If so, could you help me with the following problem? I got into a discussion about submarine escape systems and we got into this interesting idea: A sphere of two (three, four) meters diameter is submerged at 20.000 feet under water. Inside is normal atmospheric pressure. If this sphere was to be released from its constraints, at which speed would it emerge from the water? How high would be the maximum acceleration?
does the atmospheric pressure inside really matter as opposed to it's overall density compared to the surrounding water? wouldn't that in turn depend large parts on the material that composes the spheres? would it be comparable to the following situation?; take a balloon of air and a rubber ball into a pool, the balloon will more or less have the density of the air you put in. the rubber ball is much more dense but not as much as the water. submerge the balloon and release it, it will shoot out. take the rubber ball, it will float up much slower. keeping the escape sphere and the entire submarine at normal pressure does mean you can rise quickly without possibly dieing because of the gasses in the blood expanding. good idea that.
I know what would happen roughly, but I want to know whether the parameters would reach dangerous levels. The air pressure is equivalent to the density; the density of a gas is described by its pressure. Since the sphere would have to be incompressible - after all there are people inside - the density of the sphere would remain constant throughout the travel. The sad thing is, I have no idea how to describe the mathematic problem and my even-more-geeky friend is currently not online ...
yes I know it would remain constant but unless it's just an air bubble there'd be some other form of material involved. unless the word "escape vehicle" and "bubble of air escaping from this hatch I oppened"( the escaping bubble would obviously not be constant btw) now mean the same thing. then you need to make the entire thing have the density to just float on the surface. then you need to make sure that the materials you use can actually handle the pressure and still be light enough to have that density. I'd worry about those things before considering if the occupants might need helmets or cushioned interiors.
The outer hull could be negligible. Any density between water and lighter-than-air is enough to swim. Such spheres exist (guess how Picard got down there, huh). The frustrating thing is, without engineering knowledge I can't give any numbers.
I know they exist but I was under the impression that bathyscaphes and spheres and miniature subs had very slow and controlled de- and ascends... and also I'm a student of applied biology so this is outside my field of study. also instead of having weights and ballast tanks to controll the ascend I was under the impression that your escape vehicle would just naturally float and the problem was the speed at wich it would go or rather, how quickly it would slow. and if such an ascend would smash open craniums and perhaps cause back problems.
Yeah, thats why I asked for the acceleration. Over a few g it would become unhealthy ... Until it eventually becomes body retrieval instead of escape capsule
wich is why I was wondering about the density of the entire vehicle instead of its internal pressure, the entire last 7 posts have been the result of a miscommunication. anyways I don't know is my awnser
submarines can perform rapid assents yes? surely some geek sight has info on outdated submarines and that might be used to estimate how your sphere would perform.
yeah if the cabin is kept presurized at the same level troughout then it shouldn't kill anyone THAT way. problem is the capsules go up, but how fast and will that, at the end kill the occupants or not?
I didn't learnt physics in english, so maybe I'm missing some conventions The acceleration comes from arquimedes' principle and gravity so you have: a=-g(sphere mass)+(water density)(volume of the sphere)(g) --> This would be the maximum acceleration ever, taking everything at the bottom if you want to consider water compressible. After the movement begins, the friction comes into play, fortunately for you, Stokes already made a formula for friction on spheres in viscous fluids: Friction=6*pi*radius*Water's viscosity*sphere's speed At some moment, if the sphere is deep enough, the speed will be enough and the friction force will equal the normal acceleration and the sphere will move at constant speed from that point. Equaling a to friction will give you terminal speed (given that there's enough water to reach that speed, I guess there is) This is of course assuming a sphere able to endure the pressure (that's a problem). I hope this helps you. Also, never again use imperial units please.
Haha, I only did so because an american construed the problem, when I discussed it with my friends we quickly switched to 14.000 meters
this is excellent. If you love someone (United States and burma/myanmar) don't try to change them, even if they are ridiculous
Nicer: {Dx= x's density; Vx= x's viscosity} Frictionless acceleration A= g*4/3*pi*r*(Dw-Ds) Friction force F= -6*pi*r*Vw*s Terminal Speed St= 2*g*(Dw-Ds)/9*Vw
Looks good. Wouldn't the water's viscosity reduce as the water becomes less dense? Wouldn't this cause the sphere to accelerate slightly until breach point? I got mid level marks in the few physics courses I took on my way to a Bio degree, so I am far from an expert. Also, It would be so nice if the world would just embrace SI. http://upload.wikimedia.org/wikipedia/commons/c/c8/English_length_units_graph.png I chortled when I saw that 2 hands is = 1 shaftment.
According to that article, (that I just read), viscosity in liquids is independent from pressure and density (because liquids compress too little, almost nothing) but they vary heavily with temperature so it does matter. But sea temperature charts are weird: Because water's density is weird also: But you can see that most of the deep sea will be between 5 and 10 degrees celsius so it's not much variation for most of the travel.
I prefer it this way because sometimes you need fish to survive winters by staying in the dense part of a pond.
