Passing electric current through seawater... Electrolysis will occur, producing hydrogen and chlorine gas (and some oxygen too).
It's not all positive, the are some negatives to this technology as well!
DARPA’s silent MHD magnetic drives for replacing naval propellers
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Re: DARPA’s silent MHD magnetic drives for replacing naval propellers
#72I wonder if it sounds like whales humping or a seismic anomaly…
It was Paganini
Re: DARPA’s silent MHD magnetic drives for replacing naval propellers
#73Earlier quoted context omitted.
semi absurd is kinda why DARPA exists!
What? VLSI, VHDL, Multics, Hypertext, GaAs semiconductors, autonomous navigation, GPS, and packet switched networking were a few things they funded. Totally absurd, right? For every successful tech, they probably explored scores that didn't pan out. Basic, high risk research has huge payoffs across society even if you don't like who's funding it or why.
I think that was the point.
Re: DARPA’s silent MHD magnetic drives for replacing naval propellers
#74Earlier quoted context omitted.
Yeah, no. Once it's known that it's possible to achieve, some enterprising company will quickly replicate it. Unless, of course, it needs unobtainable levels of power.
Well, people are talking about 90% efficiency up-thread. You can't need unobtainable levels of power and still have 90% efficiency, as people move boats around every day. Also, about the need for a coolant, well, the fixed costs for it are on the order of a few $100/m on most cities nowadays. If people start to use lots of it, the fixed costs will fall to zero. (The variable cost isn't high, but it also doesn't dicta…
You can absolutely have an energy requirement cliff that has to be exceeded for a thing to work before you can even measure it's efficiency. Trying to push something from standstill vs. keeping it moving.
Re: DARPA’s silent MHD magnetic drives for replacing naval propellers
#75> The MHD drive does not have moving parts, reducing noise and vibration, making it harder to detect via sonar Uh what? Sonar is active detection, using the bouncing of emitted sound waves, no? Then I don't see how a silent engine makes it harder to detect via sonar if the signals will still bounce just as hard from the hull.
There is passive sonar too, which is just listening.
Relevant to this: unimaginably vast amounts of effort have gone into making propellers a little bit quieter so they are harder to hear while still allowing reasonably high speeds. A lot of that is to do with avoiding cavitation at the prop tip, which is a) noisy, and b) very destructive. no prop, no prop noise...
Re: DARPA’s silent MHD magnetic drives for replacing naval propellers
#76Re: DARPA’s silent MHD magnetic drives for replacing naval propellers
#77Isn't this the plot for Hunt for Red October?
Engage the caterpillar dive, Vasily!
Re: DARPA’s silent MHD magnetic drives for replacing naval propellers
#78[dead]
Re: DARPA’s silent MHD magnetic drives for replacing naval propellers
#79> The MHD drive does not have moving parts, reducing noise and vibration, making it harder to detect via sonar Uh what? Sonar is active detection, using the bouncing of emitted sound waves, no? Then I don't see how a silent engine makes it harder to detect via sonar if the signals will still bounce just as hard from the hull.
What you are describing is active sonar. The downside of active sonar is that it also clearly reveals your own position.
As such, modern submarine warfare relies mostly on passive sonar - very sensitive microphone arrays (sometimes towed behind) to listen for audio signatures of surface and subsurface ships.
This means that submarine navies (and anti-submarine surface fleets to some degree) put a high priority on the ability to run quietly. A lot of work is put into things like propellor design to minimise the noise but there's a limit to how far you can go to eliminate cavitation and other noise sources. MHD, which would just be water flowing through a pipe, can potentially be much quieter.