Thomas Slawson

Evaluation of Predictive Methods for Airblast Propagation Through an Enclosed Structure

Accurate predictions of peak pressure and impulse values of explosively-generated shock waves within a structure are both of interest to structural engineers and are difficult to generate analytically. On one hand, rudimentary scoping programs, such as BlastX, are simple to use and obtain general pressure-impulse predictions for a given scenario. The primary drawback to such programs is their lack of detail and their inability to account for any complexity within a structure. On the other hand, existing advanced hydrocodes, such as CTH, are capable of accurately modeling blast-wave characteristics in a very detailed environment. The tradeoff in this instance is that CTH requires advanced training, tools, and resources that are often not readily available. As a result, the structural engineer is often required to determine whether a simple “scoping” of the blast environment is sufficient, or whether the additional resources and expenditures are justified in providing a more accurate model. The focus of this paper is to evaluate the analytical and computational predictive methods described above—including the required simplifying assumptions, strengths, and limitations of each—by comparing the results of their respective analyses of the same target structure and comparing their results to data gathered from a 1/8-scale experiment of the structure in question.

Multiscale Semi-Lagrangian Reproducing Kernel Particle Method for Modeling Damage Evolution in Geomaterials

Damage processes in geomaterials typically involve moving strong and weak discontinuities, multiscale phenomena, excessive deformation, and multi-body contact that cannot be effectively modeled by a single-scale Lagrangian finite element formulation. In this work, we introduce a semi-Lagrangian Reproducing Kernel Particle Method (RKPM) which allows flexible adjustment of locality, continuity, polynomial reproducibility, and h- and p-adaptivity as the computational framework for modeling complex damage processes in geomaterials. Under this work, we consider damage in the continua as the homogenization of micro-cracks in the microstructures. Bridging between the cracked microstructure and the damaged continuum is facilitated by the equivalence of Helmholtz free energy between the two scales. As such, damage in the continua, represented by the degradation of continua, can be characterized from the Helmholtz free energy. Under this framework, a unified approach for numerical characterization of a class of damage evolution functions has been proposed. An implicit gradient operator is embedded in the reproduction kernel approximation as a regularization of ill-posedness in strain localization. Demonstration problems include numerical simulation of fragment-impact of concrete materials.