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Designers of tank containment systems for liquefied natural gas (LNG), as well as for those of other liquid cargo, have wrestled with it for years: How can the impact of sloshing loads on a tank, and on its carrying vessel, be minimized or even eliminated? In the April 2010 issue of (mt) magazine, we explored the various types of LNG tank containment systems in an in-depth feature by DNV’s Tony Teo, who gave us a good primer on the intricacies of analyzing and minimizing sloshing loads.

Tom Lamb, emeritus research scientist and adjunct professor in the Department of Naval Architecture and Marine Engineering at the University of Michigan, contacted me recently and told me about an innovative approach to the problem. He says that a new type of tank—the cubic doughnut tank system, or CDTS—offers significant reduction of the impact of sloshing on membrane linings and supporting insulation boxes. The design of the CDTS features 12 identical, intersecting cylinders that, together, make up the 12 edges of a cube. The original design, begun more than 30 years ago, called for a closing cap where the intersecting cylinders met in the center of each face.

The design lay dormant until Lamb and ALTAIR Engineering’s Regu Ramoo began developing it five years ago. They soon realized that all the center caps would have to be connected via a cross-bracing structure. The design is thought to offer substantially increased volumetric efficiency over a spherical tank. “I think this offers significant benefits,” says Lamb, “including elimination of the sloshing problem and significantly lower acquisition and lifecycle costs. Also, it can be used in a smaller size for carriage/storage of compressed natural gas.”

Part of the reason sloshing would be eliminated is due to the fact that partial filling of tanks—a real challenge with membrane tanks—would no longer be required. And Lamb says that a vessel’s construction schedule would be significantly reduced compared to that of a membrane tank system.

Lamb tells me that advanced structural analysis of both LNG and CNG tanks, as well as concept designs for carriers and FPSOs, has been completed, and that structural detail development and detailed sloshing simulations are underway. If you’d like to learn more about the CDTS program, you can download a paper on the subject presented by Tom Lamb and Regu Ramoo at the 2010 Offshore Technology Conference. Go to http://dx.doi.org/10.4043/21055-MS

WTC ship details emerging

Followup to my August blog post on the ship discovered beneath the World Trade Center site in New York: The team tasked with unearthing, preserving, and studying the vessel now says the section that was found is part of what was likely a two-masted trade vessel. Maritime historian Norman Brouwer is quoted by OurAmazingPlanet.com as saying the ship was a Hudson River sloop and was probably 60 to 70 feet in length.