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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

#101

Post by gpm »

ImPostingOnHN wrote: post #96
gpm wrote: post #93

Earlier quoted context omitted.

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.

In context I'm arguing for use on commercial surface boats and ships.

But they too have alternators (and/or dedicated generators)... because it turns out electricity is really useful.

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

#102

Post by atonse »

jasonwatkinspdx wrote: post #63
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.

Magneto Hydrodynamic Drives have been a publicly researched concept since the 60s. Magnetic pumps are used routinely in industry. You're definitely exaggerating how visionary Clancy was.

I'm not talking about him coming up with the ideas. But him weaving it as a thing the US Navy had been concerned about the Soviets building – I am saying it's very likely that the US Navy's concern about these drives being used in subs wasn't made up, and maybe some related conversations he had with contacts/sources, that turned out to be one of many seeds that made for a compelling story.

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

#103

Post by AlbertoGP »

A couple of years ago someone built a model submarine with an actual MagnetoHydroDynamic drive:

“Magnet Powered Submarine - The Hunt for Red October IRL!” https://www.youtube.com/watch?v=nFsiydplCtw

The corresponding blog entry includes the STL files for 3D-printing the submarine’s hull:

https://www.kjmagnetics.com/blog.asp?p=red-october

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

#104

Post by rektide »

MilStdJunkie wrote: post #47
bombcar wrote: post #39

Earlier quoted context omitted.

I mean rockets are absurd - burn gas to throw it behind you to push off against. Works in space (the NYT regrets the error). https://www.nytimes.com/2001/11/14/news/150th-anniversary-18...

That's very true, but "efficient" isn't usually an adjective thrown at a rocket.

Uhhh I feel like rocket makers are obsessed with efficiency. A modest half a percent makes a huge difference in fuel fraction & lift capabilities.

Rockets may be broadly inefficient but they are as efficient as we can make them.

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

#105

Post by c_o_n_v_e_x »

cyberax wrote: post #32
aardvarkr wrote: post #21

Earlier quoted context omitted.

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.

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.

The government can and does lock down intellectual property for national security reasons.

The US government effectively locked down Juliet Marine Systems' IP, and gave the inventor no compensation for doing so. Took about more than 5 years for the inventor get any relief.

https://www.boatblurb.com/post/the-us-military-ghost-ship-is...

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

#106

Post by MilStdJunkie »

rektide wrote: post #104
MilStdJunkie wrote: post #47

Earlier quoted context omitted.

That's very true, but "efficient" isn't usually an adjective thrown at a rocket.

Uhhh I feel like rocket makers are obsessed with efficiency. A modest half a percent makes a huge difference in fuel fraction & lift capabilities. Rockets may be broadly inefficient but they are as efficient as we can make them.

I understand. They're the only orbital game in town, and will be until . I guess what I'm, saying, it's more that "efficient" isn't a word that pops up in your head when you imagine "rocket". It's like a demure Dodge Hellcat owner, or a contemplative WWE star.

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

#107

Post by Turing_Machine »

denton-scratch wrote: post #95
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…

> 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-f…

> But you don't need that if the vessel is electric-powered, like a nuclear-powered sub

Yep.

> I believe some modern warships use a traditional motor to drive a generator, which drives an electric motor for propulsion

Sure, like a diesel-electric locomotive.

It turns out in some situations it's better to eat the conversion loss from electric generation rather than using a direct mechanical linkage, because then you can use flexible cables and electrical control systems rather than a bunch of mechanical folderol

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

#108

Post by cyberax »

gpm wrote: post #40
cyberax wrote: post #32

Earlier 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.

If it needs unobtainable levels of power, that means it's not efficient. If it's efficient you can use a diesel generator in place of your diesel engine and obtain the same amount of power.

Not quite. It might be efficient, but only if you need megawatt-level propulsion power.

This is not uncommon in engineering in general. There are many, many examples of devices that are highly efficient but only at higher power levels/speeds.

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

#109

Post by cyberax »

c_o_n_v_e_x wrote: post #105
cyberax wrote: post #32

Earlier 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.

The government can and does lock down intellectual property for national security reasons. The US government effectively locked down Juliet Marine Systems' IP, and gave the inventor no compensation for doing so. Took about more than 5 years for the inventor get any relief. https://www.boatblurb.com/post/the-us-military-ghost-ship-is...

The US government won't be able to lock down a company in Sweden or Turkey. It's not like the principles of MHD propulsion are in any way secret. It's just that we now have much better superconducting magnets.
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