NUWC Newport engineer David Daily makes a safer football helmet

NEWPORT — When Dr. David Jesse Daily was a student at Brigham Young University, a colleague shared a party trick in which someone puts water in a glass bottle, quickly taps the top of the bottle, and bottom of the bottle breaks.

This piqued Daily’s interest.

Now a mechanical engineer in the sensor and sonar systems department at the Naval Undersea Warfare Center division in Newport, he used high-speed cameras to capture the moment of impact. He observed that bubbles were created at the bottom of the bottle by the impact and that the collapse of these bubbles broke the bottle.

“The impact created a distinct type of acceleration-based cavitation, which occurs when liquid suddenly accelerates and changes to a vapor state – seen as bubbles,” Daily said. “The collapse of the cavitation bubbles is what causes the bottle to rupture.”

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Eventually, this research led Daily to design a football helmet that attenuates frontal impacts, reducing the incidence of concussions.

Special Sudden Motion Activated Cavitation (SMAC) tubes were built daily which allowed him to test his theories and applications of acceleration-based cavitation.

For part of his doctoral thesis, Daily derived a new cavitation number based on acceleration. He completed this work in graduate school and, years later, presented his work at Newport Division’s informal “Intellectual Storytime” as a solution requiring a problem.

After his presentation, he began working with Dr. Jesse Belden and Aren Hellum of the Underwater Warfare Weapons, Vehicles and Defensive Systems department on possible applications of this acceleration-based cavitation.

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During acceleration-based cavitation, the kinetic energy of the impact is transferred into the cavitation bubbles until the bubbles reach their maximum size. The cavitation bubbles then begin to collapse and transfer their energy back into kinetic energy, re-accelerating the bottle. The whole process takes between 5 and 20 milliseconds.

When applied to an object like a football helmet, a cavitation device – for example, a tube containing water – can reduce the severity of an impact and possibly the severity of traumatic brain injury. Daily looked at common impact locations on football player helmets. These locations differed depending on the position of the player.

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Daily’s helmet is designed to mitigate the most common frontal impacts experienced by linemen. The cavitation tubes were able to lengthen the overall impact duration by 20%, which could theoretically allow cerebrospinal fluid to more effectively cushion the brain and prevent traumatic brain injury.

A common cause of injury is when the head suddenly snaps back and then whips forward, causing the brain to impact the front of the skull, then rebound and impact the back of the skull. This type of impact, known as a “backlash”, is thought to be one of the causes of concussions.

Daily’s “resting cavitation” device could potentially slow and attenuate these impacts, reducing the incidence of concussions. Although a cavitation feature on a helmet does not eliminate the effects of an impact, it could provide some impact reduction as a compact, passive device. This cavitation device might add just enough extra protection to be a game-changer.

Daily’s research has three different purposes:

• Understand the physics and how acceleration impacts are elongated due to cavitation

• Understand potential applications (eg adding water filled tubes to football helmets)

• Understand industrial applications (for example, adding a cavitation chamber to traditional shock absorbers)

A patent for parts of his quiescent cavitation work has been filed and Daily hopes to continue this research in the future.

“I would like to build more cavitation prototypes to study the potential for reducing traumatic brain injury as well as the use of cavitation in various automotive and safety applications,” Daily said.

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