![]() |
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. |
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. |
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 ... |
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/...urbulence.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: |
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: Quote:
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: |
Quote:
So what OKO sais makes alot of sense to me. |
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. |
Quote:
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) |
Quote:
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. |
Ok...let's not turn this into a flame war. Let cooler heads prevail until Jamie and/or Hutch addresses this issue.
|
Quote:
|
Quote:
Quote:
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. |
Quote:
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. ;) :) |
Quote:
|
Now everyone can see my typos. :shifty: :lol:
I'm not sure that's going to happen... but we can try. :up: |
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. |
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. |
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. Quote:
|
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: |
Quote:
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? |
All times are GMT -5. The time now is 10:35 PM. |
Powered by vBulletin® Version 3.8.11
Copyright ©2000 - 2025, Jelsoft Enterprises Ltd.
Copyright © 1995- 2025 Subsim®
"Subsim" is a registered trademark, all rights reserved.