Attenuation of shock waves in a duct. Effects of resistance and expansion regions

When a vacuum accident occurs in a beam line at a synchrotron radiation facility, to protect the experimental facilities from shock waves, an acoustic delay line (ADL) is installed in the beam line. In this study effects of ADL were evaluated for models of a single-element wedge type (backward slope type, forward slope type, orifice type, expansion region type, expansion+orifice type) and models of a composite-element type (double backward slope type, double forward slope type, central concave type, central convex type, and double central concave type). Each wedge element have angle 30°, 45°, or 60° without or with holes. Experiments were carried out using a shock tube with a blast-wave generator. The pressure decay was evaluated by transmitted factor and reflected factor for the incident blast wave. As the results, the expansion+orifice type model showed the best (i.e., lowest) transmitted decay factor. Further, perforation were effective to improve the reflective decay drastically in the single type, but not so much in the composite type. (author)