Title: Classification of machine learning frameworks for data-driven thermal fluid models

Abstract

Thermal fluid processes are inherently multi-physics and multi-scale, involving mass-momentum-energy transport phenomena at multiple scales. Thermal fluid simulation (TFS) is based on solving conservative equations, for which – except for “first-principles” direct numerical simulation – closure relations (CRs) are required to provide microscopic interactions or so-called sub-grid-scale physics. In practice, TFS is realized through reduced-order modeling, and its CRs as low-fidelity models can be informed by observations and data from relevant and adequately evaluated experiments and high-fidelity simulations. This paper is focused on data-driven TFS models, specifically on their development using machine learning (ML). Five ML frameworks are introduced including physics-separated ML (PSML or Type I ML), physics-evaluated ML (PEML or Type II ML), physics-integrated ML (PIML or Type III ML), physics-recovered (PRML or Type IV ML), and physics-discovered ML (PDML or Type V ML). The frameworks vary in their performance for different applications depending on the level of knowledge of governing physics, source, type, amount and quality of available data for training. Notably, outlined for the first time in this paper, Type III models present stringent requirements on modeling, substantial computing resources for training, and high potential in extracting value from “big data” in thermal fluid research. Here themore » current paper demonstrates and investigates ML frameworks in three examples. First, we utilize the heat diffusion equation with a nonlinear conductivity model formulated by convolutional neural networks (CNNs) and feedforward neural networks (FNNs) to illustrate the applications of Type I, Type II, Type III, and Type V ML. The results indicate a preference for Type II ML under deficient data support. Type III ML can effectively utilize field data, potentially generating more robust predictions than Type I and Type II ML. CNN-based closures exhibit more predictability than FNN-based closures, but CNN-based closures require more training data to obtain accurate predictions. Second, we illustrate how to employ Type I ML and Type II ML frameworks for data-driven turbulence modeling using reference works. Third, we demonstrate Type I ML by building a deep FNN-based slip closure for two-phase flow modeling. The results show that deep FNN-based closures exhibit a bounded error in the prediction domain.« less

Authors:

Chang, Chih-Wei  ^[1];

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Dinh, Nam T. ^[1]

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1. North Carolina State University, Raleigh, NC (United States)

Publication Date:

Fri Oct 12 00:00:00 EDT 2018

Research Org.:

North Carolina State University, Raleigh, NC (United States)

Sponsoring Org.:

USDOE Office of Nuclear Energy (NE); USDOE Office of Nuclear Energy (NE), Nuclear Energy University Program (NEUP)

OSTI Identifier:

1613917

Alternate Identifier(s):

OSTI ID: 1636957

Grant/Contract Number:  

NE0008530; AC05-00OR22725

Resource Type:

Accepted Manuscript

Journal Name:

International Journal of Thermal Sciences

Additional Journal Information:

Journal Volume: 135; Journal Issue: C; Journal ID: ISSN 1290-0729

Publisher:

Elsevier

Country of Publication:

United States

Language:

English

Subject:

42 ENGINEERING; thermal fluid simulation; closure relations; multiscale modeling; machine learning framework; deep learning; data driven; convolutional neural networks; classification