Biomedical Engineering Reference
In-Depth Information
period is approximately T=0.018 sec. This would appear to be the resonant
oscillation of the air column in the barrel. The expression for the resonant
frequencies of an open tube in air is
nc
f
(12)
2
L
where n is an integer greater than zero, c is the speed of sound in air and L is
the length of the barrel. Assuming a standard atmosphere, c= 1118 ft/s (340.9
m/s), the predicted fundamental period for a 10 foot tube is 55.9 Hz. The
resulting period is 0.0179 seconds. It seems clear that this trailing oscillation is
simply the decaying response of the air column in the tube. This feature might
provide a secondary means of verifying a CFD analysis that modeled the ball
moving all the way down the tube and exiting at the muzzle.
Reproduced with permission. Copyright retained by Inderscience Publishers.
Figure 38. High Pass Filtered Data From the Pressure Sensor.
A final observation based on high-speed video from many firings is that
the gun recoils. Between the time at which the breech seal is punctured and the
time the ball exits the muzzle, the barrel clearly moves backwards - the
