ABS provided its Approval In Principle (AIP) to ConocoPhillips for its new proprietary Prism/Pyramid tank concept for large LNG carriers.
A key feature of this tank's unique shape reduces free surface area thus reducing the high impact sloshing loads and resonance period in the tank, the company says.
The free surface reduction resulting from the design is important because, according to hydrodynamic experts at ABS, the impact pressure due to sloshing motion from the cryogenic liquid cargo inside tanks is one of the most critical load factors when designing containment systems for LNG carriers.
ConocoPhillips Marine contracted for model tests on the prism/pyramid tank design with one of the leading hydrodynamic laboratories in the world, the Marine Technology Research Institute (Marintek) in Norway. The critical ship motion responses and sloshing impact conditions were calculated with North Atlantic environment conditions.
Specifics of the tank testing and motion responses involved a four tank scenario for an LNG vessel in the range of 235,000 cu m. Vessel designs for this size historically have called for five or six tanks. Irregular wave conditions were simulated with three different filling levels for the tanks and various ship headings. The test results of the comparison and pressure tests showed the design was acceptable and the loads on the ConocoPhillips Prism/Pyramid tank were equal to or less than those experienced on a traditionally designed 138,000 cu m ship.
3/15/05
