MARIN opens LNG sloshing testing facility
MARIN will soon begin testing in its Multiphase Wave Lab to primarily examine sloshing impacts in LNG tanks.
The unique test facility has been established under a large-scale, collaborative research project entitled the Sloshing of Liquefied Natural Gas (SLING), writes David Tinsley. The endeavour has broad participation from across industry and academia, and is backed by the Dutch government.
The primary aim of SLING is to optimise membrane cargo tank design and reduce capital and operating costs for ‘small-scale’ and feeder LNG carriers and LNG bunker barges, so as to help support increased use of ‘cleaner’ LNG fuel by strengthening the transport infrastructure.
The key to designing cost-effective LNG tanks is a shift to a first principles approach to the assessment of sloshing impacts. Due to the motions of a ship in a seaway, surface waves are formed in the tanks that impact the tank walls, posing risks of damage to the structure. The challenge with sloshing is that it involves a liquid, a vapour and a structure that interact in different phases.
SLING is focused on researching the complex multi-phase physics and on drawing up a representative design methodology.
The Multiphase Wave Lab provides for multiple test setups in a controlled environment. The heart of the installation is a 15m-long, 55t autoclave, with thermal oil heating, rectangular tank, wave maker, steam boiler, gas and cooling water systems, and vacuum and pressure systems. The wave maker is installed at one end of the tank, and an instrumented, transverse wall is located at the other end.
Within the autoclave, temperature and pressure can be set across a wide range, between 5°C and 200°C and between 5mbar and 10 bar, respectively, in various gas compositions. For the SLING project, sulphur hexafluoride (SF6) and helium (He) are used as simulation gases. MARIN contracted the German company DILO for the design, construction and installation of the gas handling plant.
The solution adopted is an alternative to tests with LNG, which would introduce constraints relating to ATEX, the name commonly used for the two European Directives for controlling explosive atmospheres. The newly-installed facility instead uses water and different gas mixture compositions, pressure and temperature combinations to create, test and validate a physical model. In addition to reducing explosion risks during tests, this safer alternative allows MARIN to compensate for scaling effects more effectively than testing scaled-down models with LNG.
The resulting, validated model will then be used to calculate the forces exerted on the tank walls when LNG is rolling back and forth during heavy sea conditions, and thereby help determine designs for the appropriate load.
The SLING programme is sponsored to the tune of €5.3m (US$6.5m) by the technology foundation Applied and Engineering Sciences (AES), part of the Netherlands Organisation for Scientific Research (NWO), through its Perspectief funding instrument. The participants include four Dutch universities, Bureau Veritas, Nippon Kaiji Kyokai, Shell, Total, technology firms, shipowner Anthony Veder, and Damen Shipyards, as well as MARIN.
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