David J. Torres

KIVA-4

The KIVA family of codes was developed to simulate the thermal and fluid processes taking place inside an internal combustion engine. In this latest version of this open source code, KIVA-4, the numerics have been generalized to unstructrured meshes. This change required modifications to the Lagrangian phase of the computations, the pressure solution and fundamental changes in the fluxing schemes of the rezoning phase. This newest version of the code inherits all the droplet phase capabilities and physical sub-models of previous versions. The integration of the gas phase equations with moving solid boundaries continues to employ the successful arbitrary Lagrangian-Eulerian (ALE) methodology. Its new unstructured capability facilitates grid construction in complicated geometries and affords a higher degree of flexibility. The numerics of the code, emphasizing the new additions, are described. Various computational examples are performed demonstrating the new capabilities of the code.

Advances in isentropic compression experiments (ICE) using high explosive pulsed power

We are developing a prototype high explosive pulsed power (HEPP) system to obtain isentropic Equation of State (EOS) data with the Asay technique. Asay, JR (1999). Our prototype system comprises a flat-plate explosive driven magnetic flux compression generator (FCG), an explosively formed fuse (EFF) opening switch, and a series of explosively-actuated closing switches. The FCG is capable of producing /spl sim/10 MA into suitable loads, and, at a length of 216 mm, the EFF will sustain voltages in excess of 200 kV. The load has an inductance of /spl sim/3 to 10 nH, allowing up to /spl sim/7 MA to be delivered in times of /spl sim/0.5 /spl mu/s. This prototype will produce isentropic compression profiles in excess of 2 Mbar in a material such as tungsten. Our immediate plan is to obtain isentropic EOS data for copper at pressures up to /spl sim/1.5 Mbar with the prototype system; eventually we hope to reach several tens of Mbar with more advanced systems.

Effect of Die Pattern on Explosively Formed Fuse Performance

Explosively formed fuse (EFF) devices are explosively formed fuse performance for high explosive pulsed power (HEPP) applications. Such switches have been operated at currents up to 25 MA, voltages up to 500 kV, and power over 3 TW in our large-scale HEPP systems. The switch consists of a conducting foil that is driven by high explosives into a dielectric die consisting of extrusion anvils and gaps that separate them. The switch develops resistance as the foil is extruded. We have conducted tests with many foils, and many die materials and patterns. We have also performed calculations using both 2-D hydrodynamic (hydro) and magneto-hydrodynamic (MHD) codes of switches with the different die patterns. Dies with more massive corners at each extrusion position develop resistance faster, and tend to have more pronounced features in the resulting R(t) curves. In addition, the explosive drive is important as is the shape and density of the anvil bottom. These data and calculations will be discussed, along with what we have learned from MHD calculations. To date, we have been unable to calculate accurate R(t) curves accurately from first principles with MHD codes, but have gained increased insight into performance.