Tunnel-Exit Pressure and Impulse Effects on Free-Field Pressure and Impulse

摘要

This report presents the results of a series of experimental tests conducted todetermine the effect of the overpressure vs. time history exiting a shock tube was used with a 22.86-cm driver section and a 133-cm driven section to produce a short-duration, decaying, pressure-time pulse at the exit end of the tube. Seven transducer locations recorded the peak over pressure and overpressure impulse vs. time along the zero-degree line. A second series of tests was conducted using a 150-cm driver to produce a long-duration, flattop, pressure-time pulse at the exit end of the tube. Again the overpressure vs. time was recorded at selected distances for comparison with the short driver results. It was determined that the flattop, longer duration, exit-pressure pulses produce higher pressure ratios, Delta P/P sub w, for the same distance ratio, R/D sub 7, than the short-duration, exit-pressure pulse at R/D sub T greater than 10. It was determined that to correlate the impulse Is outside of the tube with the exit impulse L sub w it was necessary to scale both I sub s and R/D sub 7 by dividing each by I sub w raised to the 1/3 power (i.e. cube. rt.(I sub w)). The effect of the exiting wave shape would have some influence on the present or proposed quantity-distance safety criteria. Keywords: Airblast; Underground storage; Impulse; Blast waves; Tunnel exit pressure; Blast propagation; Quantity distance. (JHD)