Research On The Structure And Dynamics Of A Fire Extinguishing Shell Special For The Forest Fire Exitinguishing Cannon

With the development of science and technology and the continued deepening understanding of human to forest fires, a variety of new forest fire fighting equipments were developed, which have played an active role in the forest firefighting. This subject derives from the project subsidized by the public special fund of the National Ministry of Science and Technology-"Remote forest fire fighting cannon, vehicle, and shell system"(PN:2005DIB3J13) and the project subsidized by the State Forestry Adminstration-"The integrated system development of the remote, fast and secure forest fire fighting equipment"(PN:2006-48). The purpose of this paper is to research a forest fire extinguishing shell launched by high-pressure air. The shell is designed for extinguishing the crown fire which is the most difficult to fight against. The shell can auto-throw parachute to decelerate when fly to the target above the fire scene to make sure the shells explode and disperse extinguishing agent at the height just above the crown fire, thus, the optimal fire-fighting effect can be fulfilled.The classification characteristics and the present development situation at home and abroad of the forest fire extinguishing shell were described in this paper, the overall structure of the shell was determined according to the functional requirements and launching principles of the shell, the design processes of the shell profile and the main components within the shell were expounded, the structural characteristics parameters of the shell and deceleration parachute parameters were obtained.The unidirectional short-fiber-reinforced composite and random short-fiber-reinforced composite are adopted as the materials of the cylindrical part and tail part of the shell, respectively, by considering the forced characteristic of the shell while launching. The modulus and strength of the composite were calculated which is the prerequisite of the structural analysis. The strength and stiffness analysis of the important parts were done via the finite element analysis software ANSYS.The relationship between the sliding friction force of the shell and the working pressure loaded to the shell body was obtained by analyzing the sealing process of rubber seals in the cannon barrel via ANSYS software, and the interior ballistic model of the shell was finally determined. The basic ballistic model of the free-flying stage and the parachute deceleration stage was obtained by considering the free-flying stage as a single particle ballistic model, the straightening stage of the decelerating parachute as three-particle ballistic model, and the inflatable stage and the stable landing stage as double particle ballistic model.The aerodynamic characteristics parameters were obtained by means of the table-algorithm based on the analysis of flight characteristic of the fire extinguishing shell, the flight stability of the shell was studied via the stability reserves and swing features and the result shows that the shell can fly stably.