictions

The Buoyancy Can Riser Tensioner (BCRT) systems are designed to provide tension to Top-Tensioned Risers (TTRs). BCRT systems do not transfer the riser weight to the floater and they minimize the interaction between the floating platform and the riser system. For deepwater field developments, this attractive feature allows efficient design of the floaters as well as the riser systems. Although, the vertical riser load is not transferred to the hull, the BCRT system makes lateral contact with the hull at several locations. During the past 3 years, analytical models have been developed to characterize mechanics of the contact between two large floating bodies (buoyancy can and hull) and compliant guide hardware has been developed. Placement of a compliant guide between the hull and the BCRT has become the current practice for design of Spar floaters. The initial development of the analytical models and the compliant guide hardware coincided with the Horn Mountain project. The project team placed extensive instrumentation on the hull and compliant guides with a vision to confirm robustness of the guides and to calibrate analytical models used during the design phase. This paper presents a summary of the data collected on the performance of the Spar hull, compliant guides, and the riser systems for storms up to 25 ft of significant wave height. Analytical methods and predictions are presented to characterize the dynamic interaction between the BCRT system and Spar hull.© 2004 ASME