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Verification and validation as applied epistemology

McNamara, Laura A.; Trucano, Timothy G.; Backus, George A.

Since 1998, the Department of Energy/NNSA National Laboratories have invested millions in strategies for assessing the credibility of computational science and engineering (CSE) models used in high consequence decision making. The answer? There is no answer. There's a process--and a lot of politics. The importance of model evaluation (verification, validation, uncertainty quantification, and assessment) increases in direct proportion to the significance of the model as input to a decision. Other fields, including computational social science, can learn from the experience of the national laboratories. Some implications for evaluating 'low cognition agents'. Epistemology considers the question, How do we know what we [think we] know? What makes Western science special in producing reliable, predictive knowledge about the world? V&V takes epistemology out of the realm of thought and puts it into practice. What is the role of modeling and simulation in the production of reliable, credible scientific knowledge about the world? What steps, investments, practices do I pursue to convince myself that the model I have developed is producing credible knowledge?

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TYPE Conference YEAR 2007
OSTI

A taxonomy and comparison of parallel block multi-level preconditioners for the incompressible Navier-Stokes equations

Howle, Victoria E.; Shadid, John N.; Shuttleworth, Robert R.; Tuminaro, Raymond S.

In recent years, considerable effort has been placed on developing efficient and robust solution algorithms for the incompressible Navier-Stokes equations based on preconditioned Krylov methods. These include physics-based methods, such as SIMPLE, and purely algebraic preconditioners based on the approximation of the Schur complement. All these techniques can be represented as approximate block factorization (ABF) type preconditioners. The goal is to decompose the application of the preconditioner into simplified sub-systems in which scalable multi-level type solvers can be applied. In this paper we develop a taxonomy of these ideas based on an adaptation of a generalized approximate factorization of the Navier-Stokes system first presented in [25]. This taxonomy illuminates the similarities and differences among these preconditioners and the central role played by efficient approximation of certain Schur complement operators. We then present a parallel computational study that examines the performance of these methods and compares them to an additive Schwarz domain decomposition (DD) algorithm. Results are presented for two and three-dimensional steady state problems for enclosed domains and inflow/outflow systems on both structured and unstructured meshes. The numerical experiments are performed using MPSalsa, a stabilized finite element code.

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TYPE SAND Report YEAR 2007
DOIOSTI
Results 9051–9075 of 9,998
Results 9051–9075 of 9,998