Talk:Supercavitation
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[edit] Units
Should not SI units (m/s) be used as primary units and imperial units (mph) be enclosed in parentheses? Having m/s there is good. In as international project as this, usage of non standard mile and feet measures should be avoided. I'd be better to use only SI units or at least special units such as knots when talking about ships and torpedoes.
SI units should be used, with mph AND knots attached in paranthesis. Logic for this follows as, generally it would be nice if [everyone] used SI units, so to accomplish that it should be the primary units. mph and Knots should be included for those people who have no frame of reference of SI, colleges and most highschools in the United States teach SI units in they're phyiscs, chemisty, (but not in they're engineering classes...) classes. Even so, I still don't have a proper perspective on how fast 120km/h really is, and less so on m/s. Thus common alternate measurements should be included to give perspective. --ORBIT 20:42, 6 Feb 2005 (UTC) (ooops forgot a sig)
The article keeps on saying that the objects are entirely enveloped in a bubble. Doesn't the nose have to be touching water, though? And if it is, then isn't it not entirely enveloped? --69.214.226.102 15:56, 6 May 2005 (UTC)
No, it is entirly inside of a bubble. As I understand it, the nose cone has gas ejectors that effectively "blow" the bubble bigger once supercav has been reached. Please correct me if I'm wrong. --The Singularity 22:38, 9 October 2005 (UTC)
It's not necessarily completely enveloped. What you're referring to is a ventilated supercavity, but supercavitation may occur without ventilation at the proper conditions. Axda0002 16:30, 19 May 2006 (UTC)
[edit] Supercavitation used for racing
The supercavitation principle has been used for high performance racing boats for a long time. Model racing boats uses supercavitation or alternatively surface piercing exclusively, both for propellers and rudders. The "Squall" is the 1st underwater vessel to use this principle. -- Egil 07:17, 23 January 2006 (UTC)
[edit] German supercavitation
I'm going to need to see some kind of source cited (claiming that it's actually supercavitation) on this one ( http://en.wikipedia.org/w/index.php?title=Supercavitation&diff=56229956&oldid=55030731 ) - the Battleships (Japanese / German ?) guns used shells that dived under the water and curved upward to stike from underwater - they were far earlier than this. Megapixie 00:25, 1 June 2006 (UTC)
Your above description of gun shells would apply to the German Henschel Hs 293 C air-to-sea anti-ship missile and its improved follow-up version Hs 294. But I don't know if any gun shells with features and characteristics like that were in use during WWII. —The preceding unsigned comment was added by 212.144.129.254 (talk • contribs) .
- My point is that according to that definition of supercavitation - ANY weapon hitting the water at high speed could be supposed to be a supercavitation weapon. What about airplane dropped depth charges ?
- I don't believe that supercavitation was an intended part of the design of the Hs 293 C any more than it is of a battleship shell striking the water, or a general purpose bomb being used in skip bombing, or an airplane dropping depth charges. Megapixie 08:28, 24 July 2006 (UTC)
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- The IJN designed their shells with predictable underwater ballistics. I don't recall their rationale... See Peattie & Evans, Kaigun. Trekphiler 23:28, 28 February 2007 (UTC)
[edit] Russian underwater firearms
The line that says the russian underwater firearms do not supercavitate is incorrect- they do in fact supercavitate. It seems that the only information that they don't is that a few websites describe them as "drag stabilized", which doesn't mean they are not supercavitating as well. "drag stabilized" just means that stability is achieved by pulling back on the back, instead of pushing in on the sides. The stability of these is actually a complicated subject, but it will suffice to say that it gets stability from both "lift" and drag (from tail slap mostly, but also from the flat nose)
There is also information on the web saying they do supercavitate.
"Russian rifle ammunition using supercavitation for underwater use I have come across some mentions that the Russian APS underwater rifle uses supercavitating ammunition :
http://world.guns.ru/assault/as69-e.htm.
The APS is designed for special underwater cartridges, which fire 5.66 mm needle-like projectiles 120 mm long. The projectiles are stabilized using a hydrodynamic cavity, generated by the flat point of the projectile. The cartridges use standard 5.45 x 39 cases, sealed from water." http://72.14.253.104/search?q=cache:PwwmQ2YapTEJ:www.grosswildjagd.de/fundamen.htm+underwater+rifle+aps+supercavitation&hl=en&gl=us&ct=clnk&cd=7
"Soviet engineers worked on supercavitation in the 60ths. At the end of the decade O.P. Kravchenko and P.F. Sazonov have developed underwater ammunition (4.5X40 mm and 5.66X49 mm) that utilized that principle. For this ammunition the Central Institute for Precision Machine building made a underwater pistol and an assault rifle called SPP-1 and APS. " http://72.14.253.104/search?q=cache:7YBWh1Vt298J:www.stormfront.org/forum/showthread.php%3Fp%3D2866434+underwater+rifle+aps+supercavitation&hl=en&gl=us&ct=clnk&cd=1
If that is not enough evidence, I can run the numbers for you. Notice the flat tip? That is a cavitator.
The empirical equations (which can be found online in different forms, such as http://cav2003.me.es.osaka-u.ac.jp/Cav2003/Papers/Cav03-GS-6-006.pdf#search=%22supercavitation%22) show that it does infact produce a supercavity.
Cavity radius = Cavitator radius * SQRT(Cd/Cavitation number) Cavity length = Cavitator radius * SQRT(Cd*ln(1/cavitation number))/cavitation number
Cavitation number = Pressure/(0.5*density*velocity^2) Cd (drag coefficient) for a flat disk is ~0.82
If you run the numbers (Cd = 0.82, Pressure = 101kpa, Density = 1030kg/m^3, 250m/s, Cavitator radius 2mm), you will find that the initial cavity length is about 0.7 meters near the surface, which is > 0.12meters, which is the projectile length, with a 16mm maximum radius, which is >> 2.83mm, which is the projectile radius. This means the whole projectile is in the cavity.
I got those equation from Professor Emeritus Marshall Tulin (the guy that developed the theory of supercavitation in the 60s), when I met with him this week to discuss supercavitating projectiles such as these. It was clear to him as well that they are supercavitating, although he had not heard of the weapons before.
If you run numbers assuming it is not supercavitating, you will realise the reported ranges are not possible. The drag coefficient would have to be as low as 0.07 to get as far as they claim to at 5m depth and still retain 30% of the speed. 0.07 is not a reasonable number for a dart like this when not supercavitating. This approach does not explain the depth dependence on range, which is more evidence that it is faulty. Here's how I calculated the distance constant (velocity decays exponentially with distance) http://www.google.com/search?hl=en&lr=&q=1%2F%28%28%285.66mm%2F2%29%5E2*pi*.07*.5*1030kg%2Fm%5E3%29%2F26grams%29&btnG=Search
It's also worth noting that the dart would not be stable if it were not cavitating at all, or only cavitating off the back. The center of mass is roughly 1/2 chord, while the center of pressure is at 1/4 chord, which makes it unstable. If you're claiming the cavity coming off the back "drag stabilizes" it, you would be wrong. The pressure (or lack thereof) pushes normal to the surface, which is through the cg, leaving you with no stabilizing moment"
More on the subject of stability: "The pressure distribution on the disc cavitator is actually slightly stabilizing" - Marshall Tulin. Of course, this only applies to supercavitators.
If there is a way of upoading pictures for the talk page, I can show pictures of simulation, and graphs of closed form equations that predict the supercavitation (including the distance/depth curves, and just about anything else you need to know) of these projectiles.
Change it back.
---Jimmy
- The initial edit was my mistake, I should have been more careful, thanks for the correction, and information.--Sukisuki 22:06, 27 October 2006 (UTC)
[edit] Underwater Express program and supercavitation
General Dynamics, Electric Boat, Corp., Groton, Conn.,is being awarded a $5,748,078 cost-plus-fixed-fee contract for research and development to support the Underwater Express program to demonstrate stable and controllable high-speed underwater transport through supercavitation. This effort will help determine the feasibility of supercavitation technology to enable a new class of high-speed underwater craft for future littoral missions that could involve the transport of high-value cargo and/or small units of personnel. This contract contains two options, which if exercised, would bring the cumulative potential value of this contract to $37,105,768.Work will be performed in State College, Pa. (37 percent); Groton, Conn.(24 percent); McLean, Va.(14 percent); Reston, Va. (10 percent); Bethesda, Md. (12 percent); and Newport, R.I. (3 percent), and is expected to be completed October 2007.Contract funds in the amount of $3,377,441 will expire at the end of the current fiscal year. This contract is being awarded under a Defense Advanced Research Projects Agency (DARPA) Broad Area Announcement (BAA) (No. 06-13), which solicited proposals via the Federal Business Opportunities website, for advanced research and development under the provisions of FAR 6.102(d)(2) and FAR 35. In accordance with the criteria of the BAA, the General Dynamics, Electric Boat, Corp., proposal was evaluated by DARPA through the process of peer and scientific review. The Space and Naval Warfare Systems Center, San Diego, Calif., is the contracting activity (N66001-07-C-2002).
[edit] Tactical theory
I have a problem with the evident bias against supercavitators in the discussion. "Time enough to avoid"? I'm far from convinced one minute is enough for a ship to change direction. I can't help recall WW2 boats with much slower, noisy, wake-producing torpedoes successfully sinking even destroyers. I picture spreads of three or four supercavitators, fired close in, possibly in conjunction with noisemakers or autonomous decoys. Additionally, the critic seems to assume supercavitators will never be quieter, or able to be launched silently. Unfortunately, I'm insufficiently up to date on the state of the art today to correct it. Trekphiler 23:40, 28 February 2007 (UTC)
If you're referring to the "Drawbacks" section, then I also believe there's a heavy bias in it. It makes good mention of the guidance of American torpedoes as its main argument, however, I firmly remember reading that Germany's Barracuda supercavitating torpedo as well as Russia's new variant of the Shkvall, had guidance systems as well. Also, the section mentions many "unconfirmed" figures in its calculations. This quote I've found: "Already having underdone a whole range of successful tests, the designers of Barracuda boast that its capabilities are unmatched, claiming the design is 10 years ahead of American and Russian efforts. It is claimed the Barracuda is maneuverable enough even to home in on, and knock out an incoming Shkval!", which is based on the claim of the makers of the Barracuda, I believe has just as much merit as the types of figures claimed in the section.
- Looks to me as if the writer is in the grip of the guided torpedo lobby. Still. Trekphiler 00:01, 3 April 2007 (UTC)
The problem with that is that the Barracuda and Shkvall II are reported to be guided. Not only that, but the fact that both the U.S. and Germany have interest in supercavitation means that the entire second half of the section is basically false.
