Programming a Multiple-Orifice Hydraulic Decelerator.

The AAMRL Horizontal Deceleration Facility is used to conduct experimental research for the development of design criteria for aircrew personnel protection. The hydraulic deceleration device is a water-filled cylinder. A piston mounted on the front of a deceleration sled ruptures a frangible diaphragm positioned at the opening of the cylinder and displaces the water in the cylinder through the multiple orifices. As the piston travels along the cylinder it closes off the orifices thereby decreasing the available area for the water to escape. Bernoullis conservation-of-energy equation was applied to the physical state of fluid flow in the cylinder, allowing the orifice area to be determined as a function of the piston cross-sectional area, acceleration, velocity and weight of the sled. A computer program was developed to determine the appropriate plug orifice and location to produce desired acceleration-time profiles. The program corrects for the energy loss due to the vena-contracta of each plug. Data from several tests were used to determine a correction coefficient for other losses, such as those attributable to conduit length and surface roughness, as a lumped quantity. Author