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DARPA’s silent MHD magnetic drives for replacing naval propellers

naval-technology.com

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Re: DARPA’s silent MHD magnetic drives for replacing naval propellers

#91

Post by eesmith »

ckozlowski wrote: post #90
atonse wrote: post #15

Earlier quoted context omitted.

Yes! I was thinking that as I read it. Alec Baldwin even says magneto hydrodynamic drive. Yet another example of Tom Clancy’s incredible knowledge of the intricacies of what the military had on their radar and working that into great stories.

I recently re-read The Hunt For Red October, and what struck me was that there actually wasn't and mention of Magneto-hydrodynamic drive. As I recalled, the book describes a series of propellers in a duct. Certainly interesting for isolating sound, but it struck me as much more simplistic from the superconducting systems described in the movie. No shade intended towards Mr. Clancy however. I got the impression that h…

Here's one discussion in the book, clearly describing impellers in a tunnel. https://archive.org/details/huntforredoctobe0000clan_l6h7/pa...

For example, it says the US "looked at this back in the early sixties and got to the model stage before dropping it. One of the things they discovered is that one impeller doesn’t work as well as several. Some sort of back pressure thing."

Wikipedia says, at https://en.wikipedia.org/wiki/The_Hunt_for_Red_October :

> The movie is a nearly faithful depiction of the novel even though there are many deviations, including Red October traveling up the Penobscot River in Maine to dry dock, the omission of the Royal Navy task force including Ryan's time aboard HMS Invincible, and the "caterpillar drive" being described as a magnetohydrodynamic drive system, essentially, "a jet engine for the water", rather than a drive powered by a series of mechanical impellers inside flow tunnels.

Re: DARPA’s silent MHD magnetic drives for replacing naval propellers

#92

Post by marcosdumay »

Avamander wrote: post #74
marcosdumay wrote: post #54

Earlier quoted context omitted.

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.

Yes, there exist stuff that behaves like this.

MHD isn't one.

Re: DARPA’s silent MHD magnetic drives for replacing naval propellers

#93

Post by gpm »

ajnin wrote: post #82
gpm wrote: post #11

If they meet their 90% efficiency target, that's exceeding the efficiency of a normal boat. Just the propeller losses are higher than that (at ~80% efficient [1]). If it's just some REBCO super-conducting magnets and conductive surfaces it might be reasonably inexpensive too. And without moving parts it could be a maintenance win as well. I'm no sailor, but at first glance this seems like it would potentially replace…

MHD is nothing new though, so if it has not yet replaced propellers I'm guessing it is because of practical issues like corrosion, electrolysis and so on alluded to in the article that DARPA seems to have found solutions for but which are not going to be available for the general public for obvious reasons. Also it's all electric so it poses the usual problems like the added complexity of an on-board electric generat…

Per the article the previous generation was only roughly 30% efficient, which makes it just not competitive with propellers.

Swapping out your diesel motor with rotating shafts going through your hull and an alternator to generate electricity for a diesel generator that just generates electricity is reducing complexity, not adding it.

Re: DARPA’s silent MHD magnetic drives for replacing naval propellers

#94

Post by gpm »

MagicMoonlight wrote: post #53

The idea of a boat with no moving parts is weird. Since we’re already this deep into science-fiction, could we superheat air and then run the plasma through this in order to create a land or air vehicle with no moving parts?

It's been done, without superheating anything https://news.mit.edu/2018/first-ionic-wind-plane-no-moving-p...

The interesting question is could you do it efficiently and with sufficient thrust - I don't know.

Re: DARPA’s silent MHD magnetic drives for replacing naval propellers

#95

Post by denton-scratch »

ajnin wrote: post #82
gpm wrote: post #11

If they meet their 90% efficiency target, that's exceeding the efficiency of a normal boat. Just the propeller losses are higher than that (at ~80% efficient [1]). If it's just some REBCO super-conducting magnets and conductive surfaces it might be reasonably inexpensive too. And without moving parts it could be a maintenance win as well. I'm no sailor, but at first glance this seems like it would potentially replace…

MHD is nothing new though, so if it has not yet replaced propellers I'm guessing it is because of practical issues like corrosion, electrolysis and so on alluded to in the article that DARPA seems to have found solutions for but which are not going to be available for the general public for obvious reasons. Also it's all electric so it poses the usual problems like the added complexity of an on-board electric generat…

> because of practical issues

Like fitting supercooled tesla-power magnets to a moving vehicle, perhaps.

> the added complexity of an on-board electric generator

But you don't need that if the vessel is electric-powered, like a nuclear-powered sub; and I believe some modern warships use a traditional motor to drive a generator, which drives an electric motor for propulsion (i.e. an electric ship powered by a fossil-fuel generator).

Re: DARPA’s silent MHD magnetic drives for replacing naval propellers

#96

Post by ImPostingOnHN »

gpm wrote: post #93
ajnin wrote: post #82

Earlier quoted context omitted.

MHD is nothing new though, so if it has not yet replaced propellers I'm guessing it is because of practical issues like corrosion, electrolysis and so on alluded to in the article that DARPA seems to have found solutions for but which are not going to be available for the general public for obvious reasons. Also it's all electric so it poses the usual problems like the added complexity of an on-board electric generat…

Per the article the previous generation was only roughly 30% efficient, which makes it just not competitive with propellers. Swapping out your diesel motor with rotating shafts going through your hull and an alternator to generate electricity for a diesel generator that just generates electricity is reducing complexity, not adding it.

the alternator is already there, too, since modern diesel submarines are actually diesel-electric submarines, able to charge batteries with the diesel engine and then shut it off and run from the batteries to go quiet

so, the difference is between props vs. no props, which is big.

Re: DARPA’s silent MHD magnetic drives for replacing naval propellers

#97

Post by SkyMarshal »

yellowapple wrote: post #66
zrail wrote: post #6

Isn't this the plot for Hunt for Red October?

"Can you ping, Washily? One ping only, pleashe."

“If we meet the right shot, this will work. If we get some… buckaroo?…”

He needed someone on the US side to figure out he was defecting and meet him with a plan to help. He gave it 1 chance in 3. Loved that moment you reference when he realizes he did indeed meet the right shot.

Re: DARPA’s silent MHD magnetic drives for replacing naval propellers

#98

Post by mikewarot »

mrDmrTmrJ wrote: post #67
mikewarot wrote: post #61

Earlier quoted context omitted.

I suspect the Navy actually does have room temperature superconductors[1] ... which could make this a practical technology. [1] https://patents.google.com/patent/US20190058105A1/en

Google scholar shows that that patent 'author' has three patents 1. Piezoelectricity-induced High Temperature Superconductor 2. Craft using an inertial mass reduction device 3. High frequency gravitational wave generator https://patents.google.com/?inventor=Salvatore+Cezar+Pais And I think with those three "inventions" one could construct a space-ship that could travel to Alpha Centauri at a meaningful fraction of 'c…

>Extraordinary claims require extraordinary evidence

The granting of a United States patent should be sufficient evidence to at least consider it possible that such things have been achieved.

Re: DARPA’s silent MHD magnetic drives for replacing naval propellers

#99

Post by ben_w »

dghughes wrote: post #83
jandrese wrote: post #33

Earlier quoted context omitted.

I'm not sure it would be restricted so much as just way too expensive to be practical. There is also the practical considerations of generating 20T magnetic fields out in the real world and around people.

Or on the vessel itself it would have to be shielded for the people and for any equipment. I've seen experiments where a device using a paddle was put against a person's head and a strong magnetic field emitted. It was a TV reporter for Discovery Channel Canada and her jaw convulsed, she did not look pleased. I think the experiment was about spirituality of all things. How to induce a feeling of a presence to a perso…

"Trans-cranial magnetic stimulation" — it has both been called "the god helmet" and has been used in that way.

IIRC it's a pulsed field to induce electric fields in your brain, and also has an extremely short range.

Somewhat more significant to human health is that magnetic material can be rapidly drawn towards the magnets, with the force on a steel office chair can exceed its own structural capacity in standard medical magnetic equipment: https://youtu.be/6BBx8BwLhqg

At very high field strengths, you also need to account for "your blood is electrically conductive, and electrical conductors resist motion when in a magnetic field due to induced electrical currents". According to test subjects, this "tingles".

At the most extreme fields strengths we can currently make, you also have to account for the water in your body being diamagnetic and repelling the magnets, but we can't ask any of the test subjects what that feels like as they were a frog and a rat because that's all that would fit in the tube.

Re: DARPA’s silent MHD magnetic drives for replacing naval propellers

#100

Post by AustinDev »

aardvarkr wrote: post #21
gpm wrote: post #11

If they meet their 90% efficiency target, that's exceeding the efficiency of a normal boat. Just the propeller losses are higher than that (at ~80% efficient [1]). If it's just some REBCO super-conducting magnets and conductive surfaces it might be reasonably inexpensive too. And without moving parts it could be a maintenance win as well. I'm no sailor, but at first glance this seems like it would potentially replace…

I agree that an innovation of this magnitude would have a huge impact on naval propulsion if it were publicly available though I’d imagine the tech would be locked down to a ridiculous level. It’s likely destined to only appear in nuclear submarines.

The majority of DARPA research is public and you can get copies of the software or specs via an email typically.
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