| Summary: | Approved for public release; distribution is unlimited === Without nuclear testing, advanced simulation and experimental facilities, such as the National Ignition Facility (NIF), are essential to assuring safety, reliability, and effectiveness of the nuclear force; these capabilities are invaluable to the nation's Stockpile Stewardship Program (SSP). A significant information gap exists in the hydrodynamic response to nuclear detonations that occur near the earth's surface. Numerical simulation methods were used to evaluate the hydrodynamic response of earth-like materials and to develop the energy coupling/partitioning curve for low yield nuclear detonations close to the earth's surface. Using LLNL's supercomputers and GEODYN hydrodynamic code, the properties of stress, pressure, and energy were evaluated for twelve simulated 2.5kT detonations; six above the surface and six below the surface. The results indicate stronger air blasts for detonations above or near the surface and that energy coupling into the ground changes rapidly with detonation location over a very small range between the above-ground and below-ground interface. This work serves to provide a baseline model to evaluate stress, pressure, and energy in relation to nuclear yield close to the earth's surface. The results support a better understanding of the physics of near-surface detonations and also assist in planning future experimental work at NIF.
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