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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.
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The purpose of this document is to compare and contrast metrics that may be considered for use in validating computational models. Metrics suitable for use in one application, scenario, and/or quantity of interest may not be acceptable in another; these notes merely provide information that may be used as guidance in selecting a validation metric.
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The main objective of this report is to develop an exploratory mathematical analysis motivated by the Becks et al. (2005) experiments, which will be presented in Chapter 1. Related details of the resulting model will be presented in Chapter 2, and a detailed non-dimensionalization will follow in Chapter 3. During the research to be described, a potential relationship to Shannon information theory was realized, and this will be developed in Chapter 4. Several avenues for future research are suggested, and a more mathematically-oriented presentation of the non-linear dynamical properties of the equations developed in Chapter 1 may be found in Faybishenko et al. (2018).
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The Particle-in-cell (PIC) numerical approach for modeling granular solids in fluid flow has gained significant interest in recent years. Valued for its often shorter time-to-solution, the PIC formulation relies on modeling statistical groupings of particles called parcels in cooperation with a solids stress model to affect local solids velocity. This is in contrast to the discrete element model (DEM) where every particle in a system is modelled individually and directly coupled to local solids velocity through Newtonian mechanics. The U.S. Department of Energy (DOE), National Energy Technology Laboratory (NETL) develops and maintains Multiphase Flow with Interphase eXchanges (MFiX), a collection of open-source computational fluid dynamics (CFD) solvers. Included in the MFiX suite are traditional two-fluid model (TFM) and DEM solvers, and a recently added PIC solver (NETL, 2021). In general, PIC methodologies offer an accuracy trade-off in lieu of computational speed; and therefore, it is important to assess the credibility of MFiX-PIC simulations. For this purpose, a systematic verification, validation and uncertainty quantification (VVUQ) effort was initiated at NETL to assess the new PIC solver
This document derives the solutions to six test problems for a transport equation in 1D spherical coordinates. The scalar fluxes, which are the angular integrals of the solutions, are also derived and plotted.
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Hybrid method was developed based on a need to generate accurate sensitivities for specified systems with CLUTCH. This new method provides improved sensitivities with HMF-028-001, specifically with 238 U in the large reflector region. With the importance of each voxel predetermined with the adjoint flux, the hybrid method is able to generate more accurate sensitivities. More testing is needed for other types of systems and materials (i.e., thermal and intermediate energy ranges and different moderators and reflectors). Initial results are very promising and continual development of the new hybrid method is currently in progress.