China makes advances in laser-propelled submarines • Hacker News Board

Re: China makes advances in laser-propelled submarines

#11

Post by JumpCrisscross » Mon, Apr 22, 2024, 2:10 PM UTC

Staple_Diet wrote: post #10

JumpCrisscross wrote: post #9

Earlier quoted context omitted.

> this method would be much quieter Source? Cavitation on propellers is a major source of uncloaking. This sub sounds fast but traceable—perhaps more ideal for a weapon than a vehicle.

The method described in the present article doesn't rely on rotating propellers that produce vibrations, thereby reducing one of the major sources of noise.

> method described in the present article doesn't rely on rotating propellers that produce vibrations, thereby reducing one of the major sources of noise

The main source of “hull vibration and noise” from propellers is cavitation [1]. Laser propulsion directly cavitates.

[1] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4549849/

Re: China makes advances in laser-propelled submarines

#12

Post by slowmovintarget » Mon, Apr 22, 2024, 5:30 PM UTC

The very end of the article talks about "green shipping" but it seems like this propulsion method would produce crazy levels of heat. Wouldn't that have adverse impact?

Re: China makes advances in laser-propelled submarines

#13

Post by Turing_Machine » Mon, Apr 22, 2024, 9:39 PM UTC

Havoc wrote: post #6

The whole bubbles and pulsing doesn’t sound particularly silent

Yeah, if I'm understanding what's going on here, it's going to be noisy as hell.

Cavitation noise isn't the only factor making a submarine detectable, but it's definitely high on the list. It's been used to detect submarines since WWII or thereabouts.

Re: China makes advances in laser-propelled submarines

#14

Post by gus_massa » Mon, Apr 22, 2024, 9:43 PM UTC

> Design can produce almost as much thrust as a commercial jet engine,

But does it have as much thrust as a normal submarine engine?

Re: China makes advances in laser-propelled submarines

#15

Post by Turing_Machine » Mon, Apr 22, 2024, 9:44 PM UTC

Staple_Diet wrote: post #10

JumpCrisscross wrote: post #9

Earlier quoted context omitted.

> this method would be much quieter Source? Cavitation on propellers is a major source of uncloaking. This sub sounds fast but traceable—perhaps more ideal for a weapon than a vehicle.

The method described in the present article doesn't rely on rotating propellers that produce vibrations, thereby reducing one of the major sources of noise.

It sounds like it's basically a gigantic cavitation noise generator, so yeah, I'm not imagining that it could possibly be quieter.

Today's submarines go to great lengths to avoid cavitation for just that reason.

Typically there's a velocity beyond which the vessel does not go if it wants to remain stealthy, as going faster than that drastically increases the cavitation noise.

Re: China makes advances in laser-propelled submarines

#16

Post by a4000 » Tue, Apr 23, 2024, 5:24 AM UTC

It's worth pointing out that this is authored by Stephen Chen who is a bit of a joke in defence news circles with a never ending supply of articles about how China has all these amazing weapons and technological advances that render the US helpless in comparison and there is one every few days or so. https://www.scmp.com/author/stephen-chen

Re: China makes advances in laser-propelled submarines

#17

Post by LargoLasskhyfv » Tue, Apr 23, 2024, 9:03 AM UTC

Turing_Machine wrote: post #13

Havoc wrote: post #6

The whole bubbles and pulsing doesn’t sound particularly silent

Yeah, if I'm understanding what's going on here, it's going to be noisy as hell. Cavitation noise isn't the only factor making a submarine detectable, but it's definitely high on the list. It's been used to detect submarines since WWII or thereabouts.

Maybe it's a variation of a https://en.wikipedia.org/wiki/Pump-jet somehow using lasers instead of impellers to heat the inflow all internally and dampened/mostly silenced to the outside? Also enabling https://en.wikipedia.org/wiki/Supercavitation by emitting some of the 'exhaust' from the tip of the bow?

Re: China makes advances in laser-propelled submarines

#18

Post by Eddy_Viscosity2 » Wed, Apr 24, 2024, 12:31 AM UTC

LargoLasskhyfv wrote: post #17

Turing_Machine wrote: post #13

Earlier quoted context omitted.

Yeah, if I'm understanding what's going on here, it's going to be noisy as hell. Cavitation noise isn't the only factor making a submarine detectable, but it's definitely high on the list. It's been used to detect submarines since WWII or thereabouts.

Maybe it's a variation of a https://en.wikipedia.org/wiki/Pump-jet somehow using lasers instead of impellers to heat the inflow all internally and dampened/mostly silenced to the outside? Also enabling https://en.wikipedia.org/wiki/Supercavitation by emitting some of the 'exhaust' from the tip of the bow?

It says its using lasers to vaporize seawater all around the submarine which would create a submarine sized super cavity which would have very very low resistance. The problem is what happens when the bubbles collapse. That's what causes the cavitation noise, its when the bubbles collapse. They can do so with such force that they can pull metal out of nearby surfaces.

Re: China makes advances in laser-propelled submarines

#19

Post by LargoLasskhyfv » Wed, Apr 24, 2024, 2:14 PM UTC

Eddy_Viscosity2 wrote: post #18

LargoLasskhyfv wrote: post #17

Earlier quoted context omitted.

Maybe it's a variation of a https://en.wikipedia.org/wiki/Pump-jet somehow using lasers instead of impellers to heat the inflow all internally and dampened/mostly silenced to the outside? Also enabling https://en.wikipedia.org/wiki/Supercavitation by emitting some of the 'exhaust' from the tip of the bow?

It says its using lasers to vaporize seawater all around the submarine which would create a submarine sized super cavity which would have very very low resistance. The problem is what happens when the bubbles collapse. That's what causes the cavitation noise, its when the bubbles collapse. They can do so with such force that they can pull metal out of nearby surfaces.

Yah. Meanwhile elsewhere people have torn apart the news. Seems that it is just a concept, no test in reality at all, not even parts of it in a lab. Maybe late april joke?

Re: China makes advances in laser-propelled submarines

#20

Post by Eddy_Viscosity2 » Wed, Apr 24, 2024, 8:40 PM UTC

LargoLasskhyfv wrote: post #19

Eddy_Viscosity2 wrote: post #18

Earlier quoted context omitted.

It says its using lasers to vaporize seawater all around the submarine which would create a submarine sized super cavity which would have very very low resistance. The problem is what happens when the bubbles collapse. That's what causes the cavitation noise, its when the bubbles collapse. They can do so with such force that they can pull metal out of nearby surfaces.

Yah. Meanwhile elsewhere people have torn apart the news. Seems that it is just a concept, no test in reality at all, not even parts of it in a lab. Maybe late april joke?

It felt like I was reading from 'three body problem'. I wonder if the author was inspired by the sci fi there.