3 ms·

> 1 bar is acutally not that bad. That does not mean anything. The weight of a 1 cm² column of air is 1 kg. So 1 ton for 1 m². Let's say a square profile hype

> 1 bar is acutally not that bad. That does not mean anything. The weight of a 1 cm² column of air is 1 kg. So 1 ton for 1 m². Let's say a square profile hyperloop tunnel 1 m high decompressing will be the equivalent of dropping one tonne for each meter. The shock will propagate at the speed of sound.

j-pb 6y ago
You neglect the friction that even laminar flow would experience while flowing into the tube. If you make small fins at the top of the tube you can even exagerate the effect and introduce turbulence, which further reduces flow rate. There is a reason why pipelines need pumping stations every couple miles, to keep the fluid at speed. Sure the wave might propagate at the speed of sound but that doesn't matter much if its pressure gradient is slow enough. https://en.m.wikipedia.org/wiki/Hagen–Poiseuille_equation#Poiseuille's_equation_for_an_ideal_isothermal_gas https://en.m.wikipedia.org/wiki/Hagen–Poiseuille_equation#Po... Edit: To give a good analogy: Electricity also travels at the speed of light through a cable, however due to resistance you will get different current reading depending on where you measure. Edit2: I reread your argument, and there is also a flaw in your energy calculation. The energy per time is not proportional to the length of the tunnel, but proportional to the size of the inlet. Your calculation would be if you remove the entire top of the tunnel at once, over it's entire length.
- himinlomax 6y ago
  Turbulence in a near vacuum? I'm more than rusty on my statistical mechanics, but what you describe will only matter long after most of the potential energy has done its damage.
  - j-pb 6y ago
    Don't look at the wavefront of the first 100m, the pod there is gone anyways in case of a bomb. Turbulence on the phase of what comes after the near vacuum. The plug essentially plugs itself from resticted airflow. If you want to be extra safe you could even add small tesla valve style fins around the border of the tube, to increase turbulence.
  - himinlomax 6y ago
    What about what's right outside the damn pipe? Or do you plan on laying said pipes only in the desert?

j-pb 6y ago

You neglect the friction that even laminar flow would experience while flowing into the tube. If you make small fins at the top of the tube you can even exagerate the effect and introduce turbulence, which further reduces flow rate. There is a reason why pipelines need pumping stations every couple miles, to keep the fluid at speed. Sure the wave might propagate at the speed of sound but that doesn't matter much if its pressure gradient is slow enough. https://en.m.wikipedia.org/wiki/Hagen–Poiseuille_equation#Poiseuille's_equation_for_an_ideal_isothermal_gas https://en.m.wikipedia.org/wiki/Hagen–Poiseuille_equation#Po... Edit: To give a good analogy: Electricity also travels at the speed of light through a cable, however due to resistance you will get different current reading depending on where you measure. Edit2: I reread your argument, and there is also a flaw in your energy calculation. The energy per time is not proportional to the length of the tunnel, but proportional to the size of the inlet. Your calculation would be if you remove the entire top of the tunnel at once, over it's entire length.

himinlomax 6y ago
Turbulence in a near vacuum? I'm more than rusty on my statistical mechanics, but what you describe will only matter long after most of the potential energy has done its damage.
- j-pb 6y ago
  Don't look at the wavefront of the first 100m, the pod there is gone anyways in case of a bomb. Turbulence on the phase of what comes after the near vacuum. The plug essentially plugs itself from resticted airflow. If you want to be extra safe you could even add small tesla valve style fins around the border of the tube, to increase turbulence.
- himinlomax 6y ago
  What about what's right outside the damn pipe? Or do you plan on laying said pipes only in the desert?