Type 09V/09VI (095/096) Nuclear Submarine Thread


FairAndUnbiased

Junior Member
Registered Member
I agree with the general direction of your comment but few technical corrections and explanations are necessary for a more complete picture:



1. This "obsession" is the most fundamental thing in submarine warfare.

In surface ASW helicopters and planes can test the unindentified contact with buoys. If it's an allied sub they will have procedures to identify it even if they do not have the signature. If it's not identified and it persists on engagement course you can use small charges to warn it off. You do not have to use lethal force if you are a surface vessel because you do not need to hide your location. You're in the open calling out the other guy hiding underwater : who are you, show yourself.

A submarine can't do the same without revealing its position and once that's done the game for the sub is up. Because of that collecting signatures is the only way in which the submarine can identify targets. If you don't have a matching signature you have an unidentified noise source that may or may not be an enemy ship and considering that there are only so many submarine types in service among many navies of the world it's a mistake you don't want to make. An Indian Kilo, a Russian Kilo and a Vietnamese Kilo won't sound that differently if you have to guess which is which.

2. Not just the west but Russia and China and everyone else do it as well.

For obvious reasons PLAN doesn't use nuclear subs as standard intelligence tool. There's not enough of them and many are too noisy for effective intel gathering. Americans do it on a regular basis because of the relative stealthiness of their subs. Russians track American carriers and subs as much as possible. Everyone uses static networks and sensors planted at key locations to gather data.

Once China has sufficient number of sufficiently quiet SSNs you will see the same "obsession". There's just no other way. Even if you managed to steal the entire databank from your enemy you need to verify it, and then verify it again, and again because you have no idea if this is legitimate information or deliberate disinformation. So in short - nothing beats your own intelligence gathering and even then it's not perfect.



The background noise level is a factor in determining detection distance.

This is the passive sonar equation:

SL − PL − NL − AG = DT

SL - source level [dB]
PL - propagation loss (energy over distance in medium) [dB]
NL - noise level (background noise) [dB]
AG - array gain [dB]
DT - detection threshold [dB]

For theoretical maximum range DT=0 which then gives us:

SL-NL + AG = PL

PL = 10 log R


where R is the distance at which the wave will expire (propagation loss is equal to wave energy)

R= 10 ^ (PL /10) [m]

Explanation:

Every soundwave is the wave of linear pressure in a given medium. The pressure is generated by energy radiated from the source. For example a propeller physically moves an amount of water creating increased pressure on one side of the blade and a vacuum on the other side which is the source of cavitation.

A wave is energy propagating in a specific pattern creating a distortion of the medium. This distortion has specific characteristics with which we describe a wave - phase, frequency, amplitude, polarity etc. The distortion is in the behavior of particles that form that medium - here: molecules of water.

The medium at background state has some kind of behavior and an energy level describing it. Then the wave enters the medium and that behavior changes wherever the wave propagates. It's all about the movement and energy of the particles that make the wave possible.

If the particles at "background state" have low energy then a high energy wave can travel very far before it looses its energy by interacting with the inertia of the medium. This is why gamma rays in space travel for lightyears. Not only it's the most energetic wave but there's no background energy to counter it.

In water the acoustic pressure wave (soundwave) has plenty of particles that have their own energy which is why the usual soundwave travels for hundreds of thousands of kilometers at best. After that its energy is expended and the particles that were acted on by the wave's energy take the energy from the background which is now higher.

That's the background noise.

What the background noise does is limiting the distance at which the wave - a very specific pattern - remains that specific pattern or something sufficiently similar that a computer processing that pattern can say "this is 79,5% general match and 95% specific match to this ship signature".

In short if the background noise is strong enough it doesn't matter how well you know the signature. What you will get is the equivalent of a movie with the sound off- a person's mouth will move but no sound will come out, only the background noise.




If your sub has source level below background noise level the acoustic wave generated by the submarine will immediately be interfered with by the acoustic waves in the background. If background level is greater than source level there is no propagation. No propagation means no signature. No signature means invisibility.

This is why everyone is researching active sonar and distributed sensor networks. The era of listening in silence is over. The era of poking with sticks begins.



Every submarine emits low frequency noise. Just the stretching of the hull during change of depth creates a low frequency wave. The standard frequency range for detection is 5 to 200 Hertz.

5 Hertz is not audible but you can feel it.

The reason why lower frequency noise can be heard at larger distances has to do with whether you can tell the wave apart from the background.

That has to do with characteristics of the wave. High frequency sound is high energy wave. That wave goes everywhere and interferes with the medium turning itself into background noise. High frequency waves are like a swarm of bees and the environment around them behaves accordingly but from afar you can't tell if its a swarm of bees or a cloud or just a shadow. Low frequency waves are looooooooooooong waves. Like snakes. You can always tell it's a snake because it's long.

You can tell the wave apart from the background because it doesn't interact well with it. Quite literally many of the waves that carry you as you swim in water are acoustic waves. They don't hurt at all unless they throw you against something. In contrast high frequency sonar pings can physically hurt and raise the temperature of the diver's body if he's nearby in water.


Parting remark:

Good point on the Bohai Sea. Also note that if you have a secure body of water for testing it becomes the ideal honeypot where the enemy will have to use its actual best capability to gather valuable information. And thus - so will you.
I have to caution that when you say background level it refers to the total background sound power, not the spectral power density.

A signal in general can have lower total power than background but higher spectral power density at a particular frequency. This can be seen in a Fourier transform where background has mostly low frequency components while a specific noise source has low amplitude but concentrated at high frequency.
 

ZeEa5KPul

Senior Member
Registered Member
What measures do submarines have to defend themselves against active sonar? Since the options available to aircraft aren't available to submarines (like jamming and stealth shaping) because of the different physics of sound and EM waves, it's going to be picked up by active sonar even if its passive emissions are 0 dB.
 

plawolf

Brigadier
What measures do submarines have to defend themselves against active sonar? Since the options available to aircraft aren't available to submarines (like jamming and stealth shaping) because of the different physics of sound and EM waves, it's going to be picked up by active sonar even if its passive emissions are 0 dB.
Acoustic tiles can reduce bounce back of active sonar and so functions similar to RAM on aircraft. But get an active sonar close enough to a sub and it will be detected. This is why navies favour helicopters and sonar buoys for ASW.

If you get pinged by sonar buoys and an ASW helicopter then comes over with its dipping sonar, it’s game over for the sub.
 

Maikeru

Junior Member
Registered Member
What measures do submarines have to defend themselves against active sonar? Since the options available to aircraft aren't available to submarines (like jamming and stealth shaping) because of the different physics of sound and EM waves, it's going to be picked up by active sonar even if its passive emissions are 0 dB.
Stealth shaping for submarines:
Please, Log in or Register to view URLs content!
 

Tam

Brigadier
Registered Member
Stealth shaping for submarines:
Please, Log in or Register to view URLs content!

I guess that could work but I wonder about the compromises in hydrodynamic design.

A sub can be very quiet passively at slow speeds, and tiles and shaping, partially resistant to active sonar. But when it starts to move around and over a speed threshold, the water flowing around the hull, around the sail, fins and so on, starts to create flow noise.

Will flat surfaces increase the surface drag of the submarine and reduce the skin strength of the submarine under the underwater pressure stress. The reason why cylindrical design is used is because you can exert equal pressure in all directions outward to counter the crushing pressure exerted equally around the cylinder. This makes me think that for this, it is difficult to use a single hull submarine design. Better to have an inner cylindrical pressure hull with the flat sided non pressure outer hull to counter the active sonar.

A lot of this makes think that a double hull might be more convenient for the active counter of sonar and passive control of noise. A double shell around the submarine to prevent noise from leaking out and yet the thinner outer shell is more malleable to be pressed into any desired form to counter active sonar.
 
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MarKoz81

New Member
Registered Member
What measures do submarines have to defend themselves against active sonar? Since the options available to aircraft aren't available to submarines (like jamming and stealth shaping) because of the different physics of sound and EM waves, it's going to be picked up by active sonar even if its passive emissions are 0 dB.

The physics of sound and EM waves are exactly the same and both are the same general concept - wave of matter. The difference is in frequency which defines the "size" of portion of energy. Smaller sizes - higher frequencies - can affect smaller constituent elements of matter. Larger sizes - lower frequencies - can affect only larger portions of matter. If you direct a gamma ray (1,24*10^20Hz) at a building you will cause decay of atoms in the walls but won't affect the walls. If you direct an infrasound (20Hz) wave at the same building it will break its walls but won't affect the atoms. The priciples of wave mechanics, reflection, refraction, propagation etc are the same. It's just that at different scales the effects appear as different to us because acting at small scales it's many elements being affected and in large scales it's only few.

Just as stealth aircraft were partly inspired by the development of submarine tactics during the Cold War so "stealth" is now being adapted to submarines:

Type-212CD-Submarine-Scale-Drawing.jpg

It won't have exactly the same effect because the medium of soundwaves is different from the electromagnetic spectrum but the wave mechanics is the same and so the reduction in detection by sensors using the wave mechanics will be proportional.

Jamming is already used extensively. What do you think a decoy is?

The term "jamming" comes from the action of filling the seeker's signal processor with false signal so that it can't tell it apart from the real signal - from the target. An infrared flare is jamming so much photons onto the matrix of the seeker that it can't tell them apart from photons from the exhaust of the engine. Aircraft deploying flares always makes a sharp turn to remove as much of the exhaust signature from the matrix while the flare follows the same trajectory. The seeker sees less of the exhaust's signature and more of the flare's signature and follows the stronger signal.


Finally active sonar is much more limited than passive sonar due to the mechanics of soundwave propagation.

This table compares maximum detection range for a given sound pressure level. The first column is the level, the second column is the passive sonar and the last column is active sonar. Pay attention to how drastically different the maximum detection ranges are for passive and active sonar. It's caused by doubling of distance of propagation:

Range for passive sonar: R= 10 ^ (PL /10)
Range for active sonar: R= 10 ^ (PL /20)

This is why at 15dB the difference between passive and active sonar is ~25m but at 35dB it is 3 kilometers.

320px dystanse.jpg

The signal strength is also affected by "sonar cross section" which adds "target strength" measured in dB. The target strength in the side aspect is several times greater that target strength in frontal aspect.

If the sonar hits the submarines side the reflection will be stronger. If it hits the bow the reflection will be weaker. Add stealth shaping of the hull and the anechoic tiles and some of the energy is dissipated outward (shaping), some inward (tiles) and some will be lost to distance.

You need a very powerful source to be able to see sufficiently far. And that's why the Soviets used depth charges for sounding out enemy subs. Tu-142s would drop passive sonobuoys and then drop small bombs to produce the signal.

Active sonar will start to become a problem once large underwater drones start operating in something resembling pre-programmed swarms. Swarming underwater is almost impossible due to how water limits exchange of information necessary for swarming but the drones can have pre-programmed behavior timed the same way torpedoes are. Then if you have some of the drones with towed arrays and other drones sweeping the area with intense sonar it will be a more effective version of sonobuoys.

I'm assuming USN and PLAN have already worked on that, as would most likely other serious navies. I know for a fact that the German research ship Planet has already been tested (close to a decade ago) in tandem with one of the Type 212A subs and several sonar-carrying underwater drones. The drones were emitting active sonar signal, the sub was just listening in. The results were promising even in the shallow waters of the eastern Baltic so the results wouldn't be that much worse at open sea - and in many cases better.

I think the future of submarines lies in the same niche as it is with manned aircraft. Small number of manned fighters or even bombers as command nodes and large number of unmanned large aircraft and even larger number of smaller UAVs and UCAVs. Except that underwater there will be less real-time adaptation because much more will have to be pre-programmed. Drones will do the active search, drawing of attention and even blind attack/provocations then subs will take their shots at great distances - much greater than today - and run. Nothing else will be safe because the amount of buoys and depth charges that can be thrown by a surface task force is just orders of magnitude greater than anything that the sub can do.

I am very much curious if 09V will try to pre-empt this trend or whether it will try to close the gap with American submarines and will leave any radical changes for a 09VII. The production capacity is there so perhaps small increments with moderately-sized productions runs is the way to go. We shall see.

I'll end here. While superficially constructive this is going awfully close to an off-topic and off-topics are orc-work!

One more thing:

I have to caution that when you say background level it refers to the total background sound power, not the spectral power density.

A signal in general can have lower total power than background but higher spectral power density at a particular frequency. This can be seen in a Fourier transform where background has mostly low frequency components while a specific noise source has low amplitude but concentrated at high frequency.

Sound power level is not sound pressure level which is the property measured in dB in sonar equations. Levels are measured in dB in both instances but sound power is the power of the sound source measured in watts while sound pressure is measured in pascals. These are two different properties.

Background noise level is the overall generalized level of sound pressure at all frequencies.

Fourier transform extracts frequencies from the time series describing the signal.

If the sound pressure level of the source signal is lower than the sound pressure level of "background noise" then the hydrophone registers no signal and the analyzer can only run Fourier transforms of the background noise.

Your comment is only creating confusion. And creating confusion is orc-work!
 

Tam

Brigadier
Registered Member
What is the role of the Type-054A now?

In the past 5 years, China has launched 25 destroyers (both Type-052D and the Type-055)

But surface ships are acutely vulnerable to surprise submarine torpedo attacks, which the Chinese Navy can expect.

And when I look at the overall PLAN Orbat, I see a shortage of ASW frigates to provide convoy escort, patrol local waters and also provide an ASW screening ship for higher value surface warships.

My guestimate is that a notional Type-054B would approach the same cost as a Type-052D destroyer. That is based on the Type-054B using a comparable level of electronics fitout as the Type-055, European frigates or Japanese destroyer escorts - and their known costs.

So it wouldn't make sense to build Type-054B frigates to screen a Type-052D destroyer.

What you want is a low-value ASW screening ship that an opposing submarine doesn't want to engage.
For that purpose, a cheaper Type-054A has the exact same ASW capabilities as a more expensive Type-054B.

The lower-performing radar and electronics suite of the Type-054A wouldn't be an issue, as the Type-052D would be providing long-range radars and air defence.

Anyway, back on topic.

A bit out of topic. Sorry.

Don't think the 054B will approach the cost of the 052D. Two phase arrays working at the same wavelength will have the same density of Rx/Tx elements, and the spacing between each element is about 1/2 of the wavelength. This does not change even if the technology behind the elements changes, and applies the same for both AESA and PESA.

Assuming that the wavelengths of the 054B's search radar and the Type 346A of the 052D is about the same, the element density of both their arrays should be about the same.

Assuming the dual sided array we have seen is for the 054B, its side is only 2.9 meters at X and Y dimensions, and you have two sides. The 052D's main Type 346A arrays are about 4.3 meters estimated in both X and Y dimensions and there are four of them. So the number of AESA elements and modules on the 052D are far greater than the 054B. The greatest cost of these radars lies with each module, and there would be thousands and thousands of them, probably well over 5000 per face on the 052D. Consequentially, the radar on the 052D remains significantly more powerful.

So there is no way the 054B's search radar would cost more than the 052D's, and that probably accounts a considerable chunk of the systems package. AESAs are notorious for being expensive. Adding to the cost of the 052D would be the cooling systems needed for its humongous radars, which has to be embedded in the hull. For the 054B, using the rotating dual sided radar, only a small cooling system is placed within the radar. For the same reasons, the power systems feeding to the radars and cooling systems would be much more powerful on the 052D than on the 054B, which means more generators and other power related infrastructure and so on. The IT systems would have to be more complex to process the information from the larger radars and so on.

There is a serious possibility that the 054B might use the X-band AESA fire control radars from the 055 and that may raise the bill. That's going to raise the upfront cost, but one radar set can replace three mechanical fire control and surface search radars instead. Your med to long term maintenance costs are cheaper because the radar is non mechanical and solid state, compared to the mechanical radars that is subject to wear and tear and requires periodic inspection. Having said to be fair, the dual sided search radar which is rotational, will be subject to wear and tear compared to the fixed main radars of the 052D. But again, this is only a possibility. The 054B might also well retain the old mechanical fire control radars to lower cost and stick to the proven.

The issue with drive trains, IEPS likely with diesel electrics vs. two GT two diesels in CODAG, isn't likely to make a dent in terms of cost compared to the sensor and weapons system integration.

Based on this, the 054B isn't going to cost as much as the 052D, although it will cost more than a 054A on the upfront costs, but at the same time, its not likely the 054B will challenge the 052D for air protection missions either, and like its predecessor, will focus more on a closer range air defense bubble. However, on the mid to long term costs, a 054B with its AESAs can offer potentially better running costs over the 054A in terms of mechanical maintenance costs, offer potentially greater reliability, as in less moving parts, with much greater combat potential especially in AAW.

IMO conclusions, 054B still offers a plate to the ASW table.

Will cost less than a 052D.
Higher upfront costs but lower long term costs than 054A.
The potential of IEP.
The potential for a longer deck for a larger ASW helicopter.
If U-VLS is used, the potential for a new ASROC missile.
Directed high speed digital communications (CEC) with other ships equipped with the same.
 
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Tam

Brigadier
Registered Member
The physics of sound and EM waves are exactly the same and both are the same general concept - wave of matter. The difference is in frequency which defines the "size" of portion of energy. Smaller sizes - higher frequencies - can affect smaller constituent elements of matter. Larger sizes - lower frequencies - can affect only larger portions of matter. If you direct a gamma ray (1,24*10^20Hz) at a building you will cause decay of atoms in the walls but won't affect the walls. If you direct an infrasound (20Hz) wave at the same building it will break its walls but won't affect the atoms. The priciples of wave mechanics, reflection, refraction, propagation etc are the same. It's just that at different scales the effects appear as different to us because acting at small scales it's many elements being affected and in large scales it's only few.

Just as stealth aircraft were partly inspired by the development of submarine tactics during the Cold War so "stealth" is now being adapted to submarines:

View attachment 77463

It won't have exactly the same effect because the medium of soundwaves is different from the electromagnetic spectrum but the wave mechanics is the same and so the reduction in detection by sensors using the wave mechanics will be proportional.

Jamming is already used extensively. What do you think a decoy is?

The term "jamming" comes from the action of filling the seeker's signal processor with false signal so that it can't tell it apart from the real signal - from the target. An infrared flare is jamming so much photons onto the matrix of the seeker that it can't tell them apart from photons from the exhaust of the engine. Aircraft deploying flares always makes a sharp turn to remove as much of the exhaust signature from the matrix while the flare follows the same trajectory. The seeker sees less of the exhaust's signature and more of the flare's signature and follows the stronger signal.


Finally active sonar is much more limited than passive sonar due to the mechanics of soundwave propagation.

This table compares maximum detection range for a given sound pressure level. The first column is the level, the second column is the passive sonar and the last column is active sonar. Pay attention to how drastically different the maximum detection ranges are for passive and active sonar. It's caused by doubling of distance of propagation:

Range for passive sonar: R= 10 ^ (PL /10)
Range for active sonar: R= 10 ^ (PL /20)

This is why at 15dB the difference between passive and active sonar is ~25m but at 35dB it is 3 kilometers.

View attachment 77462

The signal strength is also affected by "sonar cross section" which adds "target strength" measured in dB. The target strength in the side aspect is several times greater that target strength in frontal aspect.

If the sonar hits the submarines side the reflection will be stronger. If it hits the bow the reflection will be weaker. Add stealth shaping of the hull and the anechoic tiles and some of the energy is dissipated outward (shaping), some inward (tiles) and some will be lost to distance.

You need a very powerful source to be able to see sufficiently far. And that's why the Soviets used depth charges for sounding out enemy subs. Tu-142s would drop passive sonobuoys and then drop small bombs to produce the signal.

Active sonar will start to become a problem once large underwater drones start operating in something resembling pre-programmed swarms. Swarming underwater is almost impossible due to how water limits exchange of information necessary for swarming but the drones can have pre-programmed behavior timed the same way torpedoes are. Then if you have some of the drones with towed arrays and other drones sweeping the area with intense sonar it will be a more effective version of sonobuoys.

I'm assuming USN and PLAN have already worked on that, as would most likely other serious navies. I know for a fact that the German research ship Planet has already been tested (close to a decade ago) in tandem with one of the Type 212A subs and several sonar-carrying underwater drones. The drones were emitting active sonar signal, the sub was just listening in. The results were promising even in the shallow waters of the eastern Baltic so the results wouldn't be that much worse at open sea - and in many cases better.

I think the future of submarines lies in the same niche as it is with manned aircraft. Small number of manned fighters or even bombers as command nodes and large number of unmanned large aircraft and even larger number of smaller UAVs and UCAVs. Except that underwater there will be less real-time adaptation because much more will have to be pre-programmed. Drones will do the active search, drawing of attention and even blind attack/provocations then subs will take their shots at great distances - much greater than today - and run. Nothing else will be safe because the amount of buoys and depth charges that can be thrown by a surface task force is just orders of magnitude greater than anything that the sub can do.

I am very much curious if 09V will try to pre-empt this trend or whether it will try to close the gap with American submarines and will leave any radical changes for a 09VII. The production capacity is there so perhaps small increments with moderately-sized productions runs is the way to go. We sNichall see.

I'll end here. While superficially constructive this is going awfully close to an off-topic and off-topics are orc-work!

One more thing:



Sound power level is not sound pressure level which is the property measured in dB in sonar equations. Levels are measured in dB in both instances but sound power is the power of the sound source measured in watts while sound pressure is measured in pascals. These are two different properties.

Background noise level is the overall generalized level of sound pressure at all frequencies.

Fourier transform extracts frequencies from the time series describing the signal.

If the sound pressure level of the source signal is lower than the sound pressure level of "background noise" then the hydrophone registers no signal and the analyzer can only run Fourier transforms of the background noise.

Your comment is only creating confusion. And creating confusion is orc-work!


Nice chart but it makes me wonder how whales do it? After all, their cries and songs can still be heard as far as 10,000 miles away.
 

Tam

Brigadier
Registered Member
It's an idea that's been around for a while. That no one's picked it up indicates that there are problems.

From what I can see it looks like a double hull built around a Type 212 hull. That will do wonders for the 212's wet area.
 

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