The near wake flow field associated with hypersonic blunt bodies is characterized by complex physical phenomena resulting in both steady and time dependent pressure loadings on the base of the vehicle. Here, we focus on the unsteady fluid dynamic pressure fluctuation behavior as a vibratory input loading. Typically, these flows are characterized by a locally low-pressure, separated flow region with an unsteady formation of vortical cells that are locally produced and convected downstream into the far-field wake. This periodic production and transport of vortical elements is very-well known from classical incompressible fluid mechanics and is usually termed as the (Von) Karman vortex street. While traditionally discussed within the scope of incompressible flow, the periodic vortex shedding phenomenon is known for compressible flows as well. To support vehicle vibratory loading design computations, we examine a suite of analytical and high-fidelity computational models supported by dedicated experimental measurements. While large scale simulation approaches offer very high-quality results, they are impractical for design-level decisions, implying that analytically derived reduced order models are essential. The major portions of this effort include an examination of the DeChant-Smith Power Spectral Density (PSD) [1] model to better understand both overall Root Mean Square (RMS) magnitude and functional maximum associated with a critical vortex shedding phenomenon. The critical frequency is examined using computational, experiments and an analytical shear layer frequency model. Finally, the PSD magnitude maximum is studied using a theory-based approach connecting the PSD to the spatial correlation that strongly supports the DeChant-Smith PSD model behavior. These results combine to demonstrate that the current employed PSD models provide plausible reduced order closures for turbulent base pressure fluctuations for high Reynolds number flows over range of Mach numbers. Access to a reliable base pressure fluctuation model then permits simulation of bluff body vibratory input.
Microstructural variabilities are among the predominant sources of uncertainty in structural performance and reliability. We seek to develop efficient algorithms for multiscale calcu- lations for polycrystalline alloys such as aluminum alloy 6061-T6 in environments where ductile fracture is the dominant failure mode. Our approach employs concurrent multiscale methods, but does not focus on their development. They are a necessary but not sufficient ingredient to multiscale reliability predictions. We have focused on how to efficiently use concurrent models for forward propagation because practical applications cannot include fine-scale details throughout the problem domain due to exorbitant computational demand. Our approach begins with a low-fidelity prediction at the engineering scale that is sub- sequently refined with multiscale simulation. The results presented in this report focus on plasticity and damage at the meso-scale, efforts to expedite Monte Carlo simulation with mi- crostructural considerations, modeling aspects regarding geometric representation of grains and second-phase particles, and contrasting algorithms for scale coupling.