Long-Running Underwater Robot Lost At Sea

this_boat_is_real writes "Somewhere off the coast of Chile a pioneering underwater robot named Abe lies in a watery grave today. The Autonomous Benthic Explorer was one of the first truly independent research submersibles, being both unmanned and un-tethered to its launching ship. While on its 222nd research dive on Friday all contact with the craft was lost, the Woods Hole Oceanographic Institution has announced."

they where right!

[jisou]

all the movies form the fifties about giant sea monsters being released by earthquakes are true! We must prepare are selves by watching hours of scifi original movies! Its also no coincidence, 222nd dive? that's 1/3 evil.

Re:floaties?

[Volante3192]

Touché, vulgar anonymous poster.

The people that design these things are smart. Smarter than the average poster here in their field. If Joe Armchairengineer can think it up, I'm pretty damn confident that the engineers behind ABE thought of it too.

In fact, from the WHOI release, there's this nugget:

ABE was equipped with several independent systems to bring it back to the surface at the end of a dive or should a fault occur. The Melville remained in the vicinity to see if ABE had resurfaced, at first searching for ABE’s strobe lights in the darkness. Researchers tried to establish radio contact with ABE in the event it had surfaced, but attempts turned up nothing.

Re:they where right!

[Volante3192]

That, or the fact that 'benthic' is an adjective referring to the bottom of the ocean.

http://www.merriam-webster.com/dictionary/benthic [merriam-webster.com]

Re:Cthulhu strikes again!

[John Saffran]

There's been sounds from a very large biological creature recorded around the area .. it's 4 noisier than a blue whale and is known as The Bloop (http://en.wikipedia.org/wiki/Bloop)

Re:I have to assume there will be a followup desig

[Anonymous Coward]

The replacement for ABE is Sentry. http://www.whoi.edu/page.do?pid=38095

The cost of running support ships limits the number of subs used and the amount of science which is done.

Re:they were right!

[Bottles]

Film. The camera ran out of film.

You kids...

Re:floaties?

[Solandri]

It's been a while since I worked with the WHOI folks so my memory is a bit hazy. But generally these underwater submersibles come with:

• A descent weight, used to make the craft negatively buoyant for the initial descent, then dropped to leave it neutrally buoyant.
• An ascent weight, dropped at the end of the mission to make the neutrally buoyant craft positively buoyant.
• A bladder which can be pumped with oil from a reservoir tank to fine-tune buoyancy.

Air doesn't work because of the enormous pressure involved. A 3000 psi scuba tank could only inflate a balloon down to about 2000 meters. Below that, the water pressure is greater than that inside the tank, and opening the valve would result in water forcing the balloon into the tank, rather than air inflating the balloon. A 10000 psi high pressure tank would work at 5000 meters, but would only result in about a 30% increase in volume, meaning you'd need a very big tank to be able to raise the entire craft in a catastrophic failure. Furthermore, the air would expand as the craft rose, risking rupturing the balloon. That's why the buoyancy control uses an oil bladder - oil is relatively incompressible.

Dropping the ascent weight helps raise the craft at the end of a mission. But usually they're relatively lightweight so you can attach them manually. The 17-inch glass spheres [benthos.com] typically used to house equipment provides over 50 pounds of buoyancy. The failure of one of these spheres at a depth of 3000 meters (~4500 psi) would release (4500 psi) * 4/3 * pi * (8.5 inches)^3 = 1.3 MJ of energy. A stick of dynamite is about 2.1 MJ, so losing one sphere is pretty much guaranteed to cause all the other spheres to fail. If the remainder of the craft somehow survived all that energy release, the loss in buoyancy would overwhelm what buoyancy you'd get by dropping the ascent weight.

Re:they were right!

[snart]

Better yet, see the director's cut. The added 20 or so minutes completely alter the film. It goes from a really good flick a nearly great flick. And Ed Harris is a total babe.

Re:floaties?

[Solandri]

This is why such a balloon would need a _valve_ or a hole at the bottom, to allow excess gas to escape. It's precisely the same reason that SCUBA and deep sea divers doing a "free ascent" need to exhale quite a lot on their way up, lest they try to hold the expanding gas in their lungs and do something really destructive to their delicate alveoli and even give themselves serious embolisms.

Right. I wasn't saying the balloon idea was impossible, just explaining why it's inferior to oil and static pressure sphere buoyancy.

I am curious about the failure mechanism of these spheres. I can easily believe that an old, fatigued sphere can begin to crack and fail the rest of hte way catastrophically, but I'm curious how the failure spreads. Spewing glass shards cracking the other spheres? Shock wave directly cracking the sphere, or shock wave smacking the spheres against each other? Is the blast or shock wave from the failed sphere basically spherical, or is it directional from the way the sphere fails?

One of the Benthos reps (actually, he was one of the founders of the company) gave us a presentation which touched on sphere failures. It's an implosion which almost instantly turns the glass sphere into powder. The energy released goes into pulverizing the glass, and generating an inverse pressure wave which spreads outward disrupting or destroying any nearby equipment.

He also mentioned one unusual case where the vacuum valve for the sphere failed. If you didn't read the link I gave, the spheres is actually two hemispheres placed atop each other (this lets you put equipment and stuff inside). There's a small quarter-inch hole with a valve on it used to pump the air out of the sphere. The vacuum allows ambient air pressure to hold the two halves together. As it turns out, one of these spheres used only for floatation had this valve fail at depth. Instead of destroying the sphere, the water pressure simply filled the sphere very rapidly with water. All the netting which had been outside the sphere was forced through the quarter-inch hole into the sphere.