Numerical study of CFD simulations for compact counter-recoil design of EOD water cannon
Explosive Ordnance Disposal (EOD) robots armed with a water cannon are deployed to disarm the improvised explosive devices. It is critical that the water cannon produces as little recoil force as possible when fired. Otherwise, the robot may be rendered immobile or damaged. In a previous work, a recoilless water cannon was designed through a specific combination of firing experiments and Computational Fluid Dynamics (CFD) simulations. The final design was conceived, prototyped and tested with real bullets. The testing results were found to be satisfactory. In this work, the CFD simulations of the final design was carried out and closely investigated. Numerical study and error analysis were performed in an attempt to find the most suitable and efficient CFD setups for this problem. Two different CFD programs, three different flow domains, and various mesh resolutions were tested.
The mechanics of the impulsive water cannon
Abstract A model is proposed to describe the operating characteristics of the impulsive water cannon. The important parameters governing the system dynamics are identified and the influence of these on performance is studied with the aid of a unique ‘ 1 1 2 D ’ finite-difference code. The algorithm upon which this code is based is described as are its principle features. The results of the calculations are compared with recently developed incompressible theory and with experiment.
Live birth in the Devonian period
The extinct placoderm fishes were the dominant group of vertebrates throughout the Middle Palaeozoic era, yet controversy about their relationships within the gnathostomes (jawed vertebrates) is partly due to different interpretations of their reproductive biology. Here we document the oldest record of a live-bearing vertebrate in a new ptyctodontid placoderm, Materpiscis attenboroughi gen. et sp. nov., from the Late Devonian Gogo Formation of Australia (approximately 380 million years ago). The new specimen, remarkably preserved in three dimensions, contains a single, intra-uterine embryo connected by a permineralized umbilical cord. An amorphous crystalline mass near the umbilical cord possibly represents the recrystallized yolk sac. Another ptyctodont from the Gogo Formation, Austroptyctodus gardineri, also shows three small embryos inside it in the same position. Ptyctodontids have already provided the oldest definite evidence for vertebrate copulation, and the new specimens confirm that some placoderms had a remarkably advanced reproductive biology, comparable to that of some modern sharks and rays. The new discovery points to internal fertilization and viviparity in vertebrates as originating earliest within placoderms.