Sonar experts: How much sound crosses a layer?

[Molon Labe]

Have you tried 1.03 public beta yet? The SSP effects are MASSIVE. It seems like even very loud sounds cannot be heard across the layer.

Back in SC, when the layer effect was barely perceptible, it was a bit dissapointing but soon people explained to me how the SSP was supposed to work, and eventually I could use it a bit and see a small effect. I'm happy to see a stronger effect, but I'm in need of re-convincing that this is as it should be.

Are there any sonar experts that can comment on this? Thanks.

[Bill Nichols]

It really depends on how much the water temperature (sound speed) changes across the layer. I remember in the Med, during the summer, a very strong layer at about 100-150 feet. It was so strong that we often couldn't hear nearby surface ships until we came up to periscope depth. Had more than one 'Emergency Deep' as a result :o

[Molon Labe]

It really depends on how much the water temperature (sound speed) changes across the layer. I remember in the Med, during the summer, a very strong layer at about 100-150 feet. It was so strong that we often couldn't hear nearby surface ships until we came up to periscope depth. Had more than one 'Emergency Deep' as a result :o

I'll have to play around and see if there are "strong" and "weak" layers in the game. Does the game choose the exact SSP profile at random within the specified SSP type, or does the exact shape of the SSP depend on things like depth and time of day or any of that sort of thing?

[sonar732]

"Strong" and "Weak" is determined by the "bend" of the SSP. The greater the bend...the stronger the layer. I've seen examples of SSP's where it "jacknifed" at the layer and it was really strong vrs. one that doesn't bend at all produces no layer basically.

[Driftwood]

It will be interesting to see how or if this "new" aspect of DW effects torp evasion tactics.

[SeaQueen]

I'm happy to see a stronger effect, but I'm in need of re-convincing that this is as it should be.

Are there any sonar experts that can comment on this? Thanks.

I haven't looked at the patch yet, but in addition to the temperature gradient, how effective the layer is should depend a lot on the frequency of the sound. Do you see the effect in narrowband or broadband?

Low frequency noise should require a lot deeper duct to be trapped because the cutoff frequency of the duct decreases with depth. Any sound waves with a frequency lower than the cutoff frequency won't "fit" in the surface duct and won't be trapped. Similarly, high frequency noise should not require as deep a duct to be trapped.

At some distance, even with a strong duct, you should still be able to detect because you're getting direct path energy. Also, if the duct is weak, it will leak more energy than a strong duct.

Actually trying to estimate the effectiveness of sonar in the ocean can get you a PhD in oceanography and physics because the answer is almost always, "it depends on a lot of stuff.."

[SeaQueen]

I'll have to play around and see if there are "strong" and "weak" layers in the game. Does the game choose the exact SSP profile at random within the specified SSP type, or does the exact shape of the SSP depend on things like depth and time of day or any of that sort of thing?

From what I can tell, it depends quite a bit on the bathymetry. I'm sure there's also a stochastic component as well.

It ought to also depend on the season and windspeed.

If you can imagine, in a summer month, the sea surface temperature is much higher, and it cools as you go deeper so the sound speed will be higher near the surface and drop as you go deeper. That would drive the sound waves down, so unless the water is deep enough so that pressure can dominate temperature enough to push the sound speed higher again, you end up with a bottom limited case. In the winter, the sea surface temperature is not so high, so there might not be so strong a temperature gradient. So maybe it's not as bad.

Additionally the surface duct depth probably ought depend on the wind speed some how too. Strong winds would create a deeper isothermal mixed layer, while low winds ought to make it almost go away.

My suspicion is, though that a lot of the interelatedness of the environmental variables isn't there in DW. I know there's no correlation between sea state and wind speed, for example. One could spend a whole lifetime developing a sonar model. With a little bit of research online, you can do a lot to make sure everything is set up the way it "ought to be." In order to have as accurate an SSP for the given scenario as possible.

[Bellman]

Speaking as a layman and with respect to those who I suspect know far more in real life about this topic,
it simply amazes me the extent to which we all endlessly speculate about what real-life elements of sonar
performance are included in the sim. Unless and until SAS expand on their somewhat brief manual exposition
we are indulging in a rather pointless exercise. :yep:

[SeaQueen]

Speaking as a layman and with respect to those who I suspect know far more in real life about this topic,
it simply amazes me the extent to which we all endlessly speculate about what real-life elements of sonar
performance are included in the sim. Unless and until SAS expand on their somewhat brief manual exposition
we are indulging in a rather pointless exercise. :yep:

Yeah... that's why I get really annoyed when people say things like, "the sonar ranges are too short [long]" and you never see anyone say what the SSP looked like, what season it was, what the seastate was, how deep the water was, etc.. The truth of the matter is that any estimate of sonar performance has to be qualified with an extensive description of the environmental conditions in which that performance was achieved.

Unfortunately, too often the only environmental qualification I see is that the detection took place in Tom Clancy land.

And if you really want to get into it, any good sonar model has to go hand-in-hand with a good global climatology.

In truth, outside of classified discussions, nobody really knows how good a given system will perform against a given target and that's how it should be.

[sonar732]

Speaking as a layman and with respect to those who I suspect know far more in real life about this topic,
it simply amazes me the extent to which we all endlessly speculate about what real-life elements of sonar
performance are included in the sim. Unless and until SAS expand on their somewhat brief manual exposition
we are indulging in a rather pointless exercise. :yep:

Here, Here! :yep:

[OKO]

let me give you a very good link about it :

http://www.fas.org/man/dod-101/navy/docs/es310/SNR_PROP/snr_prop.htm

suggest you read that, than we continue talking about it
for our own culture and to know how to use it in DW

[LuftWolf]

That's a good read, OKO, for sure.

I've read it before and will read it again, now that it is very relevant to the sonar model we are now working with.

I've said it before and I'll say it again here... thank you SCS! :up: :rock: :arrgh!:

[sonar732]

Check this one out also!

http://www.fas.org/man/dod-101/navy/docs/es310/uw_acous/uw_acous.htm

[OKO]

on your link, we could see the increase of dB when increasing speed is NON LINEAR =>

http://www.fas.org/man/dod-101/navy/docs/es310/uw_acous/IMG00006.GIF


What I said for a long time ... when lots of people said it was linear ...
So we can consider the increase of the dB should be not as linear as the one in actual DW (with sound fix) nor than the one of LWAMI.
it's not + 1db per knots or per 2 knots, but rather near no difference at slow speed and huge one when increasing speed
like 2dB beetween 5 and 10 knts, and 10 dB beetween 15 and 17.

I remember how peoples said DW stock wasn't good here.
We could see now, stock DW was probably more close to the real thing than the actual values .....

THIS need a real new work.

[sonar732]

So, if we combine the new values in 1.03B with the original sonar sound vrs. speed issue we'd be in business! :rock: :rock:

[Amizaur]

:-) this is graph of sonar self-noise, so it's conected with hydrodynamic, "flow" noise. Well, it's even not flow noise itself but "sonar self noise" ! Flow noise at zero speed should be rather zero don't you think ? So I guess on your graph it's combination of sonar self noise with flow noise.
First, nobody said flow noise is linear :-). But the noise generated by a sub so combination of few kinds of noise, al low speeds machinery noise predominates, at high speeds in modern subs rather flow noise predominates. The flow noise is not linear. But this graph don't look good for me. Because from what I know the flow noise in general is proportional to sixth power of the speed (may be other power at lower speeds maybe). So it's raising curve as you think. BUT it is not raising curve if you plot it on a logarythmic graph !! It becomes the opposite then, because logarytm or a^x is stronger function than even x^6. On your graph the noise is in dB and speed in kts - and the curve is raising. This would lead to an absurd on the very right side of the graph, because more you are going to the right (higher speed) faster the noise (in dB) raises, so at some point increase of speed by 1kts would lead to several dB of noise increase so noise would double or raise 10 times with 1kts of speed increase ! Don't you feel something is wrong here ?
The graph of flow noise can't raise higher and higher on the right.
So even if this graph of sonar self noise is correct (because for example it's determined not only by flow noise but other things) it has not much to do with submarine self-noise which is combination of flow noise and few other kinds of noise. If sonar self noise is combination of constant base 50dB + flow noise, then it could look like on your graph but you'd be surprised how it looks more to the right :-).
Well ok I have found my Excel spreadsheet with noise calculations and made a combination of constant base NL and a flow noise. After a while I have found a combination of parameters that give quite similar result, look (click on the lower graph to enlarge):

http://www.fas.org/man/dod-101/navy/docs/es310/uw_acous/IMG00006.GIF

http://img373.imageshack.us/img373/2084/flownoiseplusconstant2ou.th.jpg (http://img373.imageshack.us/my.php?image=flownoiseplusconstant2ou.jpg)

Look at the red line, looks quite similar. But the first impression is wrong, when you take a second look at what happens more to the right and understand what's happening - it's actually a dB scale sum of constant 20dB noise with a flow noise. Look at second graph, it's same function but showed more to the right and with the flow noise part showed in black, as you see the red line is starting from base 20dB but later it becomes more and more similar to the black line.

http://img373.imageshack.us/img373/2306/flownoiseplusconstant28gx.th.jpg (http://img373.imageshack.us/my.php?image=flownoiseplusconstant28gx.jpg)

The black line is flow noise and I guess it's quite different from what you could expect. But the red line, sum of 20dB and flow noise at first look quite different than it becomes later. So not always looking at begin of an graph can give you good understanding of what will happen later, if you don't know what function or sum of functions the graph shows. The begin may look quite different from the rest of graph.

But I think the graph you showed is not very precise and maybe also the sonar flow noise at low speeds is little different function because it don't look like speed^6 function. So it's either more complicated (and even less connected with submarine noise) or not very precise...

[OKO]

sure Amizaur : my graph wasn't very accurate, it was just an example.
But personnal experience abord sailing ships and my love for physics (even if I'm not a physicina myself) just show me there is real gaps in this matter
For example, on my ship, well ... my father ship, a catana of 44ft, I could see it's quite easy to go to 10 knts, even with low wind speed (15 or 17 knts), without near any perturbations at the tail of the ship, and the perturbations will start around 11 to 12 knts.
From that speed, we really need more wind to get over this gap (our personnal best speed is 21.3knts on this boat, with 40/45 knts of wind "au portant" and the smallest sail)
It's simply due to the hull shape.

I'm convinced there is some gap also for sub hulls.
Because they are also subject to physical laws.
So, gap changing drastically the noise generated.
There is a before and after the gap
after the gap, water perturbations start and make much more noise than the noise generated by the sub itself.
This gap is not modelised at this time
and this is domageable for tactics.
because I'm convinced a good commander of a real sub KNOW this gap and know when he can go over this or when he can't, because he will risk counter-detection

This gap should be VERY different, depending on sub tech
Well all read Akula is as quiet as US subs AT LOW SPEED and NOT on high speed.
I think it's just because this gap is reached earlier with the Akula than with a 688i and furthermore with the Seawolf.

Seawolf is known to be "silent until 20 knts"
20knts is his gap, before he is really stealthy, after he make much more noise.
I think this gap should be around 12 or 14 knts for 688i, and beetween 8 to 10 knts with Akula.
At this time this isn't modelised at all
We have a progressive and linear curve that doesnt' reflect this kind of real problems.

Of course, these data should be one of the most secret ones.
But with some talk and tought, we could find something much closer to the real thing than what we have actually.
I'm still convinced the original data were closer to the real thing than what we have from the sound vs speed fix ... or with the LWAMI.

[Amizaur]

I say you again that original data was ZERO, not any noise increase with speed at all :-D. The SCS noise-speed fix changed this to 10 points (so 20dB) of linear function of speed for SSNs.
I'm not sure about what "gap" you are talking here. If you have water drag in mind (which is quite complicated function of the speed in the water) or difference between laminar and turbulent flow maybe ?
The noise generated is related to both drag and flow kind (turbulent being more noisy) but don't know if it's related so directly to make same plot and to make assumptions about noise created by an object in water from the knowledge of it's drag characteristics. And even if you have plotted function of object's drag in the water vs speed on logarythmic scale for drag, you'd be surprised how the graph looks :-). It bends in the other side than you expect :-).
For sure the Seawolf (and every modern sub) is designed to reduce turbulence and reduce flow noise (or rather to increase the speed at which the flow noise becomes noticeable). And if the machinery noise is low and not increase much with speed, and the flow noise is reduced so that it becomes to show up only at 20kts, then you get a quieter sub than can run faster being quiet. But this would also mean being quieter from competition at lower speeds :-). The situation you describe would occur if there is a minimum amount of machinery noise that CAN'T be reduced even at stop (why?), but on the other hand it is dampened so good that it don't increase with speed almost at all and stays on this lowest level up to 20kts. And then at 20kts the flow noise shows up and raises further with the speed. So base noise level at 0, 5, 10, 15 kts, and then flow noise becomes to show and kicks in at 20kts and higher. Well little strange, if there is some machinery that makes some noise at idle (and you can't reduce it to non-measurable value) then the machinery would make increased noise at half speed or full speed... Or do we assume that every piece of Seawolf's propulsion (reactor and it's cooling, steam generators and turbines, reduction gear and shaft, propulsor) is working or rotating with same speed at 5kts than when at 25kts ?
What is true that the machinery noise raises slower than flow noise and that's why the flow noise predominate at some speed. But I don't believe that it's 110db, 110db, 110db and suddenly starts to raise 120 130 140. It may raise slower at low speeds, and become to raise faster when flow noise predominates. It may be at 20kts in Seawolf and 10kts with 688I maybe, and maybe not. We don't know at what speed the flow noise predominates for modern subs. But I have assummed that it's about 20kts for Seawolf and about 10kts for 688I and set the machinery and flow noise graphs to reflect this. Currently I can't model this in speed-noise curves (because they ARE linear in DW from the very start, it was SC were they were non-linear) but I know it CAN be done, because the FFG has non-linear curve, or more precisely have some flat area on the beginning of the later-linear graph. I can't make sub curves same way because this affects sub minimum speed. It can be compensated and it is compensated for FFG (it can stop) but I don't know exactly how and can't do this. But I plan to find how it was done for FFG and then I could add flat area on beginning of sub's noise graph, even 15kts of it :-). I will plot supposed sub noise profile and then find what possible to achieve DW noise curve would fit best to it. Possible to achieve in DW are linear with some flat area on beginning. Non linear noise function was in Sub Command only and was not very fortunate because even flow noise curve raises sharply at some speed range, but then becomes to flatten in dB scale. In SC it raised faster and faster with speed hitting max already before flank speed.
I think current model is better and more accurate, if I knew how to compensate the minimum RPM value effect on minimum speed it would be even better with flat beginning possible.

[OKO]

I say you again that original data was ZERO, not any noise increase with speed at all :-D.

I didn't find again the post when I tested this (dated, as my screens, from mars of this year)
but still have the screens that prove there WAS change depending on the speed =>

With Stock DW
KILO at 12 knts

http://okof4.free.fr/images/DW/screenshots/KILO_12.jpg

KILO at 17 knts

http://okof4.free.fr/images/DW/screenshots/KILO_17.jpg

you can see a real difference here.
So, it wasn't 0 Amizaur ...
As I tested it, I remember there was a real huge gap at some speed with ALL subs, not only the KILO.

I think pictures speak by themselves.

[OKO]

The situation you describe would occur if there is a minimum amount of machinery noise that CAN'T be reduced even at stop (why?)

it's a fact known for all nukes
even at complete stop they still make noise, and there is very few difference beetween a nuke at stop and a nuke at 5 or 7 knts

But I don't think you get my point :
As I told you, there is always, on every hull, a time where you start creating hydrodynamical perturbations, when the laminar flow start to become not so laminar, and here turbulence are created.
As I told you, I could see that each time I go sailing, on the rear of my boat.
that's because my hulls (its a multihull) are optimised for cruise at 10 to 11 knts.
If I go over this speed, even if I could go much faster (well ... its still a sailing boat anyway ...) I will have much more turbulence in my wakes.
but before 10 knts, if you look at the wakes, you have the impression that the ship is stopped
and suddenly, if you go over that speed, you see wakes coming.
It's the time the hydrodynamical flow stop to be absolutly laminar along my hulls.
Not only this slowly brake the increase of speed, but also from this point, I start to need more energy (from the wind) to increase the speed than I needed before 10 knts.
Just because I've got out of the optimal flow, starting turbulence.
And turbulence for subs is noise.

So, for subs, there is also a critical point like this.
A point where a real commander will know he will produce much more noise.
And this is an important tactical thing.
Tactical thing that doesn't exist at this time in DW, but existed in stock DW, as the screens above could show you

[OKO]

I have to say that anyway i don't know if stock DW had good values ...
I just saw that there was a gap, that's all.

[Amizaur]

So you have only those two pictures, not a test mission where it could be repeated and measured ? From this one case ? I'm sorry but I have done not one, but dozen of tests, in different scenarios and different ways to measure noise level and I'm absolutely sure it was constant in 1.01. There were also later available some ways to measure this directly, something like Debugoutput showing platform noise level, results were the same.
The difference could be because of cavitation, but you said it wasn't.
I see there are two pictures, how were they made ? Was it a Kilo that run at 12kts and then increased speed to 17kts ? Or was it the same mission run two times, once with Kilo set to 12kts, and second time with Kilo set to 17kts ? Because you can't compare results from 2 different runs even of the same scenario. Water conditions are different each time, layer depth is different and detection ranges can vary, so the strentgh of the signal.
If you can replicate the situation and send me the mission I could check it, at least in few ways. But that would have to be two Kilos in same mission, one going 12kts and the other 17kts and generating different amount of noise. Or Kilo going 12, and after reaching a waypoint speeding to 17kts but in the same mission.

About the noise becoming stronger with turbulent flow - of course but I'm not sure the difference is so sharp UNDERWATER, where is no air which can mix with water causing bubbles, splashing and noise. And the speed at which flow becomes turbulent can be different at differents part of the sub, just like local Mach number can be different around differents parts of a plane.
The flow probably becomes turbulent on low scale (close to submarine skin) much sooner than 20kts, only the shapes of hull are designed to keep the flow smooth and produce less noise. It's my guess of course but it's hard for me to imagine fully laminar water flow around sub surface at speed of 15kts or more. I think the noise level of flow would increase more or less smoothly, if the shape of sub is designed properly (so modern sub).
The really sharp increase in noise level underwater is connected with cavitation rather, which occurs only at much higher speeds, like for propeller blade or Shkval torpedo.
But as I said you could probably clearly see on the graph of broadband noise where the flow noise becomes to predominate other noises - the plot would become to raise faster from there.

[OKO]

I took this screens with a scenario I made 8 month ago
i used twice the same scenario, just changed the speed of the KILO.

Whether you like it or not, I got this result.
Now try something if you don't believe me =>
desinstall DW and reinstall it without patching
then proceed to this very simple verification : put a KILO at 1000 ft and do the test.
I did it with both KILO and 688i and had the same result, but I can't remember the speed at which the 688i started to make big noise, this test was made 8 month ago, BEFORE the sound fix.
Anyway, this is another subject, I don't care about older values, i care about actual ones, which are wrong.

About turbulence, I explain you what I COULD SEE each time i'm sailing, this mean beetween 4 and 6 times a year.
but maybe you have more experience than me on this subject, even if I sail for 35 years on many different ships.
Now, as I see you don't even trust me about my tests (at least you didn't said I lies ...) I don't see any reason to continue this discussion ...

but fact are :

1) ANY NAVAL HULL in the world, made by human (i don't know about ET ones ...) have a critical point at which turbulence start to be created, and this point depends DIRECTLY to the type of hull (the form and the length) and allow most mdern ship to have best performance (ie step forward) in this matter, because more research was made to delay this critical point.

2) at this critical point, the non linear flow not only produce turbulence but start also to reduce the hydrodynamical performance of the ship (mean it need more power than before to increase the speed), if you stll don't believe me, just read some physics basics.

3) when turbulence are created, not only more opposition to advancing is generated, but also NOISE is generated, and MUCH MORE NOISE than before turbulence occurs.
Simple example is the washout on sonar when you reach 14knts with the 688i, when it is 8 knts with the Akula
You didn't ask yourself why there is difference here ? it's mainly due to the hull hydrodynamical performance, not only the sonar sensitivity.

4) NOTHING OF THIS is modelised in actual DW nor LWAMI, and didn't even approach this, all sound profiles are absolutly linear actually, that is not correct and not realistic.

5) I never said original was realistic, but i said It was closer to the real thing than what we have actually, because i could saw a gap I don't see anymore in the actual DW with sound fix


You see, military are actually trying to reproduce the skin of the shark to use it for subs skins, and on competition sailing boats, and you know why ?
guess ...
to delay to the maximum the time the turbulence start to be generated.
because when turbulence start to be generated, this degrade the hydrodynamic performance and cause NOISE.

So actually, our sound profile for subs are not realistic.
whether you like it or not ...

[OKO]

nothing better than some links =>

http://www.npmoc.navy.mil/KBay/backgroundnoise.htm

HYDRODYNAMIC NOISE

Self noise resulting from the flow of water past the hydrophones of the hull-borne sonar, its supports, and the hull structure of the platform is hydrodynamic noise. In submarines, this type of noise also includes the noise generated by turbulent pressures upon the hydrophones from flow eddies, as well as vibrations from the submarine's plating and sonar gear. In addition, the water flow around the sonar dome sometimes creates the major portion of self noise. This noise is known as flow induced resonance, or FIR.

http://en.wikipedia.org/wiki/Turbulence

Consider the flow of water over a simple smooth object, such as a sphere. At very low speeds the flow is laminar; i.e., the flow is smooth (though it may involve vortices on a large scale). As the speed increases, at some point the transition is made to turbulent ("chaotic") flow. In turbulent flow, unsteady vortices appear on many scales and interact with each other. Drag due to boundary layer skin friction increases. The structure and location of boundary layer separation often changes, sometimes resulting in a reduction of overall drag. Because laminar-turbulent transition is governed by Reynolds number, the same transition occurs if the size of the object is gradually increased, or the viscosity of the fluid is decreased, or if the density of the fluid is increased.

http://www.cora.nwra.com/~werne/eos/text/turbulence.html

and the last (i won't spend all my time to prove you my assertions ...)

http://kr.cs.ait.ac.th/~radok/physics/f2.htm

Turbulent flow

At a critical velocity, a laminar flow becomes turbulent. If for a tube with a circular cross-section the the expression vd/n (v average velocity, d tube diameter) serves as critical number R, the validity of Poiseuille's Law ends at R = 2000, when turbulence begins. In a tube with a diameter of 1 cm, through passes water at 10ºC, R = 2000 yields a mean velocity of about 26 cm/sec. Through this tube, a slower flow, as every flow with a smaller value of R will be laminar (layered). If the velocity increases to this value of if you obtain it by enlargement of the tube diameter or heating of the water (decrease of m), there will occur the change over. The amount of fluid for a given pressure drop will then be smaller than the value, given by Poiseuille's formula, that is, the resistance experienced by the flow increases. The causes of turbulence were not yet known in 1935.


Now we need to determine the critical point for all subs
it's not so difficult to evaluate, as I said before.
And, more difficult, we need to evaluate what happen at the critical point, how much is the gap.
We could talk about that if you have finished to contest physical law :hmm:

[Bellman]

Very educational but still not sure how relevant to sim actualite. :roll:

I think OKO has a point about the 'gap' - the changing turbulence characteristics around the hull with speed.
MSGallileos photos of the Virgimia 's wide apperture flank arrays prompted my remark:
I just feel in my bones that this rigout should give better prow and stern arc coverage. Flow turbulence is not uniform
around the 'sides' of the sub. compare air flows in wind tunnels around very similar shaped aircraft fuselages.
Turbulence can be at reduced levels in 'certain' areas.
This may or may not be relevant as the apperture spread may just overcome the barriers of migratory turbulence.

But the manouvering for ''clearing the baffles'' takes on a new meaning when the hull side blind spot moves position.
It means that not only are these 'spots 'transitory but it may mean that certain areas may become relatively
more receptive depending on speed and angle of inclination.

But when one returns from 'Space' the acid test is what can be modelled in the sim and what is ? :hmm:

[drEaPer]

About the noise becoming stronger with turbulent flow - of course but I'm not sure the difference is so sharp UNDERWATER, where is no air which can mix with water causing bubbles, splashing and noise.

Correct me if Im wrong, but this argumentation(no air underwater) rules out cavitation, yet it happens. There is always air in water. I guess some "O's" are detaching from the H²O through mechanical force (creating kinda vacuum which then "sucks" the air out of the water, contrary to boiling where the heat is the reason).
So what OKO sais makes alot of sense to me.

[FERdeBOER]

Sorry if I'm saying a stupidity, but my English is not so good to follow so complex conversation, but I want to say two things:

Of course there is air in sea water. If not, the fishes couldn't breathe. :yep:

Another thing: the phisycs on the air could not be applied to water. Both are fluids, of course, but liquids (water in this case) are much more dense and complex than the air.
In fact, there no exits a unique formula for the speed of sound in the water. There are one for each place, even for each season, and all this formulas are made by empiric experients, no theorical.

[OKO]

Another thing: the phisycs on the air could not be applied to water. Both are fluids, of course, but liquids (water in this case) are much more dense and complex than the air.
In fact, there no exits a unique formula for the speed of sound in the water. There are one for each place, even for each season, and all this formulas are made by empiric experients, no theorical.

Thats true : if both are fluid, the water have much more viscosity than the air, I can't remember the value exactly but this should be around 100 times.
As you said, most of sound propagation in water are empiric, but there at least a quite known formula to help to compute when turbulence start : it's the Law of Poiseuille, which, coupled with Reynolds number can tell you at what time a hull will start to create turbulence.
The Reynolds number is used to transpose the turbulence effect to a same hull at different scales.

Sound propagation in the water and the time laminar flow become turbulent are 2 different things.
First is mainly from experience (even some formula exist) the other is very well known and ""easily"" calculable (if you have the right data ... including hull size and form and viscosity of the environment)

[Wim Libaers]

About the noise becoming stronger with turbulent flow - of course but I'm not sure the difference is so sharp UNDERWATER, where is no air which can mix with water causing bubbles, splashing and noise.

Correct me if Im wrong, but this argumentation(no air underwater) rules out cavitation, yet it happens. There is always air in water. I guess some "O's" are detaching from the H²O through mechanical force (creating kinda vacuum which then "sucks" the air out of the water, contrary to boiling where the heat is the reason).
So what OKO sais makes alot of sense to me.

No, the reason for cavitation is not a chemical reaction where water decomposes (but chemical reactions might happen as a consequence of the high temperature reached when bubbles collapse during cavitation). It simply is that, at high flow speeds, pressure is reduced, so dissolved air will easily go out of solution, and water will boil at lower than normal temperatures. This is also why cavitation is less likely to happen when deep: the pressure is much higher, so (at the same temperature) you need a much faster flow to lower te pressure enough to start the boiling. It obviously also becomes easier with increasing temperature.

Of course, as soon as the bubbles come into a region of slower flow, they are not stable and will collapse. This is noisy and may damage the screw.

[sonar732]

Ok...let's not turn this into a flame war. Let cooler heads prevail until Jamie and/or Hutch addresses this issue.

[drEaPer]

About the noise becoming stronger with turbulent flow - of course but I'm not sure the difference is so sharp UNDERWATER, where is no air which can mix with water causing bubbles, splashing and noise.

Correct me if Im wrong, but this argumentation(no air underwater) rules out cavitation, yet it happens. There is always air in water. I guess some "O's" are detaching from the H²O through mechanical force (creating kinda vacuum which then "sucks" the air out of the water, contrary to boiling where the heat is the reason).
So what OKO sais makes alot of sense to me.

No, the reason for cavitation is not a chemical reaction where water decomposes (but chemical reactions might happen as a consequence of the high temperature reached when bubbles collapse during cavitation). It simply is that, at high flow speeds, pressure is reduced, so dissolved air will easily go out of solution, and water will boil at lower than normal temperatures. This is also why cavitation is less likely to happen when deep: the pressure is much higher, so (at the same temperature) you need a much faster flow to lower te pressure enough to start the boiling. It obviously also becomes easier with increasing temperature.

Of course, as soon as the bubbles come into a region of slower flow, they are not stable and will collapse. This is noisy and may damage the screw.

Thats what I said. Dunno how that chemical stuff comes up, I didnt say anyhting about that. I said mechanical (A spinning prop being the mechanical force creating a vacuum because the flow cannot keep up with the pace, therefore reducing the pressure which produces bubbles). My point was, that there is, and always will be air in h2O! Anyhow, thx for more input :)

[Wim Libaers]

Thats what I said. Dunno how that chemical stuff comes up, I didnt say anyhting about that.

Actually, you did. Removing an oxygen atom from a water molecule would be a chemical reaction (one that isn't likely to happen though).

I said mechanical (A spinning prop being the mechanical force creating a vacuum because the flow cannot keep up with the pace, therefore reducing the pressure which produces bubbles). My point was, that there is, and always will be air in h2O! Anyhow, thx for more input :)

In water as it occurs in nature, yes (except perhaps in very hot springs), but it is possible to get the air out of water.

The "O" in H2O is not air, the air in water is just like the air we breathe, mostly nitrogen (N2) and oxygen (O2) plus some smaller amounts of other gases. This is dissolved in water, and goes out of solution when pressure is lowered or temperature raised. If you boil some water and see bubbles forming long before you reach the boiling point of water, that's dissolved air going out of solution. This is also the air that fish breathe (the O in H2O is not accessible for their metabolic mechanism), which explains why fish have problems in warm water: there is not enough dissolved air at elevated temperatures.

[LuftWolf]

Ok...let's not turn this into a flame war. Let cooler heads prevail until Jamie and/or Hutch addresses this issue.

Jamie and Hutch HAVE addressed this issue... it's called the Sound vs. Speed hotfix, which adds 5 Passive SL's to diesel/electrics and 10 Passive SL's to ALL nuke subs at top speed, regardless of make or max speed. :-?

It's going to take a lot of convincing and solid evidence for me to think that what Amizaur engineered for the current LWAMI is not a better modelling job than what is in DW 1.00 or DW 1.01HF or DW 1.02/3.

Perfect. No. Linear. Yes.

Specific for each platform in a sensible way that contributes significantly to a good gaming experience, you bet. :up:

So, it's not a finished product, and perhaps when we have more information about the thrust parameters, it can be made better, but what's in the mod now is a high fidelity and top quality database addition that makes DW a sigificantly better game and simulator, IMHO. ;) :)

[sonar732]

Ok...let's not turn this into a flame war. Let cooler heads prevail until Jamie and/or Hutch addresses this issue.

Jamie and Hutch HAVE addressed this issue... it's called the Sound vs. Speed hotfix, which adds 5 Passive SL's to diesel/electrics and 10 Passive SL's to ALL subs at top speed, regardless of make or max speed. :-?

It's going to take a lot of convincing and solid evidence for me to think that what Amizaur engineered for the currentl LWAMI is not a better modelling job and DW 1.00 or DW 1.01HF or DW 1.02/3.

Perfect. No. Linear. Yes.

Specific for each platform in a sensible way that contributes significantly to a good gaming experience, you bet. :up:

So, it's not a finished product, and perhaps when we have more information about the thrust parameters, it can be made better, but what's in the mod now is a high fidelity and top quality database addition, IMHO. ;) :)

By me saying let's let Jamie and Hutch address this is for them to explain the situation vrs. everyone who didn't write the code to go at each other's throats.

[LuftWolf]

Now everyone can see my typos. :shifty: :lol:

I'm not sure that's going to happen... but we can try. :up:

[LuftWolf]

OKO, I'm sorry but there is absolutely no increase of platform sound by speed in stock DW 1.0/1.01.

I have tried confirmation tests just now with the original database and it simply isn't there. (Not to mention the experience of many many players from the "early days")

In addition, if it were there, then the fundamental understanding of how the passive SL and thrust dialogues work in the DW modding community is fundamentally wrong.

I'm sorry, but stock DW 1.0/1.01 has no sound vs speed function at all.

[OKO]

So ... I don't know why I had this values ...
tested with all subs at that thime ...
anyway, as I already said, I don't care about older values, but about the new ones.
The debate is not to know if there was or not a sound gap on stock DW but to know why there is not on the actual values.

[moose1am]

Well I must agree ... here here! I am very new to this game but I have read over the last year all that I can find about how this game should work. I still have a lot to learn as this is a very complicated game if you really dig into everything. I found some information about sound layers and ocean environments and learned about layers, sound channels and how different ocean conditions Temp and Density caused by both temp and chemcial compostion of the water can effect the speed of sound waves. I use to play Subcommand a bit and tried to use the SSP buoy to figure out where the layers were located. I never really could figure out how the sonar worked in the different layers as I really didn't play the game very long.

But I sure am glad to see that someone is saying that the ocean environment is very important to determining how far or well you can hear an enemey ship in the distance on your passive and active sonar screens.

What we have is a lot of very important variables that effect sound wave propagations and that should effect the game play.

Depth and ocean bottom type are suppose to effect how the sound waves bounce around or change directions.

Being new to DW and even SC I sometimes wish that I could detect the enemy ships further away just to make the game more fun. When I first started playing Subcommand I went around never finding the enemy for long periods of time and finally tired of the game. I just put the game aside for a while but never forgot about it. I just told myself that I would get back to the game in the future. I just have so many other interests going on at this time that it's hard for me to dedicate too much time to this game. But time is what it takes to really learn this game.

I like the idea of reading the manual and or the tutorials and finding that the game works as described in the manual. As long as it's possible to figure out the game by reading how it's played I am going to be happy at this time. I like the idea of realism but I would not know what it real or not at this point in time. And as far as sound wave propagation most people have no idea on how it really works in the real ocean as it's not that easy to figure out. That is why this subject is classified in the real world.

I am just glad that someone said that there are lots more variables to this game that most people realize. We must not forget that when we complain about detection ranges so quickly. Not saying to stop complaining but to qualify your complaints with all the very important variables. Maybe there is a real reason why you can't detect somone out in the big blue ocean. From the deep blue to the litteral zones there are changing sea conditions that can effect what you can or can't hear.

Speaking as a layman and with respect to those who I suspect know far more in real life about this topic,
it simply amazes me the extent to which we all endlessly speculate about what real-life elements of sonar
performance are included in the sim. Unless and until SAS expand on their somewhat brief manual exposition
we are indulging in a rather pointless exercise. :yep:

Yeah... that's why I get really annoyed when people say things like, "the sonar ranges are too short [long]" and you never see anyone say what the SSP looked like, what season it was, what the seastate was, how deep the water was, etc.. The truth of the matter is that any estimate of sonar performance has to be qualified with an extensive description of the environmental conditions in which that performance was achieved.

Unfortunately, too often the only environmental qualification I see is that the detection took place in Tom Clancy land.

And if you really want to get into it, any good sonar model has to go hand-in-hand with a good global climatology.

In truth, outside of classified discussions, nobody really knows how good a given system will perform against a given target and that's how it should be.

[Molon Labe]

This started off pretty good, but this has gotten way off topic. I'm only asking about what sound propagation should be like in the real world and whether or not this is modeled well in 1.03. Specific performance characteristics of any sensor against any object is well outside the scope of this discussion. I doubt I'm asking for anything that's classified. :zzz:

I think all this off topic speculation has turned away the people who have the answers sought. :cry:

And thanks, Bill! That helps a bit. :up:

[SeaQueen]

The SSP effects are MASSIVE. It seems like even very loud sounds cannot be heard across the layer.

Are there any sonar experts that can comment on this? Thanks.

Whether sounds can be heard across a thermal layer depends on a lot of things.

In real life, even very strong ducts will leak energy. How much of that energy depends on things like the frequency of the sound. Sounds in the hundreds of hertz would require a surface duct so deep to be trapped that they simply don't occur. Even so, whether the energy leaked is enough to be detected depends on the sonar set, and how far away you are.

Also, as you get very close, you will receive direct path sound because the layer doesn't reflect sound as efficiently.

In real life there's also other interesting effects associated with fronts and eddy currents where sound leaks out of a surface duct because of changes in temperature across a front. A good example of where this sort of thing can occur is up around the Ryuku Islands northeast of Taiwan. There, the Kuroshio current spills lots of cold, salty, water over through the islands where it swishes around with the sub-tropical waters shallow waters on the shelf and all kinds of unpredictable things happen. These things have their biggest effect on medium and high frequency sounds.

So.... the answer to your question, in brief is "maybe, but not necessarily." Is this helpful?

[Molon Labe]

Yes, thank you.

[Hutch]

let me give you a very good link about it :

http://www.fas.org/man/dod-101/navy/docs/es310/SNR_PROP/snr_prop.htm

suggest you read that, than we continue talking about it
for our own culture and to know how to use it in DW

Figure 13 on that link is what's new in the patch. DW now traces that farthest-reaching ray that still penetrates the layer. Beyond that range, no detection. Up to that point, there's a slight range penalty for the curve of the ray, which usually results in a negligible signal loss. Note that those rays work in both directions- if you're hiding just above or below the layer, your cross-layer detections are going to be short.

[OKO]

very nice comments, Hutch.
We can see now strong effect on the sound propagation model.
experimented sub commander could take lots of advantage of this
thanx for this great improvment

On what you said, are we able to use the BD formula to find the shadow zone ?

http://www.fas.org/man/dod-101/navy/docs/es310/SNR_PROP/IMG00016.GIF
and
http://www.fas.org/man/dod-101/navy/docs/es310/SNR_PROP/IMG00017.GIF

?

[Driftwood]

EXCELLENT QUESTION OKO! I'm anxious to hear the answer to that! :up:

[compressioncut]

very nice comments, Hutch.
We can see now strong effect on the sound propagation model.
experimented sub commander could take lots of advantage of this
thanx for this great improvment

On what you said, are we able to use the BD formula to find the shadow zone ?

http://www.fas.org/man/dod-101/navy/docs/es310/SNR_PROP/IMG00016.GIF
and
http://www.fas.org/man/dod-101/navy/docs/es310/SNR_PROP/IMG00017.GIF

?

I don't mean to sound flippant but those formulas are painfully out of date, particularly if you are sub up against a towed array ship. The array can be placed anywhere in the water column.

Moreover, why would a sub captain want to do exactly what can be easily predicted? "Alright the layer depth is 70 meters, lets put the sub at 130m! The skimmers will never expect that!"

Presumably, it might work just fine against AI units.

[Angle]

Well, did some testing with seastate 3(or 2. forgot), month june, surface duct, or convergence zone settings. Middle of the atlantic. Seawolf vs cargo ships starting 10miles apart.

Looks like the layer is just an adjustable "hard cap" on the sensor detection range. Kind of like detecting a cavitating ship back in SC(SCX) with the hull array. It would just pop up when it entered the threshold range.

What got my attention was playing the FFG. Noticed that dropping the towed array below a layer had no affect on ownship's SNR on the broadband. So i wondered if range+layer would degrade SNR or just cut it off. It seems to be a cutoff.

[Driftwood]

What about active sonar? Any testing done on that? Sure would be helpful to us bubbleheads when going up against a P3.

[Kazuaki Shimazaki II]

I don't mean to sound flippant but those formulas are painfully out of date, particularly if you are sub up against a towed array ship. The array can be placed anywhere in the water column.

Moreover, why would a sub captain want to do exactly what can be easily predicted? "Alright the layer depth is 70 meters, lets put the sub at 130m! The skimmers will never expect that!"

Presumably, it might work just fine against AI units.

I would think that actually a Captain will do exactly that. Tactics are dominated by Physics as much as by Psychology, if not more. If by going at 130m, he has a reasonable assurance that the enemy won't detect him, that's exactly the depth he'd be at.

The enemy may also KNOW that any sub coming in at him will be coming in at 130m, but if he can't arrange for that layer to be scanned, the sub still wins. In fact, a plan that relies on a Physical Factor like this may well be more reliable than one that's based on Psychology - second guessing the enemy and hoping he won't think of what I'm thinking and come up with counters.

By having a superior intuition of the physics involved in a situation, a commander gains the advantage.

[LuftWolf]

Well, did some testing with seastate 3(or 2. forgot), month june, surface duct, or convergence zone settings. Middle of the atlantic. Seawolf vs cargo ships starting 10miles apart.

Looks like the layer is just an adjustable "hard cap" on the sensor detection range. Kind of like detecting a cavitating ship back in SC(SCX) with the hull array. It would just pop up when it entered the threshold range.

What got my attention was playing the FFG. Noticed that dropping the towed array below a layer had no affect on ownship's SNR on the broadband. So i wondered if range+layer would degrade SNR or just cut it off. It seems to be a cutoff.

The modelling of the sonar in 1.03 is fairly complicated. The behavior can be seen in a many different ways.

What you get in one case may not at all be like in another case.

Generally speaking it is more like what you read in the publically available sonar literature with two features that have been simplified so that it can run on a PC without dragging down the processor (the sound modelling being done in the acoustics engine takes up a significant amount of processor resources as it is modelled now): it is a single path model, meaning that all frequencies from the same contact travel along a single path rather than their path being frequency dependent; the shadow zones are rather stryking so sometimes contacts will completely cut out rather than fade away. I'm not sure whether this is realistic but it seems there would be some beam spreading in real life that is not modelled.

All of these features vary greatly by environment along all of the parameters that can be set in the mission editor.

[MaHuJa]

The figure Hutch mentioned:
http://www.fas.org/man/dod-101/navy/docs/es310/SNR_PROP/IMG00015.GIF

...does make me wonder about one thing - generally speaking you could say that it's "how far between the lines"* that says how much of the sound reaches that point. In the illustration, looking at two places, right above the sub, and the place where the drawn line 'touches' the layer, it seems that right above the layer has far more distance between the lines (which should correspond to weaker sound)

*(This example should of course be done with far more lines, and make sure the 'start angle' of each was the previous +n, )

What I'm trying to say, is that based on what I've read about it, the sound should get weaker until at the layer it's completely faded, instead of being full power until the layer instantly cuts it off.

I have, however, not really that much of a clue on how the reality of it is. But if I'm wrong, then I'd like to know how my theory is off.

[LuftWolf]

What I'm trying to say, is that based on what I've read about it, the sound should get weaker until at the layer it's completely faded, instead of being full power until the layer instantly cuts it off.

I think you're right MaHuJa, it's just that modelling that in DW probably would have taken up too much of the system resources to do properly. According to the developers, there is a lot going on in the background for the sound propagation modeling as it stands now.