No abstract

No abstract

No abstract

The periodic coupled wakes of two spheres, placed side by side in a uniform stream at low Reynolds numbers, are studied experimentally and by Direct Numerical Simulations. Different regimes of interaction are observed, depending on the separation distance between the spheres. For touching spheres, a single wake is found. At small gap sizes, the two wakes interact strongly, and out-of phase shedding occurs. In-phase shedding is observed experimentally for intermediate gap sizes, whereas DNS does not reveal a preferred phase difference between the two wakes. At distances above three sphere diameters, shedding is uncorrelated. Variations of the critical Reynolds number and shedding frequencies with separation distance are shown.

PBXs are complex composites geometrically (irregularly shaped grains vary greatly in size), and constitutively (grains are anisotropic, twin and fracture). Heterogeneity at the grain scale results in localized damage and the creation of hot spots. To develop accurate, quantitative and predictive models it is imperative to develop a sound physical understanding of the grain scale material response. Numerical simulation is a useful tool to further model development. Here an inherent advantage of a particle method in discretizing geometrically complex materials is exploited to import three-dimensional material configurations from x-ray microtomography data, i.e. "real" microstructures. Numerical simulations determine representative volume element size and generate statistics on grain scale strain heterogeneity. These statistics calibrate the Stochastic Transformation Field Analysis bulk constitutive model.