Trans Atlantic Tunnel?

"Currents, waves, buoyancy ... are something which the Archimedes ( submerged ) bridge can handle via adjusting its waving with the external forces, even utilizing them ..."

And how would you be adjusting the waving of the tunnel? I suggest any answer must first carefully and clearly specifiy how the tunnel is actually constructed and just how rigid, flexible or articulated it would be as there is a variety of structures that different people seem to be talking about, with very different characteristics.
 
Returning to the problem of generating a vacuum again, what level of vacuum are we talking about here? I am not a vacuum expert like pdf27 but I have several years experience of working with them. Getting down below 1mm Hg of pressure is quite easy, a simple rotary pump does the job cheaply and efficiently. But going down to the ultravacuum level, which is what I assume some people are talking about, is much more difficult. At such low pressures you essentially require gas molecules to randomly move out of the chamber and that is a statistical exercise i.e. it takes time and there's not much you can do to speed the process up. A colleague of mine has a high vacuum chamber of about a cubic meter in volume that takes 6+ hours to evacuate when all is working well.
The system I work on is around 300 cubic metres and borderline ultra high vacuum. It takes us around two months to get it down to this pressure from atmospheric pressure, and we have a team of about 6 working full time on it to maintain these pressures. It'd be a bit easier with a simpler system, but because you're proposing a system with seawater on the outside and vacuum on the inside this is emphatically NOT a simple system. To be honest I can't see any way this could practically have leaks found except by people walking around inside it in space suits looking for salt deposits/steam. Fixing it is going to be a nightmare too - you're essentially going to have to do it from the outside using some sort of mini submarine with an airlock on it to let repair work be carried out from the outside.

In reality I think you're limited to about 700 mbar or so due to the requirement to keep water liquid and allow safe access to the tunnels in an emergency (that's slightly lower pressure than inside a commercial airliner, but not excessively so - and that'll probably be the regulatory limit you have to work to). Given the suggested bullet-in-a-barrel maglev design, you're going to have to have cross-tunnels every hundred metres or so just to let the air get out from in front of the train.
 
Since it's a maglev and all cars are motor cars (true?), i'm thinking you could send the cars in such frequency that their vibracions interfere destructively with each other, resulting in a zero net vibration caused by the train.
You still have to deal with the weight of the train, which I figure will not be less than several hundred tons.

Ugh... 30m is around 4 atm.... less than 6, but it's still quite a bit of pressure.
30m is the absolute minimum distance to avoid shipping (I don't know about weather), and for safety's sake I'd want it a bit more, below where a guy in a scuba-suit could get to.

I think the only reasonable depth consideration is to avoid being obstacle for ship traffic.

Currents, waves, buoyancy ... are something which the Archimedes ( submerged ) bridge can handle via adjusting its waving with the external forces, even utilizing them ...
WTF are you talking about?

Come to think of it, where does the 6m width figure for the tunnel come from?
I figure 6m is about the minimum needed to allow a pair of 1973 Tube Stock (London Underground) trains to pass each other. That is, I figure the minimum, bare-bones size any tube could be, and makes no account for any sort of safety measures.

So, do you really need a vacuum-filled tunnel because I don't see how it can work?
Without vacuum what the fastest you could go, a few hundred kph? The emptier the vacuum the faster it can go. Mind you, the emptier the vacuum, the more engineering issues you have as well.

One way (maybe) to do away with the issue of joints is to print the tunnel on a 3D printer hung in water below a big ship (think, Maersk E-Class big) like an old America's cup monohull with the bulb on the end of the keel. This of course presents its own problems, like time, if you're printing at 1mm/second you're making 86.4m/day, at which point a 4,900 km tunnel is going to take you 155 years to complete. Jointless tunnel though :D.
 
Without vacuum what the fastest you could go, a few hundred kph? The emptier the vacuum the faster it can go. Mind you, the emptier the vacuum, the more engineering issues you have as well.
I would think a millibar or so should work fine. No need for a high grade vacuum, just one good enough to massively reduce air resistance.
One way (maybe) to do away with the issue of joints is to print the tunnel on a 3D printer hung in water below a big ship (think, Maersk E-Class big) like an old America's cup monohull with the bulb on the end of the keel. This of course presents its own problems, like time, if you're printing at 1mm/second you're making 86.4m/day, at which point a 4,900 km tunnel is going to take you 155 years to complete. Jointless tunnel though :D.
Except you need those joints for allowing for continental drift, for instance. Of course, you don't really need the thousands of joints that building it in sections would require.
 
I would think a millibar or so should work fine. No need for a high grade vacuum, just one good enough to massively reduce air resistance.
Down to a millibar you're going to get all sorts of problems with outgassing and with water evaporating. You get away from some of the problems (more complicated pumps, conductance, etc.) but not the worst ones.

Except you need those joints for allowing for continental drift, for instance. Of course, you don't really need the thousands of joints that building it in sections would require.
If you're only allowing for continental drift, tides, etc. then there is no reason that the expansion joint has to be underwater. The easiest way is probably a sliding tunnel section where it comes out of the water - shifting it a few cm is quite easy on land, a nightmare underwater.
 
Down to a millibar you're going to get all sorts of problems with outgassing and with water evaporating. You get away from some of the problems (more complicated pumps, conductance, etc.) but not the worst ones.
Very true. I was addressing your earlier comment
The system I work on is around 300 cubic metres and borderline ultra high vacuum. It takes us around two months to get it down to this pressure from atmospheric pressure, and we have a team of about 6 working full time on it to maintain these pressures.
and pointing out that even low vacuum should work fine. 'work fine' being relative, of course. Yes, there will be weird stuff with outgassing, and your going to have to have LOTS of pumps.
If you're only allowing for continental drift, tides, etc. then there is no reason that the expansion joint has to be underwater. The easiest way is probably a sliding tunnel section where it comes out of the water - shifting it a few cm is quite easy on land, a nightmare underwater.
Oh. Very good. For some reason, that didn't occur to me. But, yes that would make a LOT of sense.
 
If what we need is to increase the speed by a factor 10, seeing how air resistence increases with the square of the speed and is linear with the air density, we might only need to reduce the atmospheric pressure to 1%, that's to 10 mbar. How much easier would be 10 mbars to obtain than 1 mbar?
 
If what we need is to increase the speed by a factor 10, seeing how air resistence increases with the square of the speed and is linear with the air density, we might only need to reduce the atmospheric pressure to 1%, that's to 10 mbar. How much easier would be 10 mbars to obtain than 1 mbar?
In pumping terms, there really isn't any difference - you use the same technology. Higher acceptable pressures **might** let you get away with fewer pumps (would if it were a vacuum vessel in air, in water it will critically depend on the temperature being as you're above the triple point). If the tunnel goes above about 3 deg C then it won't help at all, if you can keep it cooler then it might.
 
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