Microscopic Description of the Fission Process is an interesting set of slides dealing with this credibility building exercise where empirical closure is concerned. The question addressed on slide 3 is, "Why focus on the microscopic nuclear theories?" Here are the reasons given:
Why:The Advanced Simulation and Computing (ASC) Verification & Validation (V&V) program exists to establish a technically rigorous foundation of credibility for the computational science and engineering calculations required by the NNSA Stockpile Stewardship Program. This program emphasizes the development and implementation of science-based verification and validation methods for the support of high-consequence decisions regarding the management of the U.S. nuclear stockpile. The V&V process reduces the risk of incorrect stockpile decisions by establishing that the calculations provide the right answers for the right reasons.
-- Verification and Validation: Credibility in Stockpile Modeling and Simulation
This illustrates the idea that the credibility of validation has more to do with the quality of the model's physical and theoretical basis as opposed to the coverage or quantity of experimental data (though validation experiments are still quite necessary). Part of the goal of any continuing validation process (link by way of Dan Hughes' site) is to reach the point where all of the empirical closures (constitutive relations or sub-grid scale parameterizations in the context of large multi-physics codes) have sound theoretical and physical basis.
With a fundamental picture of nuclei based on the correct microphysics, we can remove the empiricism inherent today, thereby giving us greater confidence in the science we deliver to the programs
- The nuclear many-body problem is very complex, computationally difficult
- Much of the progress in the past 50 years has been based on empirical models (most with microscopic degrees of freedom) tuned to experimental data
- This highly limits our predictive capability
- And it is difficult to estimate the uncertainties
- How can we do Quantification of Margins and Uncertainties?
That fact sheet mentioned above also has a good list of the sorts of deliverables that we should expect as consumers of simulation-based decision support:
- Documented analysis and conclusion of the confidence level of the models as a result of the V&V activities.
- Repository of test results associated with unit / regression / system tests, verification and validation tests and/or list of test data used.
- Documented code (feature) and solution (model) verification.
- Documented V&V environment (constraints, assumptions, and tools).
- Repository of code versions, fixes, and other patches used during the V&V phase.
The entire point of requiring the VV&UQ process is not that we hope to prove a model implementation is correct or true (an impossible task), but that we understand the importance of generating credible results that faithfully represent the reality of interest through sound physical reasoning, and which are shown to be useful for a particular purpose. VV&UQ is the set of best practices for providing unimpeachable, science-based support for decisions that matter.