C ontinuing a long history of providing aeroderivative turbines to ships, General Electric Co. has begun its latest round of marine certification testing of the LM6000 engine. The engines have already logged some 290,000 hours of sea time on oil rigs and aboard barges.

The American Bureau of Shipping in Houston is expected to certify the gas turbine this year after the engine completes the ship's service and propulsion endurance tests.

According to Jeff Martin, director of U.S. government programs for GE Transportation's marine business, the endurance test consists of a thousand hours of engine operation at various power levels conducted in eight-hour shifts. The engine rests for an hour between shifts. Half the test is conducted at constant speed, to reflect power generator loads. The other half takes place with turbine speed varying along the cubic load power curve to represent propulsion loading, Martin said.

GE plans to nameplate the engine at a power level better than 36 MW based on the U.S. Navy standard day conditions. That's a rating conducted at sea level at an ambient 100°F, 40 percent relative humidity, with an inlet loss of 4 inches and an outlet loss of 6 inches of water.

Gas turbine marine propulsion has pushed some pretty big ships around, including the 26,537-long-ton, 694-foot GTS Callaghan cargo vessel. GE's latest marine engine (inset) is now testing for ABS certification.

Already certified by the Norwegian classification organization Det Norske Veritas for floating processing and storage operations, the ABS badge will qualify the engine for several new naval programs that require electric and mechanical drive service. Plans for the Navy's new DD(X) class destroyers call for permanent magnet synchronous propulsion motors that will be backed up with advanced technology induction machines. Multiple gas turbine generator trains will make electricity for the propulsion motors and for ships' service distribution.

The LM6000 engine engine, which GE introduced in 1990, shares its heritage with the company's CF6-80C2 aircraft turbofan, a powerplant that's logged nearly 100 million hours aloft. The ship engine comes packaged in a marine-worthy enclosure without a fan, and with a modified C6 low-pressure compressor and high-efficiency blading and a high-strength shaft on the low-pressure stage.

GE supplied LM2500 engines in the late 1960s for the GTS Adm. Wm. M. Callaghan , a roll-on/roll-off vessel in the Military Sealift Command fleet. The engines replaced a set of Pratt & Whitney FT4s.

F or decades, engineers and mathematicians have wondered what Gustave Eiffel was thinking when he designed his famous tower. A math professor at Michigan Technological University in Houghton and an engineering professor at the University of Colorado at Boulder believe they may have come up with an answer.

Iosif Pinelis, the mathematician in Michigan, became intrigued by the problem in 2002, when Colorado mechanical engineering professor Patrick Weidman visited Michigan Tech. Weidman discussed theories that attempted to explain the Eiffel Tower's elegant design. Mathematician Christophe Chouard argued that Eiffel engineered his tower so that
its weight would counterbalance the force of the wind. Another theory held that the wind pressure is counterbalanced by tension among the elements of the tower. Chouard had an equation to back his theory, but Weidman had doubts.

"Weidman and the mathematicians whom he had consulted could only find one solution, a parabola, of the infinitely many solutions that Chouard's equation must have," Pinelis said.

Weidman asked Michigan Tech's mathematicians if they could come up with any other solutions, so Pinelis took up the challenge. He found that all of the existing solutions to Chouard's equation must either yield a parabola or explode to infinity at the top.

"The Eiffel Tower does not explode to infinity at the top, and its profile curves inward rather than outward," Pinelis said. "That pretty much rules out Chouard's equation."

Weidman, meanwhile, searched historical records and found an 1885 letter from Eiffel to the French Civil Engineering Society. Eiffel wrote that he had indeed planned to use tension among the construction elements as a counterbalance to wind loads. In light of that find, Weidman and his colleagues developed an equation whose solutions yielded a figure in the true shape of the Eiffel Tower.

A report of the investigation by Weidman and Pinelis appeared in the French journal Comptes Rendus Mecanique under the title, "Model Equations for the Eiffel Tower Profile: Historical Perspective and New Results."

"The funny thing for me was that you didn't have to go into the historical investigation to find out the truth," Pinelis said. "The math confirms the logic behind the design. For me, it was more fun to go to the math."

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