Final Report Summary - SAFEOFFLOAD (Safe offloading from floating LNG Platforms)
The topics that the SAFEOFFLOAD project addressed were the environmental conditions that influence the whole FLNG system; the interaction between the environment and the production and shuttle vessels and the responses of the vessels. The goal of the project was to optimise the system to maximise operability and safety.
The objectives of this project were the following :
- To provide tools that will allow the maximisation of the weather windows during which FLNG barges can be offloaded and FLNG can be operated. An optimised hull design and an active heading control strategy may reduce motion levels.
- To maximise the safety and efficiency of the offloading operation, minimise the possibility of collision or breakage of cryogenic lines.
- To have the capability to predict the behaviour of vessels during offloading.
- To have the capability to make the best, rational, real-time, risk-based decisions whether to proceed with approach and offloading.
- To understand the physical processes that govern the vessel motions during offloading.
- To have the capability to analyse the offloading process for design: specify environmental criteria, perform dynamic analysis, optimise hull shape, moorings and systems.
- To provide motion ranges for design of high-pressure, cryogenic pipes and flexible connectors for offloading.
- To provide a prototype of a decision support system that monitors continuously the environment and combines this information with weather forecasts and simulations of vessel motions.
The work was organised in seven technical Work packages (WP) that concern the research and technology development activities that form the body of the project.
WP 1 (Design solutions for floating LNG platforms) dealt with the design concepts that were considered in the project. Initial configurations were derived from existing studies by some of the partners as well as from their knowledge of other solutions. Improved designs were developed based on the results of hydrodynamic analysis and model tests in WP3 to WP6.
WP 2 (Environmental models in normally mild areas) concentrated on environmental winds, waves and currents, including spectral and probabilistic models. It paid particular attention to directional effects that may excite ship roll. Long-term data were analysed in terms of the persistence of severe conditions that prevent operations and weather windows in which operations may be performed. Representative data sets were provided to subsequent WPs for response analysis. Also, investigated in this WP were temporal and spatial models that can be used in combination with conventional forecasting to predict environmental conditions in the near term. Probabilistic models of relevant wave parameters were developed.
WP 3 (Hydrodynamics of multi-bodies) concentrated on hydrodynamic tools and models relevant to responses to waves. A sophisticated, second order, wave diffraction theory was extended to treat large, closely spaced, multiple, large bodies that can move independently. A fully non-linear boundary element method was developed and tested against the diffraction theory. A code was developed for the low speed manoeuvring of the tankers. The hydrodynamic models were tested against physical model tests in WP4.
WP 4 (Model tests) dealt with model tests. It included the tests in the wind tunnel, which determine the wind loads in the platform and LNG tankers as well as the shielding effect when the two vessels are in proximity. Model tests were made with the models under the action of waves to validate the numerical tools and to examine the behaviour of the modified hulls.
WP 5 (Solutions for offloading) studied the approach manoeuvre of the tanker for offloading and its station keeping under the effect of the environmental disturbances. The role of dynamic positioning in tandem situations was investigated.
WP 6 (Decision support methods for offloading operations) covered the development of a procedure to aid real time decisions concerning approach, mooring and offloading. It developed a manoeuvring simulation tool that is able to simulate the approach and departure conditions from offloading vessels.
WP 7 (Risk and availability assessment of production and offloading operations) concerned long-term analysis. It provided a risk assessment, developed design criteria and assessed the operability of the system in terms of production and offloading. It relied on input from all the other workpackages.
A consistent risk-based approach for the offloading operations from LNG terminals has been proposed. It is impracticable to define generally applicable weather limitations because such limitations will be system specific and will be related to economic risk. Therefore in SAFEOFFLOAD, the developments of limiting weather conditions have been exemplified for specific cases. The met-ocean data and models provided by WP 2 have been used in the study. The limit states considered were: mooring line failure (station keeping) and excessive relative motion (offloading).
The objectives of this project were the following :
- To provide tools that will allow the maximisation of the weather windows during which FLNG barges can be offloaded and FLNG can be operated. An optimised hull design and an active heading control strategy may reduce motion levels.
- To maximise the safety and efficiency of the offloading operation, minimise the possibility of collision or breakage of cryogenic lines.
- To have the capability to predict the behaviour of vessels during offloading.
- To have the capability to make the best, rational, real-time, risk-based decisions whether to proceed with approach and offloading.
- To understand the physical processes that govern the vessel motions during offloading.
- To have the capability to analyse the offloading process for design: specify environmental criteria, perform dynamic analysis, optimise hull shape, moorings and systems.
- To provide motion ranges for design of high-pressure, cryogenic pipes and flexible connectors for offloading.
- To provide a prototype of a decision support system that monitors continuously the environment and combines this information with weather forecasts and simulations of vessel motions.
The work was organised in seven technical Work packages (WP) that concern the research and technology development activities that form the body of the project.
WP 1 (Design solutions for floating LNG platforms) dealt with the design concepts that were considered in the project. Initial configurations were derived from existing studies by some of the partners as well as from their knowledge of other solutions. Improved designs were developed based on the results of hydrodynamic analysis and model tests in WP3 to WP6.
WP 2 (Environmental models in normally mild areas) concentrated on environmental winds, waves and currents, including spectral and probabilistic models. It paid particular attention to directional effects that may excite ship roll. Long-term data were analysed in terms of the persistence of severe conditions that prevent operations and weather windows in which operations may be performed. Representative data sets were provided to subsequent WPs for response analysis. Also, investigated in this WP were temporal and spatial models that can be used in combination with conventional forecasting to predict environmental conditions in the near term. Probabilistic models of relevant wave parameters were developed.
WP 3 (Hydrodynamics of multi-bodies) concentrated on hydrodynamic tools and models relevant to responses to waves. A sophisticated, second order, wave diffraction theory was extended to treat large, closely spaced, multiple, large bodies that can move independently. A fully non-linear boundary element method was developed and tested against the diffraction theory. A code was developed for the low speed manoeuvring of the tankers. The hydrodynamic models were tested against physical model tests in WP4.
WP 4 (Model tests) dealt with model tests. It included the tests in the wind tunnel, which determine the wind loads in the platform and LNG tankers as well as the shielding effect when the two vessels are in proximity. Model tests were made with the models under the action of waves to validate the numerical tools and to examine the behaviour of the modified hulls.
WP 5 (Solutions for offloading) studied the approach manoeuvre of the tanker for offloading and its station keeping under the effect of the environmental disturbances. The role of dynamic positioning in tandem situations was investigated.
WP 6 (Decision support methods for offloading operations) covered the development of a procedure to aid real time decisions concerning approach, mooring and offloading. It developed a manoeuvring simulation tool that is able to simulate the approach and departure conditions from offloading vessels.
WP 7 (Risk and availability assessment of production and offloading operations) concerned long-term analysis. It provided a risk assessment, developed design criteria and assessed the operability of the system in terms of production and offloading. It relied on input from all the other workpackages.
A consistent risk-based approach for the offloading operations from LNG terminals has been proposed. It is impracticable to define generally applicable weather limitations because such limitations will be system specific and will be related to economic risk. Therefore in SAFEOFFLOAD, the developments of limiting weather conditions have been exemplified for specific cases. The met-ocean data and models provided by WP 2 have been used in the study. The limit states considered were: mooring line failure (station keeping) and excessive relative motion (offloading).
