How can I determine velocity inside a steel pipe?

Question

An object traveling inside a steel pipe needs to know its velocity. How can it measure its velocity without placing anything (like a wheel) in contact with the pipe?

Edit: joe g - The object itself needs to know its velocity, not an external observer. And yes, the pipe is very long. Thank you for your effort.

Answer 1

Interesting question! Some ideas that come to mind:

1. If there is still air in the pipe, you can measure the air speed of the object by attaching an anemometer to it. This is not so good if the object is big enough relative to the pipe cross section to move a significant volume of air as it passes.

2. Use an accelerometer and measure the acceleration over known periods of time relative to a known velocity (e.g., v=0 before you start moving).

3. Use an external positioning system (e.g., GPS) to measure position at a known interval of time to compute velocity.

4. Use a doppler measurement of apparent speed - probably doppler radar would work well with a steel pipe. This would require some experimentation to calibrate your measurement system, due to the fact that the reflected energy would be at an angle to the velocity vector of interest. You would need to do some experimentation to determine the typical cosine error that you observe in the doppler measurements.

5. If the the pipe is at a known angle from horizontal (and the angle is not equal to zero), then you could measure differences in atmospheric pressure over a known period of time. This will give you the vertical portion of the velocity vector - it is trivial to compute the velocity vector using trigonometry.

Answer 2

use a sonic velocity probe at one end of the pipe to measure the speed of the object inside, unless you are talking about a really long pipe in which this would not be practice, or a pipe closed on each end.