The role of unsteadiness in direct initiation of gaseous detonations

An analytical model is presented for the direct initiation of gaseous detonations by a blast wave. For stable or weakly unstable mixtures, numerical simulations of the spherical direct initiation event and local analysis of the one-dimensional unsteady reaction zone structure identify a competition between heat release, wave front curvature and unsteadiness. The primary failure mechanism is found to be unsteadiness in the induction zone arising from the deceleration of the wave front. The quasi-steady assumption is thus shown to be incorrect for direct initiation. The numerical simulations also suggest a non-uniqueness of critical energy in some cases, and the model developed here is an attempt to explain the lower critical energy only. A critical shock decay rate is determined in terms of the other fundamental dynamic parameters of the detonation wave, and hence this model is referred to as the critical decay rate (CDR) model. The local analysis is validated by integration of reaction-zone structure equations with real gas kinetics and prescribed unsteadiness. The CDR model is then applied to the global initiation problem to produce an analytical equation for the critical energy. Unlike previous phenomenological models of the critical energy, this equation is not dependent on other experimentally determined parameters and for evaluation requires only an appropriate reaction mechanism for the given gas mixture. For different fuel–oxidizer mixtures, it is found to give agreement with experimental data to within an order of magnitude

Interweaving Media

Five artists working in wood, glass, clay, metal and fiber collaborate with Pollack’s design team to create a new line of fabrics. Pollack, the NYC textile design firm founded by Mark Pollack 76 TX, embarked on a two-year project with Rachel Doriss 99 TX, to collaborate with five artists and designers working in different media. The goal? To create a line of newly released fabrics—called simply The Makers Collection. In the end, Pollack selected knit designer Liz Collins 91 TX/ MFA 99 TX in Brooklyn, ceramicist Nathan Craven MFA 08 CR in Roswell, NM, glass artist Katherine Gray MFA 91 GL in Los Angeles, furniture designer Matthias Pliessnig 03 FD in Providence and jewelry artist and former RISD faculty member Klaus Bürgel, who divides his time between New York City and Massachusetts. Each artist was chosen based on clear evidence of individual expertise in his or her preferred medium.https://digitalcommons.risd.edu/risdxyz_fall2013/1001/thumbnail.jp