And I can't believe there is THIS kind of exchange going on on a movie message board!
LMAO!
You should look up the thread concerning Submarine operating procedures and the long arguments over just what property of physics is responsible for bouyancy and how a Sub maintains its bouyancy.
After an exhaustive argument about what actually bouyancy is and is not and in cases quoting directly from US Navy official manuals, there were still idiots insisting that bouyancy was due to density. They argued that you change the density of the sub to make it rise or sink. Density has nothing to do with bouyancy other than in an incidental and indirect fashion.
You don't change the density of the sub, you change the amount of water displaced by the sub.
Also I guess you must be new because these "movie" message boards are not exclusive to talking ONLY about a specific movie. Often people who are regulars here come on here to discuss the topics the movie is about, not the movie itself.
Wanna discuss WW2 in Europe? Go the the "Saving Pvt Ryan" message board.
Wanna talk consiracy theories? Go to the "United 93" or "World Trade Center" boards.
Wanna talk NASA and the space program? got to the "Apollo 13" boards.
Wanna talk about Subs? Go to "Das Boot","Run Silent Run Deep","Red October","Crimson Tide", "Down Periscope", or any other number of boards.
Technical details of US Depth Charges of WW2.
http://www.hnsa.org/doc/depthcharge6/index.htmAnd so sorry but you are wrong in your post.
Just like the guys that kept arguing that it is DENSITY that you must change, you get the principle right but you misread the cause.
You are right when you talk of a reintrant jet, etc.. but wrong in calling it cavitation. It is the collapse of the bubble and the re-intrant jet as you call it that causes the damage but cavitation has nothing to do with it.
Underwater detonations SUPERFICIALLY resemble cavitation bubbles when the bubble created collapses. But they are NOT the same thing.
Cavitation bubbles form because of a region of low pressure creates a vacuum bubble which then collapses when the bubble moves out of the low pressure region.
The bubble from an explosive blast forms because of the high pressure shockwave, then collapse as the pressure moves outwards leaving the low pressure bubble behind.
The effects of underwater explosions, such as that generated by torpedoes or mines, are much more devastating than a similar explosion in air. Over the last decade a numerical code on underwater explosion and bubble dynamics has been jointly developed by faculties at the Department of Mechanical Engineering, NUS, and researchers from the Institute of High Performance Computing (IHPC), to understand better the underwater explosion phenomenon and its devastating effects.
Figure 1 gives an example of the detailed results of our simulation run. Figure 1(a)shows an explosion which takes place near a flat vertical immobile solid plate. A bubble forms at the epicentre of the explosion (Figure 1(b)which grows very rapidly to its maximum volume. It then collapses rapidly while moving towards the plate. At the same time, a high-speed jet is formed, propagating though the collapsing bubble. A very high pressure is generated on the plate as the jet impacts on the other side of the bubble, while the bubble continues to contract until it reaches its minimum volume. In Figure 1(j),the bubble starts re-expanding again and the process repeats itself despite the much lower expansion and implosion energies.
The potential devastating effect of an underwater explosion on a ship is shown in Figure 2.At the moment of explosion, a shock wave propagates through the water (in a few milliseconds). This shock wave will have a first damaging impact on the ship body (Figure 2(a)).This figure also shows the creation of a bubble at the epicentre of the explosion. The high pressure gas bubble expands very rapidly. At the same time, the ship will bend upwards and its hull is weakened (Figure 2(b)).After reaching its maximum volume, the bubble collapses eventually due to the effect of inertia. The pressure will now be lower than the surrounding reference pressure, causing the ship body to bend downwards (Figure 2(c)).During this collapse phase the bubble is attracted to the ship body. In the final phase of the collapse, a high-speed jet is formed. This high-speed jet can easily cut through the ship body. This mechanism has been identified as being a second cause of damage (and probably even the most devastating one) that appears during an underwater explosion (Figure 2(d)).After the bubble has reached its second minimum a similar cycle can begin. However, as the bubble has lost much of its energy, the following oscillations will not have as great destructive power in general.
Some small-scale experiments have been carried out and were compared successfully with the obtained numerical results like in Figure 1.The validated code can be applied to other relevant engineering problems, for example, in cavitation on ship propellers (where tiny vapour bubbles can cause a lot of damage on these propellers) or in medical applications. The method of imploding micro-bubbles with ultrasound in biological flows to remove kidney stone or growth is also based
on the same physics, but on a much smaller scale of course. This research is carried out in collaboration with Assoc Prof Yeo Khoon Seng of ME Department and IHPC (Institute of High Performance Computing).
http://www.eng.nus.edu.sg/EResnews/0306/rd/rd_12.htmlAnd here is a popular video demonstrating the effect on a surface vessel just as is shown in figure 2.
http://www.youtube.com/watch?v=RV8MF-440xgand here is aillustration of the effect against a Submarine as in thwe case of Depth Charges.
http://www.fas.org/man/dod-101/navy/docs/es310/uw_wpns/IMG00003.GIFI joined the Navy to see the world, only to discover the world is 2/3 water!
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