We report development and application of a fluid-structure interaction (FSI) solver for compressible flows with large-scale flow-induced deformation of the structure. The FSI solver utilizes partitioned approach to strongly couple a sharp-interface immersed boundary method based flow solver with an open-source finite-element structure dynamics solver. The flow solver is based on a higher-order finite-difference method on Cartesian grid and employs ghost-cell methodology to impose boundary conditions on the immersed boundary. A higher-order accuracy near the immersed boundary is achieved by combining the ghost-cell approach with a weighted least-square error method based on a higher-order approximate polynomial. We present validations for two-dimensional canonical acoustic wave scattering on a rigid cylinder at low Mach number and flow past a circular cylinder at moderate Mach number. The second order spatial accuracy of the flow solver is established by performing a grid refinement study. The structure solver is validated with a canonical elastostatics problem. The FSI solver is validated with published measurements and simulations for the large-scale deformation of a thin elastic steel panel subjected to blast loading in a shock tube. The solver correctly predicts oscillating behavior of the tip of the panel with reasonable fidelity and computed shock wave propagation is qualitatively consistent with the published results. In order to demonstrate the fidelity of the solver and to investigate coupled physics of the shock-structure interaction for a thin elastic plate, we employ the solver for simulating 6.4 kg TNT blast loading on the thin elastic plate. The initial conditions of the blast are taken from field tests reported in the literature. Using numerical schlieren, the shock front propagation, Mach reflection and vortex shedding at the tip of the plate are visualized during the shock wave impact on the plate. We discuss coupling between the non-linear dynamics of the plate and blast loading. The plate oscillates under the influence of blast loading and restoring elastic forces. The time-varying displacement of the tip of plate is found to be superimposition of two dominant frequencies, which correspond to first and second mode of natural frequency of a vibrating plate. The effects of material properties and length of the plate on the flow-induced deformation are briefly discussed. The proposed FSI solver is demonstrated as a versatile computational tool for simulating the blast wave impact on thin elastic structures and given results will be helpful to design thin structures subjected to realistic blast loadings.

Results from numerical simulations of two-dimensional, shear-thinning Carreau fluid flow over an unconfined circular cylinder are presented in this paper. Parametric sweeps are performed over the various Carreau model parameters and trends of the time-averaged force coefficients and vortex characteristics are reported. In general, increased shearthinning results in lower viscous forces on the body but greater pressure forces, resulting in a complex non-monotonic drag response. Lift forces generally increased with shear-thinning due to the dominant pressure contribution. The decrease in fluid viscosity also led to shorter vortex formation lengths and the consequent rise in Strouhal frequency of vortex shedding. It is expected that these results will be useful for verification of computational models of unsteady non-Newtonian flows. Non-Newtonian fluids are routinely encountered in the form of industrial fluids (e.g. polymer solutions, emulsions, molasses, silicone oils) in several arenas such as the food, paper, process engineering [1] and biochemical industries. Many common biological fluids like honey, blood, synovial fluid, saliva, and semen also belong to this class of fluids. Non-Newtonian fluids are characterized by complex constitutive properties, such as shear-dependent viscosity, fluid elasticity and the dependence of fluid properties on deformation history. Fluids like blood can be characterized as viscous inelastic and are classified as shear-thinning or shear-thickening based on the influence of deformation on fluid viscosity. A simple inelastic viscous fluid may be represented as a Generalized Newtonian fluid, in which shear-stress has linear proportionality with shear-rate, but the coefficient of proportionality has a non-linear dependence on shear-rate. Generalized Newtonian fluids are commonly modeled using the power-law or the Carreau-Yasuda models [2,3]. A large body of work involving simulations of flow of power-law fluids over bluff bodies exists. For instance, Bell and Surana [4] performed finite-element simulations of power-law flow through 2D ducts, inside square, driven cavities and in sudden expansions. Chhabra and colleagues have analyzed steady power-law flow over unconfined [5] and confined [6] circular cylinders. Additionally, stability analysis was performed for the wake of the unconfined cylinder [7]. The group also modeled unsteady flow over unconfined circular cylinder [8] and heat-transfer in steady flow [9]. Finally, data is also available for power-law flow past elliptic [10], square [11] and triangular [12] cylinders.

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Ocular trauma is one of the most common types of combat injuries resulting from the exposure of military personnel with improvised explosive devices. The injury mechanism associated with the primary blast wave is poorly understood. We employed a three-dimensional computational model, which included the main internal ocular structures of the eye, spatially varying thickness of the cornea-scleral shell, and nonlinear tissue properties, to calculate the intraocular pressure and stress state of the eye wall and internal ocular structure caused by the blast. The intraocular pressure and stress magnitudes were applied to estimate the injury risk using existing models for blunt impact and blast loading. The simulation results demonstrated that blast loading can induce significant stresses in the different components of the eyes that correlate with observed primary blast injuries in animal studies. Different injury models produced widely different injury risk predictions, which highlights the need for experimental studies evaluating mechanical and functional damage to the ocular structures caused by the blast loading.

Ocular trauma is one of the most common types of combat injuries resulting from the interaction of military personnel with improvised explosive devices. Ocular blast injury mechanisms are complex, and trauma may occur through various injury mechanisms. However, primary blast injuries (PBI) are an important cause of ocular trauma that may go unnoticed and result in significant damage to internal ocular tissues and visual impairment. Further, the effectiveness of commonly employed eye armor, designed for ballistic and laser protection, in lessening the severity of adverse blast overpressures (BOP) is unknown. In this paper, we employed a three-dimensional (3D) fluid-structure interaction computational model for assessing effectiveness of the eye armor during blast loading on human eyes and validated results against free field blast measurements by Bentz and Grimm (2013). Numerical simulations show that the blast waves focused on the ocular region because of reflections from surrounding facial features and resulted in considerable increase in BOP. We evaluated the effectiveness of spectacles and goggles in mitigating the pressure loading using the computational model. Our results corroborate experimental measurements showing that the goggles were more effective than spectacles in mitigating BOP loading on the eye. Numerical results confirmed that the goggles significantly reduced blast wave penetration in the space between the armor and the eyes and provided larger clearance space for blast wave expansion after penetration than the spectacles. The spectacles as well as the goggles were more effective in reducing reflected BOP at higher charge mass because of the larger decrease in dynamic pressures after the impact. The goggles provided greater benefit of reducing the peak pressure than the spectacles for lower charge mass. However, the goggles resulted in moderate, sustained elevated pressure loading on the eye, that became 50-100% larger than the pressure loading experienced by the unprotected eye after 0.2 ms of impact of blast wave, for lower as well as higher charge mass. The present model provides fundamental insights of flow and pressure fields in the ocular region, which helps to explain the effectiveness of the eye armor. Since the measurements of these fields are not trivial, the computational model aids in better understanding of development of PBI.