Prof. John Marks Dewey Profile

Prof. John Marks Dewey

Professor Emeritus at Univ of Victoria

SPIE Involvement:

Author

Publications (3)

Proceedings Article | 17 March 2005 Paper

High-speed photography of microscale blast wave phenomena

John Dewey, Harald Kleine

Proceedings Volume 5580, (2005) https://doi.org/10.1117/12.580096

KEYWORDS: Magnesium, Cameras, Silver, High speed photography, Explosives, Photography, Video, Visualization, High speed cameras, Nd:YAG lasers

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High-speed photography has been a primary tool for the study of blast wave phenomena, dating from the work of Toepler, even before the invention of the camera! High-speed photography was used extensively for the study of blast waves produced by nuclear explosions for which, because of the large scale, cameras running at a few hundred frames per second were adequate to obtain sharp images of the supersonic shock fronts. For the study of the blast waves produced by smaller explosive sources, ever-increasing framing rates were required. As a rough guide, for every three orders of magnitude decrease in charge size a ten-fold increase of framing rate was needed. This severely limited the use of photography for the study of blast waves from laboratory-scale charges. There are many techniques for taking single photographs of explosive phenomena, but the strongly time-dependent development of a blast wave, requires the ability to record a high-speed sequence of photographs of a single event. At ICHSPP25, Kondo et al of Shimadzu Corporation demonstrated a 1 M fps video camera that provides a sequence of up to 100 high-resolution frames. This was subsequently used at the Shock Wave Research Center of Tohoku University to record the blast waves generated by an extensive series of silver azide charges ranging in size from 10 to 0.5mg. The resulting images were measured to provide radius-time histories of the primary and secondary shocks. These were analyzed with techniques similar to those used for the study of explosions from charges with masses ranging from 500 kg to 5 kt. The analyses showed the cube-root scaling laws to be valid for the very small charges, and provided a detailed record of the peak hydrostatic pressure as a function of radius for a unit charge of silver azide, over a wide range of scaled distances. The pressure-radius variation was compared to that from a unit charge of TNT and this permitted a detailed determination of the TNT equivalence of silver azide as a function of peak pressure and radius. The availability of the Shimadzu high-speed framing camera has made it possible to perform experiments at the laboratory scale that previously could be done only on large-scale field trials. At the laboratory scale, many experiments can be performed on the same day, as compared to the months or even years required for the preparation of large-scale field experiments. The economic savings are even greater.

Proceedings Article | 1 April 1991 Paper

Analysis of results from high-speed photogrammetry of flow tracers in blast waves

John Dewey, Douglas McMillin

Proceedings Volume 1358, (1991) https://doi.org/10.1117/12.23963

KEYWORDS: Photogrammetry, Particles, Time metrology, High speed photography, Explosives, Spherical lenses, Numerical simulations

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Proceedings Article | 1 April 1991 Paper

High-speed time-resolved holographic interferometer using solid state shutters

Roberto Racca, John Dewey

Proceedings Volume 1358, (1991) https://doi.org/10.1117/12.23983

KEYWORDS: Solid state physics, Holographic interferometers, Solid state lasers, Camera shutters, Beam splitters, Spatial frequencies, Multiplexing, Holographic interferometry, Holograms, Holography

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