A Popular Bottle-Breaking Trick Is Giving Insight to Brain Injuries

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Summary: Researchers provide an alternative formula to predict when cavitation will happen. The formula may be used to better predict brain injuries caused by high velocity impact.

Source: Brigham Young University.

Cavitation makes bottles shatter; the same thing could be happening brain trauma.

As many YouTube videos show, striking the top of a liquid-filled bottle can shatter the bottom. Now researchers are hoping to use new knowledge of that party trick to help fill a gap in something much more serious: brain research.

A study by engineering professors from Brigham Young University, Utah State University and the Tokyo University of Agriculture and Technology details exactly what happens when a liquid at rest – like the water in a bottle – is suddenly put into motion. Using high-speed photography, the team shows how the swift acceleration causes small bubbles to form in the liquid and then rapidly collapse, releasing a destructive shockwave.

The proper term for the phenomenon is called cavitation, a process well known to engineers for causing damage in pipes and marine propellers. The new study, published in the Proceedings of the National Academy of Sciences, details an alternative formula that more accurately predicts when cavitation will happen.

While the finding has immediate implications for many industrial processes interrupted by cavitation-induced damage, there’s also growing evidence linking cavitation to brain trauma.

“The brain is surrounded by fluid, and when you have impact, it’s possible you are experiencing cavitation within that fluid,” said study co-author Scott Thomson, associate professor of mechanical engineering at BYU.

Fluid dynamics experts know how to predict when cavitation will occur in a fluid already in motion, but their formula doesn’t work so well when a resting fluid is rapidly accelerated. The new study fixes that problem by finalizing a new equation that considers a fluid’s depth and acceleration.

For the brain, knowing this alternative cavitation formula could be used to better predict brain injuries caused by high-velocity impact. “And once we’re able to predict when that will happen, we can better design safety devices to help prevent serious brain damage,” Thomson said.

Those safety devices could be for athletic applications, such as football helmets, or even military applications.

“If a blast wave is above a certain magnitude, there may not be much we can do to prevent brain injury for a soldier,” said study author Tadd Truscott, associate professor of mechanical engineering at Utah State University. “But maybe a helmet can be developed to detect when that trauma has happened so a soldier can be removed from the front line and be saved from repeat exposure to blasts.”

About this neuroscience research article

Former BYU Ph.D. student Zhao Pan, now in the Department of Mechanical and Aerospace Engineering at Utah State University, was lead author on the study. Co-authors included BYU grad Randy Hurd, now a Ph.D. candidate at Utah State, and BYU grad Jesse Daily, now with the Naval Undersea Warfare Center.

Source: Todd Hollingshead – Brigham Young University
Image Source: NeuroscienceNews.com image is credited to BYU Photo.
Video Source: Video credited to Dave Linger.
Original Research: Full open access research for “Cavitation onset caused by acceleration” by Zhao Pan, Akihito Kiyama, Yoshiyuki Tagawa, David J. Daily, Scott L. Thomson, Randy Hurd, and Tadd T. Truscot in PNAS. Published online July 24 2017 doi:10.1073/pnas.1702502114

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Abstract Cavitation onset caused by acceleration

Striking the top of a liquid-filled bottle can shatter the bottom. An intuitive interpretation of this event might label an impulsive force as the culprit in this fracturing phenomenon. However, high-speed photography reveals the formation and collapse of tiny bubbles near the bottom before fracture. This observation indicates that the damaging phenomenon of cavitation is at fault. Cavitation is well known for causing damage in various applications including pipes and ship propellers, making accurate prediction of cavitation onset vital in several industries. However, the conventional cavitation number as a function of velocity incorrectly predicts the cavitation onset caused by acceleration. This unexplained discrepancy leads to the derivation of an alternative dimensionless term from the equation of motion, predicting cavitation as a function of acceleration and fluid depth rather than velocity. Two independent research groups in different countries have tested this theory; separate series of experiments confirm that an alternative cavitation number, presented in this paper, defines the universal criteria for the onset of acceleration-induced cavitation.

“Cavitation onset caused by acceleration” by Zhao Pan, Akihito Kiyama, Yoshiyuki Tagawa, David J. Daily, Scott L. Thomson, Randy Hurd, and Tadd T. Truscot in PNAS. Published online July 24 2017 doi:10.1073/pnas.1702502114

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