Underwater shockwaves threaten submarines and their crew. To better understand the explosions and implosions that create these waves, University of Rhode Island engineering researchers are conducing experiments for the U.S. Navy.
“It’s cutting-edge research,” mechanical engineering graduate student Payam Fahr says. “Not very many people are able to test under these extreme environments and discover what we can.”
The experiments, which began in June 2013, rely on a new 7-foot-tall, 2,000-galloon underwater pressure vessel in Professor Arun Shukla’s Dynamic Photomechanics Lab. Painted in a Rhody motif, the steel tank resembles a cross between a pressure cooker and a space station module. Inside, engineers hang air-filled vessels and ring them with sensors.
Outside, 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 – record the action inside the tank.
The setup allows researchers to monitor the displacements, stresses, velocities and other dynamic phenomena caused by shockwaves emitting from an explosion or an implosion. (An implosion occurs when a gas-filled structure collapses under pressure and water rushes in, generating shockwaves.)
One experiment takes less than a millisecond, but researchers will spend months poring over the results. Shukla and his team 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. The issue has become particularly pressing as submarines carry increasingly more containers outside the hull where they are vulnerable to shockwaves. The Office of Naval Research is currently contributing about $850,000 toward the research.
“It 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.”