The statement was made in direct reference to submarines - why would you exclude materials from such a discussion?
SSKs
- Thread starter zoolander
- Start date
Because I can have a big sub and a small sub made of Identical materials sharing identical bla. bla. bla. everything.
Does the small sub have an advantage in sonar detection?
I recommend people read the following three FAS links for that part.
Underwater Acoustics
Sonar Performance
Sonar Systems
Any discussion beyond that, as Todjaeger says, turns circular pretty fast.
Grand Danois
Entertainer
Well, I thought the discussion went on the size of the sub?
Anyhow, I if can apply a material which halves the return through dissipating/absorbing/reflecting the energy to the larger (2xA) plate, as such the same energy is 'returned', but if the sensor you pick up the signal with is equal you get half the return, half the force per area of the sensor, as the sensor area is the same ?
Edit: re-reading it, I can see it was lamely formulated, but I guess the gist is discernible.
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@Todjaeger
You wrote;
"As I understand it, at a basic level you are correct on what an active sonar does. A 'ping' or sound pulse is emitted into the water, and the kinetic energy of the 'sound' wave will propagate through the water,"
That's OK.
Now, this energy is distributed in the wave that expands.
Now the energy is proportional to the amplitude of the wave, or rather in longitudinal (spelling?) waves like pressure waves (sound) the amplitude is the compression of water molecules. The more compressed the molecules are at a "wave top" the more energy. But as the wave expands, friction bla bla etc. the energy is dispersed and the amplitude of the wave drops. anyway our wave then hits an object and is reflected back to you (the sonar). How much energy is reflected? that, as far as I can see, must, amoung other things, be a function of the surface area that the wave is reflected on, ie. how much of the wave which is reflected .
Though I am not quite certain on how it really works when you "pick up" the sound wave.
I quess that there are other very important issues, like the porosity(spelling) of the material that affects how the wave is reflected, though we ignore those for now.
You wrote;
"As I understand it, at a basic level you are correct on what an active sonar does. A 'ping' or sound pulse is emitted into the water, and the kinetic energy of the 'sound' wave will propagate through the water,"
That's OK.
Now, this energy is distributed in the wave that expands.
Now the energy is proportional to the amplitude of the wave, or rather in longitudinal (spelling?) waves like pressure waves (sound) the amplitude is the compression of water molecules. The more compressed the molecules are at a "wave top" the more energy. But as the wave expands, friction bla bla etc. the energy is dispersed and the amplitude of the wave drops. anyway our wave then hits an object and is reflected back to you (the sonar). How much energy is reflected? that, as far as I can see, must, amoung other things, be a function of the surface area that the wave is reflected on, ie. how much of the wave which is reflected .
Though I am not quite certain on how it really works when you "pick up" the sound wave.
I quess that there are other very important issues, like the porosity(spelling) of the material that affects how the wave is reflected, though we ignore those for now.
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Shouldn't the sensor should pick up the same signal in both cases, since the two plates return the same signal (per construction)? (Or did I misunderstand you?)
And yes. We are talking about subs. I thought that one reason for building conventionally propelled attack subs was that they can be made smaller than nuclear driven subs. And that gives them an advantage vis a vis sonar detection (and yes there are other factors, like material choises).
Though I read that "people in the know" said that that was not the case and I like an explaination on why.
Ah - I'm pretty sure the manner in which diesel electrics "run silent" is more to do with their ability to switch their generators off and run on battery power than it is a size thing. Nuclear reactors, on the other hand, must always be running and thus (when the power plants are considered in isolation, rather than using submarine types as examples) could create more noise than a battery. I would think the size disparity is simply an issue of nuclear reactors requiring more space and enabling a larger mission set. Happy to stand corrected on any of that though.
Grand Danois
Entertainer
I'd like an explicit, but general explanation too from e.g. GF. (which was what you requested, but that shouldn't stop us from discussing).
Well, the acoustic sensor measures pressure or force per area and not the total energy reflected. (On the other side, a larger sub has a larger diameter/less curvature and should be more reflective, but should be a more marginal consideration.)
What I do know for sure is that nuclear subs demand complex infrastructure to build and support, which also makes them very expensive, this is probably the most significant advantage SSKs have over SSNs.
Yes. Assuming that the distance between "our plates" and sonar is much greater than the dimensions of the plates. We can perhaps treat the reflection as originating in a point.
If the larger plate reflects twice the energy of the smaller. The two otherwise identical (let's assume, spherical) waves travels back to our sensor. But in one wave there is twice as much energy, that must translate into a greater amplitude of the wave, which for these waves means that there is a higher pressure.
BUT energy (of the wave) is the square of the amplitude. So inorder to double the amplitude (the pressure) you have to quadruple the energy. so if the amplitude/pressure is the only thing the sensor picks up, a doubling of the reflected energy won't result in a doubling of the amplitude/pressure of the wave?? Not certain
(I have a feeling that I missed a lecture or two some years back...)The only country retaining SSKs while operating SSNs are currently Russia and China. China because it only has a handful SSNs, while Russian SSKs were purpose-built for littoral operations (with the Black Sea Fleet and Baltic Fleet). At least in the past 30 years.
Grand Danois
Entertainer
I can definitely see what you're getting at. If I was to give a proper answer I'd also have to check up with books as I'm not entirely sanguine treating a curved surface (point) as a plate(s, multiple points).Yes. Assuming that the distance between "our plates" and sonar is much greater than the dimensions of the plates. We can perhaps treat the reflection as originating in a point.
If the larger plate reflects twice the energy of the smaller. The two otherwise identical (let's assume, spherical) waves travels back to our sensor. But in one wave there is twice as much energy, that must translate into a greater amplitude of the wave, which for these waves means that there is a higher pressure.
BUT energy (of the wave) is the square of the amplitude. So inorder to double the amplitude (the pressure) you have to quadruple the energy. so if the amplitude/pressure is the only thing the sensor picks up, a doubling of the reflected energy won't result in a doubling of the amplitude/pressure of the wave?? Not certain
It may even be that the size does not matter at all, evrything else being equal?
http://www.physicstutorials.org/index.php/home/waves/water-waves
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Grand Danois
Entertainer
Of course mission & environment are important factors.
weasel1962
New Member
Re:
Whilst UK and France no longer has diesels in its inventory, UK still helps canada maintains its previously owned upholders whilst France builds scorpenes for every navy that wants one. Not exactly a clean break. The only other country to operate nuke subs is the US (whilst India and Brazil may be next in line to acquire that capability and join the list of countries that operate both nuke and diesel powered subs).
Whilst UK and France no longer has diesels in its inventory, UK still helps canada maintains its previously owned upholders whilst France builds scorpenes for every navy that wants one. Not exactly a clean break. The only other country to operate nuke subs is the US (whilst India and Brazil may be next in line to acquire that capability and join the list of countries that operate both nuke and diesel powered subs).
Ananda
The Bunker Group
Just wandering if UK shipbuilding industries still maintain their capability or more precisse know how for developing future SSK or just like US where they stop with Barbel the UK industry stop after Upholder.
Afterall like Netherlands that after Walrus eventhough they try to sell their Moray SSK concepts, however fail to attract export orders which from what I heard due to Export customers doubt whether the Dutch industries still capable building advance SSK efectively and efficiently after long gap with Walrus.
it's not just an issue of plates reflecting pulses or acting as reffractors. nominally yes, that is the case, but there are a whole pile of other variables at play here - and even in identical positional circumstances, the assumption that a smaller sub is harder to target or locate is not necessarily true. Thats been regularly confirmed in a number of different international ASW exercises.
the initial belief and somewhat appropriate for the time that smaller means harder to detect. nobody is going to give a detailed response because it gets down to some specifics about how signal management between platform types is conducted.
I have worked on 3 different classes of subs and been involved with UDT for 5 different navies, including some involvement with sig management on a nuke and with a 1200 tonner at the other end of the scale. Inherently, nukes have the greater potential to actively manage their battlespace.
this does not mean that that its a universal truth (some large nukes definitely radiate out of proportion to smaller boats - but that inherently flies back to some basic design flaws.
you cannot exponentially scale smaller sub technology solutions to nukes (and vice versa)
GD's analogy about B2, F-22 and F117 is highly relevant.
fluid dynamics and aerodynamics are kissing cousins.
Todjaeger
Potstirrer
The reason I stated that the experiment you suggested does not correlate to the submarine size question is that in the plate experiment, you were using two differently sized plates, of the same material. With two differently sized submarines, the chances of them both being built using the exactly same material is slim to virtually none. In addition, the type and layout of machinery is going to be different between different classes of subs, as is the internal and external shape and fittings.
Where one can run into a size limitation is that there is potential for certain types of acoustic reduction to require a certain size/volume/mass in order to be efficient and/or effective.
As an example of what I mean, I present the W.A.G. Institute-created material Rubbermaidium®
It is a material which has a weight of ~1g per cm^3, and when applied to a submarine hull in layers at least 50 cm thick, can reduce the acoustic signature (at least for certain frequencies) significantly. In short, if one is willing to add 'dead' weight onto a submarine, as well as increase the overall width of the hull by 1m, then Rubbermaidium® can be used. As a result, such a material might be better and more easily utilized aboard a larger submarine, because a potentially lower overall percentage of the submarines mass and size/volume would be taken up by the Rubbermaidium® layer.Incidentally, it is not true that diesel submarines are automatically smaller than nuclear submarines. The French Rubis-class SSN has a surface displacement of ~2,400 tons, while the RAN Collins-class SSG/SSK surfaced is ~3,000 tons and the Japanese Oyashio-class SSG/SSK is ~2,700 tons surfaced.
As a side note, the reason why a diesel sub on batteries can be quieter than a nuke boat is that the diesel can potentially turn off all onboard machinery for periods of time. A nuke boat always has to have machinery running to maintain the reactor. These pumps, being mounted within the hull of the nuke boat create an acoustic signature, just like every other moving or mobile part of a submarine.
-Cheers
I agree, but Plz understand which page I am on. Assuming that size (rather surface area) matters in sonar detection and ofcourse depending on how significant it is, you should be at an stealth advantage, everything else equal, by building the smaller sub. This smaller sub, you can then fit all the gadgets and materials that will make it more stealthy.
True.
I also belive that f.ex. a stirling engine or fuelcell types are simply more quiet than nuclear power plants. The work stroke of a stirling engine, is (or can be) a slow isoterm expansion, it is virtually soundless. And I don't think a fuel cell makes noise at all. (Ofcourse further down the line you have moving parts, that makes noise, as always)
Todjaeger
Potstirrer
I do understand what 'page' you are on. What I was attempting to illustrate is that 'everything else' is not equal in submarine sizes. Some solutions are only viable or effective when done to certain minimum scales. Hence my example with a material that had to be a half-metre thick to be effective.
Another way to look at the situation is from the perspective of soundproofing a room, with the stipulation that all the soundproofing done/material used has to be contained within the room itself, and with the added requirement that a useful/usable space needs to be maintained within the room as well. In this case, a room with dimensions of 3m x 3m x 3m can be soundproofed, but not the extent that a larger room, which is 10m x 10m x 10m can. The smaller room is already limited in terms of useful space, just because it is so small (27m^3). This means that any soundproofing material added to the room would reduce the interior space even further, until whatever is deemed the minimum useful space is reached. In the case of the larger room, up to 973m^3 of soundproofing can be added. making the soundproofed internal size of the larger room the same as the un-soundproofed size of the smaller room.
Granted this example is rather crude and does not have anywhere near the level of variables that come into play in terms of ASW and sub detection, but it should hopefully make it understood that submarine size does not have a direct impact on the ease or difficulty in detection.
-Cheers
The ssks are not just ideal for littoral purposes, but for fleet tasks, the first line you want to have in your fleet might be a few subs, imagine using a ssn of 7000 tonnes facing an ssk of 1500 tonnes, imaging what will be more easy to detect, for the own noise produced, for the active sonar signature,note that own reduction (of active signature) systems might work for certains distances but if you are close enough to the source of the ping they wont be useful, one thing is that that system reduces a bit the signature but it is found, other that makes it disappear (probably at distance quite away from the source of the ping), so using similar active sonar systems in the fleets (via helos or ships) or using similar passive sonar systems in the fleets (via sonobuooyes or subs), the ssn is probably going to be discovered first (in the distances where the stealth system is not useful), and count also the aip systems working well instead of the standard batteries....and it doesnt need to be fleet vs hostile fleet, but independent-front force ships couple with their subs versus ...
Its interesting note that collins in tonnes is twice the scorpene (one of the scorpene, as far i remember there where 3 sizes), but in volume is not much bigger, i put better figures:
Type: submarine scorpene
Displacement: 1,565 tons (CM-2000)
1,870 tons (AM-2000)
2,000 tons (S-BR)[1]
Length: 61.7m (CM-2000)
70m (AM-2000)
75m (S-BR)[1]
Beam: 6.2 m
Draft: 5.8 m
vs collins:
3,051 tonnes (3,003 long tons) (surfaced)
3,353 tonnes (3,300 long tons) (submerged)
Length: 77.42 metres (254.0 ft)
Beam: 7.8 metres (26 ft)
Draught: 7 metres (23 ft) at waterline
and vs los angeles class us navy ssn:
Surfaced: 6,082 tonnes (5,986 long tons)
Submerged: 6,927 tonnes (6,818 long tons)
Length: 362 ft (110 m)
Beam: 33 ft (10 m)
Draft: 31 ft (9.4 m)
:daz
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Todjaeger
Potstirrer
Have you been paying attention to the last ~two pages? The ease or difficulty of detecting a submarine is essentially independent of size.
As for specific information on what is or is not effective vs. active pings, or anything relating to distance is not discussed in public settings.
Now a modern diesel-electric sub might well be quieter operating on batteries and/or the AIP than a nuclear boat, it is not a fact. In other words, it does not apply in all cases.
Also, the assumption has been made that the SSN will be detected first. That is a false assumption, since there is the distinct possibility that the SSN would never be detected, nevermind 'first'. Secondly, the assumption that a nuclear boat is 'noisier' than a conventional boat is just that, an assumption, which is not the same as being a fact/correct/true.
The way a nuke submarine can operate is different in some areas from the way a conventional or diesel-electric sub can operate. One of the most significant of which I am aware of is the ability for a nuke boat to conduct long distance/duration transits and patrols while remaining submerged the entire time except for when leaving or entering port. Some of the larger 'fleet' diesels as well as some with AIP systems are capable of doing this to an extent as well, but not to the same degree. A nuke boat's dive endurance limitation AFAIK is dictated by the food supply and need to maintain crew health and morale. A conventional sub can have a greater need for oxygen to run the engines, and likely a more limited (if available at all) method for onboard oxygen generation due to a smaller powerplant (in terms of electricity output).
-Cheers