The experimental facility is designed to simulate the pressures up to a half-mile deep in the ocean so scientists can study underwater shockwaves and the stresses, velocities and other dynamic phenomena caused by explosions and implosions.
“There are extreme pressures deep in the ocean, and the pressure pulses created by implosions can travel great distances,” said Arun Shukla, URI professor of mechanical engineering. “Implosions even a considerable distance away might destroy a submarine, but that phenomenon is not well understood.”
According to Shukla, the U.S. Navy is increasingly housing weapons and other materials in cylindrical tubes on the outside of its submarines. If one of those tubes were to succumb to the pressures of the deep sea and implode, it might destroy the submarine and other nearby submerged structures.
“When a cylinder implodes, the walls of the cylinder move inward very quickly, which leads to acceleration of the water to follow the walls of the cylinder. When the tube flattens and the walls come to a sudden rest, the water following the walls also stops. This action of water against the wall generates a shock wave that could be 10 times greater than the implosion itself,” Shukla said.
The 2,000-gallon underwater pressure vessel now housed in Shukla’s Dynamic Photomechanics Laboratory was purchased this year with an $850,000 grant from the U.S. Office of Naval Research, which has also committed $625,00 for conducting research using the facility.
For the first experiment, the steel tank was filled with water to 95 percent of its capacity and topped off with nitrogen pressurized to 350 pounds per square inch, the equivalent of the pressures 700 feet below the ocean’s surface. Suspended in the water was an air-filled metal tube surrounded by a series of pressure sensors that can capture data in a fraction of a microsecond. Following a controlled implosion, the tube was significantly damaged.
That first test lasted less than one millisecond, but it was recorded by three high-speed cameras that can shoot up to 675,000 frames per second – more than 22,000 times faster than an average video camera. Shukla and his team of graduate students will spend months poring over the results.
The scientists are particularly interested in understanding how the implosion takes place, how far its shockwaves travel and the pressure they would exert on a host vessel. They also want to know if one container imploding will spark a cascading reaction of implosions in nearby containers.
“This work is important for the safety of naval structures and our defense systems because something could happen far away and the emanating shockwaves could travel and damage our structures,” Shukla says. “We don’t know enough about the consequences.”
“We’re conducting cutting-edge research using state-of-the-art technical equipment,” added mechanical engineering doctoral student Sachin Gupta. “This is a unique facility to discover interesting new physics occurring under extreme deep-sea environments.”
(left to right) Mechanical engineering students Sachin Gupta, Christopher Shillings and Payam Fahr ensure the implosion experiment is ready to start. Photo by John Peterson.