Numerical analysis of the operation of a water cannon
Department of Mechanical Engineering
Master of Science
Geskin, E. S.
Sodhi, R. S.
This study was designed to investigate the operational process of a launcher for generation of high speed water projectiles, and it involved the optimization of the geometry of a launcher body. The objective of the optimization of the internal geometry was to increase the effective momentum of the projectile while the optimization of the external geometry resulted in the reduction of the mass of the launcher.
In the course of the optimization of the internal geometry the exit velocity variation was determined, and used to compute an effective projectile momentum, which actually affects a workpiece. In this research, it was assumed that the effective momentum is generated if the velocity of the impacting fluid exceeds the critical velocity. A cutoff factor was introduced in order to separate a part of projectile which generates an effective momentum. A numerical model of the process developed by G. Atanov was used to determine the exit water velocity while a C++ program was developed in order to determine the effective momentum of the projectile at various launcher geometries. The optimization involved the approximation of the internal launcher geometry by a combination of a cylinder (barrel) and two cones (nozzle), the length and diameters of which constituted the process. The near optimal values of these variables were determined and have shown that the optimization of the nozzle geometry enables an increase in the effective momentum of a projectile by 40%.
The second problem surveyed the effect of the variation of the external geometry of the water cannon on its weight. An array of the cannon geometries, which assured the sufficient strength of the construction, was investigated and a shape minimizing the mass of the device was found. The Atanov model was used to determine the pressure distribution within the water cannon, and the computation package Pro-MECHANICA was applied to determine the stresses in the cannon body. The external geometry was selected so that at each cross section the actual stresses, static, and dynamic did not exceed the critical stresses determined by the use of the von Mises criterion. The analysis was carried out at the external geometry of the existing cannon prototype and had shown that the geometry optimization enables a reduction of the cannon mass by 15 %.
The third part of the experiment was devoted to investigate water slug-target interaction. It was carried out through an assimilation of a demining and a concrete demolition processes with a high-speed water projectile. The experiment has shown the importance of stand-off distance with different types of targets.
njit-etd2007-002 (72 pages ~ 7,812 KB pdf)
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Created March 30, 2011