By Katherine H. Crawford, Office of Naval Research Public Affairs
Earlier this month, scientists sponsored by the Office of Naval Research
(ONR) performed experiments to better understand the motions, forces
and pressures generated by waves on boats with high-speed planing hulls. |
Planing
hulls are like those used on a speedboat - they're designed to produce
lift and allow the watercraft to glide on top of the water, skimming
more quickly over its surface. At higher speeds, waves become a problem.
The higher the crests of the waves, the more the boat will rise to the
top of the wave and then fall back down to the wave's trough with great
force. This is known as "wave slam."
"When a hull is going at speed and it hits a wave, it's like hitting
a wall - it's a violent collision, and the forces are very large,"
said Dr. Bob Brizzolara, a program officer with ONR's Sea Warfare and
Weapons Department. "This causes injuries to Sailors - commonly
back and leg injuries - and also can degrade the structure of the vessel."
This research was motivated by a series of workshops ONR program officers
held with personnel from the Navy small combatant craft commands about
high-priority challenges that ONR could help with. One identified challenge
was the need to carry greater loads while maintaining their speed capabilities.
To do this, some structural weight would need to be shed. Since the
hull is the heaviest part of a vessel, Brizzolara and his team began
there, investigating ways to save weight.
"To deal with the effects of wave slams, the Navy must have strong
boats that are forced to reduce speed in higher seas," said Dr.
Carolyn Judge, an associate professor in the U.S. Naval Academy (USNA)'s
Naval Architecture and Ocean Engineering Department, as well as a current
Young Investigator Program recipient working with Brizzolara on this
research. "Mitigating the problem of wave slams will allow Navy
boats to travel faster in higher seas states as well as allow for lighter
boat structural designs."
Working with Naval Surface Warfare Center (NSWC) Carderock Division,
USNA and the University of Iowa, ONR is considering ways to reduce hull
weight while maintaining structural adequacy. For unmanned craft, it
might be possible to reduce weight even further, allowing additional
payload to be carried.
"We're working to understand the pressures on the hull that are
due to the wave slamming, since right now, they are not well understood,"
Brizzolara said. "We'd like to be able to save weight in the structure
so we can carry more fuel and payload, but we don't understand those
pressures well enough to be able to start taking weight out of the structures."
The team is executing the research in two parts: experimentally with
scale models and using computer simulations. The scale models are tested
in the large tow tank at NSWC Carderock.
Computer simulations for planing hulls are being developed by the University
of Iowa, a challenging problem due to the complexity of planing hull
physics. The model results will be used to develop computer simulations
that are more realistic and accurate. This will vastly increase the
numbers of tests that can be run since the computer simulations are
much less expensive than experimental testing. |
WEST
BETHESDA, Md. (April 3, 2015) A ship hull model attached to a high-speed
sled moves through waves at the David Taylor Model Basin at Naval Surface
Warfare Center, Carderock, during Office of Naval Research -sponsored
research. The research studies the fundamental physics of the water-impact
of high-speed planing hulls and to measure the slamming loads and resulting
motions of the craft upon re-entry into the water. (U.S. Navy photo
by John F. Williams/Released)