April 22, 2013
Credit: FRANK MORRING, JR./AW&ST
A relatively simple technology originally developed to smooth potentially dangerous vibrations in the defunct Ares I crew launch vehicle is finding its way into the wider world as a way to steady buildings, aircraft, ships and other structures reacting to winds, waves and even earthquakes.
The passive technology, which uses the weight of a liquid coupled to a structure to dampen shaking, swaying, fluttering and other oscillations, might be able to help prevent future nuclear-plant radiation leaks by using the water in spent-fuel storage pools to steady reactors and their containment structures during earthquakes.
Given the serious radiation danger from power-plant failures like the one at Japan’s Fukushima Daiichi nuclear plant after the March 2011 earthquake and tsunami, the safety return on NASA’s $5 million investment in what it is calling fluid structure coupling (FSC) technology could be significant.
Engineers at NASA Marshall have expanded their early analytical and experimental work on the Ares I thrust oscillation problem to encompass a host of potential applications like the nuclear-plant example, including stabilizing tall buildings in earthquakes and high winds, ships and drilling platforms in rough seas, and fluttering aircraft wings.
The Ares I application used FSC to calm vibrations set up in the vehicle stack as its solid-fuel first stage neared propellant burnout. The thrust oscillation posed a danger to astronauts in the Orion crew capsule at the top of the stack.
While some details of ways FSC can be used in weapons and launch systems remain veiled by International Trade in Arms Regulations (ITAR), the agency has been quietly promoting its civil applications, according to Rob Berry, chief technology manager of the FSC project here.
“Once you get the concept, it’s allowed us to ask a lot more questions in a lot more places,” Berry says. “We’re saying anywhere fluid and structures coexist, you can control the coupling. The question is, can you control enough fluid, enough coupling, to make it worth your while?”
For the Ares I, engineers developed an FSC device sunk in the liquid oxygen (LOX) tank that would dampen vibrations along the length of the stack. But the technique can also apply to side-to-side motion, and other types of vibration as well. The FSC project is using the 40-story vehicle dynamics test facility originally built for the Saturn Moon rocket, and later modified to handle the Ares I, to demonstrate just how little fluid is needed to stabilize a tall building.
The team has mounted oscillating weights near the top of the structure that are massive enough to get the whole building moving with an easily perceptible sway. But as long as an FSC device inside an off-the-shelf green plastic pipe holding 13,000 lb. of water is activated, the oscillating weights barely move the building. “We’re able to get greater than a four-times reduction [in lateral motion],” says Berry, noting that the water in the FSC pipe has only 0.3% of the mass of the building.