Towards a General Methodology for Modeling the Pressure Buildup behind Porous Media that is Impinged by a Shock Wave

There are several scenarios where shock waves impinge on porous media. Each of these scenarios requires different numerical and experimental approaches to predict the intricate shock diffractions and the developing flow fields. As a result, a universal technique to model them all does not exist. In terms of protective structures, designers are ultimately required to predict the pressure build up and developing loads behind porous media that are used as passive protection to hinder the shock propagation and mitigate the overall load inflicted by it on a structure. Following an experimental study of the parameters affecting the pressure build up in a confined volume behind porous filters impinged by normal shock waves, a new constitutive model that provided the non-dimensional behavior of the results was derived (Ram & Sadot 2013). A more in-depth analysis of the governing physics led to a new understanding of the universality of shock-porous barrier interactions. The results showed that porous barriers placed in the flow field acted as low pass filters on the pressure wave. These findings provided a physical basis to formulate a new approach that enables studying interactions of shock waves and porous barriers. The approach, addresses every porous barrier along with the air confined in it as a single mechanical system. Using this perspective, a transfer function that links the imposed load at the frontal face of the porous barrier and the developing loads behind it can be found (Ram & Sadot 2015). This methodology was applied to the case where an explosion-generated blast wave impinged on the frontal façade of a structure having a complex inner geometry. A rapid prediction of the developing loads inside the structure was obtained. This approach can replace the need to use a grueling CFD code to simulate the phenomenon (Ram, Nof & Sadot 2016). The methodology was also employed to study the pressure buildup, following shock impingement, behind an array of perforated plates. This scenario was poorly understood due to the very complicated shock induced flow field. This method led to a new understanding of the pressure buildup behind a set of perforated plates including the influence of different porosities, different number of plates and different gasses.