Experimental and numerical analysis of water blast mitigation: Focusing on solid water barriers, water sprays,and water-sheets
Abstract
Zakrajsek, Andrew James. M.S.M.E., Purdue University, May 2012. Experimental and Numerical Analysis of Water Blast Mitigation: Focusing on Solid Water Barriers, Water Sprays, and Water-Sheets. Major Professor: Steven F. Son. School of Mechanical Engineering. An explosion yielding a blast wave can cause catastrophic damage to people and property. To mitigate damage from such an event, a number of investigators have proposed the use of water in various configurations as a shield around a target. Water is very easily controlled, stored, and acquired which makes it a robust choice for a possible source of a readily available blast mitigant. Multiple water configurations were experimentally and numerically tested to compare and understand the potential of various water configurations as possible blast mitigants. The study of multiple water configurations yielded two main focuses for this research. One of the focuses of this research was to compare multiple water configurations to better explain the underlying physical blast mitigating mechanisms associated with water blast mitigation and blast mitigation in general. The other focus was to highlight the most advantageous water configuration for possible large scale blast mitigation shielding for a high risk target. The experimental work was completed by testing multiple water configurations under blast loading. Each water configuration was experimentally tested with an explosively driven shock tube and specific diagnostic measurement equipment. The water configurations tested include solid water barriers, water sprays, and water-sheets. The mass of water was shown to be relatively similar for the solid water barriers, water-sheet, and water spray. Therefore general blast mitigating comparisons between each water configuration were made knowing minimal mass loading effects were present. The results of each water configuration test helped highlight specific advantageous blast mitigating mechanisms. These advantageous mitigating mechanisms were shown to be; continuous surface areas, impedance mismatches, unconfined masses, controlling for breakup of water configuration, and mass loading. The understanding of these blast mitigating mechanisms meet the first focus and can be used to help design future water mitigation systems or other blast mitigating materials. The most advantageous blast mitigating water configurations was found to be an unconfined free-flowing water-sheet. Here, an approximate water-sheet thickness of 0.3 cm was tested. The results show that the water-sheet mitigates the initial peak overpressure and impulse of the blast. Further insights into the underlying physics are revealed by a numerical simulation using Sandia's CTH hydrocode. In simulations and experiments, the air behind the water-sheet experiences two distinct pressure peaks. An initial pressure rise results from the passage of a low pressure blast wave (M ≈ 1) through the intact sheet and into the air downstream of the water-sheet. Following this, the water-sheet breaks apart due to an increase in pressure on the forward surface caused by the buildup of the subsonic detonation products. Passage of the detonation products after breakup results in a second rise in pressure behind the water-sheet. In simulations, an initial perturbation of the water-sheet is shown to affect the breakup time significantly. Additional simulations show that increasing the sheet thickness tends to increase the blast wave mitigation. These results indicate that it may be possible to optimize the thickness and surface morphology of a water-sheet to effectively mitigate damages due to explosive blast waves through the use of a water-sheet shield.
Degree
M.S.M.E.
Advisors
Son, Purdue University.
Subject Area
Engineering|Mechanical engineering
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