Welcome & Overview
Trudy Hoye, NAFEMS Technical Working Groups Manager
Introduction to the Impact, Shock & Crash Working Group
Gino Duffett, Impact,Shock & Crash Working Group Chair
Tim Brewer, Jeffrey Heylmun, Benjamin Shields and Peter Vonk (Synthetik Applied Technologies LLC)
Question & Answer Session
There are several accepted technical approaches for calculating airblast loads on structures, with varying levels of technical complexity and fidelity. The most basic approaches calculate pressure and impulse loads as a function of charge weight and distance, whilst semi-empirical methods, such as the Kingery-Bulmash equations include some additional parameters to the loading equations related to the orientation of the target relative to the propagating shock front.
The employment of physics-based approaches, such as computational fluid dynamics, provide methods to fully account for the key phenomena associated with explosive events. This has clear benefits over empirical, semi-empirical and closed-form solutions, in that each calculation can account for the unique geometric conditions present within the analysis domain, and consequently achieve far more representative and potentially accurate results. And given the now low cost of accessing computing hardware, these methods can be practically and economically applied to find significant design efficiencies – lowering project costs whilst improving safety.
This webinar will describe several different approaches to modelling detonation within explosive materials which transition from unreacted energetics to detonation products, including pressure-based activation models with multi-step Arrhenius reaction rates, and simple, yet practical models based on empirically derived detonation velocities. Phenomena such as size effect (decrease of the detonation velocity with decreasing charge radius), and detonation front curvature (induced by edge lag of the front as energy is lost to the exterior of the charge) will be discussed. Furthermore, the effective modelling of afterburn (i.e., under-oxygenated explosives continuing to burn after detonation) will also described.
The development and implementation of various equations of state facilitates modelling of diverse materials under extreme conditions, with consideration of phenomenologies such as excitation, dissociation and ionization of nitrogen and oxygen in air at higher energies and temperatures, cavitation, and sympathetic detonation.
Meshing schemes to effectively capture the inherent physics of airblast simulations will also be discussed along with concepts such as adaptive mesh refinement (AMR), dynamic load balancing, and options for mesh refinement, unrefinement, relaxation and coarsening that can keep cell counts relatively constant during a calculation while still capturing key features (e.g. shocks, interfaces) with high accuracy. Allowing CFD codes to solve engineering-scale simulations at an affordable computational cost.
Finally, example studies to validate the fundamental numerics of CFD solvers will be presented that demonstrate effective application to multi-phase compressible flow problems for high-explosive detonation, explosive safety, and airblast.
This event is being hosted by the NAFEMS Impact, Shock and Crash Working Group (ISCWG). For more information and to get involved go to the Impact, Shock and Crash Working Group webpage.
Tim Brewer, Synthetik Applied Technologies LLC
Tim Brewer is COO at Synthetik Applied Technologies LLC with over 18 years’ experience providing support to the U.S. government in research and development efforts related to combustion, detonation, extreme loading, and explosive effects. He has also generated a variety of software tools for design and analysis related to airblast and shock.
He is familiar with the various commercial and government documents and software relevant to explosive effects and has developed and is experienced with many of the engineering tools and numerical approaches for determining response subject to extreme loads. Tim is also accredited by the Department of Homeland Security (DHS) as an Assessor for the BPATS (Best Practices for Anti-Terrorism Security) scheme.
Jeffrey Heylmun, Benjamin Shields and Peter Vonk (all Synthetik Applied Technologies LLC)