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Researchers at the Iowa
State University Center for Nondestructive Evaluation (CNDE) have
demonstrated the capability to locate air leaks in simulated
spacecraft by listening for the noise generated by the turbulent air
rushing out of the leak. What's different about their approach
is that the noise they are monitoring is in carried by the skin of
the spacecraft itself. CNDE researchers Dale Chimenti, Ron
Roberts, and Steve Holland have worked on this technique over the
past four years under NASA sponsorship, and recently the
investigators have won a NASA STTR technology transition award to
team with a small company who can begin the process of moving their
development into the field. NASA wants a workable product for
both the International Space Station and for the next generation
manned spacecraft, once the Shuttle is retired. The CNDE
method holds significant promise over other proposed methods because
it does not require listening for noise from the propagated through
the air of the spacecraft. On the Space Station the walls ceiling
and floor are covered with instruments, storage areas, and
life-support systems. The trick is to locate the leak
sufficiently well to permit astronauts to decide which instrument
rack to empty in order to find the leak. Once found, most small
leaks (less than 5 mm diameter) can be easily fixed with a
NASA-approved patch kit. Because of all the space debris and danger
of micrometeorites in low Earth orbit, NASA is concerned that a leak
to the pressure vessel of a long-endurance spacecraft will occur.
(Several impacts have occurred, but none yet have pierced the
pressure vessel where the astronauts live and work.)
The method being pursued by the CNDE researchers is unusual because
it exploits a random noise signal (from the leak itself) to perform
the location. To accomplish this, the random signal must first be
changed to a deterministic signal, done by monitoring two channels
of a 64-element acoustic array. One element acts as the reference
and a cross-correlation operation between that element and each of
the others in the array effectively eliminates the random nature of
the noise signal. Performing a two-dimensional spatial Fourier
transform on the array data and summing over a predetermined
frequency range yields a bright spot in two-dimensional wavenumber
space corresponding to the direction of the leak signal, and hence
the leak itself. The linked video, produced entirely by Aerospace
Engineering Deptartment undergraduate students Ricky Reusser and
Steve Sulhoff, shows the students attaching the transducer to the
simulated spacecraft skin, taking data with a computer, and
processing the data in real-time to demonstrate the accuracy and
sensitivity of the method. At the end of the video they show
how their results can be used to locate the actual leak in the
simulated aluminum spacecraft skin.
Mac version of video:
http://home.eng.iastate.edu/~rreusser/leakdetection_h264lq.mov
(needs Apple Quicktime 7 player; free download)
PC version of video:
http://home.eng.iastate.edu/~rreusser/leak3.mpg
(will play on Windows Media Player)
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Information
provided by:
Dale E.
Chimenti 515 /294-5853, -5021
Professor, Aerospace Engineering fax: 294-3262, -7771
Senior Scientist, Center for NDE chimenti@iastate.edu
1200 Howe Hall, Iowa State Univ, Ames IA 50011-2271 USA
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(Posted August 14,
2007) |