Daily Archives: December 7, 2008

Energy, With a Twist

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Turning a problem into a solution: aquatic clean energy from vortex-induced vibration?

Review of a paper on extracting energy from ocean currents, over at Skulls in the Stars

What is vortex induced vibration? In short, it is an effect by which little ‘whirlpools’ of fluid form in the wake of an obstructing object and regularly detach from it and are pulled downstream. These vortices carry energy and momentum (or, more accurately, the fluid which they consist of carries it) and when a vortex leaves, the obstruction itself gets a little ‘kick’ of motion from its departure. Vortices tend to leave the obstruction from opposing sides of it, and the net result is that the obstruction experiences an oscillatory force transverse to the direction of fluid flow.

Disney Goes to War

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Disney goes to war

“Nose art” and the equivalent of heraldic icons, courtesy of Walt Disney.

According to the late WW II aviation enthusiast and author Jeffrey Ethell, “the Disney industry was pervasive in American culture and it influenced nose art in a number of different ways. Combat crews copied Disney cartoon characters because they were suitable subjects for humorous and patriotic themes. Disney’s influence also included studio artists, who joined the military and then contributed their talents to the creation of nose art. Disney Studios and the U.S. government had a history of cooperation. At the beginning of the war in 1939, Walt Disney and his artists designed and painted squadron and unit insignia. Disney raised the spirit of the troops when he transformed the ‘once staid military heraldry format created during World War I’ into inspired designs. By the end of World War II, Disney’s five-man staff assigned to insignia completed over 1,200 unit insignias, never charging a fee to the military.”

Toil and Trouble

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More bubbles in microgravity

You need to a flashplayer enabled browser to view this YouTube video

I find it interesting that, contrary to terrestrial experience with drops on a surface, the colliding drops tend to scatter rather than coelesce. In microgravity the drops are spherical, which is the minimum-energy configuration, so I expect this presents an activation barrier of sorts. The collision needs to be strong enough to perturb the shape of the drops, so that combining them doesn’t represent a configuration that requires more energy than is present.