Physics and Engineering Models

Models are mathematical equations and tables that describe physical entities and processes; and are the vehicle by which new scientific understanding is written into the integrated codes. This subprogram funds the critical skills charged with the development, initial validation, and incorporation of new models into the Integrated Codes. Model development converts the results of theories and experiments into simulation capabilities and is inextricably linked to the Science Campaign. 

Nuclear weapons simulations rely on accurate descriptions of a great variety of physical processes. These processes include vibration of the warhead during re-entry, detonation and burning of high explosives, extreme compression of uranium and plutonium, radiation transport, and generation of energy through nuclear reactions. The Physics and Engineering Models (PEM) sub-program is directly responsible for providing the capability to accurately simulate all of these processes.

Benefits

PEM provides the models and databases used in simulations supporting the U.S. nuclear weapon stockpile.  These models and databases describe physical and engineering processes occurring during the operation of a nuclear weapon. The capability to accurately describe these processes is required for annual assessment, design, qualification and certification of warheads undergoing Life Extension Programs, resolution (and in some cases generation) of Significant Finding Investigations, and the development of future stockpile technologies.

High Explosives

This area develops and delivers predictive energetic and reactive material models for nuclear performance and safety simulations.  Such models reduce the need for expensive calibration experiments and enable predictions when such experiments are not possible.  This area relies on specialized physics codes informed by theory and small-scale experiments.  The resulting models are integrated into ASC safety and design codes to improve our predictive capability.

Equation of State

This area develops and delivers science-based models for describing the thermodynamic properties of materials.  Development of these predictive models requires the integration of advanced theory, specialized computer codes, and experimental data to produce phase diagrams, accurate equations of state (EOS) for all phases, and models for kinetic effects as materials change phases.  Resulting EOS databases, in forms sharable between laboratories, are integrated in to ASC safety and design codes to improve our predictive capability.

Nuclear Properties

This area develops and delivers accurate nuclear cross-section evaluations and databases that are required by ASC integrated safety, design, and diagnostics codes.  These nuclear properties databases, produced in forms sharable between laboratories, rely on specialized nuclear physics codes that integrate experiment, models, and theory.  Scope includes properties for neutron interactions with weapon materials, thermonuclear fusion reactions, and data for radiochemistry detectors.

Plasma and Radiative Properties

This area develops and delivers science-based models and databases to represent the interactions of radiation with matter and the behavior of plasmas at extreme temperatures, pressures, and densities.  Products include opacity and plasma equation of state databases for pure materials and mixtures in local thermodynamic equilibrium (LTE) and advanced physics treatments for non-LTE (NLTE) situations, plasma transport, and surface effects.  The models and databases are required by ASC integrated design codes for improved predictive capability.

Advanced Hydrodynamics

This area develops and delivers physically-grounded models for complex hydrodynamic flows.  Models must represent various hydrodynamic instabilities, turbulence, and ejecta, and are developed from a combination of theory, high-performance computer simulations, and the analyses of experimental data.  The resulting models are integrated in to ASC safety and design codes to improve our predictive capability.

Material Strength and Damage

This area develops and delivers predictive science-based models for the dynamic strength, damage, and failure response of materials across a wide range of extreme conditions (e.g., pressure, temperature, strain rate) unique to weapons. Development of these predictive models requires the integration of theory, specialized computer codes, and experimental data to produce process aware representations of material behavior. These models rely on building an intimate understanding of the relationship between evolving microstructure and its effect on the thermo-mechanical response of materials.  The resultant models are implemented into ASC integrated engineering and physics codes.

Support for Non-Stockpile Nuclear National Security Missions

This area includes important PEM activities that are directly aligned with initiatives to support non-stockpile nuclear security missions.  This area provides support for physics and code improvements supporting missions such as nuclear forensics, nuclear counter-terrorism, emergency response, and foreign assessments.   Our over-arching objective is to enable the use of ASC codes and databases for priority applications in this mission space.  In addition, cross-cutting initiatives such as academic alliances and Russian programs are included here.

Thermal & Fluid Response

This area develops and delivers predictive science-based models that capture complex thermal and fluid transport in materials.  The application scope covers design through manufacturing with specific emphasis on response to abnormal fire environments.   Models are developed through integration of theory, computational simulation and analyses of experimental data.  The resulting models are implemented into the ASC integrated engineering and physics codes.

Aerodynamics & Vibration

This area develops and delivers predictive science-based models that capture complex aerodynamic and aerothermal flows and response for gravity and reentry systems.  This also includes models that capture the resultant structural vibration and mechanical response.  Models are developed through integration of theory, computational simulation and analyses of experimental data.  The resulting models are implemented into ASC integrated engineering and physics codes.

Radiation & Electrical Response

This area develops and delivers predictive science-based models that capture material and electrical system effects produced by exposure to x-ray, gamma or neutron radiation.  Scope includes development of complex models for integrated circuits and discrete electronic components such as transistors.  Models are developed through integration of theory, computational simulation and analyses of experimental data.  The resulting models are implemented into ASC integrated engineering and physics codes.