Mesoscale calculations have been conducted in order to gain further insight into the dynamic compaction characteristics of granular ceramics. The primary goals of this work are to numerically determine the shock response of granular tungsten carbide and to assess the feasibility of using these results to construct the bulk material Hugoniot. Secondary goals include describing the averaged compaction wave behavior as well as characterizing wave front behavior such as the strain rate versus stress relationship and statistically describing the laterally induced velocity distribution. The mesoscale calculations were able to accurately reproduce the experimentally determined Hugoniot slope but under predicted the zero pressure shock speed by 12%. The averaged compaction wave demonstrated an initial transient stress followed by asymptotic behavior as a function of grain bed distance. The wave front dynamics demonstrate non-Gaussian compaction dynamics in the lateral velocity distribution and a power-law strain rate-stress relationship.

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Mesoscale hydrodynamic calculations have been conducted in order to gain further insight into the dynamic compaction characteristics of granular ceramics. With a mesoscale approach each individual grain, as well as the porosity, is modeled explicitly; the bulk behavior of the porous material can be resolved as a result. From these calculations bulk material characteristics such as shock speed, stress and density have been obtained and compared with experimental results. A parametric study has been conducted in order to explore the variation and sensitivity of the computationally derived dynamic response characteristics to micro-scale material properties such as Poisson's ratio, dynamic yield and tensile failure strength; macro-scale parameters such as volume fraction, particle morphology and size distribution were explored as well. The results indicate that the baseline bulk Hugoniot response under-predicts the experimentally measured response. These results are sensitive to the volume fraction, dynamic yield strength and particle arrangement, somewhat sensitive to failure strength and insensitive to the micro-scale Hugoniot and grain morphology. A discussion as to the shortcomings in the mesoscale modeling technique, as well as future considerations, is included.

In this work, we characterize the lift and lateral forces on a two-seam versus four-seam knuckleball and measure the viscous shear stress. We believe these measurements to be the first reported for slowly rotating baseballs. Our findings indicate the seam acts to either delay or advance separation depending upon the ball angle; these results are supported with flow visualization. The combined effect produces significant lift and lateral forces that can rapidly change as the ball rotates. Furthermore, we found the shear stress to be asymmetric which can result in significant in-flight torque. Together, asymmetries in force and shear stress produce the complicated flight trajectories that can confound the hapless batter.

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